Stability Analysis of a Grid-tied Interlinking Converter System with the Hybrid AC/DC Admittance Model and Determinant-based GNC

This paper is mainly focused on the stability-related issues of a grid-tied interlinking converter system. First, hybrid AC/DC admittance characteristics of an interlinking converter operating under unity and non-unity power factors are analyzed separately. Then, by using the hybrid AC/DC admittance and determinant-based General Nyquist Criterion (GNC), the stability assessment, instability root cause identification, and instability mitigation of a grid-tied interlinking converter system are studied. In addition, decoupled mitigation of the AC- and DC-side instabilities are discussed based on the hybrid AC/DC admittance characteristics. The study results show that when an interlinking converter operates under unity power factor, the stabilities of the AC and DC sides are decoupled and can be regulated independently. To be more specific, the DC-side stability is subjected to the d-axis admittance, DC admittance, and their coupling admittances while the AC-side stability is dominated by the q-axis admittance. According to the hybrid AC/DC admittance characteristics, this paper further reveals that the DC-side stability is determined by the d-axis controllers. In contrast, the AC-side stability is governed by the q-axis controllers and the phase-locked loop (PLL). Finally, the analysis presented in this paper is verified based on frequency- and time-domain simulations in the Matlab/Simulink environment.