Patent GB-1449409-A (GB)
Title: Linear motor stator and a controlsystem therefor
IPC: H02P25/06
Filed: 1974-08-16
Abstract: 1449409 Automatic control of current and phase angle SIEMENS AG 16 Aug 1974 [17 Aug 1973] 36261/74 Heading G3R [Also in Division H2] A synchronous linear motor comprises an elongate travelling-field stator winding 4b whose input is fed by a static frequency changer 6b whose output voltage and frequency are controlled in dependence on the position relative to the winding 4b of a vehicle 2 carrying an exciter winding 3, the relative position being calculated by a computing circuit in dependence on the voltage, current and frequency prevailing at the winding input and on the resistance and inductance values of the winding. The vehicle 2 runs along a series of threephase stator windings 4a, 4b, 4c which respectively constitute the sections a, b, c of a track and which are fed by respective frequency changers 6b, 6c each controlled by a regulating device 8b, 8c producing control signal Sb, Sc. The voltage and current at each winding input 5b, 5c may be detected by voltage and current transformers 9b, 9c; 10b, 10c and the computing circuit calculates the pole position of the winding 3 at each time instant t in terms of the phase angle between the main field voltage induced in the stator winding by movement of the winding 3 and (1) the winding input voltage or (2) the winding input current or (3) a reference signal r of frequency f. The winding 3 may be super-conductive or a conventional winding on an iron core or may be replaced by a permanent magnet. It may be supplied with constant or variable D.C., or A.C. Fig. 2 shows the regulating device 8b for the frequency changer 6b comprising rectifier 11 and inverter 12, of which the latter is controlled by a unit 19 in dependence on the magnitude |U| and phase angle #U of the winding input voltage and on the reference signal r produced by a signal generator 16 in the form of sine and cosine signals of like amplitude and frequency. The device of Fig. 2 includes a computing circuit 15 which receives the following seven signals:-(1) the frequency f of the signal input to generator 16; (2) the resistance R of the stator winding 4b and of the exciter winding 3 (when present); (3) the inductance L of the stator winding and of the exciter winding 3 (when present), the values R and L being pre-set or measured during vehicle operation; (4) and (5) the magnitude |I| and phase angle #i of the winding input current sensed by transformer 10 and produced by an oscillation analyzer 20 controlled by the signal r; and (6) and (7) the magnitude |U| and phase angle #U of the winding input voltage respectively produced at the outputs of a decoupler 23, which is provided to effect continuous adjustment of the regulating action (if such is needed) in accordance with the momentary operating condition of the motor 3, 4b. The computing circuit 15 produces an output signal # representative of the phase angle between the induced main field voltage Uh and a unit vector E of the reference signal r, Fig. 3 (not shown), the latter being a vector diagram which is discussed to explain how the angle #, (#-#U) or (#-#i) may be used to control the unit 19. However, further control loops are included to produce optimum operation of the motor corresponding to the condition #=#i and the winding current I at a minimum, with a large number of poles on the vehicle 2 to produce a desired thrust set by a journey computer 28 in which a travel programme F is stored. The desired optimum value of current |I|* may be set by a potentiometer but, as shown, is provided by a master frequency or speedcontrol loop comprising a comparator 27 fed with signals f* and f from computer 28 and a voltage angle controller 32 and a frequency controller 26. The desired and actual values of current |I|* and |I| are fed to a comparator 24 supplying a current magnitude controller 25. A current phase angle controller 22 receives the output of a comparator 21 fed with the signals # and #i. Motor operation for constant current phase angle and variable magnitude or constant magnitude and variable phase angle is discussed, Fig. 4 (not shown), these operations being facilitated by continuous adjustment of the gains of the amplifiers 29a, 29b, 29c, 29d of the decoupler 23 in response to a signal K produced by the computing circuit 15. For lower dynamic regulating requirements only a single gain adjustment is made or decoupler 23 is omitted and members 22, 25 are connected to circuit points B and A. A comparator 31 compares the phase angle #U with a desired phase angle #U* set at zero, whereby the anglecontroller 32 is controlled to ensure that its output frequency f corresponds to the output frequency of the changer 6. In this way, stalling of the motor upon load increase is also prevented. The device of Fig. 2 is completed by a phase rotator 17 and a co-ordinate converter 18 for the unit 19 and members 36, 37 which produce an output signal x(t) representative of the vehicle position for use by the journey computer 28. The frequency changer 6 may be of the intermediate circuit or direct type, the latter if the exciter winding 3 is super-conductive. Rectifier 11 may be controlled or uncontrolled. If the former, the signal |U| is fed to its control unit and not to the unit 19. Circuit 15 is described, Figs. 7, 8 and 9 (not shown). Control of the motor when passing from section b to section c. This is provided by the circuit shown in Fig. 6, which provides for control of the comparators 21c and 24c in the regulating device 8c whereby the stator winding currents I b I c  are maintained equal during changeover from section b to c, the vector requirements for this condition being discussed, Fig. 5 (not shown). A changeover switch 40c supplies the comparator 21 with a desired value signal #c from computing circuit 15c or with a signal from point 43c, which receives signals #b, #d in time succession from sections b and d (not shown). Switch 38c supplies the comparator 24c with a desired value signal |I c |* from controller 26c or with a signal from point 41c, which receives signals |I b |*, |I d |* in time succession from sections b and d. Likewise the regulating devices for sections b and d receive the signals |I c |* and #c for circuit points 42c and 44c. As the vehicle nears the end of section b, switches 38c, 39c, 40c are in their upper position, so that the frequency changer 6c is controlled by the desired values |I b |* and #b for the section b. During passage from section b to c, switches 38c, 39c, 40c are changed to their lower position and the corresponding switches in the regulating device 8b are changed to their upper position so that control changes to the device 8c, the frequency changer 6b being made inoperative when the vehicle has left the section b.