Abstract: A closed loop control system achieves high speed operation commensurate with low resolution A/D converters which, at the same time, is capable of accepting and using higher resolution control signals. A control loop includes a differencing device for providing an error signal produced as a difference between a reference value and an output value related to the controlled parameter, D/A converter and integrator, producing an output value for device control. The feedback loop includes an A/D converter. The reference value and reference value input to the differencing device as well as the D/A converter accept digital signals of resolution greater than those produced by the A/D converter.

Abstract: A convertor connection for connection to a DC circuit includes current sensing members for forming a quantity corresponding to the direct current of the convertor connection. An indicating arrangement is provided for indicating asymmetrical operating conditions, which includes a first band pass filter connecting to the current sensing members which let through frequencies in a frequency band located between zero and the fundamental frequency of the AC component during undisturbed operation. When the output signal of the first filter exceeds a predetermined value, through a second filter an asymmetry indicating signal is emitted. The release of an output signal is prevented by a delay arrangement if the duration of the asymmetrical operating condition is less than a predetermined time.