Research On Control Strategies And Device Of Modularized Three-level Active Power Filter

The power electronic devices which are applied to the actual industrial will generate harmonic currents in the grid. Usually Active Power Filter (APF) is adopted to eliminate the harmonic currents to prevent pollution of the grid. Due to the structural characteristics of three-level APF, it has a greater application prospects in the application of high voltage and high power, compared with the traditional two-level APF. Neutral Point Clamped (NPC) three-level APF in three-phase three-wire system is used as the research object of this paper. The paper researchs on the key control strategies of three-level APF, and designs the software and hardware of the device.The mathematical model of three-level APF is the foundation of APF control strategy design. The paper introduces the working principle of three-level APF, and derives the component of the reference currents at different control objectives. Based on the main circuit topology of three-level APF, the paper establishes the mathematical model of three-level APF in abc coordinates and dq coordinates.Three-level SVPWM modulation and neutral-point balance control is the premise to ensure the three-level APF working. Using the method that the reference vectors decompose, the paper gives the SVPWM modulation algorithm of three-level APF. Analysing of the impact of the three-levels of the vectors on neutral-point, according to the principle of charge balance the paper puts forward a simple neutral-point voltage balance control strategy based on the time factor. In order to control unbalance of DC capacitors voltages.Current tracking control strategy is the key factor to determine the compensation effect of three-level APF. According to the control target of three-level APF and theinstantaneous reactive power theory, the paper makes a detailed analysis of ip-iq harmonic current detection method to ensure the accuracy and rapidity of the reference current. Based on the mathematical model of the three-level APF, the relative control functions about forward decoupling PI control, predictive current control, deadbeat control and sliding mode control are derived, and the control strategies of three-level APF are verified by simulation.The parallel control strategy is the core technology of three-level APF in parallel. In this paper, including centralized control, master-slave control module and module distributed control these three kinds of parallel control mode are analyzed and simulated.To compare the performance of current tracking control strategies, the four control methods’ simulation about about forward decoupling PI control, predictive current control, deadbeat control and sliding mode control are conducted on the semi-physical platform of AppSIM. The paper summarized the characteristics ofeach kind of current tracking control strategy by Comparison and analysis of experimental results. Through the comparison of whether or not to join neutral-point balance control, the neutral-point balance control strategy in the deadbeat controller is verified.The paper design the device of modularized three-level active power filter, completed the structure design of the device and the design of main circuit parameters. According to the theoretical derivation and simulation results, the DC link capacitor parameters, the AC side output filter inductance andresistance parameters and precharge resistor parameters are designed, and the design of the control board based on DSP+FPGA is completed. On the experiment platform the DSP and FPGA procedures of the deadbeat control and neutral-point balance control are completed, and the rationality of the design of the hardware platform and the control effectiveness of all control strategies are verified.