JP2014057475A - Voltage control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent overheat of each element constituting a circuit by single temperature measurement means.SOLUTION: A voltage control circuit includes: a circuit having inverter FETs 41A to 41F for adjusting power supplied to a supply target of the power and a reverse connection preventing FET 44 for preventing damage of the circuit due to erroneous connection; a single thermistor 46 provided at a position spaced apart from the inverter FETs 41A to 41F and the reverse connection preventing FET 44, and measuring the overheat state of the inverter FETs 41A to 41F and the reverse connection preventing FET 44 at the position; and a microcomputer 31 controlling to limit power outputted from the inverter FETs 41A to 41F when the overheat state measured by the thermistor 46 exceeds an overheat-state determination threshold defined in accordance with an applied power-supply voltage.

Description

  The present invention relates to a voltage control circuit.

  A semiconductor such as an FET (Field Effect Transistor) is mounted as a switching element in an inverter circuit that controls driving of the motor. However, semiconductors such as FETs may be damaged when the temperature exceeds a predetermined temperature. The inverter circuit for driving control of the motor senses the temperature of the element, and when the element temperature exceeds a predetermined threshold, the duty ratio of the current pulse supplied to the motor to be controlled is reduced to reduce the motor Control to reduce the rotational speed. By reducing the duty ratio of the pulse of the current supplied to the motor, the current flowing through the element of the inverter circuit is suppressed, so that the element can be prevented from overheating.

  Patent Document 1 discloses a motor control unit in which a substrate on which a temperature detection thermistor is mounted is incorporated.

JP 2006-108398 A

  However, the inverter circuit that controls the drive of the motor includes a reverse connection prevention FET provided for circuit protection in addition to the inverter FET provided in the inverter circuit that switches power supplied to the motor. Similarly to the inverter FET, the reverse connection prevention FET also becomes a heat source while the inverter circuit is operating. Furthermore, the inverter circuit that controls the drive of the motor may be provided with a coil for noise removal, and this coil also becomes a heat source during operation of the inverter circuit.

  In order to perform control to prevent overheating of the inverter circuit, it is necessary to sense the temperatures of the inverter FET, the reverse connection prevention FET, and the coil. However, providing a plurality of temperature detection sensors in the inverter circuit has a problem in that it increases the cost of a motor drive control device using the inverter circuit.

  The present invention has been made in view of the above, and an object thereof is to provide a voltage control circuit capable of preventing overheating of each element constituting a circuit by means related to a single temperature measurement.

  In order to solve the above-described problem, the voltage control circuit according to claim 1 includes a first element that adjusts power supplied to a power supply target, and a second element that prevents damage to the circuit due to erroneous connection. And a single circuit for measuring an overheat state of the first element and the second element at the provided position, and provided at a position away from the first element and the second element. When the overheat state measuring means and the overheat state measured by the overheat state measurement means exceed the overheat state determination threshold determined according to the applied power supply voltage, the power output by the first element is Control means for controlling to limit.

  This voltage control circuit sets the overheat state determination threshold value according to the voltage applied to the circuit, and when the overheat state measured by the overheat state measurement unit exceeds the overheat state determination threshold value, Restricts (suppresses) the voltage output by.

  In addition, since this voltage control circuit has an overheat state determination threshold value set according to the voltage applied to the circuit, a single temperature measurement is performed for overheating of multiple types of elements having different degrees of overheating depending on the voltage applied to the circuit. It can prevent by the means which concerns on.

  A voltage control circuit according to a second aspect is the voltage control circuit according to the first aspect, wherein the first element is a field effect transistor constituting an inverter circuit, and the second element A reverse connection prevention field effect transistor and a noise removing coil which are provided between a power supply to be applied and the first element and constitute the inverter circuit.

  According to this voltage control circuit, overheating of different types of elements constituting the inverter circuit can be prevented by means relating to a single temperature measurement.

  The voltage control circuit according to claim 3 is the voltage control circuit according to claim 1 or 2, wherein the control means outputs the voltage by reducing the duty ratio of the voltage output by the circuit. Reduce voltage.

  According to this voltage control circuit, by reducing the duty ratio of the voltage output from the circuit, it is possible to reduce the load of the elements constituting the circuit and prevent overheating of each element.

  A voltage control circuit according to a fourth aspect of the present invention is the voltage control circuit according to any one of the first to third aspects, wherein the circuit is a motor drive control circuit that controls driving of the motor.

  According to this voltage control circuit, since the element mounted on the substrate can be prevented from being overheated as described above, it is possible to control to continue driving the motor.

It is the schematic which shows the structure of the motor unit using the voltage control circuit which concerns on embodiment of this invention. It is a figure which shows an example of the board | substrate of the voltage control circuit which concerns on embodiment of this invention. It is a figure which shows the outline of the voltage control circuit which concerns on embodiment of this invention. It is a figure which shows an example of the change of the pulse output from the inverter circuit of the voltage control circuit which concerns on embodiment of this invention. It is a flowchart which shows an example of control of the motor drive control apparatus using the voltage control circuit which concerns on embodiment of this invention. It is a figure which shows an example of the correspondence of the power supply voltage and overheat state determination threshold value in the voltage control circuit which concerns on embodiment of this invention.

  FIG. 1 is a schematic diagram showing a configuration of a motor unit 10 using a voltage control circuit according to the present embodiment. The motor unit 10 according to the present embodiment in FIG. 1 is a so-called blower motor unit used for blowing air from an in-vehicle air conditioner as an example.

  The motor unit 10 according to the present embodiment relates to a three-phase motor having an outer rotor structure in which a rotor 12 is provided outside a stator 14. The stator 14 is an electromagnet in which a lead wire is wound around a core member, and constitutes three phases of a U phase, a V phase, and a W phase.

  Each of the U-phase, V-phase, and W-phase of the stator 14 generates a so-called rotating magnetic field by switching the polarity of the magnetic field generated by the electromagnet under the control of a motor drive control device 20 described later.

  A rotor magnet is provided inside the rotor 12 (not shown), and the rotor magnet rotates the rotor 12 by responding to the rotating magnetic field generated by the stator 14.

  The rotor 12 is provided with a shaft 11 and rotates integrally with the rotor 12. Although not shown in FIG. 1, in this embodiment, the shaft 11 is provided with a multi-blade fan such as a so-called sirocco fan, and the multi-blade fan rotates together with the shaft 11 so It becomes possible.

  The stator 14 is attached to the motor drive control device 20 via the upper case 13. The motor drive control device 20 includes a substrate 22 of a voltage control circuit and a heat sink 21 that dissipates heat generated from elements on the substrate 22.

  A lower case 50 is attached to the motor unit 10 including the rotor 12, the stator 14, and the motor drive control device 20.

  Subsequently, the substrate of the voltage control circuit according to the present embodiment will be described with reference to FIG. FIG. 2 is a diagram illustrating an example of the substrate 22 of the voltage control circuit according to the embodiment of the present invention. In FIG. 2, the board 22 is provided with an external connection connector 23 to which electric power is supplied from an in-vehicle battery and a control signal related to the in-vehicle air conditioner is input via a control device such as an ECU (Electronic Control Unit). It has been.

  An inverter circuit 40 for controlling power supplied to the U phase, V phase, and W phase of the stator 14 is mounted on the substrate 22. The inverter circuit 40 of the motor drive control apparatus 20 according to the present embodiment is a voltage source inverter that operates as a voltage source by connecting large-capacitance capacitors 42A, 42B, 42C, and 42D in parallel to a DC side circuit.

  The inverter circuit 40 includes inverter FETs 41A, 41B, 41C, 41D, 41E, and 41F as switching elements. The inverters FET 41A and 41D switch the power supplied to the U phase, the inverters FET 41B and 41E switch to the V phase, and the inverters FET 41C and 41F switch to the W phase. The electric power controlled by the switching of the inverters FET41A to 41F is supplied to the stator 14 via the power supply terminals 24A, 24B, and 24C.

  On the DC side of the inverter circuit 40 on the substrate 22, a noise removing coil 43 is provided, and a reverse connection prevention FET 44 and a large-capacitance capacitor 42E are provided. A microcomputer 31 for controlling the inverter circuit 40 is mounted on the substrate 22. The reverse connection prevention FET is an FET for protecting the inverter circuit 40 when the vehicle battery is connected with the opposite polarity.

  In the substrate 22 shown in FIG. 2, the inverter FETs 41A to 41F, the coil 43, and the reverse connection prevention FET 44 generate significant heat during operation. In the present embodiment, the heat sink 21 is attached by the fixing bolt 29 on the back side of the portion where the element that generates significant heat during operation is mounted.

  A thermistor 46, which is a temperature sensor that senses the temperature of the substrate, is mounted on the substrate 22 near the inverter FET 41B. In this embodiment, when there is a possibility that the temperature of the element becomes equal to or higher than a predetermined threshold, the duty ratio of the pulse of the current output from the inverter circuit 40 is reduced to prevent the element from being damaged by heat.

  FIG. 3 is a diagram schematically illustrating the voltage control circuit according to the present embodiment. The inverter FET 41 switches power supplied to the coil of the stator 14 of the motor 16. For example, the inverter FETs 41A and 41D switch the power supplied to the U-phase coil 14U, the inverter FETs 41B and 41E switch to the V-phase coil 14V, and the inverter FETs 41C and 41F switch the power supplied to the W-phase coil 14W.

  The drains of the inverters FET 41A, 41B, and 41C are connected to the positive electrode of the on-vehicle battery 80 via the noise removing coil 43. The sources of the inverters FET 41D, 41E, and 41F are connected to the negative electrode of the battery 80 via the reverse connection prevention FET 44.

  In the present embodiment, a reverse connection prevention FET 44 and a coil 43 are provided between a battery 80 as a power source and the inverter FET 41.

  In the present embodiment, the Hall element 12B detects the magnetic field of the sensor magnet 12A provided coaxially with the shaft 11. The microcomputer 31 detects the position (rotational position) of the rotor 12 based on the detected magnetic field, and controls switching of the inverter FET 41 according to the rotational position of the rotor 12.

  Further, a control signal from an air conditioner ECU for controlling the air conditioner and a resistance value signal from the thermistor 46 are input to the microcomputer 31, and the switching of the inverter FET 41 is controlled based on these input signals.

  FIG. 4 is a diagram illustrating an example of changes in pulses output from the inverter circuit 40. When the element is not overheated, a pulse having a duty ratio shown in FIG. A sine wave 60 shown in FIG. 4A shows the average voltage and frequency of the pulse shown in FIG.

  When the element may be overheated, a pulse having a duty ratio smaller than that in the case of FIG. 4A is output as shown in FIG. A sine wave 62 shown in FIG. 4B is the average voltage and frequency of the pulse shown in FIG. 4B, and the average voltage and frequency are lower than in the case of FIG.

  When the duty ratio of the pulse output from the inverter circuit 40 is reduced and the average voltage and frequency of the pulse are reduced, the current flowing through the inverter FETs 41A to 41F, which are switching elements, decreases, so that the inverter FETs 41A to 41F are overheated. Can be prevented.

  Further, in a vehicle equipped with a battery, the voltage that should originally be 12 V may vary depending on the state of charge of the battery. In the element of the inverter circuit 40 of the motor drive control device according to the present embodiment, the amount of generated heat changes depending on the voltage of power supplied from the battery via the external connection connector 23. For example, the inverter FETs 41 </ b> A to 41 </ b> F are likely to become high temperature when the battery voltage is a high voltage of about 16 V, and the reverse connection prevention FET 44 and the coil 43 are likely to become high temperature when the battery voltage is low to 8 to 11 V.

  When the battery voltage is high, a larger load is applied to the inverter FETs 41A to 41F than when the battery voltage is low, and the inverter FETs 41A to 41F are likely to be hot. In particular, when the battery voltage is 16 V, the inverter FETs 41A to 41F have the highest temperature due to the influence of the heat generated by the switching losses by the inverter FETs 41A to 41F in addition to the high voltage.

  When the voltage of the battery exceeds 16V, the time for which the inverter FETs 41A to 41F stop energizing in order to limit the current supplied to the motor becomes long, so that the current flowing through the inverter FETs 41A to 41F decreases and the inverter The temperatures of the FETs 41A to 41F are lower than when the battery voltage is 16V.

  When the voltage of the battery is low, the inverter FETs 41A to 41F are in a full-on state in order to increase the current supplied to the motor. As a result, the switching losses of the inverters FET41A to 41F are eliminated, and the low voltage of the power supplied from the battery is also affected, so that the inverters FET41A to 41F have a lower temperature than when the battery voltage is high.

  The reverse connection prevention FET 44 is in an on state when the battery polarity is correctly connected. However, when the voltage supplied from the battery is high, the inverter FETs 41A to 41F stop energization in order to limit the current supplied to the motor. While the inverter FETs 41 </ b> A to 41 </ b> F are not energized, no current flows through the reverse connection prevention FET 44, so that the heat generation of the reverse connection prevention FET 44 is suppressed.

  Further, while the inverter FETs 41A to 41F are not energized, no current flows through the coil 43. Therefore, when the voltage supplied from the battery is high, heat generation of the coil 43 is suppressed.

  When the voltage of the battery is low, the inverters FET 41A to 41F are in a full-on state, and a current continues to flow through the reverse connection prevention FET 44, so that heat generation of the reverse connection prevention FET 44 is promoted.

  When the inverter FETs 41 </ b> A to 41 </ b> F are in a full-on state, current continues to flow through the coil 43.

  FIG. 5 is a flowchart showing an example of control of the motor drive control device using the voltage control circuit according to the present embodiment.

  In the present embodiment, the microcomputer 31 sets the overheat state determination threshold value based on the voltage of the power supplied via the external connection connector 23 in step 500 of FIG. The overheat state determination threshold is, for example, a threshold that changes with respect to the power supply voltage as shown in FIG. FIG. 6 is a diagram illustrating an example of a correspondence relationship between the power supply voltage and the overheat state determination threshold in the voltage control circuit according to the present embodiment.

  In the present embodiment, the correspondence relationship between the power supply voltage and the threshold value as shown in FIG. 6 is stored in advance in a memory mounted on the substrate 22, and the measured power supply voltage is applied to the correspondence relationship to determine the overheat state. Set the threshold. The overheat state determination threshold value may vary depending on the configuration of the inverter circuit. For example, the correspondence relationship between the power supply voltage and the overheat state determination threshold may be affected by the relative positional relationship between each element and the thermistor 46 on the substrate 22. For this reason, it is preferable to determine the correspondence relationship between the power supply voltage and the overheat state determination threshold through a simulation using a computer or a test using a prototype.

  The voltage value of the electric power supplied from the battery is obtained via an external connection connector 23 as measured by an in-vehicle voltage measuring means (not shown). The voltage measuring means is provided on the substrate 22 and this voltage measurement is performed. The voltage value measured by the means may be used.

  In step 502, it is determined whether the temperature detected by the thermistor 46 is equal to or higher than the overheat state determination threshold value.

  If the determination in step 502 is affirmative, the inverter FETs 41A to 41F, the reverse connection prevention FET 44, or the coil 43 mounted on the substrate 22 may be overheated. In step 504, the duty ratio of the current output from the inverter circuit 40 is reduced as shown in FIG. 4B, or the output of the inverter circuit 40 is stopped to protect the element from overheating.

  After performing control to protect the inverter FETs 41A to 41F, the reverse connection prevention FET 44, or the coil 43 from overheating in step 504, the procedure is returned to step 500, and the procedures of steps 500 and 502 are repeated.

  If the determination in step 502 is negative, the inverter FETs 41A to 41F, the reverse connection prevention FET 44, and the coil 43 are not likely to be overheated, so in step 506, normal control of the inverter circuit 40 is performed without reducing the duty ratio.

  As described above, according to the present embodiment, the overheat state determination threshold is set according to the voltage value of the electric power supplied to the inverter circuit, and the thermistor, which is a temperature measurement means provided on the substrate, senses it. It is determined whether the measured temperature is equal to or higher than an overheat state determination threshold set in accordance with the voltage value of power. As a result, it is possible to control the inverter circuit that prevents overheating of each element whose heat generation depends on the voltage by a single temperature measuring means.

DESCRIPTION OF SYMBOLS 10 ... Motor unit, 11 ... Shaft, 12 ... Rotor, 12A ... Sensor magnet, 12B ... Hall element, 13 ... Upper case, 14 ... Stator, 14U, 14V, 14W ... coil, 16 ... motor, 20 ... motor drive control device, 21 ... heat sink, 21A ... projection, 22 ... substrate, 23 ... external connection connector, 24A, 24B , 24C: power supply terminal, 25: ground potential region, 26: insulating member, 27, 28 ... projection, 29 ... fixing bolt, 31 ... microcomputer, 40 ... Inverter circuit, 41A, 41B, 41C, 41D, 41E, 41F ... Inverter FET, 42A, 42B, 42C, 42D, 42E ... Capacitor, 43 ... Coil, 44 ... Contact prevention FET, 46 ... thermistor, 50 ... lower case, 60, 62 ... sinusoidal wave, 80 ... battery, 82 ... air conditioner ECU

Claims (4)

A circuit comprising: a first element that adjusts power supplied to a power supply target; and a second element that prevents damage to the circuit due to erroneous connection;
A single overheat state measuring means provided at a position away from the first element and the second element, and measuring an overheat state of the first element and the second element at the provided position;
When the overheat state measured by the overheat state measuring means exceeds an overheat state determination threshold determined according to the applied power supply voltage, control is performed so as to limit the power output from the first element. Control means;
Voltage control circuit with   The first element is a field effect transistor constituting an inverter circuit, and the second element is provided between a power supply for applying the voltage and the first element to constitute the inverter circuit. 2. The voltage control circuit according to claim 1, wherein the voltage control circuit is a reverse connection prevention field effect transistor and a noise removal coil.   The voltage control circuit according to claim 1, wherein the control unit reduces the voltage output from the circuit by reducing a duty ratio of a voltage output from the circuit.   The voltage control circuit according to claim 1, wherein the circuit is a motor drive control circuit that controls driving of a motor.

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