Abstract: The invention relates to a method for controlling a number of fans (2) of a heat exchanger that can be used in refrigeration, air conditioning, or process technology. The fans (2) form a number of fan groups (5), and each fan group (5) is connected to an electrical energy supply (7) selectively by means of a constant power supply (14) or by means of a variable power supply (15). The fan group (5) is operated at a constant fan speed with the constant power supply (14) and at a variable fan speed with the variable power supply (15). A power parameter (I) indicating an instantaneous total power demand of all fan groups (5) supplied by means of the variable power supply (15) is detected. At least one of the fan groups (5) that is currently being fed by means of the variable power supply (15) is switched to the constant power supply (14) if the power parameter (I) exceeds a limit value (Imax).

Abstract: A drive system comprises a brushless multi-phase motor which is supplied with power by way of an inverter including thyristors which are fired by a firing network. The firing network is supplied with information relative to the position of the rotor of the motor, by means of a transducer and this information flows by way of a logic network. Also provided is a current sensing device, a signal from which is passed through a control network to the logic circuit, and the logic circuit acts to modify the signals applied to the inverter in the event that the current flowing in one of the d.c. supply lines to the inverter exceeds a predetermined value for more than a predetermined length of time.