Half Bridge DC-AC Inverter (R Load)

P r inciple of Operation:

A single phase inverter is shown in Figure.

The analysis of the DC-AC inverters is done taking into accounts the following assumptions and conventions:

The current entering node a in Figure 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 4) that switch S1 is on for the time duration

0 ≤ t ≤ T1 and the switch S2 is on for the time duration T1 ≤ t ≤ T2. When switch S1 is turned on, the instantaneous voltage across the load is


When the switch S2 is only turned on, the voltage across the load is


The waveform of the output voltage and the switch currents for a resistive load is shown in Figure.

The r.m.s value of output voltage ν o is given by


The instantaneous output voltage ν o is rectangular in shape. The instantaneous value of ν o can be expressed in Fourier series as:

Due to the quarter wave symmetry along the time axis (Figure 3), the values of a0 and an

are zero. The value of bn is given by

Substituting the value of bn from equation 5 into equation 4 gives

The current through the resistor ( iL ) is given by

For n = 1 , equation 6 gives the r.m.s value of the fundamental component as