VARIABLE-FREQUENCY ELECTRIC DRIVE Russian patent published in 1994 - IPC

FIELD: electrical engineering. SUBSTANCE: variable-frequency electric drive has induction motor with tachogenerator on shaft. Circuits of induction motor stator are connected to outputs of power amplifiers, tachogenerator output is connected to first input of comparator unit whose second input is connected to reference input unit. Output of comparator unit is connected to harmonic phase function generator through analog-to-frequency converter. Electric drive has multiplier units whose number is equal to product of number of phases of supply circuit and number of phases of induction motor, and each power amplifier is made in form of frequency converters according to number of supply circuit phases employing double-ended ac switches with two information inputs and one power input intended for connection to corresponding phase of supply circuit; converter outputs are connected to summer outputs; summer output terminals form output of power amplifier, some of information inputs of converters are connected to outputs of multiplier units and some of inputs of multiplier units are combined and connected to output of corresponding harmonic phase function generator and other inputs are connected to power inputs of inverters, other information inputs of all inverters being combined and connected to output of constant amplitude and frequency voltage generator, the latter is made in form of square wave voltage generator. EFFECT: increased efficiency. 6 dwg