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How Inverters and Converters work in Hybrids and EVs

Learn How They Condition Electricity for Power and Recharging

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Prius inverter

3rd generation Prius inverter

© Toyota

Inverters and converters combined into one unit manage the power and recharging circuits in hybrids and electric vehicles (EVs). Here’s how inverters and converters work both individually and in tandem:

Inverter:

An inverter is an electrical device that converts electricity derived from a DC (Direct Current) source to AC (Alternating Current) that can be used to drive an AC appliance. The theory of operation is relatively simple. DC power, from a hybrid battery for example, is fed to the primary winding in a transformer within the inverter housing. Through an electronic switch (generally a set of semiconductor transistors), the direction of the flow of current is continuously and regular broken (the electrical charge travels into the primary winding, then abruptly reverses and flows back out). The in/out flow of electricity produces AC current in the transformer's secondary winding circuit. Ultimately, this induced alternating current electricity flows into--and produces power in--an AC load (for example an electric vehicle's (EV) electric traction motor). A rectifier is a similar device to an inverter except that it does the opposite, converting AC power to DC power.

Converter:

More properly called a voltage converter, this electrical device changes the voltage (either AC or DC) of an electrical power source. There are two types of voltage converters: step up (which increases voltage) and step down (which decreases voltage). The most common use of a converter is to a take relatively low voltage source and step-it-up to high voltage for heavy-duty work in a high power consumption load, but they can also be used in reverse to reduce voltage for a light load source.

Inverter/Converter Units:

An inverter/converter is, as the name implies, one single unit that houses both an inverter and a converter. These are the devices that are used by both EVs and hybrids to manage their electric drive systems. Along with a built-in charge controller, the inverter/converter supplies current to the battery pack for recharging during regenerative braking, as well as provides electricity to the motor/generator for vehicle propulsion. Both hybrids and EVs use relatively low voltage DC batteries (about 210-V) to keep the physical size (and cargo space consumed) down, but they also generally use highly efficient, and high voltage (about 650-V) AC motor/generators. The inverter/converter unit choreographs how these divergent voltages and current types work together.

Because of the use of transformers and semiconductors (and the accompanying resistance encountered), enormous amounts of heat are emitted by these devices. Adequate cooling and ventilation are paramount to keeping the components operational, and as such, inverter/converter installations in hybrid vehicles have their own dedicated cooling system (complete with pumps and radiators) that are entirely independent from the engine's cooling system.

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