Static frequency changer output voltage and frequency control - uses EMF rather than motor terminal voltage to maintain three phase motor airgap flux constant independent of load and motor speed

摘要

The method is for regulating the output voltage and frequency of an intermediate circuit. A static frequency changer is for feeding a three-phase motor driven at variable frequency and speed. This maintains the air-gap flux of the three-phase motor constant, independent of the load and motor speed, and with the least possible expense on electronics and with high accuracy. The EMF (UR) is used rather than the terminal voltage (U2) of the motor. The true value of the EMF (Uh) can be automatically derived from the motor terminal voltage (U2) by means of an arithmetic unit, and to convert the terminal voltage to the EMF an approximation formula can be used to simplify the electronic balancing network required. More specif. the approximation formula is used in a form that allows minimum expense on electronic hardware to be realised.