JP5974989B2 - Method and apparatus for switching control of power MOSFET - Google Patents

Description

  The present invention relates to a switching control method and apparatus for a power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), and in particular, when the conduction of a power MOSFET incorporated in a rechargeable battery module used in an electric vehicle or the like is cut off. The present invention relates to a switching control method and apparatus.

  A rechargeable battery module such as a lithium ion battery used in an electric vehicle such as a forklift has a battery module to a load in order to protect the battery and prevent the occurrence of ignition in the event of abnormality of the battery in the battery module. A switch using a power MOSFET that cuts off the power supply is provided.

  The switching of the power MOSFET shifts through a predetermined transition period when shifting from the on state to the off state. FIG. 4 schematically shows how the drain current changes when the power MOSFET is off and how the drain-source voltage changes. 4A shows a change in the drain current of the power MOSFET, and FIG. 4B shows a change in the drain-source voltage of the power MOSFET.

  As shown in FIG. 4A, the drain current of the power MOSFET gradually decreases from the current Ion in the on-state during the transition period from t1 to t2 when the on-state transitions to the off-state, and is zero in the off-state. Become.

  In FIG. 4A, the change in the drain current is indicated by a straight line during the transition period from t1 to t2, but the change in the drain current during the transition period depends on the transient characteristics of the load current flowing through the load.

  As shown in FIG. 4B, the drain-source voltage of the power MOSFET gradually increases from substantially zero during the transition period from t1 to t2 when the power MOSFET transitions from the on state to the off state.

  In FIG. 4B, the change in the drain-source voltage is shown by a straight line in the transition period from t1 to t2, but the change in the drain-source voltage in the transition period is the load current flowing through the load. Depends on transient characteristics.

  As shown in FIG. 4, in the power MOSFET, the drain-source voltage is substantially equal to zero in the on state, and the loss power determined by the product of the voltage and current is substantially zero. In the off state, the drain current is zero, and the power loss determined by the product of the voltage and current is zero.

  However, in the transition period from t1 to t2 from the ON state to the OFF state, the drain current and the drain-source voltage are both zero or more, and the loss power determined by the product of the voltage and the current does not become zero. The power loss causes the power MOSFET to generate heat. This loss power is referred to as switching loss.

  In order to reduce the switching loss and switching noise that occur when the power MOSFET is turned off, the current of the load circuit with an inductor (coil) is detected, and when the current of the load circuit falls below a predetermined current A technique for controlling the power MOSFET to an off state is described in, for example, Patent Document 1 below.

JP 2012-143115 A

  When the power MOSFET is turned off, the on-resistance of the power MOSFET (the value obtained by dividing the drain-source voltage by the drain current) gradually increases during the transition period in which the power MOSFET transitions from the on state to the off state. Switching loss occurs during the transition period.

  At this time, when a large current flows through the load as in an electric vehicle or the like, the switching loss also increases, and the power MOSFET may be destroyed (heat damaged) due to heat generated by the switching loss.

  In view of the above problems, the present invention reduces the power MOSFET switching loss and prevents thermal damage when the power MOSFET provided in series between the battery and the load is controlled to be in the off state. A switching control method and apparatus are provided.

  A power MOSFET switching control device according to the present invention is a power MOSFET switching control device connected in series to a battery in a battery module, the current sensor detecting a battery current flowing through the battery, and the current sensor. A current determination unit that compares the detected battery current with a predetermined threshold and determines whether or not the battery current exceeds a predetermined threshold, and a load current reduction that reduces a load current of a load fed from the battery A load current reduction requesting unit that requests the load current reducing unit to reduce the load current when the battery current exceeds the predetermined threshold; and And a power MOSFET off control means for controlling the power MOSFET to an off state when

  A switching control device for a power MOSFET connected in series to a battery in the battery module, the current sensor detecting a battery current flowing through the battery, and the battery current detected by the current sensor as a predetermined threshold value A comparison is made to determine whether the battery current exceeds a predetermined threshold, and when the battery current exceeds the predetermined threshold, the vehicle control microcontroller is requested to reduce the load current. A request signal is transmitted, and when the battery current is equal to or less than the predetermined threshold, a battery monitoring microcontroller that controls the power MOSFET to be in an off state, and controlling power supply from the battery to a vehicle load, A vehicle control microcontroller that reduces the load current of the vehicle load in response to the request signal from the battery monitoring microcontroller. Characterized by comprising a la, the.

  The switching control method for a power MOSFET according to the present invention is a switching control method for a power MOSFET connected in series to a battery in a battery module, and detects a battery current flowing in the battery and sets the battery current to a predetermined value. A current determination step for determining whether or not the battery current exceeds a predetermined threshold and a load current of a load fed from the battery when the battery current exceeds a predetermined threshold A load current reduction request step for requesting to reduce the load current, and after requesting to reduce the load current, it is determined whether or not the battery current exceeds the predetermined threshold value, and the battery current is determined to be the predetermined threshold value. A power MOSFET off control step of controlling the power MOSFET to an off state when

  According to the present invention, when the power MOSFET provided in series between the battery and the load is controlled to be turned off, the current flowing through the power MOSFET is reduced to a predetermined threshold value or less to be turned off, Switching loss of the power MOSFET can be reduced, and thermal damage can be prevented.

1 shows a configuration example of a power MOSFET switching control device. It is a figure which shows the relationship between the battery current and the timing of OFF control of power MOSFET. It is a figure which shows the example of the processing flow of the switching control method of power MOSFET. It is a figure which shows the aspect of the drain current change at the time of OFF of power MOSFET, and the drain-source voltage change.

  FIG. 1 shows a configuration example of a switching control device for a power MOSFET. As shown in FIG. 1, the power MOSFET switching control device 100 controls on / off of power MOSFETs 13 and 14 connected in series to a battery 11 in the battery module 10. The power MOSFET switching control apparatus 100 includes a battery monitoring microcontroller 1, a battery control microcontroller 2, and a vehicle control microcontroller 3.

  The battery monitoring microcontroller 1 monitors the state of the battery 11 in the battery module 10 and controls on / off of the power MOSFETs 13 and 14 connected in series to the battery 11. The diodes 15 and 16 are diodes formed together with the power MOSFETs 13 and 14, and are referred to as built-in diodes or parasitic diodes. Moreover, although the battery 11 in the battery module 10 shows one battery in FIG. 1, a plurality of batteries connected in series or in parallel may be used.

  The battery module 10 includes a current sensor 12 that detects the current of the battery 11, a voltage sensor (not shown) that detects the voltage of the battery 11, and a temperature sensor (not shown) that detects the temperature of the battery 11. The current detected by the current sensor 12 is a battery current flowing through the battery 11, a drain current flowing through the power MOSFETs 13 and 14, and a load current flowing through the load 5.

  The detection signals of these sensors are input to the battery monitoring microcontroller 1, and the battery monitoring microcontroller 1 monitors the abnormality of the battery 11 based on the detection signals of these sensors, and detects the abnormality of the battery 11. The power MOSFETs 13 and 14 connected in series with the battery 11 are controlled to be turned off.

  The battery monitoring microcontroller 1 is connected to the host battery control microcontroller 2 and notifies the battery control microcontroller 2 of the monitoring information of the battery 11. The battery control microcontroller 2 is connected to the battery control microcontroller 2 based on the monitoring information. 11 state of charge is properly managed.

  The battery control microcontroller 2 is connected to the vehicle control microcontroller 3 via a communication path connected by the connector 4 and has a function of notifying the vehicle control microcontroller 3 of the state of the battery 11.

  In response to the notification information from the battery control microcontroller 2, the vehicle control microcontroller 3 controls power supply to the load 5 of the vehicle, controls or suppresses driving of the vehicle, etc. Thus, it has a function of notifying the occurrence of an abnormality relating to the vehicle including the abnormality of the battery module and prompting the user to deal with the abnormality.

  The load 5 is supplied with electric power from the battery module 10 through a power supply path connected via the connector 4. The load 5 includes a plurality of various load circuits such as a traveling motor, a lifting motor, a light, a display, and a heater. The current consumed by each load circuit may be equivalently a current consumed by a fixed resistor or a current consumed by a variable resistor.

  In the power MOSFET switching control apparatus as described above, when the battery monitoring microcontroller 1 detects that an abnormality has occurred in the battery 11 in the battery module 10, the battery monitoring microcontroller 1 starts control to turn off the power MOSFETs 13 and 14.

  However, when the power MOSFETs 13 and 14 are turned off, the battery current (current detected by the current sensor 12) flowing through the power MOSFETs 13 and 14 is observed, and whether the battery current exceeds a predetermined threshold value Ith. Determine whether or not. The predetermined threshold value is an upper limit value of a current that allows stable switching operation without breaking (thermal damage) of the power MOSFETs 13 and 14 when the conduction of the power MOSFETs 13 and 14 is interrupted. At this time, the battery monitoring microcontroller 1 functions as a current determination unit.

  When the battery current is equal to or less than the predetermined threshold value Ith, the power MOSFETs 13 and 14 are immediately controlled to be turned off. On the other hand, when the battery current exceeds a predetermined threshold value Ith, the battery monitoring microcontroller 1 requests the vehicle control microcontroller 3 to reduce the current consumption of the load 5 via the battery control microcontroller 2. Send a signal. At this time, the battery monitoring microcontroller 1 functions as a load current reduction request means.

  In response to the request signal, the vehicle control microcontroller 3 selects a load circuit that has less trouble in traveling of the vehicle, and autonomously controls the power supply current to the load circuit that has less trouble. . Alternatively, a warning may be issued to the user driving the vehicle so as to reduce the current consumption of any load circuit of the load 5. At this time, the vehicle control microcontroller 3 functions as load current reduction means.

  After the battery monitoring microcontroller 1 transmits a request signal for reducing the current consumption of the load 5, the battery monitoring microcontroller 1 monitors the battery current (current detected by the current sensor 12), and whether the battery current has fallen below a predetermined threshold Ith. When the battery current becomes equal to or less than a predetermined threshold value Ith, the power MOSFETs 13 and 14 are controlled to be in an off state. At this time, the battery monitoring microcontroller 1 functions as power MOSFET off control means.

FIG. 2 shows the relationship between the battery current and the timing of power MOSFET off control. 2 (a) is when the battery current _{I B} is less than a predetermined threshold Ith, it illustrates aspects timing off control of the power MOSFET. As shown in FIG. 2 (a), when the battery current _{I B} is equal to or less than a predetermined threshold value Ith, the battery monitoring microcontroller 1 is immediately kept off MOSFET13,14 at timing t0 requiring interruption of battery current _{I B} And the conduction of the power MOSFETs 13 and 14 is cut off.

On the other hand, as shown in FIG. 2 (b), when the battery current I _B is greater than a predetermined threshold Ith, at timing t0 requiring interruption of battery current I _B, the battery monitoring microcontroller 1, a vehicle control microcontroller against 3, transmits a request signal to reduce the current consumption of the load 5, then monitors the battery current _{I B,} at timing t1 when the battery current _{I B} is equal to or less than a predetermined threshold value Ith, the power MOSFET 13, 14 is controlled to be in an OFF state, and conduction of the power MOSFETs 13 and 14 is cut off.

  Thus, the battery monitoring microcontroller 1 requests the vehicle control microcontroller 3 to reduce the current consumption of the load 5 in cooperation with the vehicle control microcontroller 3 via the battery control microcontroller 2. Then, the power MOSFETs 13 and 14 are controlled to be in an off state in a state where the consumption current of the load 5 becomes equal to or less than a predetermined threshold value Ith due to the request. Therefore, when the conduction of the power MOSFETs 13 and 14 is interrupted, the current flowing through the power MOSFETs 13 and 14 is reduced to a predetermined threshold value or less, the switching loss is reduced, and thermal damage to the power MOSFETs 13 and 14 can be prevented.

  FIG. 3 shows an example of a processing flow of the switching control method of the power MOSFET. When the battery monitoring microcontroller 1 shown in FIG. 1 detects that an abnormality has occurred in the battery 11 in the battery module 10, the battery monitoring microcontroller 1 starts control to turn off the power MOSFETs 13 and 14.

  The battery monitoring microcontroller 1 detects the battery current (current detected by the current sensor 12) flowing through the power MOSFETs 13 and 14 (step S1), and determines whether or not the battery current exceeds a predetermined threshold value. (Step S2). The battery monitoring microcontroller 1 immediately controls the power MOSFETs 13 and 14 to be turned off (step S5) when the battery current is equal to or less than a predetermined threshold (No in step S2).

  On the other hand, when the battery current exceeds a predetermined threshold value (Yes in step S2), the battery monitoring microcontroller 1 sends the current of the load 5 to the vehicle control microcontroller 3 via the battery control microcontroller 2. A request signal for reducing consumption is transmitted (step S3).

  In response to the request signal, the vehicle control microcontroller 3 selects a load circuit with less trouble in traveling of the vehicle, and autonomously controls the power supply current to the load circuit with less trouble. Alternatively, an alarm is issued to the user driving the vehicle so as to reduce the current consumption of any load circuit of the load 5. The user who has received the alarm selects any load circuit of the load 5 and reduces its current consumption (step S4).

  The battery monitoring microcontroller 1 transmits a request signal for reducing the current consumption of the load 5 and then returns to the process of step S1 to detect the battery current and determine whether or not the battery current exceeds a predetermined threshold value. (Step S2). The battery monitoring microcontroller 1 immediately controls the power MOSFETs 13 and 14 to be turned off (step S5) when the battery current is equal to or less than a predetermined threshold (No in step S2). When the battery current exceeds a predetermined threshold (Yes in step S2), the battery monitoring microcontroller 1 moves to the process of step S3 and repeats the same operation.

  In this way, the battery monitoring microcontroller 1 and the vehicle control microcontroller 3 cooperate to reduce the current consumption (battery current) of the load 5 and control the power MOSFETs 13 and 14 to the off state.

  In addition to the processing flow described above, the battery monitoring microcontroller 1 and the vehicle control microcontroller 3 cooperate with the vehicle control microcontroller 3 to turn off the power MOSFETs 13 and 14 in advance on the vehicle control microcontroller 3 side. A predetermined threshold Ith at the time of control is stored, and when a load current reduction request signal is received from the battery monitoring microcontroller 1, the battery current notified from the battery monitoring microcontroller 1 is equal to or less than the predetermined threshold Ith. As described above, a load circuit with less trouble in traveling of the vehicle is selected from among the loads 5, and autonomously controlled so as to limit the supply current to the selected load circuit. Or it is good also as a structure which displays the load circuit used as this predetermined threshold value Ith or less to the user who is driving this vehicle, and prompts it to restrict the current consumption of this load circuit.

Further, in the battery monitoring microcontroller 1 side stores the predetermined threshold Ith in the OFF control of the power MOSFETs 13, a difference value obtained by subtracting the predetermined threshold value Ith from the battery current _{I B} flowing current, The battery monitoring microcontroller 1 transmits the load current reduction request signal to the vehicle control microcontroller 3 together with the load current reduction request signal, and the vehicle control microcontroller 3 has less trouble in driving the load circuit that reduces the current more than the difference value. A configuration may be adopted in which processing is performed by selecting from the load circuit and limiting the current consumption of the load circuit.

  When the vehicle control microcontroller 3 receives a load current reduction request signal from the battery monitoring microcontroller 1, the vehicle control microcontroller 3 selects a load circuit with less trouble in traveling and reduces the load current. For example, in the case of a vehicle such as a forklift, the heater restricts the drive current of the forklift unloading operation, restricts the drive current of the forklift travel motor, restricts the current consumption by turning off lights or displays, etc. The load current can be reduced by selecting a load circuit with less hindrance among various load circuits, such as blocking the current and limiting the current consumption.

  Further, a configuration may be adopted in which a request signal for reducing load current is transmitted from the battery monitoring microcontroller 1 to the vehicle control microcontroller 3 without going through the battery control microcontroller 2.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various configurations or embodiments can be made without departing from the gist of the present invention. Can be taken.

DESCRIPTION OF SYMBOLS 100 Switching control apparatus of power MOSFET 1 Battery monitoring microcontroller 2 Battery control microcontroller 3 Vehicle control microcontroller 4 Connector 5 Load 10 Battery place module 11 Battery 12 Current sensor 13 Power MOSFET
14 Power MOSFET
15 Built-in diode (parasitic diode)
16 Built-in diode (parasitic diode)

Claims (5)

A power MOSFET switching control device connected in series to a battery in a battery module,
A current sensor for detecting a battery current flowing in the battery;
A current determination means for comparing the battery current detected by the current sensor with a predetermined threshold and determining whether the battery current exceeds a predetermined threshold;
Load current reducing means for reducing a load current of a load fed from the battery;
Load current reduction requesting means for requesting the load current reducing means to reduce the load current when the battery current exceeds the predetermined threshold;
Power MOSFET off control means for controlling the power MOSFET to an off state when the battery current is equal to or less than the predetermined threshold;
A switching control apparatus for a power MOSFET, comprising: A power MOSFET switching control device connected in series to a battery in a battery module,
A current sensor for detecting a battery current flowing in the battery;
The battery current detected by the current sensor is compared with a predetermined threshold to determine whether or not the battery current exceeds a predetermined threshold. When the battery current exceeds the predetermined threshold, vehicle control is performed. A battery monitoring microcontroller that transmits a request signal requesting the microcontroller to reduce the load current, and controls the power MOSFET to be turned off when the battery current falls below the predetermined threshold;
A vehicle control microcontroller that controls power supply from the battery to a vehicle load and reduces load current of the vehicle load in response to the request signal from the battery monitoring microcontroller;
A switching control apparatus for a power MOSFET, comprising:   The battery monitoring microcontroller notifies the vehicle control microcontroller of the battery current together with the request signal, and the vehicle control microcontroller exceeds a difference between the notified battery current and the predetermined threshold value stored in advance. 3. The power MOSFET switching control device according to claim 2, wherein the current consumption is reduced by limiting a current consumption of a load circuit selected from among a plurality of load circuits.   The battery monitoring microcontroller notifies the vehicle control microcontroller of the current value of the difference between the battery current and the predetermined threshold together with the request signal, and the vehicle control microcontroller notifies the difference of the notified difference. 3. The switching control device for a power MOSFET according to claim 2, wherein the current more than the current value is reduced by limiting the current consumption of the load circuit selected from among the plurality of load circuits. A switching control method for a power MOSFET connected in series to a battery in a battery module,
A current determination step of detecting a battery current flowing through the battery, comparing the battery current with a predetermined threshold, and determining whether the battery current exceeds a predetermined threshold;
When the battery current exceeds a predetermined threshold, a load current reduction request step for requesting to reduce the load current of a load fed from the battery;
After requesting the load current to be reduced, it is determined whether or not the battery current exceeds the predetermined threshold value, and when the battery current falls below the predetermined threshold value, the power MOSFET is turned off. A power MOSFET off control step to control;
A method for switching control of a power MOSFET, comprising:

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