Research On Negative-sequence And Reactive-current General Compensation In Electric Railway Based On STATCOM

In this paper, from the point of view on power, a new way of analyzing 3-phase unbalance current is given. By this way, the compensating dynamically negative-sequence and reactive-current which are generated by the electric traction load with STATCOM is realized. On the compensation side of traction-transformer for testing electric locomotive, the approach of IGBT controlling STATCOM has been used, which can be real time compensating, and by this technology, the negative-sequence current and reactive current on the power side of the transformer are decreased under the national standard. The controller is a key part of the compensation equipment. And its control circuit, current detecting circuit and synchronization trigger circuit are designed, so the instantaneous impulse current is be reduced largely when the STATCOM compensation circuit is closed, and the reliability of the equipment is improved greatly. The equipment is based on the digital signal processor (DSP), which contains multiplicate functions, such as resistance and reactive power measurement, STATCOM auto-triggering, failure auto-diagnosis, failure display and alarm. The equipment has been used in the ShangHai Railways Bureau.In addition, based on the transient reactive power theory, the paper analyzes real-time, the general detecting methods for reactive, the fundamental negative sequence and harmonic currents in three-phase circuits, and gives a new detecting way of fundamental reactive, that is the negative sequence currents-the approach of indirect FBD current detecting. The approach is efficient when the fundamental reactive and negative-sequence currents are compensated with STATCOM. Finally, the method of hardware design for the current detecting unit is detailed in this paper, which based on CPLD and DSP digital processing chips.