Power regulation method for a heating element and control system for implementing said method

Abstract

The invention relates to a power regulation method for a heating element and to a control system for implementing said method, with said method comprising applying the cycle stealing technique to adjust the power supplied to the resistive load at multiple levels, such that the modulation period is increased, reducing the frequency of the current signal that modulates the carrier, in order to reduce the generation of harmonics. The control system comprises a controller (2) connected to a power regulator (3) that acts on the heating element (1), such that said controller (2) adjusts the power supplied by the regulator (3) to the resistive load of the heating element (1) using the fine-grain cycle stealing technique.

Description

[0001] DESCRIPTION

[0002] POWER REGULATION PROCEDURE FOR A HEATING ELEMENT AND CONTROL SYSTEM TO IMPLEMENT SAID PROCEDURE

[0003] OBJECT OF THE INVENTION

[0004] The invention, as stated in the present descriptive memorandum, refers to a power regulation procedure for a Joule heating element and a control system to implement said procedure, providing advantages and characteristics, which are described in detail below.

[0005] The object of the present invention is a power regulation method for a Joule heating system that includes a resistive load which, instead of being an on / off system, is based on the application of cycle-stealing technology. A second aspect of the invention is a control system for implementing this method, comprising a controller capable of finely adjusting the regulator's power. This process and system enable high-resolution power regulation and improve the energy efficiency of the Joule heating system. By avoiding the thermal oscillation associated with traditional binary operation, a more stable temperature and more efficient energy use are achieved.

[0006] FIELD OF APPLICATION OF THE INVENTION

[0007] The field of application of the present invention falls within the sector of electrical installations, focusing particularly on those intended to generate heat by the Joule effect, especially for heating systems. BACKGROUND OF THE INVENTION

[0008] Modern heating systems operate with a binary on / off (all / nothing) action of the electrical resistors, even when using PID (Proportional-Integral-Derivative) controllers for thermostatic regulation. This binary operation causes significant temperature fluctuations, negatively impacting temperature stability and energy efficiency.

[0009] The objective of the present invention is the development of an improved process that avoids such oscillations by gradually applying power to the resistive load, avoiding the use of a binary action and, therefore, the thermal oscillation generated by said action.

[0010] Attempts have been made to solve the aforementioned technical problem by regulating the current using cycle stealing or cycle clipping techniques, but always within the same period. However, cycle stealing or cycle clipping within the same period generates high harmonics (for example, the resulting current signal exceeds the levels established by the EN61000-3-2 standard), so it has always been rejected or limited to low power levels.

[0011] As a reference to the current state of the art, it should be noted that, as the closest documents related to the object of the invention, the following can be cited: patent US6849834B2, and patent EP0188886B1.

[0012] US patent 6849834B discloses a power controller for an AC load comprising: a user interface adapted to interact with a user to produce at least one user interface signal; and a control module adapted to electrically couple a line voltage source, electrically couple the AC load, and provide electrical power to the AC load as a function of the at least one user interface signal by implementing a cycle-skipping, low-flicker control algorithm, the control algorithm comprising a plurality of cycle patterns, the cycle patterns comprising a plurality of main power levels.

[0013] Patent EP0188886B1 discloses a power control device for controlling the output power of a plurality of resistive heating elements comprising a multi-position switch for connecting the heating elements in series and in parallel and means for varying the duty cycle applied to the heating elements in both series and parallel modes.

[0014] These records do not take into account the harmonics generated by their devices and therefore probably present high harmonics and do not comply with the EN61000-3-2 standard.

[0015] As is well known, the EN 61000-3-2 standard aims to control harmonic emissions generated by electrical and electronic equipment connected to the low-voltage distribution network, thus protecting the stability and quality of the electrical network, especially in residential and commercial environments.

[0016] The standard applies to electrical and electronic equipment with an input current of 16 A or less per phase and establishes different limits depending on the equipment class, especially for low-order harmonics (the most problematic, such as the 3rd). a 5 a 7 a , etc.).

[0017] For example, for a Class A appliance, which is where heating equipment is normally grouped, the 3rd harmonic current is limited to 2.30 A (in absolute terms or as a percentage of the fundamental current).

[0018] It would therefore be interesting to have a gradual (non-binary) power regulation procedure for a Joule heating system using cycle-stealing technology that does not generate current in high harmonics, i.e., above 1.08 Amperes in the 2nd harmonic. o , 2.30 Amps for the 3rd harmonic o 0.43 Amps for the 4th harmonic oetc., and therefore comply with the EN 61000-3-2 standard.

[0019] Traditional power modulation techniques typically clip the sine wave within a single cycle or, at most, steal half-cycles. However, if instead of applying cycle-stealing at the level of a single period, the modulation period is lengthened (thus reducing the frequency of the signal modulating the carrier, for example, from 50 Hz), we can operate below the limits established by the standard while simultaneously regulating the current and, consequently, the heating power of the heating element.

[0020] For example, to apply a 50% reduction in the power of a heater powered by a 50Hz carrier current, if instead of applying a square wave modulating current with a frequency of 25Hz (one complete cycle on, one complete cycle off), the frequency of the square wave modulating current is reduced to 12.5 Hz (two complete cycles on, two complete cycles off), the result we obtain is that the resulting signal does comply with the standard because all the harmonics are below the limit established by it.

[0021] However, it does not appear that any of the existing documents, taken separately or in combination, describe a power regulation procedure or a control system with the technical characteristics of the one claimed herein.

[0022] EXPLANATION OF THE INVENTION

[0023] The power regulation procedure for a Joule effect heater and a control system to implement said procedure proposed by the invention are configured as an ideal solution to achieve the aforementioned objective, with the characterizing details that make it possible and that distinguish them being conveniently included in the final claims that accompany this description.

[0024] Specifically, what the invention proposes, as previously mentioned, is a procedure and a control system to regulate the current that feeds a heat-generating resistor. Unlike current systems, which are based on a binary on / off (all / nothing) action, even when using PID controllers for thermostatic regulation, which causes significant thermal oscillations and negatively affects temperature stability and energy efficiency, this invention is based on the application of cycle stealing technology and a control system that proposes a mechanism for the gradual application of power to the resistive load, or fine regulation, avoiding the use of a binary action and, therefore, the thermal oscillation generated by said action.

[0025] Thus, instead of using an on / off system, the system of the invention adjusts different power levels (for example, with a granularity of 16 or 32 power levels), facilitating the approach to and maintenance of the setpoint temperature much more stably than with an on / off actuator. This regulation system (fine regulation) aims to avoid sawtooth patterns in the temperature curve, thereby increasing system efficiency and reducing thermal ripple.

[0026] In short, the power regulation procedure for a Joule heating element, in particular for a heating system that includes a resistive load, comprises the application of the cycle-stealing technique, to adjust the power supplied to the load at multiple levels, in strips of more than one period or cycle, instead of applying it within a strip of a single period or cycle.

[0027] Applying the cycle-stealing technique in strips of more than one period or cycles, and therefore enlarging the modulation period, allows reducing the maximum level of harmonics, placing it below, for example, the limits established by the EN61000-3-2 standard.

[0028] The term "strips of more than one cycle" refers to strips that include both current flow for more than one cycle and no current flow for more than one cycle. For example: 1.5 cycles on and 1.5 cycles off, or 2 cycles on and 4 cycles off, or 4 cycles on and 2 cycles off.

[0029] Conversely, a single-period or single-cycle strip should be understood as any strip that includes the flow of current for one cycle or less, or the absence of current for one cycle or less. For example, 1 cycle on and 3 cycles off, or 3 cycles on and 1 cycle off.

[0030] This technique also allows for higher resolution regulation and improved thermal stability compared to the binary on / off (all / nothing) regulation technique of electrical resistors, even when using PID (Proportional-Integral-Derivative) controllers for thermostatic regulation.

[0031] For example, to achieve a 50% power reduction, instead of using the cycle-stealing technique and passing the current for one cycle on and one cycle off (25Hz), as shown in the diagram in Figure 1, the invention proposes, for example, reducing the frequency of the square wave modulator to 12.5 Hz, i.e., two cycles on, two cycles off, as shown in the diagram in Figure 2. The 25Hz solution generates harmonics that are too high, preventing compliance with current regulations; however, the 12.5Hz solution generates harmonics that are low enough to comply with current regulations.

[0032] Figures 1 and 2 show the relationship between the frequency range of a 50Hz signal modulated by a 25Hz square wave and the frequency range of a 50Hz signal modulated by a 12.5Hz square wave. It can be seen that the generated harmonic group is compressed, falling below the limits.

[0033] The invention procedure contemplates, in order to apply a 50% reduction of power, any other combination of cycle theft, which involves the passage of current for more than one cycle and the non-passage of current for more than one cycle, for example 3 cycles yes, 3 cycles no.

[0034] It is preferable to apply power reduction using cycle stealing to reduce the heater's power output through Joule heating by applying a modulating current with the highest possible frequency. For example, if the heater's power frequency is 50 Hz, to achieve a 50% power reduction, it is preferable to apply a square wave modulating current with a frequency of 12.5 Hz rather than a lower frequency, such as 6.25 Hz. This is because the shorter the modulation period, the better the system's dynamic performance and the lower the thermal micro-oscillations to which the resistive load will be subjected, provided that the previously mentioned harmonic emission levels are met.

[0035] The same calculation can also be applied to power reduction at other levels, as shown in the following table:

[0036] Figures 3-A and 3-B also show diagrams with examples of power reduction by cycle stealing, according to the procedure of the invention, specifically by 66% and 33% respectively.

[0037] In one embodiment of the invention, the power regulation procedure for a heating element comprises allowing current to flow for more than one complete cycle and preventing current flow for more than one complete cycle. The passage or prevention of current flow during incomplete cycles sometimes generates excessively high harmonics that prevent compliance with current regulations.

[0038] In another embodiment of the invention, the power regulation procedure for a heating element comprises passing current for two or more cycles and preventing the passage of current for two or more cycles.

[0039] Furthermore, to implement the described cycle-stealing procedure in an electric heating system, the control system of the invention comprises the use of a digital controller that adjusts the power supplied to the resistive load by means of a fine-step regulator, instead of simply turning it on or off completely. This controller may be microprocessor-based, which, by means of a temperature sensor, monitors the ambient temperature and adjusts the regulator's output power according to the detected temperature variations, using advanced control algorithms.

[0040] The advantages of the procedure and the system that is the subject of the invention, based on the aforementioned cycle stealing and fine regulation system, are as follows:

[0041] - Reduction of thermal oscillation:

[0042] In an on-off control system, every time the temperature exceeds the setpoint and continues heating until it reaches the hysteresis level, the room overheats, causing an excess energy flow to the outside.

[0043] - Improved energy efficiency:

[0044] The higher temperature difference between the room overheated by the on-off controller effect and the outside causes a net energy loss that is proportional to the amplitude of the oscillation.

[0045] By maintaining a more stable temperature with the cycle stealing system, energy loss is reduced and system efficiency is increased, as the system is not permanently exceeding the setpoint temperature unnecessarily.

[0046] - API compatibility with elements with Joule effect:

[0047] The process is applicable to any system with an electrical element that operates by the Joule effect. This includes, but is not limited to, electric radiators, water heaters, electric stoves, and other heating devices that use an electrical resistance to generate heat.

[0048] - Optimization of heating elements:

[0049] By allowing smooth and continuous adjustment of the power supplied to the resistive load, the present invention enables the use of a smaller variety of heating elements. The present invention makes it possible to limit the maximum power of a heating element, thus achieving thermodynamic behavior similar to that of a heating element with a lower maximum power rating.

[0050] Furthermore, the ability to dynamically adjust the power reduces the thermal oscillations of the assembly, contributing to the longevity and stability of the heating elements, as it avoids excessive thermal stress that could compromise their integrity in the long term.

[0051] In this last aspect, it is important to emphasize that the fact that the radiator is able to modulate the power of the heating load has many implications:

[0052] - Durability of mechanical components

[0053] The radiator elements are press-fitted together (not welded). This means that the radiator's watertight seal is achieved solely through contact pressure on the threaded fittings.

[0054] When the elements in contact are heated and cooled, they expand and contract accordingly, and obviously, due to their intrinsic differences in manufacturing and assembly, they do not do so in exactly the same way, creating mechanical stresses between them.

[0055] These temperature differences are obviously much more noticeable when the power control system is based on an "on-off" rather than proportionally.

[0056] The mechanical stresses generated when there are considerable and continuous thermal oscillations between elements assembled by pressure (due to interference of the thread of the bushings) cause these contact points to acquire play and eventually loosen, potentially even causing leaks of the liquid inside the radiator.

[0057] - Acoustic comfort

[0058] Radiators that experience significant temperature variations make noise when they expand and contract. This noise is related to the radiator's construction and its mounting mechanisms. Because they are assembled by pressure (and not welded), when the elements expand unevenly, stresses appear between them, as explained in the previous section.

[0059] Although the elements expand differently due to their structural and positional variations, the elements remain in the same position for a few seconds because the tension is not strong enough to overcome the static friction force necessary for them to move against each other.

[0060] When the power modulation has a regulation cycle shorter than the time needed to achieve the slippage between the two surfaces that are touching, then this slippage never occurs, and under thermal equilibrium conditions of the heated room, the characteristic "clack-clack-clack" of the radiators when they expand and contract ceases to be heard.

[0061] - Improved performance of the home's electrical network

[0062] The circuit breakers and digital electricity meters commonly found in homes have reaction curves that activate the protective devices based on the percentage of excess power and the duration of that excess. These curves are called tripping curves.

[0063] In the event that a dwelling has one, two or more radiators activated simultaneously with an on-off control, a simultaneity condition occurs in which the total current consumed by the system may exceed the contracted power or the power supported by the installation itself.

[0064] Conventional on-off controllers from all current manufacturers operate in the range of minutes, while our modulation system is capable of working with cycle steal periods below 1 second.

[0065] This allows the circuit breaker or smart meter to operate properly even when its peak current exceeds the nominal power of the installation by several times, since the protection devices provide several seconds of margin without tripping in transient conditions of peak consumption.

[0066] In conclusion, where other radiators would trigger the protections, those equipped with the control system of the invention, based on power modulation, will be able to work perfectly.

[0067] DESCRIPTION OF THE DRAWINGS

[0068] To complement the description being made and in order to help a better understanding of the characteristics of the invention, a sheet of drawings is attached to this descriptive document as an integral part thereof, in which the following has been represented for illustrative and non-limiting purposes:

[0069] Figure 1 shows a diagram of the modulated sinusoidal signal, designed to regulate power by 50% using the cycle-stealing technique according to the previous technique, i.e., one cycle on, one cycle off. This modulated sinusoidal signal generates harmonics that are too high, preventing compliance with current regulations. Figure 2 shows a diagram of the modulated sinusoidal signal, designed to regulate power by 50% using the cycle-stealing technique according to the procedure of the invention, i.e., two cycles on, two cycles off. This modulated sinusoidal signal generates harmonics low enough to comply with current regulations. Figures 3-A and 3-B.Figures 4-A and 4-B show respective diagrams with various examples of sinusoidal signal modulation to achieve power regulation of 66% and 33% respectively, using the cycle-stealing technique, specifically showing two types of signal in each: an upper one applying the cycle-stealing technique according to the previous technique and a lower one applying the cycle-stealing technique according to the procedure of the invention. Figures 4-A and 4-B show respective diagrams of an on-off system according to the current technique and a fine regulation system by cycle-stealing according to the invention, showing the differences between both diagrams of the applied power (lower graph) depending on the temperature captured by the sensor (upper graph); Figure 5.- It shows a block diagram representation of an example of the control system of the invention to implement the power regulation procedure; and figure number 6.- It shows an electrical schematic of the power regulator comprising the control system of the invention.

[0070] PREFERRED EMBODIMENT OF THE INVENTION

[0071] In view of the aforementioned figures, and in accordance with the numbering adopted, one can observe in them an example of a non-limiting embodiment of the control system to implement the regulation procedure of the invention, which comprises what is described in detail below.

[0072] Thus, as can be seen in said figures, particularly in figure 5, the control system for implementing the power regulation procedure for a heating element (1), according to the invention, comprises a controller (2), preferably a digital controller, connected to a power regulator (3) acting on the heating element (1), such that said controller (2) adjusts the power supplied by the regulator (3) to the resistive load of the heating element (1) by the fine-step cycle-stealing technique, instead of simply turning it on or off.

[0073] Preferably, said controller (2) comprises a microprocessor which, by means of a temperature sensor (4) connected to it and installed next to the heating element (1), monitors the ambient temperature and adjusts the output power of the regulator (3) according to the temperature variations detected, using advanced control algorithms.

[0074] Preferably, the system comprises a thermostat (5) or other means for inputting the temperature setpoint at which the controller (2) is to operate.

[0075] Finally, preferably the power regulator (3), whose electrical scheme is shown in figure 6, which includes optotriacs or optocoupler with triac, to isolate the power circuit from the control systems.

[0076] Figure 4-A shows the temperature fluctuation in the upper graph and the power delivered by the heater in the lower graph. While the temperature is below the set point, the power delivered is at its maximum (ON). When an upper temperature limit is exceeded, the power is deactivated (OFF) and remains deactivated until the temperature drops below a lower limit, at which point the maximum power is reactivated (ON).

[0077] Figure 4-B shows the temperature fluctuation in the upper graph and the power delivered by the heater (cycle stealing technique, the subject of the invention) in the lower graph. The power is regulated in discrete steps, much shorter in time, to reach and maintain a setpoint temperature. Preferably, as the setpoint temperature is reached, the applied power is reduced, and when the system reaches thermodynamic equilibrium, the temperature regulation will oscillate around the two power steps closest to the thermodynamic equilibrium power.

[0078] Having sufficiently described the nature of the present invention, as well as the manner of putting it into practice, it is not considered necessary to make its explanation more extensive so that any expert in the field can understand its scope and the advantages that derive from it.

Claims

CLAIMS 1.- Power regulation procedure for a heating element, in particular for a heating system that includes a resistive load, characterized by comprising the application of the cycle-stealing technique in strips of more than one period or cycle, i.e., the passage of current is allowed for more than one cycle and the passage of current is prevented for more than one cycle. 2.- Power regulation procedure for a heating element, according to claim 1, characterized in that it comprises the passage of current for more than one complete cycle and prevents the passage of current for more than one complete cycle. 3.- Power regulation procedure for a heating element, according to any of the preceding claims, characterized in that it comprises the passage of current for two or more cycles and prevents the passage of current for two or more cycles.

4. Control system for implementing a power regulation procedure for a heating element, as described in the preceding claims, characterized in that it comprises a controller (2) connected to a power regulator (3) acting on the heating element (1), such that said controller (2) adjusts the power supplied by the regulator (3) to the resistive load of the heating element (1) by the fine-step cycle-stealing technique, instead of simply turning it on or off.

5. Control system, according to claim 4, characterized in that the controller (2) is a digital controller.

6. Control system, according to claim 5, characterized in that the controller (2) comprises a microprocessor that, by means of a sensor temperature sensor (4) connected to it and installed next to the heating element (1), monitors the ambient temperature and adjusts the output power of the regulator (3) based on the detected temperature variations, using advanced control algorithms. 7.- Control system, according to claim 6, characterized in that it comprises a thermostat (5) or other means for entering the temperature setpoint at which the controller (2) must operate.

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