Research On Control Strategy Of Active Power Filter Based On T-type Three Level Converter Topology

In 21 Century, one of the most significant features is the popularity of power electronics devices in the field of terminal energy consumption. Nonlinear of power electronic devices makes power electronics device meet the demand of different energy conversion. However, it also brings serious harmonic pollution to power grid. Active power filter (APF) has the advantages of good filtering performance, strong adaptability to the power grid, small volume,and wide usage in low voltage power grid. This paper conducts a research on a control strategy of active power filter based on TNPC topology.Firstly, the working principle of T-type three level active power filter circuit is analyzed.Mathematical models of three-phase static abc coordinates, two-phase static ap coordinates and two phase rotating dq coordinates are set up respectively. Secondly, the main circuit components parameters are designed and selected, structure of the control system is established.Finally, as to three-phase three-wire circuit topology, harmonic current detection method based on ip-iq is adopted in this study.The harmonic current tracking is the core of APF, and the performance of compensator directly determines the compensation effect of APF. In this paper, the direct current control method based on quasi proportional resonant (QPR) strategy is compared and selected, and the parameter design and calculation method of QPR controller and the discrete digital algorithm are given; According to the typical industrial systems 5, 7, 11, 13 characteristic harmonic designed multiple controller of multiple QPR parallel link, analyzes the interaction and design of parallel link between attention, improve the response speed and precision control system.Simulation results verify the effectiveness of the above methods and strategies.TNPC converter has the disadvantage of unbalance of the neutral voltage. Therefore, zero sequence component of neutral voltage balance is applied in the modulation of three phase current ring output. Compared with the traditional calculation method, PI controller calculation in zero sequence component takes shorter adjustment, stronger balance ability. The algorithm can inhibit the neutral-point potential fluctuations.The research builds a hardware-in-the-loop real-time simulation experiment platform on the basis of RT-LAB. RT-LAB simulates power supply, three-level T-type active filter main circuit and nonlinear load. Control system which is self-designed based on DSP digital signal processor is adopted, carrying out harmonic compensation experiment and neutral voltage control experiment. The results further verify the validity and feasibility of harmonic current control strategy and dc side neutral-point potential control of T-type three-level active filter.