Electric power conversion system and electric power conversion device

1. An electrical power conversion system, comprising:

a motor;

an inverter circuit that outputs a U-phase current, a V-phase current, and a W-phase current to the motor;

a current sensor that detects the U-phase current, the V-phase current, and the W-phase current; and

a control circuit that controls the inverter circuit based on a torque command value and values detected by the current sensor, so that the U phase current, the V-phase current, and the W-phase current outputted from the inverter circuit are formed as sine waves; wherein:

the control circuit comprises:

a current component extraction unit that, based on the values detected by the current sensor, for each phase, extracts high frequency current components superimposed upon the U-phase current, the V-phase current, and the W-phase current; and

an AC current abnormality detection unit that detects an abnormality of an AC current flowing to the motor, based on the phases of the high frequency current components for any two phases among the U-phase current, the V-phase current, and the W-phase current;

the high frequency current components are components having a frequency that is higher than a fundamental frequency of the U-phase current, the V-phase current, and the W-phase current;

the current component extraction unit extracts the high frequency current components by determining differences between the values detected by the current sensor and three phase command currents that are calculated based on the torque command value; and

the AC current abnormality detection unit determines that there is an abnormality if a phase difference between the high frequency current components for any two phases among the U-phase current, the V-phase current, and the W-phase current is approximately 180°.

2. An electrical power conversion system according to claim 1 , wherein the AC current abnormality detection unit determines that there is an abnormality in the AC current flowing to the motor, if an amplitude of any of the high frequency current components is greater than or equal to a threshold value.

3. An electrical power conversion system according to claim 2 , wherein the AC current abnormality detection unit increases the threshold value when a rate of change of the torque command value is greater than a predetermined value.

4. An electrical power conversion system according to claim 2 , wherein the AC current abnormality detection unit increases the threshold value when the motor rotational speed is greater than a predetermined value.

5. An electrical power conversion system according to claim 1 , wherein:

the control circuit comprises a current command generation unit that, based on the torque command value, generates a current command less than or equal to a maximum current command value; and

the current command generation unit reduces the maximum current command value for the current command when it has been determined by the AC current abnormality detection unit that an abnormality has occurred.

6. An electrical power conversion system according to claim 1 , wherein:

the control circuit comprises a current command generation unit that generates a current command based on the torque command value; and

the current command generation unit stops generation of the current command when it has been determined by the AC current abnormality detection unit that an abnormality has occurred.

7. An electrical power conversion system according to claim 1 , wherein:

the control circuit comprises a volatile memory whose stored contents disappear when supply of power is terminated, and a non volatile memory whose stored contents are preserved even when supply of power is terminated;

the AC current abnormality detection unit outputs current information outputted to the motor to the volatile memory, and moreover outputs an abnormality signal to the volatile memory when it has been determined by the AC current abnormality detection unit that an abnormality has occurred; and

contents stored in the volatile memory are outputted to the non volatile memory when the abnormality signal is inputted.

8. An electrical power conversion device, comprising:

an inverter circuit that outputs a U-phase current, a V-phase current, and a W-phase current to a motor;

a current sensor that detects the U-phase current, the V-phase current, and the W-phase current; and

a control circuit that controls the inverter circuit based on a torque command value and values detected by the current sensor, so that the U-phase current, the V-phase current, and the W-phase current outputted from the inverter circuit are formed as sine waves; wherein:

the control circuit comprises:

a current component extraction unit that, based on the values detected by the current sensor, for each phase, extracts high frequency current components superimposed upon the U-phase current, the V-phase current, and the W-phase current; and

an AC current abnormality detection unit that detects an abnormality of an AC current flowing to the motor, based on the phases of the high frequency current components for any two phases among the U-phase current, the V-phase current, and the W-phase current;

the high frequency current components are components having a frequency that is higher than a fundamental frequency of the U-phase current, the V-phase current, and the W-phase current;

the current component extraction unit extracts the high frequency current components by determining differences between the values detected by the current sensor and three phase command currents that are calculated based on the torque command value; and

the AC current abnormality detection unit determines that there is an abnormality if a phase difference between the high frequency current components for any two phases among the U-phase current, the V-phase current, and the W-phase current, is approximately 180°.

9. An electrical power conversion device according to claim 8 , wherein the AC current abnormality detection unit determines that there is an abnormality in the AC current flowing to the motor, if an amplitude of any of the high frequency current components is greater than or equal to a threshold value.