Controller and control method for motor

The present invention relates to a controller for a motor equipped with plural energization systems each including a coil set of coils corresponding to plural phases and an inverter for outputting current to each phase in the coil set, and to a control method therefor.

Patent Document 1 discloses a controller equipped with inverters of plural systems that switchingly energize plural coil sets of a motor. In the controller, the total sum of phase currents is calculated at each system. If a difference in the total phase current between two systems deviates from a predetermined range, it is determined that the two systems are short-circuited. When the short-circuit is detected as above, either one of the two systems, which are compared to obtain the difference in the total phase current, is stopped.

Patent Document

Patent Document 1: JP 2013-165541 A

Problems to be Solved by the Invention

In the configuration that the total sum of phase currents is calculated at each of the coil sets, and if a difference in the resultant total phase current between energization systems deviates from a predetermined range, an inverter of either energization system is stopped, there is a possibility of erroneously stopping an inverter of the other energization system even though the system is operating normally. This is because the difference in the total phase current deviates from the predetermined range not only in case a short-circuit occurs between the energization systems but also in case one of the energization systems has any abnormality, whereas the other system operates normally.

The present invention has been accomplished in view of some of the above problems and accordingly it is an object of the present invention to provide a controller and a control method for a Motor, which can stop an inverter in a failed energization system while continuing to operate an inverter in a normal energization system as required as possible.

Means For Solving The Problems

In order to achieve the object, the present invention provides a controller for a motor equipped with a plurality of energization systems each including a coil set of coils corresponding to a plurality of phases and an inverter for outputting a current to each of the phases in the coil set, the controller comprising: a first control unit that detects an abnormality in each of the energization systems and stops the inverter of the energization system having an abnormality detected; and a second control unit that determines whether a predetermined period has elapsed after the first control unit stops the inverter of one of the energization systems, and continues to operate the inverter of the other energization system having an abnormality detected within the predetermined period.

Furthermore, the present invention provides a control method for a motor equipped with a plurality of energization systems each including a coil set of coils corresponding to a plurality of phases and an inverter for outputting a current to each of the phases in the coil set, the method comprising the steps of: determining whether an abnormality occurs in each of the energization systems; stopping the inverter of the energization system having an abnormality detected; and continuing to operate the inverter of the other energization system having an abnormality detected within a predetermined period from when the inverter is stopped.

Effects of the Invention

According to the present invention, it is possible to stop an inverter of a failed energization system as appropriate while continuing motor control as required as possible.

FIG. 1 is a schematic diagram of an electric power steering device that adopts a controller for a motor according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of the controller according to the embodiment of the present invention.

FIG. 3 is a functional diagram of the controller according to the embodiment of the present invention.

FIG. 4 is a flowchart illustrating the abnormality diagnosis procedure according to the embodiment of the present invention.

FIG. 5 is a circuit diagram illustrating a first energization system and a second energization system, which are short-circuited, according to the embodiment of the present invention.

FIG. 6 is a timing chart illustrating current detection values obtained when the first energization system and the second energization system are short-circuited according to the embodiment of the present invention.

FIG. 7 is a circuit diagram illustrating the grounded first energization system according to the embodiment of the present invention.

FIG. 8 is a timing chart illustrating current detection values obtained when the first energization system is grounded according to the embodiment of the present invention.

FIG. 9 is a circuit diagram illustrating the first energization system and the second energization system, both of which are grounded, according to the embodiment of the present invention.

FIG. 10 is a timing chart illustrating current detection values obtained when the first energization system and the second energization system are both grounded according to the embodiment of the present invention.

FIG. 11 is a circuit diagram of the motor that adopts delta-connected coil configuration according to the embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described. FIG. 1 illustrates an example of a vehicle electric power steering device to which a controller and a control method for a motor according to the present invention are applied. An electric power steering device 100 of FIG. 1 , which is installed in a vehicle 200 , generates a steering assist force with an electric motor 130 .

Electric power steering device 100 is composed of a steering wheel 110 , a steering torque sensor 120 , electric motor 130 , an electronic control unit (ECU) 150 , a reducer 160 that reduces a rotational speed of electric motor 130 and then transmits the reduced rotational speed to a steering shaft (pinion shaft) 170 , and the like. Steering torque sensor 120 and reducer 160 are disposed in a steering column 180 that accommodates steering shaft 170 .

A pinion gear 171 is provided at the tip end of steering shaft 170 . Along with the rotation of pinion gear 171 , a rack gear 172 is horizontally moved to the left or right as viewed in the travel direction of vehicle 200 . A steering mechanism 202 for a wheel 201 is provided at the opposite ends of rack gear 172 . Along with the horizontal movement of rack gear 172 , wheel 201 can change its direction.

Steering torque sensor 120 detects a steering torque of steering shaft 170 generated as a driver steers the vehicle, and then outputs a signal ST indicating the detected steering torque to electronic control unit 150 . Electronic control unit 150 includes a microcomputer 302 , inverters 1 A and 1 B for driving electric motor 130 , drive circuits 303 A and 303 B for inverters 1 A and 1 B, etc. and receives information about a state variable for determining a steering assist force such as steering torque signal ST and a vehicle speed signal VSP output from a vehicle speed sensor 190 .

When receiving steering torque signal ST, vehicle speed signal VSP, or the like, electronic control unit 150 executes PWM (pulse width modulation) control on energization to electric motor 130 based on the driving condition of a vehicle as indicated by these signals, thereby controlling the torque generated in electric motor 130 , i.e., steering assist force. In this way, electronic control unit 150 serves as a drive controller for electric motor 130 .

Regarding the inverter and the inverter drive circuit incorporated in electronic control unit 150 , the inverter can be provided alone or together with the inverter drive circuit independently outside electronic control unit 150 . In this case, electronic control unit 150 constitutes, together with the external inverter or both the external inverter and inverter drive circuit, the drive controller for electric motor 130 .

FIG. 2 illustrates an example of the circuit configuration of electronic control unit 150 and electric motor 130 . Electric motor 130 of FIG. 2 is a three-phase synchronous electric motor composed of a first coil set 2 A of star-connected three-phase coils UA, VA, and WA and a second coil set 2 B of star-connected three-phase coils UB, VB, and WB. In first coil set 2 A and second coil set 2 B, a connection point among three-phase coils U, V, and W is a neutral point.

First coil set 2 A and second coil set 2 B are disposed in an unillustrated cylindrical stator and a permanent magnet rotator 201 is rotatably provided inside a space formed at the central portion of the stator. First coil set 2 A and second coil set 2 B share a magnetic circuit. Moreover, first coil set 2 A is directly connected to a first inverter 1 A, and second coil set 2 B is directly connected to a second inverter 1 B. First inverter 1 A supplies power to first coil set 2 A, and second inverter 1 B supplies power to second coil set 2 B.

First inverter 1 A is configured by a three-phase bridge circuit including three pairs of semiconductor switches, i.e., semiconductor switches UHA and ULA for driving a U-phase coil UA of first coil set 2 A, semiconductor switches VHA and VLA for driving a V-phase coil VA thereof, and semiconductor switches WHA and WLA for driving a W-phase coil WA thereof. Moreover, second inverter 1 B is configured by a three-phase bridge circuit including three pairs of semiconductor switches, i.e., semiconductor switches UHB and ULB for driving a U-phase coil UB of second coil set 2 B, semiconductor switches VHB and VLB for driving a V-phase coil VB thereof, and semiconductor switches WHB and WLB for driving a W-phase coil WB thereof.

In this embodiment, the semiconductor switches constituting first inverter 1 A and second inverter 1 B are N-channel MOSFETs (metal oxide semiconductor field effect transistors). In first inverter 1 A and second inverter 1 B, semiconductor switches UH and UL have series-connected drain and source between a power supply VB and the ground point, and a connection point between semiconductor switches UH and UL is connected to U-phase coil U.

Furthermore, in first inverter 1 A and second inverter 1 B, semiconductor switches VH and VL have series-connected drain and source between power supply VB and the ground point, and a connection point between semiconductor switches VH and VL is connected to V-phase coil V.

Moreover, in first inverter 1 A and second inverter 1 B, semiconductor switches WH and WL have series-connected drain and source between power supply VB and the ground point, and a connection point between semiconductor switches WH and WL is connected to W-phase coil W.

First drive circuit 303 A functions to drive the semiconductor switches constituting first inverter 1 A, and includes three high-potential side drivers for respectively driving semiconductor switches VHA, UHA, and WHA as high-potential side switching elements in first inverter 1 A and three low-potential side drivers for respectively driving semiconductor switches VLA, ULA, and WLA as low-potential side switching elements in first inverter 1 A.

Second drive circuit 303 B functions to drive the semiconductor switches constituting second inverter 1 B, and includes three high-potential side drivers for respectively driving semiconductor switches VHB, UHB, and WHB as high-potential side switching elements in second inverter 1 B, and three low-potential side drivers for respectively driving semiconductor switches VLB, ULB, and WLB as low-potential side switching elements in second inverter 1 B. Note that the high-potential side switching element can be referred to as “upstream drive element” or “upper arm”. The low-potential side switching element can be referred to as “downstream drive element” or “lower arm”. In addition, a connection point between any high-potential side switching element and any low-potential side switching element serves as an output point of the inverter.

First drive circuit 303 A and second drive circuit 303 B drive the semiconductor switches constituting inverters 1 A and 1 B, respectively according to a command signal from microcomputer 302 . As described above, the motor controller of this embodiment incorporates two energization systems: a first energization system including first coil set 2 A and first inverter 1 A and a second energization system including second coil set 2 B and second inverter 1 B. Note that the first energization system and the second energization system can be referred to as a “first channel ch 1 ” and a “second channel ch 2 ”, respectively.

A power supply relay 304 A is provided between power supply VB and first inverter 1 A in order to interrupt the power supply to first inverter 1 A, and a power supply relay 304 B is provided between power supply VB and second inverter 1 B in order to interrupt the power supply to second inverter 1 B. In this embodiment, power supply relays 304 A and 304 B are configured by semiconductor switches. The semiconductor switches constituting power supply relays 304 A and 304 B are driven by drive circuits 305 A and 305 B. As power supply relays 304 A and 304 B, electromagnetic relays, each of which provides electrical switching by physically moving its contact point, may be alternatively used.

Drive circuits 305 A and 305 B for power supply relays 304 A and 304 B drive the semiconductor switches constituting power supply relays 304 A and 304 B according to a command signal from microcomputer 302 . To be specific, microcomputer 302 can interrupt power supply to first inverter 1 A and that to second inverter 1 B independently of each other. Furthermore, in order to reduce fluctuations in power supply voltage to inverters 1 A and 1 B, capacitors 306 A and 306 B are provided. More specifically, capacitor 306 A connects, to the ground point, the power supply line between power supply relay 304 A and inverter 1 A, whereas capacitor 306 B connects, to the ground point, the power supply line between power supply relay 304 B and inverter 1 B.

Also, there are provided voltage monitor circuits 307 A and 307 B for detecting coil-end voltages at coil sets 2 A and 2 B, respectively. Voltage monitor circuits 307 A and 307 B output, to microcomputer 302 , signals indicating detected coil-end voltages at coil sets 2 A and 2 B. In addition, to keep the coil-end potential in coil set 2 A fixed even when all the switching elements in inverter 1 A are turned OFF, a pull-up resistor RA for pulling up U-phase coil UA in coil set 2 A is provided. To keep the coil-end potentials in coil set 2 B fixed even when all the switching elements in inverter 1 B are turned OFF, a pull-up resistor RB for pulling up U-phase coil UB in coil set 2 B is provided. An angle sensor 308 detects the angle of rotor 201 , and outputs a signal indicating the detected angle to microcomputer 302 .

Moreover, current sensors 301 UA, 301 VA, 301 WA, 301 UB, 301 VB, and 301 WB are provided to detect current flowing in a corresponding one of three-phase coils U, V, and W, and disposed on the drive line connecting a corresponding pair of three-phase coils U, V, and W and connection points between low-potential side semiconductor switches UL, VL, and WL and high-potential side semiconductor switches UH, VH, and WH, more specifically, disposed between a corresponding pair of three-phase coils U, V, and W and output points of inverters 1 A and 1 B. Note that current sensors 301 UA, 301 VA, 301 WA, 301 UB, 301 VB, and 301 WB can be also referred to as “current detecting resistors”, “current detecting devices”, or “current detecting means”.

FIG. 3 is a functional block diagram illustrating an example of the function of controlling inverters 1 A and 1 B, which is implemented by microcomputer 302 . A target assist torque calculating unit 6 calculates a target assist torque, i.e., a target value of an output torque of electric motor 130 based on steering conditions such as a steering torque and a vehicle speed. In this example, target assist torque calculating unit 6 individually sets a target assist torque for the first energization system and that for the second energization system, aiming at generating a steering assist force corresponding to the total sum of a motor torque generated through energization control over the first energization system and that generated through energization control over the second energization system.

An angle calculating unit 10 receives a signal from angle sensor 308 and then calculates the angle of rotor 201 of electric motor 130 . A motor rotational speed calculating unit 5 calculates the rotational speed (rpm) of electric motor 130 based on information about the calculated angle of rotor 201 from angle calculating unit 10 and then outputs a signal indicating the calculated motor rotational speed to an output voltage calculating unit 4 .

Output voltage calculating unit 4 receives data about a target assist torque in each energization system, data about the rotational speed of electric motor 130 , and a d-axis actual current value I d and a q-axis actual current value I q at each energization system, both of which are calculated by a three-to-two phase converting unit 11 . Output voltage calculating unit 4 calculates a d-axis voltage command value V d 1 and a q-axis voltage command value V q 1 of first inverter 1 A and a d-axis voltage command value V d 2 and a q-axis voltage command value V q 2 of a second inverter 1 B, and then outputs the calculated values.

Three-to-two phase converting unit 11 calculates a d-axis actual current value I d 1 and a q-axis actual current value I q 1 of the first energization system based on output signals from current sensors 301 UA, 301 VA, and 301 WA, i.e., detection values of actual currents flowing through the respective phases in first coil set 2 A. In addition, three-to-two phase converting unit 11 calculates a d-axis actual current value I d 2 and a q-axis actual current value I q 2 of the second energization system based on output signals from current sensors 301 UB, 301 VB, and 301 WB, i.e., detection values of actual currents flowing through the respective phases in second coil set 2 B. Three-to-two phase converting unit 11 outputs data about d-axis actual current value I d 1 and q-axis actual current value I q 1 of the first energization system and data about d-axis actual current value I d 2 and q-axis actual current value I q 2 of the second energization system to output voltage calculating unit 4 and target assist torque calculating unit 6 , respectively.

Then, d-axis voltage command value V d 1 and q-axis voltage command value V q 1 output from output voltage calculating unit 4 are input to a first output duty calculating unit 7 A. First output duty calculating unit 7 A calculates a d-axis duty Dutyd 1 and a q-axis duty Dutyq 1 of PWM control on first inverter 1 A, based on d-axis voltage command value V d 1 , q-axis voltage command value V q 1 , and the power supply voltage of first inverter 1 A.

Furthermore, d-axis voltage command value V d 2 and q-axis voltage command value V q 2 output form output voltage calculating unit 4 are input to a second output duty calculating unit 7 B. Second output duty calculating unit 7 B calculates a d-axis duty Dutyd 2 and a q-axis duty Dutyq 2 of PWM control on second inverter 1 B based on d-axis voltage command value V d 2 , q-axis voltage command value V q 2 , and the power supply voltage of second inverter 1 B.

A first two-to-three phase converting unit 8 A receives d-axis duty Dutyd 1 and q-axis duty Dutyq 1 output from first output duty calculating unit 7 A and also information about the rotor angle in electric motor 130 . First two-to-three phase converting unit 8 A calculates, based on these, duty command values DutyU 1 , DutyV 1 , and DutyW 1 of three phases in first coil set 2 A, and then outputs the calculated values. In addition, a second two-to-three phase converting unit 8 B receives d-axis duty Dutyd 2 and q-axis duty Dutyq 2 output from second output duty calculating unit 7 B and also information about the rotor angle in electric motor 130 . Second two-to-three phase converting unit 8 B calculates, based on these, duty command values DutyU 2 , DutyV 2 , and DutyW 2 of three phases in second coil set 2 B, and then outputs the calculated values.

A first dead time compensation unit 9 A receives duty command values DutyU 1 , DutyV 1 , and DutyW 1 output from first two-to-three phase converting unit 8 A. First dead time compensation unit 9 A compensates for the dead time thereof to obtain, by calculation, duty command values DutyU 1 , DutyV 1 , and DutyW 1 and then outputs the calculated values to inverter 1 A.

In addition, a second dead time compensation unit 9 B receives duty command values DutyU 2 , DutyV 2 , and DutyW 2 output from second two-to-three phase converting unit 8 B. Second dead time compensation unit 9 B compensates for the dead time thereof to obtain, by calculation, duty command values DutyU 2 , DutyV 2 , and DutyW 2 , and outputs the calculated values to inverter 1 B.

The dead time compensation means the processing for holding down a voltage drop etc. that will occur with a dead time voltage at the time of PWM control for retarding, by the dead time, the rising edge of a PWM signal as obtained by comparing a triangular wave with a command value to thereby generate a gate signal of the switching element so as not to cause a short-circuit between upper and lower arms of inverters 1 A and 1 B.

An inverter output ON/OFF determination unit 12 receives output signals from current sensors 301 UA, 301 VA, and 301 WA of the first energization system and output signals from current sensors 301 UB, 301 VB, and 301 WB of the second energization system, and controls outputting an OFF command signal for the first energization system and an OFF command signal for the second energization system according to current detection values. The OFF command signal for the first energization system output from inverter output ON/OFF determination unit 12 is input to a first energization system ON/OFF control unit 13 A. After receiving the OFF command signal, first energization system ON/OFF control unit 13 A turns OFF all the switching elements in first inverter 1 A, hereby stopping first inverter 1 A. Note that stopping the inverter is to suspend current output from the inverter to the coil.

Likewise, the OFF command signal for the second energization system output from inverter output ON/OFF determination unit 12 is input to a second energization system ON/OFF control unit 13 B. After receiving the OFF command signal, second energization system ON/OFF control unit 13 B turns OFF all switching elements in second inverter 1 B, hereby stopping second inverter 1 B.

Furthermore, the OFF command signal for the first energization system and that for the second energization system, which are output from inverter output ON/OFF determination unit 12 are input to target assist torque calculating unit 6 . Then, target assist torque calculating unit 6 calculates a target assist torque for each energization system according to whether inverter output ON/OFF determination unit 12 outputs a command to stop first inverter 1 A or second inverter 1 B.

Referring to the flowchart of FIG. 4 , how inverter output ON/OFF determination unit 12 controls stopping inverter 1 A or 1 B is described next. The routine in the flowchart of FIG. 4 is executed by microcomputer 302 interruptedly at a predetermined time interval. The predetermined time interval at which microcomputer 302 executes the routine may be, for example, about 1 ms.

First, in step S 501 , microcomputer 302 determines whether an abnormality detection counter CA reaches a predetermined value C 1 or more. Note that zero is, for example, initially set to this abnormality detection counter CA for the first energization system and to an abnormality detection counter CB for the second energization system as described below. Moreover, in microcomputer 302 , predetermined value C 1 is set to, for example, 5.

When detecting that abnormality detection counter CA for the first energization system has a value less than predetermined value C 1 , microcomputer 302 proceeds to step S 502 , hereby determining whether an abnormality confirmation flag FA for the first energization system is ON or whether an absolute value of the total sum of phase currents flowing in the coils of first coil set 2 A in the first energization system remains higher than a predetermined current SLC for a predetermined time T 1 or more.

The condition that an absolute value of the total phase current exceeds predetermined current SLC implies that the total phase current deviates from a predetermined range including zero. Note that in microcomputer 302 , predetermined current SLC and predetermined time T 1 are set as a reference for determining whether the energization system is normal or abnormal. Predetermined current SLC satisfies the condition of SLC>0 A and is set to, for example, 10 A. Predetermined time T 1 is set to, for example, 5 ms.

When the energization system is operating normally, the total phase current approximates zero. Provided that an absolute value of the total phase current is around zero, microcomputer 302 determines that the phase currents in the energization system concerned are normal. On the other hand, if the total phase current deviates from zero by a predetermined value or more for predetermined time T 1 or more, microcomputer 302 determines that the phase currents in the energization system concerned are abnormal. Note that the condition that an absolute value of the total phase current approximates zero implies that the absolute value of the total phase current is within a predetermined range including zero. The predetermined range can be considered almost zero, taking into account any detection error.

In this example, if abnormality confirmation flag FA for the first energization system is OFF, indicating that an abnormality in the first energization system is not confirmed and also, if an absolute value of the total phase current in first coil set 2 A does not remain higher than predetermined current SLC over predetermined time T 1 or more, that is, if phase currents in the first energization system are normal, microcomputer 302 proceeds to step S 503 . In step S 503 , microcomputer 302 determines whether abnormality detection counter CB for the second energization system reaches predetermined value C 1 or more. Note that in microcomputer 302 , predetermined value C 1 is set to, for example, 5.

Abnormality detection counter CB for the second energization system has a value less than predetermined value C 1 , microcomputer 302 proceeds to step S 504 , hereby determining whether abnormality confirmation flag FB for the second energization system is ON or whether an absolute value of the total sum of detection values of phase currents flowing in the coils of second coil set 2 B at the second energization system remains higher than predetermined current SLC over predetermined time T 1 or more.

In this example, if abnormality confirmation flag FB for the second energization system is OFF, indicating that an abnormality in the second energization system is not confirmed and also if an absolute value of the total phase current in second coil set 2 B does not remain higher than predetermined current SLC over predetermined time T 1 or more, that is, if phase currents in the second energization system are normal and also those in the first energization system are normal, microcomputer 302 ends this routine at this point and continues to operate the inverters of the first energization system and the second energization system as in the normal time.

On the other hand, if an absolute value of the total phase current in first coil set 2 A exceeds predetermined current SLC and such abnormality in the total phase current is observed over predetermined time T 1 or more, microcomputer 302 proceeds to step S 505 from step S 502 .

In step S 505 , microcomputer 302 determines whether abnormality confirmation flag FB for the second energization system is OFF or whether abnormality detection counter CB for the second energization system reaches predetermined value C 1 or more.

Then, if abnormality confirmation flag FB for the second energization system is OFF and if abnormality detection counter CB for the second energization system reaches predetermined value C 1 or more, microcomputer 302 proceeds to step S 506 to set ON abnormality confirmation flag FA for the first energization system, indicating that an abnormality in the first energization system is confirmed. In this example, if microcomputer 302 detects an abnormality in the total phase current at the first energization system ahead, the condition that abnormality confirmation flag FB for the second energization system is OFF is established in step S 505 and then, the microcomputer proceeds to step S 506 .

Note that abnormality confirmation flags FA and FB are initially set OFF. After switched to ON, the flags are kept ON unless being reset at workshop, etc. In step S 506 , abnormality confirmation flag FA for the first energization system is switched to ON, microcomputer 302 proceeds to step S 507 to output an OFF command to inverter 1 A in the first energization system. As a result, all the switching elements constituting first inverter 1 A in the first energization system are turned OFF to stop first inverter 1 A.

At this time, microcomputer 302 keeps power supply relay 304 A ON. If charges in capacitor 306 A are emitted or power supply voltage VB increases after power supply relay 304 A is turned OFF, even when first inverter 1 A is turned OFF, current might flow to first inverter 1 A from second inverter 1 B being under the switching operation, due to a parasitic diode of a MOSFET of first inverter 1 A, with the result that the total phase current in the second energization system might deviate from zero. In view of the above, microcomputer 302 keeps power supply relay 304 A ON. Microcomputer 302 can, however, turn OFF power supply relay 304 A if there are no fears that capacitor 306 A discharges and power supply voltage VB increases after turning OFF power supply relay 304 A.

After issuing an OFF command for the first energization system in step S 507 , microcomputer 302 proceeds to step S 508 to increment abnormality detection counter CA for the first energization system by predetermined value AC from a previous value. Note that in microcomputer 302 , predetermined value AC is set to, for example, 1.

As described above, microcomputer 302 increments abnormality detection counter CA for the first energization system and then proceeds to step S 501 at the next timing of interruptedly executing the routine. In step S 501 , if determining that abnormality detection counter CA for the first energization system is less than predetermined value C 1 , the microcomputer proceeds to step S 502 to determine that abnormality confirmation flag FA for the first energization system is ON, hereby proceeding to step S 505 .

Then, in step S 505 , if determining that abnormality confirmation flag FB for the second energization system is OFF, the microcomputer proceeds to steps S 506 to S 508 to reincrement abnormality detection counter CA for the first energization system. To be specific, during the delay time after abnormality confirmation flag FA for the first energization system is switched to ON to thereby stop inverter 1 A until abnormality detection counter CA for the first energization system is incremented up to predetermined value C 1 , microcomputer 302 does not proceed to step S 503 and subsequent steps, and neither confirmed is an abnormality in the second energization system as described later.

Abnormality detection counter CA is incremented each time the microcomputer interruptedly executes this routine. This routine is executed interruptedly at regular time intervals. Thus, a requisite period until abnormality detection counter CA for the first energization system is incremented up to predetermined value C 1 is defined according to predetermined value C 1 and the time interval at which the routine is interruptedly executed.

If abnormality detection counter CA for the first energization system is incremented up to predetermined value C 1 after abnormality confirmation flag FA for the first energization system is switched to ON, microcomputer 302 determines, in step S 501 , that abnormality detection counter CA for the first energization system reaches predetermined value C 1 or more and thus proceeds to step S 503 , skipping step S 502 .

That is, during a period until abnormality detection counter CA for the first energization system is incremented up to predetermined value C 1 , even if an absolute value of the total phase current in the second energization system remains higher than predetermined current SLC over predetermined time T 1 or more, such abnormality in the second energization system is not confirmed in response to the detection thereof and inverter 1 B in the second energization system is kept operating, not stopped.

In other words, during a period from when an abnormality is confirmed in the first energization system until abnormality detection counter CA is incremented up to predetermined value C 1 , the detection of an abnormality in any phase current at the second energization system is considered invalid. Similar to the case no abnormality is found, inverter 1 B in the second energization system continues to drive the motor under the control.

If microcomputer 302 proceeds to step S 503 after a predetermined time from when confirming an abnormality in the first energization system, abnormality detection counter CB for the second energization system is not incremented. Thus, microcomputer 302 determines that abnormality detection counter CB for the second energization system is less than predetermined value C 1 and then proceeds to step S 504 .

In this example, if any phase current in the second energization system is abnormal, and an absolute value of the total phase current in second coil set 2 B remains higher than predetermined current SLC over predetermined time T 1 or more, microcomputer 302 proceeds from step S 504 to step S 509 .

In step S 509 , microcomputer 302 sets ON abnormality confirmation flag FB for the second energization system and in subsequent step S 510 , issues an OFF command for the second energization system, hereby turning OFF all the switching elements constituting second inverter 1 B for the second energization system to stop second inverter 1 B. In addition, microcomputer 302 proceeds to step S 511 to increment abnormality detection counter CB for the second energization system by predetermined value ΔC 1 from the previous value.

Meanwhile, if no abnormality is found in phase currents at the second energization system when abnormality detection counter CA reaches predetermined value C 1 after the confirmation of an abnormality in the first energization system, microcomputer 302 skips steps S 509 to S 511 and ends this routine. In this case, inverter 1 A of the first energization system is stopped due to an abnormal phase current in first coil set 2 A. Meanwhile since phase currents in second coil set 2 B are normal, second inverter 1 B of the second energization system continues to drive the motor.

As described above, even when any phase current in the second energization system is abnormal, during a predetermined period from when an abnormality in the first energization system is confirmed until abnormality detection counter CA reaches predetermined value C 1 , microcomputer 302 does not proceed to step S 509 and subsequent steps. As a result, second inverter 1 B of the second energization system keeps operating. Even at the time when abnormality detection counter CA reaches predetermined value C 1 , if any phase current in the second energization system is still abnormal, second inverter 1 B of the second energization system is stopped.

The processing flow is described above, focusing on the case an abnormality is found in any phase current in the first energization system as an example. In case an abnormality is found in any phase current at the second energization system as well, microcomputer 302 executes similar processing.

More specifically, if an abnormality is found in any phase current at the second energization system while no abnormality is found in phase currents at the first energization system, with the result that the total phase current in second coil set 2 B deviates from zero by a predetermined value or more over a predetermined time or more, microcomputer 302 proceeds from step S 504 to steps S 509 to S 511 , hereby setting ON abnormality confirmation flag FB for the second energization system to start incrementing abnormality detection counter CB.

Even if microcomputer 302 detects an abnormality in any phase current at the first energization system after setting ON abnormality confirmation flag FB for the second energization system, the microcomputer continues to operate inverter 1 A of the first energization system without confirming the abnormality in the first energization system, until detecting in step S 505 that abnormality detection counter CB reaches predetermined value C 1 or more, in other words, after the lapse of a predetermined time from when inverter 1 B in the second energization system is stopped.

When the predetermined period has elapsed from when inverter 1 B in the second energization system is stopped, if an abnormality is found in phase currents at the first energization system, microcomputer 302 proceeds from step S 505 to step S 506 to confirm the abnormality in the first energization system following the confirmation of the abnormality in the second energization system.

Here, if an abnormality is found in any phase current at both of the first energization system and the second energization system substantially at the same time, according to the processing illustrated in the flowchart of FIG. 4 , microcomputer 302 determines that any phase current in the first energization system is abnormal ahead of the determination as to the abnormality in any phase current at the second energization system. Thus, the abnormality in the first energization system is first confirmed. After a predetermined period has elapsed from then, the abnormality is confirmed in the second energization system.

That is, according to the processing illustrated in the flowchart of FIG. 4 , the abnormality determination for the first energization system is prioritized. However, the abnormality determination for the second energization system can be prioritized instead. Note that if each energization system has no abnormality, target assist torque calculating unit 6 assigns, for example, a half of the requisite total target assist torque evenly to each of the first energization system and the second energization system. The requisite total target assist torque is defined depending on steering conditions such as a steering torque and a vehicle speed.

Meanwhile, if an abnormality is confirmed in either one of inverters 1 A and 1 B, by which the failed one is stopped and the other keeps operating, target assist torque calculating unit 6 sets to zero the target assist torque for the energization system having the abnormality confirmed, while assigning the total target assist torque to the other energization system so as to get the inverter of the other system to generate the requisite total target assist torque that is defined depending on steering conditions such as a steering torque and a vehicle speed.

Besides, the target assist torque for the other normal energization system can be arbitrarily set lower than the total target assist torque but higher than half of the total target assist torque.

Next, a detailed description is given of advantageous functions and effects from the processing executed by microcomputer 302 as illustrated in the flowchart of FIG. 4 , taking a fault mode as an example. FIG. 5 illustrates a short-circuit between the energization systems as an example of the fault mode. More specifically, in the illustrated example, a short-circuit occurs between a W-phase drive line of first coil set 2 A and a U-phase drive line of second coil set 2 B.

When a short-circuit occurs between the energization systems as above, for example, if the inverters of both the energization systems are controlled to enable current flow from the U-phase to the V-phase, a current flowing into the U-phase leaks to a short-circuited path through the W-phase in the first energization system. The current flowing into the short-circuited path is not detected by current sensors 301 UA, 301 VA, and 301 WA.

Provided that the direction in which the current flows into the motor, that is, the direction leading to the neutral point is called a “positive” direction, whereas the direction in which the current flows out of the motor, that is, the direction away from the neutral point is called a “negative” direction, the total sum of currents detected by current sensors 301 UA, 301 VA, and 301 WA deviates to the positive side from zero, or a normal value (no abnormality) as illustrated in FIG. 6 because the current leaking to the short-circuited path, i.e., the current flowing in the negative direction is not detected.

On the other hand, in the second energization system, the leak current from the first energization system flows into the U-phase. Such current flowing in the positive direction is not detected by current sensors 301 UA, 301 VA, and 301 WA. Regarding the current flowing in the negative direction, the leak current from the first energization system is included in the detection result. Thus, as illustrated in FIG. 6 , the total sum of phase currents in the second energization system deviates to the negative side from zero, or a normal value (no abnormality).

In such fault mode, if microcomputer 302 executes the processing illustrated in the flowchart of FIG. 4 , the microcomputer first detects an abnormality in the total phase current at the first energization system, hereby turning OFF all the switching elements constituting first inverter 1 A of the first energization system.

In case a short-circuit occurs between the first and second energization systems, if the total phase current in the first energization system is abnormal, the total phase current in the second energization system is abnormal as well. As mentioned above, however, during a predetermined period from when an abnormality in the first energization system is confirmed to thereby stop first inverter 1 A, second inverter 1 B is not stopped in response to the detection of an abnormality in the second energization system.

Then, when confirmed that the total phase current in the first energization system is abnormal, hereby turning OFF all the switching elements constituting first inverter 1 A of the first energization system, no current flows from the first energization system to the second energization system through the short-circuited path. As a result, the total phase current in the second energization system is restored to substantially zero, or a normal value.

Here, after a predetermined period has elapsed from when an abnormality in the first energization system is confirmed, followed by stopping first inverter 1 A, second inverter 1 B is stopped in response to the detection of an abnormality in the second energization system. Thus, in case of a short-circuit between the systems, it is determined at the end of the procedure whether the total phase current in the second energization system, which is no longer affected by the short-circuit, is normal.

Accordingly, even if the total phase current looks like abnormal in both the energization systems due to any short-circuit, it is possible to avoid stopping the inverters of both the energization systems and allow the inverter of one of the energization systems to continue to drive the motor.

By this control, electric power steering device 100 can continuously generate a steering assist force even in case of a short-circuit between the energization systems.

Regarding a period from when an abnormality is confirmed in the first energization system till an abnormality diagnosis on the second energization, the period is adjusted so that the switching elements in inverter 1 A of the first energization system can be stabilized in OFF state, and the total phase current in the second energization system can be restored to substantially zero, or a normal value in case of a short-circuit between the systems.

To be specific, in case of a short-circuit between the two energization systems, even if the switching elements in first inverter 1 A of the first energization system are turned OFF, the microcomputer makes an abnormality diagnosis on the second energization system before the total phase current in the second energization system can be restored to the normal value, unless enough time is ensured as a delay time till the abnormality diagnosis. This leads to the possibility of diagnosing both the energization systems as being abnormal and stopping the inverters thereof even though one of the energization systems can continue to drive the motor.

To avoid such situation, predetermined value C 1 is set to ensure enough time after stopping the inverter of one of the energization systems in case of a short-circuit between the systems, so that the total phase current in the other energization system can be restored to the normal value.

FIG. 7 illustrates a fault mode that one of the first and second energization systems has an abnormality, and the other is normally operating. More specifically, in the illustrated example, a W-phase drive line of the first energization system is short-circuited to the ground point, and the second energization system has no fault such as a short-circuit.

According to such fault mode, as illustrated in FIG. 7 , a current passing through the W-phase of the first energization system leaks to the ground point before flowing into current sensor 301 WA, as illustrated in FIG. 8 , the total phase current deviates to the positive side from zero, whereas the total phase current in the second energization system is kept at around zero, or a normal value.

In the above fault mode, if the total phase current in the first energization system deviates to the positive side from zero, an abnormality in the first energization system is confirmed. However, even if the total phase current in the first energization system is abnormal, such abnormality does not affect the phase currents in the second energization system. Accordingly, after a predetermined period has elapsed from when the abnormality in the first energization system is confirmed, the phase currents in the second energization system become normal, whereby inverter 1 B in the second energization system keeps operating.

To be specific, according to the processing illustrated in the flowchart of FIG. 4 , if one of the two energization systems has an abnormality, whereas the other energization system is normally operating, the inverter of the failed energization system is stopped but the inverter of the normal energization system can keep operating and continue to drive the motor, hereby generating a steering assist force continuously.

FIG. 9 illustrates a fault mode that the first energization system and the second energization system both have an abnormality. To be specific, in the illustrated example, the W-phase drive line of the first energization system is short-circuited to the ground point and likewise, the W-phase drive line of the second energization system is short-circuited to the ground point.

In such fault mode, as illustrated in FIG. 9 , current passing through the W-phase of the first energization system leaks to the ground point before flowing into current sensor 301 WA. Thus, as illustrated in FIG. 10 , the total phase current in the first energization system deviates to the positive side from zero. Likewise, current passing through the W-phase of the second energization system leaks to the ground point before flowing into current sensor 301 WB. Thus, as illustrated in FIG. 10 , the total phase current in the second energization system deviates to the positive side from zero.

In the above fault mode, if the total phase current in the first energization system deviates to the positive side from zero, an abnormality in the first energization system is first confirmed. In response to the confirmation of the abnormality in the first energization system, the inverter of the first energization system is stopped. As a result, the total phase current in the second energization system is not restored to a normal value. Then, after a predetermined period has elapsed from when the abnormality in the first energization system is confirmed, an abnormality in the second energization system is also confirmed, hereby stopping the inverters of the two energization systems. This makes it possible to stop the inverters of both the failed energization systems and prevent the failed systems from continuing to drive the motor.

If the two energization systems have different faults, as in the short-circuit between the two energization systems, the total phase current deviates from a normal value in both the energization systems. However, an abnormality in one energization system is first confirmed to stop the inverter thereof, after which an abnormality in the other energization system is confirmed based on the total phase current thereof. Thus, if the total phase current in the other energization system is still abnormal even after stopping the inverter of the one energization system, the two energization systems are concluded to have different faults. The different faults of the energization systems can be distinguished from a short-circuit between the energization systems.

In other words, even if the total phase current is abnormal in both the energization systems, in case of a short-circuit between the energization systems, the inverter of either one of the energization systems can keep operating and continue to drive the motor. Meanwhile, in case of different faults at the energization systems, the inverters of the two energization systems are stopped, hereby avoiding erroneous control on the motor.

FIGS. 6, 8, and 10 each illustrate an additional value of the total sum of current detection values in the three phases of the first energization system and the total sum of current detection values in three phases of the second energization system.

As illustrated in FIG. 6 , in case of a short-circuit between the two energization systems, if the total phase current in one energization system deviates to the positive side, while the total phase current in the other energization system deviates to the negative side, the additional value approximates zero under the operations of the inverters in both the energization systems, because the deviation to the positive side in the one energization system cancels out the deviation to the negative side in the other energization system.

If the inverter of the one energization system is stopped, the total phase current in the one system equals zero. In addition, since no current flows into the other energization system through the short-circuited path, the total phase current in the other system is restored to zero. Hence, the additional value is held at substantially zero before and after the abnormality confirmation.

In other words, in case of a short-circuit between the two energization systems, although the total phase current becomes an outlier from zero at the respective energization systems, an additional value is held at substantially zero before and after stopping the inverter of one of the energization systems. In other words, when the total phase current becomes an outlier at both the energization systems, if an additional value of the total phase currents is substantially zero and is still kept at substantially zero even after stopping the inverter of one of the energization systems, the two energization systems can be diagnosed as being short-circuited.

On the other hand, as illustrated in FIG. 8 , if one energization system has an abnormality, while the other energization system is normally operating, an additional value deviates from zero before stopping the inverter of the failed energization system. By stopping the inverter of the failed energization system, the additional value is restored to zero.

Here, it is assumed that, after stopping the inverter of one of the energization systems in response to the detection of an abnormality in the total phase current, a predetermined period has elapsed so that the abnormality detection counter is incremented up to predetermined value C 1 and in such a state, the total phase current in the other energization system becomes normal. Under this condition, if the additional value is close to zero before the inverter of the one energization system is stopped, it is accordingly determined the two energization systems are short-circuited. Meanwhile, the additional value is not zero before the inverter of the one energization system is stopped, it is determined as above that only the one energization system has a fault.

Comparing the fault mode that a short-circuit occurs between the two energization systems as illustrated in FIG. 6 and the fault mode that the energization systems have different faults as illustrated in FIG. 10 , the total phase current becomes an outlier at both the energization systems before stopping the inverter of the one energization system in response to the detection of an abnormality in the total phase current, in the respective fault modes.

In the fault mode that a short-circuit occurs between the two energization systems, the additional value of the total phase currents, which are both outliers, is close to zero. Meanwhile, in the fault mode that the energization systems have different faults, the additional value of the total phase currents, which are both outliers, might not be close to zero. Thus, if the additional value of the total phase currents, which are outliers, is close to zero, it is determined that the two energization systems are short-circuited.

Moreover, it is assumed that the total phase current becomes an outlier at both the energization systems before stopping the inverter of one of the energization systems in response to the detection of an abnormality in the total phase current. On this assumption, even when a predetermined period has elapsed after the inverter of the one energization system is stopped until the abnormality detection counter is incremented up to predetermined value C 1 , if the total phase current in the other energization system is still an outlier, it is determined that the two energization systems have different faults.

Hereinbefore, the present invention is described in detail on the basis of the preferred embodiments but it is obvious that one skilled in the art can make various modifications within the basic technical ideas and teachings of the present invention.

The controller for a motor according to the present invention is also applicable to an electric motor where three-phase coils U, V, and W are connected by means of delta connection as well as electric motor 130 having three-phase coils U, V, and W star-connected.

FIG. 11 illustrates the layout of current sensors 301 in the electric motor having delta-connected three-phase coils U, V, and W. In the illustrated example of FIG. 11 , current sensors 301 U, 301 V, and 301 W are provided between output points of inverters 1 A and 1 B and connection points of delta-connected three-phase coils U, V, and W.

In addition, the controller for a motor according to the present invention is applicable to a device equipped with three or more coil sets composed of three-phase coils U, V, and W, and three or more inverters for driving the respective coil sets.

Furthermore, the controller of the present invention can be applied not only to the electric motor that generates a steering assist force in a vehicle electric power steering device but also to various motors such as a motor serving as an actuator for a variable valve mechanism of an engine and a motor used for driving a pump.

In addition, if any one of plural energization systems has a fault, a warning device such as a warning lamp or buzzer can be operated to inform a driver of the vehicle about an abnormality etc. in an electric power steering device incorporating the electric motor.

1 A first inverter

1 B second inverter

2 A first coil set

2 B second coil set

4 output voltage calculating unit

5 motor rotational speed calculating unit

6 target assist torque calculating unit

7 A first output duty calculating unit

7 B second output duty calculating unit

8 A first two-to-three phase converting unit

8 B second two-to-three phase converting unit

9 A first dead time compensation unit

9 B second dead time compensation unit

11 three-to-two phase converting unit

12 inverter output ON/OFF determination unit

13 A first energization system ON/OFF control unit

13 B second energization system ON/OFF control unit

130 electric motor

150 electronic control unit

301 UA, 301 VA, 301 WA, 301 UB, 301 VB, 301 WB current sensor

302 microcomputer

304 A, 304 B power supply relay

307 voltage monitor circuit

UHA, VHA, WHA, UHB, VHB, WHB high-potential side switching element

ULA, VLA, WLA, ULB, VLB, WLB low-potential side switching element