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
Transient stability analysis of Shanghai Power Grid with multiple HVDC links
With the development of China's power system, more and more HVDC links are located in close proximity in a common AC system and thus multi-infeed HVDC systems are developed. Due to the interaction between AC system and DC systems, as well as the interaction amongst DC systems, the behavior of such multi-infeed HVDC system is much more complicated than a single-infeed HVDC system. This paper investigates into an example of such multi-infeed HVDC systems, i.e. Shanghai Power Grid. There are three HVDC links terminating in the load center of Shanghai Power Grid by 2010. The inverter stations of the three HVDC links are near to each other and thus the interaction of AC and DC systems is very strong and has a great impact on the secure and stable operation of the system. Transient stability under various faults, as well as the effect of load characteristics and spinning reserve, are studied in this paper. Conclusions are obtained according to the simulation results, which provide useful instruction for the operation of Shanghai Power Grid and other similar multi-infeed HVDC systems.
Third order nonlinear distortion of SAW duplexers in UMTS system
Nonlinearity distortion characterization and accurate modeling techniques for leaky surface acoustic wave (LSAW) devices have been desired in the recently years due to the applications of the Radio Frequency (RF) SAW duplexers in the third-generation (3G) telecommunication system, such as Universal Mobile Telecommunications System (UMTS). In the work, we first discuss the approaches to measure and characterize the 3rd order harmonic generation of the resonators on lithium tantalate YXl42° wafer and YXl48° wafer, with resonance frequency of 800MHz to 900 MHz; Second, we present an effective nonlinear Butterworth-van-Dyke (BVD) model to simulate the multi-tone 3rd order intermodulation effects of a band 5 duplexer; simulation result vs. measurement of 3rd order harmonic generation, 3rd order intermodulation (IMD3) and triple beat are presented.