Motor control device

Abstract

Motor drive device (10) for driving a motor (800) having a plurality of coil sets (80, 85), each of which is formed from coils (81, 82, 83, 86, 87, 88) having a plurality of phases, the motor drive device comprising: a plurality of inverter circuits (50, 60) provided in correspondence with the plurality of coil sets and supplying electric power to the plurality of coil sets (80, 85) by converting electric power supplied from an electric power source (15); an electric power supply on / off control circuit (20, 25) which is provided in each power supply system between the electric power source (15) and the inverter circuit (50, 60), and electrically passes or interrupts the electric power source (15) to and from the inverter circuit (50, 60); a fault detection part (71, 72) which detects a fault in the inverter circuit (50, 60) in each power supply system; a drive control part (41, 42) which stops the inverter circuit from driving the motor in a failing power supply system, the failing power supply system corresponding to the power supply system having the fault detected by the fault detecting part; and an on / off control part (31, 32) which controls the electric power supply on / off circuit of the failing power supply system to be in a regenerative current conducting state when the fault detection part (71, 72) detects the fault, the regenerative current conducting state allowing the regenerative current to flow in one direction from the inverter circuit (50, 60) to the electric power source (15), and wherein: the electrical power supply on / off circuit (20, 25) includes a series connection of at least one first on / off switch (21, 26) and at least one second on / off switch (22, 27); the first on / off switch (21, 26) is a semiconductor switching element having a parasitic diode which allows a current to flow in only one direction from the inverter circuit (50, 60) to the electric power source (15); and the second on / off switch (22, 27) is a semiconductor switching element having a parasitic diode which allows a current to flow in only one direction from the electric power source (15) to the inverter circuit (50, 60); and the on / off control part (31, 41) is adapted to control the first on / off switch (21, 26) and the second on / off switch (22, 27) independently of each other; and the on / off control part (31, 41) turns off the first on / off switch (21, 26) and turns on the second on / off switch (22, 27) in the failing power supply system when the fault detection part (71, 72) detects the fault.

Description

TECHNICAL FIELDThe present invention relates to a motor driving apparatus for driving a motor, which can be used in, for example, an electric power steering system of a vehicle.BACKGROUNDA conventional motor driving apparatus includes a plurality of inverter circuits that supply electric power to coil sets of a motor. When any one of the inverter circuits or any one of the coil sets fails, the motor driving apparatus continues to supply power to the motor only through other inverter circuits that are normally operating.For example, according to a motor driving device for an electric power steering system disclosed in JP 2011-131 860 A (US 2011 / 0 156 629 A1), power supply relays are provided in power supply branch paths connecting a DC battery and inverter circuits of two power supply systems. When any one of the inverter circuits fails, a power supply relay connected to the inverter circuit of the power supply system which fails is turned off to cut off the power supply, and the motor is driven only by the other inverter circuit of the power supply system which is normally operating.Such a relay as used for interrupting the power supply from the battery to the inverter circuit may be a mechanical relay or a semiconductor relay. The semiconductor relay is used more frequently in view of space restrictions and cost restrictions. As the semiconductor relay, a MOSFET is used in more cases in a 12V power supply system in view of its on-resistance and saturation voltage loss. The MOSFET includes a parasitic diode. In view of a possibility that a power source having a reverse polarity is connected by a fault, two MOSFETs are connected in series such that the flow directions of the free-wheeling currents of the respective parasitic diodes are opposite to each other.A motor generally functions as a generator which generates an induced voltage when its rotating shaft is rotated by an external force. In an electric power steering system of a vehicle, for example, a motor is rotated by an external force when a tire of the vehicle hits and encounters an obstacle and the like.In this case, the energy of the induced voltage is regenerated from an inverter circuit to a battery through a power supply relay in a power supply system in which the power supply relay is in an on state. In a power supply system that fails, a power supply relay is turned off and all the switching elements in the inverter circuit are turned off. In this way, no current path is provided for regenerating the induced voltage. The induced voltage therefore becomes excessively high and may possibly destroy the circuit elements.US 2011 / 0 205 672 A1 discloses a microcomputer that recognizes and determines whether there is a problem with a power supply breaker of an ECU that functions as an engine controller. More specifically, the microcomputer determines whether or not there is a malfunction caused by a short circuit in a first FET based on the output voltage and the output voltage detected in a first FET and a second FET, respectively, when the switching states of the first and second FETs are both turned off. Then, the microcomputer determines whether or not there is a malfunction caused by a breakage in the first FET based on the output voltages of the first and second FETs detected when only the first FET is turned on. When the microcomputer determines that the first FET is faulty, it determines whether there is a fault caused by a short circuit or a break in the second FET by comparing the output voltage of the first FET with a charging voltage of a smoothing capacitor, which is then detected.JP 2011-176 998 A discloses a driving device formed by integrating a motor and a controller for controlling the motor, while keeping the profile as small as possible and at the same time preventing the drive systems from failing. Here, a heat sink has two heat dissipation blocks each having a wide pillar shape. The heat dissipation blocks have terminal parts at both ends, respectively. The connecting parts each have holes formed to pass through in the axial direction of a motor. A screw is inserted into the connecting part on one side in order to screw it to a motor housing. In addition, a screw is inserted into the connecting part on the other side to be screwed together with a cover to the motor housing. Two power modules each constituting two system inverters are individually arranged on the heat dissipation blocks.SUMMARYIt is therefore an object of the present disclosure to provide a motor driving apparatus for driving a motor.According to one aspect, there is provided a motor driving apparatus for driving a motor having a plurality of coil sets, each of which is formed of coils having a plurality of phases. The motor driving device includes a plurality of inverter circuits, an electric power supply on / off control circuit, a failure detection part, a driving control part, and an on / off control part.The plurality of inverter circuits are provided in correspondence with the plurality of coil sets, and supplies electric power to the plurality of coil sets by converting electric power supplied from an electric power source.The electric power supply on / off control circuit is provided in each power supply system between the electric power source and the inverter circuit, and electrically conducts or interrupts the electric power source from and to the inverter circuit.The fault detection part detects a fault in the inverter circuit in each power supply system.The drive control part stops the inverter circuit in a failing power supply system from driving the motor. The failing power supply system corresponds to the power supply system having the failure detected by the failure detection part.The on / off control part controls the electric power supply on / off circuit of the failing power supply system in a regenerative current conduction state when the failure detection part detects the failure. The regenerative current conduction state allows the regenerative current to flow in a direction from the inverter circuit to the electric power source.BRIEF DESCRIPTION OF THE DRAWINGSThe above and other objects, features and advantages of the motor driving apparatus will become more apparent from the following detailed description made with reference to the accompanying drawings.It shows: FIG. 1 is a circuit diagram of a motor driving device according to an embodiment; FIG. 2 is a schematic view of an electric power steering system in which the motor driving apparatus according to the embodiment is included; and FIG. 3 is a circuit diagram showing an operation of the motor driving device shown in FIG. 1.DETAILED DESCRIPTION OF THE EMBODIMENTA motor driving device is configured as shown in FIG. 1 and included in an electric power steering system for a vehicle according to an embodiment as shown in FIG. 2.As shown in FIG. 2, an electric power steering system 1 is configured to provide a steering assist torque to a steering shaft 92 for assisting a steering torque of a driver. A torque sensor 94 is attached to the steering shaft 92, which is coupled to a steering wheel 91 to detect the steering torque. A pinion gear 96 is mounted on an upper end of the steering shaft 92 and is engaged with a rack 97. A pair of wheels 98 are rotatably coupled to both ends of the rack 97 via tie rods or the like. The pinion gear 96 converts a rotational movement of the steering shaft 92 into a linear movement of the rack 96 so that the pair of wheels 98 are steered by an angle corresponding to an amount of the linear movement of the rack 97.The electric power steering system 1 is configured of a steering assist motor 800, a reduction gear 95 and a motor driving device 10. The steering assist motor 800 generates the steering assist torque. The reduction gear 95 is a motive power transmission device that transmits the rotational output of the motor 800 to the steering shaft 92 after the reduction of the motor rotation. The motor 800 is, for example, a three-phase alternating current (AC) brushless motor.As shown in FIG. 1, the motor 800 includes two coil sets 80 and 85. the first coil set 80 is formed of three phase coils 81, 82, and 83 for each of a U phase, a V phase, and a W phase. The second coil set 85 is formed of three phase coils 86, 87, and 88 for a U phase, a V phase, and a W phase, respectively. The motor drive device 10 is configured to drive the motor by converting direct current (DC) electric power supplied from a DC battery 15 which is an electric power source. The motor driving device 10 is configured of a first driving unit 11 and a second driving unit 12. The first drive unit 11 includes a first inverter circuit 50 provided in correspondence with the first coil set 80. The second drive unit 12 includes a second inverter circuit 60 provided in correspondence with the second coil set 85. The first drive unit 11 and the second drive unit 12 are connected to the battery 15 and the motor 800 in parallel. A drive unit and a coil set connected to the drive unit constitute a power supply system in combination. In this way, the motor driving device 10 forms two (first and second) power supply systems.The drive unit 11 of the first power supply system and the drive unit 12 of the second power supply system have generally the same configuration. The drive unit 11 will be described in detail below as a representative example. The drive unit 11 of the first power supply system includes an electric power supply on / off circuit 20, the inverter circuit 50, and a control circuit including an on / off control part 31, a drive control part 41, and a failure detection part 71. Each part in the control circuit may be formed of, for example, a microcomputer and pre-drivers.The power supply on / off circuit 20 is provided in a power supply line Ls between the battery 15 and the inverter circuit 50, and electrically connects or disconnects the battery 15 to and from the inverter circuit 15. The electric power supply on / off circuit 20 is formed of a first power supply relay 21 and a second power supply relay 22 connected in series.The first power supply relay 21 provided as a first on / off switch and the second power supply relay 22 provided as a second on / off switch are semiconductor switching elements including respective parasitic diodes. The parasitic diode of the first power supply relay 21 is arranged to conduct a current in a direction from the inverter circuit 50 to the battery 15. The parasitic diode of the second power supply relay 22 is arranged to conduct a current in a direction from the battery 15 to the inverter circuit 50.The on / off control part 31 may be implemented as a function of the microcomputer to control the on / off states of the first power supply relay 21 and the second power supply relay 22 independently of each other. More specifically, the on / off control part 31 is capable of turning on or off not only the first power supply relay 21 and the second power supply relay 22, but also turning off the first power supply relay 21 and turning on the second power supply relay 22. In the following description, "turn off" and "break" are used to denote the same operation with respect to the on / off operation of the semiconductor switching element. Similarly, "turn on" and "conduct" are used to refer to the same operation.In a case that the battery 15 is connected in a normal direction as shown in FIG. 1, that is, the first power supply relay 21 is connected to the positive electrode side of the battery 15, the electric power supply from the battery 15 to the inverter 50 is interrupted when the first power supply relay 21 is turned off. In a case where the battery 15 is connected in a reverse direction opposite to FIG. 1, that is, the first power supply relay 21 is connected to the ground electrode side of the battery 15, no voltage is supplied to the drive unit 11, and therefore all the switching elements in the drive unit 11 are turned off. However, a current flows through the parasitic diode of the first power supply relay 21, and therefore the battery 15 and the inverter circuit 50 are not interrupted. In this case, when the second power supply relay 22 is connected in series to the first power supply relay 21, the electric power supply from the battery 15 to the inverter circuit 50 is cut off.In the electric power supply on / off circuit 20 formed of the power supply relays 21 and 22 having the parasitic diodes connected in opposite current flowing directions, the electric power supply from the battery 15 to the inverter circuit 50 is interrupted regardless of the direction of connection of the battery 15 when both the power supply relays 21 and 22 are turned off.The inverter circuit 50 is a three-phase inverter in which six semiconductor switching elements 51 to 56 are connected in a bridge form. The switching elements 51 to 56 are, for example, MOSFETs, i.e., metal oxide semiconductor field effect transistors. The switching elements 51 to 56 are referred to as FETs 51 to 56.The FETs 51 and 54 form an upper-side arm and a lower-side arm of the U-phase. The FETs 52 and 55 form a high-side arm and a low-side arm of the V phase. The FETs 53 and 56 form a high-side arm and a low-side arm of the W phase. Each of the FETs 51 to 56 is turned on or off between a source and a drain according to the gate potential.The high-side arm FETs 51, 52, and 53 are connected to the power supply line Ls at the respective drains. The sources of the high-side arm FETs 51, 52, and 53 are connected to the drains of the low-side arm FETs 54, 55, and 56, respectively. The sources of the low-side arm FETs 54, 55, and 56 are grounded through the shunt resistors 57, 58, and 59, respectively. The junctions between the high-side arm FETs 51, 52, and 53 and the low-side arm FETs 54, 55, and 56 are connected to the terminals of the coils 81, 82, and 83 of the first coil set 80, respectively.The drive control part 41 is formed of, for example, a pre-driver. The FETs 51 and 56 are turned on or off by switching signals output to the respective gates from the drive control part 41, so that the power supply can be switched to the first coil set 80. The inverter circuit 50 thus converts DC power supplied from the battery 15 into the three-phase AC power. The fault detection part 71 detects a fault of the inverter circuit 50, more specifically, a short-circuit fault or the like in the FETs 51 to 56, and applies a fault detection signal to the on / off control part 31 and the drive control part 41.The drive unit 12 of the second power supply system includes, similarly to the first power supply system, an electric power supply on / off circuit 25, the inverter circuit 60, and a control circuit including an on / off control part 32, a drive control part 42, and a failure detection part 72. The electric power supply on / off circuit 25 is formed of a first power supply relay 26 and a second power supply relay 27. The inverter circuit 60 includes FETs 61 to 66 and shunt resistors 67 to 69.The motor drive device 10 is thus formed of two drive units 11 and 12. Even in the case that the inverter circuit 50 or 60 or the coil set 80 or 85 fails in one of the power supply systems, only one system which is normal (normal system) is driven to operate, while in the other system which is in a failure state (failed system), the operation is stopped. As a result, the motor 800 is continuously driven to operate. In this way, it is possible to avoid a situation in which the electric power steering system 1 suddenly stops generation of the steering assist power due to a failure in one of the power supply systems.The operation of the motor driving device 10 obtained after the failure of one of the two power supply systems will be described below with reference to FIG. 3. Here, it is assumed that the inverter circuit 50 of the first power supply system fails and the inverter circuit 60 of the second power supply system is normally operated. When the fault detection part 71 detects a fault of the inverter circuit 50, the fault detection signal is applied to the on / off control part 31 and the drive control part 41. The drive control part 41 responsively turns off all the switching elements 51 to 56, thereby stopping the inverter circuit 50 from driving the motor 800. The on / off control part 31 turns on or off the first power supply relay 21 and the second power supply relay 22, respectively, in the electric power supply on / off circuit 20. That is, the on / off control part 31 provides a regenerative current conduction state that allows a regenerative current to flow from the inverter circuit 50 to the battery 15.It is further assumed that the first coil set 80 and the second coil set 85 generate induced voltages in response to an applied external force in a state such that the inverter circuit 50 of the first power supply system stops operation. In the second power supply system which is normally in operation, the currents flowing through the parasitic diodes of the FETs 65 and 66 of the low-side arms of the V-phase and the W-phase in the upward directions (from the low potential side to the high potential side) flow from a neutral point of the star-connected coils 86 to 88 of the second coil set 85 through the V-phase coil 87 and the W-phase coil 88, as shown by the dotted arrows in FIG. 3. The current flowing out from the neutral point flows through the U-phase coil 86 and the parasitic diode of the FET 61 of the high-side arm of the U-phase in the upward direction to the power supply line Ls of the second power supply system.In the second power supply system which is normally in operation, the on / off control part 32 continues to turn on both the first relay 26 and the second relay 27 in the electric power supply on / off circuit 25. The current thus flows from the battery 15 through the second power supply relay 27 and the first power supply relay 26 to the power supply line Ls. As a result, the circuit elements of the drive unit 12 are prevented from being destroyed by the induced voltage.In the first power supply system that has failed, the currents flowing through the parasitic diodes of the FETs 55 and 56 of the low-side arms of the V phase and the W phase in the upward directions (from the low potential side to the high potential side) flow from a neutral point of the star-connected coils 81 to 83 of the first coil set 80 through the V phase coil 82 and the W phase coil 83, as shown by the dotted arrows in FIG. 3. The current flowing out from the neutral point flows through the U-phase coil 81 and the parasitic diode of the FET 51 of the high-side arm of the U-phase in the upward direction to the power supply line Ls of the first power supply system.If the on / off control part 31 of the failing power supply system turns off both the first power supply relay 21 and the second power supply relay 22 in the electric power supply on / off circuit 22, the power supply from the battery 15 to the inverter circuit 50 is completely interrupted. In this case, no route is provided to allow the regenerative current to flow from the power supply line Ls to the battery 15. As a result, circuit elements such as the second power supply relay 22 or the like are likely to be destroyed by the induced voltage applied to the power supply line Ls.According to the motor driving device 10 of the present embodiment, the failure system on / off control part 31 turns off or on the first power supply relay 21 and the second power supply relay 22 of the electric power supply on / off circuit 20, respectively. In this way, the current is allowed to flow from the power supply line Ls to the battery 15 through the second power supply relay 22 and the parasitic diode of the first power supply relay 21. Therefore, it is possible to protect the circuit elements of the drive unit 11 from destruction by the induced voltage in a similar manner to the normal operating system.As described above, the motor driving device 10 according to the present embodiment can direct the induced voltage generated in the motor 800 to the battery 15 in both the normal system and the failing system even when one of the two systems fails. For example, in the electric power steering system 1, when a wheel hits and sits on an obstacle during running of the vehicle with one of the two power supply systems thereof in the failure state, the induced voltages are generated in both power supply systems and regenerated into the battery 15 regardless of whether or not they are normally operating. In this way, it is possible to protect the circuit elements of the drive units 11 and 12 from destruction by the induced voltages.Illustratively, the first power supply system, the on / off control part 31 controls the first power supply relay 21 and the second power supply relay 22 of the electric power supply on / off circuit 20 independently in such a manner that the first power supply relay 21 and the second power supply relay 22 turn on or off, respectively. If it is not possible to control the relays 21 and 22 independently of each other, both the first power supply relay 21 and the second power supply relay 22 need to be turned on at the same time in the case that the second power supply relay 22 is turned on. That is, it is not possible to provide a function of cutting off the power supply from the battery 15 to the inverter circuit 50 which is in the failing system. However, according to the present embodiment, it is possible to cut off the power supply from the battery 15 to the inverter circuit 50 of the failure system, and ensure a current regeneration route by turning off the first power supply relay 21 and turning on the second power supply relay 22.The motor driving device 10 described above may be modified as follows. (A) In the embodiment, each electric power supply on / off circuit is formed of a series connection of a first power supply relay and a second power supply relay. Alternatively, two or more of at least one of a first power supply relay and a second power supply relay may be connected in series. Alternatively, the electric power supply on / off circuit may be formed of only the first power supply relay. In this case, the regenerative current generated when the first power supply relay is in the off state is allowed to flow from the inverter circuit to the power source through the parasitic diode of the first power supply relay. (B) In the embodiment, the on / off control part, the drive control part, and the failure detection part are provided for the first power supply system and the second power supply system, respectively. This is for functional explanation only and does not necessarily mean that these parts are physically separated from each other. That is, these parts in each power supply system may be implemented in a control program of a microcomputer. (C) The semiconductor switching element may be other than the MOSFET as long as this element includes a parasitic diode. (D) The number of power supply systems of the motor driving device is not limited to two, but may be three or more. The number of phases of the motor is not limited to three, but may be four or more. (E) The motor driving device is not limited to the application of the steering assist motor of the electric power steering system, but may be applied to other motors.

Claims

A motor driving apparatus (10) for driving a motor (800) having a plurality of coil sets (80, 85) each formed of coils (81, 82, 83, 86, 87, 88) having a plurality of phases, the motor driving apparatus comprising: a plurality of inverter circuits (50, 60) provided in correspondence with the plurality of coil sets and supplying electric power to the plurality of coil sets (80, 85) by converting electric power supplied from an electric power source (15); an electric power supply on / off control circuit (20, 25) provided in each power supply system between the electric power source (15) and the inverter circuit (50, 60) and electrically passing or interrupting the electric power source (15) to and from the inverter circuit (50, 60); a failure detection part (71, 72) that detects a failure in the inverter circuit (50, 60) in each power supply system; a drive control part (41, 42) that stops the inverter circuit in a failed power supply system from driving the motor, the failed power supply system corresponding to the power supply system having the failure detected by the failure detection part; and an on / off control part (31, 32) that controls the electric power supply on / off circuit of the failing power supply system to be in a regenerative current conducting state when the fault detection part (71, 72) detects the fault, wherein the regenerative current conducting state allows the regenerative current to flow in a direction from the inverter circuit (50, 60) to the electric power source (15), and wherein: the electric power supply on / off circuit (20, 25) includes a series connection of at least a first on / off switch (21, 26) and at least a second on / off switch (22, 27); the first on / off switch (21, 26) is a semiconductor switching element having a parasitic diode that allows a current to flow only in a direction from the inverter circuit (50, 60) to the electric power source (15); and the second on / off switch (22, 27) is a semiconductor switching element having a parasitic diode that allows a current to flow only in a direction from the electric power source (15) to the inverter circuit (50, 60); and the on / off control part (31, 41) is adapted to control the first on / off switch (21, 26) and the second on / off switch (22, 27) independently of each other; and the on / off control part (31, 41) turns off the first on / off switch (21, 26) and turns on the second on / off switch (22, 27) in the failing power supply system when the failure detection part (71, 72) detects the failure.An electric power steering system (1) comprising: the motor driving device (10) according to claim 1; a steering assist motor (800) that is driven by the motor driving device to generate a steering assist torque for assisting a steering force of a driver; and a power transmission device (95) that transmits rotation of the steering assist motor to a steering shaft (92).

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