Model reduction method for smart inverters having frequency-watt control

Abstract

This paper proposes the model reduction method for smart inverters having Frequency-Watt control. The proposed reduction method consists of the following three steps: (1) derive the mathematical model of the smart inverter connected to low-voltage feeder, (2) combine the smart inverter mathematical model developed in (1) with the mathematical models for upstream electric circuits consisting of series impedances, line impedances, and transformers, and (3) aggregate the combined models found in (2) using the Padé approximation method or the Routh approximation, which can derive the aggregate transfer functions for the system with different poles. The proposed reduction method is also designed with the current limit of smart inverters. The proposed model reduction method can generate an equivalent aggregated dynamic model for smart inverters, seen from the distribution substation. The validity of the proposed reduction method is ascertained through computational simulation on the Matlab/Simulink environment.