A multilevel advanced static VAr compensator with current hysteresis control

Abstract

In this paper, an advanced static reactive power compensator is presented. This compensator employs a multilevel voltage source inverter. In general, multilevel structures allow high voltage and high power sharing among the switching devices of the inverter. Also, these structures with proper driving sequence of the switching devices mould allow device operation at a reduced switching frequency. The multilevel structure of the inverter used in this paper employs a separate DC capacitor for each voltage level. This arrangement would eliminate the capacitor voltages' balancing problem associated with most multilevel structures. This paper introduces the current hysteresis controller to the field of multilevel advanced static reactive power compensators. This controller would force the inverter to directly generate the required reactive current. The simple current hysteresis controller would insure a reliable inverter operation with minimal harmonic distortion. The proposed system is studied using a simple mathematical model. The model presented is for a single-phase, three-level voltage source inverter based static reactive power compensator This model is adaptable to three-phase operation. Basically, the three-level model is extendible to any number of levels. The harmonic content of the inverter's line current is also examined. Finally, the model is tested under lagging and leading reactive power demands. Simulation results confirm a very promising static reactive power compensator.