Improved Algorithm for NPC Inverter Based on Simplified Sector Model

Aiming at the diode‐clamped (NPC) structure three‐level inverter's inherent DC‐side capacitor midpoint voltage offset and the traditional SVPWM algorithm's problem of multiple sector divisions and complex arithmetic, two improved SVPWM algorithms based on asymmetric sectors are proposed in the paper. Algorithm 1 involves a simplified tracking algorithm for the target magnetic chain that hides the center vector; and Algorithm 2 involves an approximate two‐level magnetic chain synthesis equivalent simplification algorithm based on the injection of virtual vectors. First, the target magnetic chain synthesis rules and PWM pulse width modulation methods of the two improved algorithms are compared with the traditional three‐level SVPWM algorithm to check their simplicity; then, a Simulink simulation platform is constructed to verify the correctness of the improved algorithms' line voltage output waveforms of the inverter under different regulation regimes, the correctness of the phase current waveforms of the loads, and the control of the voltage balance of the midpoint of the capacitor of the DC side of the inverter. Finally, a physical prototype of the vector control system for a permanent magnet synchronous motor based on the three‐level NPC inverter is built to further verify the correctness of the proposed theory and algorithm.