A Delay-Tolerable Master–Slave Current-Sharing Control Scheme for Parallel-Operated Interfacing Inverters With Low-Bandwidth Communication

Abstract

Parallel-operated inverters with common dc and ac bus can be used as an interface for dc systems connecting to an ac network. High cost and complicated wiring of communication are the main drawbacks of communication-based current-sharing methods for the parallel systems. Many new communication tools, e.g., power line communication (PLC), Bluetooth, and Zigbee modules, are cheap and require no extra wire connection, but have low communication bandwidth and low data rate, which result in a large communication delay and zero-order-hold period that could cause stability issues if used to transmit control signals. This article presents a method to mitigate the instability issue caused by communication effects, in parallel grid-tied inverter system with master-slave current-sharing control. First, the master-slave current-sharing control scheme is introduced. Then, the influence of communication delay and zero-order-hold on the system is analyzed. And design criterion to reduce the influence of low-bandwidth communication (LBCom) is studied and determined. New approaches, by designing a current reference low-pass filter and a voltage feedforward loop in slave modules, are introduced. The performance of the proposed control structure and design criteria are experimentally verified. With the proposed method, LBCom tools can be applied to systems with master-slave control architecture while keeping the robustness and transient performance, with improved modularity and operation flexibility.