Control device for rotary electrical machine and control method

1. A control device for a rotary electrical machine which is connected between a DC power source and a rotary electrical machine and which controls driving of the rotary electrical machine by converting DC power from the DC power source into AC power, the control device comprising:

a power conversion circuit which is configured from a plurality of switching elements;

a phase current detection unit which detects phase currents in the rotary electrical machine;

a phase current ratio derivation unit which derives a ratio of the phase currents detected by the phase current detection unit being equal to or greater than a reference value to the entire phase current detected, or being equal to or lower than the reference value to the entire phase current detected; and

an element fault determination unit which determines a fault status of each of the switching elements when the ratio derived by the phase current ratio derivation unit is equal to or greater than a previously established ratio threshold value.

2. The control device for a rotary electrical machine according to claim 1 , wherein the element fault determination unit determines a fault status of each of the switching elements at a fixed cycle.

3. The control device for a rotary electrical machine according to claim 1 , further comprising a fault determination permission unit which permits fault determination by the element fault determination unit, when a rotational speed of the rotary electrical machine is equal to or greater than a previously established rotational speed threshold value.

4. The control device for a rotary electrical machine according to claim 1 , further comprising a fault determination permission unit which permits fault determination by the element fault determination unit, when an amplitude of the phase currents detected by the phase current detection unit is equal to or greater than a previously established phase current amplitude threshold value.

5. The control device for a rotary electrical machine according to claim 1 , wherein, when a fault status of each of the switching elements has been determined, and the power conversion circuit is a single phase circuit, the element fault determination unit determines that the fault status of the switching element is a shorting fault when, in a state where all of the switching elements are off, the phase current detected by the phase current detection unit is equal to or greater than a previously established threshold value.

6. The control device for a rotary electrical machine according to claim 1 , wherein, when a fault status of each of the switching elements has been determined and the power conversion circuit is a multiple-phase circuit, the element fault determination unit determines that the fault status of the switching element is a shorting fault when, in a state where all of the switching elements are off, the phase current of any one phase, among the phase currents detected by the phase current detection unit, is equal to or greater than a previously established threshold value, and when the phase currents of the remaining phases flowing in an opposite direction to the phase current of the one phase are equal to or greater than a threshold value divided by (number of phases minus 1).

7. The control device for a rotary electrical machine according to claim 1 , further comprising an element shorting determination circuit which measures an element current flowing in each of the switching elements, and when the element current is equal to or greater than a previously established current threshold value, determines that shorting has occurred in the switching element.

8. The control device for a rotary electrical machine according to claim 1 , wherein, when a switching element positioned on a positive electrode side of the DC power source has a shorting fault, the element fault determination unit switches on normal switching elements which are of the same polarity as the switching element suffering the shorting fault, and when a switching element positioned on a negative electrode side of the DC power source has a shorting fault, the element fault determination unit switches on normal switching elements which are of the same polarity as the switching element suffering the shorting fault.

9. A control method for a rotary electrical machine achieved by a control device for a rotary electrical machine which is connected between a DC power source and a rotary electrical machine and which controls driving of the rotary electrical machine by converting DC power from the DC power source into AC power, the control method comprising:

a phase current detection step for detecting phase currents in the rotary electrical machine;

a phase current ratio derivation step for deriving a ratio of the phase currents detected in the phase current detection step being equal to or greater than a reference value to the entire phase current detected, or being equal to or lower than the reference value to the entire phase current detected; and

an element fault determination step for determining a fault status of each of switching elements configuring a power conversion circuit when the ratio derived in the phase current ratio derivation step is equal to or greater than a previously established ratio threshold value.