Parameters Design And Control Algorithm Of Single-phase Three-level LCL-type Converter

With the extensive application of moderm AC drive technology applied in the high-speed railway, high frequency resonance phenomenon has become increasingly prominent in the coupled system of traction network and traction drive system. In order to solve this problem, it is a new effective way to replace the L filter by using the LCL filter on the AC side of the electric traction drive system. Under the support of the National Natural Science Foundation "Modeling of dynamic and nonlinear high-speed train load and harmonic resonance suppression based on optimizing its characteristics (No.51207131)", this paper focuses on single-phase three-level neutral-point-clamped(NPC) voltage source rectifier(VSR) with LCL-filter. The research on the parameter design of LCL filter and the control algorithm are deeply studied. The main content of this paper is summarized as follows:Firstly, the topology of single-phase three-level LCL converter is analyzed, on which the mathematical model is established. Based on the working principle and mathematical model of the converter, the distribution of the high-order harmonics on the line side is analyzed, which provides the theoretical basis for the parameters design of LCL filter and the control strategy of the system.Secondly, by studying the frequency-domain impedance function of the two-port network of the LCL filter, the mathematical model of the internal current loop is established,and the high-frequency filtering effect of the LCL filter is analyzed according to the model.Then, aiming at the complexity of parameter design, this paper combines the traditional LCL filter design methods and the graph-analysis value method to deduce the relationships between total inductance, filter capacitance, resonant frequency and harmonic attenuation ratio, the damping effect. By taking into account the component constraints, an optimal design method of LCL filter parameters in the adopted converter is given, and the effectiveness of the adopted method is verified by simulation.Thirdly, in order to ensure the stable operation of the system and solve the LCL filter resonance problem, this paper analyzes the feasibility of passive damping and the virtual resistance methods applied in single phase three-level LCL converters by using current feedback method. Meanwhile, in view of design cost and power loss, a resonant damping control strategy of double band-pass filter method is tested. Simulation results have verified the effectiveness of the adopted scheme.Finally, the coupled system of traction network and traction drive system is designed on a hardware-based hardware simulation platform with RT-LAB and TMS320F28335. The correctness and effectiveness of parameter optimization design method and control algorithm applied in the single-phase three-level LCL converter are verified.