Research On The Control Method Of Cascade STATCOM Under The Condition Of Unbalanced System

Dynamic reactive power compensation is one of the important means of improving power quality.Static synchronous compensator(STATCOM) has many advantages,represents the development direction of dynamic reactive power compensation device,caused wide attention of experts and scholars both at home and abroad.Cascade STATCOM is the best solution of the current high voltage large capacity STATCOM, has a broad development prospect and unique research value.This article mainly aims at the cascade STATCOM dc side capacitor voltage balance control and control system under the condition of unbalanced device two key questions for further study.Firstly,the working principle of the cascade STATCOM is introduced in detail.According to the input and output modeling method,the mathematical model of the cascade STATCOM in ABC three-phase static coordinate system is established.In order to analyze and control the system,the mathematical model of the cascade STATCOM in the DQ two phase synchronous rotating coordinate system is deduced.The mathematical model based on the input and output modeling method is relatively simple and can meet the practical needs.Secondly,according to the cascade STATCOM DC capacitor voltage imbalance,a DC voltage hierarchical control method,the control method for the upper power phase,capacitor voltage balance control and phase balance control of three layers,the upper power control using feedback linearization and decoupling control method in the positive environment,to achieve reactive power among them,active power control and compensation device to absorb the cascade STATCOM,DC capacitor voltage balance control to ensure that the overall average voltage of all inverter unit DC stable in the reference value,the reactive power current feedback control device into the power grid,the reactive power compensation;the second layer is the DC capacitor voltage and balance control,control method by injecting zerosequence voltage,so that the energy exchange between the realization of STATCOM device in three-phase,three-phase DC side voltage average value chain equilibrium;the third layer is the DC capacitor voltage phase control,fine-tuning by the absorption and release of the active power inverter unit,the DC capacitor voltage between H bridge inverter unit equilibrium.Simulation and experimental results show that the proposed method can effectively stabilize the DC side capacitor voltage of STATCOM, with the characteristics of high precision, fast speed,simple control method and so on.Finally,in view of the control problems of STATCOM under unbalanced system conditions proposed a STATCOM double ring stacking control method based on combination of feedback linearization and repetitive control system under unbalanced and derivation of the device in the system is out of balance under the positive sequence and negative sequence environment feedback linearization control equation, through positive and negative sequence environment under two separate sets of current control loop is used to realize the compensation of unbalanced system.Among them,positive sequence current loop control compensation device required by the load reactive power, negative sequence current loop compensation load imbalance of negative sequence current. The repetitive control suppression device itself low harmonics and disturbances.Simulation results show that the method is correct and effective.The hardware platform of the dual DSP+FPGA+multiCPLD system is designed,and the experimental results are carried out on the cascade STATCOM.The experimental results show that the proposed method can effectively solve the problem of the compensation of the cascade STATCOM in the system,which has a certain reference value.