Patent GB-1379437-A (GB)
Title: Control or regulation of an asynchronous electrical machine
IPC: H02P21/10
Filed: 1972-02-14
Abstract: 1379437 Automatic control of current and phase SIEMENS AG 14 Feb 1972 [12 Feb 1971] 6745/72 Addition to 1290962 Heading G3R [Also in Division H2] A control system for an asynchronous machine 1 generally similar to that described with reference to Fig. 12 (not shown) of Specification 1290962 is modified to ensure reliable commutation of the frequency changer 2 by interposing, between the vector analyzer 5' and the angle switch 11, the circuit shown in Fig. 3 of which the components 14, 15, 16, 18, 21, 22 function to provide a control vector which rotates only in one direction. A vector rotator 18 receives from terminals 7, 8 the component voltages of the control vector supplied by the analyzer 5', which vector may briefly reverse its direction of rotation, for example at changeover from generator to motor operation, and thereby produce unsatisfactory commutation. To prevent this malfunction, the rotator 18 also receives the component voltages of a rotating vector produced by a two-phase generator 16 and thereby produces output component voltages dependent on the difference angle between the two input vectors, which output voltages are supplied to a quotient former 21 whose output is proportional to the tangent of half the difference angle. An arc tangent function generator 22 then produces an output signal directly proportional to the difference angle and this signal is fed to a proportional-plus-integral action controller 14, whose output varies the frequency of the generator 16 so that the input to the controller 14 reduces to zero by virtue of a like reduction of the difference angle, i.e. the vectors applied to rotator 18 are brought into phase. A diode 15 ensures that only positive values of the output of controller 14 are applied to the generator 16, whereby the output of the latter is a vector which rotates only in one direction and is applied at terminals 12, 13 to control the angle switch 11. A constant signal B applied to the input of generator 16 produces a minimum frequency of the latter when the output of the controller 14 is negative. The current supplied by the rectifier 2a to the inverter 2b is maintained at a value provided at the output terminal 9 of the analyzer 5', which value is derived from stator-related vector component desired values provided by the component converter 6 receiving two field-axisrelated orthogonal desired values for the stator current vector and stator-related component voltages derived from Hall probes 3 sensing the air-gap field via another vector analyzer 5. Controller 10 receives the desired value from terminal 9 and the sensed current from rectifier 2a to control the latter. The desired value signal is also applied to a member 26 forming part of a control loop for ensuring that the stator current vector accurately follows the control vector. For this purpose a transformation circuit 29 receives input voltages representative of the phase currents I R , I S , I T  of the machine 1 and produces signals I j , I r  corresponding to orthogonal component voltages of the stator current vector. These signals and those from the analyzer 5' are applied to multipliers 23, 24 whose outputs are combined at 25 to produce a second input to the member 26, which feeds a phase-correcting controller 17 with a signal representative of the sine of the  difference angle between the control and stator current vectors. The output of the controller 17 is applied to the input of the controller 14 via a multiplier 33 which varies the output in accordance with the speed of the machine 1, a threshold member 34 causing the output to be suppressed at speeds below a predetermined low value. The components and circuit connections of the members 18, 22 and 29 are described, Figs. 4, 5 and 7 (not shown).