Studies On Time Delays In Wide-Area Damping Control System And Its Compensation Methods

At present, China’s power grid has already stepped into the era of "large interconnected power grid, large unit, and high voltage". The low frequency oscillation has long been one of the key issues that interconnected power grid needs to be addressed urgently. Wide Area Measurement System (WAMS) based on Phasor Measurement Unit (PMU) provides a new technical means for low frequency oscillations analysis and suppression. The time delays of cloed-loop control is the key issue that affects stability of the wide area closed-loop control system. Based on general wide area protection and control hardware platform, time delays in wide area damping control system and compensation methods are studied. The closed-loop test of wide area damping control is also realized. The study of this thesis provides a reference for engineering applications in theoretical and technical aspect.The time delays of PMU device and wide area communication system are mainly discussed. For the former, time delays caused by phasor calculation, especially by the digital filter are analyzed. Through theoretical analysis and simulation, the model of time delays in communication system is elaborated. The measurement approach for time delays is presented as well.Based on the implementation of wide area damping controller, the impact of time delays on wide area damping control is analyzed under both steady-state and dynamic-state according to the characteristics of time delays. It is pointed out that the effect of wide area damping control will be deteriorated owing to time delays. To solve the problem, an adaptive compensation method including data synchronization and prediction at main station as well as time delay on-line measurement at substaion is proposed.In order to realize closed-loop test for wide area damping control based on hardware platform, several key issues, including data synchronization and sorting, realization of wide area damping controller and communication between wide area control main station and substation, are discussed. The effectiveness of low frequency oscillation control based on WAMS is demonstrated through closed-loop control results.