Efficient Method for Solving Dynamic Model of PV-Integrated Unbalanced Distribution Systems

The increasing number of Photovoltaic (PV) inverters in the distribution system (DS) leads to significant dynamics on DS to consider. Solving the dynamics of DS integrated with PV inverters using the existing off-the-shelf solvers is computationally expensive. In this context, this paper presents an efficient method to solve the dynamics of a practical-sized unbalanced distribution grid with a large number of PV inverters in the phasor domain. First, a set of differential and algebraic equations (DAEs) is obtained to model the PV inverters in the phasor domain. The inverter DAEs are solved by using the Backward Euler method, which is found to be nine times faster than that of the off-the-shelf solver-based approach. Then, a decoupled method is developed to solve the dynamics of PV integrated DS, where the inverter dynamics is solved by Backward Euler and the DS power flow is solved by the Fixed Point Iteration based Current Injection method. The proposed method is applied to solve the dynamics of a 2520-node three-phase feeder with 400 PV inverters in the phasor domain. Rigorous case studies demonstrate the computational efficiency of the proposed method, which is around two times faster than the corresponding phasor-based solution approach using the off-the-shelf solver.