Starting motors operating on high frequency alternating current. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric motors
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The population has accumulated a large number of power tools operating on high-frequency alternating current. The first wave of such equipment poured into the private user during the privatization of the 90s, the second - as a result of mass trips of people to work in near and far abroad. Those who somehow purchased an industrial power tool simply do not know what to do with it, because frequency converters are required to operate high-frequency motors.
A three-phase frequency converter 50/200 Hz and voltage 380 (220) / 36 V with a power of 0,4 kW can be made from a conventional electric motor and a car alternator. It is known that the operating speed of AC electrical machines (motors and generators) is equal to the AC frequency divided by the number of pole pairs of the stator winding. There is also slip (asynchrony), which is different for different electric machines, conditions and modes of operation.
Slip must be taken into account when designing electric machine frequency converters based on asynchronous motors. To round off the calculations, we will omit this circumstance for the time being. This means that in order to achieve a frequency of 200 Hz, it is necessary to spin a conventional automotive alternator up to 2000 rpm. This is easy to do with an electric motor and a belt drive. The ratio of the diameters of the driving and driven pulleys should be inversely proportional to the operating speed of the electric motor and generator.
For example, for an engine with an operating speed of 1500 rpm, a pulley with a diameter of 100 mm is required, for a generator, respectively, 75 mm (Fig. 1).
To force the generator to give 36 V instead of 12 V, it is necessary to introduce a "deceptive" resistor R into a typical circuit (Fig. 2), with the help of which the required voltage is set at the output of the device.
Details. Generator G-250-E1 (-I1; -H1); relay-regulator PP350; electric motor 1500 rpm (0,7 kW for three-phase voltage, 1,5 kW for single-phase); chemical battery or other source of constant voltage 1,5 ... 13 V (to start the generator); resistor - low-resistance rheostat; throttle; light bulb (selected when adjusting).
For a more powerful 50/400 Hz converter, a 500 rpm electric motor driven by a 3000 rpm motor can be used as a generator. To spin the generator up to a frequency of 4000 rpm, a 4 to 3 gear will be required. This is without slip! This solution has not been tested and is offered as a possible solution.
Author: V.V. Dubrovny
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