PWM Current Source Rectifiers

This chapter addresses four main aspects of the current source rectifiers (CSRs) used in high‐power AC drives, including converter topologies, pulse‐width‐modulated (PWM) patterns, power factor control, and load commutated (LC) resonance with active damping control. The filter capacitor and line inductance constitute an LC resonant circuit. The LC resonances may be excited by voltage harmonics in the utility supply or current harmonics produced by the rectifier. An active damping control scheme is elaborated, which can effectively suppress the LC resonances during system transients and also reduce the line current distortion during the steady state operation of the rectifier. With the advent of gate commutated thyristor (GCT) devices in the late 1990s, the PWM CSR using symmetrical GCT switches has become a preferred choice for current source fed medium voltage (MV) drives. The MV drive with the dual‐bridge CSR as a front end is suited for retrofit applications, where a standard ac motor is usually employed.