JP5446409B2 - Motor control device and electric power steering device - Google Patents

Description

  The present invention relates to a motor control device that drives an electric motor by receiving a DC power supply, and an electric power steering device using the motor control device, and more particularly, to the motor control device when power is turned on. It relates to current reduction.

  In a motor control device such as an electric power steering device, an open relay is provided between the battery and the motor drive circuit in order to prevent an excessive current from flowing from the battery when the motor drive circuit fails. When the motor drive circuit fails, this open relay is controlled to be in the open state (off state), thereby cutting off the power supply to the motor drive circuit.

  Conventionally, electromagnetic relays have been used as such opening relays. However, when an electromagnetic relay is used in an electric power steering apparatus, there is a problem that the relay becomes larger with the recent high output. In addition, the power consumption of the opening relay increases as the output increases.

  In order to reduce the size of the open relay and reduce power consumption, the open relay is realized with a semiconductor element such as a power MOS (Metal Oxide Semiconductor) transistor as a countermeasure to the above problem due to the high output of the electric power steering device. A configuration is also proposed.

  For example, in Patent Document 1 below, a switch (relay) for cutting off energization to a bridge circuit as a motor drive circuit when a failure of an electric power steering apparatus is detected is a field effect transistor (FET: Field). An invention is disclosed that comprises an effect transistor). As such a switch, Patent Document 1 also discloses a switch having a configuration in which two FETs are connected in series and parasitic diodes in the two FETs are arranged in opposite directions. Patent Document 2 below uses a bipolar transistor as a steering power cut-off means for stopping power supply for power steering when the battery power supply voltage is abnormally lowered in an electric vehicle with an electric power steering device such as a battery forklift. The configuration is disclosed. Further, in Patent Document 3 below, when a power MOSFET with a heat shut-off function is used as a switching element constituting a bridge circuit as a motor drive circuit, all abnormalities of the bridge circuit are detected when an abnormality such as an overheating state is detected. An electric power steering control device configured to shut off the power MOSFET and stop energization of the electric motor is disclosed.

JP-A-10-167085 Japanese Utility Model Publication No. 64-1171 Japanese Patent Laid-Open No. 11-11331

  FIG. 7 is a circuit diagram illustrating an example of a configuration of a drive unit in a conventional motor control device. Hereinafter, problems in the conventional motor control apparatus will be described with reference to FIG.

  A motor control apparatus that drives a motor by receiving a DC power supply such as a battery is usually a bridge circuit (a motor drive circuit shown in FIG. 7) composed of a plurality of switching elements such as a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor). 50), and the motor 1 is driven by on / off controlling those switching elements by PWM signals (pulse width modulation signals) U, V, W and their negative signals. For this reason, during the driving of the motor 1, the current flowing from the battery 8 serving as the DC power source to the motor driving circuit 50 varies greatly in a short time due to the on / off operation of these switching elements, and the current ripple Will occur. Therefore, in order to absorb the current ripple and suppress the fluctuation of the power supply voltage, a large-capacity capacitor is connected as a voltage stabilizing capacitor 76 between the power supply line and the ground line on the input side of the motor drive circuit. . Therefore, when the motor control device is turned on and motor driving is started, an excessive inrush current for rapidly charging the large-capacity voltage stabilizing capacitor 76 flows. As a result, an electromagnetic relay is used as the opening relay. If 65 is used, the contact of the electromagnetic relay 65 may be welded, and if a switching circuit using a semiconductor element is used as the opening relay 65, the semiconductor element may burn out. There was a risk.

  In order to avoid the failure of the release relay 65 due to such an excessive inrush current, a precharge circuit 80 for charging the voltage stabilizing capacitor 76 is provided immediately before the supply of the power supply voltage to the motor drive circuit 50 is started. Such a configuration is also conventionally known. However, when such a precharge circuit 80 is provided, the number of parts required for manufacturing the motor control device increases, resulting in an increase in cost.

  Therefore, an object of the present invention is to provide a motor control device that can reduce an inrush current at the time of power-on while suppressing an increase in parts and cost required for manufacturing.

A first aspect of the invention is a motor control device that includes a drive circuit in which a voltage stabilizing capacitor is connected in parallel, receives a supply voltage from a DC power supply, and drives an electric motor by the drive circuit.
The first field effect transistor inserted in the current supply path from the DC power supply to the drive circuit so that the parasitic diode is in the reverse direction with respect to the DC power supply, and the parasitic diode is in the forward direction with respect to the DC power supply. Open / close means including a second field effect transistor connected in series with the first field effect transistor and inserted into the current supply path ,
A free-wheeling diode disposed between the switching means and the voltage stabilizing capacitor and circulating a current supplied to the voltage stabilizing capacitor when the first and second field effect transistors are turned off;
When the supply of the power supply voltage from the DC power supply to the drive circuit is started, the first and second switching units are alternately turned on and off while gradually increasing the on-state period. Open / close control means for turning on and off the second field effect transistor ;
And a third field effect transistor that includes the freewheeling diode as a parasitic diode and discharges the electric charge accumulated in the voltage stabilizing capacitor when turned on .

According to a second invention, in the first invention,
The method further comprises an inductor inserted in a portion of the current supply path between the freewheeling diode and the voltage stabilizing capacitor.

A third aspect of the invention is an electric power steering device that applies a steering assist force by an electric motor to a steering mechanism of a vehicle,
A motor control device according to any one of the first and second inventions;
The motor control device drives an electric motor that applies a steering assist force to the steering mechanism.

In the motor control device according to the first aspect of the invention, when the supply of the power supply voltage from the DC power supply to the drive circuit is started, that is, when the power is turned on, the opening / closing means The off state is repeated alternately. Thereby, even if the capacitance value of the voltage stabilizing capacitor is large, the inrush current at the time of power-on can be reduced. Here, since the opening / closing means is composed of a field effect transistor, the opening / closing means can be turned on and off at a very high speed as compared with the case where an electromagnetic relay is used. For this reason, the ON / OFF period and cycle of the switching means can be appropriately set according to the capacitance value of the voltage stabilizing capacitor so that the inrush current is sufficiently relaxed. As a result, damage to the switching means due to the inrush current (burning of the field effect transistor) can be avoided without using a separate component such as a precharge circuit or using a large switching means. In addition, since a free-wheeling diode is provided between the switching means and the voltage stabilization capacitor, the supply current to the voltage stabilization capacitor is not cut off even if the switching means is repeatedly turned on and off when the power is turned on. . For this reason, generation | occurrence | production of the back electromotive force by the inductance component contained in the path | route of the inrush current at the time of power activation is suppressed. Thus, according to the first invention, the inrush current at the time of power-on can be surely reduced while suppressing the increase in parts and cost required for manufacturing the motor control device, and the motor control device can be reduced in size. Power consumption can be reduced.
According to the first aspect of the invention, the first and second field effect transistors constituting the opening / closing means are connected in series with each other, and the parasitic diodes of the first and second field effect transistors are opposite to each other. It has become. For this reason, even if the DC power supply is mistakenly connected in the reverse direction, an excessive current does not flow, and the motor control device can be protected from a connection error of the DC power supply.
Furthermore, according to the first aspect of the invention, the charge accumulated in the voltage stabilizing capacitor can be discharged by turning on the third field effect transistor. The diode functions as a freewheeling diode. For this reason, it is possible to realize the discharge function of the voltage stabilizing capacitor and to implement the invention while suppressing an increase in necessary components.

According to the second aspect of the invention, the inductor inserted in the current path from the DC power supply to the drive circuit can prevent the noise generated during the operation of the switching element constituting the drive circuit from flowing out. . As described above, since the freewheeling diode is provided, even if the inductance component of the current path increases due to the insertion of this inductor, the generation of the counter electromotive force due to the inductance component is suppressed when the power is turned on. Is done. Therefore, it is possible to sufficiently suppress the outflow of noise while avoiding problems such as breakage of the opening / closing means due to generation of a large counter electromotive force.

According to the third invention, in the electric power steering device, when the motor control device having the effects of the first or second invention is used, the increase in necessary parts and cost can be suppressed while the power is turned on. The inrush current can be reliably reduced, so that it is possible to increase the output of the electric power steering device while suppressing the increase in size and cost of the opening / closing means for shutting off the power supply when an abnormality such as a failure is detected. .

It is the schematic which shows the structure of the electric power steering apparatus using the motor control apparatus which concerns on this invention with the structure of the vehicle relevant to it. It is a figure which shows the structure of the motor control apparatus which concerns on one Embodiment of this invention. It is a wave form diagram which shows the opening / closing control signal in the said embodiment. It is a circuit diagram which shows the structure of the drive part in the 1st modification of the said embodiment. It is a circuit diagram which shows the structure of the drive part in the 2nd modification of the said embodiment. It is a circuit diagram which shows the structure of the drive part in the 3rd modification of the said embodiment. It is a circuit diagram which shows an example of a structure of the drive part in the conventional motor control apparatus.

<1. Electric power steering device>
FIG. 1 is a schematic diagram showing the configuration of an electric power steering device using a motor control device according to the present invention, together with the configuration of a vehicle related thereto. This electric power steering device is a column assist type electric motor provided with a brushless motor 1, a speed reducer 2, a torque sensor 3, a vehicle speed sensor 4, a position detection sensor 5, and an electronic control unit (ECU) 10 as a motor control device. It is a power steering device.

  As shown in FIG. 1, a steering wheel (steering wheel) 101 is fixed to one end of the steering shaft 102, and the other end of the steering shaft 102 is connected to a rack shaft 104 via a rack and pinion mechanism 103. Both ends of the rack shaft 104 are connected to a wheel 106 via a connecting member 105 composed of a tie rod and a knuckle arm. When the driver rotates the handle 101, the steering shaft 102 rotates, and the rack shaft 104 reciprocates accordingly. As the rack shaft 104 reciprocates, the direction of the wheels 106 changes.

  The electric power steering device performs the following steering assistance in order to reduce the driver's load. The torque sensor 3 detects a steering torque Ts applied to the steering shaft 102 by operating the handle 101. The vehicle speed sensor 4 detects the vehicle speed S. The position detection sensor 5 detects the rotational position P of the rotor of the brushless motor 1.

  The ECU 10 receives power supplied from the in-vehicle battery 8 and drives the brushless motor 1 based on the steering torque Ts, the vehicle speed S, and the rotational position P. The brushless motor 1 generates a steering assist force when driven by the ECU 10. The speed reducer 2 is provided between the brushless motor 1 and the steering shaft 102. The steering assist force generated by the brushless motor 1 acts to rotate the steering shaft 102 via the speed reducer 2.

  As a result, the steering shaft 102 is rotated by both the steering torque applied to the handle 101 and the steering assist force generated by the brushless motor 1. As described above, the electric power steering apparatus performs steering assist by applying the steering assist force generated by the brushless motor 1 to the steering mechanism of the vehicle.

<2. Motor control device>
<2.1 Motor controller configuration>
FIG. 2 is a block diagram showing the configuration of the motor control device according to the embodiment of the present invention. This motor control device is configured using an ECU 10 and drives a brushless motor 1 having three-phase windings of u-phase, v-phase and w-phase. The ECU 10 includes a drive unit 11 and a control unit 12. The drive unit 11 includes a motor drive circuit 50, a current detection resistor 51, a relay 65, a voltage stabilization capacitor 76, an inductor 74, a surge absorbing Zener diode 72, and a switch 60. The control unit 12 includes: , A microcomputer (hereinafter abbreviated as “microcomputer”) 20, a three-phase / PWM (Pulse Width Modulation) modulator 40, and a current detection circuit 14.

  The ECU 10 receives the steering torque Ts output from the torque sensor 3, the vehicle speed S output from the vehicle speed sensor 4, and the rotational position P output from the position detection sensor 5. The microcomputer 20 functions as control means for obtaining voltage command values Du, Dv, Dw used for driving the brushless motor 1. Details of the function of the microcomputer 20 will be described later.

  The three-phase / PWM modulator 40 generates three types of PWM signals (U, V, W shown in FIG. 2) having a duty ratio corresponding to the three-phase voltage command values Du, Dv, Dw obtained by the microcomputer 20. To do. The motor drive circuit 50 is a PWM voltage source inverter including six MOS-FETs as switching elements. The six MOS-FETs are controlled by three types of PWM signals U, V, and W and their negative signals. That is, two MOS-FETs are assigned to each phase in the motor drive circuit 50, and the two MOS-FETs are connected in series to form a switching element pair. An inverter is configured by connecting in parallel the number of phases between the power supply terminal and the ground terminal. Then, connection points Nu, Nv, Nw of two MOS-FETs (switching element pairs) corresponding to each phase are connected to the brushless motor 1 as output terminals of the phase in the inverter. However, the u-phase and v-phase output terminals Nu and Nv among the u-phase, v-phase, and w-phase output terminals of the inverter are connected to the motor 1 via the relay 65.

  During normal operation, the relay 65 is in a closed state (on state), and in the motor drive circuit 50 as an inverter, the two PWM states corresponding to the two MOS-FETs corresponding to each phase are two PWMs corresponding to the phase. Controlled by a signal (two PWM signals in an inverted relationship), the voltages obtained at the u-phase, v-phase, and w-phase output terminals Nu, Nv, and Nw are respectively converted to u-phase voltage, v-phase voltage, and w-phase. The phase voltage is applied to the brushless motor 1. By thus applying a voltage to the brushless motor 1, the u-phase current, the v-phase current, and the w-phase current are supplied from the motor driving circuit 50 to the brushless motor 1.

  A current detection resistor 51 is inserted between the motor drive circuit 50 and the negative power supply line (hereinafter referred to as “ground line”) Lg of the battery 8. The current detection circuit 14 detects the supply current from the motor drive circuit 50 to the motor 1 based on the voltage across the resistor 51, and outputs a current detection value Im indicating the magnitude of the supply current. This detected current value Im is input to the microcomputer 20.

  The microcomputer 20 executes a program stored in a memory (not shown) built in the ECU 10, thereby functioning as a functional unit for controlling the motor 1, a motor drive control unit 21, an overcurrent determination unit 22, a failure The detection determination unit 24 and the opening / closing control unit 26 are realized by software. Note that the overcurrent determination unit 22, the failure detection determination unit 24, and the switching control unit 26 may be realized in hardware.

  The motor drive control unit 21 receives the steering torque Ts, the vehicle speed S, the rotational position P, and the current detection value Im, and generates the voltage command values Du, Dv, Dw described above based on these. More specifically, the motor drive control unit 21 determines a target value It of current to be passed through the motor 1 based on the steering torque Ts and the vehicle speed S, and based on the target value It and the rotational position P of the rotor of the motor 1, The voltage command values Du, Dv, Dw are obtained according to the circuit equation. At this time, parameters used in the motor circuit equation are corrected based on the detected current value Im. Alternatively, the difference between the q-axis component of the current target value It and the q-axis component of the current detection value Im, and the d-axis component of the current target value It and the d-axis component of the current detection value Im The voltage values to be applied to the motor in order to cancel each difference may be obtained as the voltage command values Du, Dv, Dw. That is, the voltage command values Du, Dv, Dw may be obtained so that the motor 1 is driven by current feedback control. In this case, instead of detecting the supply current to the motor 1 using the current detection resistor 51 and the current detection circuit 14, two or three phases of the three-phase currents supplied to the motor 1 are individually detected. It is also possible to detect the q-axis and d-axis components of the current flowing through the motor 1 based on the detection results.

  The voltage command values Du, Dv, Dw generated by the motor drive control unit 21 are output from the microcomputer 20. The three-phase / PWM modulator 40 generates PWM signals U, V, W and their negative signals based on these voltage command values Du, Dv, Dw. As described above, the motor drive circuit 50 controls the conduction state (ON / OFF) of the six MOS-FETs as switching elements by these signals, so that the voltage command values Du, Dv, A voltage corresponding to Dw is applied to the motor 1. As a result, a current is supplied from the motor drive circuit 50 to the motor 1, and the motor 1 generates a steering assist force according to the steering torque Ts and the vehicle speed S.

  Based on the current detection value Im obtained by the current detection circuit 14, the overcurrent determination unit 22 determines whether or not the total current flowing through the motor drive circuit 50 (hereinafter referred to as “total current”) exceeds a predetermined allowable value. That is, it is determined whether or not the maximum value Imax of the total current that is not regarded as overcurrent is exceeded, and an H level (high level) or L level (low level) signal is determined as an overcurrent detection signal according to the determination result. Output as Soc. For example, when the total current becomes larger than the allowable value Imax because the power supply line Lp is short-circuited to the motor line, the overcurrent detection signal Soc becomes H level.

  The failure detection determination unit 24 outputs a failure detection signal Sf indicating the presence or absence of a failure based on the steering torque Ts obtained by the torque sensor 3 and the current detection value Im obtained by the current detection circuit 14. This failure detection signal Sf is, for example, H level when the value of the steering torque Ts is near the neutral point of the torque sensor 3 and the total current is greater than the predetermined current value Ia, and L otherwise. This is a level signal. Here, the predetermined current value Ia corresponds to the maximum value of the total current during normal operation with the steering torque Ts near the torque neutral point.

  The open / close control unit 26 receives the overcurrent detection signal Soc and the failure detection signal Sf, and outputs an open / close control signal Ssw based on these signals Soc and Sf. The opening / closing control signal Ssw is given to the switch 60 in the drive unit 11. Details of the open / close control signal Ssw will be described later.

  Further, the switching control unit 26 is at the H level if at least one of the overcurrent detection signal Soc and the failure detection signal Sf is at the H level, and is at the L level if both the overcurrent detection signal Soc and the failure detection signal Sf are at the L level. Is output as a relay control signal Sr. This relay control signal Sr is given to a relay drive circuit (not shown) for the relay 65. This relay drive circuit does not drive the relay 65 when the relay control signal Sr is at L level. At this time, current can be supplied from the motor drive circuit 50 to the motor 1. On the other hand, when the relay control signal Sr is at the H level, the relay 65 is driven. Thereby, the current supply from the motor drive circuit 50 to the motor 1 is interrupted.

<2.2 Configuration and operation for supplying power to the motor drive circuit>
As shown in FIG. 2, the drive unit 11 includes the switch 60 in order to control the supply / cutoff of the power supply voltage to the motor drive circuit 50. The drive unit 11 also includes a voltage stabilizing capacitor 76 connected in parallel to the motor drive circuit 50 and a surge absorbing Zener diode 72 in order to appropriately supply the power supply voltage to the motor drive circuit 50. ing. The cathode of the Zener diode 72 is connected to a positive power line (hereinafter simply referred to as “power line”) Lp of the battery 8, and the anode is connected to the ground line Lg. Further, a noise preventing inductor 74 is inserted between the Zener diode 72 and the voltage stabilizing capacitor 76 in the power supply line Lp.

  The switch 60 is inserted in a portion of the power line Lp between the battery 8 and the inductor 74, and includes a first field effect transistor (hereinafter referred to as “first FET”) 61 and a second field effect transistor ( (Hereinafter referred to as “second FET”) 62. The first and second FETs 61 and 62 are connected in series so that their parasitic diodes 61d and 62d are opposite to each other. That is, the first FET and the second FET are connected in series so that the parasitic diode 61d of the first FET 61 is in the reverse direction and the parasitic diode 62d of the second FET 62 is in the forward direction with respect to the battery 8. The gate terminals of the first and second FETs 61 and 62 are supplied with an opening / closing control signal Ssw generated by the opening / closing control unit 26 (via a predetermined interface circuit if necessary).

  According to the above configuration, an overcurrent is detected when the overcurrent is detected by the overcurrent determination unit 22 or a failure is detected by the failure detection determination unit 24 during the operation of the motor control device. When one or both of the signal Soc and the failure detection signal Sf become H level, the open / close control signal Ssw changes from H level to L level. As a result, both the first and second FETs 61 and 62 are turned off, that is, the switch 60 is opened. As a result, an excessive current is prevented from flowing from the battery 8. At this time, as described above, the relay signal Sr becomes H level and the relay 65 is also opened, so that the current supply from the motor drive circuit 50 to the motor 1 is also cut off.

  In contrast, when the overcurrent detection signal Soc and the failure detection signal Sf are both at the L level, supply of power supply voltage from the battery 8 to the motor drive circuit 50 via the switch 60 and the inductor 74 is started. The operation (hereinafter referred to as “when the power is turned on”) is as follows. In the following description, it is assumed that the voltage stabilizing capacitor 76 is in a discharged state and does not accumulate charges immediately before power is turned on.

  If the switch 60 changes from the open state (off state) to the closed state (on state) and maintains the on state as it is, the capacitance value of the voltage stabilizing capacitor 76 is large, which is excessive. There is a possibility that current flows and the first and second FETs 61 and 62 burn out. In contrast, in this embodiment, when the power is turned on, the open / close control signal Ssw changes as shown in FIG. That is, the open / close control signal Ssw changes alternately and repeatedly between the H level and the L level, and during this change period, the H level period becomes gradually longer, and after the predetermined period, the H level continuously changes to the H level. Become. Typically, the open / close control signal Ssw is generated by the open / close control unit 26 as a voltage signal in which the duty ratio indicating the ratio of the H level period gradually increases from 0 to 1 (hereinafter referred to as open / close control at power-on). (It is assumed that the duty ratio of the signal Ssw gradually increases from 0 to 1).

  According to such an opening / closing control signal Ssw, when the power is turned on (typically, when an ignition switch (not shown) is turned on and an electric power steering apparatus including the ECU 10 is started), the switch 60, that is, the first and The second FETs 61 and 62 alternately repeat the ON state and the OFF state, and the ON state period (ON period) is gradually increased in the repetition, and the second FETs 61 and 62 are continuously turned ON after a predetermined period. In this way, when the first and second FETs 61 and 62 are repeatedly turned on and off, an excessive inrush current does not occur, and the change in the value of the current flowing through the switch 60, that is, the first and second FETs 61 and 62, is more than conventional. The voltage stabilizing capacitor 76 is charged to the power supply voltage (the voltage of the battery 8) more slowly than before. Therefore, the first and second FETs 61 and 62 constituting the switch 60 are not burned out by the inrush current.

  Further, as shown in FIG. 3, in the periods T1, T3, T5, and T7 in which the switching control signal Ssw is at the H level among the periods in which the duty ratio of the switching control signal Ssw changes, the switch 60 and the inductor 74 are connected from the battery 8. Current flows to the voltage stabilization capacitor 76 (and the motor drive circuit 50) through the switch 60, and the current supply from the battery 8 is cut off by the switch 60 in the periods T2, T4, T6, and T8 when the switching control signal Ssw is at the L level. The However, since the inductor 74 is inserted between the switch 60 and the voltage stabilizing capacitor 76, the current going to the voltage stabilizing capacitor 76 or the like does not suddenly become zero, and the Zener diode 72 → the inductor 74 → The circulating current Icir flows through the path from the voltage stabilizing capacitor 76 to the Zener diode 72, and charging to the voltage stabilizing capacitor 76 continues. That is, the surge absorbing Zener diode 72 functions as a free-wheeling diode in the periods T2, T4, T6, and T8. Thereby, even if the inductor 74 has a large inductance value, a large back electromotive force is not generated when the current supply from the battery 8 is interrupted by the switch 60.

<3. Effect>
As described above, according to the present embodiment, the switch 60 for preventing an excessive current from flowing from the battery 8 as the DC power source when an abnormality such as a failure occurs is realized by the FET, and the power is turned on. Sometimes, since the duty ratio of the switching control signal Ssw gradually increases from 0 to 1 (FIG. 3), the inrush current can be reduced even if the capacitance value of the voltage stabilizing capacitor 76 is large. Here, since the switch 60 is composed of an FET, it is possible to control the on / off of the switch 60 at a very high speed compared to the case of using an electromagnetic relay (the switching speed is, for example, several tens of nanoseconds to Hundreds of nanoseconds). For this reason, the on / off period and cycle of the switch 60 can be appropriately set according to the capacitance value of the voltage stabilizing capacitor 76 and the inductance value of the inductor 74 so that the inrush current is sufficiently relaxed. As a result, it is possible to avoid damage to the switch due to the inrush current (burning of the FET constituting the switch) without using a separate component such as a precharge circuit or a large switch. . Further, since the surge absorbing Zener diode 72 functions as a freewheeling diode during the off period during the on / off operation of the switch 60 at this time, the inrush current path has a large inductance component such as the noise preventing inductor 74. Even if it contains, generation | occurrence | production of a counter electromotive force is suppressed.

  Thus, according to the present embodiment, it is possible to reliably reduce the inrush current when the power is turned on while suppressing an increase in parts and cost required for manufacturing the motor control device, thereby improving the quality of the motor control device. Can be improved. It is also possible to reduce the motor control device and reduce power consumption.

  In the above embodiment, the first and second FETs 61 and 62 constituting the switch 60 are connected so that the parasitic diodes 61d and 62d are opposite to each other (FIG. 2). Even when they are connected in the opposite direction, an excessive current does not flow, and the motor control device can be protected from a connection error of the battery 8.

  Furthermore, in the above embodiment, since the surge absorbing Zener diode 72 functions as a freewheeling diode when the power is turned on, it is not necessary to newly provide a freewheeling diode if the motor control device has the surge absorbing Zener diode 72.

  Furthermore, in the electric power steering device that uses the motor control device according to the above embodiment as an ECU, the inrush current at the time of power-on can be surely reduced while suppressing the increase in necessary parts and cost, so that the current at the time of failure etc. It is possible to increase the output of the electric power steering device while suppressing the increase in size and cost of the opening / closing means provided to shut off the supply.

<4. Modification>
<4.1 First Modification>
In the drive unit 11 in the above embodiment, as shown in FIG. 2, the two FETs 61 and 62 constituting the switch 60 have the parasitic diode 61 d of the first FET 61 closer to the battery 8 in the opposite direction to the battery 8. The parasitic diode 62d of the second FET 62 far from the battery 8 is connected so as to be in the forward direction with respect to the battery 8, but the configuration of the switch 60 is not limited to this. For example, instead of such a configuration, the parasitic diode 61 d of the first FET 61 closer to the battery 8 is in the forward direction with respect to the battery 8, and the parasitic diode 62 d of the second FET 62 far from the battery 8 is in the reverse direction with respect to the battery 8. The first and second FETs 61 and 62 may be connected so that That is, the configuration shown in FIG. 4 may be adopted as the configuration of the drive unit 11. In this configuration, a switch 60B shown in FIG. 4 is used in place of the switch 60 shown in FIG. 2, and the motor control device adopting this configuration also has the same effect as the above embodiment.

<4.2 Second Modification>
Further, in the drive unit 11 (FIG. 2) in the above embodiment, the switch 60 is configured by two FETs 61 and 62, but instead of this, as shown in FIG. The second FET 62 including the parasitic diode 62d may be omitted (short circuit removal), and the switch may be configured by only the first FET 61 including the parasitic diode 61d in the reverse direction with respect to the battery 8. In this case, during the off periods T2, T4, T6 and T8 (see FIG. 3) of the switch 60C when the power is turned on, the circulating current Icir is routed along the path of the Zener diode 72 → the inductor 74 → the voltage stabilizing capacitor 76 → the Zener diode 72. Flows. In this case, if the battery 8 is erroneously connected in the reverse direction, an excessive current flows. Therefore, it is preferable to separately provide a means for preventing the battery 8 from being erroneously connected.

<4.3 Third Modification>
Furthermore, in the drive unit 11 (FIG. 2) in the above embodiment, the surge absorbing Zener diode 72 functions as a freewheeling diode when the power is turned on (when the switch 60 is off). It may be used and the freewheeling diode need not be a Zener diode. For example, instead of or together with the surge absorbing Zener diode 72, as shown in FIG. 6, a third field effect transistor (hereinafter “discharge FET”) for discharging the charge accumulated in the voltage stabilizing capacitor 76 is used. 73) may be provided. In this case, in the discharging FET 73, the cathode (and drain terminal) of the parasitic diode 73d is connected to the connection point between the second FET 62 and the inductor 74, and the source terminal is connected to the ground line Lg. Thus, the parasitic diode 73d functions as a freewheeling diode when the power is turned on. That is, during the off periods T2, T4, T6, and T8 of the switch 60 when the power is turned on (see FIG. 3), the circulating current Icir flows through the path of the parasitic diode 73d → the inductor 74 → the voltage stabilizing capacitor 76 → the parasitic diode 73d. Flowing.

  Note that the first and second modified examples (FIGS. 4 and 5) described above function as a freewheeling diode instead of or together with the surge absorbing Zener diode 72, similarly to the configuration shown in FIG. A discharge FET 73 including a parasitic diode 73d that can be used may be used. When the configuration including such a discharge FET 73 is employed, a control signal for controlling on / off of the discharge FET 73 is generated in the microcomputer 20, for example. Further, in the configuration shown in FIG. 6, a switch 60 </ b> B shown in FIG. 4 may be used instead of the switch 60.

<4.4 Other Modifications>
The motor control device according to the embodiment and the modification thereof is a device for driving the three-phase brushless motor 1, but the present invention is not limited to this. As is apparent from the above description, the present invention is also applicable to a motor control device for driving other types of electric motors such as a brushless motor having a number of phases other than three phases and a motor with brushes.

  In the above-described embodiment and its modifications, the inductor 74 is inserted in the power supply line Lp as a path for supplying current from the battery 8 to the motor drive circuit 50. Such an inductor 74 is used as a component. Even if it is not done, the present invention can be applied. Even in this case, since the current path such as the power supply line Lp includes an inductance component, an element that functions as a free-wheeling diode at the time of supplying current is required.

  The present invention can be applied not only to the above-described column assist type electric power steering apparatus but also to a pinion assist type or rack assist type electric power steering apparatus. The present invention can also be applied to motor control devices other than the electric power steering device.

  DESCRIPTION OF SYMBOLS 1 ... Brushless motor, 10 ... ECU (motor control apparatus), 60, 60B, 60C ... Switch (switching means), 61 ... 1st FET (1st field effect transistor), 62 ... 2nd FET (2nd field effect) Transistor), 61d, 62d ... parasitic diode, 72 ... surge absorbing Zener diode, 73 ... discharge FET (third field effect transistor), 73d ... parasitic diode, 74 ... inductor, 76 ... voltage stabilizing capacitor, Lp ... Power line (current supply path), Lg... Ground line (current supply path).

Claims (3)

A motor control device including a drive circuit in which a voltage stabilizing capacitor is connected in parallel, receiving power supply voltage from a DC power supply and driving the electric motor by the drive circuit;
The first field effect transistor inserted in the current supply path from the DC power supply to the drive circuit so that the parasitic diode is in the reverse direction with respect to the DC power supply, and the parasitic diode is in the forward direction with respect to the DC power supply. Open / close means including a second field effect transistor connected in series with the first field effect transistor and inserted into the current supply path ,
A free-wheeling diode disposed between the switching means and the voltage stabilizing capacitor and circulating a current supplied to the voltage stabilizing capacitor when the first and second field effect transistors are turned off;
When the supply of the power supply voltage from the DC power supply to the drive circuit is started, the first and second switching units are alternately turned on and off while gradually increasing the on-state period. Open / close control means for turning on and off the second field effect transistor ;
A motor control apparatus comprising: a third field effect transistor including the freewheeling diode as a parasitic diode and discharging the charge accumulated in the voltage stabilizing capacitor when turned on. .   The motor control device according to claim 1, further comprising an inductor inserted in a portion of the current supply path between the freewheeling diode and the voltage stabilizing capacitor. An electric power steering device for applying a steering assist force to a steering mechanism of a vehicle by an electric motor,
A motor control device according to claim 1 or 2 ,
The electric power steering apparatus, wherein the motor control apparatus drives an electric motor that applies a steering assist force to the steering mechanism.

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