Investigation of Reactive Power Control and Compensation for HVDC systems

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Zhang, Yi
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This thesis attempts to investigate the performance of various reactive power compensation devices, examine the mechanism of reactive power compensation for HVDC systems, and develop guidelines for the design of reactive power compensation schemes for HVDC systems. The capabilities of various reactive power compensators to enhance power system stability are compared in both steady and transient states. An understanding of the capabilities of these compensators provides a basis for further investigation of their performance in HVDC systems. The reactive power requirements of HVDC converters are studied. The voltage dependencies of the HVDC converters at different control modes are derived, which allow for predictions of how HVDC converters impact AC system voltage stability. The transient performance of reactive power compensation options for HVDC Systems is studied by comparing their behavior during DC fault recovery, Temporary Overvoltage (TOV), and commutation failure. How to quantify the system strength when reactive compensators are connected to the converter bus is investigated. A new series of indices are developed based on the Apparent Short Circuit Ratio Increase (ASCRI). The inertia of a synchronous condenser and its impact on the frequency stability of an AC/DC system are discussed. By modelling the inverter side AC system in greater detail, the frequency stability and rotor angle stability following fault transients is examined based on time domain simulation. Finally, a guideline for designing dynamic reactive power compensation for HVDC systems is proposed.
Reactive Power Compensation, HVDC