Voltage-Modulated Direct Power Control and Resonant Regulators for 3-Phase Grid-Connected Inverter under Voltage Distortion

The voltage-modulated direct power control (VM-DPC) technique for a 3-phase grid-connected inverter is robust to operate under a weak grid condition due to the absence of a phase-locked loop. This study further evaluates the VM-DPC technique under grid voltage harmonics, orders 5th, 7th, 11th, and 13th, with a total harmonic distortion (THD) of 4.69%. We also proposed a multi-resonant (MR) controller in parallel with the VM-DPC controller to suppress the voltage harmonics. Experiments of a 5-kVA inverter were implemented on a hardware-in-the-loop real-time simulator with control schemes developed on a TMS320F25379D microcontroller. The VM-DPC scheme alone regulated the grid current with a THD of 0.73% and 5.10% under the sinusoidal and distorted voltage conditions respectively, which was found to be better than the conventional synchronous reference frame control. The VM-DPC+MR scheme further improved the grid current quality with a THD of 0.36% and 1.12% under the sinusoidal and distorted voltage conditions respectively.