Method and system for increasing heating power

Abstract

Summary: Method and system for increasing heating power, according to the invention, features a digital command / control strategy and path, of the direct current passed through non-ideal heating elements, of resistive-inductive (RL) type, based on a pulse modulation technique, to modify the effective value of electric current without variation of electrical voltage amplitude, a fact which improves the adjustment linearity of the systems that implement it. The summary of the invention will be published together with figure 3.

Description

[0001] The invention relates to a method and system for increasing the heating power of non-ideal heating elements, of resistive-inductive (RL) type, with an effect on increasing the active electrical power consumed and dissipated as heat, as a result of modifying the electrical supply technique, achieved through pulse-width modulated (PWM) direct current voltage pulses.

[0002] For the purpose of modifying the power of ideal resistive (R) direct current electric heaters, several solutions are known (Practical Electronics for Inventors, ISBN: 978-1-25-958754-2) which consist, mainly, of strategies and ways for the variation of the direct current supply voltage amplitude, the modification of the effective supply voltage by providing pulse-width modulated direct current voltage pulses, at a fixed fundamental switching frequency and with a fully variable duty cycle, or the alteration of the electrical resistance by introducing / eliminating elements connected in series / parallel in the supply circuit.

[0003] Some of the disadvantages of the described solutions are related to that, in the case of non-ideal direct current electric heaters, of resistive-inductive (RL) type, the variation of the direct current supply voltage amplitude requires additional electrical equipment / electronic conversion devices, and the modification of the effective supply voltage by providing pulse-width modulated (PWM) direct current voltage pulses, allows only the decrease of their heating power relative to the nominal parameters, while, if the duty cycle is maximum, the effective value of the electric current increases nonlinearly because it is limited only by the resistive component, as well as when the waveform of the electric current is attenuated by the inductive component, the adjustment is not linear over the entire variation interval of the duty cycle, and in another case, additional electric heaters and / or switching apparatus are required.

[0004] The nonlinearity of the solutions, which consist of modifying the effective supply voltage by providing only pulse-width modulated direct current pulses, with the maintenance of a constant fundamental switching frequency, is given by the fact that, the inductive behavior at the switching (connection / disconnection) of non-ideal direct current electric heaters, is absent when the duty cycle tends towards maximum (e.g. over approx. 90%), a case equivalent to a zero switching frequency and associated with magnetic saturation, due to the permanent supply, or is excessive when the duty cycle tends towards zero (e.g. below approx. 10%), a case equivalent to a high switching frequency and associated with inductive filtering, due to excessively short pulses.

[0005] The invention solves, mainly, the technical problems in that, it avoids the necessity of varying the direct current supply voltage amplitude of non-ideal direct current electric heaters, therefore it does not involve additional electrical equipment / electronic power conversion devices, but uses direct current supply circuits and digital command / control systems, which provide pulse-width modulated direct current voltage pulses, according to another command / control strategy, and at the same time there are not necessary additional electric heaters and / or switching apparatus, which would modify the electrical connections.

[0006] Method and system for increasing heating power, according to the invention, it surprises the presented disadvantages and problems, in that it assumes, mainly, a digital command / control strategy and path, of the direct current passed through non-ideal heating elements, of resistive-inductive (RL) type, based on a pulse modulation technique, to modify the effective value of electric current without variation of electrical voltage amplitude, a fact which improves the adjustment linearity of the systems that implement it.

[0007] The invention has the following advantages: The method and system introduce new digital command / control possibilities for increasing the heating power of non-ideal heating elements; The method and system do not require other additional electrical equipment / electronic conversion devices, or other electric heaters and / or switching apparatus compared to those available; The method and system allow the modification of the effective value of the electric current without variation of the electrical supply voltage amplitude; The method and system improve the adjustment linearity of the power of non-ideal direct current electric heaters.

[0008] Below is further given an embodiment of the invention in connection with the following figures: Fig. 1 - Method for increasing heating power, of non-ideal direct current electric heaters. Fig. 2 - System for increasing heating power, of non-ideal direct current electric heaters. Fig. 3 - Effects of the method and system for increasing heating power, of non-ideal direct current electric heaters (suggestive representation).

[0009] Method for increasing heating power using the proposed system, is characterized mainly, in that, it constitutes a driving technique for increasing the effective supply current of non-ideal heating elements 1, of resistive-inductive (RL) type, by ensuring direct current voltage pulses 2, modulated both in frequency (PFM), as well as in width (PWM) by the microcontroller for command / control 3, provided to the electronic switch 4, such that it involves the decrease of fundamental switching frequency (e.g. by ½) below the saturation frequency of the inductive components, proportionally with the increase of the temperature reference 5 (e.g. by ½), together with nonlinear assignment of a duty cycle, which is additionally limited strictly above the minimum possible value of 0% (e.g. min. 10%) and strictly below the maximum possible value of 100% (e.g. max. 90%), a fact which ensures the adjustment linearity of the digital command / control system which it modifies.

[0010] System for increasing heating power using the described method, is characterized mainly, in that, it consists of the microcontroller 3, which allows the modification of the heating power in connection with the variation phenomenon of magnetic saturation of the non-ideal heating elements 1, inversely proportional with the change of the switching frequency, at values below their saturation frequency, depending on the value of the temperature reference 5, capable of commanding / controlling the electronic switch 4, in the supply circuit, with continuous pulses 2, modulated in frequency (PFM), but also in width (PWM) of limited size, a fact which ensures the implementation of the adjustment method.

[0011] The invention assumes that, in the electrical supply which it digitally commands / controls, when the fundamental pulse-width modulation frequency is decreased (e.g. by ½) below the saturation frequency of the resistive-inductive heating elements, the normal operation region decreases proportionally (e.g. by 50%), a fact which allows the existence of an extended operation region (e.g. of 40%), an action for which keeping the duty cycle constant, determines the increase of the effective electric current (e.g. doubling), respectively the increase of the heating power stage (e.g. doubling), due to the magnetic saturation of the inductive parts, while, the modification of the duty cycle is possible, but in an interval with lower and upper limitation (e.g. min. 10% and max. 90%).

[0012] The linearity of the invention, which consists of modifying the effective value of the electric current disproportionately to the effective supply voltage, formed by providing modulated direct current voltage pulses, both in lower and upper limited width, as well as of low fundamental switching frequency, is given by the fact that, the inductive behavior at the switching (connection / disconnection) of non-ideal direct current electric heaters, is still present when the duty cycle tends towards the imposed upper limit (e.g. at max. 90%), as well as admissible when the duty cycle tends towards the imposed lower limit (e.g. at min. 10%).

[0013] Method and system for increasing heating power, according to the invention, can be reproduced with the same performances and characteristics whenever is necessary, for any application compatible with it, a fact that constitutes an argument in favor of meeting the criterion of industrial applicability.

Claims

1. Method for increasing heating power, characterized in that, it ensures the adjustment linearity of the digital command / control system which it modifies, as it constitutes a driving technique for increasing the effective supply current of non-ideal heating elements (1), of resistive-inductive (RL) type, by ensuring direct current voltage pulses (2), modulated both in frequency (PFM), as well as in width (PWM) by the microcontroller for command / control (3), provided to the electronic switch (4), such that it involves the decrease of fundamental switching frequency below the saturation frequency of the inductive components, proportionally with the increase of the temperature reference (5), together with nonlinear assignment of a duty cycle, which is additionally limited strictly above the minimum possible value of 0% and strictly below the maximum possible value of 100%.

2. System for increasing heating power, according to claim 1, characterized in that, it ensures the implementation of the adjustment method, as it consists of the microcontroller (3), which allows the modification of the heating power in connection with the variation phenomenon of magnetic saturation of the non-ideal heating elements (1), inversely proportional with the change of the switching frequency, at values below their saturation frequency, depending on the value of the temperature reference (5), capable of commanding / controlling the electronic switch (4), in the supply circuit, with continuous pulses (2), modulated in frequency (PFM), but also in width (PWM) of limited size.

3. Method and system for increasing heating power, according to claim 1 and claim 2, characterized in that, the fundamental pulse-width modulation frequency is decreased below the saturation frequency of the resistive-inductive heating elements, and the normal operation region decreases proportionally, a fact which allows the existence of an extended operation region, an action for which keeping the duty cycle constant, determines the increase of the effective electric current, respectively the increase of the heating power stage, due to the magnetic saturation of the inductive parts, while, the modification of the duty cycle is possible, but within an interval with lower and upper limitation.

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