On the Instability Mechanism of PV-Thermal-Bundled Power System Under Different PV Penetration Ratios

In the photovoltaic (PV)-thermal-bundled power system, the increasing PV penetration poses instability risk. Through establishing the small-signal model and solving the eigenvalues of return ratio matrix, the system stability can be evaluated with the generalized Nyquist stability criterion. However, the expressions of eigenvalues are irrational functions, which leads to the complexity of analyzing the system stability and the difficulties to accurately reveal the instability mechanism. To address this issue, the stability analysis method based on the admittance matrix elements is proposed, which does not need to calculate the eigenvalues of return ratio matrix, thus simplifying the stability analysis. In addition, this method can describe the system stability margin clearly. With this stability analysis method, the stability of the PV-thermal-bundled power system is clarified under different renewable penetration ratios, and the causes of the system instability are investigated. Finally, the hardware-in-the-loop results confirm the effectiveness of the proposed stability analysis method and the accuracy of the stability analysis results.