Contents 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].
