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Digital signal processing (DSP)-based implementation of a modified space-vector modulation strategy for balancing the DC-bus capacitor voltages of a three-phase neutral-point clamped bidirectional converter is presented. The proposed modulation strategy is simple in nature. It first identifies the switching states responsible for the unbalancing of capacitor voltages and then, based on the knowledge of polarity of capacitor voltage difference and direction of power flow, uses the appropriate redundant switching vectors to achieve the balancing of capacitor voltages. The analysis and control of the converter is described. The proposed control algorithm is validated through experimental results obtained on a laboratory prototype of the converter. The performance of the converter is found excellent in terms of the line-side and load-side power quality. A perfect balancing of the DC-bus capacitor voltages is achieved under balanced as well as unbalanced load conditions. The performance of converter is also investigated with distorted mains voltages and found satisfactory. DSP of dSPACE has been used for real-time simulation and implementation of the proposed control algorithm.
Date of Publication: July 2009