JPH11252932A - Device for protecting inverter from heat and method for protecting against heat for conductive heating unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for protecting an inverter from heat which is capable of achieving protection against heat properly, even if a temperature sensor is installed at a remote place from the inverter. SOLUTION: The generation of heat by an inverter 12 is suppressed by reducing a current demand value Ia of the inverter 12 with a motor electric control unit(ECU) 22, and by giving the corrected current demand value to a drive circuit 18 of the inverter 12 as a current command value I. In this case, a temperature sensor 16 is mounted at a place remote from the inverter 12. Based on the detected value of this temperature sensor 16 and the current value of the inverter 12, the current demand value Ia is corrected to calculate the current command value I.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal protection device for an inverter and a method for thermal protection of a conductive heating element. The present invention relates to a technology for efficiently performing thermal protection control according to the following.

[0002]

2. Description of the Related Art Semiconductor power switch elements such as thyristors and bipolar transistors are used in inverters used for driving motors. Since these elements are weak to heat, various measures against heat generation are taken so as not to cause element destruction due to heat even under the most severe conditions, taking into account the operating temperature, operating time, rated current value, etc. I have. For example,
A temperature sensor is provided on the side of the inverter, and when a detected value of the temperature sensor is equal to or more than a predetermined value, a required current value for the inverter is multiplied by a coefficient less than 1 to actually provide a drive circuit for the inverter. A contrivance has been made to reduce the given command value.

[0005] FIG. 5 is a diagram for explaining such a contrivance in the prior art. The horizontal axis of FIG. 5 shows the temperature detected by the temperature sensor, where Ta and Tb are fixed values.
On the other hand, the vertical axis in the figure shows the limiting ratio at each of the detected temperatures. According to the prior art, as shown in FIG.
When the value detected by the temperature sensor is equal to or greater than Ta, the required current value is gradually limited, and the detected value is Tb and the required current value is 0, that is, the motor drive by the inverter is stopped.

[0004]

However, since a large amount of noise is generated from the above-mentioned semiconductor power switch element, if a temperature sensor such as a thermistor or a thermocouple is arranged in the immediate vicinity of the semiconductor power switch element, a detection signal will not be generated. These noises are superimposed, and accurate heat countermeasure control cannot be performed. For this reason, the temperature sensor must be mounted separately from the semiconductor power switch element.

[0005] However, if the temperature sensor is mounted away from the semiconductor power switch element in this way, there arises a problem that a difference occurs between the value detected by the temperature sensor and the actual temperature of the semiconductor power switch element. .
This temperature error increases as the current flowing through the semiconductor power switch element increases.

[0006] Due to this temperature difference, over-protection or under-protection may occur in measures against heat generation of the semiconductor power switch element. For example, in FIG.
If Ta or Tb is determined on the basis of the maximum current that may flow through the inverter, and the value is used for the heat generation countermeasure control, over-protection is usually provided. Further, when an unexpectedly large current flows through the semiconductor power switch element due to a failure of a driving motor or a power supply, protection becomes insufficient.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object the advantage that the temperature sensor is mounted at a distance from a conductive heating element such as a semiconductor power switch element of an inverter. It is another object of the present invention to provide an inverter thermal protection device and a thermal protection method for a conductive heating element, which can perform thermal protection for them.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention reduces the current requirement for an inverter in accordance with the temperature of the inverter and provides the corrected current requirement to a drive circuit of the inverter. An inverter thermal protection device for suppressing heat generation of the inverter by means of a temperature sensor for indirectly detecting the temperature of a semiconductor power switch element included in the inverter, and a current value based on the current value of the inverter together with a value detected by the temperature sensor. Means for correcting the required value to calculate the corrected required current value.

The present invention also provides a current control circuit for a conductive heating element with a corrected current request value obtained by adding a correction according to the temperature of the heating element to an actual current request value. In the thermal protection method for suppressing heat generation of a body, a temperature sensor is provided apart from the heating element, and a correction based on a current value of the heating element together with a value detected by the temperature sensor is added to the current request value, and the correction is performed. It is characterized in that a required current value is calculated.

In the present invention, a temperature sensor is mounted at a position distant from the heating elements, such as a semiconductor power switch element or the like included in the inverter, and the temperatures thereof are indirectly detected. . Then, based on both the detected value from the temperature sensor and the current value of the inverter, the actual current required value is corrected,
The corrected current request value is provided to the drive circuit of the inverter. In this way, for example, as the current value of the inverter increases, the detection value of the temperature sensor at which the limitation of the current request value starts to be applied can be reduced. For this reason, when the current value of the inverter is small and the allowable heat generation level of the inverter can still be expected, it is possible to avoid unnecessary limitation of the current request value. Thus, according to the present invention, thermal protection can be suitably performed even when a temperature sensor is installed at a distance from a conductive heating element in an inverter or the like.

[0011]

An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a motor drive system according to an embodiment of the present invention. The system shown in FIG. 1 controls the drive of a vehicle drive motor 14 in a hybrid electric vehicle. In particular, according to the present invention, a semiconductor power switch element (power transistor) (not shown) included in the inverter 12 is thermally protected. You.

In the system shown in FIG. 1, electric power is supplied from a battery to an inverter, and the electric power is converted into a three-phase alternating current by the inverter and supplied to the motor 14. The drive circuit 18 includes a motor ECU (Electric Control).
The drive circuit 18 controls the drive of the inverter 12 in accordance with the current command value I, and controls the current value supplied to the motor 14. . The motor ECU 22 controls the EV (El
ectric Vehicle) —Receives a required current value Ia from the ECU 20. In normal times, the received current required value Ia is used as a current command value I in principle.
Give 8 When the inverter 12 (or the semiconductor power switch element included therein) becomes relatively hot, the current command value Ia actually received is multiplied by a coefficient less than 1 (output limiting coefficient α) to obtain the current command value. Output I as a small value. The EV-ECU 20 is a conventionally known electronic control device that determines the current request value Ia in consideration of the accelerator opening of the electric vehicle and the like.

A temperature sensor 16 composed of a thermistor or a thermocouple is attached to the inverter 12 at a position distant from a semiconductor power switch element included therein.
The signal is transmitted to the CU 22 as an electric signal at any time. By attaching the temperature sensor 16 at a position distant from the inverter 12, it is possible to prevent noise generated from the inverter 12 from affecting the detection signal of the temperature sensor 16.

When it is considered that the semiconductor power switch element of the inverter 12 generates a certain amount of heat or more, the motor ECU 22 determines the value detected by the temperature sensor 16 and the current command value I currently given to the drive circuit 18. Based on
A corrected current request value is calculated by restricting the current request value Ia, and the corrected current request value is given to the drive circuit 18 as a current command value I. Specifically, in the motor ECU 22, the temperature sensor 16
The output limiting ratio α (0% to 100%) is calculated on the basis of the detected value obtained at step (1) and the current command value I currently given to the drive circuit 18, and this is multiplied by the current request value Ia. Thus, the current command value I is calculated.

FIG. 2 is a diagram for explaining how the required current value Ia is limited by the motor ECU 22. FIG. 2 shows two lines indicating two output limiting ratios α. The line indicated by A is a comparative example of the output restriction line shown in FIG. 5, and the line indicated by B is an output restriction line in the present motor drive system. Both output limit lines are
In either case, the output limit starts at the lower reference value Ta or TA, and the current command value becomes 0 at the higher reference value Tb or TB.
Is common in that However, while the reference values Ta and Tb are fixed values in the output limiting line according to the prior art shown in A, the reference values TA and TB are used as variables of the current of the inverter 12 in the output limiting line in the present motor drive system. Given.

FIG. 3 is a diagram showing a table for providing reference values TA and TB. The contents of the table shown in FIG. 3 are stored in advance in a memory (not shown) of the motor ECU 22, and the motor ECU 22 specifically calculates the output restriction line shown in FIG.
The output limiting ratio α is derived therefrom. That is, the motor E
The CU 22 uses the current command value (currently corresponding to the current flowing in the semiconductor power switch element of the inverter 12) currently given to the drive circuit 18 for the heat protection process, based on the table shown in FIG. Read the values TA and TB. Then, those values are specifically applied to the output limiting line shown in FIG. 2B, and the output limiting ratio α in the detected temperature value obtained from the temperature sensor 16 is obtained. For example, if the current command value I currently given to the drive circuit 18 is 20
If [A], the motor ECU 22 reads from the table shown in FIG. 3 stored in a memory (not shown) that the corresponding reference values TA and TB are 99 and 109, respectively. Then, the limitation of the current command value starts at 99 [° C.], an output limiting line at which the current command value becomes 0 at 109 [° C.] is derived, and the output limiting rate α corresponding to the current temperature detection value is determined. Thus, in this motor drive system,
The required current value Ia is corrected based on the current value of the inverter 12 in addition to the value detected by the temperature sensor 16.

FIG. 4 is a flowchart illustrating a specific process of the motor ECU 22. As shown in the figure, first, when the motor ECU 22 receives the current request value Ia from the EV-ECU 20, it is recorded from a table stored in a memory (not shown) corresponding to the current command value currently given to the drive circuit 18. The reference values TA and TB that are present are read out (S10
1). Then, an output limiting line is derived using these values, and an output limiting ratio α corresponding to the detected temperature value obtained by the temperature sensor 16 is calculated (S102). Next, the current command value I is calculated by multiplying the required current value Ia received from the EV-ECU 20 by the output limiting ratio α (S10).
3). Thereafter, the current command value I thus obtained is sent to the drive circuit 18 (S104).

According to the motor drive system described above, the current flowing through the inverter 12 can be controlled even when the output is already limited according to the conventional output limit line (see FIG. 2A). If the output is small and no output restriction is actually required, such unnecessary restriction is not applied. Therefore, the heat resistance of the inverter 12 can be sufficiently exhibited, and the power performance of the electric vehicle can be increased.

Further, since an optimum output limit map can be provided for each current value in the inverter 12, it is possible to avoid a rapid change in the current value even when the output is actually limited. For example, a change in the torque of the motor 14 can be maintained smoothly.

The above-described motor drive system according to the present embodiment can be variously modified. For example, in the above description, the current limitation of the inverter was described. However, the same applies to the chopper circuit. When the current control circuit supplies a current based on the instruction input to the conductive heating element, the instruction input is performed according to the temperature of the heating element. In the case of limiting the temperature, it is possible to suitably achieve thermal protection by performing the same operation as described above.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a motor drive system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a map for determining a limitation on a current command value in a motor ECU.

FIG. 3 shows characteristic values Ta and T in the map shown in FIG.
It is a figure which shows the table which gives b for every output current.

FIG. 4 is a flowchart illustrating processing in a motor ECU.

FIG. 5 is a diagram illustrating heat protection by current command value limitation according to the related art.

[Explanation of symbols]

Ia current required value, I current command value (corrected current required value), 10 battery, 12 inverter, 14 motor, 16 temperature sensor, 18 drive circuit, 20EV-E
CU, 22 Motor ECU.

Claims (2)

[Claims] 1. An inverter thermal protection device for reducing a required current value of an inverter according to a temperature of the inverter and supplying the corrected required current value to a drive circuit of the inverter, thereby suppressing heat generation of the inverter, wherein the inverter includes: A temperature sensor for indirectly detecting the temperature of the semiconductor power switch element to be detected, and correcting the current request value based on the current value of the inverter together with the value detected by the temperature sensor to calculate the corrected current request value. Means, and an inverter thermal protection device comprising: 2. A method according to claim 1, wherein a current control circuit for the conductive heating element is provided with a corrected current request value obtained by adding a correction according to a temperature of the heating element to an actual current request value. In the thermal protection method for suppressing, a temperature sensor is provided separately from the heating element, and a correction based on a current value of the heating element is added to the current request value together with a value detected by the temperature sensor, and the corrected current request value is added. A heat protection method characterized by calculating