JP2016208667A - Overcurrent protective device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overcurrent protective device capable of correctly determining an overcurrent, if a current measurement value becomes abnormal.SOLUTION: The overcurrent protective device includes: a temperature measurement unit which measures the temperature of an element in an inverter, to output the temperature measurement value of the element; a load current measurement unit which measures a load current flowing between the inverter and a load, to output a current measurement value of the load current; and a microcomputer which controls the electric conduction of the element on the basis of the current measurement value, and estimates the element temperature from the current measurement value to derive the temperature estimation value of the element. The microcomputer determines that the electric conduction current of the element is an overcurrent when the current measurement value is a predetermined threshold or lower and the temperature measurement value is different from the temperature estimation value by a predetermined difference or greater.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an overcurrent protection device.

  2. Description of the Related Art Conventionally, in a transistor protection circuit, a technique for determining that an overcurrent has been detected when a signal level input by measuring a drain current exceeds a predetermined reference voltage is known (for example, see Patent Document 1). ).

Japanese Patent Laid-Open No. 07-84655

  However, in the above-described prior art, when the measured value of the current becomes abnormal, the signal level compared with the reference voltage also becomes abnormal, so that the overcurrent cannot be correctly determined. Therefore, an object of the present invention is to provide an overcurrent protection device that can correctly determine an overcurrent even if a current measurement value becomes abnormal.

One idea is that
A temperature measuring unit that measures the temperature of the element in the inverter and outputs a temperature measurement value of the element;
A load current measurement unit that measures a load current flowing between the inverter and a load and outputs a current measurement value of the load current;
A microcomputer that controls energization of the element based on the current measurement value, and estimates the temperature of the element from the current measurement value to derive a temperature estimation value of the element;
The microcomputer determines an energization current of the element as an overcurrent when the measured current value is equal to or less than a predetermined threshold value and the measured temperature value and the estimated temperature value are more than a predetermined difference. A protection device is provided.

  According to one aspect, even if the current measurement value becomes abnormal, the difference between the temperature measurement value and the temperature estimation value is taken into account, so that an overcurrent can be correctly determined.

It is a figure which shows an example of a structure of a drive system provided with an overcurrent protection apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating an example of a configuration of a drive system including an overcurrent protection device 1. The drive system of FIG. 1 includes a motor 10, an inverter 30 that drives the motor 10, and an overcurrent protection device 1. The overcurrent protection device 1 is a device that protects elements in the inverter 30 from overcurrent.

  The inverter 30 is an example of a drive circuit that drives the three-phase motor 10. The inverter 30 includes a series circuit in which a high-side element and a low-side element are connected in series, three in number, which are the same as the number of phases of the three-phase motor 10. The first-phase series circuit includes an element 31 provided on the high-side power supply potential 40 side with respect to the intermediate node 37 and an element 32 provided on the low-side ground potential 41 side with respect to the intermediate node 37. . Similarly, the second-phase series circuit includes a high-side element 33 with respect to the intermediate node 38 and a low-side element 34 with respect to the intermediate node 38, and the third-phase series circuit includes an intermediate node 39. In contrast, a high-side element 35 and a low-side element 36 with respect to the intermediate node 39 are included.

  Each of the elements 31 to 36 is a switching element that is turned on / off according to a drive signal supplied from the microcomputer 50. As a specific example of the switching element, a transistor such as an IGBT having a reflux diode connected in parallel can be given.

  The motor 10 is an example of an inductive load connected to the intermediate nodes 37, 38, and 39, and is a power source that moves the vehicle, for example.

  The overcurrent protection device 1 includes, for example, a temperature measurement unit 44, a load current measurement unit 20, and a microcomputer 50.

  The temperature measurement unit 44 measures the temperature of a specific element in the inverter 30 and outputs a temperature measurement value Ts of the specific element. The specific element in the inverter 30 may be all of the elements 31 to 36 or a part of the elements 31 to 36.

  For example, the temperature measurement unit 44 measures the temperature of an element (that is, an element on the same chip as the temperature measurement unit 44) formed on the chip on which the temperature measurement unit 44 is provided, and the temperature measurement element 44 An element temperature signal representing the temperature measurement value Ts is output. For example, the temperature measurement unit 44 that outputs the temperature measurement value Ts of the element 31 is provided on the same chip as the element 31. The temperature measurement unit 44 can increase the measurement accuracy of the temperature measurement value Ts by measuring the temperature of the elements on the same chip. The temperature measurement unit 44 may be provided for all of the elements 31-36, or may be provided for some of the elements 31-36.

  The load current measuring unit 20 measures a load current Im flowing between the inverter 30 and the motor 10 and outputs a current measurement value Ima of the load current Im. The load current measurement unit 20 is, for example, a current sensor that monitors a current wiring connecting the inverter 30 and the motor 10 and outputs a load current signal representing the current measurement value Ima.

  The microcomputer 50 controls energization of each element 31-36 in the inverter 30 based on the current measurement value Ima, and estimates the temperature of each element 31-36 in the inverter 30 from the current measurement value Ima. The temperature estimated value Te of the elements 31-36 is derived. Since the load current Im flows through each element 31-36, the energization current Ic of each element 31-36 increases as the load current Im increases. On the other hand, the temperature of each element 31-36 increases as the conduction current Ic of each element 31-36 increases. That is, the temperature of each element 31-36 correlates with the current value of the load current Im. In addition, since the energization of each element 31-36 is controlled based on the current measurement value Ima, the energization time and the current value of the energization current Ic of each element 31-36 are determined according to the current measurement value Ima. Therefore, the microcomputer 50 can estimate the temperature of each element 31-36 from the measured current value Ima of the load current Im, and can derive the estimated temperature value Te of each element 31-36.

  Next, when the microcomputer 50 controls the energization of each element 31-36 based on the current measurement value Ima, the current measurement value Ima becomes an abnormal value (for example, zero) due to an abnormality of the load current measurement unit 20. Let us consider a case in which a failure that decreases rapidly occurs.

  When the microcomputer 50 detects a decrease in the current measurement value Ima input by feedback, the microcomputer 50 performs negative feedback control so that the actual load current Im increases, thereby controlling the energization of each element 31-36. Therefore, when the failure occurs, the energization current Ic flowing through each element 31-36 starts to increase compared to the normal time, so that the temperature measurement value Ts that is an actual measurement value of the temperature of each element 31-36 is also higher than the normal time. Also starts to rise. However, even if the load current Im starts to increase, the current measurement value Ima remains lowered to an abnormal value due to the failure. Therefore, the microcomputer 50 controls energization of each element 31-36 so that the load current Im further increases by feedback input of the current measurement value Ima. As a result, the energization current Ic flowing through each element 31-36 becomes excessive (that is, the overcurrent flows through each element 31-36), and the temperature measurement value Ts of each element 31-36 further increases. Become.

  On the other hand, since the microcomputer 50 estimates the temperature of each element 31-36 from the current measurement value Ima, the current measurement value Ima drops to an abnormal value (for example, zero) when the failure occurs, so that each element 31-31. A temperature estimate Te lower than the actual temperature of -36 is derived. That is, the temperature estimated value Te is lower than that in the normal state and deviates from the temperature measured value Ts.

  Therefore, the microcomputer 50 reduces the current measurement value Ima to a predetermined threshold value Ith or less and the temperature measurement value Ts of the element in the inverter 30 and the temperature estimation value Te of the element deviate by a predetermined difference or more. The energization current Ic flowing through the element is determined as an overcurrent. According to this determination method, even if the current measurement value Ima becomes abnormal, the difference between the temperature measurement value Ts and the temperature estimation value Te is taken into account, so that the overcurrent can be correctly determined.

  The threshold value Ith is a value larger than zero. Of the elements 31-36 in the inverter 30, the measured temperature value Ts and the estimated temperature value Te may be compared with some or all elements.

  Further, since the microcomputer 50 has the function of comparing the temperature measurement value Ts and the temperature estimation value Te in this way, the overcurrent determination variation range can be reduced. The overcurrent determination variation range refers to the lowest lower limit current value (determination variation lower limit) at which the energization current Ic is not determined to be an overcurrent and the highest upper limit current value (determination variation upper limit) at which the energization current Ic is not determined to be an overcurrent. It is an abnormal current region between.

  Further, when the microcomputer 50 determines that the energization current Ic of at least one element in the inverter 30 is an overcurrent, the microcomputer 50 stops controlling the energization of each element 31-36 based on the current measurement value Ima. The microcomputer 50 controls the energization of each element 31-36 by supplying a predetermined drive signal for reducing the current value of the energization current Ic of each element 31-36 to the normal current region. Start. The normal current region is a normal current region whose current value is lower than the determination variation lower limit. By starting such control, the microcomputer 50 can protect each element 31-36 from overcurrent and can continuously operate in the normal current range, and operate each element 31-36 in the abnormal current range. It is possible to avoid a decrease in service life due to.

  On the other hand, when the current measurement value Ima exceeds the predetermined threshold value Ith, the microcomputer 50 does not determine that the energization current Ic of each element 31-36 in the inverter 30 is an overcurrent. Alternatively, when the measured temperature value Ts of the element in the inverter 30 and the estimated temperature value Te of the element do not deviate by a predetermined difference or more, the microcomputer 50 does not determine the energization current Ic flowing through the element as an overcurrent. .

  By the way, the overcurrent protection device 1 may include an element current measurement unit 45. The element current measuring unit 45 measures the energization current Ic of a specific element in the inverter 30 and outputs a current measurement value Ica of the energization current Ic of the specific element. The element current measurement unit 45 is provided, for example, on the same chip or a different chip as the element to be measured for the energization current Ic, and outputs an element current signal representing the current measurement value Ica. For example, the element current measuring unit 45 may be provided on a semiconductor substrate different from the element to be measured for the energization current Ic. The element current measurement unit 45 may be provided for all elements of the elements 31-36, or may be provided for a part of the elements 31-36.

  According to the above determination method, the microcomputer 50 determines that the element current measurement unit 45 itself determines that the energization current Ic of a specific element is an overcurrent based on the current measurement value Ica and turns off the element having the characteristic. The energization current Ic flowing through the specific element can be determined as an overcurrent. Therefore, the microcomputer 50 outputs a predetermined drive signal for reducing the current value of the energization current Ic of each element 31-36 to the normal current range before the specific element is turned off by the element current measuring unit 45. By supplying, control of energization of each element 31-36 can be started. Thereby, a sudden change in the load current I due to the specific element being turned off can be suppressed.

  Further, the state where the current measurement value Ima falls below a predetermined threshold value Ith and the temperature measurement value Ts of the element in the inverter 30 and the temperature estimation value Te of the element deviate by a predetermined difference or more is referred to as “state X " For example, when the state X is established and the measured current value Ima and the measured current value Ica of the element deviate by a predetermined second difference or more, the microcomputer 50 converts the energization current Ic flowing through the element into an overcurrent. Is determined. According to this determination method, even if the current measurement value Ima becomes abnormal, the difference between the current measurement value Ima and the current measurement value Ica is also taken into account, so that it is possible to correctly determine the overcurrent and to determine the overcurrent. The variation range can be further reduced.

  On the other hand, when the current measurement value Ima and the current measurement value Ica of the element do not deviate by a predetermined second difference or more, the microcomputer 50 does not determine that the energization current Ic flowing through the element is an overcurrent.

  Incidentally, there may be a case where the temperature measurement value Ts of the element in the inverter 30 is abnormal due to a failure of the temperature measurement unit 44. Therefore, a state in which the state X is established and the current measurement value Ima and the current measurement value Ica of the element are different from each other by a predetermined second difference is referred to as “state Y”. In the microcomputer 50, the state Y is established, the current measurement value Ica of the element is equal to or greater than a predetermined current threshold (for example, the lower limit of determination variation), and the temperature measurement value Ts of the element is equal to the temperature of the element. When higher than the estimated value Te, the energizing current Ic flowing through the element is determined as an overcurrent. According to this determination method, even if the temperature measurement value Ts of the element is abnormal, the overcurrent can be correctly determined.

  Further, when the microcomputer 50 controls the energization of each element 31-36 based on predetermined input information input to the microcomputer 50 separately from the current measurement value Ima, the microcomputer 50 determines the input information and the current measurement value Ima. The temperature estimated value Te may be derived. Examples of the input information include vehicle information that represents the operating state of the vehicle on which the microcomputer 50 is mounted. Specific examples of the vehicle information include accelerator pedal opening information and vehicle speed information.

  The overcurrent protection device has been described above by way of the embodiment, but the present invention is not limited to the above embodiment. Various modifications and improvements such as combinations and substitutions with some or all of the other embodiments are possible within the scope of the present invention.

  For example, the inverter does not drive a motor but may drive another inductive load.

1 Overcurrent Protection Device 20 Load Current Measuring Unit 30 Inverter 31-36 Element 44 Temperature Measuring Unit 45 Element Current Measuring Unit 50 Microcomputer

Claims (1)

A temperature measuring unit that measures the temperature of the element in the inverter and outputs a temperature measurement value of the element;
A load current measurement unit that measures a load current flowing between the inverter and a load and outputs a current measurement value of the load current;
A microcomputer that controls energization of the element based on the current measurement value, and estimates the temperature of the element from the current measurement value to derive a temperature estimation value of the element;
The microcomputer determines an energization current of the element as an overcurrent when the measured current value is equal to or less than a predetermined threshold value and the measured temperature value and the estimated temperature value are more than a predetermined difference. Protective device.

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