Research On Shunt Active Power Filter Based On Model Predictive Control

Nonlinear power electronics devices are widely used in many fields such as industry and life,with the rapid development of power electronics technology.The widespread application of these devices produces a great deal of harmonics,which degrades power quality.An active power filter(APF)has been applied to various harmonic compensation conditions because of its strong harmonic compensation capability and adaptive ability of complex harmonic components.This dissertation studies the key technologies of an APF:harmonic current detection,DC-link voltage control and harmonic current control.Under unbalanced three-phase grid voltages and containing high-order harmonics,the conventional phase-locked loop in the i_p-i_q detection based on instantaneous reactive power theory cannot implemet accurate phase locking of the grid voltage.Against this problem,a dual second-order generalized integrator is used to separate the fundamental positive sequence component of the grid voltage,and a synchronous reference frame phase-locked loop is employed to phase lock this signal.DC-link voltage control adopts a combination of PI control and sliding mode control.The PI control parameters are adjusted by sliding mode controller.This method can suppress the effects on DC-link voltage control produced by parameter variations and external disturbances,and has strong robustness.An improved model predictive voltage control is proposed.The control converts the optimization target in value function of the model predictive current control from the compensation current provided by the APF to the inverter output voltage.The range of inverter output voltage vectors involved in rolling optimization is narrowed according to the phase of the voltage vector corresponding to the inverter output voltage reference.The response speed of the system is improved by reducing the amount of calculations in the sampling period and the number of rolling optimization to improve computing efficiency.The switching frequency control term is added in the value function;then the switching frequency is reduced,the switching loss is decreased,and the multi-objective control of harmonic current and switching frequency is implemented.The proposed detection and control are verified by simulation and experiment.Simulation results and experimental results indicate that the improved phase locked loop with a dual second-order generalized integrator can effectively suppress the effects of unbalanced three-phase grid voltages and high-order harmonics on the phase locking.The sliding mode PI control of the DC-link voltage has small overshoot and a high system response speed.The improved model predictive voltage control has a small tracking error of the compensation current,a small THD(Total Harmonic Distortion)of the grid current,and a low system switching frequency.