Chapter 1
Introduction
Nowadays, carbon dioxide (CO2) production and emission by the power conversion process in power plants and other gasoline engines are considered as one of factors of air polluted, ozone depletion, acid rain, and global warming problems. The scarcely of both crude oil and gasoline will also be significant in the near future. Therefore, many research works have been doing recently in order to discover new energy sources. One of them is st fuel cells, which are expected to help and solve the above-mentioned problems in the 21 century. Fuel cells show the obvious advantages of high efficiency production, low power density needed, and less noise operated system with a clean operation compared with gasoline engines. This research is to study the basic concept and characteristics of an electric drive system of wheelchair, using the fuel cells. In experiments, we started the study by using the low capacity fuel cells with 200 W. However, this low power can be applied to small size equipment, therefore, the electric wheelchair is proposed. In the original wheelchair, the lithium-ion battery is used as a main electric power supply, and also used the motor control system is composed a switching relay. Here, we used the fuel cells instead of lithium-ion battery with a new control circuits design. The Electric Double Layer Capacitors (EDLCs) is used for an energy buffering device, power flow managements in control circuit and blower fan control. In this work, the main study is focused on the characteristics of the fuel cells and the environmental effects; temperature, humidity, and pressure. Using higher power of fuel cells will be continued for the further works. The applications to drive a larger size car will also be investigated
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Chapter 2. Component Overview used in electric drive of wheelchair 2.1Fuel Cells
2.1.1 Introduction of fuel cells In this research objectives to investigate fuel cells applications used as a power source of an electric wheelchair. Fuel cells have obvious advantages in high efficiency, clean power in conversion process, quiet when it is operation and low power densities. The fuel cell was invented in 1839 by Sir William Grove when he tried reversing the process of splitting water using electricity (electrolysis). The first fuel cells capable of generating significant power were not produced until 1959 where they were used in demonstrations to power a welding machine and a tractor. NASA used fuel cells in the space program and much research continued to make them a better power source for transportation. 2.1.2Basic operation of fuel cells All fuel cells combine hydrogen and oxygen (the fuel) to produce electricity, water and heat. Like a battery, a fuel cell has a positive electrode (anode) and negative electrode (cathode) between which electricity moves, and a solution (electrolyte) that carries ions between the electrodes. The basic fuel cells concept involves converting chemical energy directly to electrical energy. Fuel cells produce electricity by electrochemically combining fuel (hydrogen) and oxygen (from air) through electrodes and across an ion-conducting electrolyte. The basic structure of fuel cell is shown in figure 1.the main function of the electrode is to bring about a reaction between the reactant and the electrolyte. The anode, used as the negative post in the fuel cells. disperses the hydrogen gas equally over the entire catalyst surface and conduce the electron for use as power in external circuit. The cathode, used as the positive post in the fuel cell, distributes the oxygen fed to it into the catalyst. surface and conduct the electron back from the external circuit. The catalyst is a special material used to facilitate the oxygen and hydrogen reaction. Useful Power
A Fuel inlet (Hydrogen)
Depleted Fuel Out
Oxidant Inlet (from Humid Air)
+Ions C h a G n a n s e l
or -Ions
C h a G n a n s e l
Electrolyte
Anode
Unused Air & Product water
Cathode
Figure 2.1 Basic structures of fuel cells -2-
The PEM (Proton Exchange Membrane) fuel cells is one of the most promising fuel cell types, and is often considered a potential replacement for the internal combustion engine in transportation applications the PEM fuel cells consist of porous carbon electrodes bound to thin sulphonated polymer membrane. The anode, and net cell reactions of the PEM fuel cell can be represented as -Anode reactionR(a -Cathode reactionRc(
):H 2
O ):2 +4H
2H +
+
+ 4e
+ 2 e\u2212
\u2212
2H 2O(l )
(2.1) (2.2)
-Overall reaction: H +1 O 2 2 2
H 2O(l ) +Heat(Q) +ElectricalEnergy
(2.3)
2.1.3The PEM fuel cells The diagram above illustrates how a PEM (Proton Exchange Membrane) fuel cell works. Hydrogen gas is fed into the fuel cell at left and oxygen (from air) is fed at right. The hydrogen gas reacts with a catalyst (leftmost gray panel), which separates it into individual atoms. The hydrogen atoms are attracted to the oxygen on the other side and must pass through a membrane (middle gray panel) to reach the oxygen. The membrane is a special type that only lets the protons (or hydrogen ions) through and will not allow electrons to pass. So the electrons must separate from the atoms at the left electrode and travel through the electrical circuit to rejoin the atoms on the other side of the membrane. The hydrogen ions, electrons and oxygen all combine on the other side at the right electrode to produce water and heat as the only byproducts of the reaction. 2.1.4Fuel cells in Experimental Study In this project used PEM fuel cells were used for supplies electric power to drive 2 DC motors in electric wheelchair. The specifications of the fuel cells are shown in table 2.1
(a)
-3-
(b) Figure 2.2(a) PEM fuel cell stack,(b) Hydrogen storage alloy
Fuel cell type PEM Rated output power 200 W Maximum output power 250-280 W Rated output voltage 24 V Maximum output voltage 36 V Maximum fuel input pressure 0.05 Mpa o Operating Temperature 5-40 C Table 2.1 specifications of fuel cells 2.2 Electric Double Layer Capacitors 2.2.1 Introduction of Electric Double Layers Capacitors (EDLCs) The components used to storage energy are known as capacitors. The volume of storied is farad (F) in case of ordinary capacitor has capacity in milli-farad to pico-farad but EDLCs have capacity in several hundred to thousand farads. In this research EDLCs are employed to storage energy generated from the fuel cells when motor system does not need energy. The reason why EDLCs are used for energy storage is that they can rapidly to charged and discharged much faster than ordinary batteries or other storages device. However, the converter circuit is required in this case of charged and discharged. Batteries store electricity by converting it to chemical energy. Capacitors, which have been used for long time in electronics circuits store electricity as it is without carrying out any conversion. Although the storage capabilities of capacitors used to be much smaller than that of batteries, nowadays the large capacity have been developed. EDLCs are often called super- or ultra-capacitors.
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collector + + +
polarizing electrods
+ + + +
-
-
collector
electrolyte +
separator + + + + + + + -
electric double layers +
-
Figure 2.3 Principle of electric double layer capacitor When two carbon rods are immersed in a thin sulfuric acid solution, separated each other and applied a slowly raising voltage from zero toward 1.5 volts, almost nothing happens up to 1 V, then at a little over 1.2 V, small bubbles would appear on the surface of the both electrodes. By raising voltage more, should be get vigorous generation of bubbles. Those bubbles at the voltage above 1 V indicate electrical decomposition of water. Below the decomposition voltage, while the current does not flow, there an "electric double layer" does occur at the boundary of electrode and electrolyte. The electrons are charged across the double layer and form a capacitor. When bubbles are coming up at voltages above 1 V, this indicates the capacitor is breaking down by over-voltage causing decomposition of the electrolyte. EDLCs using water-soluble or aqueous electrolytes can be used at a withstanding voltage of about 1 V. Electrical double layer works as an insulator only below the decomposing voltage. When the usable voltage is V and the capacity C then the stored energy U will be, U = CV /2 (2.4) Hence, the higher rated voltage V is desirable for larger energy density capacitors. Up to now, capacitor rated voltage with an aqueous electrolyte is about 0.9V per cell and with non-aqueous electrolyte is 2.3 to 3.3 V for each cell. Figure 2.3 illustrates the structure of a typical EDLC.Small EDLCs up to 100 farads are now quite popular. There is a big merit in using an electric double layer in place of plastic or aluminum oxide films in a capacitor. Since the double layer is very thin, as thin as one molecule with no pin 2 2 holes, the capacity per area is quite large at 2.5~5 μF/cm . Even if a few microfarads/cm are obtainable, the energy density of capacitors is not too large by using aluminum foil or such. For increased capacitance, electrodes are made from special materials that have a very large surface area, such as activated carbon. Activated carbons are famous for their 2 surface areas of 1000 to 3000m /g. How could it be possible to accommodate such a large area within one gram of carbon. 2
-5-
2.2.2 EDLCs Capacitor in Experimental Study
The most important device is used in research for stored energy from fuel cells generation system is EDLCs. EDLCs used in this study have capacity=1350farads,votage=2.7 V. photograph of the EDLCs is shown in figure 2.4,which constructor is consist of 4 EDLC units.
Figure 2.4 EDLCs in experimental study
2.3 DC-DC converter circuit
2.3.1 Introduction of basic principle of DC-DC converter circuit Before designing dc-dc converter circuit, it is necessary to know about basic principle of the dc-dc converter circuit. This research study about DC motor control for the example speed control direction control the simple are increase or decrease voltage is supplied by control from dc-dc converter circuit. The step down dc-dc converter is buck converter and the step up converter is a boost converter. In this research both of the buck and the boost converter were used to control the voltage in the motor control circuit. 2.3.2 Buck converter Buck conversion is step-down conversion if take a look at the fuel cells generation system was use buck topology in EDLCs charged system and Motor control system. In other thing, Buck converter is explained in the fuel cells connected with EDLCs at first. 2.3.3 Basic Circuit Operation
The operation of the buck converter is explained first. This circuit can operate in any of the three states as explained below. The first state corresponds to the case when the switch is ON. In this state, the current through the inductor rises, as the source voltage would be greater than the output voltage, whereas the EDLCs current may be in either direction, depending on the inductor current and the load current. When the inductor -6-
current rises, the energy stored in it increases. During this state, the inductor acquires energy. When the switch is closed, the elements carrying current are shown in red color in Figure 2.5, whereas the diode is in gray, indicting that it is in the off state. In Figure 2.5(a), the EDLCs are getting charged, whereas it is discharging in Figure 2.5(b). Blocking Diode
L
Fuel cells
r
o
24 V
+
+
D
-
EDLCs
+ Vo -
(a)
Blocking Diode
L
Fuel cells
r
o
24 V
+
+
D
-
EDLCs
+ Vo -
(b) Figure 2.5 first state of buck converter circuit The equations that govern the operation of the circuit in the first state are shown below. diL dt
VFC −Vo
=
dvO dt
L
=
i L −VO / X EDLCs EDLCs
(2.5) (2.6)
The second state relates to the condition when the switch is off and the diode is ON. In this state, the inductor current free-wheels through the diode and the inductor supplies energy to the RC network at the output. The energy stored in the inductor falls in this state. In this state, the inductor discharges its energy and the EDLCs current may be in either direction, depending on the inductor current and the load current Figure 2.6 Illustrates the second state.
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Blocking Diode
L
Fuel cells
r
o
+
+
24 V
D
-
EDLCs
+ Vo -
(a) Blocking Diode
L
Fuel cells
r
o
+
+
24 V
D
-
EDLCs
+ Vo -
(b) Figure 2.6 Buck converter in second state The equations that govern the operation of the circuit in the second state are shown below. diL dt dvO dt
VO
=−
=
(2.7)
L
i L −VO / X EDLCs EDLCs
(2.8)
When the switch is open, the inductor discharges its energy. When it has discharged all its energy, its current falls to zero and tends to reverse, but the diode blocks conduction in the reverse direction. In the third state, both the diode and the switch are OFF and Figure 2.7 illustrates the third state. During this state, the EDLCs discharge its energy and the inductor is at rest, with no energy stored in it. The inductor does not acquire energy or discharge energy in this state.
-8-
Blocking Diode
L
Fuel cells
r
24 V
o
+
+
D
-
EDLCs
+ Vo -
Figure 2.7 Buck converters at third state The equation that governs the operation of the circuit in the third state is shown below. VO / X EDLCs
dvO
=−
dt
(2.9)
EDLCs
When the circuit receives a periodic signal, the response of the circuit also becomes periodic. Here it is assumed that the source voltage remains constant with no ripple, and the frequency of operation is kept fixed with a fixed duty cycle. If the RC time constant due to the load resistor and the filter capacitor is very large compared to the cycle period of the switching frequency, the output voltage is more or less constant, with no noticeable ripple. When both the input voltage and the output voltage are constant, the current through the inductor rises linearly when the switch is ON and it falls linearly when the switch is OFF. Under this condition, the current through the capacitor also varies linearly when it is getting charged or discharged. 2.3.4 Buck Converter Circuit Design Blocking Diode
L
Fuel cells
r
o
24 V
+
+
D
-
EDLCs
+ Vo -
Figure 2.8 VO
Duty ratio (D)= V
FC
(2.10)
The inductor is determined from:
(1−D ) XC = Lmin 2f
(2.11)
If we design for continuous inductor current. Let the inductor be 25% larger -9-
Than minimum to ensure that inductor current is continuous: L =1.25L min The EDLCs is selected using from: EDLCs =
ΔVo Vo
1 −D ⎛ ΔVo ⎞ 2 ⎟ 8L⎜⎜ ⎟f V ⎝ o ⎠
(2.12) (2.13)
=The output voltage ripple.
2.3.5 Boost converter step-up converter
Boost conversion is step-up conversion if take a look at the fuel cells generation system was use boost topology in EDLCs discharged and supplied energy to system when the case of system need high power. Figure. 2.9 is shown the basic boost converter. This circuit is used when a higher output voltage than input is required. Input
Vin
L
+ EDLCs
D
Vx
Q
Output
C1
Vo
-
Figure 2.9 Boost Converter Circuit While the transistor is ON Vx =Vin, and the OFF state the inductor current flows through the diode giving Vx =Vo. For this analysis it is assumed that the inductor current always remains flowing (continuous conduction). The voltage across the inductor is shown in Figure 2.10and the average must be zero for the average current to remain in steady state V inton =+(Vin −Vo)toff =0
(2.14)
This can be rearranged as Vo Vin
=
T toff
=
1
(1−D )
(2.15)
And for a lossless circuit the power balance ensures Io Iin
=(1 −D )
- 10 -
(2.16)
(Vin)
VL
ton
T toff
Inductor current
T Vin-Vo Time
Figure 2.10 Voltage and current waveforms (Boost Converter) Since the duty ratio "D" is between 0 and 1 the output voltage must always be higher than the input voltage in magnitude. The negative sign indicates a reversal of sense of the output voltage.
- 11 -
Chapter 3 Electric Wheelchair System and new modified system
3.1 Introduction of Electric Wheelchair
A wheelchair is a small vehicle to help and facilitate someone who cannot walk by self. The conventional wheelchair was moved manually, but when motor drive system is developed, it can be used in many applications. Then, wheelchair was changed from manual wheelchair to electric wheelchair. Presently, many kinds of electric wheelchair, batteries to power in the DC motor drive system. In this research, to study one of the fuel cells applications, we focus on the DC motor drive system and its power flow management.
3.2 Electric wheelchair to investigated in research study
The original electric wheelchair used lithium-ion battery as power supplies to the DC motors and drive system, which employed a relay algorithm for switching direction and speed control. The photographs of the original electric wheelchair are show in figure 3.1
Figure 3.1 Photographs of original wheelchair before modified (a) Front view (b) Side view (c) Back view (d) Joy stick This electric wheelchair is manufactured by AISIN Company and the table 3.1 is shown the electric wheelchair specifications. 106×64×88cm Side Weight 23 kg. Lithium-ion 25.9V × 6Ah Battery type 2 DC motor 24V 90W × 2 Motors Maximum Speed 6km/hr Table 3.1 Specifications of electric wheelchair from AISIN Company
- 12 -
3.2 Explanation of new modified system In the new modified system, the power supply is changed from lithium-ion battery to fuel cells and a chopper circuit is newly designed. The simple diagram of new modified system is shown in figure 3.2. Fuel Cells Generation System
EDLC CAPACITOR
Joy Stick
Energy Storage
Main Control And Motors Drive System
Left Motor
Right Motor
Figure 3.2.Simple diagram of new modified system The simple diagram on figure 3.2 can be separated to explain 5 parts individually and this chapter explains its structure and simple diagram but does not explain all the details of each part because perfect details of each part are explained in other chapter. -Fuel cells generation system. This part is very important and main part of this research study. The power supply is changed from lithium-ion to the low power fuel cells. The fuel cells need the control circuit for Blower fan and energy storage and control circuit necessary. All the details of the fuel cells generation system are explained in chapter 2. -Energy storage There are many storage devices can be used in this part but EDLCs are the most interesting. Because of in EDLCs’ characteristics, for the example, EDLC capacitor can be charged and discharged at extremely high speed. All the details of EDLCs are explained in chapter 2. - Main control and motor drive system This part will be explained in chapter 4. -Left motor and right motor This wheel chair system was use 2 DC motors, rated of power =90 watts × 2, rated of voltage=24volt. -Joystick A Joystick was used in this research, which has 4 normal on switches. - 13 -
Hydrogen Control Storage Fuel Cells Box Alloy
Figure 3.3 Drawing layout of new modified design (Top view)
- 14 -
Chapter 4 Main control and motors drive circuit
4.1Introduction in motors drive circuit system To control the DC motor, a circuit well known as a full bridge circuit is widely used. The basic of the full bridge circuit is shown in figure 4.1(a) each side of the DC motor needs 4 MOSFET switching devices. It is easy to control the motor for traction system forward, backward operation and speed adjustment by feeding PWM to MOSFET switching. However, if the system has 2 DC motors in the wheelchair system and use full bridge for the chopper circuit, 8 MOSFET switching devices must be used in this system. But for this research, a new topology of the chopper for motor control is proposed to left and right motors. The new designed topology is shown in figure 4.1(b) this chopper use 6 MOSFET switching devices and used Q3 and Q4 to share the current path in the case of controlling motor forward or backward. Therefore, this chopper circuit can save the number of switching device, power, and can increase total efficiency.
Q1
Q3
D1
+
Q2
M
D3
Q1
+
-
D2
Q3
D1
Q4
D4
Q2
M
D3
Q5
+
-
D2
Q7
D5
D4
Q4
Q6
M
D7
-
D6
Q8
D8
(a) Blocking Diode
Q1
Fuel cells
r
o
24V
+
Q3
D1
C1
+
DC-CT(L)
M1
+
-
Left Motor Q2
D2
Q5
D3
Q4
M2
-
D5
DC-CT(R)
Right Motor D4
Q6
D6
(b) Figure4.1 (a) Full bridge circuit (b) new designed chopper circuit
To explain this circuit simple manner, what follow is described by separating some operation conditions. First, when the main motors are controlled in condition 1,the left motor and the right motor go forward, in condition 2 the one motor goes forward and the one goes backward and condition 3 both of motors go the one backward. In this section is only basic motors control explained, and the detail of motor control circuit will be explained in the next section.
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4.1.1Condition 1 left motor and right motor in forward operation This condition can occurs when the wheelchair goes forward both of the motors must go forward and the speeds of the motors depend on PWM signals fed into Q1 and Q5.In drive operation case where Q3 and Q4 are fed PWM signal of duty cycle=0.5 at frequency 1 KHz. All of the PWM signals are generated a PWM generator of the MCS51 micro-controller.
(a) Blocking Diode
Q1
Fuel cells
r
o
24V
Q3
D1
PWM
PWM
+
C1
+
DC-CT(L)
M1
Q2
D2
PWM
+
-
Left Motor OFF
Q5
D3
Q4 PWM
M2
-
DC-CT(R)
Right Motor D4
Q6 OFF
(b)
Figure4.2. (a) The direction of wheelchair moving (b) Motors Control Circuit operated in condition 1
For explain this condition and how does the circuit work can be used signal diagram as follow figure 4.3 This circuit used PWM signal operated at different frequency Q1, Q2, Q5, Q6 are used PWM signal operated at 10 KHz, Q3 and Q4 are used PWM signal operated at 1 KHz.
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Q1 Q2 Q3 Q4 Q5 Q6 VL
5V
0V
5V
0V
5V
0V
5V
0V
5V
0V
5V
0V
IL
24V
0V
IR
24V
VR
0V
Figure 4.3 Signal Diagram of circuit when operated at condition1
The speeds of left motor and right motor depend on duty cycle of PWM signal if duty cycle is increased this mean the RMS voltage of VR and VL are increased, too. The most important things of this circuit operation are Q3 and Q4.Because the Q1 and Q5 are required Q4 for switch connected to ground and make the current flow pass the armature coil of DC motor and make the motors go forward motoring. VL and VR from signal diagram in figure4.3 VL is output voltage as supplied to left motor and VR is output voltage as supplied to right motor. 4.1.2Condition2 left motor in forward operation and right motor in backward operation This condition can occur when the wheelchair pivots right, the left motor must go forward and the right motor must go backward. The direction of the current and energy flow can be represent on figure 4.4(a)
(a) - 17 -
Blocking Diode
Q1
Fuel cells
r
24V
o
Q3
D1
PWM
PWM
+
C1
+
DC-CT(L)
M1
D2
OFF
OFF
+
-
Left Motor Q2
Q5
D3
Q4
M2
-
DC-CT(R)
Right Motor D4
Q6
PWM
PWM
(b)
Figure 4.4 (a) The direction of wheelchair moving (b) Motors Control Circuit operated in condition 2 This condition can be explained by the signal diagram is shown in figure 4.5 Q1and Q6 are fed PWM signal by MCS51 micro-controller at frequency=10KHz.Q3 and Q4 are always fed PWM signal frequency=1 KHz, duty cycle=50%. Take a look figure 4.5 Voltage and current of right motor are negative side. Therefore, voltage across at right is minus value this means right motor goes backward. However, the speed of the motor depends on the duty cycle of the PWM signal.
Q1 Q2 Q3 Q4 Q5 Q6 VL
5V
0V
5V
0V
5V
0V
5V
0V
5V
0V
5V
0V
IL
24V
0V
24V
VR
0V
IR -24V
Figure 4.5 Signal Diagram of circuit when operated at condition 2
- 18 -
4.1.3 Condition 3 both of motors in backward operation This condition can be occurred when the wheelchair moves backward. Both of the motors must rotate backward. The direction of the current and the energy flow can be represented in on Figure 4.6
(a) Blocking Diode
Q1
Fuel cells
r
o
24V
Q3
D1
PWM
OFF
+
C1
+
DC-CT(L)
M1
D2
PWM
Q4 PWM
(b)
OFF
+
-
Left Motor Q2
Q5
D3
M2
-
DC-CT(R)
Right Motor D4
Q6 PWM
Figure 4.6 (a) The direction of wheelchair moving (b) Motors Control Circuit operated in condition 3 This condition can be represented by a signal diagram as shown in figure6.7 Q2and Q6 are fed PWM signal by MCS51 micro-controller at frequency=10KHz.Q3 and Q4 are always fed PWM signal frequency=1 KHz, duty cycle=50%. Take a look figure 4.7 Voltage and current of right motor are negative side. Therefore, voltage across at right is minus value this mean the right motor goes backward. However, the speed of the motor is depends on duty cycle of the PWM signal.
- 19 -
Q1 Q2 Q3 Q4 Q5 Q6 VL
5V
0V
5V
0V
5V
0V
5V
0V
5V
0V
5V
0V
24V
IL
0V
-24V 24V
VR
IR
0V
-24V
Figure4.7 Signal Diagram of circuit when operated at condition 3
4.1.4 Summarized of all condition Condition Forward Turn Left Turn Right Pivot Left Pivot Right Backward Stop
Switching MOSFET gate signal
Q6 OFF
Q5 PWM
Q4 PWM
Q3 PWM
Q2 OFF
Q1 PWM
OFF
PWM
PWM
PWM
OFF
OFF
OFF
OFF
PWM
PWM
OFF
PWM
OFF
PWM
PWM
PWM
PWM
OFF
PWM
OFF
PWM
PWM
OFF
PWM
PWM
OFF
PWM
PWM
PWM
OFF
OFF
OFF
OFF
OFF
OFF
OFF
Table 4.1Signals at each switching when operated in basic condition
4.2 Control Circuit explanation
This wheelchair system using a micro-controller AT89C51ED2 (8 bits micro controller), which is capable to generated PWM waveform and all parts control in the system for the example input direction control from Joy Stick, blower EDLCs charged and discharged control regeneration over voltage resister discharged control, etc. The block diagram of the electric wheelchair controller is shown in figure 4.9
- 20 -
D9
Q10
Q9
Fuel cell M3
24V
Q7
Q1
Q3
D1
Q5
D3
D5
D7 +
C1
DC-CT(L)
+
L1 C2
Blower Motor
R32
-
+
Left Motor
EDLC
Q8
M1
Q2
-
DC-CT(R)
Right Motor Q4
D2
M2
D4
Q6
D6
D8
C1 voltage detect
Blower control
Chopper 4 control
EDLCs voltage detect
Chopper 1 control
Regeneration Over voltage protection
Regeneration Current Detection
Microcontroller
Chopper 2 control
Chopper 3 control
Regeneration Current Detection
Joy Stick and Speed control
Figure 4.9Main control circuit From the diagram in figure 4.9 every part is controlled by 8 bit micro controller. Q1 and Q2 is MOSFET switching for controlled the left side motor and PWM signal at frequency=10KHz is fed by chopper 1 control, Q3 and Q4 is MOSFET switching for controlled both of motors and share current path and the PWM signal at frequency=1KHz is fed by chopper 2 control, Q5 and Q6 is MOSFET switching for controlled the right side motor and PWM signal frequency =10 KHz is fed by chopper 3 control. However, the duty cycle of PWM signal is depends on speed control. Q7 and Q8 is MOSFET switching for control charged and boost of power to main system and the PWM signal is fed by chopper 4 control. Q9 is MOSFET switching for control power flow to regenerative over voltage-discharged resister. Q10 is MOSFET switching for controlled fuel cells blower voltage. As below are block diagram explanations. -Micro controller: To used for control all part in chopper circuit, Generated PWM signal for con trolled of all MOSFET switching, input of direction controlled from Joy Stick, input of voltage and current detect. -Chopper 1 control: Dead time compensation for protected of over current sort to ground at Q1 and Q2 -Chopper 2 control: Dead time compensation for protected of over current sort to ground at Q3 and Q4 -Chopper 3 control: Dead time compensation for protected of over current sort to ground at Q5 and Q6 -Chopper 3 control: Dead time compensation for protected of over current sort to ground at Q7 and Q8 *The schematics of control circuit are shown in Appendixes A and
- 21 -
4
Generation Not full Motoring charged (Need high power)
VB
Oxigen
Blower
Steam
EDLC
CAPACITOR
Gage
Hydrogen Storage Alloy
Hydrogen
Fuel Cells Stack
DC MOTOR
Discharged Resister
Mode 1
or VB
Oxigen
Blower
Steam
EDLC
DC MOTOR
CAPACITOR
Hydrogen Storage Alloy
5
Stop
Full charged
Stop
VB
Generation Not full charged
Hydrogen
Blower
Fuel Cells Stack
Discharged Resister
Oxigen
Steam
EDLC
DC MOTOR
CAPACITOR
Hydrogen Storage Alloy
6
Gage
Stop
Hydrogen
Gage
VB
Discharged Resister
Fuel Cells Stack
Oxigen
Blower
Steam
EDLC
CAPACITOR
Hydrogen Storage Alloy
Gage
Hydrogen
DC MOTOR
Fuel Cells Stack Discharged Resister
Mode 6
7
Generation
Full Regeneration charged
VB
Blower
Oxigen
Steam
EDLC
DC MOTOR
CAPACITOR
Hydrogen Storage Alloy
8
Generation Not fullRegeneration charged
Gage
Hydrogen
Fuel Cells Stack
Discharged Resister
Mode 7
VB
Blower
Oxigen
Steam
EDLC CAPACITOR
Hydrogen Storage Alloy
Gage
Hydrogen
Fuel Cells Stack
DC MOTOR
Discharged Resister
Mode 8
Table4.2Power flow control managements in control circuit
- 23 -
Chapter 5 Experimental Results
5.1 Fuel Cells Experimental Results
For use fuel cells in application the most important things are characteristics of fuel cell. Because of the fuel cells are completely different from conventional battery (Lead-Acid battery). For example, the fuel cells cannot recharged electrically unlike normal batteries or conventional batteries (If fuel cell is charged it will be broken) fuel cells have high inner resistance, fuel cell is very sensitive to environmental factors (temperature, pressure, humidity) 5.1.1Experimental study when connect fuel cells with resistance load The first of experiment was fuel cell characteristics in order to supply a resistance load. The circuit diagram of experiment is shown in figure 5.1.The Blower is supplied by an external power supply and its voltage was 22 V, H2=0.02Mpa then to set RL After that measured load voltage, current and power output. VB
Blower Oxygen Steam
RL
Gage
Hydrogen Storage Alloy
Hydrogen
Fuel Cells Stack
Figure 5.1 the circuit diagram of experimented set up
Before do the experimental fuel cells must be warm up less than 5 minutes. o Hydrogen pressure =0.02Mpa,Temperature=20.4 C Humidity=96.8%,Envelopment Pressure=999.5Hpa Blower Voltage=22V
30 28 26 24
) (V 22 e g a tl 20 o V t 18 u p t u O16 14 12 10
0
2
4
6
8
Output Current(A)
(a)
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10
12
14
o Hydrogen pressure =0.02Mpa,Temperature=20.4 C Humidity=96.8%,Envelopment Pressure=999.5Hpa
200
Blower Voltage=22V
190 180 170 160
) (tW150 u 140 p t u 130 O r e 120 w o P 110 100 90 80 70
2
3
4
5
6
7
8
9
10
11
12
13
Output Current(A)
(b) Figure5.2 Experimental results PEM fuel cell characteristics (a) V-I curves (b) P-I curves 5.1.2 Experimental study about sensitive of fuel cells are performed by environmental factors (Temperature, Humidity, Pressure)
30
Condition1 Condition2 Condition3
28 26 24 22
) 20 (V18 e g 16 a lt o 14 V t 12 u p t 10 u O 8 6 4 2 0
0
2
4
6
8
10
Output Current(A)
(a)
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12
14
200
Condition1 Condition2 Condition3
190 180 170 160
) 150 W t( 140 u 130 p t u 120 O r 110 e w 100 o P 90 80 70 60 50
2
3
4
5
6
7
8
9
10
11
12
13
Output Current(A)
(b)
Figure 5.3 Experimental results PEM fuel cell characteristics compare when the environment is different (a) V-I curves (b) P-I curves o Condition1. Hydrogen pressure =0.02Mpa,Temperature= 20.4 C
Humidity=96.8%, Environment Pressure=999.5Hpa,BlowerVoltage=22V o Condition2. Hydrogen pressure =0.02Mpa,Temperature= 7 C Humidity=72.3%, Environment Pressure=1026Hpa,BlowerVoltage=22V o Condition3. Hydrogen pressure =0.02Mpa,Temperature=24. 7 C Humidity=71.2%, Environment Pressure=1013Hpa,BlowerVoltage=22V
From this experimental results can be show the fuel cells is very sensitive to environmental factors (temperature, pressure, humidity) 5.1.3 Experimental study of step load is change In the case of step load change, when this case is occurred fuel cell can be operated or not is proposed of this experimental study. About experiment fuel cells is connected as follows shown in figure 5.4, S1 is electronics switch and the switching frequency was set at 20 kHz and measured load voltage and load current waveform where measured, which is shown this show in figure 7.5
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VB
Blower Oxygen
R2
Steam
R1
S1
Hydrogen Storage Alloy
Gage
Hydrogen
Fuel Cells Stack
Figure 5.4 Circuit diagram of experiment set up
6.5 6.0 5.5
e 5.0 g a lt o V 4.5 4.0 3.5 3.0 2.5 -1.0x10
-4
-5.0x10
-5
0.0
5.0x10
-5
1.0x10
time(s)
Figure 5.5 Load voltage and waveform
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-4
45 40 35 30
) (A t 25 n e rr u C 20 15 10 5 0 -1.0x10
-5.0x10
-4
-5
0.0
5.0x10
1.0x10
-5
-4
time(s)
Figure 5.6 Load current waveform 5.1.4Experiment about air volume in Fuel cell Fuel cell needs oxygen for chemical reaction. The oxygen volume is controlled and supplied to fuel cell by blower. In this experiment if blower voltage is low this mean low air or oxygen volume to flow into fuel cell and blower voltage is high this mean high air or oxygen volume to flow into fuel cell. Figure 6. Shows the variation of the output power during blower voltage is changed after 1 minute. Hydrogen pressure=0.02MPa,T=2.7 C Humidity=58.1 % ,Pressure=1000HPa o
160
decrease increase
140 120
) W (t u 100 tp u o r 80 e w o 60 P d a o L 40 20 0
5
10
15
20
25
30
Blower voltage(V)
Figure 5.7The relation between output power and voltage of the blower in fuel cell
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5.1.5 Hydrogen pressure In this experimental hydrogen pressure is controlled by gage pressure. The blower is supplied by external DC power supply and voltage =22 V. We changed hydrogen pressure from 0.005 –0.04 MPa, and changed load resistant. Blower voltage=22V,T=7.9 C,Humidity=68.60%,Pressure=1006HPa o
Hydrogen pressure=0.005MPa Hydrogen pressure=0.01 MPa Hydrogen pressure=0.015MPa Hydrogen pressure=0.02 MPa Hydrogen pressure=0.025MPa Hydrogen pressure=0.03 MPa Hydrogen pressure=0.035MPa Hydrogen pressure=0.04 MPa
140
120
) W r( e w o P 100 t u p t u O d a o 80 L
60
3
4
5
6
7
8
Load Output Current(A)
Figure 5.8 Graph of Power versus Load output current in case the different of hydrogen pressures are fed into fuel cells. 5.2 Motors control Circuit Testes and Experimental Results 5.2.1 PWM signal measurement 5V
Q1
5V
Q3
5V
Q4
5V
Q5
Figure 5.9 PWM signal at Q1, Q3, Q4 and Q5 when operated at forward condition - 29 -
5.3.2 Test of output power of motors control circuit 200
150
) W (r e w100 o P t u p t u O 50
0 0
20
40
60
80
100
Duty cycle of PWM(%)
Figure 5.10 Graph power output versus duty cycle of PWM signal 5.3.2 Test of efficiency in motors control circuit 100 90 80 70
) 60 % ( y c 50 n ie icf 40 f E 30 20 10 0
0
20
40
60
80
100
Duty cycle of PWM Signal(%)
Figure 5.11 Graph efficiency versus duty cycle of PWM signal
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5.3 Fuel Cells connected with control circuit experimental Results -
Experiment about power from fuel cell when drive at no load condition
This experiment is focused on characteristic of fuel cells when drive a wheelchair in each condition. The graph of this experimented are shown in Figure 5.12 in standby or stop mode fuel cells operated power for 3 main parts control circuit, the blower and EDLCs. If user start to run forward at the first time motors need high power for moving and fuel cells can operated at this case.
140
140
140
120
120
120
120
) W 100 ll( e C l e 80 u F f o 60 r e w o P 40
) W 100 ll( e c l e 80 u F f o 60 r e w o P 40
) W 100 ll( e c l e 80 u F f o 60 r e w o P 40
) W 100 ll( e C l e 80 u F f o 60 r e w o P
20
20
20
20
0
0
0
-1.0x10
0
-5.0x10
-1
0.0
5.0x10
-1
1.0x10
0
-6.0x10
-1
-4.0x10
-1
Time(s)
STOP
FORWARD
-2.0x10
-1
0.0
2.0x10
4.0x10
-1
-1
6.0x10
-1
140
40
-6.0x10
-1
-4.0x10
Time(s)
STOP
STOP
TURN LEFT
-1
-2.0x10
-1
0.0
0 2.0x10
-1
4.0x10
-1
6.0x10
-1
-6.0x10
-1
-4.0x10
Time(s)
STOP
STOP
TURN RIGHT
-1
-2.0x10
-1
0.0
2.0x10
-1
Time(s)
STOP
STOP
BACKWARD
Figure 5.12 Graphs of Power from fuel cell drive at no load condition
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4.0x10
-1
6.0x10
-1
Chapter 6 Conclusion
Fuel cells is the electric power source equipment that using hydrogen and oxygen as the fuel in its chemical reaction and converts directly to electricity. However, the fuel cell is different from the conventional battery for example, it has high inner resistant, fuel cells are sensitive from environment factors (temperature, humidity, pressure), the important thing is characteristics of the fuel cell and making the control circuit support for application. For this study, because of limit power of the fuel cells, the wheelchair was selects for this research study. About motors control circuit, this research is tried to used newly chopper topology for save of power in system and increase of efficiency of chopper circuit Moreover, power flow controlled managements is necessary to study and applied to chopper circuit and this research present of this technique, energy stored device such as EDLCs was use to control circuit for stored energy from fuel cell. About experimental result in the drive operation when wheelchair goes forward for the start time motors need high power for start moving and fuel cell can be support and operated. The problem from this study: for the example, when start the fuel cell doesn’t convenient and difficult, the hydrogen storage alloy cannot store much more hydrogen hence, wheelchair cannot run for long time. About control circuit: control circuit is very large size and heavy. If we can solve these problem for the future study fuel cell is very interesting and can be use for high efficiency battery supplies in electric vehicle. Further of study for continue this research about the fuel cells, to develop the component for stored hydrogen much more and enough for long time operation and safety, making the control circuit for fuel cells consider environment factors (temperature, humidity, pressure). About control circuit, using high technology for micro-controller such as 32-bit micro-controller, SH micron and DSP. To reduces the side of control circuit and using the fuel cells for power supplied in larger size of car.
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Acknowledgment I would like to express my gratitude to Associate Professor Toshihiko Noguchi for suggestions, many ideas and support during my research from start until finish this research. And, I would like to thankfully to Mr.Kazuo Saito (Research Associate) for many helps and suggestions all the time when I made this research. Special thanks give to Mr.Keita Nakai the author’ Tutor for every things to help, support and idea. And also I would like to thank every body in Nuguchi laboratory and power laboratory for friendly and kindness. Moreover, I would like to thank to Thai people in Nagaoka for helps and support during stay in Japan. In addition I would like to thank to Nagaoka University of Technology, Division of International Affairs and Pathumwan Institute of Technology for support in exchange student program. Furthermore, I would like to express my gratitude to Mr.Sakon Udomsiri, Mr.Yuttana Pipattawatchai and all teacher staffs for knowledge and idea in electronics engineering for prepared before came to make this research in Japan. Finally, I would like to thank to my family, every friend and seniors for their great morale and spirit along of study.
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Reference [1] Ali Emadi, Mehrdad Ehsani and John M. Miller, “Vehicular electric power system: land, sea, air and space vehicles,” Marcel Dekker,Inc., 2004 [2] Gregor Hoogers, “Fuel cell technology handbook,” CRC Press, 2002 [3] Iqbal Husain, “Electric and hybrid vehicles : design fundamentals,” CRC Press, 2003 [4]Issa Batarseh, “Power Electronics Circuits,”John Wiley&Sons,Inc., 2004 [5]Rong-Jong Wai and Rou-Yong Duan, “Hight-Efficiency Power Conversion for Low power Fuel cell Generation System,”IEEE transactions on power electronics, VOL. 20,NO.4,July 2005 [6] Sitichote Janpaiboon, “Study on Mini Fuel-Cell and Its Application to Motor Drive of Electric Vehicle,” Nagaoka University of Technology, 2004
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5.4 Bill of all electronics devices Item Count Label-Value 1 5 1uF 2 2 0.1uF 3 12 1uF
Attributes POLAR0.6 RAD0.2 RAD0.2
4 5 6 7 8
4 1 2 5 29
10nF 3.3nF 33uF 10uF DIODE
RAD0.2 RAD0.2 RAD0.2 POLAR0.6 DOIODE0.4
9 10 11
1 1 10
DIODE CONN IRFB61N15B NDMOS
DIODE0.4 DB9/F TO-220AB
D14
12
10
10
AXIAL0.4
R1,R1,R2,R2,R3,R4,R5,R6, R9,R10,
13
13
1k
AXIAL0.4
R7,R9,R10,R11,R13,R17, R18,R19,R20,R26,R30,R33, R51,
14
8
82k
AXIAL0.4
R8,R23,R25,R27,R29,R31, R34,R35,
15 16
2 19
330 10k
AXIAL0.4 AXIAL0.4
R11,R12 R13,R14,R15,R16,R21,R21, R22,R42,R43,R44,R45,R46, R47,R48,R49,R50,R52,R53, R54,
17 18 19
4 3 4
240k
AXIAL0.4 SIP2 SOIC-8
R24,R28,R32,R36 S1,S2,S3 U1,U2,U3,U4,
20 21
1 1
78L10 78L05
22 23
4 2
LM5107
74LS04 74F132
Designation C3,C4,C5,C6,C28 C7,C8 C9,C11,C13,C15,C18,C19, C20,C21,C22,C23,C24,C25,
C17
C10,C12,C14,C16
C27,C28 C30,C31,C32,C33,C34 D1,D2,D3,D4,D5,D6,D7,D8, D10,D10,D11,D12,D13,D15, D16,D17,D18,D20,D21,D24, D25,D26,D26,D27,D27,D28, D29,D38,D39,
J1 Q1,Q2,Q3,Q4,Q5,Q6,Q7,Q8, Q9,Q10,
TO-92 TO-92
U5 U6
DIP14 DIP14
U11,U13,U18,U11A U11,U12
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24 25
4 4
26 27
2 4
28 29 30
1 1
1
LM311 DIP14 74LS125 DIP14 BUFFER3S TLP250 DIP8 100kvar SIP3 11.0592MHZ XTAL1 AT89C51ED2 DIP40 MAX232 DIP14
U15,U16,U23,U24 U19,U20,U21,U14A, U22 U7,U8 VR1,VR2,VR3,VR4 XTAL1 U9,
U17
D. Print Circuit Board of Main Circuit in Unit (inch)
*(Scale down)
5. 0
G N D
4. 0 U5 7812
Q1
Q9
+ + 2 5 4 V V
V a lv e S w
P 2
P 1
P 4
P 3
P 6
Q3
P 5
P 8
P 7
V (E D L C )
Q7
Q5
R 1 1
C9 C10
3. 0
D18 R9
D14 R5
D12 R3
D10 R1
D16 R7
C11C12
D1
D23 D24
2. 0
1. 0
C15 C16 GND VC1 ( ) +5V Fan Sp-C + 5V
U6
2 1 R
Q1 0
Q2
X
0
0 1.
R4 D13
R8 D17
R6 D15 Q6
Q4
C2 EDLC
L1
Q8 DC MOTORS DRIVE C IRCUI T FOR ELECTRICWHEELCHAIR
D20
+ Motor Left
+ GND GND + FCValve SW FC Fan
Y
D7
D8
D6
R2 D11
R1 0 D19
D21
0
D4
D2
C14 C13
D5
D3
0 2.
+ MotorRig ht
NOGUCHI LAB
0 4.
.0 3
0 5.
0 7.
.0 6
NOGUCHI LABORATORY
ENGINEER: Chan Anyapo TITLE: PHONE: ENGINEER:
Department of Electrical Electronics an d Info rmation Eng ineering
DC Motor drive Circui t
PART NO.:
REV:
PHONE:
Nagaoka University of Technology
01
DATE:
13-Sep-2006
Motor control(2006-07-20) Mechani cal Layer 4
FILE NAME:
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LAYER :
.GBL .GTL .GTO
GER BER:
F. New Modified Model Drawing outline 2 /1 /8 6 0 0 2
/1 1
d et a e r C f o te a D
r ai ch ele h W irc ct le E
le it T
5
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6
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6
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t n e m m o C
m et s sy d e fii d o m w e n re a e ni l e ul B
) m (m rs te e m li il
ti n U
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m et s ys dl o e r a e ni l k c al B
64
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.9 2 2
2 / 1
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