Share

TB 143 1999 SC 14 WG 14.25 Cross-modulation of harmonics in HVDC schemes

Harmonic cross-modulation is a term used to describe the variety of frequency interactions around the two converters that comprise and HVDC link and the effect on and interactions with the DC system and both AC systems. Because there are two converters involved, as well as two AC systems and any number of coupled frequencies, the number of interactions to be considered is infinite. Questions to be answered are : which interactions are the strongest, and whether they are likely to cause steady state or transient problems, and how to determine these interactions.

 Download TB from ecigre website 

TABLE OF CONTENTS

1 INTRODUCTION

      1.1 Dominant Harmonic Cross-Modulation Effects

2 CROSS-COUPLING CHARACTERISTICS OF HVDC CONVERTERS

      2.1 The HVDC Converter as a Modulator

            2.1.1 Transfer of Non-characteristic Harmonic Voltage from the ac to dc side

            2.1.2 Transfer of non-characteristic Harmonic Current from the dc to ac side

            2.1.3 Effect of Switching Instant Variation

            2.1.4 Harmonic Transfer Generalization

3 COMPUTATIONAL MODELLING OF CROSS MODULATION AROUND HVDC CONVERTERS AND LINKS

      3.1 Time domain Modelling

      3.2 Frequency domain Modelling

      3.3 Direct Linearised Solution Method

            3.3.1 Linearization of harmonic transfers

            3.3.2 Linearity and time varying systems

4 CROSS-MODULATION AT A SINGLE CONVERTER

      4.1 Steady state-Transfer from unbalance to the 3rd and 9th harmonics

      4.2 Transient-Composite Resonance

            4.2.1 HVDC converter dc side impedance

            4.2.2 Composite resonance calculation

      4.3 Transient-Core saturation instability

5 CROSS-MODULATION THROUGH A HVDC LINK

      5.1 Harmonic transfer across the dc Link

            5.1.1 Negative Sequence Unbalance in remote end converter

            5.1.2 Ideal conditions in remote end converter

6 REPORTED EXPERIENCES

      6.1 Kingsnorth

      6.2 Chateauguay

      6.3 Gezhouba-Shanghai

      6.4 Quebec-New England Phase II

            6.4.1 Induced 60Hz Component in the dc current

            6.4.2 Geomagnetic induced currents, GIC

            6.4.3 DC saturation by Ground Electrode Current

      6.5 New Zealand Hybrid Extension

      6.6 Backwaters Back to back HVDC Intertie