| In new high-voltage and power converter, multilevel inverters have many advantages comparing with the two-level inverters, such as control flexibly, high inverter efficiency, suitable for high-voltage and high-power output. Meanwhile, it is possible to enhance the quality of inverter’s output voltage obviously by using multi-level inverters.Therefore, with the development of power devices, multilevel inverter has broad application prospects in high-voltage and high-power field.The five-level diode-clamped converter has various advantages compared with three-level converter, but its DC-capacitor voltage is difficult to balancing. Due to different problem existing in low and high modulation of five-level diode-clamped converter, a new optimizing DC-capacitor voltage balancing algorithm for a five-level diode-clamped converter is proposed in this paper, which accomplishes DC-capacitor voltage balancing in whole modulation, this paper mainly includes the following contents:Firstly, this paper focuses on the DC-capacitor voltage balancing and vector sequences switch mechanism of a SVM modulated five-level diode-clamped converter as modulation index is less 0.5, the five-level diode-clamped converter voltage balancing strategy based on objective function optimization is analyzed. On the basis of seven segment and five segment vector sequences, this paper comes to two vector sequences selection rules according to reference vector location.Secondly, because the effect of nearest three vector SVM method based on objective function optimization is restricted by modulation index and power factor, the five-level diode-clamped converter can hardly output active power in high modulation. Due to this problem, DC-capacitor voltage balancing method for a five-level diode-clamped converter with high modulation index and high power factor is proposed. The algorithm takes advantage of the six effective vectors of the inner hexagon, and the problem of DC-capacitor voltage balancing is restricted by power factor of five-level diode-clamped converter is resolved.Finally, the algorithm for corresponding simulation and experiment platform based on above theory is proposed in this paper. According to the simulation and experimental results, the controlling algorithm proposed by this paper can balance DC-capacitor voltage quickly in whole modulation, meanwhile the peak value of capacitor voltage ripple is low, DC-capacitor voltage and has a good dynamic performance in a variety of emergencies.In addition, the distortion rate of output current is low,whose THD parameters is ideal. |
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