Study on the pure DC transmission scheme for China's future power transmission from the West to the East
In the year after 2015, China's national power grid interconnection will have been completed. Most likely, there will be four synchronous power systems, that is, big East China power grids, central China power grids, South China power grids and Northwest China power grids. For the long distance (more than 1000 km) bulk power (more than 50 GW) transmission from the West to the East, if the pure DC transmission scheme is adopted, there will be more and more HVDC links feeding power to different points in the same synchronous AC network. An important issue arising in such a situation is the influence of the multiinfeed HVDC links on the security of the AC systems. This paper analyzes the transient stability of each system under various AC and DC disturbances. The recovery characteristics of the multiinfeed HVDC links are also investigated. The results show that pure DC power transmission from the West to the East of China is technically feasible
Observer-based decentralized control of inter-area oscillation in Multi-infeed HVDC system
An important concern in the operation of multi- infeed HVDC systems is the inter-area low frequency oscillation due to the long-distance bulk-power transmission. In this paper, a decentralized coordinated control design is presented for improvement of inter-area oscillations in the multi-infeed HVDC system. The DC modulation controller are designed based on LQR optimal method and decentralized observers. Without degradation of controller performance, only the local measurement output is required for each damping controller, which greatly reduces the communication burden. A 7-generator, 2-HVDC system was used as the test system. The eigenvalue analysis and nonlinear time domain simulation have demonstrated the validity of the proposed decentralized controllers.
Geomagnetic micropulsations due to the motion of ocean waves
When sea waves move in the magnetic field of the earth, electric currents are generated in the water volume. These currents give rise to a small magnetic field which perturbs the earth's field. For plane trochoidal waves, this perturbing field decays exponentially with altitude and lies in a vertical plane which is oriented in the direction of wave propagation. The magnitude of the perturbing field also depends upon the magnitude and dip angle of the earth's field, and upon the height, wavelength, and propagation direction of the sea waves. For north-south waves, sea state 5, and an altitude of 100 feet, the perturbation is of the order of 0.1 gamma.