Power supply unit for a heating element

Abstract

The invention relates to a power supply unit (1) for a heating element (10.1) of an electric heater (10) with a connector (2) for connecting the power supply unit to an AC voltage source (20) that can generate a load voltage (V1, V2), and a modification unit (3), which can for controlling the temperature of the heating element (10.1) convert the load voltage (V1, V2) into a modified voltage (M), wherein a pulse unit (4) for providing a pulse sequence (P) is provided, wherein the modification unit (3) can modulate the load voltage (V1, V2) with the pulse sequence (P) to generate the modified voltage (M), and wherein the pulse sequence (P) is variable in order to modify the adjusted voltage (M) and thus control the temperature of the heating element (10.1).

Description

[0001] The invention relates to a power supply unit for a heating element of an electric heater with a connector for connecting the power supply unit to an AC voltage source that can generate a load voltage, and a modification unit, which can for controlling the temperature of the heating element convert the load voltage into a modified voltage. Further, the invention relates to a method for powering a heating element of an electric heater.

[0002] Electric heaters can be used to heat, for example, air or water to a desired temperature. The element that actually emits the heating power is referred to as the heating element, which is typically in direct contact with the medium to be heated.

[0003] To supply the heating element with electrical energy so that it heats up, a voltage source is required that provides a load voltage. Typically, the voltage source is an AC voltage source that supplies a harmonic alternating load voltage. The load voltage may, for example, have a voltage of 230 volts and a frequency of 50 Hz. However, other voltages and frequencies are also possible, particularly depending on the part of the world in which the heater is located or the type of power grid to which the heater is connected.

[0004] To transfer the current from the voltage source to the heating element, the heater includes a power supply unit that can be connected to the AC voltage source via a connector. Specifically, the heater can be connected to a power outlet via a cable. In order to control the power and thus the temperature of the heating element, the AC voltage cannot simply be passed directly through the heating element; instead, a modification unit is connected upstream of the heating element. This modification unit allows the load voltage to be adjusted and converted into a modified voltage, thereby varying the power of the heating element.

[0005] For this purpose, it is known that the modification unit may, for example, be designed as a half-wave rectifier, which allows only the positive portions of the load voltage to pass through. With a harmonic alternating voltage as the load voltage, this allows the power of the heating element to be reduced by half. Alternatively, or in addition to such a half-wave rectifier, a phase angle control can be provided, in which, for example, part of the load voltage is cut off using thyristors.

[0006] Although these methods allow for a technically simple way to modify the load voltage and thus control the power of the heating element, they often result in negative interference with other electrical devices and therefore do not provide sufficient electromagnetic compatibility. In some cases, the modification units may even have adverse effects on individuals. In terms of electromagnetic compatibility, the modification units often do not pass the flicker test or the harmonics test, which may cause issues with other electrical devices. Furthermore, noticeable flickering and / or humming may occur.

[0007] Based on this, the invention aims to provide a power supply unit with enhanced electromagnetic compatibility.

[0008] This task is solved in a power supply unit of the type mentioned at the beginning by a pulse unit for providing a pulse sequence, wherein the modification unit can modulate the load voltage with the pulse sequence to generate the modified voltage, and wherein the pulse sequence is variable in order to modify the adjusted voltage and thus control the temperature of the heating element.

[0009] By modulating the load voltage with the pulse sequence, the load voltage can be modified, allowing the power consumption of the heating element to be controlled. By changing the pulse sequence, the modified voltage can also be altered and adjusted, resulting in the ability to vary the heating power or the temperature of the heating element. Furthermore, modulating the load voltage with the pulse sequence ensures that the fundamental shape of the load voltage remains unchanged or is only slightly modified, which guarantees good electromagnetic compatibility and ensures compliance with the flicker and the harmonics test. The modification unit can be designed as a modulation unit. Therefore, the modified voltage can be a modulated voltage.

[0010] In view of the load voltage and the modified voltage, it has proven to be advantageous when the frequency and the amplitude of the modified voltage correspond to the frequency and the amplitude of the load voltage.

[0011] This means that the frequency and the amplitude remain the same, or rather that the modulation using the pulse sequence has no or no significant impact on the frequency and the amplitude of the voltage. Since the voltage profile of the modulated and modified voltage is very close to the voltage profile of the load voltage before the pulse sequence is superimposed, a high level of electromagnetic compatibility is ensured. The waveform of the load voltage can correspond to the envelope curve of the modified curve.

[0012] However, although the voltage profile does not change significantly, the modulation changes the effective voltage value, meaning that the load voltage and the modified voltage have different average voltages, thereby changing the effective power of the heating element and / or the temperature of the heating element. The average voltage of the load voltage is higher than the average voltage of the modified voltage, meaning the modification unit serves so lower the effective voltage value and therefore also the effective power supplied to the heating element.

[0013] According to an advantageous refinement of the invention, it is provided that the pulse duration and / or the period duration of the pulsed signal is adjustable. By changing the pulse duration and / or the period duration, the modified voltage or the effective value of the modified voltage can be adjusted. To simplify control, it may be advantageous to adjust either the pulse duration or the period duration. Advantageously, the amplitude of the pulse sequence remains constant. The individual pulses can be designed as rectangular signals, allowing the pulse sequence to switch abruptly between two different voltage levels. In the case of a change in pulse width, this is referred to as pulse width modulation, whereas a change in the period and thus the spacing between two pulses is referred to as pulse pause modulation. In both cases, the modified load is generated by modulating the load voltage with the periodical rectangular signals of the pulse sequence.

[0014] To ensure a good match between the waveforms before and after modulation, meaning the load voltage and the modified voltage, the pulse frequency of the pulse sequence is higher than the frequency of the load voltage. Preferably, the frequency is more than twice as high, particularly preferably more than five times as high, and especially preferably more than six times as high as the frequency of the load voltage. Due to the higher frequency of the pulse sequence, which can also be adjustable and does not necessarily have to remain constant, small portions of the load voltage can be cut out at many points, so that the fundamental waveform is preserved as accurately as possible. In contrast to a phase angle control, e.g. leading-edge or trailing edge control, many small sections are cut out of the waveform instead of removing larger sections at the beginning or end.

[0015] The pulse unit can be connected to an external power supply for generating the pulsed signals or the pulse sequence. This power supply can advantageously be the AC voltage source to which the power supply unit or the heater can be connected via the connector. The pulse unit can be electronically connected to the modification unit by means of electric conductors. Further, the elements can be arranged on a common circuit board and be designed as SMDs.

[0016] According to a further aspect of the invention, the power supply unit has a switch, in particular a rotary switch, for adjusting the pulse duration and / or the period duration. By operating the switch or rotating the rotary switch, the pulse duration or the period duration can be changed manually, thereby altering the effective and average value of the modified voltage. For example, if the temperature of the medium to be heated is too high, operating the switch can shorten the pulse durations, resulting in larger gaps between individual pulses. This leads to a reduction in the effective voltage value of the modified voltage, and vice versa.

[0017] Furthermore, an automatic setpoint / actual value control can also be implemented. This means that the desired temperature can be set via a corresponding controller, and depending on the deviation between the setpoint and actual value, the pulse duration and / or period duration of the pulse sequence is adjusted automatically. For controlling, a PID controller can be used, which can be coupled to a temperature sensor that measures the temperature of the medium to be heated. Alternatively or additionally, a temperature sensor can be provided to measure the surface temperature of the heating element. Both temperature sensors can be integrated into the control loop controlling the pulse sequence.

[0018] According to a particularly advantageous refinement of the invention, it is proposed that the modification unit is designed as an AC Chopper. The AC Chopper works by chopping the AC waveform of the load voltage at specific points. Due to the chopping, the load voltage is modified, and thus the modified voltage is generated. Through the AC Chopper, small portions can be cut out from the load voltage, particularly periodically and depending on the pulse sequence, so that the basic waveform is preserved. It may be provided that the pulse sequence determines which areas of the load voltage are chopped by the AC Chopper. It may be arranged that the load voltage can pass through the AC Chopper when the pulse sequence reaches its high value, i.e., when a certain voltage is present at the pulse sequence input of the AC Chopper. If the pulse sequence has a low value and, for example, no voltage is present at the pulse sequence input of the AC Chopper, the load voltage cannot pass through the AC Chopper, and thus the load voltage is chopped. Due to the rapid switching between low and high voltages of the pulse sequence, portions of the load voltage can periodically be cut out without altering the amplitude or frequency of the load voltage. As described above, the pulse sequence can periodically switch between its low voltage value and its high voltage value.

[0019] Furthermore, the AC Chopper can multiply the load voltage and the pulse sequence. The pulse sequence can take values of zero or one, meaning that when a pulse is present, the value is set to one and when no pulse is present the value is set to zero. When a pulse is present, the load voltage can pass through the AC Chopper, in particular without changing the load voltage. When no pulse is present and the value is therefore zero, there is no voltage at the output of the AC Chopper. This change between the voltage of the load voltage and zero at the output of the AC Chopper generates the chopped modified voltage. In other words, the AC Chopper can function as an AND gate, allowing the load voltage to pass only when there is a voltage at the input for the pulse sequence. This makes it possible to cut out portions of the load voltage waveform between two pulses, thereby reducing the effective voltage value at the output of the AC Chopper, i.e., the modified voltage.

[0020] With regard to the design of the modification unit, it has proven advantageous if it is designed as a semiconductor. This design allows the pulse sequence to be modulated onto the load voltage, or rather the load voltage to be modulated by the pulse sequence. The semiconductor may have two inputs, one for the load voltage and one for the pulse sequence, as well as an output for the modulated voltage. Due to the low switching times of semiconductors, very short pulses can be processed, allowing the load voltage to be chopped very finely if necessary. The finer the load voltage is divided, the better the electromagnetic compatibility can be.

[0021] According to an advantageous refinement of the invention, it is provided that the modification unit is designed as a CMOS. CMOS stands for Complementary Metal-Oxide-Semiconductor, and a CMOS is based on the combination of p-channel (PMOS) and n-channel MOSFETs (NMOS) in a complementary arrangement. CMOS devices are characterized by very high switching speeds and require no or minimal energy in the idle state. They are also less susceptible to interference signals.

[0022] According to an alternative embodiment, it is provided that the modification unit is designed as an IGBT. IGBT stands for Insulated Gate Bipolar Transistor, and such a transistor combines the advantages of MOSFETs and bipolar transistors. In particular, an IGBT is characterized by low drive power and a low voltage drop in the conducting state. Furthermore, high switching speeds can also be achieved with an IGBT.

[0023] According to an advantageous refinement of the invention, it is provided that a rectifier, in particular a full-wave rectifier, is provided for generating a rectified load voltage. A rectifier is capable of converting the complete cycle of the alternating load voltage into a rectified alternating current. This ensures that the rectified voltage no longer contains any negative voltage components after rectification. It may be provided that the negative voltage components are set to zero or that the negative wave components are changed into positive wave components. This is made possible by a full-wave rectifier.

[0024] With regard to the connection of the rectifier, it has proven advantageous if it is connected between the connector for connecting with the voltage source and the modification unit. At the input, the load voltage provided by the voltage source can be present, and at the output, a rectified load voltage can be present. The rectified load voltage can then be modulated onto the pulse sequence. The rectification can thus occur before modulation and, therefore, before the actual power control.

[0025] With regard to the initially mentioned task, an electric heater with a heating element and a power supply unit for supplying electrical energy to the heating element is proposed, wherein the power supply unit is designed in the manner described above, and wherein the heating element is designed as an impedance, in particular as a resistive load. Through this design, the heating element heats up depending on the current flowing through the heating element. The heating and, thus, the temperature of the heating element can be varied by adjusting the modified voltage that is supplied to the heating element via the pulse sequence. By varying the pulse sequence, e.g., by varying the pulse duration and / or the period duration, the potential difference over the heating element and thus, the thermal power output by the heating element, can also be adjusted. The heating element can convert the electrical power into thermal power, which can then be used to heat a medium or a medium flow.

[0026] With regard to the electric heater, it has proven advantageous if it is designed as a convection heater, a radiant heater, a flow heater, or a boiler. A convection heater is primarily used to heat air. The convection can be purely passive in nature, but alternatively, a fan can be provided to accelerate the air to be heated, ensuring improved heat transfer from the heating element to the air. Typical examples of such active convection heaters are, for example, fan heaters or hair dryers. A radiant heater is characterized by a high surface temperature and primarily heats objects by radiating heat rather than through heat transfer via convection. The heating element can therefore also be designed as an infrared heating element. A flow heater and a boiler are primarily used to heat water. A flow heater heats a water flow, which can be directly used after heating. A boiler, on the other hand, heats a water reservoir or maintains the water in a reservoir at a certain temperature, allowing it to be used at a specific time. The heating element can, especially in the case of air heating, be mounted on a wall or ceiling. It is also possible to mount it on the floor or on a stand, particularly a movable stand.

[0027] Further, the electric heater can comprise a control loop, wherein the power supply unit, in particular the modification unit and the pulse unit, is integrated into the control loop for regulating the temperature of the heating element. The control loop can comprise one or more thermometers and one or more controls, in particular PID-controls, that control the pulse sequence and therefore the effective voltage value of the modified voltage that is supplied to the heating element.

[0028] With regard to the initially mentioned task, a method for powering a heating element of an electric heater with a power supply unit, particularly with a power supply unit as described above, is suggested, wherein the power supply unit has a connector for connecting it to an AC voltage source that can generate a load voltage, and a modification unit, which for controlling the temperature of the heating element converts the load voltage into a modified voltage, and with a pulse unit that provides a pulse sequence, wherein the modification unit modulates the load voltage with the pulse sequence thereby generating the modified voltage, and wherein the pulse sequence is being varied in order to modify the adjusted voltage and thus control the temperature of the heating element. The advantages already described in regard to the power supply unit and the heater are achieved.

[0029] In view of the method, it is proposed that that the effective voltage value of the load voltage is being reduced by the modulation with the pulse sequence, wherein the overall frequency and the amplitude of the load voltage remains unchanged. The effective voltage value is modified depending on the pulse sequence, so that the voltage across the heating element and thus the power of the heating element can be regulated. The modification unit is advantageously designed such that the overall amplitude and frequency of the voltage are not changed, but only the effective value of the voltage.

[0030] According to an advantageous refinement of the method, it has proven beneficial if the pulse duration and / or the period duration is adjusted depending on the desired temperature of the heating element. For example, if the heating element has not yet reached its setpoint temperature, the pulse duration can be extended while keeping the period duration constant, as this results in a smaller portion of the load voltage being cut out. The adjustment of the pulse duration and / or the period duration can be carried out manually, for instance, by turning a rotary controller, or by a control loop as explained above.

[0031] Overall, the method may provide that the output voltage is segmented by the pulse sequence. The larger the portions that are cut from the load voltage and not allowed to pass through the modification unit, the less power reaches the heating element, and the less it heats up.

[0032] Further details and advantages will be explained below with reference to the attached drawings. These show: Fig. 1a schematic view of a circuit diagram of a heater according to a first embodiment; Fig. 2voltages at different locations of the heater according to Fig. 1; Fig. 3a schematic view of a circuit diagram of a heater according to a second embodiment; Fig. 4voltages at different locations of the heater according to Fig. 3.

[0033] The representation of Fig. 1 schematically and in a simplified manner shows a block diagram of an electric heater 10, which can be used to heat air. The heater 10 comprises a heating element 10.1, which is designed as an ohmic resistor and heats up when electrical energy is supplied. This heat can then be transferred to the passing air to warm it.

[0034] The heater 10 includes a power supply unit 1, which allows the heater 10 to be connected to an AC voltage source 20, as shown in Fig. 1. For this connection, the power supply unit 1 features a connector 2, which can be a plug that is inserted into a socket, enabling the heater 10 to be connected to a public AC power grid in a conventional manner. If this alternating voltage V1 were to be applied directly to the heating element 10.1, it would heat up excessively, potentially causing damage. Therefore, the power supply unit 1 comprises a modification unit 3, which regulates and reduces the effective voltage value of the load voltage V1 generated by the AC voltage source 20. To regulate the voltage applied to the heating element 10.1, the modification unit 3 is coupled with a pulse unit 4. This pulse unit 4 provides a pulse sequence P of periodic pulses, which allows the effective voltage value of the load voltage V1 to be reduced if desired.

[0035] The diagrams in Fig. 2 illustrate the voltage curves at different points of the power supply unit 10. Between the AC voltage source 20 and the input of the modification unit 3, a harmonic AC voltage V1 is initially present, as shown in the upper diagram of Fig. 2. At the input of the modification unit 3 for the pulse sequence P, a periodic pulsed square wave signal is present and supplied to the modification unit 3, as illustrated in the middle diagram of Fig. 2.

[0036] The modification unit 3 functions as an AC chopper, which can modulate the load voltage V1 with the pulse sequence P. In this process, the voltage V1 and the pulse sequence P are multiplied, so that whenever a pulse is present at the input for the pulse sequence P, the load voltage V1 can pass through the modification unit 3, whereas when no pulse is present at the corresponding input, the voltage is blocked. Consequently, due to the high frequency pulses of the pule sequence, periodic segments can be cut out of the waveform of the load voltage V1 depending on the pulse sequence P.

[0037] At the output of the modification unit 3, the modified voltage M is present. As shown in Fig. 2, the amplitude and frequency of the modified voltage M match those of the load voltage V1, meaning that the envelope curve of the modified voltage M corresponds to the waveform of the original load voltage V1. Thus, the fundamental waveform remains unchanged by the modification unit 3. This ensures good electromagnetic compatibility of the heater 10 and prevents interference with other devices. Nevertheless, the effective value of the modified voltage M is lower than that of the load voltage V1, reducing the thermal power of the heating element 10.1 accordingly.

[0038] By adjusting the pulse sequence P, the portion of the load voltage V1 that is cut out can be varied. If the pulse spacing is increased while maintaining the same pulse width, larger sections of the load voltage V1 are cut out, decreasing the power of the heating element 10.1. Conversely, if the pulse width is increased while keeping the period constant, a larger portion of the load voltage V1 can pass through the modification unit 3, and a smaller portion is cut out. This increases the effective voltage value of the modified voltage M and thus the power of the heating element 10.1. Consequently, the power of the heating element 10.1 can be regulated by adjusting the pulse width.

[0039] The second embodiment, as illustrated in Figs. 3 and 4, differs in that a full wave rectifier 5 is placed upstream of the modification unit 3. This full wave rectifier 5 converts the harmonic AC load voltage V1 into a rectified AC load voltage V2. In this process, the negative voltage components of the load voltage V1 are inverted into positive components, resulting in the rectified pulsating load voltage V2 shown in Fig. 2. However, this rectification has no significant effect on the effective value of the load voltage V1, V2.

[0040] At the input of the modification unit 3, the pulsed load voltage V2 is now present, which is then modulated by the pulse sequence P in the manner previously described to set the effective voltage value. The result at the output of the modification unit 3 is again a voltage waveform that matches the load voltage V1 in terms of frequency and amplitude but has a lower effective value due to the removed segments of the load voltage V2. For further details, reference is made to the description of the first embodiment.

[0041] Overall, by adjusting the pulse sequence P and particularly the pulse width, the effective voltage value of the load voltage V1, V2 can be reliably controlled, allowing the heating power of the heating element 10.1 to be adjusted. Additionally, high electromagnetic compatibility can be ensured, as the fundamental waveform of the load voltage V1, V2 and the modified voltage M remain consistent.Bezugszeichen:

[0042] 1power supply unit 2connector 3modification unit 4pulse unit 5rectifier 20AC voltage source 10heater 10.1heating element Ppulse sequence V1load voltage V2load voltage Mmodified voltage

Claims

1. Power supply unit for a heating element (10.1) of an electric heater (10) with a connector (2) for connecting the power supply unit to an AC voltage source (20) that can generate a load voltage (V1, V2), and a modification unit (3), which can for controlling the temperature of the heating element (10.1) convert the load voltage (V1, V2) into a modified voltage (M), characterized by a pulse unit (4) for providing a pulse sequence (P), wherein the modification unit (3) can modulate the load voltage (V1, V2) with the pulse sequence (P) to generate the modified voltage (M), and wherein the pulse sequence (P) is variable in order to modify the adjusted voltage (M) and thus control the temperature of the heating element (10.1).

2. Power supply unit according to claim 1, characterized in that the frequency and the amplitude of the modified voltage (M) correspond to the frequency and the amplitude of the load voltage (V1, V2).

3. Power supply unit according to claims 1 or 2, characterized in that the pulse duration and / or the period duration of the pulsed signal is adjustable.

4. Power supply unit according to one of the preceding claims, characterized in that the frequency of the pulse sequence (P) is higher than the frequency of the load voltage (V1, V2).

5. Power supply unit according to one of the preceding claims, characterized by a switch, in particular a rotary switch, for adjusting the pulse duration and / or the period duration.

6. Power supply unit according to one of the preceding claims, characterized in that the modification unit (3) is designed as an AC Chopper.

7. Power supply unit according to one of the preceding claims, characterized in that the modification unit (3) is designed as a semiconductor.

8. Power supply unit according to claim 7, characterized in that the modification unit (3) is designed as a CMOS.

9. Power supply unit according to claim 7, characterized in that the modification unit (3) is designed as an IGBT.

10. Power supply unit according to one of the preceding claims, characterized by a rectifier (5), in particular a full wave rectifier, for generating a rectified load voltage (V2).

11. Power supply unit according to claim 1, characterized in that the rectifier (5) is connected between the connector (2) for connecting with the voltage source (20) and the modification unit (3).

12. Electric heater with a heating element (10.1) and a power supply unit (1) for supplying electrical energy to the heating element (10.1) according to one of the preceding claims, wherein the heating element (10.1) is designed as an impedance, in particular as a resistive load.

13. Electric heater according to claim 12, characterized in that the electric heater (10) is designed as a convection heater, a radiant heater, a flow heater, or a boiler.

14. Method for powering a heating element (10.1) of an electric heater (10) with a power supply unit (1), particular with a power supply unit (1) according to one of the claims 1 to 11, wherein the power supply unit (1) has a connector (2) for connecting it to an AC voltage source (20) that can generate a load voltage (V1, V2), and a modification unit (3), which for controlling the temperature of the heating element (10.1) converts the load voltage (V1, V2) into a modified voltage (M), characterized by a pulse unit (4) that provides a pulse sequence (P), wherein the modification unit (3) modulates the load voltage (V1, V2) with the pulse sequence (P), thereby generating the modified voltage (M), and wherein the pulse sequence (P) is being varied in order to modify the adjusted voltage (M) and thus control the temperature of the heating element (10.1).

15. Method according to claim 14, characterized in that the effective voltage value of the load voltage (V1, V2) is being reduced by the modulation with the pulse sequence (P), wherein the overall frequency and the amplitude of the load voltage (V1, V2) remains unchanged.

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