The Research Of DC-side Voltage Balance Control Strategy Of The Single-phase Cascaded H-bridge Rectifier

As a multilevel converter,the cascaded H-bridge rectifier(CHBR)is widely used on the high-voltage and high-power fields,due to its modularity,extendibility,and desired control performance.For CHBR,a quick-response and effective DC capacitor voltage balance control method is an essential prerequisite to guarantee the system stability.Hence,the DC-side voltage balance control is an interesting field to research,and a variety of strategies have been proposed to maintain the DC-side voltage balance.As all the units of CHBR are equivalent,a model of the simplified single-phase PWM rectifier is established to analyze the working principle of CHBR.Two current control methods are introduced in detail,including the method using the proportion resonant(PR)controller in the static coordinate system and the strategy using the proportional integral(PI)controller in the rotating coordinate system(which is called as virtual vector control method).Based on the virtual vector control method,the mathematical model of the DC-side voltage of each unit is established,and its influencing factors are analyzed.The stable operating region(SOR)of the two-cell CHBR(2C-CHBR)is studied.According to the controlling principles,the operating loci of different balance methods are drawn in SOR.The degree of imbalance for 2C-CHBR is defined to evaluate the control capacity of different balance methods.The existing balance methods are unsuitable for multi-level CHBR or cannot take advantage of SOR.According to the operating locus in SOR,a novel balance method with the widest regulation range is proposed in this paper.The proposed balance method can take advantage of SOR of the single 2C-CHBR with a simple calculation.Based on the analysis of SOR of 2C-CHBR,SOR of the multi-cell CHBR is analyzed.A criterion is defined to evaluate the utilization of the SOR under different balance methods.Optimal expansion of the proposed balance method is obtained,after comparing the utilization of SOR with different expansion.Finally,experimental platforms of 4C-CHBR are built.The validity and effectiveness of the proposed method are verified through simulations and experiments.75 figures,6 tables,61 references.