A circuit topology is proposed for single-phase online UPS systems. The proposed circuit incorporates a built-in bidirectional AC/DC converter, which provides power factor correction and active power filtering. The input stage, based on a bidirectional AC/DC converter, functions as a rectifier with unity power factor correction for normal AC line mode operation, and as an active power filter for outage mode operation. During input power failure, the bidirectional AC/DC converter functions as an active power filter, providing reactive power to the load. Simultaneously, the DC/AC voltage inverter output stage supplies real power from the battery bank to the critical load. The real power capability is improved compared with that of a conventional online UPS system, and extra loads can be connected to the UPS system during outage. The power circuit of the proposed UPS system is presented and analysed. Circuit models are derived and a UPS digital control system using a digital signal processor (DSP) is developed. Finally, simulated and experimental results obtained from a laboratory prototype are presented to confirm the feasibility and features of the proposed UPS scheme.

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-Inrush currents generated by unloaded power characteristics of circuit breaker also have a strong influence transformer often reduce power quality on the system. To to determine the correct instant of mechanical closing time. produced by the power transformer. As a result, the inrush current is well suppressed with such a new control approach.

This paper proposes the dynamic analysis of the leakage current corrosion for the non-grounded DC railway systems. In the non-grounded DC traction system, the current leaks from the track to the earth, sometimes for positive, sometimes for negative, thus this behavior to be similar AC power supply system. It is not unlike the diodegrounded system which only permits current to leak from the track to the earth and come back from the leakage diode to the negative side of the traction power substation. The electrical corrosion by AC current is less than by DC current, essentially. The corrosion quantity is proportioned to the leakage current corrosion to integral of the time. This paper uses Kaohsiung Mass Rapid Transit (MRT) as an example to simulate multiple traction substations and multiple trains for the non-earth system DC traction system.

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