ANALYSIS AND PERFORMANCE EVALUATION OF SOFT-SWITCHED SINGLE-PHASE THREE-LEVEL RECTIFIER

Abstract

The conventional converters have inherent drawbacks like high current harmonics, low power factor and non-sinusoidal line currents. To improve the power factor and reduce the current harmonics several circuit topologies of the ac to dc converters have been proposed in past few years. However the conventional converters also have inherent drawbacks like high dv/dt and high power problems. By using the Multilevel PWM topology in the high power and/or high voltage single phase applications, significant advantages can be achieved over the conventional boost converter. In Multilevel Converters, the boost inductor size can be greatly reduced and the semiconductor device voltage rating is also drastically reduced. So as a result, the converter power density and efficiency will be improved and cost will be reduced for high voltage/high power applications. However, as the switching frequency increases, switching losses and EMI noises also increases. So, soft switching topologies are used to reduce switching losses, stress on switches and EMI noises. In this dissertation report, various three level PWM control topologies are discussed in detail and simulations are carried out. It is demonstrated that the input current is sinusoidal and the input power factor is almost unity. Capacitor voltage balancing is also achieved. The concept of Non-dissipative snubber is introduced and a "Soft-Switched Single-Phase Three-Level Rectifier" using passive lossless snubber is analyzed in detail and PSIM simulation is carried out to investigate its performance.