Adjustable-speed power unit with doubly fed machine

A numerical model of an adjustable-speed power unit utilizing a doubly fed machine with a 12-pulse cycloconverter in the rotor circuit was developed. The synchronous frame vector control scheme with impressed rotor voltages was employed to control the produced active and reactive powers of the unit. Both steady-state and transient operation of the system were numerically simulated and analysed. First, the behaviour of the system at a constant speed was investigated to evaluate the quality of the control. Second, the operation of the system connected to the power network through a long power line was simulated. The machine was driven by a Francis turbine regulated so that its speed was optimal with respect to the demanded active power.