Research On Cascade STATCOM Control Strategy

Due to the increasingly strict requirements for power quality in industrial production and living needs,ordinary reactive power compensation devices can no longer meet the requirements of high voltage and large capacity,and the proposal of multi-level technology effectively solves this problem.The cascaded STATCOM(Static Synchronous Compensator)with multi-level topology is a compensation device combining current conversion technology and high-power switching devices.Good compensation performance and dynamic response make it a focus of attention and research.Although the cascaded STATCOM has a simple structure and a wider compensation range,it still needs to focus on the problems of DC-side capacitor voltage balance control and fault handling.This article first discusses the development process of STATCOM and current research status at home and abroad,and compares and analyzes commonly used multilevel topologies and modulation techniques.Because the cascaded H-bridge STATCOM topology not only reduces the switching frequency,but also reduces harmonics and expands capacity simply,so choose the cascaded H-bridge topology and carrier phase-shifted pulse-width modulation(CPS-SPWM)technology.By establishing a mathematical model of the cascaded STATCOM to analyze its working principle,and deriving a mathematical model of the cascaded STATCOM in a rotating coordinate system,it provides a theoretical basis for designing and analyzing the controller and improving system performance.The different loss differences of each unit of the cascaded STATCOM directly affect the imbalance of the voltage on the DC side.Therefore,while implementing the system reactive power compensation,solving the problem of the balance of the cascaded STATCOM DC side voltage is also the key to be studied.In order to improve the compensation accuracy and dynamic response speed of the cascaded STATCOM steady-state conditions,a hierarchical control strategy is adopted in this paper,which is controlled from the total DC side voltage,the phase-to-phase DC bus voltage,and the H-bridge sub-module capacitor voltage.The voltage injection enables the active power to be distributed reasonably,and the capacitor voltage of the H-bridge sub-module is balanced by the active vector superposition.And the control strategy and voltage stabilization control are simulated and verified by Matlab/Simulink.The simulation results show that the control effect is good and the reactive power compensation performance is stable.Finally,the hardware circuits of the cascaded STATCOM are designed,and the experimental platform is verified by experiments.The experimental results are consistent with the simulation results,which further verifies the effectiveness of the control strategy.