Modeling Voltage Source Converter Interfaced Equipment for Power System Harmonic Analysis

Abstract

The use of voltage source converter (VSC) has been widely accepted in present power systems for interfacing renewable energy generations, high voltage direct current (HVDC) transmission, flexible alternating current transmission systems (FACTS), and other applications. Due to the converter’s power electronic composition, there is a need to evaluate VSC’s harmonic impacts using tools such as harmonic power flows and frequency scans. For power system planning, there is a significant need for a harmonic model that can represent the harmonic characteristics of VSC equipment. This thesis first clarifies the harmonic characteristics of the VSC-interfaced equipment. The main concern regarding VSC-interfaced equipment is their impact on low-order harmonics because such harmonics are more prevalent in current power systems. The main objective of this thesis is to develop models of VSC-interfaced equipment at low-order harmonics based on the response of VSC-interfaced equipment to such harmonics. This thesis then proposes analytical harmonic models for four types of VSC-interfaced equipment: three-phase VSC, single-phase VSC, doubly-fed induction generator (DFIG), and VSC-HVDC. The results show that all these equipment can be modeled as harmonically coupled impedance matrices. The only exception is the single-phase VSC that has a form of a Thevenin circuit at the 3rd harmonic. Methods to determine the model parameters have been developed for each type of equipment. The validity of the proposed harmonic models and the impacts of various VSC design parameters have been demonstrated using extensive simulation studies and lab experiments. Case studies have demonstrated the effectiveness of the proposed models for harmonic power flow studies.