Research On Cascaded STATCOM In Steady State Reactive Compensation Of Power Supply System

Reactive power compensation is helpful in improving the power factor of the power system,reducing the power loss during the use of the equipment and the power transmission,improving the voltage quality.The corresponding compensation by the reactive power compensation device can ensure the smooth operation of the power system.In urban power supply systems,the stability of the voltage is critical,and reactive power compensation can effectively improve the stability of the voltage and the power factor of the system.Static Synchronous Compensator(STATCOM)has the ability of reactive power bidirectional regulation,which fully meets the requirements of power system for reactive power compensation.It has become an ideal substitute for traditional reactive power compensation equipment and has broad industrial application prospects.In this paper,the control method of H-bridge serial cascaded STATCOM in steady state reactive compensation of power supply system is studied.For the cascaded STATCOM with three-phase H-bridge series structure,this thesis focuses on the structure of cascaded STATCOM with the main circuit of the series H-bridge as the triangle connection.First,this thesis based on the analysis of the working principle of the H-bridge unit,the unipolar carrier phase shifted sinuous pulse width modulation method is used to modulate the width of the trigger pulse for the series H-bridge.As for the detection of reactive current,this thesis uses the reactive current detection method based on instantaneous reactive power theory.The phase current is used as the control quantity for current tracking control.The compensation phase current command is calculated based on the PI control strategy tracking command current,and it reaches the role of compensating the load in the power supply system when the power supply system is in steady state.In addition,due to the different triggering time and loss inside each H-bridge unit of the three-phase series H-bridge cascaded STATCOM,theDC-side voltage values of each H-bridge units may be different and there are diverging trend over time.In this thesis,the DC bus voltage control of the three-phase series H-bridge cascaded STATCOM is divided into three-phase total DC-side voltage control and DC-side voltage equalization control of each H-bridge module,which can controll the voltage value across the DC side capacitor in the series H-bridge to an appropriate range.Finally,this thesis establishes a model for simulating the triangle-connected cascaded STATCOM control strategy with five H-bridges series for each phase in the SIMULINK environment of MATLAB platform.The simulation results show that the power factor of the power supply system after accessing the cascaded STATCOM is obtained which proves the correctness of the control strategy designed in this thesis.This thesis completes the hardware design of the distributed control module of a master multi-slave machine,realizes the I2 C communication between the DSP chip and the ARM chip.The feasibility of using the ARM chip STM32F103C8T6 as the distributed control chip and the DSP chip TMS320F28335 as the main control chip of the serial H-bridge cascaded STATCOM system is proved.