| Key technologies such as reference current calculation method, control strategy and optimal design of main circuit for low-voltage distribution network active power filter (APF) are deeply studied in this dissertation. APF can deal with power quality problems, but there are many technical issues to be sloved in process of engineering applications. The research on low-voltage distribution network APF is of great importance to its early industrialization application, and the main research content of this thesis are as follows:(1) A novel reference current calculation method based on composite low pass filters (LPFs) is proposed. S. Fryze, F. Buchholz, M. Depenbrock (FBD) method is studied, and the impact of low pass filter (LPF) on reference current calculation results is analyzed. Composite LPFs are designed, which is composed of two two-order Butterworth LPFs. According to the fluctuation of load current and the lowest frequency of harmonic currents, choice of LPFs is made by fuzzy reasoning. Compared with traditional methods, the contradiction issue between accuracy and dynamic performance for reference current calculation algorithm is resolved with this method. Even under conditions of asymmetry power grid voltage, dynamic changing frequency and amplitude of harmonic currents, this reference current calculation method is of the high accuracy and fast dynamic response, meanwhile it is of simple principle. Correctness and effectiveness of the method is proved by theoretical analysis and simulation results.(2) Predictive current control strategy based on space vector pulse width modulation (SVPWM) is proposed. Adaptive linear neuron (Adaline) is used to predict the reference current for next control cycle, and the learning rate for Adaline is regulated online with fuzzy algorithm.The delay caused by zero-order hold of APF control system is effectively compensated, and the output current of APF can track to predictive reference current fast and exactly with SVPWM mehtod. Simulation results confirmed that, compared with control strategy without reference current predictive algorithm, steady state and dynamic performance of APF with predictive current control strategy is markedly improved.(3) Stability of APF control strategy is analyzed here, which is ayalzed with current control loop and voltage control loop. Predictive current control consists of reference current predictive algorithm and SVPWM method, so its stability depends on the stability of two parts. The equivalent structure of predictive current control is built, then the stability of reference current predictive algorithm is analyzed with Lyapunov function, and stability of APF with SVPWM part is analyzed based on the transfer function of SVPWM loop. As to stability of DC voltage control, equivalent structure of DC voltage control predictive current control is built, and Routh criterion is exployed for stability analysis. With method mentioned above, stability of low-voltage distribution network APF is analyzed after its developement.(4) Optimal design method of output filter for low-voltage distribution network APF is proposed. Structure and parameters of the main circuit for Low-voltage distribution network APF are studied, and detailed analysis of functions and design principles for output filter are developed. Design steps of the output filter are decomposed in accordance with its function, and inductor in the VSI side is designed taking compensation capacity and performance into accounts. While inductor in the power grid side and hign pass filter are designed according to the characteristics of high-order harmonic, and parameters of output filter are optimized with genetic algorithm.(5) Low-voltage distribution network APF of 120A rated current is designed, and it is successfully applicted in harmonic suppression project for some mining companies in Guangxi province. Main circuit of low-voltage distribution network APF is design with ptimization method, which souldly meets the requirements of the harmonic suppression. Reference current is calculated with the method based on composite LPFs, and preditictive control is used to ensure that output cuurent can tracks reference current fast and exactly. Experimental results show that effective harmonic suppression and fast dynamic response are realized by low-voltage distribution network APF by adopting the proposed techniques. However, there are still a small amount of harmonic currents in power grid after compensation by APF. So further analysis of factors which affect compensation performance of APF is taken, and a number of possible improvements are proposed. At last, a comprehensive compensation system for harmonic suppression and reactive power compensation is proposed, which is composed of APF and capacitors, and the practical engineering results confirm that the comprehensive compensation system has obvious effect in harmonic suppression and reactive power compensation. Moreover, it is a cost-effective solution, and the application future is bright.
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