Study On The Topology Of A Novel General D-STATCOM And Its DC Voltage Control Strategy

The power quality problem of the grid is increasingly serious.However,the power equipment is more demanding for the power quality.The D-STATCOM is the best device for regulating reactive power and other power quality problems at present.In this paper,two commonly used multilevel inverter topologies:the multilevel topology of the H-bridge unit and the diode clamped multilevel topology are first analyzed.Based on the advantages and disadvantages of the two topologies,a new general hybrid multilevel topology is proposed.The principles of compensating the reactive power and three-phase imbalance by using the D-STATCOM device of the new general hybrid multilevel topology are introduced,and the mathematical model is built.The basic principle is to make the output voltage of the main inverter and the compensation current perpendicular to each other,so as to ensure the three-phase DC voltage balance of the main inverter when the main inverter is compensated for unbalanced compensation.In this paper,an instruction current is used instead of compensation current to calculate the angle between the output voltage and the instruction current,and then the output voltage of the main inverter is obtained.The output voltage of the slave inverter can be obtained by subtracting the output voltage of the main inverter from the total output voltage.The factors that affect the DC voltage fluctuation of the capacitor are analyzed theoretically,that is,the capacitance and the active current.Considering that in the three-phase unbalance operation condition,the whole system is a complex nonlinear system,and the inverter units differ from each other,there-layer control is performed on the DC voltage.The first layer:when all inverter DC voltage is regarded as a whole,and it is ensured that the DC side capacitance is equal to the system active power exchange,the sum DC voltage is controlled;the second layer:the negative sequence current may cause unbalanced phase voltage,and the value of the change in the active energy of this leg is injected into the output voltage of each phase of the chain H-bridge arm,so as to achieve the phase balance control;and the third layer:based on results of the foregoing two layers of control,active power of each H-bridge unit flows freely in every phase,thereby achieving balanced phase voltage control.Finally,based on the above theory,the correctness of the above theory and the feasibility of the control strategy are verified by performing MATLAB/Simulink simulation.In addition,the result of the experimental test on the experimental platform shows that the control strategy proposed in this paper is effective and feasible.