A Model Predictive Control-Based STATCOM for Weak Grid Voltage Enhancement

Abstract

This paper presents a model predictive control (MPC) technique for the control of reactive power flow from a static synchronous compensator (STATCOM) into a weak power system network. The MPC strategy enables the STATCOM to mitigate weak phase voltage magnitudes in a distribution grid. The weak voltage magnitudes usually emanate from large inductive loads connected to the grid’s point of common coupling (PCC). The MPC utilizes a finite control set of voltage vectors to minimize a cost function, which reduces the errors between set references and the corresponding predicted variables. The references in the cost function are set by two outer loop controllers. A time delay compensation strategy is introduced and proposed for selecting the gains of the outer loop controllers.  An LC filter was also designed at the STATCOM’s output terminals to confine the harmonics in the injected compensation current to permissible limits. A robust all high pass filter dual second order generalized integrator (AHPF-DSOGI) based phase locked loop (PLL) is developed and proposed for synchronization of the STATCOM into the weak grid. The overall MPC strategy on the STATCOM enables shunt injection of compensation currents at the PCC while mitigating harmonics and consequently improving power quality. The STATCOM effectively regulated the bus voltage when required by switching between the capacitive and inductive modes. Results showing the efficacy of integration of the STATCOM to the grid and robust capabilities of the STATCOM in mitigating voltage swell and dip, as well as harmonics, are presented.