Techniques for attaching a low per-unit current harmonic correction PWM inverter cell to the input stage of an industrial drive

This paper compares and contrasts the functional operation of a range of harmonic correction circuit topologies using a three-phase PWM bridge that draws low distortion AC supply currents and that can be attached to diode rectifiers in standard industrial drive systems using inductor sizes with a per-unit impedance in the range 0.01 to 0.05 pu. The three-phase PWM bridge used are operated with current ratings around 0.2 to 0.4 pu as compared with 1 pu for a standard PWM rectifier. The harmonic correction topologies considered have a range of potential advantages, such as: (a) low ^dv/_dt stresses between the rectifier output terminals and the AC supply neutral; (b) controlled rectifier output voltage; (c) can be placed on top of a diode rectifier operating at the standard output voltage; (d) balanced supply currents with an unbalanced ac supply voltage; and (e) bidirectional power flow. The relative advantages and disadvantages of each topology ore described together with appropriate current control techniques. SPICE simulations are used to obtain performance curves and to investigate the operation of novel circuit topologies