Research On Cophase Power Supply System Based On Three-phase Transformer And DN Power Supply Mode

Electrical locomotive is the load of electric traction power supply system. It is a frequently-changing single phase A.C. load, has the low Power factor, leads to large harmonics and reactive power, causes heavy unbalanced three phase of Power system.it not only affects the power system, but also resulting in the worst effect of communication defense. Especially needing neutral section insulator in every supply sector, which conditions normal work of high speed and loading railway. The main solutions are:use the balance-transformer or phase-conversing connection, add compensating device and so on. But these solutions cannot realize complete balancing for power supply system, which confines the developing of high-speed and heavy-duty railways. So to develop a new electric traction power supply system which can solve the above problem completely is undeniably meaningful.For the widely-adopted YN, d11traction transformer and DN power supply (a power supply system with direct feeding and adding returning line) a corresponding co-phase power supply system is produced. In this paper, a balance-compensating device composed of active filters, through real-time detecting on the comprehensive compensating current, controlling on balance-compensating device, and compensating on wattless power and harmonic current, the purpose to keep the three-phase current in balance from the primary side of the traction transformer is achieved. In the paper, the principle of balance-compensating is analyzed. The relationship between the instruction current required and the load current is deduced. The method to generate instruction current is studied. Then the adjusting and controlling plan of three-phase four-bridge balance-compensating device is studied.In order to verify the possibility of this co-phase power supply system, MATLAB/SIMULINK is used to build model and make simulation. The final simulating result shows that the co-phase power supply structure, the detecting method on comprehensive compensating current and the adjusting and controlling plan of the balancing compensating device given in this paper can be realized.