| The running distance of urban rail transit is short and the starting braking is frequent. In the early days, the braking resistance was used to transform the braking energy into heat energy. Not only a great deal of energy was wasted, but the heat released also increased the temperature rise of the tunnel. It is the most mature way to utilize regenerative braking energy by using energy feedback converter to feed the braking energy to AC traction power grid, which is the most mature method of regenerative braking energy utilization in urban rail transit. Compared with the two level, the three level energy fed converter has advantages in efficiency, cost, and so on. It is a development direction. In this paper, a diode clamped three level energy fed converter controller is developed in combination with the "three level Metro regenerative braking energy feed converter" project. Combined with the project, the main work of this paper is as follows:Working principle analysis. The main circuit topology and working principle of diode clamped three level inverter, and based on the mathematic model of fed converter to establish three level in ABC coordinate and dq coordinate respectively using vector analysis method. Based on the mathematical model of the three level converter in the dq coordinate system, the voltage and current double closed loop control model is established. Finally, two modulation strategies of SPWM and equivalent SVPWM are analyzed in detail, and the characteristics of the two modulation strategies are discussed.Control algorithm, simulation, verification. Based on the MATLAB/Simulink platform,a simulation model of diode clamped three level converter is built according to the parameters of the metro power supply system. In the open loop simulation, the driving waveform and the line voltage and phase voltage waveform of the inverter output are observed, and the correctness of the main circuit parameters and modulation strategy is verified. Study on the neutral point voltage clamp control algorithm using SVPWM modulation, and the simulation is carried out; in the closed-loop test is mainly observed in the phase current waveform of AC DC voltage surge and anticlimax side, tested in double loop control system has stability and good dynamic response speed.Hardware design of controller and main circuit. Based on the technical requirements of the "three level Metro regenerative braking energy feed converter" project, the interface board based on FPGA+ARM control core is designed. The interface board has 24 analog signal processing circuit, 44 digital signal isolation circuit and 12 way PWM signal isolation amplifier circuit. In addition, based on the three level experimental platform, the diode clamped three level converter main circuit board is designed. Based on this, the three level experimental platform is built.System experiment verification. In this paper, the modulation and control algorithm of diode clamped three level converter is programmed based on Quartus platform, and the algorithm is debugged on the three level experimental platform. The open closed loop experiment and grid connected experiment are completed. The experimental results show that: (1) the controller based on ARM+FAPGA can satisfy the requirements of sampling accuracy,computing speed, storage and communication. (2) modulation and control algorithm can meet the expected design, system can realize constant current control, reactive power compensation and other functions; neutral point clamped control algorithm can quickly control of midpoint voltage offset, and can make the initial midpoint voltage offset of zero return. |
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