Introduction

The topics covered in this chapter are as follows:

• •  EV and HEV configuration based on power converters

•  Classification of converters

•  Principle of Step Down Operation

•  Buck Converter with RLE Load

•  Buck Converter with RL Load and Filter

Electric Vehicle (EV) and Hybrid Electric Vehicle (HEV) Configurations

In Figure 1 the general configuration of the EV and HEV is shown. Upon examination of the general configurations it can be seen that there are two major power electronic units

• • DC-DC converter

• DC-AC inverter

Usually AC motors are used in HEVs or EVs for traction and they are fed by inverter and this inverter is fed by DC-DC converter (Figure 1). The most commonly DC-DC converters used in an HEV or an EV are:

• •  Unidirectional Converters: They cater to various onboard loads such as sensors, controls, entertainment, utility and safety equipments.

  •  Bidirectional Converters: They are used in places where battery charging and regenerative braking is required. The power flow in a bi-directional converter is usually from a low voltage end such as 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 batteries know as buck mode operation.

Both the unidirectional and bi-directional DC-DC converters are preferred to be isolated to provide safety for the lading devices. In this view, most of the DC-DC converters incorporate a high frequency transformer.