A Multifunctional Series Power Quality Conditioner Based on Asymmetry Cascade Multilevel Inverter and Its Strategy

This paper presents a multifunctional series power quality conditioner (MSPQC), which is composed of series active part and shunt passive part. The asymmetry cascade multilevel inverter (ACMI), with the characteristics of good waveform tracing capability, low switching losses, and easy to implement in large scale, is employed to design the main circuit of the series active part. The control strategy for the MSPQC is also introduced. In this control strategy, the series active part is controlled work as a fundamental sinusoidal current source in phase with the fundamental positive sequence component of the feeder-terminal voltage, and the magnitude of the sinusoidal current is determined by the error signal between the RMS value of the load fundamental voltage and its reference value. With this control strategy, the MSPQC can realize the functions including the power supply voltage disturbance (such as harmonics, sags and unbalance) isolation, load harmonic current compensation, load fundamental voltage regulation, power factor correction at the feeder-terminal, and fault current limitation. Compared with previous series hybrid active power filters, this MSPQC has many advantages, such as high operation efficiency, simplified control system, and good compensation performances. The mathematical derivations and digital simulations explain and verify the validity and feasibility of the MSPQC