In recent years, the world-wide use of high voltage direct current (HVDC) power transmission has increased sharply. Most of the recent projects involve transmitting large amounts of power from remote generations to load centers, where the short-circuit capacity at the receiving bus is often only a few times that of the rated DC power transfer — indicative of a weak AC support that is more susceptible to various operational problems, such as harmonic amplification, poor voltage regulation and adverse effects on the firing control. This report is on a two-part investigation. The first part deals with the harmonics characteristics of an inverter with weak AC support under balanced and unbalanced network conditions using the two most common firing schemes; the individual pulse control and the equidistant pulse control. The second part examines the operational behavior of the inverter with weak AC support when supplementary VAR support in the form of static VAR compensator is used. Aside from dynamic and transient behaviors, the study also looked into possible interaction between the inverter and the thyristor-controlled reactor at the harmonic level.

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