Multigroup-multiphase rotating-electric-machine driving apparatus

1. A multigroup-multiphase rotating-electric-machine driving apparatus that drives a multigroup-multiphase rotating electric machine having independent multigroup-multiphase armature windings and magnetic-field poles formed of permanent magnets, the multigroup-multiphase rotating-electric-machine driving apparatus comprising:

a multigroup-multiphase electric-power conversion apparatus provided with two or more groups of electric-power conversion apparatuses that are provided corresponding to multigroup-multiphase armature windings and each of which performs electric-power conversion between the multiphase armature winding of the corresponding group and a DC power source;

a smoothing capacitor connected with the DC side of the multigroup-multiphase electric-power conversion apparatus; and

a control apparatus configured in such a way as to be able to separately control the two or more groups of electric-power conversion apparatuses,

wherein each of the two or more groups of electric-power conversion apparatuses includes two or more switching devices to be controlled by the control apparatus, and

wherein when a connection between the DC power source and the multigroup-multiphase electric-power conversion apparatus is cut off, the control apparatus controls the two or more switching devices so that respective states of the two or more groups of electric-power conversion apparatuses are each switched stepwise from an all-phase short-circuiting state to an all-phase cutoff state at different timings.

2. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 1 , wherein when an estimation value of an induction voltage in the multigroup-multiphase rotating electric machine is the same as or smaller than a predetermined voltage value and one of the two or more groups of electric-power conversion apparatuses is in an operational state that satisfies the equation (1) below, the control apparatus controls the switching devices so that the state of the one of the two or more groups of electric-power conversion apparatuses is switched from the all-phase short-circuiting to the all-phase cutoff state:

½ C ( V 0v 2 −V dc 2 )>√{square root over (3)} LI 21st 2   (1)

C: electrostatic capacitance of smoothing capacitor

V ov : allowable power-source voltage

V dc : present voltage charged in smoothing capacitor

L: inductance of motor

I 1st : effective value of current flowing in the one of the two or more groups of electric-power conversion apparatuses.

3. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 2 , wherein when the one of the two or more groups of electric-power conversion apparatuses is in the all-phase short-circuiting state and the other one of the two or more groups of electric-power conversion apparatuses is in an operational state that satisfies the equation (2) below, the control apparatus controls the switching devices so that the state of the other one of the two or more groups of electric-power conversion apparatuses is switched from the phase short-circuiting state to the all-phase cutoff state:

½ C ( v ov 2 −V dc 2 )>√{square root over (3)} L I 2st 2   (2)

C: electrostatic capacitance of smoothing capacitor

V ov : allowable power-source voltage

V dc : present voltage charged in smoothing capacitor

L: inductance of motor

I 2st : effective value of current flowing in the other one of the two or more groups of electric-power conversion apparatuses.

4. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 1 , wherein when the two or more groups of electric-power conversion apparatuses are in the all-phase cutoff state, the control apparatus controls the switching devices so that the respective states of the two or more groups of electric-power conversion apparatuses are each switched stepwise to the all-phase short-circuiting state at different timings.

5. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 2 , wherein when the two or more groups of electric-power conversion apparatuses are in the all-phase cutoff state, the control apparatus controls the switching devices so that the respective states of the two or more groups of electric-power conversion apparatuses are each switched stepwise to the all-phase short-circuiting state at different timings.

6. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 3 , wherein when the two or more groups of electric-power conversion apparatuses are in the all-phase cutoff state, the control apparatus controls the switching devices so that the respective states of the two or more groups of electric-power conversion apparatuses are each switched stepwise to the all-phase short-circuiting state at different timings.

7. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 4 , wherein when the all-phase cutoff state is switched to a three-phase short-circuiting state, the control apparatus controls the switching devices so that at a timing when a q-axis current flowing in one of the two or more groups of electric-power conversion apparatuses becomes positive, the state of the other one of the two or more groups of electric-power conversion apparatuses is switched from the all-phase cutoff state to the all-phase short-circuiting state.

8. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 5 , wherein when the all-phase cutoff state is switched to an all-phase short-circuiting state, the control apparatus controls the switching devices so that at a timing when a q-axis current flowing in one of the two or more groups of electric-power conversion apparatuses becomes positive, the state of the other one of the two or more groups of electric-power conversion apparatuses is switched from the all-phase cutoff state to the all-phase short-circuiting state.

9. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 6 , wherein when the all-phase cutoff state is switched to an all-phase short-circuiting state, the control apparatus controls the switching devices so that at a timing when a q-axis current flowing in one of the two or more groups of electric-power conversion apparatuses becomes positive, the state of the other one of the two or more groups of electric-power conversion apparatuses is switched from the all-phase cutoff state to the all-phase short-circuiting state.

10. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 4 , wherein when the all-phase cutoff state is switched to the all-phase short-circuiting state, the control apparatus switches the state of one of the two or more groups of electric-power conversion apparatuses from the all-phase cutoff state to the all-phase short-circuiting state and then switches the state of the other one of the two or more groups of electric-power conversion apparatuses from the all-phase cutoff state to the all-phase short-circuiting state.

11. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 5 , wherein when the all-phase cutoff state is switched to the all-phase short-circuiting state, the control apparatus switches the state of one of the two or more groups of electric-power conversion apparatuses from the all-phase cutoff state to the all-phase short-circuiting state and then switches the state of the other one of the two or more groups of electric-power conversion apparatuses from the all-phase cutoff state to the all-phase short-circuiting state.

12. The multigroup-multiphase rotating-electric-machine driving apparatus according to claim 6 , wherein when the all-phase cutoff state is switched to the all-phase short-circuiting state, the control apparatus switches the state of one of the two or more groups of electric-power conversion apparatuses from the all-phase cutoff state to the all-phase short-circuiting state and then switches the state of the other one of the two or more groups of electric-power conversion apparatuses from the all-phase cutoff state to the all-phase short-circuiting state.