METHOD FOR REGULATING A HEATER AND THE HEATER

Abstract

A method for regulating a heater including at least one heating element having a temperature-dependent electrical resistance is disclosed. The method may include determining, with a regulating unit of the heater, a current heating behaviour of the heating element based on a time profile of the resistance of the heating element. The heating element may exhibit (i) an NTC heating behaviour at temperatures below a transition temperature, (ii) a PTC heating behaviour at temperatures above the transition temperature, and (iii) a transition between the NTC heating behaviour and the PTC heating behaviour at the transition temperature and a resistance minimum. The method may further include determining, with the regulating unit, at least one input parameter for the heating element based on the current heating behaviour. The method may also include regulating, with the regulating unit, the heating element via the at least one input parameter.

Claims

1. A method for regulating a heater including at least one heating element having a temperature-dependent electrical resistance, the method comprising: determining, with a regulating unit of the heater, a current heating behaviour of the at least one heating element based on a time profile of the resistance of the at least one heating element with a regulating unit of the heater, the at least one heating element exhibiting (i) an NTC heating behaviour at temperatures below a transition temperature, (ii) a PTC heating behaviour at temperatures above the transition temperature, and (iii) a transition between the NTC heating behaviour and the PTC heating behaviour at the transition temperature and a resistance minimum; determining, with the regulating unit, at least one input parameter for the at least one heating element based on the current heating behaviour; and regulating, with the regulating unit, the at least one heating element via the at least one input parameter.

2. The method according to claim 1, wherein regulating the at least one heating element via the at least one input parameter includes adjusting a required heating output when the at least one heating element is exhibiting the PTC heating behaviour.

3. The method according to claim 1, wherein: regulating the at least one heating element via the at least one input parameter includes regulating the at least one heating element to a maximum output when the at least one heating element is exhibiting the PTC heating behaviour; the maximum output is defined at a threshold resistance, which correlates to a threshold temperature; and the threshold temperature is smaller than a Curie temperature of the at least one heating element and greater than the transition temperature.

4. The method according to claim 1, further comprising: verifying, with the regulating unit, a state of the at least one heating element after checking the time profile; and discontinuing, with the regulating unit, the regulating of the at least one heating element and interrupting an energy supply of the at least one heating element for a defined time interval when (i) the at least one heating element has a temperature above a threshold temperature and (ii) the temperature cannot be reduced under the threshold temperature by regulating the at least one heating element via the at least one input parameter.

5. The method according to claim 1, wherein: determining the current heating behaviour of the at least one heating element includes checking, with the regulating unit, the time profile of the resistance of the at least one heating element and searching for a behaviour which can be interpreted as the transition between the NTC heating behaviour and the PTC heating behaviour in the at least one heating element; when the searched behaviour is present, (i) the method further comprises determining, with the regulating unit, a currently detected heating behaviour of the at least one heating element and (ii) the regulating unit determines the at least one input parameter for the at least one heating element based on the currently detected heating behaviour; and when the searched behaviour is not present, the regulating unit determines the at least one input parameter for the at least one heating element based on a previously detected heating behaviour.

6. The method according to claim 5, wherein: checking the time profile of the resistance of the at least one heating element includes measuring a current on the at least one heating element within a predetermined time window with the regulating unit; measuring the current includes increasing, with the regulating unit, a counter when a currently measured current value is higher than all previously measured current values; and the method further comprises establishing, with the regulating unit, the current heating behaviour to be interpreted as the transition when the counter exceeds a predetermined counter-threshold value.

7. The method according to claim 6, wherein determining the currently detected heating behaviour includes: increasing, with the regulating unit, a duty cycle of a PWM-signal for an initial current currently applied to the at least one heating element for a predetermined time interval by a predefined value and sensing a corresponding change of the current of the at least one heating element; and reducing, with the regulating unit, the duty cycle of the PWM-signal for the initial current currently applied to the at least one heating element for the predetermined time interval by the predefined value and sensing a corresponding change of the current of the at least one heating element.

8. The method according to claim 7, wherein determining the currently detected heating behaviour further includes: determining, with the regulating unit, that the currently detected heating behaviour is the PTC heating behaviour when (i) increasing the duty cycle increases a resistance calculated from the sensed current and (ii) reducing the duty cycle decreases the resistance calculated from the sensed current; and determining, with the regulating unit, that the currently detected heating behaviour is the NTC heating behaviour when (i) increasing the duty cycle decreases the resistance calculated from the sensed current and (ii) reducing the duty cycle increases the resistance calculated from the sensed current.

9. The method according to claim 8, further comprising: repeating, with the regulating unit, the process of determining the currently detected heating behaviour when the regulating unit was unable to determine the currently detected heating behaviour; and repeating the process of determining the currently detected heating behaviour includes increasing and reducing the duty cycle for the predetermined time interval by a second predefined value which is higher than the predefined value.

10. The method according to claim 8, wherein determining the currently detected heating behaviour further includes determining, with the regulating unit, whether the resistance calculated from the sensed current increases or decreases via a ramp determination.

11. A heater, comprising: a regulating unit configured to carry out the method according to claim 1; and at least one heating element having a temperature-dependent electrical resistance; wherein the at least one heating element exhibits a transition between an NTC heating behaviour and a PTC heating behaviour at a transition temperature and a resistance minimum; wherein the at least one heating element exhibits the NTC heating behaviour at temperatures below the transition temperature; and wherein the at least one heating element exhibits the PTC heating behaviour at temperatures above the transition temperature.

12. The method according to claim 1, wherein regulating the at least one heating element via the at least one input parameter includes adjusting the at least one input parameter.

13. The method according to claim 1, wherein: the at least one heating element has a Curie temperature; and regulating the at least one heating element via the at least one input parameter includes preventing the at least one heating element from reaching the Curie temperature.

14. The method according to claim 1, wherein the at least one input parameter includes at least one of a current and a voltage.

15. The method according to claim 1, further comprising: measuring a current on the at least one heating element; measuring a voltage on the at least one heating element; and calculating the resistance of the at least one heating element.

16. The method according to claim 5, further comprising, when the searched behaviour is present, determining whether the searched behaviour was caused by an environment of the at least one heating element.

17. The method according to claim 7, wherein the predefined value is 10% of the duty cycle.

18. The method according to claim 8, wherein determining the currently detected heating behaviour further includes determining, with the regulating unit, the resistance minimum of the at least one heating element.

19. The method according to claim 9, wherein the second predefined value is 20% of the duty cycle.

20. The method according to claim 9, wherein the predefined value and the second predefined value are different.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] It shows, in each case schematically

[0028] FIG. 1 shows a view of a switching circuit with a heater according to the invention;

[0029] FIG. 2 shows a temperature-resistance characteristic curve of a heating element with a temperature-dependent resistance;

[0030] FIG. 3 shows a diagram of a method according to the invention for regulating the heater according to the invention;

[0031] FIG. 4 shows an illustration of an establishment step of the method according to the invention;

[0032] FIG. 5 shows an illustration of a verification step of the method according to the invention.

DETAILED DESCRIPTION

[0033] FIG. 1 shows a view of a heater 1 according to the invention and an energy source 2, which are electrically interconnected into a switching circuit 3. Advantageously, the heater 1 can be provided for a battery-electric motor vehicle and the energy source 2 be a traction battery of the motor vehicle. Here, the heater 1 comprises a heating element 4 with a temperature-dependent resistance and a regulating unit 5 with a switch 6 and a micro controller 7. Here, the heating element 4 is a PTC thermistor and can be in particular a ceramic PTC thermistor. The microcontroller 7 generates a square-wave signal i.e. PWM-signal of variable width i.e. with a variable duty cycle after the switch 6 closes and opens. By way of this, the current on the heating element 4 is varied and the heating element 4 regulated to the required heating output. The voltage on the heating element 4 is not directly affected by the switch 6 and is constant. The micro controller 7 can additionally read out the current and/or the voltage on the heating element 4. This information can be used for regulating the heating element 4 to the required output and to calculate the resistance R of the heating element 4.

[0034] FIG. 2 shows a temperature-resistance characteristic curve of the heating element 4. At temperatures below a transition T_Ü, the heating element 4 exhibits an NTC heating behaviour and above the transition temperature T_Ü a PTC heating behaviour. The transition temperature T_Ü corresponds to a resistance minimum R_MIN. In addition, a threshold temperature T_TH is defined which corresponds to a threshold resistance R_TH. The threshold temperature T_TH is above the transition temperature T_Ü and below a Curie temperature T_CURIE, at which the heating element 4 is physically destroyed.

[0035] Here, the regulating unit 5 regulates the heating element 4 maximally to a maximum output which lies at the threshold temperature T_TH and the threshold resistance R_TH. By way of this, the overheating protection of the heating element 4 is realised at the threshold temperature T_TH and not at the Curie temperature T_CURIE. Accordingly, a safe working range I of the heating element 4 is below the threshold temperature T_TH and the threshold resistance R_TH and an unsafe working range II above the threshold temperature T_TH and the threshold resistance R_TH.

[0036] In the unsafe working range II, an offset range II-A can be additionally defined in which the temperature and the resistance of the heating element 4 can briefly be without overheating of the heater 1. By contrast, the temperature and the resistance of the heating element 4 must not be in a remaining working range II-B of the unsafe working range II since the overheating of the heater 1 can very probably be not prevented. A division of the unsafe working range II into the working ranges II-A and II-B takes place at a limit temperature T_G which is calculated from the threshold temperature T_TH with an offset. Accordingly, a corresponding limit resistance R_G is calculated from the threshold resistance R_TH with an offset.

[0037] FIG. 3 shows a diagram of a method 8 according to the invention for regulating the heater 1 according to the invention. There, the method 8 is started in an initial step 9 in that for example the heater 1 is switched on. After the initial step 9 the regulating unit 5 proceeds to a check.

[0038] During the check, the regulating unit 5 checks in an establishment step 12 the time profile of the resistance R of the heating element 4. The resistance R is here calculated from the current and the voltage measured on the heating element 4. There, the regulating unit 5 determines a behaviour that can be interpreted as transition between the NTC heating behaviour and the PTC heating behaviour in the heating element 4. When the searched behaviour is present, the regulating unit 5 proceeds to a verification step 13 in which the regulating unit 5 determines the current heating behaviour of the heating element 4. In a following determination step 14, the regulating unit 5, dependent on the current heating behaviour, determines the at least one input parameter for the heating element 4. When the behaviour searched for by the regulating unit 5 is not present, the regulating unit 5, after the establishment step 12, proceeds directly to the determination step 14. The determination step 14 and the verification step 13 are explained in more detail in the following by way of FIG. 4 and FIG. 5.

[0039] In the establishment step 12, the regulating unit 5 determines a behaviour which can be interpreted as transition between the NTC heating behaviour and the PTC heating behaviour. Making reference to FIG. 2, the resistance R of the heating element 4 falls to the resistance minimum R_MIN and rises from the resistance minimum R_MIN when the heating element 4 changes out of the NTC heating behaviour into the PTC heating behaviour or from the PTC heating behaviour into the NTC heating behaviour. In the establishment step 12, the regulating unit 5 can determine this behaviour and thereby the transition between the NTC heating behaviour and the PTC heating behaviour. This is explained in more detail in the following by way of FIG. 4.

[0040] FIG. 4 shows in the lower diagram the time profile of the resistance R on the heating element 4 and in the upper diagram the profile of a counter Z both based on the measured current values on the heating element 4. There, the heating element 4 is initially heated and proceeds from the NTC heating behaviour into the PTC heating behaviour. In the process, the resistance R falls before the transition and increases again after transition. Thereafter, the heating element 4 is cooled and proceeds out of the PTC heating behaviour into the NTC heating behaviour. The resistance R in the process falls before the transition and increases again after the transition. Here, the regulating unit 5 measures in the establishment step 12 the current of the heating element 4 within a predetermined time window t 1. While measuring the current, the regulating unit 5 increases the counter Z when the currently measured current value is higher than all current values measured before that. Making reference to the upper diagram, the regulating unit 5 establishes the behaviour that is similar to the transition when the counter Z exceeds a counter threshold value Z_MAX.

[0041] However, the resistance R of the at least one heating element 4 can also fall and rise conditional on the surroundings and without the transition—for example through a change of the fluid flow. Accordingly, the resistance R in the PTC heating behaviour rises during environmental heating of the heating element 4 and in the NTC heating behaviour during environmental cooling of the heating element 4. In order to exclude environmental errors, the regulating unit 4 verifies in the verification step 13 the heating behaviour that is currently present. This is explained in more detail in the following by way of FIG. 5.

[0042] In the following safeguarding step 10 the regulating unit 5 verifies the state of the heating element 4. When the heating element 4 is overheated and the temperature cannot be reduced by reducing of duty cycle of the PWM-signal for the applied current, the regulating unit 5 discontinues the regulating in an interruption step 11 and interrupts the energy supply of the heating element 4 for a defined time interval of for example 30 seconds. In the safeguarding step 10, the heating behaviour of the heating element 4 is also taken into account. In particular, this can prevent the switching off of the heating element 4 during NTC heating behaviour due to the incorrectly detected overheating. When the heating element 4 is not overheated with the current input parameters or when the temperature can be reduced by a normal way, the regulating unit 5 in a following regulating step 15 regulates the heating element with the input parameters. Following the regulating step 15, the regulating unit 5 again proceeds to the establishment step 12.

[0043] FIG. 5 shows in the upper diagram a time profile of duty cycle DC of the PWM-signal for current on the heating element 4. In the lower diagram, a time profile of the resistance R on the heating element 4 is shown. The resistance R is calculated from the current measured on the heating element 4. When during the establishment step 12 the behaviour that is similar to the transition was established, the current heating behaviour is determined in the verification step 13. Making reference to the upper diagram, the duty cycle DC of the PWM-signal for an initial current I_0 on the heating element 4 in each case for a time interval t_2 is reduced and increased by 10% each. The duty cycle DC of the PWM-signal for the initial current I_0 is the value currently applied to the heating element 4 at the start of the verification step 13. Making reference to the lower diagram, the resistance R of the heating element 4 also changes with the change of the duty cycle DC of the PWM-signal for the current I_0. The mentioned change of the resistance R is evaluated by the regulating unit 5 by way of a ramp determination.

[0044] When the resistance R falls during the reduction of the duty cycle DC of the PWM-signal for the initial current I_0 and rises during the increase of the duty cycle DC of the PWM-signal for the initial current I_0, the regulating unit 5 determines the current heating behaviour as the PTC heating behaviour. This behaviour corresponds to the behaviour of the current on the heating element 4, whereby the current on the heating element 4 rises during the reduction of the duty cycle DC of the PWM-signal for the initial current I_0 and falls during the increase of the duty cycle DC of the PWM-signal for the initial current I_0. When the resistance R during the reduction of the duty cycle DC of the PWM-signal for the initial current I_0 increases and falls during the increase of the duty cycle DC of the PWM-signal for the initial current I_0, the regulating unit determines the current heating behaviour as NTC heating behaviour. This behaviour corresponds to the behaviour of the current on the heating element 4, whereby the current on the heating element 4 falls during the reduction of the duty cycle DC of the PWM-signal for the initial current I_0 and rises during the increase of the duty cycle DC of the PWM-signal for the initial current I_0. Should it not be possible to unambiguously determine the heating behaviour, the regulating unit can repeat the verification step and reduce and increase the duty cycle DC of the PWM-signal for the initial current I_0 for example by 20% in each case.

[0045] In FIG. 5, the resistance R falls during the reduction of the duty cycle DC of the PWM-signal for the initial current I_0 and increases upon the increase of the duty cycle DC of the PWM-signal for the initial current I_0. Accordingly, the heating element 4 exhibits the PTC heating behaviour. Making reference to FIG. 3, the at least one input parameter for the heating element 4 is now determined in the determination step 14 dependent on the determined PTC heating behaviour.

[0046] The method 8 makes possible the safe regulating of the heater based on the resistance of the heating element 4. By way of this, cost-intensive temperature sensors are no longer required and the costs of the heater can be advantageously reduced.