Two-Stage Protection for Multi-Channel Power Electronic Converters Fed Large Asynchronous Hydro-Generating Unit

Multi-channeled voltage source inverter (VSI) provided in rotor circuit of doubly fed induction machine (DFIM) ensures control of real and reactive power of the machine alongwith speed variation. VSI is significantly impacted during grid disturbances since DFIM is very sensitive to the grid disturbances as stator/rotor circuit is directly connected to the grid. This paper presents two stage protection circuit for the multi-channeled VSI since it is useful for the continuous operation of the unit in case of marginal grid disturbances. Control system for the dc link chopper circuit protection and crowbar protection is developed based on the dc link voltage of the VSI. In addition, it provides the activation status of the protection circuits during grid disturbances which is economically helpful for the plant authorities. Two-stage protection circuit for a 250 MW DFIM with five channel back-to-back three level VSI is simulated in Matlab/Simulink. A 2.2 kW DFIM is tested in the laboratory to validate the simulation results.