Distributed Carrier Phase Shifting Control Method for Modular Interleaved Parallel Inverters

Modular parallel inverters with interleaving are a cost-effective approach to improve system performances. In this article, a simple distributed carrier phase shifting control method with the local controller is proposed. First, the resultant current harmonics for modular parallel inverters are analyzed considering the crystal oscillator frequency deviation. Then, a NOR gate circuit-based synchronous signal generator is constructed, which generates a common low-frequency digital synchronous signal to trigger the carrier phase shifting control. With the carrier phase detection and error compensation considering the time delay, a proportional carrier phase shifting controller with detailed parameter design considerations is proposed to dynamically adjust the carrier relative phase angles of parallel modules until they are properly interleaved. The proposed method has overcome the issue of a single point of failure (i.e., high reliability) and is immune to sampling error and line impedance voltage drop (i.e., high accuracy). Finally, different carrier phase shifting methods are compared and the experimental results have verified the effectiveness of the proposed method.

I. Introduction

Due to limited voltage or current ratings of commercial active switches, a single inverter is unable to meet the demand for large capacity such as photovoltaic (PV) systems, battery energy storage systems (BESS), and vehicle-to-grid systems (V2G). Alternatively, a modular inverter has been a popular choice as a building block to achieve even higher power and is conducive to realizing “” redundancy [1]. With the application of centralized control [2], master–slave control [3], distributed control [4], and droop control [5], the coordinated control of low-frequency active/reactive power for modular series or parallel inverters system has been well resolved in the recent years. Interleaving is a favorable means to optimize the high-frequency performances such as resultant current harmonics and common-mode voltage [6], [7], [8]. Modular parallel inverters usually adopt independent controllers to improve system reliability. However, they cannot work synchronously with itself. Even if the parallel modules have the same nominal carrier frequency, the real ones may be varied considering the crystal oscillator frequency deviation. Therefore, the carrier phase shifting angle between the parallel modules will be time-varying. To realize the coordinated control of the pulsewidth modulation (PWM) sequences, it is required that the carriers of the parallel modules have the same switching frequency but are phase displaced with respect to one another by a fixed phase shifting angle. Currently, the carrier phase shifting control is mainly divided into four categories: centralized control [9], [10], [11], [12], [13], [14], [15], [16], master–slave control [17], [18], distributed control [19], and decentralized control [20], [21], [22], [23], [24], [25], [26], [27].