Improved Low Voltage Ride Through by A STATCOM Based on Neutral Point Piloted (NPP) Multilevel Inverter

Abstract

By ever-increasing utilization of renewable energy systems, grid codes impose strict standards for current compensation, especially for asymmetric grid faults namely low voltage ride through (LVRT) codes. On the other hand, multilevel voltage source inverters have achieved prominent attention considering their lower dv/dt and harmonic content. This paper introduces a STATCOM based on neutral point piloted inverter (NPPI) for the first time. The studied 5-level NPPI has a single dc bus which feds all phases of the inverter and each phase contains two internal flying capacitors. A control system has been developed for NPPI-STATCOM through which the voltage of dc bus capacitor is controlled at its reference and using redundant switching states, the voltages of internal capacitors are balanced as well. Thus, NPPI-STATCOM control system is capable of balancing the voltage of internal capacitors even being connected to a faulty grid while positive and negative-sequence reactive currents being injected to the grid. Several simulation results in MATLAB/SIMULINK confirm the above claims indicating the performance of NPPI-STATCOM and the developed control system.