The Analysis and Measurement of Harmonics in the Vicinity of an HVDC Inverter

Abstract

High voltage DC (HVDC) transmission systems are designed to interface with the AC network in such a way as to have considerable operating flexibility and minimal harmonic impact. Filter design as well as gating controls are designed at the inverter with the stated objective in view. Sometimes designs and operating regimes are an engineering compromise relating to the amplitude of several harmonic voltages and currents, inverter performance at the power frequency, operational power level, SCR or valve parameters (eg. margin angle), and equipment requirements. The harmonic impact of an inverter is considered in this paper with regard to network harmonic response. An analysis procedure based on the harmonic power flow algorithm is described and required models, points of modeling questions, shortcomings, and advantages of the procedure are described. The procedure is illustrated for a twelve pulse, bipolar HVDC inverter with high pass, 11th, and 13th harmonic filters on the AC bus. The general approach, and modelling details are verified by measurements on the Square Butte HVDC system. Tests were performed at and near the Arrowhead terminal of this system (operated as an inverter); measurement of harmonics in bus voltage, line current, and currents in shunt capacitors were made. Also, certain converter currents and parameters were recorded. Since the objective was to verify network response, some measurements were made in the AC network remote to the HVDC inverter.