Research On Key Techniques And Experiments Of Affecting Compensation Performance For Shunt Active Power Filter

In recent years, with the power electronics thriving, power electronics devices are widely applied, but harmonic and reactive power bring much aging serious harm to power systems in the process of application. Shunt active power filter(SAPF) which is a mainstream device of harmonic suppression and reactive power compensation device is playing an important role in power quality field. So far, the launch of the domestic SAPF has not happened yet, and its compensation performance remains to be improved, thus affecting the compensation performance of the key techniques has become one of the research frontier.Compensation current detection is an important technology in the development process of SAPF. And whether the detection is fast and precise has a significant impact on the compensation performance.The traditional F.Buchholze M.Dpendbrock(FBD) harmonic detection method has been analyzed, and based on this analysis, an improved FBD method is proposed. Firstly, the phase locked loop(PLL) is substituted for using sine and cosine signal calculation module of fundamental positive sequence voltage. While the power supply voltage is substituted for the fundamental positive sequence voltage to be implemented into participating in the calculation of equivalent conductance to reduce detection error, and low pass filters(LPF) are replaced by using mean filters to reduce the delay. Simulation results show that the method can detect all kinds of current component real-time and accurately in the system.Main circuit parameters of SAPF are one of the determining factors which affect the system compensation performance. The calculation formulas of three important parameters(DC side voltage, AC inductance and DC side capacitance) are studied in this thesis. Firstly, the thesis analyzes the effect of commutation process on the AC harmonic current in the three-phase bridge rectifier with inductance obstruction load, and the load current expression with consideration of commutation overlap angle is deduced; secondly, the DC side voltage setting value is deduced based on the derivation of the formula; then when the current changes drastically, the change rate of compensation current can track the reference current; When the current changes slowly, fluctuations are less than the maximum allowable value in engineering in a switch cycle, thus the calculation formula of inductance is deduced; Finally, the use of the AC component of load instantaneous active power is the buffering power which is exchanged between the load and SAPF, and the formula of the DC side capacitor capacity is derived. The simulation and experimental results verify the correctness and rationality of the theoretical derivation.In order to improve the control performance of SAPF, two kinds of control methods are considered: current control and direct power control. First of all, based on voltage space vector pulse width modulation(SVPWM) current controlling based on indeterminate frequency hysteresis compared with the traditional hysteresis control, it is concluded that the former in the compensation effect, the switching frequency and DC voltage utilization have certain advan- tages. Then the direct power control(DPC) strategy based on pq theory is put forward. Har- monic and reactive power which is detected is regarded as the reference compensation power first, then its detection value and the harmonic and reactive power of filter output are sent into two corresponding hysteresis comparator. According to hysteresis comparator’s output and power supply voltage vector position angle, the expected corresponding switch states of the output voltage vector of the bridge arm are obtained by looking up the switch chart. The simulation results show that SAPF designed based on this control strategy has good harmonic compensation effects. Finally, direct power control based on power supply voltage and virtual flux is proposed. The approach adopts power supply power to control SAPF, thus omits the load harmonic and reactive power detection and calculation part, and estimates the virtual flux to calculate the active and reactive power, which can omit the power supply voltage sensors. Simulation results show that compared with the traditional method of DPC, this method has a simpler system structure, which can reduce the number of sensors effectively, and the power source current distortion as well as the control properties of the instantaneous power will also be optimized.Finally, the software system design has been studied, and the hardware platform is promoted based on the previous work, and the comprehensive experiments based on the experimental system have been done to verify the key techniques in the thesis that is mentioned above. According to the two groups of contrast experiments, the validity and feasibility of the research work in this thesis is concluded by analyzing the experiment results.