Control device and failure determination method

1. A control device that controls a motor via an inverter circuit that supplies power converted from direct current to three-phase alternating current to the motor, the control device comprising:

a current sensor that detects AC current of each phase of three-phase alternating current provided at an output of the inverter circuit,

wherein the control device calculates three estimated DC current values by using a duty value of a PWM signal for controlling switching of the inverter circuit and an AC current value of two phases among three phases detected by the current sensor, and determines a failure of the current sensor on the basis of a change in each of the estimated DC current values that have been calculated, the control device configured to determine that the current sensor fails in a phase having a smallest frequency of the estimated DC current values that have been calculated.

2. The control device according to claim 1 , wherein, when a change tendency of one of the three estimated DC current values is different from a change tendency of another one of the three estimated DC current values, it is determined that a current sensor that has detected an AC current value that has not been used for calculation of the one of the three estimated DC current values having a different change tendency is a failure.

3. The control device according to claim 1 , wherein

a duty value of a U-phase PWM signal is defined as Du, a duty value of a V-phase PWM signal is defined as Dv, a duty value of a W-phase PWM signal is defined as Dw, a U-phase AC current value is defined as Ius, a V-phase AC current value is defined as Ivs, and a W-phase AC current value is defined as Iws, and

the control device

calculates a first estimated DC current value Idce 1 by using Du, Dv, Dw, Ivs, and Iws,

calculates a second estimated DC current value Idce 2 by using Du, Dv, Dw, Iws, and Ius,

calculates a third estimated DC current value Idce 3 by using Du, Dv, Dw, Ius, and Ivs, calculates a fourth estimated DC current value Idce 4 by using Du, Dv, Dw, Ius, Ivs, and Iws, and

determines a phase in which the current sensor fails and a type of a failure based on a comparison result between a difference between a value obtained by subtracting the fourth estimated DC current value Idce4 from each of the first estimated DC current value Idce1, the second estimated DC current value Idce2, and the third estimated DC current value Idce3 and a three-phase sum current value Isum, and a predetermined threshold Ihys.

4. The control device according to claim 3 , the control device configured to

calculate the first estimated DC current value Idce1, the second estimated DC current value Idce2, the third estimated DC current value Idce3, and the fourth estimated DC current value Idce4 by using the following formulae,

when the three-phase sum current value Isum is positive and Determination Formula 1-1 is satisfied, increase a determination parameter Njudge1 by 1,

when the three-phase sum current value Isum is negative and Determination Formula 1-2 is satisfied, decrease the determination parameter Njudge1 by 1,

when the three-phase sum current value Isum is positive and Determination Formula 2-1 is satisfied, increase a determination parameter Njudge2 by 1,

when the three-phase sum current value Isum is negative and Determination Formula 2-2 is satisfied, decrease the determination parameter Njudge2 by 1,

when the three-phase sum current value Isum is positive and Determination Formula 3-1 is satisfied, increase a determination parameter Njudge3 by 1,

when the three-phase sum current value Isum is negative and Determination Formula 3-2 is satisfied, decrease the determination parameter Njudge3 by 1, and

determine a phase in which the current sensor fails and a type of a failure based on change amounts of the determination parameters Njudge1, Njudge2, Njudge3 in a predetermined time,

Idce1=(−Ivs−Iws)×Du+Ivs×Dv+Iws×Dw

Idce2=Ius×Du+(−Ius−Iws)×Dv+Iws×Dw

Idce3=Ius×Du+Ivs×Dv+(−Ius−Ivs)×Dw

Idce4=(−Ivs−Iws)×Du+(−Ius−Iws)×Dv+(−Ius−Ivs)×Dw

Idce1−Idce4>Isum+Ihys   Determination Formula 1-1

Idce1−Idce4<Isum−Ihys   Determination Formula 1-2

Idce2−Idce4>Isum+Ihys   Determination Formula 2-1

Idce2−Idce4<Isum−Ihys   Determination Formula 2-2

Idce3−Idce4>Isum+Ihys   Determination Formula 3-1

Idce3−Idce4<Isum−Ihys   Determination Formula 3-2.

5. The control device according to claim 3 , the control device configured to

correct the predetermined threshold by adding a change amount of a target DC current to a predetermined value, and

determine the phase in which the current sensor fails and the type of the failure based on a comparison result between a value obtained by subtracting the fourth estimated DC current value Idce4 from each of the first estimated DC current value Idce1, the second estimated DC current value Idce2, and the third estimated DC current value Idce3 and the predetermined threshold in which a difference with the three-phase sum current value Isum has been corrected.

6. The control device according to claim 1 , the control device configured to

perform first determination of determining a phase in which the current sensor fails and a type of a failure by collating a change in each of the estimated DC current values that have been calculated, with a first determination table, and

when the failure of the current sensor cannot be determined by the first determination, perform second determination of determining the phase in which the current sensor fails and the type of the failure by collating a change in each of the estimated DC current values that have been calculated, with a second determination table.

7. The control device according to claim 1 , the control device configured to

perform third determination of determining the failure of the current sensor based on a change in each of the estimated DC current values that have been calculated, in a first time, and

when the failure of the current sensor cannot be determined by the third determination, perform fourth determination of determining the failure of the current sensor based on a change in each of the estimated DC current values that have been calculated, in a second time longer than the first time.

8. The control device according to claim 1 , the control device configured to

perform fifth determination of determining the failure of the current sensor based on a frequency of each of the estimated DC current values that have been calculated, in a third time, and

when the failure of the current sensor cannot be determined by the fifth determination, perform sixth determination of determining the failure of the current sensor based on the frequency of each of the estimated DC current values that have been calculated, in a fourth time longer than the third time.

9. The control device according to claim 1 , the control device configured to determine that the current sensor fails in a phase having a smallest difference between a maximum value and a minimum value of the estimated DC current values that have been calculated.

10. The control device according to claim 9 , the control device configured to

perform seventh determination of determining the failure of the current sensor based on the difference between the maximum value and the minimum value in each of the estimated DC current values that have been calculated, in a fifth time, and

when the failure of the current sensor cannot be determined by the seventh determination, perform eighth determination of determining the failure of the current sensor based on the difference between the maximum value and the minimum value in each of the estimated DC current values that have been calculated, in a sixth time longer than the fifth time.

11. A method of determining a failure of a current sensor performed by a control device that controls a motor via an inverter circuit that supplies power converted from direct current to three-phase alternating current to the motor,

wherein a current sensor that detects alternating current of each phase of three-phase alternating current is provided at an output of the inverter circuit,

the method comprising, by the control device,

calculating estimated DC current values by using a duty value of a PWM signal for controlling switching of the inverter circuit and an AC current value of two phases among three phases detected by the current sensor, and

by the control device, determining a failure of the current sensor on the basis of a change in the estimated DC current values that have been calculated, the control device configured to determine that the current sensor fails in a phase having a smallest difference between a maximum value and a minimum value of the estimated DC current values that have been calculated.

12. A control device that controls a motor via an inverter circuit that supplies power converted from direct current to three-phase alternating current to the motor, the control device comprising:

a current sensor that detects AC current of each phase of three-phase alternating current provided at an output of the inverter circuit,

wherein the control device calculates three estimated DC current values by using a duty value of a PWM signal for controlling switching of the inverter circuit and an AC current value of two phases among three phases detected by the current sensor, and determines a failure of the current sensor on the basis of a change in each of the estimated DC current values that have been calculated, the control device configured to:

perform first determination of determining a phase in which the current sensor fails and a type of a failure by collating a change in each of the estimated DC current values that have been calculated, with a first determination table, and

when the failure of the current sensor cannot be determined by the first determination, perform second determination of determining the phase in which the current sensor fails and the type of the failure by collating a change in each of the estimated DC current values that have been calculated, with a second determination table.