Ankit Mishra | ME/2K14/26 |
Regenerative Braking System LITERATURE REVIEW
Regenerative Braking : The concept When a conventional vehicle applies its brakes, kinetic energy is converted to heat as friction between the brake pads and wheels. This heat is carries away in the airstream and the energy is effectively wasted .The total amount of energy lost in this way depends on how often, how hard and for how long the brakes are applied. Regenerative brake is an energy recovery mechanism which slows a vehicle by converting its kinetic energy into another form, which can be either used immediately or stored until needed. The scope for regenerative braking comes from the fact that in the city drive, almost 65% of the total energy is wasted during the braking. Regenerative braking utilizes the fact that an electric motor can also act as a generator. The vehicle's electric traction motor is reconnected as a generator during braking and its output is connected to an electrical load. It is this load on the motor that provides the braking. An early example of this system was the Energy Regeneration Brake, developed in 1967 for the Amitron. During braking, the traction motor connections are altered to turn them into electrical generators. The motor fields are connected across the main traction generator (MG) and the motor armatures are connected across the load. The MG now excites the motor fields. The rolling locomotive or multiple unit wheels turn the motor armatures, and the motors act as generators, either sending the generated current through onboard resistors (dynamic braking) or back into the supply (regenerative braking) For a given direction of travel, current flow through the motor armatures during braking will be opposite to that during motoring. Therefore, the motor exerts torque in a direction that is opposite from the rolling direction. Braking effort is proportional to the product of the magnetic strength of the field windings, times that of the armature windings.
There are different types of ways in which the regenerative braking can be used in a vehicle, essentially different in the way the energy is stored. Usually, the energy is stored in an electrochemical cell, or capacitor, or flywheel and sometimes in compressed air. The different types of regenerative braking are Electric, Hydraulic braking, Using flywheel, compressed air, Nitilon spring. The Regenerative Braking helps us to store the energy that is usually lost to the environment, but it is not a perpetual machine, and hence, we cannot use all the energy that is being lost. Various techniques are being used to increase the efficiency of these brakes, by using different type of processes by which the energy is saved. Usually, regenerative braking helps us to save around 8-25% of energy. With the use of some other techniques, this can be increased to 40% and even above.
NEW TECHNIQUES BEING USED With time, the use of advanced materials like the piezoelectric material has been tested and the results show that Using Piezoelectric materials and Permanent magnets, it is possible to save energy to higher percentages. The use of such materials give a strong future to this regenerative Braking.
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The widest use of regenerative braking is in the Metropolitan rail system. Even Delhi Metro uses the regenerative braking so as to reduce the wastage of energy, as well as proper distribution of power and smooth distribution. With synchronized timetables, the energy can efficiently be used. Apart from saving the energy in the automobile, the energy is also saved in power banks stationed with the rail lines and hence, can be used by any locomotive, irrespective of which has saved the energy. The rails use on-board energy system and stationary energy systems. This saved energy helps the corporation to use in accelerating the loco, when there is a need to accelerate number of vehicles, thus helping the proper use of energy distribution. ADVANTAGES OF REGENERATIVE BRAKING 1. Exhaust emissions were reduced by about 35 per cent (Such emissions include nitrogen oxide, carbon monoxide, carbon dioxide, total hydrocarbons and particulates.) 2. Cost of engine maintenance was reduced by at least 50 per cent because there was less wear on the brakes and tires and less lubricating oil was needed. 3. Environment friendly. 4. Noise level was lower by 30 per cent.
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