Prediction on future DC power system
Analyzed some serious issues, including power energy quality and large area power interruption, require complex method to overcome in 3-phase power system, so, suggested to go other way, proposed independent full DC power system to become one of main power systems in the future. The authors emphasized the necessity and capability of full DC power systems in the significance of technology and energy saving, so that safer, more reliable, stable, flexible and controllable DC power grids could serve the people better than that of the present AC power systems. Presented brief structure of full DC power system where DC power would be produced from multi-phase generator-rectifier group in power station, consumers take power from DC bus, which benefits motor control and energy flow between loads connected the same DC bus without 3 phase balance problems, and DC-DC converters based Duty-Cycle control implement commutations at two terminals of HVDC transmission lines, which reduce the technical difficulties than that in 3-phase AC commutation station. Non-crystal material with about 15 kHz of frequency could be selected for advanced isolators, so as to get smallest power consumption. Some new technology lifting DC voltage in geometrical progression was suggested to be available at the sent terminal of HVDC line. With the development of renewable power systems and their energy storages, DC interconnection grids could be a better choice than AC interconnection grids because no frequency and phase shift problems need to be considered. Bulky 3-phase transformer with industrial frequency and vary kinds of compensators for AC power qualities could be saved. The authors suggested scientific policy for economically implementing full DC power systems step by step. It could be predicted that people would see 3 kinds of power systems, full AC, full DC and hybrid AC-DC systems operating simultaneously by the middle of 21 century.