Abstract: A method of and apparatus for regulating the control voltage of a three-phase inverter supplying an a.c. motor are provided, the inverter having a power stage implemented with semiconductor switches, and the output voltage of each inverter phase being measured in the voltage control. For rapidly improving the curve shapes of the inverter output by means of feedback, the control voltage of the pulse width modulator of each inverter phase is regulated by a voltage regulator. The control voltage obtained as output of the voltage regulator is derived from an actual value voltage formed from the output voltage of each inverter phase and a reference voltage.

Abstract: The invention concerns, first, a signalling procedure for a lift, whereby the control system and the users of the lift are informed on lift calls and the state of the lift, e.g. position, movement and availability, by using serial communication between the control system computer and the actuating and signalling means in the lift car and on each floor level, and, second, a signalling system applying the said procedure. To avoid abundant and complicated wiring and to increase standardization in the design of the lift system main panel and call button stations, the signalling system of the invention employs the polling principle in its internal communication, whereby data are transmitted bi-directionally using digital series loops, one of which connects the devices in the lift car, controlled by and communicating via a microprocessor, another connects the corresponding shaft and door devices, while a third loop is used for communication with the external world.

Abstract: A method of and apparatus for controlling a braking resistor, provided in a d.c. circuit of a frequency converter, by rectifying a mains voltage, by means of a first rectifier bridge connected to a three-phase mains supply, to form an actual value voltage; comparing said actual value voltage and a reference voltage; and operating a switch in series with the braking resistor to cause the latter to conduct when the comparison indicates that the actual value voltage is greater than the reference voltage. The reference voltage is formed from a rectified voltage obtained from the three-phase mains supply and rectified by a second rectifier bridge.