Maximizing photovoltaic system power output with a master-slave strategy for parallel inverters

Abstract

Parallel inverters are commonly used for connecting photovoltaic (PV) and other renewable energy sources to Microgrids (MGs). One of the greatest challenges in MG operation is maximizing the PV system's performance while also enhancing the MG's reliability and efficiency. The PV inverters waste power if the shared load power is less than their maximum output power. When shared load power surpasses the PV inverter's maximum output power, the system may become unstable since PV sources are intermittent. This study proposes a master-slave control system for controlling parallel inverters connected to a PV system. The master inverter is connected to Energy Storage Devices (ESDs) and is responsible for maintaining stable voltage on the load bus. The PV units are connected via slave inverters and are managed using a dual-loop Proportional Integrator Derivative (PID) control approach, with the outer loop maximizing solar panel output. The system is built on a Direct-Quadrature-Zero (d-q-0) inverter architecture, and the controller guarantees that all inverter currents remain in phase to reduce circulating current and enhance overall system efficiency. The simulation model evaluates a system comprising three inverters, with the master inverter powered by ESDs. The PV Units power the other two Slave Inverters. The system is evaluated using four case studies featuring various load and radiation change scenarios. The results demonstrate that the system is highly reliable and operationally efficient, with the absence of circulating currents among the inverters. Moreover, the system is capable of precisely monitoring the MPPs of PV modules with 100% efficiency and a minimal 0.002% fluctuation, while also responding to changes in under 50 ms.