Method for increasing the maximum speed of a synchronous motor with a given exciting field power and terminal voltage and apparatus therefor

摘要

An apparatus and method for increasing the maximum speed of rotation of a synchronous machine having constant excitation field strength is disclosed. The synchronous machine is preceded by a converter, which has an adjusted current reference value as an input. The adjusted current reference value comprises an active-current reference value and a reactive-current reference value. For actual speeds nist, the absolute value ¦nist¦ of which is above a predetermined value no, the amplitude of the active-current reference value is limited to a value which is inversely proportional to the factor ¦nist¦/no. The value no is a predetermined speed at which the sum of the magnet wheel voltage of the synchronous machine and the voltage drop in the stator winding is maximally equal to the largest possible output voltage of the converter. To obtain the adjusted current reference value, a reactive-current reference value shifted 90 DEG relative to the active-current reference value is vectorially added to the active-current reference value, the amplitude of the reactive-current reference value being proportional to the factor (1-no/¦nist¦). A reactive current is thus generated in the machine. The voltage drop across the reactance of the synchronous machine caused by this reactive current is 180 DEG out of phase with the speedproportional magnet-wheel voltage. The magnet wheel voltage can therefore be increased beyond the terminal voltage, so that the speed of rotation of the machine can be increased.