Coupling-related Instability Mechanism and Mitigation Analysis of the Instantaneous Power Based Current Controlled Inverter

Instabilities related to sequence-couplings of current controlled inverters (CCIs) have been recognized recently, but limited to accurate stability analysis of CCIs synchronized to the grid by the phase-locked loop (PLL). As for CCIs, another feasible grid-synchronization method is based on the instantaneous power (IP) theory, while instability recognitions of the IP-based CCI (IP-CCI) are lacking. Therefore, this paper reveals the instability mechanism and mitigation of the IP-CCI by comparison with the PLL-based CCI (PLL-CCI). Specifically, sequence-admittances of the IP-CCI are modeled, and interactions between sequence-couplings and circuit-coupling of the CCI-grid system are analyzed further. Simultaneously, influences of different system parameters on instabilities of the IP-CCI are thoroughly studied. Studies indicate that sequence-admittances of the IP-CCI exhibit closer sequence-couplings in comparison to that of the PLL-CCI, and negative damping of the IP-CCI is resulted from sequence-couplings, which clarifies interactive instabilities of the grid-connected IP-CCI are coupling-related. Therefore, corresponding instability mitigation can be achieved via sequence-decoupling methods, like the studied controller parameters regulation methods and the filter-based methods. Whereas, the stability deterioration level of sequence-couplings is grid-impedance-dependent, which means the weak grid would limit the decoupling performance. Nyquist plots, simulations and experiments are carried out to verify the studied coupling-related instability of the IP-CCI.