Generalized PWM-based method for multiphase neutral-point-clamped converters with capacitor voltage balance capability
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This paper presents a generalized pulse width modulation (PWM)-based control algorithm for multiphase neutral-point-clamped (NPC) converters. The proposed algorithm provides a zero sequence to be added to the reference voltages that contributes to improve the performance of the converter by: 1) Regulating the neutral-point (NP) current to eliminate/attenuate the low-frequency NP voltage ripples; 2) reducing the switching losses of the power semiconductors; and 3) maximizing the range of modulation indices for linear operation mode. The control method is formulated following a carrier-based PWM approach. Hence, dealing with complex space-vector diagrams to solve the modulation problem for multiphase converters is avoided. The recursive approach means that it can be easily extended to n-phase converters without increasing the complexity and computational burden, making it especially attractive for digital implementation. The proposed method allows regulating the NP voltage without the need for external controllers; therefore, no parameter tuning is required. The algorithm has been tested in a four-leg NPC converter prototype performing as a three- and four-phase system and operating with balanced and unbalanced loads.
CitationLópez, I., Ceballos, S., Pou, J., Zaragoza, J., Andreu, J., Ibarra, E., Konstantinou, G. Generalized PWM-based method for multiphase neutral-point-clamped converters with capacitor voltage balance capability. "IEEE transactions on power electronics", 12 Juny 2017, vol. 32, núm. 6, p. 4878-4890.