Method of operating electric heater and electric heater

Abstract

The invention relates to a method of operating an electric heater and an electric heater. Specifically, the invention relates to a method (2) for operating an electric heater (1) having at least two resistive elements (TFR1, TFR2). A pulse width modulated operating voltage (U) is applied to the resistive elements (TFR1, TFR2) such that the voltage pulses of the respective voltages (UTFR1, UTFR2) at the resistive elements (TFR1, TFR2) are shifted in time, thereby reducing the maximum current (IMAX) in the heater (1). The invention also relates to an electric heater (1) for carrying out the method (2) according to the invention.

Description

Technical Field

[0001] The invention relates to a method for operating an electric heater for a battery-electric vehicle, the electric heater having at least two resistance elements, according to the preamble of claim 1. The invention also relates to an electric heater for carrying out the method. Background Art

[0002] In battery-electric vehicles, fluids can be heated using electric heaters, which can then be used to heat various vehicle components. To generate heat, the electric heaters can, for example, incorporate thick-film elements or so-called TFR elements (TFRs). These thick-film elements can be connected to flat tubes through which the fluid flows in a heat-transferring manner. When voltage is applied to the heater, heat is generated in the thick-film element, which is then transferred to the fluid.

[0003] CN 211831201 U discloses, for example, an electric heater having a TFR element.

[0004] In battery-electric vehicles, heating power requirements must be met across a wide voltage range. For example, the traction battery of a battery-electric vehicle can provide a voltage between 250 V and 900 V, depending on its state of charge. To ensure controllability and regulation of the heater at high voltages, the heater can be controlled using a PWM signal (Pulse Width Modulation). However, this approach cannot reduce the maximum current in the heater. This overloads the supply network and can potentially exceed predefined current limits. Summary of the Invention

[0005] It is therefore an object of the present invention to provide an improved or at least alternative embodiment of a method of operating an electric heater, wherein the disadvantages are overcome.It is also an object of the present invention to provide a corresponding heater for carrying out the method.

[0006] According to the invention, this object is achieved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0007] The invention is based on the general idea of providing a suitable design of the thick film element in the electric heater and a suitable electrical interconnection to ensure powerful and efficient heating and minimized load on the power supply network.

[0008] A method according to the present invention is provided for operating an electric heater for a battery electric vehicle, the electric heater having at least two resistive elements. The heater is operated at an operating voltage that is between a minimum voltage and a maximum voltage and is pulse-width modulated with a duty cycle. The heater is controlled and / or regulated to generate a heating power between the required minimum and maximum heating powers. According to the present invention, the heater can operate at operating voltages within a first voltage range having relatively low voltage values, within a second voltage range having relatively medium voltage values, and within a third voltage range having relatively high voltage values. When the heater is operated at an operating voltage within the first voltage range, the resistive elements are connected in parallel with each other, and the operating voltage is pulse-width modulated with a duty cycle equal to 100% and applied to the resistive elements. When the heater is operated at an operating voltage within the second voltage range, the resistive elements are connected in parallel with each other, and the operating voltage is pulse-width modulated with a duty cycle between 100% and 50%. The operating voltage is applied to the resistive elements in such a manner that voltage pulses corresponding to the respective voltages at the resistive elements of the operating voltage alternate in time. When the heater is operated at an operating voltage within a third voltage range, the resistive elements are connected in parallel with each other, and the operating voltage is pulse-width modulated with a duty cycle between 50% and 0%. The operating voltage is applied to the resistive elements in such a manner that voltage pulses corresponding to respective voltages at the resistive elements of the operating voltage alternate in time.

[0009] The required minimum heating power is the minimum heating power that the heater should provide according to external specifications. The required maximum heating power is the maximum heating power that the heater should provide according to external specifications. Therefore, the required minimum heating power and the required maximum heating power may be specified externally, for example, and may differ from the minimum and maximum heating powers that the heater can generate. For example, the operating voltage may be provided by the traction battery of a battery electric vehicle. The traction battery provides a DC voltage between the minimum and maximum voltages (e.g., between 250 V and 900 V), which is then pulse-width modulated and provided to the heater as the operating voltage.

[0010] Within the first voltage range, an operating voltage is supplied to the heater at a relatively low voltage value. Because the operating voltage within the first voltage range is low, the maximum current flowing through the heater is also low. At this operating voltage, the heating power achieved by the heater is lower than the required maximum heating power, even at a 100% duty cycle, and the heating power generated by the heater does not need to be reduced.

[0011] In the second voltage range, the operating voltage is provided to the heater at a relatively medium voltage value. At a duty cycle of 100%, the heating power generated by the heater will exceed the required maximum heating power. To this end, the operating voltage is pulse-width modulated, thereby reducing the heating power generated by the heater to the required value. The operating voltage is applied to the resistor element in such a way that the voltage pulses of the individual voltages at the resistor element corresponding to the operating voltage alternate in time. In other words, the voltage pulses are shifted in time so that the voltage pulses of a single voltage at one resistor element are located between the voltage pulses of a single voltage at another resistor element. For example, the individual voltages at the resistor element corresponding to the operating voltage can be shifted relative to each other by half the cycle duration of the pulse-width modulated operating voltage. The individual voltages are applied alternately to the resistor element over time, and the individual currents also flow alternately in the resistor element over time. As a result, at least the average current in the heater can be reduced.

[0012] Within the second voltage range, the duty cycle of the pulse-width modulated operating voltage varies between 100% and 50%. Within the second voltage range, the duty cycle of the pulse-width modulated operating voltage may decrease from 100% to 50% as the operating voltage increases. An overlap time, during which the voltage pulses corresponding to the respective voltages at the resistive element of the operating voltage overlap in time, is not zero but may be minimized. In particular, the overlap time may be less than the product of a period duration of the pulse-width modulated operating voltage and a difference between double the duty cycle and 100%, divided by 100%.

[0013] In the third voltage range, the operating voltage is provided to the heater at a relatively high voltage value. Similar to the second voltage range, at a 100% duty cycle, the heating power generated by the heater will exceed the required maximum heating power. To this end, the operating voltage is pulse-width modulated to reduce the heating power generated by the heater to the required value. The operating voltage is applied to the resistor element in such a way that the voltage pulses of the individual voltages at the resistor element corresponding to the operating voltage alternate in time. In other words, the voltage pulses are shifted in time so that the voltage pulses of a single voltage at one resistor element are located between the voltage pulses of a single voltage at another resistor element.

[0014] Within the third voltage range, the duty cycle of the operating voltage varies between 50% and 0%. Within the third voltage range, as the operating voltage increases, the duty cycle of the pulse-width modulated operating voltage can decrease from 50% to 0%. Because the duty cycle is between 50% and 0%, the overlap time of the voltage pulses of the individual voltages at the resistive elements corresponding to the operating voltage can be zero. To this end, the individual voltages at the resistive elements corresponding to the operating voltage can be shifted relative to each other by half the cycle duration of the pulse-width modulated operating voltage. As a result, the voltage pulses of the individual voltages at the resistive elements corresponding to the operating voltage do not overlap in time. Therefore, the individual currents at the resistive elements also do not overlap in time. As a result, the maximum current in the heater—which is the sum of the individual currents at the resistive elements—is always equal to the corresponding individual currents at the respective resistive elements. The maximum current at the heater is thus reduced.

[0015] In summary, the heater can be controlled and / or adjusted to a heating power between a minimum required heating power and a maximum required heating power over a wide voltage range. The maximum current during heater operation can be reduced, thereby reducing the load on the power supply network. The control unit can be easily implemented using a small number of switching elements, such as IGBTs.

[0016] The resistance of the resistance element can be selected so that the heater provides the required minimum heating power at the minimum voltage. This means that the minimum heating power of the heater can be achieved even at a low operating voltage.

[0017] At least one of the resistance elements may comprise at least two resistance bars that can be connected in series and in parallel with each other. Thus, depending on the operating voltage applied, the resistance bars of the resistance element may be connected in parallel or in series. The individual resistance bars may be connected in parallel at relatively low and / or relatively medium voltage values of the operating voltage, and in series at relatively medium and / or relatively high voltage values of the operating voltage. In this way, the resistance of the resistance element may be varied, and further variations may be achieved by operating the heater. Alternatively or additionally, the individual resistance bars or some of the resistance bars of the resistance element may be switched off depending on the operating voltage. Thus, the operating voltage may be applied only to a single resistance bar or some of the resistance bars of the resistance element. Here, further variations may also be achieved by operating the heater.

[0018] In a first possible embodiment of the method, the heater can in particular be operated with an operating voltage only in the three voltage ranges mentioned above.

[0019] In order to define the three voltage ranges, a first voltage and a second voltage can be defined. The first voltage can be defined as a voltage that generates the required maximum heating power at a duty cycle equal to 100%. The second voltage can be defined as a voltage that generates the required maximum heating power at a duty cycle equal to 50%. Within the first voltage range, the operating voltage can be provided with a relatively low voltage value between the minimum voltage and the first voltage. In the second voltage range, the operating voltage can be provided with a relatively medium voltage value between the first voltage and the second voltage. In the third voltage range, the operating voltage can then be provided with a relatively high voltage value between the second voltage and the maximum voltage. In other words, the entire voltage range between the minimum voltage and the maximum voltage provided by the traction battery of the battery electric vehicle can be divided into three voltage ranges.

[0020] In a second possible embodiment of the method, the heater can be operated within a fourth voltage range having relatively very high voltage values. When the heater is operated at an operating voltage within the fourth voltage range, the resistive elements can be connected in series with one another. When the resistive elements are connected in series, the maximum current in the heater can be reduced while the generated heating power remains constant.

[0021] In order to define the four voltage ranges, a first voltage and a second voltage can be defined. The first voltage can be defined as the voltage that generates the required maximum heating power at a duty cycle equal to 100%. The second voltage can be defined as the voltage that generates the required maximum heating power at a duty cycle equal to 50%. Within the first voltage range, the operating voltage can then be provided with a relatively low voltage value between the minimum voltage and the first voltage. In the second voltage range, the operating voltage can then be provided with a relatively medium voltage value between the first voltage and the second voltage. In the third voltage range, the operating voltage can then be provided with a relatively high voltage value between the second voltage and twice the first voltage. In the fourth voltage range, the operating voltage can then be provided with a relatively very high voltage value between twice the first voltage and the maximum voltage. In other words, the entire voltage range between the minimum voltage and the maximum voltage provided by the traction battery of the battery electric vehicle can be divided into four voltage ranges.

[0022] In the present invention, the relatively low voltage value is smaller than the relatively medium voltage value, the relatively high voltage value, and the relatively very high voltage value. The medium voltage value is smaller than the relatively high voltage value and the relatively very high voltage value. The relatively high voltage value is smaller than the relatively very high voltage value. The voltage ranges assigned to the respective voltage values do not overlap and are adjacent to each other. The voltage range covers the entire voltage range supplied to the heater between the minimum voltage and the maximum voltage.

[0023] The present invention also relates to a heater for heating a fluid in a battery-electric vehicle. The heater comprises at least two resistance elements and at least three flat tubes, each resistance element having an electrical resistance, through which a fluid can flow. The resistance elements and flat tubes are stacked such that each resistance element is arranged between two flat tubes. Preferably, the number of flat tubes in the heater exceeds the number of resistance elements by one. The resistance elements are connected to adjacent, i.e., neighboring, flat tubes in a heat-transferring manner. The heater further comprises a control unit for controlling and / or regulating the resistance elements. According to the present invention, the heater is configured to perform the above-described method.

[0024] The resistance elements of the heater can be, in particular, thick film heating elements or so-called TFR heating elements. In particular, the resistance elements can be flat. For example, the resistance elements can be connected to adjacent flat tubes using a thermally conductive adhesive. Other thermally conductive contact media are also possible. The resistance elements can be identical components. They can have a mirror-symmetrical design to improve heat transfer between the resistance elements and the flat tubes, i.e., the fluid flowing therein. The resistance of at least some of the resistance elements can be different or the same.

[0025] The resistive elements of the heater can be connected in parallel with one another. Thus, the heater can be configured to perform the method according to the first embodiment described above. Alternatively, the resistive elements of the heater can be connected in parallel and in series with one another. In this manner, the heater can be configured to perform the method according to the first and / or second embodiments described above.

[0026] At least one of the resistor elements may include at least two resistor bars, each having a resistance. The resistor bars of the resistor element may be connected in parallel with one another. The resistances of at least some of the resistor bars of the resistor element may be different or the same. The resistor bars of the resistor element may be connected in parallel and in series with one another. Individual resistor bars or some of the resistor bars of the resistor element may be switchable. In this manner, the resistance of the resistor element may be adjustable, i.e., varied depending on the operating voltage.

[0027] Further important features and advantages of the invention are apparent from the dependent claims, the drawings and the associated description of the drawings with reference to the drawings.

[0028] It is to be understood that the features mentioned above and those still to be explained below can be used not only in the combination indicated in each case but also in other combinations or alone, without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components.

[0030] They are schematically shown in the following figures respectively.

[0031] Figure 1 is a cross-sectional view of a heater according to the present invention, the heater having two resistive elements;

[0032] Figure 2 is a view of a heater according to the present invention in a first embodiment;

[0033] Figures 3 to 5 is a time correlation diagram of each voltage at the resistance element of the heater according to the present invention in different voltage ranges in the first embodiment;

[0034] Figure 6 is a voltage dependence diagram of the heating power of the heater according to the present invention in the first embodiment;

[0035] Figure 7 is a voltage dependence diagram of the current in the heater according to the present invention in the first embodiment;

[0036] Figure 8 and Figure 9 1. FIG. 1 is a view of a heater in different switching states according to a second embodiment of the present invention;

[0037] Figure 10 is a voltage dependence diagram of the heating power of the heater according to the present invention in the second embodiment;

[0038] Figure 11 is a voltage dependence diagram of the current in the heater according to the present invention in the second embodiment;

[0039] Figure 12 and Figure 13 1 and 2 are views showing the heater according to the present invention in different switching states in a third embodiment. DETAILED DESCRIPTION

[0040] Figure 1 A cross-sectional view of a heater 1 according to the invention is shown, which is configured for use in a battery electric vehicle and is used to heat a fluid F. To this end, the heater 1 carries out a method 2 according to the invention, as will be explained in more detail below. The heater 1 comprises two resistance elements TFR1 and TFR2 and three flat tubes 3 through which the fluid F flows. The resistance elements TFR1 and TFR2 are thick film heating elements or so-called TFR heating elements and are flat. In the heater 1, the resistance elements TFR1 and TFR2 are stacked and connected to the flat tubes 3 in a heat-transferring manner. This allows the resistance elements TFR1 and TFR2 to transfer the generated heat to the fluid F in the flat tubes 3. The resistance elements TFR1 and TFR2 can be identical components and have the same resistance within the range of manufacturing tolerances.

[0041] Figure 2 The figure shows an electric heater 1 according to the present invention in a first embodiment. In the first embodiment, the resistance elements TFR1 and TFR2 are connected in parallel with each other. The heater 1 includes a control unit 4 for controlling and / or regulating the resistance elements TFR1 and TFR2. The control unit 4 includes switching elements HS (HS: high side) and LS (LS: low side) for switching and protecting the respective resistance elements TFR1 and TFR2. The switching elements HS and LS are, for example, IGBTs. The heater 1 is provided to perform the following operations, which will be referred to below. Figures 3 to 7 Method 2 according to the invention is explained in more detail.

[0042] Figures 3 to 5 A time correlation diagram of the operating voltage U at the resistance elements TFR1 and TFR2 of the heater 1 in the first embodiment is shown. Figure 6 A voltage dependence diagram of the heating power Q in the heater 1 in the first embodiment is shown. Figure 7 A voltage dependence graph of the current I in the heater 1 in the first embodiment is shown.

[0043] refer to Figure 6 In method 2, heater 1 is operated at an operating voltage U, where operating voltage U is between a minimum voltage U_MIN and a maximum voltage U_MAX. Minimum voltage U_MIN and maximum voltage U_MAX are specified by the voltage available from the traction battery of the battery-electric vehicle. Operating voltage U is pulse-width modulated, for example, using a square wave signal with a DC duty cycle between 0% and 100%. When operated at operating voltage U, heater 1 generates heating power Q. In method 2, heater 1 is controlled and / or regulated such that heating power Q lies between the required minimum heating power Q_MIN and the required maximum heating power Q_MAX. The resistances of resistor elements TFR1 and TFR2 are selected so that minimum heating power Q_MIN is achieved at minimum voltage U_MIN. To define a voltage range, a first voltage U_PWM-ON and a second voltage U_PWM-50 can be defined. Thus, first voltage U_PWM-ON is the voltage that achieves maximum heating power Q_MAX at a DC duty cycle of 100%. Therefore, the second voltage U_PWM-50 is a voltage that can achieve the maximum heating power Q_MAX when the duty cycle DC is equal to 50%.

[0044] refer to Figure 6, the operating voltage U can be provided in a first voltage range I, a second voltage range II, and a third voltage range III. In the first voltage range I, the operating voltage U has a relatively low voltage value between the minimum voltage U_MIN and the first voltage U_PWM-ON. In the second voltage range II, the operating voltage U has a relatively medium voltage value between the first voltage U_PWM-ON and the second voltage U_PWM-50. In the third voltage range III, the operating voltage U has a relatively high voltage value between the second voltage U_PWM-50 and the maximum voltage U_MAX.

[0045] refer to Figure 3 In a first voltage range I, operating voltage U is pulse-width modulated with a DC duty cycle of 100% and applied to resistive elements TFR1 and TFR2 of heater 1. A single voltage U_TFR1 is applied to resistive element TFR1, and a single voltage U_TFR2 is applied to resistive element TFR2. In the first voltage range I, heating power Q remains below the maximum heating power Q_MAX, even with a DC duty cycle of 100%. Heating power Q achieves maximum heating power Q_MAX solely through the first voltage U_PWM-ON.

[0046] refer to Figure 4 In a second voltage range II, an operating voltage U is pulse-width modulated with a duty cycle DC between 100% and 50% and applied to the resistive elements TFR1 and TFR2 of heater 1. As the operating voltage U increases, the duty cycle DC decreases from 100% to 50%. The voltage pulses of the individual voltages U_TFR1 and U_TFR2 at the resistive elements TFR1 and TFR2 alternate in time, that is, are displaced in time from one another. Here, the individual voltages U_TFR1 and U_TFR2 are equal to one another. The displacement of the individual voltages U_TFR1 and U_TFR2 relative to one another minimizes the overlap time t_UB of the individual voltage pulses. In this example, the individual voltages U_TFR1 and U_TFR2 are displaced relative to one another by half the period duration T of the pulse-width modulated operating voltage U. In the second voltage range II, a heating power Q greater than the maximum heating power Q_MAX can be achieved. By reducing the duty cycle DC, the heating power Q can be adjusted to lie between the minimum heating power Q_MIN and the maximum heating power Q_MAX.

[0047] refer to Figure 5In the third voltage range III, the operating voltage U is pulse-width modulated with a DC duty cycle between 50% and 0% and applied to the resistive elements TFR1 and TFR2 of heater 1. Needless to say, in practice, the entire range between 50% and 0% is not used. In particular, a DC duty cycle close to 0% may be irrelevant in practice. As the operating voltage U increases, the DC duty cycle decreases from 50% to 0%. The voltage pulses of the respective voltages U_TFR1 and U_TFR2 at the resistive elements TFR1 and TFR2 alternate, that is, are shifted in time. Here, the respective voltages U_TFR1 and U_TFR2 are equal to each other. The shift of the respective voltages U_TFR1 and U_TFR2 relative to each other is such that the overlap time t_UB is zero. In this example, the respective voltages U_TFR1 and U_TFR2 are shifted relative to each other by half the period duration T of the pulse-width modulated operating voltage U. In the third voltage range III, a heating power Q greater than the maximum heating power Q_MAX can be achieved. By reducing the duty cycle DC, the heating power Q can be adjusted to lie between the minimum heating power Q_MIN and the maximum heating power Q_MAX.

[0048] Reference again Figure 6 , heater 1 is controlled and / or regulated to a heating power Q between a minimum heating power Q_MIN and a maximum heating power Q_MAX at any operating voltage U. Heater 1 achieves its maximum heating power Q_MAX within the first voltage range I only at the first voltage U_PWM-ON, even at a duty cycle of 100%. Therefore, at point P1, a maximum heating power Q equal to Q_1 is achieved at an operating voltage U equal to U_1. On the other hand, in the second and third voltage ranges II and III, heater 1's heating power Q is reduced by pulse-width modulation of the operating voltage U, with a duty cycle between 100% and 0%. Therefore, at point P2, a heating power Q greater than the maximum heating power Q_MAX can be achieved by operating a voltage U equal to U_2 and a duty cycle of 100%. However, because the duty cycle is lower than 100%, in method 2, heating power Q at point P2 is reduced to the maximum heating power Q_MAX. Independently of the example shown here, in voltage ranges II and III, the heating power Q can be adjusted by further reducing the duty cycle DC so that the heating power Q lies between the minimum heating power Q_MIN and the maximum heating power Q_MAX.

[0049] refer to Figure 7In method 2, the maximum current I_MAX and the average current I_AVR in heater 1 also decrease. In heater 1, when operating voltage U is applied, currents I_TFR1 and I_TFR2 flow through resistor elements TFR1 and TFR2, respectively. When operating voltage U is applied to both resistor elements TFR1 and TFR2, since resistor elements TFR1 and TFR2 are connected in parallel, a current I_TFR1 + I_TFR2, or 2*I_TFR1 or 2*I_TFR2, flows in heater 1.

[0050] In a first voltage range I, a pulse-width modulated operating voltage U between a minimum voltage U_MIN and a first voltage U_PWM-ON is applied to resistor elements TFR1 and TFR2 with a duty cycle equal to 100%. Individual currents I_TFR1 and I_TFR2 flow continuously through resistor elements TFR1 and TFR2. Maximum current I_MAX is equal to the sum of the individual currents I_TFR1 and I_TFR2, i.e., double the individual currents (2*I_TFR1 or 2*I_TFR2). Because the individual currents I_TFR1 and I_TFR2 flow continuously through resistor elements TFR1 and TFR2, average current I_AVR is equal to maximum current I_MAX. In voltage range I, the respective individual currents I_TFR1 and I_TFR2 increase as operating voltage U increases from the minimum individual current I_TFR-MIN. In the first voltage range I, the maximum current I_MAX and the average current I_AVR increase from twice the minimum individual current 2*I_TFR-MIN to a current I_PWM-ON corresponding to the first voltage U_PWM-ON.

[0051] In the second voltage range II, a pulse-width modulated operating voltage U, between the first voltage U_PWM-ON and the second voltage U_PWM-50, is applied to the resistor elements TFR1 and TFR2, with a duty cycle DC between 100% and 50%. In the second voltage range II, the individual voltages U_TFR1 and U_TFR2 at the resistor elements TFR1 and TFR2, as well as the individual currents I_TFR1 and I_TFR2, overlap only during the overlap time t_UB. As a result, the maximum current I_MAX remains equal to the sum of the individual currents I_TFR1 and I_TFR2, i.e., double the individual currents 2*I_TFR1 and 2*I_TFR2. The average current I_AVR no longer corresponds to the maximum current I_MAX and decreases with increasing operating voltage U and, correspondingly, with decreasing duty cycle DC and, correspondingly, with decreasing overlap time t_UB. Thus, the average current I_AVR decreases from the current I_PWM-ON corresponding to the first voltage U_PWM-ON to the current I_PWM-50 corresponding to the second voltage U_PWM-50.

[0052] In the third voltage range III, a pulse width modulated operating voltage U between the second voltage U_PWM-50 and the maximum voltage U_MAX with a duty cycle DC between 50% and 0% is applied to the resistor elements TFR1 and TFR2. Because the voltage pulses of the individual voltages U_TFR1 and U_TFR2 at the resistor elements TFR1 and TFR2 do not overlap - see Figure 5 - The individual currents I_TFR1 and I_TFR2 also do not overlap. As a result, the maximum current I_MAX is equal to a single current I_TFR1 or I_TFR2. The average current I_AVR continues to decrease from the current I_PWM-50 corresponding to the second voltage U_PWM-50 as the operating voltage U increases and, correspondingly, as the duty cycle DC decreases.

[0053] Figure 8 and Figure 9 1 shows a view of a heater 1 according to the invention in a second embodiment. In the second embodiment, the resistor elements TFR1 and TFR2 can be switched in parallel and in series with each other. For this purpose, the control unit 4 of the heater 1 contains an additional switching element LS. Figure 8 In the example, the resistor elements TFR1 and TFR2 are connected in parallel. Figure 9 The resistor elements TFR1 and TFR2 are connected in series. The heater 1 is provided to perform as will be referred to below. Figures 10 to 11 Method 2 according to the invention is explained in more detail.

[0054] Figure 10 A voltage dependence diagram of the heating power Q in the heater 1 in the second embodiment is shown. Figure 11 A voltage dependence graph of the current I in the heater 1 in the second embodiment is shown.

[0055] refer to Figure 10 , an operating voltage U can be provided in a first voltage range I, a second voltage range II, a third voltage range III, and a fourth voltage range IV. In the first voltage range I, the operating voltage U is between the minimum voltage U_MIN and the first voltage U_PWM-ON. In the second voltage range II, the operating voltage U is between the first voltage U_PWM-ON and the second voltage U_PWM-50. In the third voltage range, the operating voltage U is between the second voltage U_PWM-50 and twice the first voltage 2*U_PWM-ON. In the fourth voltage range, the operating voltage U is between twice the first voltage 2*U_PWM-ON and the maximum voltage U_MAX.

[0056] refer to Figure 10 , the heater 1 is regulated and / or controlled in the voltage ranges I to III as described above. In the fourth voltage range IV, the resistance elements TFR1 and TFR2 are connected in series with each other. Figure 11 The resistance of heater 1 thus increases within the fourth voltage range IV and is the sum of the resistances of the respective resistance elements TFR1 and TFR2. Consequently, the current I_TFR-SR-ON flowing through the resistance elements TFR1 and TFR2 decreases at the same operating voltage U. The maximum current I_MAX then corresponds to the current I_TFR-SR-ON and is less than the maximum current I_MAX of the parallel-connected resistance elements TFR1 and TFR2.

[0057] Refer to above Figures 2 to 11 In the description of the heater 1 , for simplicity, it is assumed that the resistor elements TFR1 and TFR2 have the same resistance. However, it should be understood that the resistor elements TFR1 and TFR2 may also have different resistances. In addition, the heater 1 may also have more than two resistor elements TFR1 and TFR2.

[0058] Figure 12 and Figure 13 1 shows a view of an electric heater 1 according to the invention in a third embodiment. In the third embodiment, each of the resistance elements TFR1 and TFR2 has two resistance bars R1 and R2. The resistance bars R1 and R2 can have the same or different resistances. In addition, the heater 1 can also have more than two resistance bars R1 and R2. The resistance bars R1 and R2 can be connected in parallel and in series with each other. In order to control the resistance bars R1 and R2, the control unit 4 of the heater 1 contains additional switching elements LS and HS. Figure 12 In the resistor bars R1 and R2 are connected in parallel and Figure 13 In method 1, resistor bars R1 and R2 are connected in series. In method 2, resistor bars R1 and R2 can be connected in parallel in voltage ranges I and II, and in series in voltage range III and, optionally, in voltage range IV. Furthermore, each resistor bar R1 and R2 can be turned off. Overall, this allows for better control of heater 1 in method 2 and can further reduce the maximum current I_MAX.

Claims

1. A method (2) for operating an electric heater (1) for a battery electric vehicle, the electric heater (1) having at least two resistance elements (TFR1, TFR2), in, The heater (1) is operated with an operating voltage (U) which is between a minimum voltage (U_MIN) and a maximum voltage (U_MAX) and is pulse width modulated with a duty cycle (DC), and wherein the heater (1) is controlled and / or regulated to generate a heating power (Q) between a required minimum heating power (Q_MIN) and a required maximum heating power (Q_MAX), It is characterized in that When the heater (1) operates at an operating voltage (U) in a first voltage range (I) having a relatively low voltage value, the resistance elements (TFR1, TFR2) are connected in parallel with each other, and the operating voltage (U) is pulse-width modulated at a duty cycle (DC) equal to 100% and applied to the resistance elements (TFR1, TFR2), When the heater (1) is operated at an operating voltage (U) in a second voltage range (II) having a relatively medium voltage value, the resistance elements (TFR1, TFR2) are connected in parallel with each other, and the operating voltage (U) is pulse-width modulated with a duty cycle (DC) between 100% and 50% and applied to the resistance elements (TFR1, TFR2) so that voltage pulses of the respective voltages (U_TFR1, U_TFR2) at the resistance elements (TFR1, TFR2) corresponding to the operating voltage (U) alternate in time, and When the heater (1) is operated at an operating voltage (U) in a third voltage range (III) having a relatively high voltage value, the resistance elements (TFR1, TFR2) are connected in parallel with each other, and the operating voltage (U) is pulse-width modulated with a duty cycle (DC) between 50% and 0% and applied to the resistance elements (TFR1, TFR2) so that voltage pulses of the respective voltages (U_TFR1, U_TFR2) at the resistance elements (TFR1, TFR2) corresponding to the operating voltage (U) alternate in time.

2. The method (2) according to claim 1, It is characterized in that In the second voltage range (II), the operating voltage (U) is applied to the resistance element (TFR1, TFR2) such that an overlap time (t_UB) is minimized, in which the voltage pulses of the respective voltages (U_TFR1, U_TFR2) at the resistance element (TFR1, TFR2) corresponding to the operating voltage (U) overlap in time.

3. The method (2) according to claim 1 or 2, It is characterized in that In the second voltage range (II), the operating voltage (U) is applied to the resistance element (TFR1, TFR2) such that an overlap time (t_UB) is less than the product of a period duration (T) of the pulse-width modulated operating voltage (U) and a difference between double the duty cycle (DC) and 100%, divided by 100%, in which overlap time (t_UB) the voltage pulses of the respective voltages (U_TFR1, U_TFR2) at the resistance element (TFR1, TFR2) corresponding to the operating voltage (U) overlap in time, and / or In the second voltage range (II), the operating voltage (U) is applied to the resistance elements (TFR1, TFR2) so that the individual voltages (U_TFR1, U_TFR2) at the resistance elements (TFR1, TFR2) corresponding to the operating voltage (U) are shifted relative to each other, preferably by half a period duration (T) of the pulse-width modulated operating voltage (U).

4. The method (2) according to any one of the preceding claims, It is characterized in that In the third voltage range (III), the operating voltage (U) is applied to the resistance element (TFR1, TFR2) such that an overlap time (t_UB) is equal to zero, during which voltage pulses of the respective voltages (U_TFR1, U_TFR2) at the resistance element (TFR1, TFR2) corresponding to the operating voltage (U) overlap in time.

5. The method (2) according to any one of the preceding claims, It is characterized in that In the third voltage range (III), the operating voltage (U) is applied to the resistance elements (TFR1, TFR2) such that the individual voltages (U_TFR1, U_TFR2) at the resistance elements (TFR1, TFR2) corresponding to the operating voltage (U) are shifted relative to one another, preferably by half a period duration (T) of the pulse-width modulated operating voltage (U).

6. The method (2) according to any one of the preceding claims, It is characterized in that The resistance of the resistance elements (TFR1, TFR2) is selected such that the heater (1) generates the required minimum heating power (Q_MIN) at the minimum voltage (U_MIN).

7. The method (2) according to any one of the preceding claims, It is characterized in that In the second voltage range (II), as the operating voltage (U) increases, the duty cycle (DC) of the pulse width modulated operating voltage (U) decreases from 100% to 50%, and / or In the third voltage range (III), as the operating voltage (U) increases, the duty cycle (DC) of the pulse width modulated operating voltage (U) decreases from 50% to 0%.

8. The method (2) according to any one of the preceding claims, It is characterized in that At least one of the resistance elements (TFR1, TFR2) comprises at least two resistance bars (R1, R2) that can be connected in series and in parallel with each other, wherein the resistance bars (R1, R2) of the resistance elements (TFR1, TFR2) are connected in parallel or in series with one another depending on the operating voltage (U), and / or A single resistor strip or some resistor strips (R1, R2) of the resistance element (TFR1, TFR2) are switched off according to the operating voltage (U), so that the operating voltage (U) is applied only to a single resistor strip or some resistor strips (R1, R2) of the resistance element (TFR1, TFR2).

9. The method (2) according to any one of the preceding claims, It is characterized in that The first voltage (U_PWM-ON) is defined as a voltage that generates the required maximum heating power (Q_MAX) at a duty cycle (DC) equal to 100%, and the second voltage (U_PWM-50) is defined as a voltage that generates the required maximum heating power (Q_MAX) at a duty cycle (DC) equal to 50%, In the first voltage range (I), the operating voltage (U) is provided with a relatively low voltage value between the minimum voltage (U_MIN) and the first voltage (U_PWM-ON), In the second voltage range (II), the operating voltage (U) is provided with a relatively intermediate voltage value between the first voltage (U_PWM-ON) and the second voltage (U_PWM-50), and In the third voltage range (III), the operating voltage (U) is provided with a relatively high voltage value between the second voltage (U_PWM-50) and the maximum voltage (U_MAX).

10. The method (2) according to any one of the preceding claims, It is characterized in that When the heater (1) operates at an operating voltage (U) in a fourth voltage range (IV) having a relatively very high voltage value, the resistance elements (TFR1, TFR2) are connected to each other in series.

11. The method (2) according to claim 10, It is characterized in that The first voltage (U_PWM-ON) is defined as a voltage that generates the required maximum heating power (Q_MAX) at a duty cycle (DC) equal to 100%, and the second voltage (U_PWM-50) is defined as a voltage that generates the required maximum heating power (Q_MAX) at a duty cycle (DC) equal to 50%, In the first voltage range (I), the operating voltage (U) is provided with a relatively low voltage value between the minimum voltage (U_MIN) and the first voltage (U_PWM-ON), In the second voltage range (II), the operating voltage (U) is provided with a relatively intermediate voltage value between the first voltage (U_PWM-ON) and the second voltage (U_PWM-50), In the third voltage range (III), the operating voltage (U) is provided with a relatively high voltage value between the second voltage (U_PWM-50) and double the first voltage (2*U_PWM-ON), and In the fourth voltage range (IV), the operating voltage (U) is provided with a relatively very high voltage value between double the first voltage (2*U_PWM-ON) and the maximum voltage (U_MAX).

12. An electric heater (1) for a battery electric vehicle, the electric heater (1) being used to heat a fluid (F), in, The heater (1) comprises at least two resistance elements (TFR1, TFR2) and at least three flat tubes (3), wherein each resistance element has an electrical resistance, and a fluid (F) can flow through the flat tubes (3). The resistor elements (TFR1, TFR2) and the flat tubes (3) are stacked together so that each resistor element (TFR1, TFR2) is arranged between two flat tubes (3). wherein the resistance elements (TFR1, TFR2) are connected to adjacent flat tubes (3) in a heat transfer manner, and The heater (1) comprises a control unit (4) for controlling and / or adjusting the resistance elements (TFR1, TFR2), It is characterized by: The heater (1) is configured to perform a method (2) according to any one of the preceding claims.

13. The heater (1) according to claim 12, It is characterized by: The resistance elements (TFR1, TFR2) are connected in parallel with each other, and / or The resistance elements (TFR1, TFR2) can be connected in parallel and in series with each other, and / or At least some of the resistance elements (TFR1, TFR2) have different resistances, and / or The resistance of at least some of the resistance elements ( TFR1 , TFR2 ) is the same.

14. The heater (1) according to claim 12 or 13, It is characterized by: At least one of the resistance elements (TFR1, TFR2) comprises at least two resistance strips (R1, R2), each having a resistance.

15. The heater (1) according to claim 14, It is characterized by: The resistor bars (R1, R2) of the resistor elements (TFR1, TFR2) are connected in parallel with each other and / or The resistance bars (R1, R2) of the resistance elements (TFR1, TFR2) can be connected in parallel and in series with one another, and / or The resistance of at least some of the resistance strips (R1, R2) of the resistance element (TFR1, TFR2) is different, and / or The resistance of at least some of the resistance strips (R1, R2) of the resistance element (TFR1, TFR2) is the same, and / or Individual resistor strips or some resistor strips ( R1 , R2 ) of the resistor element ( TFR1 , TFR2 ) can be switched off.

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