Abstract: The integral part of a power controller and of a PI speed controller is formed by a common integrator, both controllers always being engaged. With this linear interlinking of the two controllers, stability can be assured in the two limit cases of the network (rigid network and ohmic island) as well as practically in all cases in between.

Abstract: In a power control for a turbo-generator, the acceleration power of the difference between the mechanical power supplied to the turbo-generator set and the power delivered by it is determined and, if the supplied power preponderates, a correction signal directed toward closing control valves is fed to the power control by means of a valve positioning controller, Thereby, the power control need not be disconnected in the event of disturbances such as load shedding and network short circuit, but can practically remain engaged continuously.

Abstract: A system for selecting a signal having a median frequency from a plurality of periodic signals of different frequencies. In one embodiment, three such periodic signals are converted into corresponding pulse sequences, each having a duty cycle of approximately unity and a frequency which corresponds to the frequency of its associated periodic signal. An output signal is generated which assumes a first logic state when a positive signal slope of a first pulse sequence, which places the first pulse sequence in a first logic state and occurs while the output signal is in a second logic state, is followed by a further positive signal slope of a second pulse sequence, while the first pulse sequence is in its first logic state. The output signal assumes a second logic state when successively negative pulse sequence slopes occur.