Power control of electric heating elements using thyristor voltage and resistance converters

  This article investigates the energy efficiency of thyristor converters with an active load. The conversion of electric energy in a “thyristor converter – electric heating element” installation is considered from the standpoint of electromagnetic theory. The energy characteristics of the considered installation was calculated in the MATLAB environment. When thyristor voltage converters are operated under the mode of controlling the power of active load, passive power was found to be generated at the input during the non-conductive state of the converter (thyristor is locked). The use of passive power allows additional thermal energy to be obtained by means of an extensive use of voltage, without increasing the current consumption. An increase in the depth of power control of electric heating elements by thyristor voltage converters leads to a significant increase in passive power. In the active power control range (50–100% of the nominal value), the factor accounting for variations in the total power in the converter due to an incomplete use of the voltage at the input of the considered installation decreases from 1.0 to 0.93. This reduces the power factor of the load converter from 0.97 to 0.925. Despite the high value of the load power factor (in the control interval 0–50% of the rated power value), the factor accounting for variations in the total power was found to be reduced to 0.66. As a result, the power factor of the converter with the load is reduced by ~ 33%. In order to increase the efficiency of converting electrical energy to control the active load power, it is proposed to use thyristor resistance converters that vary the electrical resistance of the load over time. It is shown that unsatisfactory operation of a thyristor voltage converter can be caused by inefficient use of voltage at the input of the “thyristor converter – electric heating element” installation. When using thyristor resistance converters, the current non-sinusoidality factor does not exceed 1.5 % and the voltage non-sinusoidality factor in a 0.38 kV network does not exceed 0.2 %.

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