Power electronics digital notes b. Tech III year

 
Figure: 5.8 Single phase Full Bridge DC-AC inverter with R load current directions 
The voltage and current waveforms across the resistive load are shown in Figure below 
Figure: 5.9 Single phase Full Bridge DC-AC inverter waveforms
Single Phase Full Bridge Inverter for R-L load:
A single-phase square wave type voltage source inverter produces square shaped output voltage for a 
single-phase load. Such inverters have very simple control logic and the power switches need to operate 
at much lower frequencies compared to switches in some other types of inverters. The first generation 
inverters, using thyristor switches, were almost invariably square wave inverters because thyristor 
switches could be switched on and off only a few hundred times in a second. In contrast, the present day 
switches like IGBTs are much faster and used at switching frequencies of several kilohertz. Single-phase 
inverters mostly use half bridge or full bridge topologies. Power circuits of these topologies are shown in 
in Figure below. 

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Figure: 5.10 Single phase Full Bridge DC-AC inverter with L load
The above topology is analyzed under the assumption of ideal circuit conditions. Accordingly, it is 
assumed that the input dc voltage (Edc) is constant and the switches are lossless. In full bridge topology 
has two such legs. Each leg of the inverter consists of two series connected electronic switches shown 
within dotted lines in the figures. Each of these switches consists of an IGBT type controlled switch 
across which an uncontrolled diode is put in anti-parallel manner. These switches are capable of 
conducting bi-directional current but they need to block only one polarity of voltage. The junction point 
of the switches in each leg of the inverter serves as one output point for the load.