Dual Neutral-Point-Clamped Converters with Synchronized PWM for Photovoltaic Installations

Abstract - A novel method of synchronized pulsewidth modulation (PWM) has been modified and disseminated for control of dual (cascaded) neutral-point-clamped converters, supplied by two insulated strings of photovoltaic panels and connected to grid by a three-phase transformer with open-end windings on primary side. Specialized strategy and scheme of synchronized PWM, applied for control of dual converters, provide in this case: a) continuous phase voltage synchronization and required voltage regulation in the system by the corresponding control of modulation indices of the two converters; b) elimination of undesirable common-mode voltages both in each inverter and in the load, and c) an improvement of effectiveness of operation of the system due to flexible control of switching frequencies of inverters as function of DC voltages of photovoltaic panels. Simulations give a behavior of dual-converter-based photovoltaic system with three basic versions of synchronized PWM.