Abstract
Power electronics and their thermal protection systems that are designed on the basis of modern methods of thermal calculations work efficiently under specified operating conditions in a particular operating range of temperatures and modes beyond which the form of the transition process can change. Consequently, the extent of oscillation in the transition process increases along with the initial voltage and current fluctuations. These changes are dangerous if the boundary values of the component parameters are underestimated due to heating.The study suggests a method of integrated electrothermal calculation in order to ensure thermal protection of pulse converters for electric power by creating combined models of the circuit elements in the form of a system of differential equations. Analysis of the characteristic roots of solutions of the differential equations of the system state in the form of matrix exponentials gives an idea about the nature of the transition process. This allows setting a threshold value of fluctuations and a time frame of the transition process while enabling a heated device. It becomes possible to stabilize the transition process by heating the components and to choose magnetic materials of inductors, taking into account the thermal processes.As a result of this approach, thermal protection of power transformers extends to providing troublefree operation at nonstationary modes of the components and extreme temperatures; it becomes possible to reduce the complexity and rigidity of the requirements to establishing a time frame for restarting the device.
Highlights
Nowadays, one of the most urgent problems of power electronics is to minimize the size and to optimize power supply for semiconductor converters
Dangerous are the reclosing modes in which the heated appliance with lowered boundary values gets a thermal stress. These processes must be modelled by solving the problem in a methodological way, calculating the electrothermal processes that are combined in the device and selecting the elements of the circuit so as to reduce the amount of thermal stress and soften the character of the transition process when the heated converter is switched on
The matrix of variable coefficients for the circuit of a step-down pulsewidth modulator (PWM) converter should include changing resistance of the transistor, diode and inductor ∆r(θVT, θVD, θL ), a change in the magnetic permeability of the inductor core, as well as the capacitance change ∆C(θC), where θ = T − 25 °C is a temperature of a particular component that differs from 25 °C
Summary
One of the most urgent problems of power electronics is to minimize the size and to optimize power supply for semiconductor converters. According to previous research [1], almost 60 % of accidents occur as a result of semiconductor converters overheating In this case, every 10 °C increase in temperature doubles the accident rate. In order to ensure trouble-free operation of a converter, it is necessary to stabilize the thermal conditions This can be done with the help of methodological and circuit approaches. Dangerous are the reclosing modes in which the heated appliance with lowered boundary values gets a thermal stress These processes must be modelled by solving the problem in a methodological way, calculating the electrothermal processes that are combined in the device and selecting the elements of the circuit so as to reduce the amount of thermal stress and soften the character of the transition process when the heated converter is switched on
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