Control And Design Of Three-Phase Three-Wire Shunt Active Power Filter

The harmonic pollution of power system is becoming more and more serious with the using of power electronic equipment in power system. The harmonics should be compensated because it can do much harm to the power system。Active power filter (APF) is one of the most important approaches to control power quality based on advanced power electronics. The shunt active power filter plays the most important role in the past or future.Main circuit design is a key part of the systematic design. Based on the model of three-phase three-wire shunt active power filter, the operation of it adopting space vector control is studied and analyzed to reveal the relation of main parameters of APF. According to requirement of instant current tracking, the estimating formula of output inductance is proposed and the critical value of dc bus voltage is derived. The method applied to design parameters of LCL output filter is introduced in detail.Real-time and accurate harmonic detection is the key for practical active filter implementation. The d-q detection method based on Park transformation is researched, and its current detection error is analyzed deeply, including influences of phase errors of PLL (phase-locked loop), time delay of sampling and error of low-pass filter. A sliding-window iterative algorithm is applied in the computation to detect the harmonic components generated by nonlinear loads, which improves the real-time, tracing performances with less computation.The dc side voltage of APF should be well controlled for its practical use. The closed loop of dc side voltage are modeled and analyzed. An applied soft-startup scheme is also been introduced. Output current control decides its compensation effect directly. For the shunt APF, the paper puts forward three control methods of current loop: one is proportion-integral control, another is advance proportion-integral control, and the last is proportion-integral control plus repetitive control algorithm. The proportion-integral control plus repetitive control algorithm are adopted to correct the output current waveform of the voltage source inverter in the APF. In this control strategy, the proportion-integral control is used to guarantee system dynamic performance and the repetitive control loop is to improve current waveform quality.In terms of the proposed control approaches and operation principle, a three-phase three-wire shunt active power filter is established and corresponding experiment and simulation studies are done. Through the simulation and experiment, it can be verified that the key techniques for APF described in this paper, including control strategy, main circuit design, harmonic detection and application solutions, etc, is viable and effective, which ensures the performance of active power filter.