Simplified Dynamic Model of the Electric Load Supplied by a Switching Power Supply

Non-induction-motor loads are represented by static load models in existing electric load models. The electric loads supplied by switching power supply are typical non-induction-motor loads and occupy a large proportion of the nonindustrial electric load. In this paper, a simulation model of a switching power supply with a full-bridge structure is built, and the existing static load model is applied to fit the dynamic characteristics of the switching power supply. Simulation results show that the accuracy of the power function static load model is higher than that of the polynomial static load model, but the power function model still cannot accurately describe the dynamic response of switching power supply under voltage sag and voltage recovery, and cannot describe the impact of voltage sag degree on the dynamic characteristics. Therefore, a simplified dynamic model is proposed in this paper to describe the dynamic characteristic of the switching power supply precisely. In this simplified model, two transfer functions are employed to represent the amplitude and phase relationships between the output positive sequence current and the input positive sequence voltage, respectively. Additionally, two coefficients related to the degree of voltage sag are used to describe the influence of fault severity on the dynamic characteristic of the switching power supply. Simulation results reveal the accuracy of the proposed simplified dynamic model of the switching power supply is higher than that of the existing static load model at varying degrees of voltage sag faults.