Research On The Key Issues Of Active Power Filter With LCL Filter

Active power filter is a high-performance harmonic control device. Based on the research object of the LCL type three-level active power filter, this paper has probed into the system modeling, phase-locked loop, system control and parameters design.As for the poor performance of the traditional phase-locked loop under non-ideal condition, a phase-locked method based on complex filter matrix decoupling has been proposed. Combined with first-order complex filters and phase shift operators, complex filter matrix has been constructed and the orthogonal signal generator(OSG) has been realized through the design of matrix operation. The OSG module possesses the function of the frequency selection and the orthogonal signal extraction, which enables it to extract the fundamental component and the orthogonal component. Besides, a crossing feedback structure has been designed and the positive and negative sequence extraction and decoupling of the original signal has been realized. The module has been embedded in the phase detector, and the parameters design and system discretization design have been carried on. Starting strategy has been proposed in view of the problem that long time of frequency estimation at the start of PLL. The simulation and experimental results show that, under the non-ideal condition of unbalanced grid voltage, distortion, frequency fluctuation and so on, the phase lock strategy can accurately detect frequency and phase.In order to solve the problem of variable coupling and nonlinear characteristics of three-phase active power filter, the third chapter has proposed a quasi-sliding mode variable structure control method of APF based on state feedback exact linearization algorithm. With the affine nonlinear system model of APF system, it is verified that the system meets the controllability conditions and involutive conditions. The nonlinear coordinate change matrixes and the state variable feedback equations of the system have been derived via the diffeomorphism relationship. It has realized variable decoupling on synchronous reference frame and system resonant poles configured to the origin. For the feedback decoupling system, the sliding mode function has been designed based on the system relative degrees, and the quasi sliding mode controller has been constructed by introducing saturation function. Then a detailed analysis of the system structure and the robustness has been conducted. After that, the DC side voltage is divided into two levels’ control, using power PI controller to control the average voltage, and negative sequence current controller to control the phase voltage equilibrium. The steady state and dynamic performance and anti-interference ablitity are verified through simulation and experiment.To improve the performance of the control system, this paper has proposed the double closed-loop control strategy of APF current based on reduced order state feedback exact linearization. Based on LCL modeling and the zero pole placement of transfer function, the feedback transfer functions and the feedback coefficients are derived for the six kinds of single state feedback, and a detailed analysis of the feasibility of each scheme and high-pass filtering schemes has been conducted. Then the transformation relationship between different schemes and their advantages and disadvantages are derived. On this basis, with filter capacitor voltage regarded as the input and output respectively, two systems of reduced order state feedback exact linearization have been constructed. Double loop control has been designed with the outer loop as the grid side current control, and inner loop filter capacitor voltage control. Tracking control has been achieved as well as active damping of single state feedback. According to the performance of the APF system, the design of the controller parameters has been completed. The simulation and experimental results have verified the effectiveness of the control algorithm.The selection of system parameters has a great effect on the compensation characteristics and high frequency performance of APF system. This paper has conducted a detail analysis of system DC capacitor parameters and the parameters of LCL filter, and has proposed a 3D graphical LCL parameters design scheme based on constraints. The limit for harmonic tracking speed has been calculated according to harmonic change rate, followed by the calculation of the harmonic content of APF output voltage, inverter side current and grid side current. Then the maximum single harmonic value has been set instead of high frequency THD model as the high frequency harmonic constraint. By the establishment of the constraint functions, the range of parameters in 3-dimensional space has been calculated through 3D graphical method, and verified through the simulation.The thesis includes 83 figures, 9 tables and 154 literautre references.