Introduction

The topics covered in this chapter are as follows:

• •  DC-AC Converters

•  Principle of Operation of Half Bridge DC-AC Inverter (R Load)

•  Half Bridge DC-AC Inverter with L Load and R-L Load

•  Single Phase Bridge DC-AC Inverter with R Load

•  Single Phase Bridge DC-AC Inverter with R-L Load

DC-AC Converters

In Figure 1 a configuration of an EV. In this figure it can be seen that the traction motor requires AC input. The main source of electrical power is the battery which is a DC source. The DC output of the battery is bucked or bossted according to the requirement and then converted into AC using a DC-AC inverter . The function of an inverter is to change a dc input voltage to a symmetric ac output voltage of desired magnitude and frequency. The output voltage waveforms of ideal inverters should be sinusoidal. However, the waveforms of practical inverters are non-sinusoidal and contain certain harmonics.

Figure 1 : Configuration of electric vehicle

Principle of Operation of Half Bridge DC-AC Inverter (R Load)

A single phase inverter is shown in Figure 2 . The analysis of the DC-AC inverters is done taking into account following assumptions and conventions:

• • The current entering node a in Figure 2 is considered to be positive.

• The switches S₁ and S₂ are unidirectional, i.e. they conduct current in one direction.

• The current through S₁ is denoted as i₁ and the current through S₂ is i₂.

The switching sequence is so design ( Figure 3 ) that switch S₁ is on for the time duration and the switch S₂ is on for the time duration . When switch S₁ is turned on, the instantaneous voltage across the load is

                                                                                                                           (1)