JP5574155B2 - Motor control device - Google Patents

Description

  The present invention relates to a motor control device for driving a three-phase brushless motor. A three-phase brushless motor is used, for example, as a generation source of steering assist force in an electric power steering apparatus.

  The drive circuit of the brushless motor used in the electric power steering apparatus includes a switching element such as an FET (Field Effect Transistor). When a failure occurs in the switching element, the brushless motor becomes a load when the steering wheel is operated, and there is a possibility that the steering becomes heavy. In order to cope with such a problem, a relay is inserted in the connection between the brushless motor and the drive circuit. For example, in the case of a three-phase brushless motor, a relay is inserted into each of the two-phase motor connections, and these relays are turned off when there is no control and when the switching element fails.

JP 2008-67429 A JP 2009-71975

In the above prior art, when the switching element in the motor drive circuit fails, the relay is turned off, so the brushless motor cannot be driven. Therefore, in the electric power steering device, it is not possible to generate a steering assist force (assist force).
An object of the present invention is to provide a three-phase brushless motor by another normal two-phase when one switching element in the driving circuit of the three-phase brushless motor fails to open or when two in-phase switching elements fail to open. It is providing the motor control apparatus which can drive.

In order to achieve the above object, an invention according to claim 1 is a motor control device for controlling a three-phase brushless motor (18), comprising two switching elements (31 _UH , 31 _UL ; 31 _VH , 31 _VL ; 31 _WH , 31 _WL ) are connected in series corresponding to each of the three phases, and three series circuits are connected in parallel between the power source (33) and the ground (34). Means (41, 42) for turning off all the switching elements when the connected driving circuit (30) and one switching element among the plurality of switching elements or two switching elements having the same phase are opened. , S1), and means (41) for monitoring an induced voltage corresponding to at least one of the two normal phases other than the failure phase corresponding to the switching element that has failed open, Control means (41, 43, S2 to S5) for controlling the switching elements corresponding to the normal phase so that a current of the same phase flows in the normal phase with respect to the induced voltage of the normal phase monitored by the monitoring means. ) and viewing including, said control means, when at least one of the induced voltage in the normal phase of the two normal phases is larger than the positive polarity of a predetermined threshold value (Vth1), the high-side of the normal phase The first means (43) for turning on the switching element and turning on the other low-side switching element of the normal phase, and the induced voltage of at least one normal phase of the two normal phases has a predetermined negative threshold ( Vth2) is turned on when the low-side switching element of the normal phase is turned on and the second high-side switching element of the other normal phase is turned on. (43) including a still, alphanumeric characters in parentheses represent corresponding constituent elements in an embodiment described later, of course, the scope of the invention is not limited to this embodiment. The same applies hereinafter.

In the above configuration, when one of the plurality of switching elements or two switching elements having the same phase has an open failure, all the switching elements are turned off. As a result, the driving of the three-phase brushless motor is stopped. Thereafter, the induced voltage corresponding to at least one of the two normal phases other than the failure phase corresponding to the switching element that has failed open is monitored. Then, the switching element corresponding to the normal phase is controlled such that a current having the same phase flows in the normal phase with respect to the induced voltage of the normal phase being monitored .
Specifically, the induced voltage (V _U ) of at least one normal phase (U phase) out of two normal phases (for example, U phase and V phase ) is greater than the positive threshold (Vth1). Sometimes, the normal-phase high-side switching element (31 _UH ) is turned on, and the other normal-phase (V-phase) low-side switching element (31 _VL ) is turned on. In this case, since a current having the same phase as the induced voltage generated in this phase flows from the power source (33) to the normal phase U-phase field coil (18U), the brushless motor (18) Driven.
Further, when the induced voltage (V _U ) of at least one normal phase (U phase) of two normal phases (for example, U phase and V phase) becomes smaller than the negative polarity threshold (Vth2), The normal-phase low-side switching element ( _31UL ) is turned on, and the other normal-phase (V-phase) high-side switching element ( _31VH ) is turned on. In this case, since a current having the same phase as the induced voltage generated in this phase flows from the power source (33) to the normal phase U-phase field coil (18U), the brushless motor (18) Driven.
Therefore, when the three-phase brushless motor is used in an electric power steering apparatus, even when the switching element is open-circuit failure, it is possible to perform steering assist.

The invention described in 請 Motomeko 2, the time the switching element is turned on by the control means is a motor control device according to claim 1 is constant. In this configuration, when the switching element is turned on by the control means, the switching element is turned off when a predetermined time has elapsed since the turning on.

According to a third aspect of the present invention, the time during which the switching element is turned on by the first means is the predetermined positive polarity after the induced voltage becomes larger than the positive first threshold value (Vth1). The time until the switching element is turned on by the second means is less than a predetermined first threshold value (Vth2) having a negative polarity. 5. The motor control device according to claim 4, wherein the motor control device is a period from when it becomes a predetermined second threshold value having a negative polarity. In this configuration, in the first means, the switching element is turned on for a period from when the induced voltage becomes greater than the positive first threshold value to below the predetermined second positive threshold value. . On the other hand, in the second means, the switching element is turned on during a period from when the induced voltage becomes smaller than the negative first threshold value until it becomes equal to or higher than the predetermined negative second threshold value.

  The positive first threshold value and the positive second threshold value may be the same value. The negative first threshold value and the negative second threshold value may be the same value.

1 is a schematic diagram showing a schematic configuration of an electric power steering device to which a motor control device according to an embodiment of the present invention is applied. It is the schematic which shows the electric constitution of ECU as a motor control apparatus. It is a flowchart which shows operation | movement of the motor control part when a failure generate | occur | produces. It is explanatory drawing for demonstrating the operation example of a two-phase drive part when one or both of a pair of FET corresponding to a W phase carries out an open failure. It is explanatory drawing for demonstrating the other operation example of a two-phase drive part when either one of a pair of FET corresponding to a W phase carries out an open failure. It is explanatory drawing for demonstrating the further another example of operation | movement of a two-phase drive part when either one of a pair of FET corresponding to a W phase carries out an open failure.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device to which a motor control device according to an embodiment of the present invention is applied.
The electric power steering apparatus 1 includes a steering wheel 2 as a steering member, a steering mechanism 4 for turning the steered wheels 3 in conjunction with the rotation of the steering wheel 2, and steering assistance for assisting the driver's steering. And a mechanism 5. The steering wheel 2 and the steering mechanism 4 are mechanically coupled via a steering shaft 6 and an intermediate shaft 7.

  The steering shaft 6 extends linearly. Steering shaft 6 includes an input shaft 8 connected to steering wheel 2 and an output shaft 9 connected to intermediate shaft 7. The input shaft 8 and the output shaft 9 are connected via a torsion bar 10 so as to be relatively rotatable on the same axis. That is, when the steering wheel 2 is rotated, the input shaft 8 and the output shaft 9 rotate in the same direction while rotating relative to each other.

  A torque sensor 11 disposed around the steering shaft 6 detects a steering torque applied to the steering wheel 2 based on the relative rotational displacement amounts of the input shaft 8 and the output shaft 9. The steering torque detected by the torque sensor 11 is input to an ECU (Electronic Control Unit) 12. Further, the vehicle speed detected by the vehicle speed sensor 23 is input to the ECU 12.

  The steered mechanism 4 includes a rack and pinion mechanism including a pinion shaft 13 and a rack shaft 14 as a steered shaft. The steered wheel 3 is connected to each end of the rack shaft 14 via a tie rod 15 and a knuckle arm (not shown). The pinion shaft 13 is connected to the intermediate shaft 7. The pinion shaft 13 rotates in conjunction with the steering of the steering wheel 2. A pinion 16 is connected to the tip of the pinion shaft 13 (the lower end in FIG. 1).

  The rack shaft 14 extends linearly along the left-right direction of the automobile. A rack 17 that meshes with the pinion 16 is formed at an intermediate portion in the axial direction of the rack shaft 14. By the pinion 16 and the rack 17, the rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. The steered wheels 3 can be steered by moving the rack shaft 14 in the axial direction.

When the steering wheel 2 is steered (rotated), this rotation is transmitted to the pinion shaft 13 via the steering shaft 6 and the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into an axial movement of the rack shaft 13 by the pinion 16 and the rack 17. Thereby, the steered wheel 3 is steered.
The steering assist mechanism 5 includes an electric motor 18 for assisting steering and a speed reduction mechanism 19 for transmitting the output torque of the electric motor 18 to the steering mechanism 4. In this embodiment, the electric motor 3 is a three-phase brushless motor. The speed reduction mechanism 19 includes a worm gear mechanism that includes a worm shaft 20 and a worm wheel 21 that meshes with the worm shaft 20. The speed reduction mechanism 19 is accommodated in a gear housing 22 as a transmission mechanism housing.

The worm shaft 20 is rotationally driven by the electric motor 18. The worm wheel 21 is coupled to the steering shaft 6 so as to be rotatable in the same direction. The worm wheel 21 is rotationally driven by the worm shaft 20.
When the worm shaft 20 is rotationally driven by the electric motor 18, the worm wheel 21 is rotationally driven and the steering shaft 6 rotates. The rotation of the steering shaft 6 is transmitted to the pinion shaft 13 via the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. Thereby, the steered wheel 3 is steered. That is, the wheel 3 is steered by rotating the worm shaft 2 by the electric motor 18.

  The electric motor 18 is controlled by the ECU 12 as a motor control device. The ECU 12 controls the electric motor 18 based on the steering torque detected by the torque sensor 11, the vehicle speed detected by the vehicle speed sensor 23, and the like. Specifically, the ECU 12 determines a target assist amount using a map in which the relationship between the steering torque and the target assist amount is stored for each vehicle speed so that the assist force generated by the electric motor 18 approaches the target assist amount. Control.

In this embodiment, the electric motor 18 is driven without a position sensor. That is, it is driven without using a position sensor for detecting the rotation angle (position) of a rotor such as a resolver. In this embodiment, the rotation angle of the rotor is calculated based on the induced voltage of the electric motor 18.
FIG. 2 is a schematic diagram showing an electrical configuration of the ECU 12 as a motor control device. The electric motor 18 includes a stator having a U-phase field coil 18U, a V-phase field coil 18V, and a W-phase field coil 18W, and a permanent magnet that receives a repulsive magnetic field from the field coils 18U, 18V, and 18W. And a rotor that has been made.

The ECU 12 includes a drive circuit 30 that generates drive power for the electric motor 18 and a control unit 40 that controls the drive circuit 30. The control unit 40 is composed of a microcomputer including a CPU and a memory storing an operation program for the CPU.
The drive circuit 30 is a three-phase bridge inverter circuit. In the drive circuit 30, a series circuit of a pair of FETs (field effect transistors) 31 _UH and 31 _UL corresponding to the U phase of the electric motor 18, a series circuit of a pair of FETs 31 _VH and 31 _VL corresponding to the V phase, A series circuit of a pair of FETs 31 _WH and 31 _WL corresponding to the W phase is connected in parallel between the DC power supply 33 and the ground 34. Further, regenerative diodes 32 _{UH to} 32 _WL are connected in parallel to the FETs 31 _{UH to} 31 _WL in such a direction that a forward current flows from the ground 34 side to the DC power supply 33 side.

Hereinafter, among the pair of FETs of each phase, the one on the power source 33 side may be referred to as “high-side FET”, and the one on the ground 34 side may be referred to as “low-side FET”. In addition, the six FETs 31 _{UH to} 31 _WL are collectively referred to as “FET 31”. Similarly, the six regenerative diodes 32 _{UH to} 32 _WL are collectively referred to as “regenerative diode 32”.

The U-phase field coil 18U of the electric motor 18 is connected to a connection point between a pair of FETs 31 _UH and 31 _UL corresponding to the U-phase. The V-phase field coil 18V of the electric motor 18 is connected to a connection point between a pair of FETs 31 _VH and 31 _VL corresponding to the V-phase. W-phase field coil 18W of the electric motor 18 is connected to the W-phase to the connection point between the pair of _{FET 31} WH, _{31 WL} corresponding. Each connection line for connecting the field coils 18U, 18V, 18W of each phase and the drive circuit 30 includes current sensors 51 _U , for detecting the phase currents I _U , I _V , I _W of each phase. 51 _V and 51 _W are provided.

The control unit 40 functions as a plurality of function processing units by executing a predetermined operation program stored in the memory. The plurality of function processing units include a failure determination unit 41, a sine wave driving unit 42, and a two-phase driving unit 43.
The sine wave drive unit 42 drives the electric motor 18 by a sine wave by controlling each FET 31 in a normal time when no failure has occurred in the FET 31. Each phase voltage V _U , V _V , V _W of the electric motor 18 is given to the sine wave drive unit 42. Further, the sine wave driving unit 42, the steering torque detected by the torque sensor 11, a vehicle speed detected by the vehicle speed sensor 23, the phase of the phase current detected by the current sensor _{51 U, 51 V, 51 W} I _U , I _V , and I _W are input. The sine wave drive unit 42, for example, drives the electric motor 18 in a sine wave by a 180 ° energization method, calculates an induced voltage (counterelectromotive force) of each phase, and calculates a rotation angle of the rotor based on the calculated voltage. . Further, the sine wave drive unit 42 detects, for example, a map in which the relationship between the steering torque and the target assist amount (current target value) is stored for each vehicle speed, the steering torque detected by the torque sensor 11, and the vehicle speed sensor 23. The target assist amount is determined based on the determined vehicle speed. The sine wave driving unit 42 then assists (torque) generated by the electric motor 18 based on the target assist amount, the phase current detected for each phase, and the rotor rotation angle calculated from the induced voltage. Each of the FETs 31 is subjected to PWM (Pulse Width Modulation) control so as to approach the target assist amount.

The failure determination unit 41 performs control for stopping the electric motor 18 when an abnormality of the electric motor 18 is detected, determines whether or not an open failure has occurred in the FET 31, and an open failure has occurred in the FET 31. If there is an open failure, the FET 31 in which the open failure has occurred is identified.
When the failure determination unit 41 determines that an open circuit failure has occurred in the FET 31 and the FET 31 in which the open circuit failure has occurred is identified, the two-phase drive unit 43 has a normal two-phase electric motor 18. Is driven. More specifically, when one of the six FETs 31 or two in-phase FETs 31 has an open failure, when the failure determination unit 41 identifies the FET 31 in which the open failure has occurred, the two-phase The drive unit 43 drives the electric motor 18 with two normal phases.

FIG. 3 is a flowchart showing the operation of the motor control unit 40 when a failure occurs.
When the failure determination unit 41 detects that an operation failure (failure) has occurred in the electric motor 18 when the electric motor 18 is sine wave driven by the sine wave drive unit 42, the failure determination unit 41 stops the motor in the sine wave drive unit 42. The command is given (step S1). When the sine wave drive unit 42 receives the motor stop command from the failure determination unit 41, the sine wave drive unit 42 stops the sine wave drive and turns off all the FETs 31. Thereby, the electric motor 18 stops.

Thereafter, the failure determination unit 41 determines whether or not there is a possibility of an open failure based on the phase voltages V _U , V _V , and V _W (step S2). Specifically, failure determination unit 41 has one of phase voltages V _U , V _V , and V _W greater than a predetermined ground level VG (for example, 0.5 [V]) and a predetermined power supply level VB (for example, If it is lower than 5.0 [V]), it is determined that an open failure may have occurred. The reason why this determination is appropriate will be described. When a short circuit failure has occurred in any of the high side FETs 31 _UH , 31 _VH , and 31 _WH , the phase voltages V _U , V _V , and V _W are equal to or higher than a predetermined power supply level VB, and the low side FETs 31 _UL , 31 _VL , 31 _WL is short-circuited, each phase voltage V _U , V _V , V _W is equal to or lower than a predetermined ground level VG. Therefore, when each phase voltage V _U , V _V , V _W is larger than the predetermined ground level VG and lower than the predetermined power supply level VB, no short circuit failure has occurred in any of the FETs 31. It can be determined that it may have occurred. Note that this determination does not need to check all the phase voltages, and can be performed by checking any one phase voltage.

When it is determined that there is no possibility that an open failure has occurred (step S2: NO), the failure determination unit 41 performs processing other than the two-phase drive control described later (hereinafter referred to as “other processing”). Is performed (step S6). This “other processing” includes not performing any processing. When it is determined that there is a possibility that an open failure has occurred (step S2: YES), the failure determination unit 41 performs a process for identifying a failure location (step S3). Specifically, the failure determination unit 41 turns on each FET 31 individually. When the high-side _{FET31 UH, 31 VH,} 31 _WH individually turned on, when the phase voltage _{V U, V V, V W} has changed beyond a predetermined power level VB is the FET is normal, When the low-side FETs 31 _UL , 31 _VL , 31 _WL are individually turned on and the phase voltages V _U , V _V , V _W change below a predetermined ground level VG, the FETs are normal. Therefore, when each FET 31 is turned on individually, the failure determination unit 41 determines that the FET has an open failure when there is no change in the phase voltages V _U , V _V , and V _W. This determination does not need to check all the phase voltages, and can be performed by checking any one phase voltage.

  When the failure determination unit 41 cannot identify the FET 31 in which the open failure has occurred by the failure point identification process (step S4: NO), the failure determination unit 41 performs a process other than the two-phase drive control ("other process"). Perform (step S6). On the other hand, when the FET 31 in which the open failure has occurred can be identified by the failure location identification process (step S4: YES), the failure determination unit 41 causes the two-phase drive unit 43 to start the two-phase drive control (step S4). S5). However, when only one FET 31 has an open fault or when only one FET 31 having an open fault has the same phase, the FET 31 having the open fault can be identified. Only in this case, the process proceeds to step S5 and the two-phase drive control is started. If the FET has an open failure in two or more of the three phases, even if those FETs 31 in which the open failure has occurred can be identified, the process does not proceed to step S5, but step S6. Migrate to

In step S5, specifically, the failure determination unit 41 notifies the two-phase drive unit 43 of the phase corresponding to the FET 31 in which the open failure has occurred. Thereby, the two-phase drive unit 43 starts the two-phase drive control. In the following, a phase corresponding to the FET 31 in which an open failure has occurred may be referred to as a “failure phase”, and the other phases may be referred to as “normal phases”.
Hereinafter, the two-phase drive control by the two-phase drive unit 43 will be described. First, the concept of two-phase drive control will be described. When all the FETs 31 in the drive circuit 30 are turned off, the rotor of the electric motor 18 is rotated when the driver is rotated by the driver. When the rotor of the electric motor 18 rotates, an induced voltage is generated in the field coils 18U, 18V, 18W of the stator. The induced voltage of each phase has a sine waveform whose phase is shifted by 120 °.

  If a drive voltage equal to or higher than the induced voltage generated in the field coils 18U, 18V, and 18W by steering can be applied, the electric motor 18 can be driven and assist can be performed. If the polarity of the current flowing from the drive circuit 30 toward the electric motor 18 is positive, the phase relationship between the voltage and the current when the electric motor 18 operates as a generator is reversed, and the phase relationship is the same during assist. It becomes. Therefore, in the state where almost no current flows, if a current having the same phase as the induced voltage generated in the field coils 18U, 18V, and 18W can be passed through the field coil even instantaneously, the assist can be performed.

Therefore, the two-phase drive unit 43 causes the electric motor 18 to generate assist force by controlling the drive circuit 30 so that a current having the same phase as the induced voltage flows through the two normal-phase field coils. More specific description will be given with reference to FIG.
FIG. 4 is an explanatory diagram for explaining an operation example of the two-phase drive unit 43 when one or both of the pair of FETs 31 _WH and 31 _WL corresponding to the W-phase has an open failure. In FIG. 4, V _U represents an induced voltage of the U phase that is one normal phase (first normal phase), and V _V represents an induced voltage of the V phase that is the other normal phase (second normal phase). Is shown. Further, S _U represents a control signal for the FETs 31 _UH and 31 _UL corresponding to the U phase which is the first normal phase, and S _V is an FET 31 _VH and 31 _VL corresponding to the V phase which is the second normal phase. The control signal for is shown.

When the control signal S _U corresponding to the U phase is at the H level, the high side FET 31 _UH corresponding to the U phase is turned on, and when the control signal S _U is at the L level, the low side FET 31 _UL corresponding to the U phase is Turned on. Similarly, when the control signal S _V corresponding to the V-phase is at the H level, the high side FET 31 _VH is turned on corresponding to the V phase, when the control signal S _V is at the L level, the low side corresponding to the V-phase The FET 31 _VL is turned on.

Predetermined threshold Vth1 greater period of polarity induced voltage _{V U} is positive in the first U-phase is normal phase (t3 to t4, t11 to t12) in the two-phase driving section 43, a first The U-phase high-side FET 31 _UH that is the normal phase is turned on, and the V-phase low-side FET 31 _VL that is the second normal phase is turned on. In the period (t5 to t6, t13 to t14) in which the induced voltage VV of the _V phase that is the second normal phase is larger than the positive polarity threshold value Vth1, the two-phase driving unit 43 The V-phase high-side FET 31 _VH that is the normal phase is turned on, and the U-phase low-side FET 31 _UL that is the first normal phase is turned on. As a result, during a period in which the induced voltage of each normal phase is greater than the positive polarity threshold value Vth1, a drive voltage equal to or higher than the induced voltage of that phase is applied to the field coil of that phase, so that the electric motor 18 is driven. be able to. As a result, the steering assist by the electric motor 18 is possible. Note that the period from when the FET 31 is turned on to when it is turned off may be a predetermined period (constant pulse width), as indicated by a broken line in FIG.

  The higher the rotational speed of the rotor rotated by steering, the higher the induced voltage and the higher the frequency. However, as described above, when the period during which the FET 31 is turned on is a period in which the induced voltage exceeds the threshold value, or when the period during which the FET 31 is turned on is a fixed time, the period during which the FET 31 is turned on is Since the voltage is shortened accordingly, the voltage applied to the electric motor 18 is eventually increased. Therefore, when the rotational speed of the rotor increases, the assist time (assist total time) automatically increases.

  Instead, the pulse width may be changed according to the induced voltage level (rotation speed). That is, the pulse width is increased as the induced voltage level (rotational speed) increases. Further, the pulse width modulation control (PWM control) may be performed according to the induced voltage level (rotation speed) to turn on / off the FET 31 and change its duty ratio. That is, the duty ratio is increased as the induced voltage level (rotational speed) increases.

  As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, in a period in which the induced voltage of each normal phase is larger than the predetermined threshold value Vth1 having a positive polarity, a voltage equal to or higher than the induced voltage of that phase is applied to the field coil of that phase. The FET 31 corresponding to the normal phase is controlled. However, instead of such control, in the period in which the induced voltage of each normal phase with respect to each magnetic pole is smaller than a predetermined threshold value of negative polarity, the voltage higher than the induced voltage of that phase is a field coil of that phase. The FET 31 corresponding to the normal phase may be controlled as shown in FIG.

Specifically, as shown in FIG. 5, when the failure phase is, for example, the W phase, the induced voltage V _U of the U phase that is the first normal phase is smaller than a predetermined threshold value Vth2 having a negative polarity. In the period (t7 to t8, t15 to t16), the two-phase drive unit 43 turns on the low-side FET 31 _UL of the U phase that is the first normal phase and the high side of the V phase that is the second normal phase. The FET 31 _VH is turned on. In the period (t1 to t2, t9 to t10) in which the induced voltage VV of the _V phase that is the second normal phase is smaller than the negative polarity threshold value Vth2, the two-phase driving unit 43 The V-phase low-side FET 31 _VL that is the normal phase is turned on, and the U-phase high-side FET 31 _UH that is the first normal phase is turned on. Note that the period from when the FET 31 is turned on to when it is turned off may be a predetermined constant period (constant pulse width) as indicated by a broken line in FIG. Further, as described above, the FET may be turned on / off by pulse width control (PWM).

Further, both the control described with reference to FIG. 4 and the control described with reference to FIG. 5 may be performed. FIG. 6 shows an operation example of the two-phase drive unit 43 when such control is performed. In FIG. 6, V _U represents an induced voltage of the U phase that is one normal phase (first normal phase), and V _V represents an induced voltage of the V phase that is the other normal phase (second normal phase). S _U represents a control signal for the FETs 31 _UH and 31 _UL corresponding to the U phase which is the first normal phase, and S _V represents an FET 31 _VH and 31 corresponding to the V phase which is the second normal phase. _The control signal with respect to _VL is shown.

In addition, various design changes can be made within the scope of matters described in the claims.
The present invention can also be applied to a three-phase brushless motor used for applications other than the electric power steering device.

18 ... Electric motor, 30 ... Drive circuit, 31 ... FET, 33 ... Power supply, 34 ... Ground, 40 ... Control part

Claims (3)

A motor control device for controlling a three-phase brushless motor,
A drive circuit comprising three sets of series circuits each having three switching elements connected in series corresponding to each of the three phases, and the series circuits connected in parallel between the power source and the ground;
Means for turning off all switching elements when one of the plurality of switching elements or two switching elements in phase with each other has an open failure;
Monitoring means for monitoring an induced voltage corresponding to at least one of the two normal phases other than the failure phase corresponding to the switching element that has failed open;
Wherein as in-phase current with respect to the induced voltage of the normal phase being monitored by the monitoring means to flow to its normal phase, see containing and control means for controlling the switching element corresponding to the normal phase,
The control means includes
When the induced voltage of at least one normal phase of the two normal phases becomes greater than a predetermined positive polarity threshold, the high-side switching element of the normal phase is turned on and the low-side switching of the other normal phase A first means for turning on the element;
When the induced voltage of at least one normal phase of the two normal phases becomes smaller than a predetermined negative threshold, the low-side switching element of the normal phase is turned on and the high-side switching of the other normal phase And a second means for turning on the element . The motor control device according to claim 1, wherein a time during which the switching element is turned on by the control unit is constant . The time during which the switching element is turned on by the first means is from the time when the induced voltage becomes greater than the predetermined first threshold value having a positive polarity until the time when the induced voltage becomes equal to or lower than the predetermined second threshold value having a positive polarity Period,
The time for which the switching element is turned on by the second means is from the time when the induced voltage becomes smaller than the predetermined negative first threshold value until the time when the induced voltage becomes equal to or higher than the predetermined negative second threshold value. The motor control device according to claim 1, wherein the motor control device is a period .

Images