RCPI controller-based multilevel multistring grid following inverter for large rooftop PV power plant application

Abstract

The modular multilevel grid following string inverter (MMGFSI) has gained popularity in large rooftop solar photovoltaic power (PV) plant applications, with grid-integrated net metering facility. The performance of the standard PI controller-based MMGFSIs during grid load disturbances is not satisfactory due to the wide ripples, low dynamic performance, and low steady-state precision of the inverter current feedback regulation. This study proposes a repetitive control proportional-integral (RCPI) controller approach for the cascaded H-bridge (CHB) five-level grid following inverter to synchronize with the grid and satisfy enhanced power quality standards IEEE519 for large rooftop solar PV plant application system. Additionally, this proposed control topology performance has compared to PI controller-based MMGFSI’s and repetitive controller cascaded PI controller-based MMGFSI’s system. The proposed RCPI MMGFSI’s system performance has been tested on a PSIM simulation environment on a grid-connected, photovoltaic (PV) system with a diversity of linear and nonlinear load disturbances to show the viability and resilience of the suggested repetitive control strategy in practice. To provide the necessary carrier control signal for the sinusoidal pulse width modulation block (SPWM), a cycle delay has introduced in the RCPI feedback path. As a result, reducing grid-side harmonic distortion lowers the cost of the LCL filter connected to the inverter output This RCPI-based MMGFSI has 4.1 percent less overall harmonic distortion than the conventional PI controller-based MMGFSI and 0.21 percent less total harmonic distorted than repetitive cascaded PI controller-based MMGFSI’s system. Additionally, a hardware prototype has RCPI controller MMGFSI’s implemented to evaluate the five-level CHB MLI structure and switching topology.