| The scheme of cophase traction power supply system fixed three problems introduced by traditional traction power supply system, including negative sequence, a large amount of harmonics and reactive power. It removes the barrier for the speed-up of the traction caused by the neutral section insulators, and makes traction power supply green, high-efficiency and smart.This paper focuses on the research of cophase traction power supply core unit called power flow control device. In this paper, the working principle of cophase power flow control device was analyzed, different control strategies of PWM rectifier and grid-connected inverter were investigated and compared, the best solution was selected and approved by simulation, and the schemes of hardware and software were presented in this paper. In this project, a cophase traction power supply power-flow-control-device was constructed and the grid-connected experiment has been done to verify the feasibility and reliability of the control strategy referred in this paper. Finally, this paper shows the test results of PWM rectifier’s input power factor, the inverter’s frequency-phase-track function, and reactive power compensation. The errors occurred in development process were analyzed and the solutions were given.In this design, single-phase full bridge AC-DC-AC circuit topology was used, using TMS320F28335(TI DSP C2000) as control unit. At rectifier stage, a PWM rectifier was built using the fixed switching frequency and bipolar modulation. Direct current PI control strategy with both voltage and current loops was designed to track the grid current. Test results show that this system responses was fast and stable. With high power factor, there is no pollution to power grid. At the inverter stage, a full-bridge inverter was constructed with fixed switching frequency and unipolar modulation. Output current was controlled by a PI controller, a digital phase-locked-loop was used for synchronizing frequency and adjusting the phase of the output current. Reactive power compensation and active power regulation were realized for the grid power.In this experiment device, all necessary signals in the main circuit were amplified and modulated, and then12-bits ADCs inside TMS320F28335were used for sampling signals. The precision of output voltage and current is up to1%, and the precision of frequency and phase is up to0.5%, input power factor reaches0.98. Due to the reactive power compensation, the output power factor of grid power source reaches0.98. In this device, a4.3inch touchable LCD was used as interface, displaying the output waveform and the curve of spectral characteristics and parameters including input/output voltage, current, frequency, phase-difference, power, THD, and the efficiency of main board. A virtual numeric keyboard was designed so that parameters could be typed in easily. Furthermore, self-examine, protection of over voltage and over current were implemented, and device could recover automatically while faults were cleared. |
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