Key Techniques Of High Power Shunt Active Power Filter Based On Repetitive Control Strategy

High power Shunt Active Power Filter (SAPF), controlled as harmonic current sources, is suitable to compensate a large number of current type harmonic sources in power system. Therefore, study on the main circuit design and control strategy for SAPF has important theoretical and practical significance. Several key techniques of 260kVA three-phase three-wire industrial SAPF based on repetitive control strategy are studied in this thesis.A high power converter containing low stray inductance is critical for safe and efficient operation of switching modules. Based on the principle and analysis of reducing equivalent stray inductance in planar busbar, a new physical structure for a high power voltage source converter applied in SAPF is constructed and it reduces the turn-off voltage spike of power devices and EMI issues greatly.LCL filter is gradually widely used in high power SAPF for its good performances, while design of a proper LCL filter is difficult due to many variable parameters. An LCL filter design method is proposed taking such critical factors as voltage drop across filtering inductors, reactive power capacity of filtering capacitors, bypass effect for switching ripples, resonance frequency into account, which is simple, explicit and suitable for practical application.The physical structure of thermal design plays a significant part in long term reliable operation of high power SAPF. However, the physical structure design for a high power SAPF is difficult when a myriad of heating elements are contained. To deal with this problem, a physical structure with separated duct is designed which could not only guarantee good heat dissipation effects for power modules but also decrease the number of fan as well as volume of the equipment greatly as a result of uniform heat dissipation for all passive components in the main circuit.The compensation precision of SAPF relies heavily on the design of current loop controllers. Since the reference and feedback signal of the current controller are composed by different harmonic components and the bandwidth of conventional Proportion-Integral (PI) controller is limited, this controller cannot control the output current waveform without any steady error. This paper puts forward a double-loop composite controller composed by a PI inner loop and repetitive controller external loop to improve the output current waveform and the design method is given in detail. The controller could not only acquire high compensation precision when used to suppress odd harmonic, even harmonic current and negative sequence parts created by unbalanced load, but also guarantee excellent dynamic response performance.The DC bus voltage control is critical for safe and good operation of high power SAPF when it operates at such dynamic processes as startup, connecting with grid, as well as load change. In this paper, soft startup and impact suppression techniques are proposed to guarantee no voltage overshoots or sags in DC bus during startup and grid connection dynamic processes. Subsequently, a novel controller for DC bus voltage regulation is put forward according to the small signal model based on the instantaneous power balance in AC and DC sides of three-phase SAPF.