Specific Capacity of Power Inductors and Capacitors

Abstract

Factors imposing limitations on the specific reactive power that can be passed through materials of power inductors and capacitors are considered. These factors can be conditionally divided into those related to energy and thermal constraints. Energy constraints are stemming from the finite specific energy capacity of materials and the preset conversion frequency. Thermal constraints arise from heat losses in a real reactive element and from imperfect cooling conditions. Thermal operating conditions of different materials are calculated taking into consideration the dielectric loss tangent, the maximum operating temperature, and thermal resistance of the element. A universal procedure for calculating the optimal conversion frequency and maximum permissible specific reactive power of active materials is proposed. By using the proposed procedure, it is possible to select the reactive material operation mode in which its energy and thermal capabilities are used to the full extent. The assessment of materials by the maximum permissible specific reactive power that is used in this study differs from the conventionally applied approach to considering the performance factor and Steinmetz parameters; nonetheless, it is their logical extension. The developed calculation procedure is supposed to be applied in practical engineering calculations: it uses generally accepted parameters given by producers in the descriptions of materials. Also, to simplify the calculations, the amplitude and frequency nonlinearities of losses are not considered in the analysis. The analysis carried out in accordance with the proposed procedure has shown that high-frequency materials with low energy capacity have the highest specific reactive power capacity in the range of conversion frequencies from 0.3 to 3 MHz. According to the analysis results, high-frequency capacitor ceramics and nickel zinc ferrites with low permeability are the most promising materials. In case of using reactive components without active materials, a high specific reactive power is achievable in the frequency range 3...300 MHz. Reactive elements with a high Q-factor can be implemented in this frequency range without using materials having high permittivity or permeability. Reactive elements constructed without using active materials can operate in the regular design mode at temperatures close to the conductor melting point.