Research On DC Capacitor Voltage Control And Soft-start Of Active Power Filter

At present, based on fast and controllable power conversion for search and object, power electronic technologies have increasing applied to the field of industrial control with its characteristics of safety, saving, convenience, etc. Comfort of people’s living standards has been improved greatly. But a considerable part of the nonlinear load contains harmonics, which cause serious pollution to power quality and safety such as industry, residential daily needs. Active power filter(APF) can effectively improve the quality of electric energy, which has a prominent effect in restraining dynamic harmonic and compensating reactive.When APF puts into the grid, the problems of voltage and current impulse are existed. Because of the complexity of APF, it needs more advanced and effective control strategies. The soft-start design of APF can avoid the impact of voltage and current impulse on the system. Aiming at the disadvantages of traditional PI controller, this thesis puts forward the two improved algorithms of expert PI control and PI control. Comparing with the traditional PI control algorithm, the simulation result indicates that the two improvedt algorithms are more effective and superior. The main contents are below:(1) Taking the three-phase voltage-type APF as an example, describe APF classification, system structure and principle. To describe common harmonic detection methods and focus on the harmonic detection based on instantaneous reactive power. The derived mathematical model and the principle discussion lay the theoretical foundation for the study of control strategy and soft start. To determine the inductance on AC side, DC side capacitor and capacitor and capacitor voltage parameters.(2) To introduce the basic theory of the DC capacitor voltage control(the law of conservation of energy exchange) in detail and analyze the reasons for voltage fluctuation of the DC capacitor. The DC capacitor voltage control is introduced in detail. The transfer function is calculated and parameter calculation methods are given. APF simulation model realizes the control of the DC capacitor based on the conventional PI control strategy.(3) To put forward the method of improved PI expert control, the composition, principle and the PI parameters adjustment rules are studied in detail. The simulation results show that the improved expert PI control can eliminate the overshoot and oscillation of the system when compared to the conventional PI control,.(4) To analyze the necessity of APF soft start and introduce several methods to solve impulse voltage at startup from the aspects of hardware and software. Considering the device itself, the capacitor voltage values are larger, the more conducive to the stability of voltage. Combining with the existing methods, the thesis puts forward an improved multi PI controller to control APF soft-start. The simulation results show that the method can guarantee the smooth startup of APF. By comparing with the expert PI control, the thesis obtains the advantages and disadvantages of two methods. The simulation results show that using the expert PI control capacitor voltage start has better effect and the design is more complex. Multi PI control has fewer parameters than PI control and it has the advantage of simple design.