Research On Control Algorithms Based On Hybrid Active Power Filter

Nonlinear devices result in high harmonic content and low power factor in powergrid, which seriously affects the power quality. The most effective solution for it is touse filters. Traditional solution for the harmonic current is to install a Passive Filter(PF), which will be replaced by new equipments due to the limitations such as onlythe given harmonics can be filtered and resonance can be caused in some situation forthe grid. The Hybrid Active Power Filter (HAPF) effectively combines advantages ofboth the Active Power Filter (APF) and the PF, so it has become an importantresearch area of eliminating harmonic and compensating reactive power. In this paper,the object of study is the HAPF, which PF and APF are installed in parallel, and theresearch contents include the operational principle of the PF and the APF, detectingalgorithms and control algorithms, the design about the main circuit, and so on. Themain emphases and innovations are as follows:This paper adopts a more optimal scheme in parameters configuration of the PF.The optimal rated voltage and rated capacity are selected according to thereactive-power compensation capacity, while power capacitors also meet threeverifications of over-voltage, over-current and capacity balance. The simulationexperiment confirms that the power capacitors selected by this method can not onlyimprove filtering characteristics and amplify capacity of reactive power compensation,but also contribute to cost reduction.The important things about the Shunt APF are the harmonic detection methods andPWM control methods. This paper elaborates the instantaneous reactive theory basedp-q mode and ip-iqmode detection methods. The analysis indicates that the ip-iqdetection method is better than the p-q detection method. The hysteresis control is themost widely used in APF. The hysteresis is simple and good stability, but itsswitching frequency is high and unstable, which leads to higher switching losses,greater mechanical noise. In this paper, two improved methods are adopted to copewith the shortcoming of traditional hysteresis control. The first adopted method is theadaptive-hysteresis control, which changes its bandwidth on the basis of the referencecurrent, source voltage, DC side capacitor voltage. We analyses the relationship ofswitching frequency and result of harmonic compensation, which can cause theadaptive-hysteresis control to satisfy the requirements of compensation and minimumswitching frequency. The second method adopted is the voltage space vector baseddouble hysteresis control. The inner hysteresis is used in process of the steady-stateresponse and to output the position of error current vector. The optimal voltage isselected according to the location of the reference voltage vector and error current.The outer hysteresis comparator is used in the process of the transient response, anddetermines whether to switch the power devices, which can limit the error current vector to improve the control precision. The simulation results show that the twomethods can not only effectively eliminate harmonic, compensate reactive power,reduce and stabilize switch frequency but also have excellent control effect.