Grid coupling of cage-rotor induction generator through BTB-VSC with critical load support at grid islanding

Abstract

An indirect current control scheme for three-phase Back-to-Back Voltage Source Converter (BTB-VSC) with grid coupled cage-rotor induction generator (CRIG) is proposed in the paper. The system caters load at local and utility grid at its two supply ends. The considered system has flexibility of bidirectional power flow control between the two sources through a common d.c. link in grid coupled mode. The system also has a capability to feed a critical load connected at the utility grid from CRIG supply under utility grid failure. The proposed scheme regulates the VSC at one end to retain rated conditions under isolated operation of CRIG, and controls the power flow across the d.c. link by controlling the VSC at grid side to acts as STATCOM mode. This improves the power-quality on grid side and regulates the d.c. bus voltage constant in grid connected mode. The regulation of frequency at CRIG terminals is done by transfer of real power from/to the utility grid, to draw rated load at CRIG terminals and the voltage on CRIG terminals is maintained by compensation of reactive power demand through the switching of VSC. In case of grid supply failure the islanded BTB-VSC link is controlled to feed the critical load connected at utility grid and draws a power from CRIG supply. The scheme enforces drawl of only rated real power current from the CRIG terminals. The proposed scheme has fast response, easily implementable and requires lesser hardware. The Implementation scheme made through simulation in Matlab/Power System Blockset and the effectiveness of the system is presented through simulation results.