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Ultra-low-frequency oscillation with almost constant amplitude is a kind of frequency oscillation in power system. It has occurred in several hydro-dominant islanded power systems. With the nonlinearity of hydraulic turbines, a nonlinear model of power system is built in the paper. Stability and performance of both linear and nonlinear models are analyzed and compared. Particularly stable limit cycle...
Islanded operation of HVDC sending system can reduce the influence of HVDC fault on the parallel AC system, enhance the security of the system and increase the transmission capacity. Due to relatively small system inertia and ESCR, there are difficulties of the frequency and voltage control in the islanded sending system. The conventional analysis are focuses on the process after HVDC bipolar trip...
This paper presents a radiation-hardened-by-design digital delay locked loop (DLL) for DDR2 memory interface. The DLL utilizes thermometer coding with bubble correction and phase combination to cope with single event effects (SEEs). In addition, phase interpolation and duty cycle corrector are employed to achieve both high resolution and low duty cycle distortion. The proposed DLL is designed and...
Voltage stability is a crucial factor in power system operation. When bus voltage exceeds the operation limits because of change of the operation mode, load in the network or the environmental factors, appropriate control actions should be taken to guarantee a secure system operation, avoiding emergency situations or voltage collapse. Development and improvement of the algorithm for voltage security...
Model reference adaptive system(MRAS) is introduced in speed estimation for salient pole permanent magnet generator(PMSG) in wind turbine system. Firstly, current model for the salient pole PMSG is established and used as adjustable model, and the salient pole PMSG itself is used as reference model, then the adaptive law is derived. The estimated speed is used for the control of PMSG wind turbine...
The continuous cyclical load disturbances can lead to forced power oscillations of power systems. Based on the single-machine infinite-bus system, the differences in the energy conversion characteristics between the forced power oscillation and the weak damping free oscillation are analyzed and the mechanism of the forced power oscillation caused by cyclical load disturbances is presented. Using energy...
The electromagnetic characteristic and rotor vibration characteristic of turbine-generator are analyzed when rotor winding inter-turn short circuit fault has happened. This paper reveals that exciting magnetic force Ff is constant in a fixed condition whereas the exciting current If increases in case of rotor inter-turn fault. This paper also finds relevant characteristic parameters. Based on the...
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