초록 ▼

The invention relates to an inverter circuit for operating an asynchronous motor having an adjustable speed. The inverter has its output frequency regulatable by a frequency regulator and the D.C. supply has its voltage regulatable by a voltage regulator. There is a desired value frequency regulator

The invention relates to an inverter circuit for operating an asynchronous motor having an adjustable speed. The inverter has its output frequency regulatable by a frequency regulator and the D.C. supply has its voltage regulatable by a voltage regulator. There is a desired value frequency regulator having a signal (f) and voltage and current measuring devices having output signals (E) and (I). A control circuit processes these signals (f, E, I) to form input values for the referred to voltage and frequency regulators. The control circuit includes a computer circuit which, from at least two output values and at least one constant, calculates a computed value of the third output value which, together with the first-mentioned output values, given by way of computation a substantially constant slip frequency for a given desired value, and this computed value is compared with a value substantially corresponding to the actual third output value. The three output values are interlinked in the computer circuit in such a way that a constant slip frequency is obtained for the desired frequency value that is fed in. The D.C. voltage supplied to the inverter is regulated so that this condition is maintained independently of the load. The result of this is that the nominal slip for a nominal load also occurs on partial load and this leads to the desired constant speed. This slip frequency can be kept constant even at low loads in that the air gap magnetization is made substantially proportional to the rotor current, i.e. there is under-magnetization.

대표청구항 ▼

An inverter circuit assembly for operating an adjustable speed asynchronous motor with a constant slip frequency, comprising an inverter, a three phase rectifier for converting a three phase supply to DC, a pair of conductors between said rectifier, and said inverter, a voltage regulator for regulat

An inverter circuit assembly for operating an adjustable speed asynchronous motor with a constant slip frequency, comprising an inverter, a three phase rectifier for converting a three phase supply to DC, a pair of conductors between said rectifier, and said inverter, a voltage regulator for regulating the output voltage of said rectifier, a frequency regulator for regulating the output frequency of said inverter, a frequency setting control device having a data value (f), a voltage measurer and a current measurer between said rectifier and said inverter having data values (E) and (I), a control unit for processing said values (f), (E) and (I) to form control signals for said voltage regulator and said frequency regulator, a computer circuit in said control unit having a built in constant (k1) inversely proportional to the predetermined slip frequency and a constant (k2) proportional to the winding resistance of the motor stator, said computer circuit being operable to calculate a computed value based on two of said three data values and said constants, and a comparator in said control unit for controlling said voltage regulator which inputs and compares the other one of said three data values and said computed value, said frequency regulator being controlled by said computed value when said data value (f) is a compared value, and said frequency regulator being controlled by said data value (f) when one of the other of said data values is a compared value.