GB1439372A - Regulating systems of rotary field electric machines - Google Patents

Abstract

1439372 Control of AC motors DEUTSCHE AUTOMOBIL GmbH 9 July 1973 [10 July 1972] 32547/73 Heading H2J A regulating system of a rotary field electric machine includes a function generator which designates rotor frequency as a function of stator frequency and has a characteristic such that, for each stator frequency, the designated rotor frequency will result in the calculable minimum electrical losses for the machine, and the regulating system operates to maintain the relationship between stator frequency and designated rotor frequency. Fig. 4 shows the application of the invention to an asynchronous machine 3, e.g. a motor, the function generator 7 having a characteristic W 2 (rotor frequency) equal to function W 1 (stator frequency) obtained by calculation and experiement to ensure that, at every operating point of the machine, the sum of the iron and copper losses is a minimum. An adding element 4 forms a signal W 1 indicative of desired stator frequency, from a signal n representative of the speed of the machine and the output signal W 2 of the generator 7. An inverter 2 is controlled by the signal from element 4 (which also supplies the generator 7) and by the output signal from a current regulator 6 receiving a desired current signal I 1 and a measured current signal. The inverter 2 is controlled to maintain the minimum electrical loss condition for a (shaded) operating range between the characterstics #=# max. and #=# min. shown in Fig. 3, that is as long as the relationship W 2 =f(W 1 ) does not designate a value of W 2 which falls outside the shaded area for a given current I 1 . If this condition is not met, the constant current control is modified by use of a known system, Fig. 1 (not shown), wherein the desired current signal I 1 is obtained from a function generator (5) receiving the signal W 2 from generator 7 and having a characteristic relating I 1 and W 2 , whereby the machine flux density is maintained constant at a desired value, Fig. 2 (not shown). Thus, in a practical case for a motor 3, the inverter 2 may be controlled whereby the motor operating characteristic follows the curve of minimum flux density (# min.) for small torques up to a rotor frequency W* 2 determined by theory or experiment, after which the characteristic follows the maximum flux density curve for increasing torques. This produces a higher efficiency for the low torque range compared with known regulating systems.