Patent GB-1290962-A (GB)
IPC: H02P21/12
Filed: 1970-08-13
Abstract: 1290962 Automatic speed and current control SIEMENS A G 13 Aug 1970 [14 Aug 1969 22 April 1970] 39150/70 Heading G3R [Also in Division H2] An asynchronous motor 1 is supplied from a frequency changer 2, current transformers being connected to a unit 8 for providing quadrature signals Ij, Ir, which are applied to controllers 9. The output voltages of these controllers are converted in unit 10 into corresponding three-phase components for controlling the frequency changer 2. The signals Ij, Ir, are transmitted through proportional-action members 4a and are subtracted in unit 4b from the output voltages of detectors 3 which respond to the air-gap field. The factor of the members 4a depends on the ratio between rotor stray inductance and the main inductance of the motor. A vector analyzer 5 receives signals related to the rotating field and provides sine and cosine components of a unit vector which always points in the direction of the axis of the field. The unit 6 receives signals b, w, related to the rotor field axis, and the sine and cosine field components, to provide at its output the reference signals for the controllers 9. This arrangement provides separate torque and field regulation by adjusting the signals b and w individually. The signal w may be derived from a controller 110 which compares the desired and actual speed for superimposing speed-regulation upon the torque regulation. In a modification, the signals b, w, are derived from direct current controllers having integralproportional action, Fig.4 (not shown). To overcome delay effects, the control vector formed by the output voltages of these controllers is added to a vector perpendicular thereto so that the sum vector is advanced in the direction of rotation of the field. The magnitude of the added vector is proportional to the angular velocity, the stator current, and the stray-field time constant of the motor. The main-field time constant is compensated for by rotation of the vector opposite to the direction of the field. In another arrangement, the motor is supplied from a rectifier-frequency converter combination, 2a, 2b, associated with a current controller 64. A signal representing the magnitude of the control vector for the stator current appears at the output terminal 37 of the vector analyzer 51, while sine and cosine signals, representing the angular position of the vector, appear at terminals 13, 14. Signals representing six discrete angular positions are produced in switch 65 which transmits firing pulses to the rectifiers of the inverter 2b whereby the stator current vector follow the control vector. A phase correcting controller 74 is associated with the switch 65. The inverter comprises six controlled rectifiers in a three-phase bridge arrangement, and six commutating rectifiers connected in parallel therewith through capacitors forming oscillation circuits with the stator phase windings. Smoothing of the field-component voltages at the output of the units 4b, to remove harmonics due to slotting of the rotor, is provided by a harmonic-free two-phase generator 114 whose frequency is determined by the output of a proportional-plus-integral controller 115 to the input of which is applied a signal representing the phase displacement between vectors related to the rotating field and the generator respectively. The sine and cosine voltages set up at terminals 110, 111, and the component voltages to be smoothed are multiplied in unit 116. A divider 119 provides a signal proportional to the tangent of the difference angle. A second order delay member comprises an integrator 122 associated with amplifier 121. The smoothed output is developed at terminals 126, 127, associated with multipliers 124, 125.