Development Of The Physical Simulation Experiment Platform Of HVDC System

With the development of the society, there is further demand for electricity in our country. Building "Transmission electrical power from West to East" and "Exchange electrical power between South and North" projects are the desirability for the unbalanced resources distribution and the unbalanced demands. High-voltage direct current (HVDC), which fits for transmitting electrical power in long distance and large capacity and will be widely used.This paper developes a practical simulating platform of HVDC for simulation. And proposes control strategy of novel STATCOM based on modular multilevel converter with single-star configuration. The main tasks of the paper are organized as follows:(I) Taking 6 pulsations of HVDC system as example, analyzes the converter commutation of rectifier and inverter for HVDC, including the relationship between the inverter turn-off angle and parameters of system. The system control mode is discussed and compared. And the transfer functions of HVDC are also developed. Aim at the control strategy called "rectifier constant DC current, inverter constant turn-off angle", the design methods of the parameters for controller are given out. An improvement program of constant DC current control with a feedforward control point is researched and put forward. The simulation and experimental results show that the strategy with feedforward control point has more excellent dynamic and static characteristics than without feedforward control point.(II) Overall design schemes of practical simulating platform of HVDC are researched and presented. The main circuit and control circuit construction is designed through both hardware and software. The main circuit is 12 pulsations HVDC converter, and core controller circuit based on DSP, detecting and protecting circuit, trigger circuit of thyristors are included in the control circuit. The software includes programs of DSP and upper computer, and the control methods for HVDC system is due to the DSP program. The detecting and protecting circuit mainly collects the DC current and input voltage and gets synchronizing signal. The protecting circuit prevents damaging to devieces from excessive output current. The trigger circuit improves the output power to drive the thyristors. Control program, AD detecting, firing angle datum detecting and upper machine communication is included by DSP software. Using the LabView to make a interface program to communicate with the lower dsp by Modbus communication protocol. With experimental of the simulating platform, the results show that the platform has reached all the requirements of the design.(Ⅲ) Through the analysis of a modular multilevel converter (MMC) based on the double-star chopper-cells (DSCC) configuration, this paper presents a static synchronous compensator (STATCOM) topology using the MMC based on the single-star chopper-cells (SSCC) configuration, and compares with the STATCOM based on the single-star bridge cells (SSBC), the single-delta bridge cells (SDBC), and the DSCC configurations. The proposed SSCC-based MMC-STATCOM is only half of the DSCC-based MMC-STATCOM and can save about 13.4% of the IGBTs than the SSBC-based STATCOM. A comprehensive capacitor voltage control strategy using direct current control for the SSCC-based MMC-STATCOM is presented, and an improved phase-phase capacitor voltage balance control scheme is proposed. The improved scheme does not need to to perform complex calculations on zero sequence voltage compensation quantity. The simulation results show that the proposed SSCC-based MMC-STATCOM has excellent dynamic and static characteristics and verifies the feasibility and effectiveness of the proposed topology of STATCOM and its control schemes.