A Main-Project Report On SUPERCAPACITORS AND BATTERY POWER MANAGEMENT FOR HYBRID VEHICLE APPLICATIONS USING MULTI BOOST AND FULL BRIDGE CONVERTERS Is submitted to JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY ANANTAPUR, ANANTAPUR. In partial fulfillment of the t he requirements For the award of the degree of BACHELOR OF TECHNOLOGY IN ELECTRICAL AND ELECTRONICS ENGINEERING During the year 2011-2012 Submitted By P. GURUNADHAM S. JANARDHAN K. DILEEP KUMAR A. JAYA KRISHNA D. HARIBABU
084E1A0217 084E1A0220 084E1A0211 084E1A0221 084E1A0218
Under the esteemed mentorship of Mr. K.MUNIGURU RAJAPRAKAS RAJAPRAKASH H B.Tech., Assistant Professor, Department of E.E.E., S.I.S.T.K
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING SIDDARTHA INSTITUTE OF SCIENCE & TECHNOLOGY (An ISO 9001:2000 Certificate Institution) (Approved by A.I.C.T.E. New Delhi & Affiliated to J.N.T.U.A., Anantapur) Siddhartha Nagar, Narayanavanam road, Puttur-517583
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DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING SIDDARTHA INSTITUTE OF SCIENCE & TECHNOLOGY (An ISO 9001:2000 Certificate Institution) (Approved by A.I.C.T.E. New Delhi & Affiliated to J.N.T.U.A., Anantapur) Siddhartha Nagar, Narayanavanam road, Puttur-517583
CERTIFICATE This is to certify that the MAIN PROJECT report entitled SUPERCAPACITORS AND BATTERY POWER MANAGEMENT FOR HYBRID VEHICLE APPLICATIONS USING MULTI BOOST AND FULL BRIDGE CONVERTERS has been submitted by : P. GURUNADHA GURUNADHAM M S. JANARDHAN K. DILEEP KUMAR A. JAYA KRISHNA D. HARIBABU
084E1A0217 084E1A0220 084E1A0211 084E1A0221 084E1A0218
In the department of Electrical and Electronics Engineering, SIDDARTHA INSTITUTE OF SCIENCE AND TECHNOLOGY , Puttur and is submitted to JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY, ANANTAPUR in partial fulfillment of the requirements for the award of B.Tech, Degree in Electrical and Electronics Engineering. This work has been carried out under my guidance and supervision during the year 2011-12.
Project Guide: Mr. K.MUNIGURU RAJAPRAKASH Assistant Professor, Department of E.E.E., S.I.S.T.K,
B.Tech,
Head of the Department: Mr. S.RAMESHM.E., Associate Professor, Department of E.E.E., S.I.S.T.K
Submitted for the Viva-Voce held on: _______________
Internal Examiner
External Examiner
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DECLARATION
We here by inform that the main project entitled “ SUPERCAPACITORS AND BATTERY POWER MANAGEMENT FOR HYBRID VEHICLE APPLICATIONS USING MULTI BOOST AND FULL BRIDGE CONVERTERS ”
is carried by us during the month of Feb-Mar, 2012 is
an original work submitted by us to the DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING, S.I.S.T.K, PUTTUR. P. GURUNADHAM S. JANARDHAN K. DILEEP KUMAR A. JAYA KRISHNA D. HARIBABU
084E1A0217 084E1A0220 084E1A0211 084E1A0221 084E1A0218
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ACKNOWLEDGEMENT The satisfaction that accompanies the successful completion of any task would be incomplete without the mention of the people who made it possible, without whose guidance, encouragement and help this venture would not have been success. The acknowledgement transcends the reality of formality when we would like to express deep gratitude and respect to all those people behind the screen who guided, inspired and helped for me for the completion of my project presentation in time and up to the standards. I
express
out
deep
sense
of
gratitude
to
our
project
guide
Mr. K.MUNIGURU RAJAPRAKASH, B.Tech, Asst. Professor, for his guidance and
supervision at all levels of my project presentation. I indebted to his valuable suggestions and sustained help in completion of my project presentation. I express my deep sense of gratitude to Mr. S. RAMESH, M.E., Head of the department of Electrical and Electronics Engineering for his valuable guidance and constant encouragement given to me during this presentation First and Foremost, I express my sincere gratitude to out honorable chairman Dr. K.ASHOKA RAJU Ph.D., and also deep sense
principal
of gratitude gratitude to our honorable
Dr. USHAA ESWARAN Ph.D., for having provided all the facilities and
support in completing my project presentation successfully. .
I also thankful to All staff members of EEE department, for helping me to
complete this presentation by giving me valuable suggestions. I express my sincere thanks to All my friends who have supported me in the accomplishment of this project presentation. Last but not the least, the one above all of us, the omnipresent God, for answering our prayers for giving us the strength to plod on despite our constitution wanting to give up and throw in the towel, thank you so much Dear Lord. Thank you for showing us the path . . .
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CONTENTS Abstract
1 +8
1. Introduction
2
1.1 Energy storage unit
5
1.2 Comparison of supercapacitor with lithium-ion (general capacitor)
7
1.3 Advantages and limitations limitations of supercapacitors
8
1.4 Proposed block diagram
9
1.5 Power Flow
10
2. Effectiveness of battery-supercapacitor combination in electric vehicles
12
2.1. Energy management
14
2.1.1 Energy management functions can be separated into two groups
15
2.2 Component Modeling
16
2.2.1 Battery Bank
16
2.2.2 Supercapacitor Bank
17
2.2.3 Electrical Load
18
2.3 Vehicle energy storage system using supercapacitors
18
2.3.1 System specifications
18
2.3.2. The topology of bi-directional DC/DC converter
20
2.4 Vehicle application requirements
21
3. Ultracapacitor-battery interface for power electronic applications
23
4. DC/DC converters topologies and modeling
26
4.1. Multi boost and Multi full bridge converters modeling
27
5. Design for experimental results
31
5.1 Experimental setup at reduced scale
34
5
6. Simulation results
36
6.1 General
37
6.2 Introduction to Matlab
37
6.3 The Matlab System
38
6.3.1 Desktop tools and development environment
38
6.3.2 The Matlab mathematical function library
39
6.3.3 The Matlab language
39
6.3.4 Graphics
39
6.3.5 The Matlab external interfaces
39
6.3.6 Matlab documentation
39
6.3.7 Matlab online help
40
6.3.8 The role of simulation in design
40
6.3.9 Sim power systems libraries
41
6.3.10 Matlab Library
43
6.4 Full bridge converter simulation circuit for Np = 2
43
6.5 Boost converters simulation results
47
6.5.1 Simulation circuit for boost converter
47
6.6 full bridge converters simulation results
51
Conclusion
55
References
56
6
LIST OF FIGURES 1. Converter topologies for ECCE Hybrid Vehicle
4 +8
(a). first solution
4
(b). second solution
4
2. Overview of energy storage unit Battery
5
3. Supercapacitor equivalent circuit
8
4. Electric vehicle/hybrid electric vehicle system using supercapacitors
9
5. Power flow to the ESU
10
6. System configuration of the supercapacitor implemented
19
7. The bi-directional DC/DC converter(full-bridge type topology)
20
8.
(a). Multi boost Converter topology
27
(b). Multi full bridge converter topology
28
(a). Multi boost control strategy
30
(b). Multi full bridge control strategy
30
9.
10. Full bridge converter with chopping devices
33
11. Boost and full bridge converters experimental setup
34
(a). Boost converters setup for Np = 2
34
(b). Full bridge converter setup for Np = 1
35
12. Full bridge converter simulation circuit for Np = 2
44
13.
(a). Super capacitor modules voltages
45
(b). Super capacitor modules currents
45
(a). Battery current control result
46
(b). DC-link and active load currents
46
14.
15. Simulation circuit for boost converter
47
16. Super capacitor modules experimental and simulation voltage results (a). First module voltage
48 48
(b). Second module voltage
48
7
17. Super capacitor modules experimental and simulation current results
49
(a). First module current
49
(b). Second module current
49
18. DC-link voltage and current experimental validation
50
(a) Multi boost output current (IL )
50
(b) Battery current experimental result
50
19. Simulation circuit for full bridge converter
52
20.
(a). Super capacitors module voltage and current
53
(b) DC-link and active load experimental currents
53
21. High frequency planar transformer voltages and currents
54
(a) Transformer input and output voltages
54
(b) Transformer input and output currents
54
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ABSTRACT This paper presents supercapacitors and battery association methodology for ECCE Hybrid vehicle. ECCE is an experimental Hybrid Vehicle developed at L2ES Laboratory in collaboration with the Research Center in Electrical Engineering and Electronics in Belfort (CREEBEL) and other French partners. This test bench has currently lead-acid batteries with a rated voltage of 540 V, two motors each one coupled with one alternator. The alternators are feeding a DC-bus by rectifiers. The main objective of this paper is to study the management of the energy provides by two supercapacitor packs. Each supercapacitors module is made of 108 cells with a maximum voltage of 270V. This experimental test bench is carried out for studies and innovating tests for the Hybrid Vehicle applications. The multi boost and multi full bridge converter topologies are studied to define the best topology for the embarked power management. The authors propose a good power management strategy by using the multi boost and the multi full bridge converter topologies. The simulation results of the two converter topologies are presented.
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CHAPTER-1
INTRODUCTION
10
1.INTRODUCTION In the last few years the pollution problems and the increase of the cost of fossil energy (oil, gas) have become planetary problems. The car manufacturers started to react to the urban pollution problems in nineties by commercializing the electric vehicle. But the battery weight and cost problems were not solved. The batteries must provide energy and peaks power during the transient states. These conditions are severe for the batteries. To decrease these severe conditions, the super capacitors and batteries associate with a good power management present a promising solution. Environmental issues create a demand for more energy efficient vehicles.
A conventional vehicle with an internal combustion engine (ICE), converts chemically stored energy (gasoline, ethanol, diesel etc.) into kinetic energy in a process afflicted with significant power losses. Combining the ICE with an electric energy storage and drive system can improve the fuel efficiency through several means. The electrical propulsion system allows the combustion engine to operate closer to its optimal operating point through supplying the wheels with extra power when needed and absorb power when the ICE produces excess power. Another benefit with hybrid electric vehicles (HEV) is that when braking, the energy can be absorbed by the electrical system, instead of converting all kinetic energy into heat via friction brakes. The electrical energy storage typically consists of a battery with more or less complex support-electronics for charge control and error prevention.
The storage unit has to store relatively large amounts of energy and handle high power. With current battery technology, the energy storage capacity comes at a cost of decreased power capability and the lifetime of the modern batteries is dependent of the charge cycles. By introducing a supercapacitor as aid, the battery could be spared from the power peaks and thus allow allow the battery to be optimized for energy energy storage or extend the lifetime o f a given battery, which in turn could lower the cost of the entire unit. To fully utilize the supercapacitor, a voltage converter is needed, which naturally should be as efficient and simple as possible. With the converter it is also possible to have sophisticated
11
control of the power flows, which can improve the system if proper strategies are used. Interesting previous works made before this report include, “Comparing DC-DC Converters for Power Management in Hybrid Electric Vehicles” (Shupbach & Balda 2003), which is a study of different topologies for supercapacitor handling. An in-depth report on control strategies and optimizations are Andersson and Groot (2003) M.Sc thesis report “Alternative Energy Storage System for Hybrid Electric Vehicles”. The work “Comparison of Simulation Programs for Supercapacitor Modeling” by Andersson and Johansson (2008) has also been a useful resource for modeling of the supercapacitor. Doerffel (2007) have studied the ageing and deteriation processes of lithium-ion batteries, and how to measure the state of health.
To ensure a good power management in hybrid vehicle, the multi boost and multi full bridge converters topologies and their control are developed. Two topologies proposed for the power management in ECCE Hybrid Vehicle are presented in Fig.1.
Figure 1 . Converter topologies for ECCE Hybrid Vehicle
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1.1 Energy storage unit: The energy storage unit (ESU) in a car handles the storage of the electrical energy and functions as a buffer for the electrical machine (and the generator in the series hybrid configuration). The ESU has the possibility to either receive or deliver power from or to to the electrical machine (via a DC/AC inverter). Depending on application and dimensioning parameters, such as hybridization level and size of the vehicle, is it possible to configure the ESU in different combinations.
It is necessary to have a storage utility, which could be a battery or a supercapacitor or a combination of the both, to work as the source of energy and power in this thesis work, a combination consisting of a supercapacitor in parallel with a battery will be studied. If there is a need to control the power flow or if there is a need to have different voltage levels (i.e. the voltage over the capacitor is dimensioned to be lower than the voltage over the battery or vice versa) it can be possible or necessary to install a converter in series with the battery or the supercapacitor or both. If the converter is installed in series with the battery it is possible, with the ability of power control, to get a direct control over the power to the battery.
Another possible combination is to install two converters, one in series with the supercapacitor and one in series with the battery, but this would lead to an unnecessary complexity of the system. Therefore, in this paper, a converter has been installed in series with the supercapacitor. The configuration is presented in Figure-2.
Figure 2. Overview of energy storage unit Battery
13
The battery is suitable to provide the energy buffer to the HEV due to that battery has the ability to store relatively high levels of electrical energy. In the market of today there exist several model and sizes. The problems with batteries are mainly the cost, lifetime and size. Supercapacitors also called ultracapacitors and electric double layer capacitors (EDLC) are capacitors with capacitance values greater than any other capacitor type available today.
Capacitance values reaching up to 400 Farads in a single standard case size are available. Supercapacitors have the highest capacitive density available today with densities so high that these capacitors can be used to applications normally reserved for batteries. Supercapacitors are not as volumetrically efficient and are more expensive than batteries but they do have other advantages over batteries making the preferred choice in applications requiring a large amount of energy storage to be stored and delivered in bursts repeatedly. The modern supercapacitor is not a battery per se but crosses the boundary into battery technology by using special electrodes and electrolyte. Several types of electrodes have been tried and we focuse on the double-layer capacitor (DLC) concept. It is carbonbased, has an organic electrolyte that is easy to manufacture and is the most common system in use today. A supercapacitor is a component which has relatively high specific power ability in Comparison to batteries much like a capacitor, while it has much higher specific energy than a conventional capacitor, more like a battery. In order to have high capacitance, the isolator is very thin, usually in order of tenths of nm (Lai et al. 1992). The maximum voltage difference between the electrodes is related to the dielectric breakdown of the isolator, which in turn is related to its thickness and material.
Due to the thin isolator in supercapacitor, the maximum voltage per cell becomes relatively low, in order of 2-4V to avoid dielectric breakdown. The supercapacitor can not only be charged and discharged more than one million times but also be stored with ten
14
times more energy than conventional electrolytic capacitors. In contrast, the supercapacitor has the merits of a rapid charge and discharge of energy and a longer life cycle, because of electrostatic nature of capacitor rather than chemical reaction.
1.2 Comparison of supercapacitor with lithium-ion (general capacitor): Function
Supercapacitor
Lithium-ion (general)
Charge time
1–10 seconds
10–60 minutes
Cycle life
1 million or 30,000h
500 and higher
Cell voltage
2.3 to 2.75V
3.6 to 3.7V
Specific energy (Wh/kg)
5 (typical)
100–200
Specific power (W/kg)
Up to 10,000
1,000 to 3,000
Cost per Wh
$20(typical)
$2 (typical)
Service life (in vehicle)
10 to 15 years
5 to 10 years
Charge temperature
–40 to 65°C (–40 to 149°F)
0 to 45°C (32°to 113°F)
Discharge temperature
–40 to 65°C (–40 to 149°F)
–20 to 60°C (–4 to 140°F)
15
1.3 Advantages and limitations of supercapacitors: Virtually unlimited cycle life; can be cycled millions of time High specific power; low resistance enables high load currents Charges in seconds; no end-of-charge termination required Advantages
Simple charging; draws only what it needs; not subject to overcharge Safe; forgiving if abused Excellent low-temperature charge and discharge performance
Low specific energy; holds a fraction of a regular battery Linear discharge voltage prevents using the full energy spectrum Limitations
High self-discharge; higher than most batteries Low cell voltage; requires serial connections with voltage balancing High cost per watt
Equivalent circuit of supercapacitor supercapacitor
Figure 3. Supercapacitor equivalent circuit
16
This equivalent circuit is only a simplified or first order model of o f a super capacitor. This causes super capacitors to exhibit behavior more closely to trans ission lines than capacitors. Below is a more accurate illustration of the equivalent circuit for a supercapacitor.
1.4 Proposed block iagram:
Figure 4. Electric vehicle/hybrid electric vehicle system using supercapacitors.
A hybrid vehicl is a vehicle which can run the mechanism by using multiple sources such as diesel, petrol, gas, electricity. A hybrid vehicle is combination of different components and so that it will provide flexibility, reliability, reliability, safe and sec red target.
Figure4 shows the operation of hybrid vehicle in two modes. One is motoring mode and the other is regenerative braking mode. The blue arrow marks indicates the flow of current in the motori g mode and the red mark indicates the flow of current in the regenerative braking mo e. During the motoring mode the hybrid vehicle takes electric 17
energy from both battery and supercapacitor i.e., the steady state energy is supplied by battery and energy at peak state (during switching, transient periods) is supplied by both supercapacitor and battery. During the regenerative mode hybrid vehicle supplies the electrical energy to both supercapacitor and battery. Since this process is recycled electrical energy is utilized efficiently. Therefore the weight of the battery decreases and life gets increased.
1.5 Power Flow: The load power, coming from the outer parts of the HEV, can be both positive and negative. A positive load power is in this work defined as that there there is a surplus of power in the outer system and the power is therefore flowing into the ESU (generator reference). If the load power is negative there is a demand for power in the external system and power is flowing out from the ESU. Inside the ESU the load power is divided between the power to the battery and power to the supercapacitor, which is demonstrated in Figure 5.
Figure 5. Power flow to the ESU
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The converter is able to divert power to or from the supercapacitor, depending on outer Circumstances such as power control strategies. These control strategies are optimized to give a better system performance and mitigating the battery stresses. In the last few years th e pollution problems an d the increase of the cost of fossil energy (oil, gas) have become planetary problems. The car manufacturers started to react to the urban pollution problems in nineties by commercializing the electric vehicle. But the battery weight and cost problems were not solved. The batteries must provide energy and peaks power during the transient states. These conditions are severe for the batteries. To decrease these severe conditions, the super capacitors and batteries associate with a good power management present a promising solution.
A Power management is nothing but efficiently directing power to different components of a system. Power management is especially important for portable devices that rely on battery power. By reducing power to components that aren't being used, a good power management system can double or triple the lifetime of a battery.
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CHAPTER-2
EFFECTIVENESS OF BATTERYSUPERCAPACITOR COMBINATION IN HYBRID VEHICLES
20
2.EFFECTIVENESS OF BATTERY-SUPERCAPACITOR COMBINATION IN HYBRID VEHICLES
A significant portion of energy is dissipated in the brakes when driving conventional gasoline-powered vehicles in urban areas, where periodic accelerationdeceleration cycles are required. Therefore, recovering this energy through regenerative breaking is an effective approach for improving vehicle driving range and this can only be accomplished by electric vehicles (EV) or hybrid-electric vehicles (HEV). Regenerative breaking in these vehicles captures some of the kinetic energy stored in the vehicle’s moving mass by operating the vehicle’s traction motor as a generator that provides braking torque to the wheels and recharges the batteries .
The battery bank of an EV is sized for peak power demand, and this often compromises the desired weight and space specifications. On the other hand, The auxiliary power unit (APU) of an HEV is designed to provide the normal average power required by the vehicle, while the battery is sized to provide power surges needed during acceleration and hill climbing and to accept momentary powers during breaking. While EVs and HEVs are more efficient than conventional vehicles in urban areas, the electric load profile consists ofhigh peaks and steep valleys due to repetitive acceleration and deceleration.
The resulting current surges in and out of the battery tend to generate extensive heat inside the battery, which leads to increased battery internal resistance – thus lower efficiency and ultimately premature failure . The problem of battery overheating and loss of capacity is more acute when batteries are near full state-of-charge (SOC) since they cannot accept large busts of current from regenerative breaking without degradation at this stage.
Supercapacitors (also referred to as ultracapacitors or electrochemical capacitors) have much greater advantage over batteries when capturing and supplying short bursts of
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power due to their higher power density limits, and ability to charge and discharge very quickly. Hence adding a supercapacitor bank will assist the battery during vehicle acceleration and hill climbing, and with its quick recharge capability, it will assist the battery in capturing the regenerative braking energy. This significant advantage a batterysupercapacitor energy storage/supply system gained attention in recent years in transportation systems as well as other applications . Applying supercapacitors also allows for a smaller battery size, and there is almost no limit to number of their chargedischarge cycles (since there are no chemical reactions involved in their energy storage mechanism). Furthermore these devices require no maintenance and do not use toxic materials.
Special considerations must be taken into account when integrating such a hybrid energy storage system to achieve optimal performance. While direct connection of the supercapacitor across the battery terminals does reduce transient currents in an out of the battery, the best way to utilize the supercapacitor bank is to be able control its energy content through a power converter. The paper reviews the direct supercapacitor-battery shunt connection, after a short section addressing component modeling issues. The desired connection is then addressed by using a DC/DC converter in the boost mode when discharging, and in the buck mode when charging the supercapacitor bank.
2.1. Energy management: management:
The expanding functions of the vehicle electric/electronic system call for significant improvements of the power supply system. A couple of years ago, broad introduction of a higher system voltage level, 42V, initially in a dual-voltage 14/42V system, was considered as a viable solution. However, the cost/benefit ratio associated with this type of configuration in systems operating at 42V or less turned out to be too low for widespread implementation. Furthermore, the electric propulsion that can be generated at this voltage level is generally considered too low to make mild-hybrid electric vehicles attractive.
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At the same time, several hardware components for the conventional 14Vsystem experienced significant technological progress. For example, enhanced 14V clawpole (Lundell) alternators were developed that can continuously generate an electric power output of 3 kW or more. AGM batteries demonstrated at least three-fold longer shallowcycle life, compared to conventional SLI batteries. Finally, the introduction of high-level energy management control strategies can ensure system robustness and optimal energy efficiency and thus help stretch the boundaries of the 14V system. 2.1.1 Energy management functions can be separated into two groups:
Power Supply Management (PSM): Control of the on-board electric generation, i.e. control of the alternator set point in conventional electrical systems, aiming at optimizing all of the following: electrical function availability, battery life, vehicle performance (e.g. reduced alternator load when maximum acceleration is demanded), or fuel consumption (e.g. reduce alternator output at idle to allow for lower idle speed). Whereas many of these functions can be considered state of the art in modern voltage regulation, particularly the latter has garnered growing attention recently. Electric generation contributes significantly to fuel consumption, at least in real-world conditions. An average alternator output of 1 kW involves as much as 1–1.4 l gasoline fuel consumption per 0 km, depending on vehicle parameters and driving conditions. Decoupling the electric generation from the loads’ demands can significantly reduce this specific fuel consumption contribution by optimizing the system efficiency of engine and alternator at any point in time. This will introduce supply voltage fluctuations into the electrical system and systematically exploit the battery as a short-term energy buffer. Significantly more advanced strategies of PSM are of course needed for HEVs, where electric generation plays a more vital role.
Power Distribution Management (PDM) is used to schedule the allocation of available power and energy to electric loads on a subsystem or component level. Effectively, it must ensure the controlled function delivery of individual electric features by prioritization. Whenever a power deficiency occurs, the PDM algorithm aims at ensuring rail voltage stability, charge balance and robustness, as well as minimizing battery charge
23
throughput in the case of peak loads. Depending on the definition of electric feature priorities, a PDM strategy can dictate a temporary functional degradation under appropriate conditions. Here, a careful balancing of priorities is required, especially for functions that are directly perceivable by the customer. Advanced PDM algorithms will schedule electric feature functionalities dynamically rather than statically.
Electric energy management actively uses the energy storage system (battery, supercapacitor, etc.) and hence relies on precise status information about this device. A battery monitoring system (BMS) has to deliver these essential inputs to the energy management control system.
2.2 Component Modeling: This section reviews the modeling of the main power system components in an electric vehicle; namely, the battery bank, the supercapacitor bank, and the electrical load. More details on electrical component modeling can be found in power electronics textbooks.
2.2.1 Battery Bank:
Batteries
are
quite
difficult
to
model
as
they
undergo
thermally-dependent
electrochemical processes while delivering and accepting energy. Thus the electrical behavior of a battery is a nonlinear function of a number of constantly changing parameters, such as internal temperature, state-of charge, rate of charge/discharge, etc. … The capacity of a battery depends on the discharge rate as wells as temperature. This relationship is described by Peuket’s equation relating the discharge current I (A) to the time t (hr) it takes it to discharge , I . Given the battery capacity CTo at temperature To, the capacity at some other temperature is computed by CT = CTo{1 +
(T-To)} where
is
a constant.
24
An approximate model that is often used for batteries is a Thevenins equivalent circuit that consists of the open circuit voltage in series with an effective internal resistance. Both voltage and resistance values are functions of the battery SOC, and these relations are generally supplied the manufacturer. SOC is defined the percentage of energy left in a battery (after supplying a certain amount of amp-hours) relative to its full capacity.
The open-circuit voltage is often approximated by a linear function of the o
SOC: Voc = a1+ a2 SOC, at some specific temperature (e.g., 80 F ). ). The battery internal resistance has static and dynamic values that depend of battery SOC, whether the battery is being charged or discharged and rate of charge/discharge. In short duration studies, however, the amount of amp-hours in and out of the battery is a small fraction of the battery capacity. Hence it is fair to assume that battery internal voltage is constant during such periods, and a quasi-steady state model with fixed open-circuit voltage and internal resistance constitutes an acceptable battery model . Note that two resistance values are used in this case, one during charging and another during discharging.
2.2.2 Supercapacitor Bank:
As in conventional capacitors, the resistance and inductance of the terminal wires and electrodes of supercapacitors are represented by a series R-L circuit. Further, nonperfect insulation between the device electrodes results in leakage current that is represented by a large shunt resistance. The difference between conventional and supercapacitors is that the latter are much more efficient, i.e., the series resistance is a lot lower and the shunt resistance is much higher in value. The self-discharge time constant of supercapacitors several orders of magnitude larger than that of conventional capacitors. More sophisticated models suitable for dynamic studies are found. The study under investigation is a short-duration analysis of the power (or current) distribution between the battery bank and supercapacitor bank during acceleration and deceleration. Hence, the leakage resistance can be ignored without much error, and the supercapacitor bank can simply be represented by a series R-C circuit.
25
2.2.3 Electrical Load:
The electrical load in electric vehicles consists mainly of an inverter-fed induction motor for motive power. During regenerative breaking, the motor is turned into a generator by reducing the frequency of its terminal voltage, thus reversing power flow and producing braking torque. Detailed modeling of inverter-fed motor drives is found in standard power electronics and drives textbooks. As far as the power source in concerned, power demand is sufficient for analysis. Since the DC bus voltage is not allowed to vary significantly from its nominal value, current demand gives a good approximation of power demand. Thus the load can be modeled simply by a time-varying current source that reverses direction as the vehicle switches from coasting or acceleration to regenerative braking.
2.3 Vehicle energy storage system using supercapacitors: 2.3.1 System specifications:
To control the energy stored in supercapacitor bank, it is need that the voltage of the supercapacitor bank should be controlled. If not, the supercapacitor voltage depends on the battery voltage, so that there is no possibility to control the energy stored in supercapacitor bank. Thus, DC/DC converter is indispensable to regulate the bank voltage level. Moreover, because the current can flow to supercapacitor when the supercapacitor is charged and the current can flow from supercapacitor when the supercapacitor is discharged, the DC/DC converter has to have a bi-directional nature. Figure 6. shows the system configuration with battery pack and supercapacitor bank as an energy storage. The DC/DC converter is on boost-mode operation as the inverter supplies traction power to the motor. On the other hands, the DC/DC converter is on buck-mode operation as the regenerative energy come to supercapacitor bank.
26
Figure 6. System configuration of the supercapacitor implemented.
Table 1. Specification of system.
From the required specification of Table 1, the number of supercapacitor cell is designed to be 30, on the basis that the maximum voltage of each supercapacitor cell is 2.3V (92% of continuous voltage rating), and the minimum voltage of each supercapacitor cell is 1.25V (50% of continuous voltage rating). As a consequence, the capacitance of the supercapacitor bank used in this study becomes 2700/30=90F and
27
equivalent series resistance (ESR) 1m×30=30m, to make the maximum stored energy become 210kJ. The the total volume and weight of the supercapacitor bank is 18l and 22kg, respectively.
2.3.2. The topology of bi-directional DC/DC converter:
There can be lots of converter topology for realizing a bi-directional DC/DC converter; single-stage buck/boost type and full-bridge type as a typical one. Full-bridge type topology has merits compared to single-stage buck/boost type topology. 1) Electrical isolation between input and output is guaranteed. 2) Higher boost ratio can be implemented. 3) System protection is possible when output stage short take place. From these facts, full-bridge type topology is employed in this study, in spite that the fullbridge type topology is somewhat bulky, requires more components rather than single stage buck/boost type.
Figure 7. The bi-directional DC/DC converter(full-bridge type topology).
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As shown in Fig. 7, the bi-directional full-bridge topology DC/DC converter is operated on boost mode at the time electric power is supplied from supercapacitor stage (low voltage stage) to battery stage (high voltage stage), and on buck mode at the time electric power is absorbed from battery stage to supercapacitor stage. Because the supercapacitor stage of the DC/DC converter has low voltage level, a current control is necessary in the cause of reducing current’s burden on semiconductors.
At the battery stage of the DC/DC converter, voltage control is necessary to match to DC bus voltage of the inverter. Also, soft switching technique of zero voltage-zero current switching is applied to this system for improving the DC/DC converter efficiency.
2.4 Vehicle application requirements: The energy storage requirements vary a great deal depending on the type and size of the vehicle being designed and the characteristics of the electric powertrain to be used. Energy storage requirements for various vehicle designs and operating strategies are shown in Table 2 for a mid-size passenger car. Requirements are given for electric vehicles and both charge sustaining and plug-in hybrids.
These requirements can be utilized to size the energy storage unit in the vehicles when the characteristics of the energy storage cells are known. In some of the vehicle designs considered in Table, ultracapacitors are used to provide the peak power rather than batteries.
For ultracapacitors, the key issue is the minimum energy (Wh) required to operate the vehicle in real world driving because the energy density characteristics of ultracapacitors are such that the power and cycle life requirements will be met in most cases if the unit is large enough to met the energy storage requirement.
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Table 2. Energy storage unit requirements for various types of electric passenger cars Type of electric driveline
Electric
Useable
Maximum
Cycle life
System
energy
pulse power at
(number of
Voltage V
storage
90-95%
cycles)
efficiency kW
300-400
15-30 kWh
70-150
2000-3000
50-70
2500-3500
Useable depth ofdischarge
deep 70-80%
6-12 kWh Plug-in hybrid
battery 100300-400
150 Wh ultracapacitors
Charge sustaining hybrid
Microhybrid
60-80%
100-150 Wh 150-200
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ultracapacitors
25-35
30-50 Wh ultracapacitors
deep
5-10
300K-500K
Shallow 5-10%
300K-500K
Shallow 5-10%
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CHAPTER-3
ULTRACAPACITORBATTERY INTERFACE FOR POWER ELECTRONIC APPLICATIONS
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3.ULTRACAPACITOR-BATTERY INTERFACE FOR POWER ELECTRONIC APPLICATIONS The electrical load in electric vehicles consists mainly of an inverter-fed induction motor for motive power. During regenerative breaking, the motor is turned into a generator by reducing the frequency of its terminal voltage, thus reversing power flow and producing braking torque. As far as the power source in concerned, power demand is sufficient for analysis. Since the DC bus voltage is not allowed to vary significantly from its nominal value, current demand gives a good approximation of power demand. Thus the load can be modeled simply by a time-varying current source that reverses direction as the vehicle switches from coasting or acceleration to regenerative braking. 1.
The role of the ultracapacitor is to maintain the battery current as constant as
possible with slow transition from low to high current during transients to limit battery stress. On the other hand, the ultracapacitor ought to charge as fast as possible without exceeding maximum current from regenerative breaking, and to discharge most of its stored energy during acceleration. Energy flow in and out of the ultracapacitor can be controlled with pulse-with-modulated (PWM) DC/DC converter.
Adding a
ultracapacitor bank to a battery- or fuel cell driven vehicle makes sense and advantages by far outweigh the disadvantages. A direct parallel connection will reduce battery stress by assisting with transient currents during acceleration and deceleration. The parallel combination of the battery system and UC bank also exhibits good performance for the stand-alone residential applications during the steady-state, load-switching, and peak power demand. Without the UC bank, the battery/fuel cell system must supply this extra power, thereby increasing the size and cost of the attery/fuel cell system .
2.
The ultracapacitor addition removes 20% of the mass of the battery pack of the
electric vehicle. Another method for reducing the size of the capacitor bank would use some battery power during each shot. If the application were to permit this, the ultracapacitor stack would still supply most of the power while the load was at its peak, but the battery would supply a lower, consistent level over the full ten-second duration. Such a hybrid approach can significantly reduce the size of the ultracapacitor stack.
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3.
Time domain and frequency domain measurements both confirmed that
ultracapacitors are very efficient for low frequency use. Both also show that the capacitance drops (with corresponding decrease in efficiency) for frequencies greater than 0.1 Hz is measured by various frequency response of ultracapacitors. The time domain measurements show that capacitor loss becomes very significant (70% for some tests) for fast discharge times . As Ultra-capacitors are always used for energy storage or energy buffer applications, their poor high frequency response makes them completely unsuitable for high frequency applications and are therefore more suitable for dc circuits. Thus the Ultracapacitors should be connected to any high frequency charging converter with a small inductance of about 20µH in series to the converter. 4.
The main problem with the application of ultracapacitors is that maximum
voltage of each cell in the stack (2 ,5 V) should not be exceeded. It is probably reasonable to limit the number of cells in series in batteries, and to match voltages of interconnected DC links using a converter containing an AC medium frequency link with transformer. 5.
Ultra-capacitors are used as an energy storage buffer by simultaneously charging
and discharging them by paralleling them to an energy source like a battery, fuel cell, DC-DC converter , etc. and a load. The voltage and current ripple caused by the charging converter can often cause over charging or temperature rise of the capacitor. The increasing filter inductance or increasing the switching frequency of the buck derived DC-DC converter that is usually used for charging will be one solution, they will significantly either increase both size and cost or increase losses in the converter. Moreover, increasing inductance requires higher turns and this increases both the radiated fields from the inductor and the inter-winding capacitance of the inductor. These radiated fields and the feed through noise through the inter-winding capacitance from the inductor mainly couple to surrounding circuits and increase EMI. Thus a better solution would be to use additional filter circuits that attenuate both voltage ripple and ripple current during charging.
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CHAPTER-4
DC/DC CONVERTERS TOPOLOGIES AND MODELING
34
4. DC/DC CONVERTERS TOPOLOGIES AND MODELING 4.1. Multi boost and Multi full bridge converters modeling
Figure 8(a) shows the multi boost converter topology. The general model for this topology is given by equation (1); where (α1) and (n) define respectively the duty cycle and parallel input converter number.
(1)
The voltage drops in the Ln and λ inductances are given by equation (2).
(2)
Figure 8 (a). Multi boost Converter topology
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Figure 8(b). Multi full bridge converter topology
The converter average model has a nonlinear behavior because of crosses between α1 control variable and Vbus1 parameter. The Vbus1, Vsc1, Vsc2, Vscn , Ich and Vbat
variables can to disturb the control, they must be measured and used in the estimate of the control law to ensure a dynamics dynamics of control . The multi boost converter topology control law which results from the boost converter modeling is presented by α1 duty cycle (3); where Np = max(n) is the maximum number of parallel converters.
(3)
The multi boost converter control strategy is presented in Fig.9 (a). It ensures the super capacitor modules discharge with variable current. The super capacitors reference current (Iscref) is obtained starting from the power management between batteries and hybrid vehicle DC-link. This control strategy includes the super capacitors and batteries current control loops. PWM1 signal ensures the multi boost converters control during
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super capacitor modules discharge. These modules being identical, the energy management between the modules and the hybrid vehicle DC-link enables to write the super capacitors current references (4).
(4)
To simplify the super capacitors current references estimation, the multi boost converter efficiency (η) was fixed at 85%.
The multi full bridge converter control strategy proposed in this paper consists to establish the full bridge converters standardized voltage . The control law which result from the multi full bridge converter modeling is presented by equation(5), where (m) defines the transformer turns ratio.
(5)
This standardized voltage is compared with two triangular carrier waves of amplitude Vmax = 1V with a switching frequency of 20 kHz. The inverter control strategy is presented in Fig. 9(b); where Q1, Q2, Q3 and Q4 are the control signals applied to K1, K2, K3 and K4 switches.
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Figure 9(a) Multi boost control strategy
Figure 9(b) Multi full bridge control strategy
Figure 9. Multi boost and Multi full bridge converters control strategy
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CHAPTER-5
DESIGN FOR EXPERIMENTAL RESULTS
39
5. DESIGN FOR EXPERIMENTAL RESULTS Wiring in power electronic design is a general problem for electrical energy system and the voltage inverters do not escape to this problem. The switch action of semiconductors causes instantaneous fluctuations of the current and any stray inductance in the commutation cell will produce high voltage variations. Semiconductors, when switching off, leads to high voltage transitions which is necessary to control within tolerable limits. The energy stored in parasitic inductances, during switching on, is generally dissipated by this semiconductor.
In the case of the single-phase inverter, each cell includes two switches and a decoupling capacitor placed at the cell boundaries, which presents a double role. It enables to create an instantaneous voltage source very close to the inverter. The (C) capacitor associated to an inductor enables to filter the harmonic components of the currents which are generated by the inverter. Parasitic inductances staying in the mesh include the capacitor inductance, the internal inductance of semiconductors and the electric connection inductances. A good choice of the components with an optimal wiring enables to minimize parasitic inductances.
Using the semiconductors modules solves the connection problems between components. All these efforts can become insufficient, if residual inductances remain too high or if the inverter type is the low voltages and strong currents for which the voltage variations are much important. In both cases, the use of the chopping devices is necessary. These devices must be placed very close to the component to avoid any previous problem.
The parameters used for experimental tests are presented in table 3. and the principle of such circuits is given in Fig. 10.
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Table 3: Full bridge experimental parameters Symbol
Value
R1= R2=R3 = R4
10
C1=C2=C3=C4
220µF
λ
25µH
m
3
Vbus1
60V-43V
C
6800 µF
L1
50µH
Name
Chopping circuits resistances Chopping circuits capacitors Battery current smoothing inductance Planar transformer turns ratio DC-link voltage Super capacitors voltage smoothing capacitor Super capacitors currents smoothing inductance
Figure 10. Full bridge converter with chopping devices
During switching off of the semiconductors, the corresponding current stored in wiring inductances circulates in the following meshes C1, D1 ; C2 , D2; C3, D3 and C4 , D4 which limits the voltages applied to the switches. When electrical energy is fully transferred in C1, C2, C3 and C4 capacitors, the current becomes null and the meshes become closed. The C1, C 2, C3 and C4 capacitors are used only for transient energy tank
41
and it is necessary to recycle this switching energy while controlling the voltage at the semiconductors boundary. This function is ensured by R1, R2, R3 and R4 resistances. R1, R2, R3 and R4 resistances are identical and C1, C2, C3 and C4 capacitors are also identical.
5.1 Experimental setup at reduced scale:
11(a) Boost converters setup for Np = 2
For reasons of cost components and safety, the experimental test benches were carried out at a reduced scale .
• The boost converter test bench Fig.11 (a) is made of: a battery module of 4 cells in series, two super capacitors modules of 10 cells (Maxwell BOOSTCAP2600) in series for each one, an active load which is used to define power request, two boost converters in parallel which ensure power management in hybrid vehicle.
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11(b) Full bridge converter setup for Np = 1 Figure 11. Boost and full bridge converters experimental setup
• For the full bridge converter test bench Fig.11 (b), a batteries module, a super capacitors module, two high frequency planar transformer, the DC/AC and AC/DC converters have been designed. The super capacitors modules voltages must be between 27 V and 13.5 V.
The batteries module which imposes the DC-bus voltage presents a rated voltage of 48 V and the DC link voltage level must be between 43 V and 60 V. The converters are controlled by a PIC18F4431 microcontroller with 10 kHz control frequencies for boost converters and 20 kHz for the full bridge converter.
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CHAPTER-6
SIMULATION RESULTS
44
6.SIMULATION RESULTS
6.1 General: Simulation has become a very powerful tool on the industry application as well as in academics, nowadays. It is now essential for an electrical engineer to understand the concept of simulation and learn its use in various applications. Simulation is one of the best ways to study the system or circuit behavior without damaging it .The tools for doing the simulation in various fields are available in the market for engineering professionals. Many industries are spending a considerable amount of time and money in doing simulation before manufacturing their product. In most of the research and development (R&D) work, the simulation plays a very important role. Without simulation it is quiet impossible to proceed further. It should be noted that in power electronics, computer simulation and a proof of concept hardware prototype in the laboratory are complimentary to each other. However computer simulation must not be considered as a substitute for hardware prototype. The objective of this chapter is to describe simulation of impedance source inverter with R, R-L and RLE loads using MATLAB tool.
6.2 Introduction to Matlab: MATLAB is a high-performance language for technical computing. It integrates computation, visualization, and programming in an easy-to-use environment where problems and solutions are expressed in familiar mathematical notation. Typical uses includes 1.
Math and computation
2.
Algorithm development
3.
Data acquisition
4.
Modeling, simulation, and prototyping
5.
Data analysis, exploration, and visualization
6.
Scientific and engineering graphics
7.
Application development, including graphical user interface building
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MATLAB is an interactive system whose basic data element is an array that does not require dimensioning. This allows you to solve many technical computing problems, especially those with matrix and vector formulations, in a fraction of the time it would take to write a program in a scalar non-interactive language such as C or FORTRAN. The name MATLAB stands for matrix laboratory. MATLAB was originally written to provide easy access to matrix software developed by the LINPACK and EISPACK projects. Today, MATLAB engines incorporate the LAPACK and BLAS libraries, embedding the state of the art in software for matrix computation. MATLAB has evolved over a period of years with input from many users. In university environments, it is the standard instructional tool for introductory and advanced courses in mathematics, engineering and science. In industry, MATLAB is the tool of choice for high-productivity research, development and analysis. MATLAB features a family of add-on application-specific solutions called ToolBoxes. Very important to most users of MATLAB, toolboxes allow you to learn and apply specialized technology. Toolboxes are comprehensive collections of MATLAB functions (M-files) that extend the MATLAB environment to solve particular classes of problems. Areas in which toolboxes are available include signal processing, control systems, neural networks, fuzzy logic, wavelets, simulation and many others.
6.3 The Matlab System: The MATLAB system consists of five main parts: 6.3.1 Desktop tools and development environment:
This is the set of tools and facilities that help you use MATLAB functions and files. Many of these tools are graphical user interfaces. It includes the MATLAB desktop and Command Window, a command history, an editor and debugger, a code analyzer and other reports, and browsers for viewing help, the workspace, files, and the search path.
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6.3.2 The Matlab mathematical function library:
This is a vast collection of computational algorithms ranging from elementary functions, like sum, sine, cosine, and complex arithmetic, to more sophisticated functions like matrix inverse, matrix eigen values, Bessel functions, and fast Fourier transforms. 6.3.3 The Matlab language:
This is a high-level matrix/array language with control flow statements, functions, data structures, input/output, and object-oriented programming features. It allows both "programming in the small" to rapidly create quick and dirty throw-away programs, and "programming in the large" to create large and complex application programs. 6.3.4 Graphics:
MATLAB has extensive facilities for displaying vectors and matrices as graphs, as well as annotating and printing these graphs. It includes high-level functions for twodimensional and three-dimensional data visualization, image processing, animation, and presentation graphics. It also includes low-level functions that allow you to fully customize the appearance of graphics as well as to build complete graphical user interfaces on your MATLAB applications. 6.3.5 The Matlab external interfaces:
This is a library that allows you to write C and FORTRAN programs that interact with MATLAB. It includes facilities for calling routines from MATLAB (dynamic linking), calling MATLAB as a computational engine, and for reading and writing MATfiles. 6.3.6 Matlab documentation:
MATLAB provides extensive documentation, in both printed and online format, to help you learn about and use all of its features. If you are a new user, start with this Getting Started book. It covers all the primary MATLAB features at a high level, including many examples. The MATLAB online help provides task-oriented and
47
reference information about MATLAB features. MATLAB documentation is also available in printed form and in PDF format. 6.3.7 Matlab online help:
To view the online documentation, select MATLAB Help from the Help menu in MATLAB. The MATLAB documentation is organized into these main topics: 6.3.8 The role of simulation in design:
Electrical power systems are combinations of electrical circuits and electromechanical devices like motors and generators. Engineers working in this discipline are constantly improving the performance of the systems. Requirements for drastically increased efficiency have forced power system designers to use power electronic devices and sophisticated control system concepts that tax traditional analysis tools and techniques. Further complicating the analyst's role is the fact that the system is often so nonlinear that the only way to understand it is through simulation. Land-based power generation from hydroelectric, steam, or other devices is not the only use of power systems. A common attribute of these systems is their use of power electronics and control systems to achieve their performance objectives. Sim Power Systems is a modern design tool that allows scientists and engineers to rapidly and easily build models that simulate power systems. Sim Power Systems uses the Simulink environment, allowing you to build a model using simple click and drag procedures. Not only can you draw the circuit topology rapidly, but your analysis of the circuit can include its interactions with mechanical, thermal, control, and other disciplines. This is possible because all the electrical parts of the simulation interact with the extensive Simulink modeling library. Since Simulink uses MATLAB as its computational engine, designers can also use MATLAB toolboxes and Simulink block sets. Sim Power Systems and Sim Mechanics share a special Physical Modeling block and connection line interface.
48
6.3.9 Sim power systems libraries:
You can rapidly put Sim Power Systems to work. The libraries contain models of typical power equipment such as transformers, lines, machines, and power electronics.
Mat lab Library
49
Mat lab Library
50
6.3.10 Matlab Library:
American utility located in Canada, and also on the experience of Ecole de Technologies superiors and Universities Laval. The capabilities of Sim Power Systems for modeling a typical electrical system are illustrated in demonstration files. And for users who want to refresh their knowledge of power system theory, there are also selflearning case studies. The Sim Power Systems main library, powerlib, organizes its blocks into libraries according to their behavior. The powerlib library window displays the block library icons and names. Double-click a library icon to open the library and access the blocks. The main Sim Power Systems powerlib library window also contains the powerguide block that opens a graphical user interface for the steady-state analysis of electrical circuits.
6.4 Full bridge converter simulation circuit for Np = 2: The simulation has been made for Np = 2 as shown in figure 12. The maximum and minimum voltages of the super capacitor modules are respectively fixed at 270V and 135V. The hybrid vehicle requested current (Ich) is respectively fixed at 100A from 0 to 0.5s, 400A from 0.5s to 18s and 100A from 18s to 20s. Battery reference current (Ibatref) is fixed at 100A independently of the hybrid vehicle power request. Super capacitor modules voltages (Vsc1, Vsc2) presented in Fig.13 (a) are identical. The currents amplitudes (Isc1, Isc2) presented in Fig.13 (b) are also identical.
Control enables to maintain the battery current (Ibat) at 100A; but around 0.5s and 18s the battery current control loop has not enough time to react Fig.14 (a). The important power of the transient states is ensured by the super capacitors modules (IL) Fig. 14(b). Simulation parameters are presented in table 4.
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Figure 12. Full bridge converter simulation circuit for Np = 2
Symbol
Table 4. Full bridge topologie simulations parameters Value Name
λ
25µH
Battery current smoothing inductance
m
3
Planar transformer turns ratio
Vbus1
604V-432V
DC-link voltage
L1=L2
50µH
Super capacitors currents smoothing inductances
52
Figure 13 (a). Super capacitor modules voltages
Figure 13(b). Super capacitor modules currents
53
Figure 14. (a): Battery current control result
Figure 14(b): DC-link and active load currents
54
6.5 Boost converters simulation results: 6.5.1 Simulation circuit for boost converter:
The boost converters experimental test is carried out in the following conditions: During the super capacitors discharge, the batteries current reference (Ibatref) is fixed at 13A so that, the super capacitors modules provide hybrid vehicle power request during the transient states. For these tests, the hybrid vehicle request (Ich) was fixed at 53A. The experimental and simulations results of the modules voltage are compared in Fig.16 (a) and Fig.16 (b). The (Isc1) and (Isc2) experimental currents are not identical Fig.17 (a), Fig.17 (b) because the super capacitors dispersion and the power electronic circuits (boost converters) inequality.
The first boost converter ensures 50% and the second ensures also 50% of the DC-link current (IL). In other words the two super capacitors modules ensure a (IL) current of 40A to hybrid vehicle as presented in Fig.18 (a), and 13A only is provided by the batteries Fig.18 (b).
Figure 15. Simulation circuit for boost converter
55
16(a) First module voltage
16(b) Second module voltage Figure 16. Super capacitor modules experimental and simulation voltage results
56
17(a) First module current
17(b) Second module current Figure 17. Super capacitor modules experimental and simulation current results
57
18(a) Multi boost output current (IL )
18(b) Battery current experimental result Figure 18. DC-link voltage and current experimental validation
58
6.6 full bridge converters simulation results: The Q1, Q2, Q3 and Q4 control signals
applied to K1, K2, K3 and K4
semiconductors. For electric constraints reasons of the available components, (transformer, IGBT, active load), the full bridge experimental test conditions are different to that of boost converters topology. The super capacitors module maximum voltage (Vsc1) is fixed at 22V because of battery module voltage (48V), the transformer turns ratio (m=3) and active load which is limited to 80V. The battery current reference (Ibatref) and active load current request (Ich) are respectively fixed at 5A and 15A.
The super capacitors power is not constant (Vsc1, Isc1) because of the consumed current by R1, R2, R3 and R4 resistances Fig.12 (a). The battery current experimental result is presented in Fig.12 (b). The voltages and currents ripples which appear in Fig. 11 (b), Fig.12 (a) and Fig. 12 (b) are caused by leakage inductances of the transformer and wiring of the power electronics devices.
The voltages and currents of the high frequency planar transformer are respectively presented in Fig. 13 (a) and Fig. 13 (b). The transformer secondary voltage (Vs2) transient which corresponds to the change of sign of the current (Is2) is caused by the transformer leakage inductance.
59
Fi ure 19.si 19.simul mulati ation on circui circuitt for for full full brid brid e conver converter ter
60
Figure 20 (a). Super capacitors module voltage and current
20(b): DC-link and active load experimental currents
61
Figure. 21(a) Transformer input and output voltages
Figure 21(b) Transformer input and output currents Figure 21. High frequency planar transformer voltages and currents
62
CONCLUSION In this paper, multi boost and multi full bridge converter topologies and their control strategies for batteries and super capacitors coupling in the hybrid vehicle applications were proposed. For reasons of simplicity and cost, the multi boost converter is the most interesting topology regarding the multi full bridge converter topology. It enables a good power management in hybrid vehicle.
Full bridge experimental tests conditions were different from that of boost converter topology, so at this time it is not easy to make a good comparison between the two topologies. However, multi full bridge converter topology is well suitable to adapt the level of available voltage to the DC-link. For low voltage and high current applications such as super capacitors, the full bridge converter seems to be less interesting because of its higher cost (many silicon and passive components), and a lower efficiency.
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REFERENCES [1] J.M Timmermans, P. Zadora, J. Cheng, Y. Van Mierlo, and Ph. Lataire. Modelling and design of super capacitors as peak power unit for hybrid electric vehicles. Vehicle Power and Propulsion, IEEE Conference, 7-9 September, page 8pp, 2005.
[2] Huang jen Chiu, Hsiu Ming Li-Wei Lin, and Ming-Hsiang Tseng. A multiple- input dc/dc converter for renewable energy systems. ICIT2005, IEEE, 14-17 December, pages 1304–1308, 2005.
[3] M.B. Camara, H. Gualous, F. Gustin, and A. Berthon. Control strategy of hybrid sources for transport applications using supercapacitors and batteries. IPEMC2006, 13-16 August, Shanghai, P.R.CHINA, 1:1–5, 2006.
[4] L. Solero, A. Lidozzi, and J.A. Pomilo. Design of multiple-input power converter for hybrid vehicles. IEEE transactions on power electronics, 20, Issue 5, 2005.
[5] Xin KONG and A. KHA. Analysis and implementation of a high efficiency, interleaved current-fed full bridge converter for fuel cell system. IEEE, 28-01 Nov, 1:474–479, 2005.
[6] M.B. Camara, F. Gustin, H. Gualous and A. Berthon. Studies and realization of the buck-boost and full bridge converters with multi sources system for the hybrid vehicle applications. Second European Symposium on Super capacitors and Applications, ESSCAP2006, Lausanne, Switzerland,2-3 November, 2006.
[7] Huang-Jen Chiu, Hsiu-Ming, Li-Wei Lin, Ming-Hsiang Tseng. A Multiple-Input DC/DC Converter for Renewable Energy Systems, Industrial Technology, ICIT2005, IEEE international Conference, 14-17 December 2005, Pages: 1304-1308.
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