Loss of excitation of SMIB power system equipped with high photovoltaic penetration with constant injected voltage

Abstract

The effect of high photovoltaic (PV) penetration with constant injected voltage on the loss of excitation phenomenon of single machine infinite bus power system with two transmission lines has been investigated. The PV modules are integrated to the power system at the same bus of the synchronous generator via DC–DC buck–boost switch mode converter, three-phase DC–AC switch mode inverter, LC filter and transformer. The constant injected voltage from the PV generator at the common coupling point at all system running conditions is achieved by controlling the duty cycle the DC–DC converter. To ensure the robustness of this integration, the system response based on a complete nonlinear dynamical mathematical model in dq stationary reference frame after step changes on the synchronous generator input mechanical power at different practical solar irradiance levels is first observed. Then, the response of the system after successive step changes on the solar irradiance levels is highlighted and compared. The loss of excitation of the synchronous generator is detected by extracting the trajectory of the impedance of the synchronous generator seen across its terminals at two practical solar irradiance levels as compared with the case of conventionally powered system without PV generator. It is concluded that the setting of the distance mho relay which works properly in case the power system is conventionally powered by the synchronous generator alone cannot detect the loss of excitation when the PV generator is integrated with the power system at all realistic solar irradiance levels. Therefore, a new setting for the distance relay has to be carried out. This new setting must be accompanied with a shift to the right such that the trajectory of the synchronous generator terminal impedance can enter the circle of the mho distance relay which in turn results in shorter tripping time in case of conventionally powered power system. All numerical simulations have been executed using MATLAB environment by constructing the code required.