Unified Active and Reactive Power Modulation of HVDC Transmission Systems

摘要

In a study conducted by the General Electric Company for EPRI, the power modulation of a high-voltage direct-current (HVDC) system for stabilization of an ac/dc network was investigated. The use of both active and reactive power modulation (as opposed to only active modulation techniques) was studied. It was found that simultaneous modulation of both dc current and voltage was more effective than just current modulation by itself, since the dc voltage modulation could be used to minimize the reactive power changes resulting from a change of the dc current. This helps stabilize the ac busbar voltages at the converters, which reduces undesirable load flow changes to voltage-dependent ac loads, thus improving the effectiveness of the dc power modulation. This unified modulation control concept was evaluated by means of digital computer studies as well as a special purpose HVDC simulator. Several combined ac/dc power transmission systems were synthesized for testing of different modulation controller concepts. An optimum controller design incorporating a linear quadratic control algorithm with full-state feedback was first studied. This provided a basis for comparison of suboptimal controller designs utilizing reduced state feedback and a Kalman filter state reconstruction technique. The Kalman filter approach results in a more practical controller than the full-state feedback does, with about the same performance. Cost-benefit studies have shown that the unified modulation controller is not costly, except in special cases where increased converter ratings might be needed to handle the required voltage control range.