Transient stability of doubly-fed induction machine in parallel to synchronous machine

Transient stability of doubly-fed induction machine (DFIM) in hydro pumped storage plant (PSP) is analyzed and compared with synchronous machine in this paper. Model of turbine governor and model of converter control of DFIM are presented as they are applied in computer software for dynamic analyses of electric-power system. The principle of frequency control-i.e., permanent droop-and control of network voltage is also proposed. The behavior of DFIM during large and small transients is compared with the behavior of synchronous machine with the help of numerical simulations. In the case of large faults crow-bar protection converts DFIM to an asynchronous machine. Due to variable speed of DFIM better transient stability of this machine can be achieved compared to a synchronous machine. Results of dynamic simulations show that DFIM has smaller and shorter oscillations of speed and active power. Besides longer critical clearing times can be achieved by DFIM.