3.3 Pulse Width Modulated Inverters

This section elaborates on some basic inverter circuit topologies. The square wave and PWM operation are described along with the harmonic spectrum of the output voltages.

3.3.1 Single-Phase Half-bridge Inverters

The power circuit topology of a single-phase half-bridge voltage source inverter is shown in Figure 3.1. As shown in Figure 3.1a, the inverter consists of two power semiconductor switching devices. Each switch is composed of a transistor (BJT, MOSFET, IGBTs, etc.) and a freewheeling diode that provides an alternating path for the current. In this circuit topology, either S1 is on or S1' is on. The freewheeling diodes conduct when the load is inductive and a sudden change in the output voltage polarity does not change the direction of the current simultaneously. Indeed, for resistive loads, the diodes do not operate. When switching device S1 is conducting, the input voltage 0.5 img appears across the load. On the other hand, when transistors S1 is turned on, the voltage across the load is reversed and is img. The switching states, the path of current flow, and the output voltage polarity are illustrated in Figure 3.2 and switching signals along with the output voltage waveform are depicted in Figure 3.3. The operation of the inverter can be well ...

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