Week 4 Session 5
Power converters are used in EVs mainly for converting input AC signals from grid to DC suitable for battery. Irrespective of this main application, it also have various applications.
(a) DC - DC converter
Usually motor which is the major part of an EV works at a voltage of 12 V, 24 V, 48 V, 72 V etc. But other systems (auxiliary systems) like horn, lights, meters, indicators, infotainment system, sensors etc. works at very low voltage for eg. 10 V. So to reduce the high voltage, a DC - DC converter has to be used. Usually buck converters are used to reduce the voltage and Boost converters are used to raise the voltage.
(b) On Board Chargers
As mentioned in the introduction, AC signals from the grid has to be converted into DC for charging batteries. There should be some provisons for protecting batteries from over charging. So status of batteries have to be sensed using sensors and power controllers will control the charging cycles such as Trickle charging, Constant current Charging and constant voltage charging.
(c) Inverter
If we are driving the vechicles using AC motors or 3 phase Induction motors in certain applications, DC supply from the battery has to be converted to AC supply. For that purpose Inverters has to be employed.
(d) Regenerative braking Converter
During regenerative breaking, mechanical energy or kinetic energy is converted to electrical energy. So an appropriate converter has to be used to convert this energy to suitable voltage and current that suits the battery specifications.
(e) Active Battery Balancing
In case of using of multiple number of cells connected in series and parallel to form a battery pack, it is important to keep voltages and charge levels in every cells as equal as possible. i.e, to get maximum life for battery it is important to keep charges of all battery equal. This function is maintained using Power converters.
(f) Motor Drive Control
Speed of motor is controlled using power converter. Throttle and braking system of the vechicle is connected to power converter. According to the input from these inputs, power converter will provide neccessary current, torque and power to the motor.
(g) Energy Management System
Power converter will control the power flow to and fro to the battery and motor according to charge available in the battery. They assist in monitoring, controlling, and optimising the power flow between battery and different components of EV in an efficient manner.