Patent GB-1469946-A (GB)
Title: Method and arrangement for the control of a converter machine  of synchronous construction
IPC: H02P25/024
Filed: 1974-04-26
Abstract: 1469946 Automatic control of load angle LICENTIA PATENT-VERWALTUNGS GmbH 26 April 1974 [28 April 1973] 18401/74 Heading G3R [Also in Division H2] A synchronous motor 5 is supplied through a frequency changer 4 whose thyristors are fired by signals az fz derived by an amplifier 3 from the output signals a - f of a firing order element 2, which receives through a selection logic unit 1 either the signals A, B, C of a rotor position sensor 6 or the signals Ta -- Tf of a ring counter 11 responsive to the output pulses U p  of a pulse generator 9, the signals A, B, C'and Ta - Tf also being fed to a digital to analogue converter 7 producing a signal # ist  representative of the actual value of rotor load angle for comparison with a desired value signal # soll  produced by an integrator 91, the resultant deviation signal ## being fed to a controller 8 which emits a signal # R  proportional to ## for combination with a signal Uf from a member 10 determining the required frequency of the motor 5, signal Uf, and desired value of rotor load angle, signal U st , the combination of XR and Uf being supplied to the integrator 91 which produces the signal # soll  for comparison with signal # ist  and with signal U st , the latter comparison producing a deviation signal U k  applied to a comparator 92 producing the pulses U p  which are also fed back to the integrator 91 to reset it, e.g. control a discharge circuit for a capacitor charged by the combined signal XR and Uf. Two modes of operation are used, respectively shown in Figures 2a and 2b, the modes being as follows:- Figure 2a U f  is maintained constant and U st  is varied, increased for example at time to by a value #U st , thus reducing U k  by a corresponding amount and delaying the next pulse U p  by a time # t  from the instant at which it would have otherwise occurred, the pulses U p  thereafter occurring at the constant frequency obtaining before the change of U st  and determined by U k . Thus the signal Td of Ta- Tf is varied as shown. Figure 2b U st  is maintained constant and U f  is varied, for example slowly increased. Hence the period of the integrator 91 is reduced and consequently also the periods of signals U k , U p , thus varying all the signals Ta - Tf as shown. The above operations ignore the effect of controller 8 since it only becomes effective above a certain value of its input signal ##. The unit 1 selects the input signals A, B, C or Ta - Tf according to the speed of the motor 5, that is during starting or normal operation. The signals A, B, C may be obtained from an optical system employing photo-transistors, a discussion being given of the adjustment of the rotor position sensor at standstill to a rotor load angle # m  corresponding to optimum starting torque and to an angle X = O for reverse drive the latter value, which corresponds to the basic wave of stator flux being perpendicular to the basic wave of rotor flux, not normally being chosen, since the motor is required to operate in a capacitive manner for reasons of commutation in the frequency changer 4.