ANALYSIS OF ENERGY CHARACTERISTICS OF AN ASYNCHRONOUS MOTOR WITH RECTANGULAR VOLTAGE POWER SUPPLY

https://doi.org/10.33815/2313-4763.2019.2.21.098-107

Abstract

Asynchronous machines are used mainly as engines. Due to the increased reliability and simplicity of the design, they are widely used in industry and on ships in the sea fleet, being the main consumers of electric energy. Despite these advantages, they have a significant drawback - poor adjustability of rotation velocity. Of all the methods being used to regulate speed such as: changing the number of pole pairs, introducing resistance into the rotor circuit, changing the rate of voltage supply, changing the frequency of the power line; the most acceptable one at current, due to modern power electronic base, should be considered the frequency method of adjustment with the intermediate conversion of the voltage of the three-phase circuit into direct current and the subsequent formation of a given sinusoidal voltage of variable frequency by pulse-duration modulation (PDM) method. Although this method allows to obtain alternating voltage of a given frequency with a sinusoidal form of wave, it has significant switching losses in the keys of the inverter, which leads to necessity of liquid cooling systems application with deionized water. This is especially true for powerful high-voltage asynchronous machines used in steering devices. It is possible to reduce these losses significantly by using the keys of the inverter to form the voltage of a given frequency of rectangular form, which will supply the power directly to the engine. Any additional losses generated in this case, and, as a result, additional heating from the higher harmonic (HV) steel and engine windings, are calculated on the basis of winding ratios. At the same time, since the ratio of the winding distribution varies very poorly, in calculations it can be accepted permanent, and by the value of the shortening factor specified for the first harmonica, it is possible to determine the appropriate coefficients of the series of HV, taken into account.