Comparative Control Strategies for a Cascaded Multilevel Inverter-Based Shunt Active Power Filter

Abstract

In modern distribution systems, the proliferation of nonlinear loads degrades voltage waveform quality at the load end, making power-conditioning equipment increasingly important for utilities and customers. Advances in power semiconductor devices and control circuits have led to a new generation of power-quality equipment, particularly active power filters (APFs). In high-voltage systems, multilevel inverters for APFs eliminate the need for bulky and costly transformers. APF control comprises two major parts: reference current computation and current control. This paper presents three fundamental reference-current generation methods: (i) instantaneous reactive power (PQ) theory, (ii) phase-locked loop (PLL) method, and (iii) fuzzy method. A comparison of control strategies for a multilevel-inverter-based shunt APF is presented. The paper also presents modeling of a cascaded multilevel inverter based APF under different control methods. The PQ method is used to obtain fundamental mains components through reference current generation. A PLL is used to obtain the fundamental mains voltage and calculate average load power. A fuzzy controller is used to obtain the fundamental mains voltage and determine total harmonic distortion (THD). Carrier phase-shifted pulse width modulation (PWM) is implemented to generate switching signals, thereby reducing individual device switching frequency. The system is modeled in the MATLAB/Simulink environment. The simulation circuit is analyzed, and results are compared for the different control methods.