Discrete pulse control of AC/DC/AC converters for minimizing reactive elements.

摘要

Three phase ac/dc/ac converters operating with reduced reactive elements have been investigated in this work. It has been determined that the voltage sourced converter circuit topology results in a lower reactive element cost than a current sourced converter, independent of the switching strategy. With the topology fixed, further reductions in reactive element requirements must be accomplished through switch modulation. For any realistic modulation strategy, filter requirements are proportional to the switching frequency. Discrete pulse switching used in soft-switched resonant converters allows for much higher switching frequencies than conventional converters.;All the concepts developed for control of reduced link converters are subjected to the practical considerations of sensor and computation requirements, and system sensitivities. In medium or high performance machine drives, the inverter modulation scheme must accomplish the task of machine torque and flux control. Current regulators typically form an integral part of torque controllers. The adjacent state discrete pulse modulated current regulator is proposed for use in reduced dc link resonant converters. This regulator requires no knowledge of load parameters and eliminates reversals in the dc link current to minimize stresses on dc link reactive elements. A direct torque controller is presented which requires less calculation than conventional stator flux field oriented controllers and also requires only a single current sensor in the dc link. The spread voltage spectrum associated with soft-switched inverters can also be achieved in hard-switched inverters. A random sinusoidal modulation scheme is proposed to eliminate the acoustic tone produced by the machine. Finally, a rectifier control scheme is proposed which uses load feedforward to improve the transient response of the bus control system.