Describing Inverter Functions in Electric and Hybrid Vehicles

Electric and hybrid vehicle technology uses both Direct Current (DC) and Alternating Current (AC). The vehicle battery produces DC, the motor produces AC, and the inverter is the electrical device that switches between these currents. This lesson discusses how the inverter operates in electric and hybrid vehicles.

Generating DC and AC

Batteries in electrical and hybrid vehicles store energy to actuate electric motors to move the vehicle. This energy discharges from the battery as DC voltage and must be recharged from a DC source. The electricity from the battery is used to power different components with different voltage requirements in the vehicle. A converter, which is often housed with the inverter, is used to increase or decrease the voltage from the battery. This DC-to-DC converter may change high battery voltage to a lower auxiliary component voltage or increase it to be used by the motor.

Motors in electric and hybrid vehicles are actually AC motor/generators that change AC energy into mechanical energy. When an AC source is applied, the motor turns and changes the AC energy into mechanical energy used to turns the wheels. When the motor/generator is turned mechanically, as when coasting or braking, it generates AC voltage, changing mechanical energy to electrical energy.

Before continuing, study this webpage to learn about the inverter in the power train.

An illustration of a simplified electric or hybrid vehicle power train system showing the energy that passes between its components. The power train system consists of the battery, inverter, motor, and the wheels. DC electricity is passed between the battery and the inverter. AC electricity is transferred between the inverter and the motor and mechanical energy is transferred between the motor and the wheels to propel the vehicle.Figure 1. Inverter in an electrical drive system. (CC BY 3.0 by Center for Advanced Automotive Technology)

Inverting between AC and DC

Inverters use diodes, capacitors, and transistors to change AC to DC and DC to AC. They use diodes and capacitors to invert the AC voltage to DC. Remember that a diode or bridge rectifier changes AC into a rough DC. The DC is smoothed out by capacitors and then regulated by a voltage regulator. Inverters use switching transistor arrays and capacitors to invert DC to AC. Transistors, such as MOSFETs (metal-oxide-semiconductor field-effect transistor) or IGBTs (insulated gate bipolar transistor) are turned on and off rapidly to produce a square wave output. Capacitors smooth out this square wave output into a sine wave or AC.

make sure to study this webpage to learn more about inverters, converters, and the control systems that use the AC and DC electricity.

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