Multi-level distribution STATCOM for voltage sag and swell reduction

Multi-level power conversion has been receiving increasing attention in the past few years for high power applications. The unique structure of the multi-level voltage source converter (VSC) allows it to reach high voltages with low harmonics without the use of transformers or series-connected, synchronised switching devices. The diode clamped multi-level VSC with its simple configuration and control structure finds application as distribution STATCOM (D-STATCOM) in custom power conditioners. This inverter has emerged as a solution for high power applications. The main purpose of the proposed diode clamped D-STATCOM is that it injects reactive power in shunt with a distribution feeder. It reduces the effect of short-term voltage sags, swells and momentary interruptions in the distribution system. This paper presents the multi-level D-STATCOM configuration consisting of a three level voltage source converter, a DC energy storage device, a coupling transformer and associated control circuits. The control is based on sinusoidal PWM and only requires the measurement of the RMS voltage at the load point. PSCAD/EMTDC simulation tool is used for modeling and simulation. Extensive simulation results are presented to verify the superiority of multi-level D-STATCOM with two level D-STATCOM.