Digital Control System Design Of DSTATCOM Based On Cascade Multilevel Converter

As one of the new generation reactive power compensation equipments used in distribution grid, Distribution STATic var COMpensator (DSTATCOM) has been extensively studied for its excellent performance. In this paper, the author have designed the digital control system of a high capacity cascade multilevel DSTATCOM which used in10KV distribution grid.Firstly, the mathematical model of the three-phase three-wire DSTATCOM was established in this paper. Then, the compensation current control strategy of the cascade multilevel DSTATCOM was studied. Because the load in distribution grid is very complex, DSTATCOM should be able to compensate harmonic current as well as compensate reactive power. Therefore the repetitive controller was introduced into the current control strategy. Repeat controller and PI controller together constitute a composite controller. Prototype experimental results show that, both the reactive power compensation and harmonic compensation performance of the DSTATCOM is very good using the composite controller.Secondly, the DC bus voltage control of the cascade multilevel DSTATCOM was studied. The establish process of the DC bus voltage was analyzed. Then, a boost method of DC bus voltage using modulation-ratio-regulation for start-up process was introduced. After that, a DC bus voltage steady-state control strategy based on power conservation law was introduced, and the validity of the method was verified by simulation results.Digital controller is the hardware foundation of the control strategy. In the last part of this paper, the function of the digital controller was introduced. Then, the author introduced the software and hardware of the digital controller and a method which realizes the CPS-SPWM modulation strategy based on FPGA.