Balanced and unbalanced ZIP load emulation by a three-phase chopper-based load emulator

• Emulation capability for all types of ZIP load models for static and dynamic loads under both balanced and unbalanced conditions. • Stability analysis presentation as well as simulation and experimental-based verification of the proposed LE performance under several test scenarios. Real-time load emulation is a commonly used method, especially in laboratory-scale studies, to flexibly emulate different load types. Such devices can receive PQ load profiles and draw active and reactive powers from the grid accordingly. Various types of power system loads can be represented by ZIP models, including impedance (Z), current (I), or power (P) profiles. In this paper, a real-time control scheme is proposed and implemented on a converter-based load emulator (LE), which enables fast and precise emulation of ZIP load models under both balanced and unbalanced conditions. Thus, any type of balanced and unbalanced load profiles could be readily emulated in real time, eliminating the need for real loads and the associated limitations. The proposed system consists of positive and negative sequence controllers in synchronous reference frame (SRF) and a reference current generator (RCG) block. This block is intended to translate the reference ZIP profiles to real-time reference currents for the control system. Additionally, the positive and negative sequence control loops employ Butterworth filters for a lower response time as well as higher emulation accuracy. Additionally, for optimal design of PI controllers’ coefficients and system stability analysis in the presence of filters, the linearized model of the proposed LE is derived. An experimental prototype of the converter-based LE has been developed to investigate the performance of the proposed control system. Simulation and experimental results demonstrate the accuracy and speed of the load emulation with this method for transient and steady-state analyses.