JP6503636B2 - Motor controller - Google Patents

Description

  The present invention relates to a motor control device, and more particularly to a motor control device provided with a charging circuit used to drive and control an electric motor mounted on a vehicle.

  Conventionally, a relay is generally used to control power supply from a battery to an electric motor or the like. For example, in an electric vehicle such as a hybrid vehicle, an electric vehicle, or an electric four-wheel drive vehicle, a power supply relay is provided between the battery and the inverter to control power supply from the high voltage battery to the inverter as a load circuit. . The power supply relay connects and disconnects the battery and the inverter according to the control state of the vehicle.

  In such a case, a large inrush current may momentarily flow from the battery to charge a large capacity smoothing capacitor connected between the DC voltage power supply line and the ground line, and the contacts of the power supply relay may be welded. is there. If this contact is welded, there is a possibility that the power supply relay can not be turned off and the current can not be cut off. Therefore, the power conversion device provided with a precharge circuit for precharging the smoothing capacitor before switching the power supply relay on is proposed. (See, for example, Patent Document 1).

JP 2001-128305 A

  In the power converter as described above, the precharge circuit includes a precharge resistor (eg, cement, hollow resistor, etc.) for limiting inrush current, and a precharge relay connected in series to the precharge resistor. Have. The precharge relay is turned on to precharge the smoothing capacitor connected in parallel to the input side of the inverter. After the smoothing capacitor is precharged, the power supply relay connected in parallel with the precharge circuit is switched on, and then the battery is connected to the inverter. Then, after turning on the power supply relay, the precharge relay is turned off.

  However, in the above-described conventional configuration, since the precharge resistor requires a large power resistance and is very large, the installation space is increased, and the power converter itself including the charging circuit is enlarged. In addition, since the charging current gradually decreases due to the pre-charge resistance, the time until the start of the inverter becomes long due to the long charging time, and there is a possibility that the driving of the electric motor can not be started early.

  The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a motor control device capable of starting up an inverter in a short time by including a charging circuit capable of suppressing inrush current and miniaturizing the device. To provide.

In order to solve the above-mentioned problems, the invention according to claim 1 relates to a motor drive circuit including a plurality of switching elements for supplying a drive current to an electric motor, and a DC power supply for driving the electric motor. A power switch comprising a semiconductor element for turning on and off a connection with the motor drive circuit to which power is supplied; and a power supply line and a ground line between the power switch and the motor drive circuit. A discharge capacitor for absorbing current ripples; a discharge circuit connected in parallel to the discharge capacitor for discharging the electric charge stored in the discharge capacitor through the discharge resistor by the on operation of the discharge switch; and controlling the motor drive circuit Control circuit, and the power switch is connected to a DC power supply path between the DC power supply and the smoothing capacitor. Is input, the control circuit, based on a potential difference between the front and rear ends of the power switch, with the said power switch so that the charging current of the smoothing capacitor becomes constant PWM control, the threshold above which the potential difference is set in advance At a certain time, the power supply switch is continuously switched by changing the switching frequency or the duty, thereby turning on / off the supply path and charging the smoothing capacitor.

  According to the above configuration, the power switch comprising the semiconductor switching element is provided between the DC power supply and the smoothing capacitor to perform the on / off operation. Therefore, it is possible to suppress the inrush current generated when the smoothing capacitor is precharged by controlling the power switch to charge the smoothing capacitor. As a result, the precharge circuit consisting of the conventional precharge resistor and the precharge relay becomes unnecessary, the installation space can be reduced, and downsizing and cost reduction of the motor control device can be achieved. In addition, the use of the power switch makes it possible to reduce the number of parts and to improve the reliability of the motor control device.

Furthermore , the power switch is PWM-controlled so that the charging current becomes constant, and the smoothing capacitor is precharged. When the potential difference between the front and rear ends of the power supply switch is larger than the threshold, the switching frequency or duty is sequentially changed to perform the switching operation repeatedly. As a result, the pre-charge time can be shortened, and initialization at the time of startup of the motor control device can be ended early, and motor drive by the inverter can be started early.

Still further , the control circuit performs duty control by setting the switching frequency to be lower than a predetermined value as the potential difference between the front and rear ends of the power switch becomes smaller. According to the above configuration, when the charging voltage of the smoothing capacitor becomes high, the switching frequency of the power switch is set low and the duty control is performed to perform precharging with a constant charging current at a predetermined value. Can be reduced.

The invention according to claim 2 is the motor control device according to claim 1 , wherein the control circuit determines that charging of the smoothing capacitor is completed when the potential difference disappears between the front and back ends of the power switch, The gist is to always switch the power switch to the on state. According to the above configuration, when there is no potential difference between the front and rear ends of the power supply switch, the power supply switch is always switched on, so precharging can be completed at an accurate timing without generating inrush current.

  According to the present invention, it is possible to provide a motor control device capable of starting an inverter in a short time, provided with a charging circuit capable of suppressing rush current and achieving downsizing of the device.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows schematic structure of the drive system of the vehicle carrying the motor control apparatus which concerns on one Embodiment of this invention. FIG. 2 is a diagram showing a circuit configuration of the motor control device of FIG. 1; The flowchart which shows the process sequence at the time of charge of the smoothing capacitor performed by a control circuit. The figure which shows the charging current-time characteristic at the time of charge of a smoothing capacitor.

Hereinafter, a motor control device mounted on a vehicle according to an embodiment of the present invention will be described based on the drawings.
FIG. 1 is a view showing a schematic configuration of a drive system of a vehicle equipped with a motor control device 1 according to an embodiment of the present invention.
As shown in FIG. 1, a vehicle (in the present embodiment, an electric four-wheel drive vehicle) comprises a DC power supply (hereinafter referred to as a high voltage battery) 11, a vehicle control unit 18, a rear wheel drive unit 20, DC power. It is a power conversion device for converting into AC power, and includes a motor control unit (ECU) 1 that controls an electric motor 12 used to drive the rear wheel 19.

  The rear wheel drive unit 20 includes an electric motor 12, a reduction gear (differential gear) 16, and a clutch 17. The clutch 17 is installed at the final stage of the reduction gear 16. For example, a three-phase brushless motor is used as the electric motor 12 for the drive source. The electric motor 12 is an IPM motor including an embedded magnet type rotor in which permanent magnets are embedded and fixed to a rotor core, or a permanent magnet type such as an SPM motor including a surface magnet type rotor in which permanent magnets are fixed to the surface of the rotor core. A synchronous motor is used.

  The high voltage battery 11 uses, for example, a high voltage (for example, 250 V) DC power supply made of a rechargeable secondary battery such as nickel hydrogen or lithium ion which can be charged and discharged. The high voltage battery 11 is disposed, for example, behind a rear seat of the vehicle. The DC voltage received from high voltage battery 11 is further boosted to a high voltage (for example, 600 V or the like) by power supply circuit 2 according to the specification of inverter (motor drive circuit) 8 (or not boosted). Supplied to

  When a high voltage DC voltage is required, the motor control device 1 boosts the DC voltage of the high voltage battery 11 by a boost converter (not shown), and the internal smoothing capacitor 7 (see FIG. 2) A power supply circuit 2 to be stabilized and an inverter 8 are included. The motor control device 1 is mounted, for example, under a rear seat of a vehicle. Further, at the time of regenerative braking of the electric motor 12, the motor control device 1 can supply power generated by the electric motor 12 to the high voltage battery 11 for charging.

  Further, the motor control device 1 includes a control circuit 10 configured of, for example, a microcomputer (hereinafter referred to as a CPU). The control circuit 10 controls the rear wheel drive unit 20 and the like. The control circuit 10 is connected to a low voltage (for example, 12 V or the like) auxiliary power supply (hereinafter referred to as a low voltage battery) 13 and controls the driving of the vehicle from a vehicle control unit 18 via a communication line (harness) The command is received by (for example, CAN). In response to the command, the control circuit 10 brings the clutch 17 into a connected state, and the driving force generated by driving the electric motor 12 is transmitted to the rear wheel 19.

Next, FIG. 2 is a diagram showing a circuit configuration of the motor control device 1 of FIG.
In FIG. 2, the electric motor 12 is a three-phase brushless motor having three-phase windings (U-phase, V-phase, and W-phase windings, not shown). The high voltage battery 11 is a high voltage DC power supply connected to the inverter 8 to drive the electric motor 12.

  As shown in FIG. 2, the power supply circuit 2 includes a power supply switch 3, a smoothing capacitor 7, and a discharge circuit 6 that constitute a charging circuit. Power supply switch 3 is inserted in series in a DC power supply path between high voltage battery 11 and smoothing capacitor 7 to control power supply to inverter 8. The discharge circuit 6 discharges the charge accumulated in the smoothing capacitor 7 after the power switch 3 is turned off in order to consume power when the inverter 8 is stopped. An inverter 8 is connected in parallel to the smoothing capacitor 7, and the electric motor 12 is connected via the inverter 8.

  The power switch 3 is a switching element (for example, a power semiconductor element such as SiC or GaN) formed of a semiconductor, and electrically switches whether to connect the smoothing capacitor 7 and the inverter 8 to the high voltage battery 11 or not. The power supply switch 3 uses a power element with high-speed switching operation and low power loss, and forms a bidirectional switch with the switching element and a diode connected in antiparallel. The power supply switch 3 is controlled by the control circuit 10, and the PWM signal output from the control circuit 10 is supplied to the gate terminal of the power supply switch 3.

  The power switch 3 prevents a large inrush current from flowing in the smoothing capacitor 7 immediately after the motor control device 1 is started, and precharges the smoothing capacitor 7 while limiting the charging current Ic. The power switch 3 is turned on / off (switching operation) when the motor control device 1 is started, turned on (conductive state) when the inverter is operating, and turned off (nonconductive state) when stopped.

  Further, the power supply switch 3 is subjected to PWM control (switching operation) by sequentially changing the switching frequency and the duty (on time) by the control circuit 10 according to the charging voltage Vd, and the smoothing capacitor 7 is precharged. After the smoothing capacitor 7 is precharged, the control circuit 10 turns on the power switch 3 at all times to connect the high voltage battery 11 directly to the inverter 8. Here, the power switch 3 can regenerate the regenerative power from the electric motor 12 to the high-voltage battery 11 side via the inverter 8 and the diode of the power switch 3 when performing, for example, a deceleration operation.

  The smoothing capacitor 7 is provided between the power supply line 14 between the power supply switch 3 and the inverter 8 and a ground line (hereinafter referred to as an earth line) 15. The smoothing capacitor 7 supplies power to the inverter 8 from the high voltage battery 11 and both in a state where the power switch 3 is always turned on. In particular, the smoothing capacitor 7 momentarily supplies high power to the inverter 8. Specifically, smoothing capacitor 7 stores charge, and discharges the stored charge when the current flowing from high voltage battery 11 to inverter 8 is insufficient. Thus, the smoothing capacitor 7 functions as a capacitor that absorbs current ripple and smoothes the power supply voltage for driving the electric motor 12. Further, in the power supply circuit 2 of the present embodiment, after the power supply switch 3 is turned off, the charge accumulated in the smoothing capacitor 7 is discharged through the discharge circuit 6.

  The discharge circuit 6 is formed by connecting a discharge resistor 4 and a discharge switch 5 which is a semiconductor switching element (for example, IGBT, MOSFET, etc.) in series, and is connected in parallel to the smoothing capacitor 7 between the power supply line 14 and the ground line 15. It is provided between. When the power switch 3 is shut off and the driving of the electric motor 12 is stopped, the charge stored in the smoothing capacitor 7 is discharged through the discharge resistor 4 by turning on the discharge switch 5. The charging voltage Vd falls rapidly.

  The inverter 8 includes six switching elements (power transistors such as IGBTs and MOSFETs) 9a to 9f. Three circuits in which upper and lower arms (for example, 9a and 9d) are formed by connecting two each of these six switching elements 9a to 9f in series are provided in parallel between the power supply line 14 and the ground line 15. It is done. The connection points of the switching elements 9a to 9f of the upper and lower arms are directly connected to one end of the three-phase winding. The other end of the three-phase winding of the electric motor 12 is connected to a common connection point (neutral point) not shown.

  Control circuit 10 controls switching elements 9 a to 9 f included in inverter 8. More specifically, control circuit 10 targets a three-phase drive current (U-phase, V-phase, and W-phase current) to be supplied to electric motor 12 based on input data (motor rotation angle etc.) Determine the value (target current). Then, the control circuit 10 outputs a PWM signal for causing each phase current value detected by a current sensor or the like (not shown) to coincide with the target current. The PWM signal of each phase output from the control circuit 10 is supplied to the gate terminals of the switching elements 9 a to 9 f included in the inverter 8. A control voltage (for example, 12 V) serving as a power supply of the control circuit 10 is supplied from the low voltage battery 13. The low voltage battery 13 may be mounted with an auxiliary battery or may be supplied with power from the high voltage battery 11 via a DC / DC converter or the like.

Next, the charging operation of the power supply circuit 2 in the present embodiment will be described.
FIG. 3 is a flowchart showing a processing procedure at the time of precharging of the smoothing capacitor 7 executed by the control circuit 10, and FIG. 4 is a view showing charging current-time characteristics at the time of precharging of the smoothing capacitor 7.

  The charge and discharge operation of the smoothing capacitor 7 is performed by the control circuit 10 when the vehicle control is stopped, that is, when the motor control device 1 that drives the electric motor 12 is started and stopped. In the present embodiment, a CPU (not shown) in the control circuit 10 reads a program stored in the ROM, and executes the processing of steps S301 to S308 shown in the flowchart of FIG. 3. The processing in the flowchart shown below is executed at predetermined time intervals.

  The charging voltage Vd of the smoothing capacitor 7 is precharged to the battery voltage Va of the high voltage battery 11 before the power switch 3 is always turned on. When the power switch 3 is normal, the charging voltage Vd of the smoothing capacitor 7 is charged to the battery voltage Va, and then the power switch 3 is switched on at all times.

  As shown in FIG. 3, the CPU of the control circuit 10 in the motor control device 1 first turns off the discharge switch 5 and the power switch 3 (step S301). Next, the switching frequency of the power switch 3 is set to a predetermined value (for example, about several kilohertz to several megahertz) (step S302). The power supply switch 3 is controlled in its switching operation with a PWM cycle shorter than the time constant due to the inductance and resistance of the bus bar or wiring in the power supply circuit 2.

  Subsequently, a first threshold and a second threshold (voltage value) for determining the charge state of the smoothing capacitor 7 are set (step S303). The first threshold is larger than the second threshold, and the second threshold is set to a value near 0V.

  Next, the CPU calculates and sets a duty ratio (= duty / PWM cycle) based on the potential difference (Va−Vd) between the front and rear ends of the power switch 3 (step S304). The duty ratio is set to a value not exceeding the allowable current of power switch 3 so that charging current Ic becomes constant at a predetermined value, and is set larger than the previous value as potential difference (Va-Vd) decreases. .

  Subsequently, the power supply switch 3 performs switching operation (PWM control) based on the set switching frequency and the value of the duty ratio (step S305), and the smoothing capacitor 7 is precharged.

  Next, the CPU determines whether the charging voltage Vd of the smoothing capacitor 7 has risen to the battery voltage Va after a predetermined time has elapsed. It is determined whether the potential difference (Va-Vd) between the front and rear ends of the power switch 3 is smaller than a first threshold (step S306). If the potential difference is greater than or equal to the first threshold value, the process proceeds to step S303 (step S306: NO), and the duty ratio is set again. If the potential difference is smaller than the first threshold (step S306: YES), it is determined whether the potential difference (Va-Vd) between the front and rear ends of the power switch 3 is smaller than the second threshold (step S307).

If the potential difference is greater than or equal to the second threshold (step S307: NO), the process proceeds to step S302, and the switching frequency is set to a value lower than the previous value (predetermined value). That is, as the potential difference decreases, the switching frequency is set to decrease, and the precharge is continued until the charge voltage Vd reaches the battery voltage Va. If the potential difference is smaller than the second threshold (step S307: YES), it is determined that the precharging is completed, and the power switch 3 is constantly switched on (step S308).
After stopping the precharging, the battery voltage Va is supplied to the inverter 8 and the flow is exited. Thereafter, the CPU executes drive processing of the inverter 8.

  In FIG. 4, the vertical axis represents the charging current, and the horizontal axis represents time. As shown in FIG. 4, while the smoothing capacitor 7 is precharged, the charging current Ic is maintained at a constant value, and the potential difference (Va-Vd) between the front and back ends of the power switch 3 becomes less than a predetermined value near 0V. When the current is reduced rapidly, the precharging is finished (charging completed). For example, as indicated by the broken line in the figure, when the conventional precharge resistor is inserted, the charging current Ic gradually decreases and the power switch 3 is turned on after the precharge, so the charging time becomes longer. .

  As described above, the potential difference (Va-Vd) between the front and rear ends of the power switch 3 is determined, and the switching frequency and the duty ratio are controlled so that the charging current Ic becomes a constant value. For example, when the charging rate of the smoothing capacitor 7 is low (the potential difference is large), duty control is performed and precharge is performed at a high switching frequency. When the charging rate of the smoothing capacitor 7 is high (the potential difference is small), duty control is performed at a low switching frequency. After that, when the potential difference approaches 0 V (VdVaVa) (the duty ratio is almost 100%), the power switch 3 is constantly turned on to end the precharging.

  Next, the operation and effects of the motor control device 1 according to the present embodiment configured as described above will be described.

  According to the above configuration, the power switch 3 composed of the semiconductor switching element is provided between the high voltage battery 11 and the smoothing capacitor 7 to perform the open / close operation. The power supply switch 3 is PWM-controlled so that the charging current Ic becomes constant at a predetermined value, and the smoothing capacitor 7 is precharged. At this time, when the potential difference (Va−Vd) between the front and rear ends of the power switch 3 is larger than the first threshold or the second threshold, the switching frequency or duty ratio of the power switch 3 is sequentially changed to perform the switching operation repeatedly. By controlling the power supply switch 3 to charge the smoothing capacitor 7, it is possible to suppress an inrush current generated when the smoothing capacitor 7 is precharged.

  In addition, when the charging voltage Vd of the smoothing capacitor 7 becomes high, the switching frequency of the power switch 3 is set low and duty control is performed to perform precharging. At this time, since the smoothing capacitor 7 is charged with a constant charge current Ic at a predetermined value, rush current is suppressed. Furthermore, since the power switch 3 is always turned on when there is no potential difference (Va-Vd) between the front and back ends of the power switch 3, precharging can be completed at an accurate timing without generating inrush current. .

  As a result, the precharge circuit consisting of the conventional precharge resistor and precharge relay becomes unnecessary, the installation space can be reduced, and downsizing and cost reduction of the motor control device 1 can be achieved. Further, the use of the power switch 3 makes it possible to reduce the number of parts and to improve the reliability of the motor control device 1. Furthermore, since the pre-charge time can be shortened, the initialization at the time of startup of the motor control device 1 can be ended early, and the motor drive by the inverter 8 can be started early.

  As described above, according to the embodiment of the present invention, it is possible to provide a motor control device capable of starting an inverter in a short time by including a charging circuit capable of suppressing rush current and achieving downsizing of the device.

  As mentioned above, although embodiment concerning this invention was described, it is also possible to implement this invention by another form.

  In the above embodiment, PWM control is performed using a switching element made of a power semiconductor for the power switch 3. However, the present invention is not limited to this, and a semiconductor switch that can shut off bidirectionally (for example, using a plurality of MOSFETs) Etc.) may be used to perform on / off operation. Moreover, you may apply the same thing as the switching elements 9a-9f which comprise the inverter 8. FIG. Furthermore, a mechanical relay may be used as the discharge switch 5.

  In the above embodiment, the potential difference (Va−Vd) between the front and rear ends of the power switch 3 is compared with the first threshold in step S306 as the setting condition of the duty ratio and the determination condition of the switching operation. Other conditions may apply instead. For example, it is determined whether the value of the duty ratio is greater than the third threshold (step S306), and if the value of the duty ratio is less than or equal to the third threshold (step S306: NO), the duty ratio is set again (step S306). S303). If the duty ratio is larger than the third threshold (YES in step S306), it is determined whether the potential difference (Va-Vd) between the front and rear ends of the power switch 3 is smaller than the second threshold (step S307).

  In the above embodiment, the processing procedure of the precharging operation to the smoothing capacitor 7 has been described on the assumption that the power switch 3 is normal. However, the present invention is not limited to this. A process of detecting a short abnormality may be executed.

  Although the example which applied this invention to the inverter 8 for the rear wheel drive unit 20 drive of a vehicle was demonstrated in the said embodiment, it is not limited to this, For example, it has a conventional power supply relay and a precharge circuit. The present invention may be applied to an inverter such as a high voltage, large current electric power steering apparatus or an electric brake apparatus, or other on-vehicle power conversion apparatus. Also, the present invention may be applied to an inverter for driving a traveling motor of a hybrid vehicle or an electric vehicle.

1: Motor control unit (ECU), 2: Power supply circuit, 3: Power supply switch, 4: Discharge resistance,
5: discharge switch, 6: discharge circuit, 7: smoothing capacitor,
8: inverter (motor drive circuit) 9a to 9f: switching element
10: Control circuit, 11: High voltage battery (DC power supply), 12: Electric motor,
13: low voltage battery 14: power supply line 15: earth line (ground line)
16: reducer, 17: clutch, 18: vehicle control unit, 19: rear wheel,
20: Rear wheel drive unit,
Vd: smoothing capacitor charging voltage, Va: battery voltage, Ic: charging current

Claims (2)

A motor drive circuit including a plurality of switching elements for supplying a drive current to the electric motor;
A power switch comprising a semiconductor element for turning on and off a connection between a DC power source for driving the electric motor and the motor drive circuit to which power is supplied;
A smoothing capacitor connected between a power supply line between the power supply switch and the motor drive circuit and a ground line to absorb current ripple;
A discharge circuit connected in parallel to the smoothing capacitor and discharging the charge accumulated in the smoothing capacitor through a discharge resistor by an on operation of the discharge switch;
A control circuit for controlling the motor drive circuit;
The power switch is inserted into a DC power supply path between the DC power supply and the smoothing capacitor.
The control circuit performs PWM control of the power supply switch so that the charging current of the smoothing capacitor is constant based on the potential difference between the front and rear ends of the power supply switch, and the potential difference is equal to or greater than a preset threshold. By continuously switching the power supply switch by changing the switching frequency or duty, the supply path is turned on / off to charge the smoothing capacitor, and the potential difference between the front and back ends of the power switch is reduced. Therefore, the motor control device performs duty control by setting the switching frequency to be lower than a predetermined value . In the motor control device according to claim 1,
The motor control device, wherein the control circuit determines that charging of the smoothing capacitor is completed when the potential difference disappears between the front and rear ends of the power switch, and the power switch is always switched to the on state .

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