Power conversion device, motor drive unit, and electric power steering device

1. A power conversion device that converts power from a power supply to power to be supplied to a motor with n-phase windings, where n is an integer of 3 or greater, the power conversion device comprising:

a first inverter connected to first ends of windings of each phase of the motor;

a second inverter connected to second ends of the windings of each phase of the motor; and

a switching circuit used to define a neutral point in the windings of each phase on a side of the first inverter; wherein

at least one of a plurality of switches included in the first inverter has a first maximum drain current tolerance capacity;

a plurality of switches included in the second inverter have a second maximum drain current tolerance capacity that is greater than the first maximum drain current tolerance capacity;

each bridge circuit of the first and second inverters includes n legs each including a low side switch and a high side switch;

the switching circuit is a power-supply-side switching circuit including a first switch to switch whether the first inverter and the power supply are connected or disconnected;

the n low side switches in the bridge circuit of the first inverter have the first maximum drain current tolerance capacity, and the n high side switches in the bridge circuit of the first inverter have the second maximum drain current tolerance capacity; and

the plurality of switches included in the first inverter and the plurality of switches included in the second inverter are operated in accordance with a pulse width modulation signal generated by a control circuit.

2. A power conversion device that converts power from a power supply to power to be supplied to a motor with n-phase windings, where n is an integer of 3 or greater, the power conversion device comprising:

a first inverter connected to first ends of windings of each phase of the motor;

a second inverter connected to second ends of the windings of each phase of the motor; and

a switching circuit used to define a neutral point in the windings of each phase on a side of the first inverter; wherein

at least one of a plurality of switches included in the first inverter has a first maximum drain current tolerance capacity;

a plurality of switches included in the second inverter have a second maximum drain current tolerance capacity that is greater than the first maximum drain current tolerance capacity;

each bridge circuit of the first and second inverters includes n legs each including a low side switch and a high side switch;

the switching circuit is a power-supply-side switching circuit including a first switch to switch whether the first inverter and the power supply are connected or disconnected;

the n low side switches in the bridge circuit of the first inverter have the first maximum drain current tolerance capacity, and the n high side switches in the bridge circuit of the first inverter have a third maximum drain current tolerance capacity that is larger than the first maximum drain current tolerance capacity and smaller than the second maximum drain current tolerance capacity; and

the plurality of switches included in the first inverter and the plurality of switches included in the second inverter are operated in accordance with a pulse width modulation signal generated by a control circuit.

3. A power conversion device that converts power from a power supply to power to be supplied to a motor with n-phase windings, where n is an integer or 3 of greater, the power conversion device comprising:

a first inverter connected to first ends of windings of each phase of the motor;

a second inverter connected to second ends of the windings of each phase of the motor; and

a switching circuit used to define a neutral point in the windings of each phase on a side of the first inverter; wherein

at least one of plurality of switches included in the first inverter has a first maximum drain current tolerance capacity;

a plurality of switches included in the second inverter have a second maximum drain current tolerance capacity that is greater than the first maximum drain current tolerance capacity;

each bridge circuit of the first and second inverters includes n legs each including a low side switch and a high side switch;

the switching circuit is a ground-side switching circuit including a second switch to switch whether the first inverter and a ground are connected or disconnected;

the n low side switches in the bridge circuit of the first inverter have the second maximum drain current tolerance capacity, and the n high side switches in the bridge circuit of the first inverter have the first maximum drain current tolerance capacity; and

the plurality of switches included in the first inverter and the plurality of switches included in the second inverter are operated in accordance with a puke width modulation signal generated by a control circuit.

4. A power conversion device that converts power from a power supply to power to be supplied to a motor with n-phase windings, where n is an integer of 3 or greater, the power conversion device comprising:

a first inverter connected to first ends of windings of each phase of the motor;

a second inverter connected to second ends of the windings of each phase of the motor; and

a switching circuit used to define a neutral point in the windings of each phase on a side of the first inverter; wherein

at least one of a plurality of switches included in the first inverter has a first maximum drain current tolerance capacity;

a plurality of switches included in the second inverter have a second maximum drain current tolerance capacity that is greater than the first maximum drain current tolerance capacity;

each bridge circuit of the first and second inverters includes n legs each including a low side switch and a high side switch;

the switching circuit is a ground-side switching circuit including a second switch to switch whether the first inverter and a ground are connected or disconnected;

the n low side switches in the bridge circuit of the first inverter have a third maximum drain current tolerance capacity that is larger than the first maximum drain current tolerance capacity and smaller than the second maximum drain current tolerance capacity, and then high side switches in the bridge circuit of the first inverter have the first maximum drain current tolerance capacity; and

the plurality of switches included in the first inverter and the plurality of switches included in the second inverter are operated in accordance with a pulse width modulation signal generated by a control circuit.

5. The power conversion device according to claim 1 , wherein

each bridge circuit of the first and second inverters includes n legs each including a low side switch and a high side switch;

the switching circuit is a neutral point relay circuit which is connected to first ends of the windings of each phase and switches whether the first ends of the windings of each phase are connected or disconnected; and

the n low side switches and the n high side switches in the bridge circuit of the first inverter have the first maximum drain current tolerance capacity.

6. The power conversion device according to claim 1 , wherein

each bridge circuit of the first and second inverters includes n legs each including a low side switch and a high side switch;

the switching circuit includes a power-supply-side switching circuit including a first switch to switch whether the first inverter and the power supply are connected or disconnected and a ground-side switching circuit including a second switch to switch whether the first inverter and a ground are connected or disconnected; and

the n low side switches and the n high side switches in the bridge circuit of the first inverter have the first maximum drain current tolerance capacity.

7. The power conversion device according to claim 1 , wherein the power conversion device includes:

a first operation mode in which power conversion is performed using the second inverter and the neutral point of the windings of each phase at the first inverter side by the switching circuit when the motor is driven at a low speed; and

a second operation mode in which power conversion is performed by n-phase energization control of the first and second inverters when the motor is driven at a high speed.

8. The power conversion device according to claim 1 , wherein the power conversion device includes:

as a first operation mode in which the first switch of the power-supply-side switching circuit is turned off, and the n high side switches are turned on and the n low side switches are turned off in the bridge circuit of the first inverter, the first operation mode in which power conversion is performed using the second inverter and the neutral point of the windings of each phase at a high side of the first inverter when the motor is driven at a low speed; and

as a second operation mode in which the first switch of the power-supply-side switching circuit is turned on, the second operation mode in which power conversion is performed by n-phase energization control of the first and second inverters when the motor is driven at a high speed.

9. The power conversion device according to claim 3 , wherein the power conversion device includes:

as a first operation mode in which the second switch of the ground-side switching circuit is turned off, and the n high side switches are turned off and the n low side switches are turned on in the bridge circuit of the first inverter, the first operation mode in which power conversion is performed using the second inverter and the neutral point of the windings of each phase at a low side of the first inverter when the motor is driven at a low speed; and

as a second operation mode in which the second switch of the ground-side switching circuit is turned on, the second operation mode in which power conversion is performed by n-phase energization control of the first and second inverters when the motor is driven at a high speed.

10. The power conversion device according to claim 5 , wherein the power conversion device includes:

as a first operation mode in which the neutral point relay circuit is turned on, and all of the n low side switches and the n high side switches are turned off in the bridge circuit of the first inverter, the first operation mode in which power conversion is performed using the second inverter and the neutral point of the windings of each phase at the neutral point relay circuit when the motor is driven at a low speed; and

as a second operation mode in which the neutral point relay circuit is turned off, the second operation mode in which power conversion is performed by n-phase energization control of the first and second inverters when the motor is driven at a high speed.

11. The power conversion device according to claim 6 , wherein the power conversion device includes:

as a first operation mode in which the power-supply-side and ground-side switching circuits are turned off, and all of the n low side switches and the n high side switches are turned on in the bridge circuit of the first inverter, the first operation mode in which power conversion is performed using the second inverter and two neutral points of the windings of each phase at a low side and a high side of the first inverter when the motor is driven at a low speed; and

as a second operation mode in which the power-supply-side and ground-side switching circuits are turned on, the second operation mode in which power conversion is performed by n-phase energization control of the first and second inverters when the motor is driven at a high speed.

12. The power conversion device according to claim 1 , wherein the power supply is a single power supply.

13. A motor driver comprising:

a motor; and

the power conversion device according to claim 1 .

14. An electric power steering device comprising the motor driver according to claim 13 .