Dynamic Circulating Current Suppression Method for Multiple Hybrid Power Parallel Grid-Connected Inverters With Model Reference Adaptive System

Abstract

Aiming at the problem of large harmonic distortion of grid-connected current in high-power grid-connected power generation system under weak sunlight, multiple hybrid power parallel inverters (MHPPIs) composed of some identical high-power inverters and one low-power inverter in parallel are proposed. According to the irradiance change of sunlight, the low-power inverter operates alone or cooperates with the switching process between the high-power inverters to ensure the low grid-connected current harmonics. Where, any inverters operate in four common working processes, such as soft start-up, steady-state operation, abrupt change of current, and soft stop. Due to the short running time of the dynamic process, most of the existing researches focus on the circulating current suppression under the steady-state condition. However, in engineering practice, the dynamic circulating current in the switching process between inverters is more likely to cause the over-current protection and other safe and stable operation problems of parallel inverters. Therefore, a dynamic circulating current suppression method with dynamic impedance matching for parallel inverters is proposed in this article. The working process of the MHPPIs is equivalent to that of two inverters. The dynamic working process is analyzed in detail, and the dynamic impedance mismatch is the main cause of the dynamic circulating current, so the dynamic virtual inductance matching is introduced to suppress it. Meanwhile, an online inductance identification method based on the model reference adaptive system is presented to compensate for the influence of inaccurate inductance parameter on the circulating current suppression and current control. An experimental prototype of equivalent MHPPIs is built and experimental results prove the validity of the proposed control method.