bipolar square wave to two level square wave

Moreover, the freewheeling diodes are needed to provide a circuit path for the discharging of the load inductances otherwise voltage spikes will appear across the semiconductor switches that will result in their failure.įigure 6.4. The freewheeling diodes provide flexibility to the inverter not only to deliver power from the input dc source to the load but also to deliver power from the load to the input dc source. When the current is positive, it flows through the semiconductor switch and when it is negative, it flows through the respective antiparallel diode or the so-called freewheeling diode. The freewheeling diodes of the inverter are needed to provide current bidirectionality to the semiconductor switches. (a) Implemented with insulated gate bipolar transistors (b) implemented with metal-oxide-semiconductor field effect transistors (c) implemented with thyristors (d) gating pulses for S 1, S 2 (e) inverter output voltage when the load is resistive. Therefore, if the output voltage v o is required to be kept constant, due to the dc input voltage variations or voltage drops within the power circuit, this is achieved through the pulse width variations of the gating signals and, consequently, the output voltage pulse widths.įigure 6.2. When the output voltage is required to be decreased, then the conduction time intervals of S 1 and S 2 are decreased. When an increase is required in the output voltage, then the conduction time intervals of S 1 and S 2 are increased. The output voltage control can be achieved by varying the pulse widths of the output voltage through the gating signals of the semiconductor switches. When S 2 or D 2 is conducting, the output voltage is v o = −V in/2. When S 1 or D 1 is conducting, the output voltage is v o = V in/2. As shown in Fig. 6.2(d) the output voltage v o is a two-level square-wave pulse (V in/2 and −V in/2). The freewheeling diodes across the switches are included in the same power module as the switches. The choice of the semiconductor switches for implementing this inverter depends on its power and switching requirements. Fig. 6.2 shows the power circuit and the generated output voltage of a single-phase half-bridge inverter.

Bipolar square wave to two level square wave