New Control Strategy For Unified Power Quality Controller

With the development of power electronics, nonlinear loads are widely used in power system, which bring about serious harmonics pollution and big current of reactive power. In the same time, the load including high-tech and high precision is developing rapidly, which ask for high quality power. In the other hand, the power net is becoming bigger, the disturbers between different parts of the power net becoming more serious. So, the power quality and safely operation of net are becoming brittle. The Unified Power Quality Conditioner (UPQC) is the powerful tool to compensate the fluctuation and harmonic of power line voltage, and reactive power and harmonic current of loads.In this paper, the topology of Active Power Filter (APF) is studied deeply, using different APF in different topologies to compose various UPQCs, and then class all the UPQCs into two different sort: direct control and direct compensation. Notice, the concept of direct control is proposed in the first time. People are used to controlling the UPQC in the way of direct compensation, i.e., it is the first step to detect and calculate the aberrance of current and voltage— the fluctuation and harmonic of power line voltage, and reactive power and harmonic current of loads, the second step is to produce the aberrance of current or voltage using the inverter to compensate the load's current or the line voltage. In this way, the precision and the real time of calculation of the aberrance will influence the effect of the compensation. However, it is puzzle to calculate aberrance of instantaneous voltage and current on power net in real time. So, a novel UPQC is proposed which used a novel strategy of control, there are no need to detect and calculate the fluctuation and harmonic of power line voltage, and reactive power and harmonic current of loads. In this control scheme the series serial active power filter is controlled as a current source and makes the input current sinusoidal, while the shunt APF is controlled as a voltage source and keeps the load voltage in the normal value. In fact, the series APF compensates the fluctuation and the harmonic of the source voltage, and the shunt APF compensates the harmonic of the nonlinear load.Firstly, the equivalence between directly control and indirectly control for APF is discussed. The compensation principle is analyzed, and simulation in PISM verified theeffectiveness of applying such control strategy in one-phase and three-phase UPQC.Then, the direct control is extended, and One-Cycle-Control (OCC) and delta invert are included. It is the first time to use OCC in UPQC to control load voltage, and it is verified feasible by simulation in PISM.In one word, this paper gives the reference of direct control strategy in UPQC, and will improve the development of the UPQC.