Patent GB-1510876-A (GB)
Title: Rotary machine
IPC: H02P6/10
Filed: 1975-06-30
Abstract: 1510876 Motor control NU-TECH INDUSTRIES Inc 30 June 1975 [1 July 1974 24 March 1975] 27569/75 Heading H2J A motor having a rotor with a magnetic field in a fixed orientation with respect to the rotor and a plurality of stator windings is controlled by generating, from voltages induced in the stator windings when the rotor is rotating, position signals at times when the rotor has known positional relationships with respect to the stator windings and applying the position signals to a power signal generator to apply power pulses to the stator windings in a predetermined sequence at a frequency no greater than a predetermined selectable frequency, the power pulses being generated at times always symmetric about the times when the torque angle is a predetermined value. As shown, the rotor 11 has a field 30 and the stator 12 has two windings 31 and 32. The power pulses 34-37 are applied to the windings by a supply 13 under control of a stepping switch 14. The position signals are provided by zero crossing detectors 14 which receive the voltages induced in the windings by rotor movement. For each complete rotation of the rotor, four position signals are generated in the 90, 180, 270 and 360 degrees positions of the rotor. The position signals are applied to two counters 18, 19 in a commutation circuit 17. The position signal derived from the voltage in one of the windings causes one counter to count up at a rate f and the other counter to count down at a rate f/2, while the position signal derived from the voltage in the other winding causes the other counter to count up at a rate f and the one counter to count down at a rate f/2. The counters provide an output signal when the count reaches zero and these output signals (four per cycle) are applied to a logic latch 23 and each indicate the time when power should be transferred from one winding to the other. The output of the latch 23 is applied to one input of an AND gate 24 whose other input is connected to the output of a speed latch 22 which is set four times per cycle by a rate variable oscillator which determines the speed at which the motor is to run. The logic latch 23 is normally set before the speed latch 22 and so the output signal from the AND gate, which is applied to the stepping switch 14, and consequently the transfer of power from one winding to the next is delayed by the difference in the setting times of the latches. The outputs of the latches are also applied to a pulse centering circuit 25 which ensures that the power pulses 34-37 are centred about the 90, 180, 270 and 360 degrees positions of the rotor, as seen in Fig. 2, by applying an inhibit signal to the gate 15 at the appropriate time. An amplitude control circuit 26 is provided to sense if the pulse duration falls below or exceeds respective predetermined angular rotational times and to correspondingly lower or increase the voltage level of the power pulses. With the above described arrangement, the speed of the motor is maintained constant (as determined by the oscillator 21) even with varying loads. For small load variations the pulse width is controlled but for large load variations the pulse amplitude is controlled. Details of the circuitry are described with reference to Figs. 4-11 and 15 and 16 (not shown). The arrangement, with suitable modifications, can be used with a motor having more than two stator windings and such an arrangement for a motor having three stator windings is described with reference to Figs. 12-14 (not shown). Starting and reversing operations are also described.