Week 4 Session 5

Power Converter: A power converter is an electrical circuit that changes the electric energy from one form into the desired form optimized for the specific load.

Types of power converters:

1. AC to AC or DC -DC converter
2. AC to DC converter
3. DC to AC converter

DC-DC converters and DC to AC converters widely used in Electric vehicle.

1.AC to AC or DC to DC converter: it is also called Choppers. These converters used for convert an Un-regulated Input in to Regulated output.

DC-DC converters in an electric vehicle may be classified into unidirectional and bidirectional converters. Unidirectional DC-DC converters cater to various onboard loads such as sensors, controls, entertainment, utility, and safety equipment. They are also used in DC motor drives and electric traction. Bidirectional DC-DC converters find applications in places where battery charging, regenerative braking, and backup power are required. The power flow in a bidirectional converter is usually from a low voltage end such as a battery or a supercapacitor to a high voltage side and is referred to as boost operation.

During regenerative braking, the power flows back to the low voltage bus to recharge the battery (buck mode). As a backup power system, the bidirectional DC-DC converter facilitates the safe operation of the vehicle when ICEs or electric drives fail to drive the motor.

2.AC to DC converter: it is also called rectifiers. These converters used to convert an AC input into DC output.

3.DC to AC converter: it is also called inverter. An inverter is a device that converts DC power from the battery to AC power in an electric vehicle motor. The inverter can change the speed at which the motor rotates by adjusting the frequency of the alternating current.

Electric vehicle needs 6 main components to operate:

• Charging port: Much like the access port for the gas tank in an internal combustion engine car, the charge port is the location where energy enters the car. We have Majority of AC supply source available at charging stations
• Onboard battery charger: Most EVs have a battery charger built into the car for level 1 or level 2 charging. This is AC charging, not DC fast charging. The charger is there to limit the total amount of power going into the battery to avoid damage to the battery or the electrical circuit the charger is plugged into.

Input to the Charging ports is AC supply. Here we use AC to DC converter. Input 230V AC supply and Output 110V or 220V DC

For Battery packs we use DC to DC converters to charge battery, we get 110V or 220V DC output. It is Un-regulated. So here we use DC -DC converter and Regulated DC Output Voltage is feed to battery pack.

• Battery packs: This is the energy reservoir that contains the energy the car will use to drive, operate the heating and cooling, and run all of the other lights and accessories. Typically battiries use direct current electricity that must be converted to AC, or alternating current, before being used in the electric motor. Sometimes, you will find direct current motors, but these are not common in mass produced electric vehicles. DC Charging is faster because it charges the batteries directly.

• Power inverter: When an EV has AC motors, the energy from the battery must be converted in order to be used. The inverter also operates when the car is using Re-generative braking converting the alternating current generated by the electric motors into direct current to be stored in the battery.

Here We use DC -AC converter ( Inverter) to convert Battery source DC into AC Source. Which is feed to AC Electric motor.( 220V DC voltage in to 440V AC voltage)

• Electric motor: The component of an electric vehicle that transforms the electrical energy from the battery into rotation that can be used to move the vehicle.
• Battery Management System: The BMS manages the electrical current flow in and out of the battery to protect the battery and extend its life. Every EV is going to have a BMS that is designed specifically for the battery in the car. Thus, modifying the battery or adding a battery could prove to be quite difficult if the BMS is not also modified to compensate.

Applications of Power converter in Electric vehicle:

1. Climatic control: Cabin colling and cabin heating (HVAC), Generally which operates in Single phase AC supply in House hold purpose. while in Electric car Which are operated DC power 110V. Here We use DC -DC converter to power the HVAC. 48V battery voltage is Step-up (Booster) to 110v DC supply.
2. Battery heating and Cooling (Sensor): Sensors are used to sense the temperature at battery and data transfer to master controller. Here we use DC-DC converter Sensor need 1.5v DC. Buck converter is used to obtain 1.5v DC.
3. Motor cooling: Motor get heat, when it operates continuously or maximum operating points. To maintain Normal temperature at motor position. Exhaust fan is used. Here we use DC-DC converter (Buck converter). Exhaust fan need 12V Dc.
4. Power Steering: In Electronic power Steering we use BLDC motors. Most electric power steering systems use a three-phase electric motor powered by a pulse width modulated DC voltage. The motor is brushless and has an operating voltage range of 9 to 16 volts. Here We Need DC-DC converter.
5. Power Steering sensor: Sensor Used in power steering to sense the direction of steering shaft. It needs 5V DC. Here we use DC-DC converter.
6. lighting System: Vehicle have many positional lights. Head lamps, tail lamps, fog lamps. Direction indicators, braking indicator. All lights work on DC Source. Here also use DC-DC converter. Here we need 0 to 12V DC voltage.
7. Wipers: Wipers are used to clean the windshield of vehicle. Here we use 12V DC motor with 55 RPM. And DC -DC Converter is used.
8. Infotainment system: The navigator, music, Bluetooth all are infotainment systems, here we use DC-DC converters and it requires 3.3V to 12V
9. The basic power windows generally have control of all the four windows and can be controlled by the driver. Here we use DC motor which is operating in 12v DC. we use DC -DC converter.
10. Vehicle Horn: It produces sound electrically using a thin metal disc and an electromagnet or solenoid. As the solenoid gets energized or triggered by the button, it exerts a force on the metal disc. The by-product of this process is a loud vehicle sound known as horns. It needs 5 to 12V DC and DC-DC converter.
11. Electric motor: Most commonly used motors are BLDC, DC motor, Induction motor. For BLDC and Induction motor need DC to AC converter. 220V DC to 440 V AC. These voltage conversions have high switching losses and heat dissipated is high. DC to AC conversion at low voltages. And then use Step-up transformer at AC Voltages to minimize losses.
12. On-Board battery charger: In generally, Ac source is widely available in charging stations. Here to charge the battery need DC source. so here AC-DC converter is used and 230v AC to 48V DC to charge the battery.