Dual Phase-Shifted PWM Method With Enhanced Harmonic Performance for Parallel NPC Converters in Grid-Connected Applications

The interleaved operation of parallel power converters by applying carrier-based pulse-width modulation (CB-PWM) techniques is a popular method to achieve very high quality output waveforms. However, considering high-power converters that require low switching frequency operation in order keep the power loss below acceptable limits, some of the harmonics may exceed the individual limits defined by grid connection standards. To face this problem, this work proposes to modify the conventional CB-PWM pulse patterns using basic preprogrammed method principles. The proposed method deals not only shaping the required harmonic profile at the grid point-of-common-coupling (PCC), but also reduces the currents total harmonic distortion factors at the load and inverter sides. To consider all these objectives, one high-order polynomial cost function has been defined. The proposed preprogrammed PWM method has been successfully validated in a dual converter system based on neutral point clamped (NPC) converters using separate dc sources.