Shared-Leg Fault Tolerant Operation of Multi-Channeled Power Converters Serving to Large Rated DFIM Unit

Abstract

In present scenario, reliable operation of power converters must be ensured to enable continuous operation of large rated generating units. With respect to this aim, this paper adopts shared-leg fault tolerant operation for a 5-channel three level neutral point clamped back-to-back power converters (3L- NPC) serving to a typical 250 MW doubly-fed induction machine (DFIM) unit. Under open switch fault condition, faulty leg is identified and isolated with the help of normalized phase current average fault diagnosis method. Thereafter, grid side converter (GSC) and rotor side converter (RSC) share a common leg to deliver the required power to the rotor circuit of DFIM. For this effective operation, double zero-sequence signal is computed and injected into vector control strategy for independent control of GSC and RSC. Furthermore, shared-leg current capability, converter output voltage capability, dc-link voltage oscillations and its thermal performance are analyzed during fault tolerant operation. From the observed test results, two operating conditions are proposed: (i) reduced real power delivery by adjusting speed of hydraulic turbine and (ii) rated real power delivery by absorbing reactive power from the grid. To examine and demonstrate the proposed methodology MATLAB/Simulink2014A tool is used for a 250 MW DFIM unit. An experimental demonstration is performed with 2.2 kW DFIM unit.