Using hysteresis current control for STATCOM applications

The shunt compensation approach for mitigating power quality (PQ) problems is popular on account of its simpler AC side coupling and lower insulation requirements. The most versatile shunt compensator is the STATCOM, which is a three-phase, voltage-source inverter, whose output current is to be controlled to achieve PQ compensation. In this paper, some aspects of current control of a STATCOM are investigated. A simple (nonpredictive) hysteresis current control scheme is considered. It is shown that, for a given STATCOM, the AC bus voltage largely decides the effectiveness of any simple hysteresis rule. Validity limits of the control laws are analytically derived and both simulation and experimental results are provided in support. Based on these derivations, a simple correction scheme is suggested. Simulation and experimental results confirm improved performance. A digital controller is used for realizing the current control. The dependence of the current harmonic spectrum on the sampling time is illustrated. Some issues regarding ripple filter design are also discussed