DETECTION OF CRITICAL OPERATING STATES OF A PTC HEATER

Abstract

A method for regulating a PTC heating with at least one PTC heating element and a control unit for controlling the PTC heating element is disclosed. The method includes: controlling with the control unit the PTC heating element to a target output via a control variable; receiving via PTC heating element, with the target output of the control unit, an electrical input power and emitting a thermal heating output to an environment; in a testing step the control unit keeps the target output constant over a predefined plateau duration and checks the PTC heating element for a critical imbalance state where the PTC heating element regulates itself by an increasing of its resistance; and after the testing step, when the control unit detects the critical imbalance state, the control unit reduces the target output in a regulating step.

Claims

1. A method for regulating a PTC heater with at least one PTC heating element and with a control unit for controlling at least one PTC heating element, comprising: controlling with the control unit the at least one PTC heating element to a target output via a control variable; receiving via the at least one PTC heating element, with the target output of the control unit an electrical input power and emitting a thermal heating output to an environment; in a testing step the control unit keeps the target output constant over a predefined plateau duration and checks the at least one PTC heating element for a critical imbalance state where the at least one PTC heating element regulates itself by an increasing of its resistance; and after the testing step, when the control unit detects the critical imbalance state of the at least one PTC heating element, the control unit reduces the target output in a regulating step.

2. The method according to claim 1, wherein in the testing step the control unit keeps the target output constant over the predefined plateau duration between 1 second and 10 minutes.

3. The method according to claim 1, wherein after the regulating step the control unit passes again to the testing step.

4. The method according to claim 1, wherein in the testing step the control unit determines the critical imbalance state at the at least one PTC heating element when the electrical input power corresponds to the target output and a control value of the control variable rises at the at least one PTC heating element.

5. The method according to claim 1, wherein in the testing step the control unit determines the critical imbalance state at the at least one PTC heating element when the electrical input power is less than the target output and a control value of the control variable is maximum at the at least one PTC heating element.

6. The method according to claim 1, wherein in the testing step the control unit does not determine a critical imbalance state and a balance state at the at least one PTC heating element when the electrical input power corresponds to the target output and a control value of the control variable at the at least one PTC heating element is constant or falls.

7. The method according to claim 1, wherein after the testing step with a balance state of the at least one PTC heating element, where the at least one PTC heating element does not regulate itself by an increasing of its resistance, the control unit checks in a verification step whether at least one of the electrical input power and the target output corresponds to an externally predetermined specification output.

8. The method according to claim 7, wherein: when the at least one of the electrical input power and the target output corresponds to the externally predetermined specification output, the method is terminated; and when the at least one of the electrical input power and the target output does not correspond to the externally predetermined specification output, the control unit increases the electrical input power via the control variable in a readjustment step.

9. The method according to claim 7, wherein the control unit increases the electrical input power in a readjustment step after a suspension time via the control variable.

10. The method according to claim 7, wherein after a readjustment step, the control unit passes again to the testing step.

11. A PTC heater, comprising: at least one PTC heating element and a control unit for controlling the at least one PTC heating element; the control unit configured to control the at least one PTC heating element to a target output via a control variable, wherein with the target output of the control unit the at least one PTC heating element receives an electrical input power and emits a thermal heating output to an environment; in a testing step, the control unit keeps the target output constant over a predefined plateau duration and checks the at least one PTC heating element for a critical imbalance state where the at least one PTC heating element regulates itself by an increasing of its resistance; and after the testing step, when the control unit detects the critical imbalance state of the at least one PTC heating element, the control unit reduces the target output in a regulating step.

12. The PTC heating according to claim 11, wherein in the testing step the control unit keeps the target output constant over the predefined plateau duration between 1 second and 10 minutes.

13. The PTC heating according to claim 11, wherein after the regulating step the control unit passes again to the testing step.

14. The PTC heating according to claim 11, wherein in the testing step the control unit determines the critical imbalance state at the at least one PTC heating element when the electrical input power corresponds to the target output and a control value of the control variable rises at the at least one PTC heating element.

15. The PTC heating according to claim 11, wherein in the testing step the control unit determines the critical imbalance state at the at least one PTC heating element when the electrical input power is less than the target output and a control value of the control variable is maximum at the at least one PTC heating element.

16. The PTC heating according to claim 11, wherein in the testing step the control unit does not determine a critical imbalance state and a balance state at the at least one PTC heating element when the electrical input power corresponds to the target output and a control value of the control variable at the at least one PTC heating element is constant or falls.

17. The PTC heating according to claim 11, wherein after the testing step with a balance state of the at least one PTC heating element, where the at least one PTC heating element does not regulate itself by an increasing of its resistance, the control unit checks in a verification step whether at least one of the electrical input power and the target output corresponds to an externally predetermined specification output.

18. The PTC heating according to claim 17, wherein: when the at least one of the electrical input power and the target output corresponds to the externally predetermined specification output, the method is terminated; and when the at least one of the electrical input power and the target output does not correspond to the externally predetermined specification output, the control unit increases the electrical input power via the control variable in a readjustment step.

19. The PTC heating according to claim 18, wherein the control unit increases the electrical input power in the readjustment step after a suspension time via the control variable.

20. The PTC heating according to claim 19, wherein after the readjustment step, the control unit passes again to the testing step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The FIGURE shows a flow chart of a method according to the disclosure.

DETAILED DESCRIPTION

[0025] The single FIGURE shows a schematic course of a method 1 according to the invention. The method 1 is provided here for regulating a PTC heater with at least one PTC heating element and with a control unit for controlling the respective PTC heating element. In the method 1 the respective PTC heating element is controlled by the control unit to an external specification output via a control variable—for example a current PWM signal. For this, the control unit specifies to the respective PTC heating element a target output and the respective PTC heating element receives an input power. The respective PTC heating element emits a thermal heating output to the environment—for example to the air flowing through the PTC heater.

[0026] When the respective PTC heating element is in a balance state, the respective PTC heating element, with the constant control variable and with constant boundary conditions, has a constant input power. The boundary conditions here can be provided by the voltage and/or the ambient temperature and/or an air quantity flowing through the respective PTC heating element. In addition, an—in a first approximation linear—correlation is present between the control variable of the control unit and the electrical input power. When the control variable rises/falls by a predetermined percentage value—for example by 2%—the electrical input power also rises/falls by this predetermined percentage value—for example by 2%. When the respective PTC heating element is in a critical imbalance state, the control variable of the control unit and the electrical input power display no or a small correlation with one another.

[0027] The control unit can now detect in a testing step whether the respective PTC heating element is in the critical imbalance state or in the balance state. For this, the control unit checks whether the input power corresponds to the target output. When the input power does not correspond to the target output, the respective PTC heating element is in the critical imbalance state. The control unit passes directly to a regulating step.

[0028] When the input power corresponds to the target output, the control unit checks further in the testing step whether the control variable is constant. When the control variable is constant, the respective PTC heating element is in the balance state and the control unit passes to a verification step. When the control variable is not constant, the control unit checks whether the control variable is rising or falling. When the control variable falls, the respective PTC heating element is in the balance state and the control unit passes to the verification step already mentioned above. When the control variable rises, the respective PTC heating element is in the critical imbalance state and the control unit passes to the regulating step already mentioned above.

[0029] When the respective PTC heating element is therefore in the critical imbalance state, the regulating step is carried out after the testing step. When the respective PTC heating element is in the balance state or respectively is not in the critical imbalance state, the verification step is carried out.

[0030] In the regulating step, the control unit reduces the input power of the respective PTC heating element via a reducing of the control variable. By way of example, in the regulating step the control unit can reduce the target output, determined by the control variable, via the control variable with 0.5% per second over 5 seconds—therefore in total by 2.5%. Thereafter, the control unit can pass again to the testing step and keep constant the set target output over the predefine plateau duration of 5-10 seconds and check whether the balance state is reached. When the balance state is not reached, after the testing step the control unit passes to the regulating step again and can reduce the target output further with 0.5% per second over 5 seconds—therefore in total by a further 2.5%.

[0031] In the verification step the control unit checks whether the input power corresponds to the external specification output. When the input power corresponds to the external specification output, the heating output emitted by the respective PTC heating element is sufficient and a stable operating point is reached. The method is terminated. When the input power does not correspond to the external specification output, the heating output emitted by the respective PTC heating element is not sufficient for heating and the control unit passes to a readjustment step. In the readjustment step the control unit waits a predetermined suspension time and thereafter increases the input power via the increasing of the control variable. Thereafter, the control unit passes again to the testing step.

[0032] In the method according to the invention, the control unit detects whether the respective PTC heating element is in the critical imbalance state or in the balance state. When the respective PTC heating element is in the critical imbalance state, the control unit can initiate the regulating of the respective PTC heating element. Thereby, critical operating points in the PTC heater are prevented. The method offers in addition a flexible and software-based solution which is able to be transferred to differing applications.