WO2009106223A2

WO2009106223A2 - Permanent-magnet-excited electric machine operated without a sensor, in particular for a fuel cell unit of a motor vehicle, and a method of operating a permanent-magnet-excited electric machine operated without a sensor

Info

Publication number: WO2009106223A2
Application number: PCT/EP2009/000896
Authority: WO
Inventors: Andreas Knoop; Michael Bader
Original assignee: Daimler Ag; Ford Global Technologies Llc
Priority date: 2008-02-25
Filing date: 2009-02-10
Publication date: 2009-09-03
Also published as: WO2009106223A3; DE102008010950A1

Abstract

The invention relates to a permanent-magnet-excited electric machine (1) operated without a sensor, in particular for a fuel cell unit of a motor vehicle, in particular an automobile, having a stator (2) comprising a stator winding (3) and a rotor mounted rotationally movably relative to the stator (2), which rotor comprises at least one permanent magnet with a north pole region and a south pole region, and having an open- and/or closed-loop control means (5), which is coupled to the stator winding (3) and is designed to energize the stator winding (3), wherein the open- and/or closed-loop control means (5) is designed to energize the stator winding (3) when the electric machine (1) is at a standstill and the rotor may be fixed in a neutral angular position other than a dead center position as a result of said energization when at a standstill.

Description

PERMANENT-MAGNET-EXCITED ELECTRIC MACHINE OPERATED WITHOUT A SENSOR, IN PARTICULAR FOR A FUEL CELL UNIT OF A MOTOR VEHICLE, AND A METHOD OF OPERATING A PERMANENT-MAGNET-EXCITED ELECTRIC MACHINE

OPERATED WITHOUT A SENSOR

The present invention relates to a permanent-magnet-excited electric machine operated without a sensor, in particular for a fuel cell unit of a motor vehicle, in particular an automobile, having a stator comprising a stator winding and a rotor mounted rotationally movably relative to the stator, which rotor comprises at least one permanent magnet with a north pole region and a south pole region, and having an open- and/or closed-loop control means, which is coupled to the stator winding and is designed to energize the stator winding. The present invention additionally relates to a method of operating such an electric machine.

In the present case, interest is primarily focused on a sensorless drive for a fuel cell system of a motor vehicle, in particular an automobile, having a hybrid drive. A sensorless drive offers advantages above all with regard to robustness and costs. In the case of sensorless drives, an electric machine has during a starting process to find its correct rotor position afresh every time for subsequent operation. This proceeds by open-loop- controlled startup of the machine at a relatively low speed and requires a period of approx. 1 to 5 seconds, known as an "initialization period". If the fuel cell system is operated using a start/stop strategy for reasons of efficiency, the above initialization period proves particularly disadvantageous and cannot be allowed for motor vehicles.

Solutions are already known from the prior art which, with regard to the above start/stop strategy, ensure quick startup of the electric machine. In accordance with a method originating from the applicant, the electric machine continues to operate at a given minimum speed when the motor vehicle has been turned off. Furthermore, document DE 101 46 964 A1 discloses a readily started structure consisting of a brushless direct current motor or a permanent-magnet-excited electric machine, in which a stator winding and an open-loop control element are mounted on a base. In this case, a rotor of the electric machine comprises a permanent magnet including a north pole and a south pole. Also mounted on the base is at least one magnetically attractive positioning element, which attracts the strongly attractive magnetic areas of the permanent magnet and thus holds the rotor in a specific position. The rotor consequently remains in a predetermined position other than a dead center position. A disadvantage of this solution is that an additional positioning element is necessary, in order to hold the rotor in the position other than the dead center position when the electric machine is at a standstill and thus to ensure quick, easy startup of the machine.

The object of the invention is to provide a permanent-magnet-excited electric machine operated without a sensor and a method of operating a permanent-magnet-excited electric machine operated without a sensor, in which measures requiring little effort are taken which ensure that the electric machine may be started up quickly from a standstill, in particular without an initialization period, under closed-loop control.

This object is achieved according to the invention by a permanent-magnet-excited electric machine operated without a sensor having the features as claimed in claim 1 and by a method having the features as claimed in claim 7.

Advantageous further developments and embodiments of the invention are indicated in the subclaims.

A permanent-magnet-excited electric machine operated without a sensor according to the invention, in particular for a fuel cell unit of a motor vehicle, in particular an automobile, has a stator comprising a stator winding and a rotor mounted rotationally movably relative to the stator, which rotor comprises at least one permanent magnet with a north pole region and a south pole region. The electric machine comprises an open- and/or closed- loop control means, which is coupled to the stator winding and is designed to energize the stator winding. An essential concept of the present invention is that the open- and/or closed-loop control means is designed to energize the stator winding when the electric machine is at a standstill and the rotor may be fixed in a neutral angular position other than a dead center position as a result of said energization when at a standstill. A basic concept of the present invention consists in other words in the open- and/or closed-loop control means of the permanent-magnet-excited electric machine being energized in such a way when the machine is at a standstill that the rotor comprising the permanent magnet is fixed or held in a neutral angular position known by the open- and/or closed-loop control means. The electric machine according to the invention makes it possible advantageously to ensure that an angular position of the rotor when the machine is at a standstill does not have to be ascertained, but rather is known by the open- and/or closed-loop control means, such that it is ensured that the electric machine may be started up directly under closed-loop control and not open-loop control. It is ensured in this way that the initialization period necessary for startup of the electric machine with regard to a start/stop strategy for a hybrid drive in a motor vehicle or with regard to quick starting of the electric machine is dispensed with. Because no further elements are necessary for holding the rotor in the known neutral angular position when the machine is at a standstill, an electric machine is thus provided which has a reduced number of components. For instance, the stator winding assumes the task of holding the rotor comprising the permanent magnet. Furthermore, the necessary current consumption is also much lower than in the case where the electric machine is operated at a minimum speed, so providing an electric machine which is energy efficient with regard to current consumption.

Provision may in particular be made for the rotor to be fixed or held by energization of the stator winding when the electric machine is at a standstill in a neutral angular position which is as far removed as possible from the dead center position. Provision may preferably be made for the rotor to be fixed or held by energization of the stator winding when the electric machine is at a standstill in a neutral angular position which is removed by an angle of from 90° to 270° from the dead center position. The neutral angular position is particularly preferably removed by an angle of from 150° to 210°, in particular 180°, from the dead center position.

Preferably, the stator winding comprises three coil strands, the electric machine being designed to operate with three-phase current. Provision may in particular be made for the stator to comprise a plurality of teeth arranged uniformly spaced over the circumference of the stator, wherein in this embodiment the stator winding may in particular take the form of a tooth winding. In one embodiment the open- and/or closed-loop control means may comprise an open- and/or closed-loop control unit, in particular a microprocessor, which is designed for open- and/or closed-loop control of the speed characteristics of the electric machine. Preferably, the open- and/or closed-loop control means comprises a voltage transformer, in particular a three phase regulator, by means of which a DC voltage may be transformed into a three-phase current for operating the electric machine.

In particular, the open- and/or closed-loop control unit of the open- and/or closed-loop control means of the electric machine is coupled to the voltage transformer, in particular the three-phase regulator, wherein the voltage transformer, in particular the three-phase regulator, is preferably coupled to three coil strands of the stator winding of the stator.

Preferably, the voltage transformer may be actuated by the open- and/or closed-loop control unit. In particular, provision may be made for the voltage transformer to be coupled to a DC voltage source, in particular a battery, the voltage transformer being capable, in particular, of transforming a DC voltage or a rectified voltage into a three- phase current, with which the electric machine may be supplied.

Preferably, the voltage transformer may comprise a bridge circuit with a plurality of transistors, wherein the electric machine may be commutated, in particular electronically. In this way it is ensured that the speed characteristics of the electric machine may be technically simply and reliably closed-loop controlled by means of the open- and/or closed-loop control unit via the voltage transformer, in particular the three phase regulator, in particular the electronic bridge circuit. With regard in particular to rapid or quick startup of the electric machine it is thus ensured that the open- and/or closed-loop control unit is capable, via the voltage transformer, in particular the three-phase regulator, in particular the bridge circuit, of energizing one or more of the coil strands of the stator winding when the electric machine is at a standstill, such that it is ensured that the rotor remains in the neutral angular position other than the dead center position and the electric machine can from the outset be closed-loop controlled and not open-loop controlled.

In one embodiment the open- and/or closed-loop control means may be designed to energize just one coil strand of the stator winding when the electric machine is at a standstill. With regard in particular to energy-efficient operation of the electric machine, it is sufficient to energize just one of the coil strands when the electric machine is at a standstill, in order to achieve with regard to rapid or quick startup of the electric machine a predefined neutral angular position of the rotor known by the open- and/or closed-loop control means.

In an alternative embodiment, the open- and/or closed-loop control means may be designed to energize at least two coil strands of the stator winding when the electric machine is at a standstill.

A method according to the invention is designed for operation of a permanent-magnet- excited electric machine operated or actuated without a sensor, in particular for a fuel cell unit of a motor vehicle, in particular of an automobile. In this case, the electric machine has a stator comprising a stator winding and a rotor mounted rotationally movably relative to the stator, which rotor comprises at least one permanent magnet with a north pole region and a south pole region, the stator winding being energized by means of an open- and/or closed-loop control means coupled to the stator winding. A basic concept of the present invention is in this case that the stator winding is energized by means of the open- and/or closed-loop control means when the electric machine is at a standstill and the rotor is held in a neutral angular position other than a dead center position as a result of said energization when at a standstill.

With regard to the method, provision may be made in particular for the stator winding to comprise three coil strands, which are energized with three-phase current by means of the open- and/or closed-loop control means.

Preferably, the speed characteristics of the electric machine are open- and/or closed-loop controlled by means of an open- and/or closed-loop control unit, in particular a microprocessor, of the open- and/or closed-loop control means.

Preferably, a DC voltage is transformed by means of a voltage transformer, in particular a three-phase regulator, of the open- and/or closed-loop control means into a three-phase current for operating the electric machine.

With regard to the method, preferably just one coil strand of the stator winding is energized by means of the open- and/or closed-loop control means when the electric machine is at a standstill. Alternatively, provision may be made for at least two coil strands of the stator winding to be energized by means of the open- and/or closed-loop control means when the electric machine is at a standstill.

Advantageous configurations of the electric machine according to the invention may be regarded as advantageous embodiments of the method according to the invention.

Further advantages, features and details of the invention are revealed by the following description of a preferred exemplary embodiment and with reference to the appended drawing.

The single figure shows a permanent-magnet-excited electric machine operated without a sensor according to one embodiment of the present invention.

A permanent-magnet-excited electric machine 1 operated without a sensor and reproduced in the figure has a stator 2, which comprises a stator winding 3. The permanent-magnet-excited electric machine operated without a sensor is understood to mean a brushless motor operated without a sensor.

The present electric machine 1 has a rotor, not shown, which comprises at least one permanent magnet. The at least one permanent magnet in this case comprises a north pole region and a south pole region. The rotor is mounted so as to be rotationally movable relative to the stator.

The stator winding 3 here comprises three coil strands 3a, 3b, 3c, which are wound in the example in grooves formed between teeth arranged evenly spaced from one another around the circumference of the stator. The stator winding 3 thus comprises three connection poles 4a, 4b, 4c, which define connection terminals of the electric machine 1.

The electric machine 1 furthermore comprises an open- and/or closed-loop control means 5, which additionally has an open- and/or closed-loop control unit 6 and a voltage transformer 7. The open- and/or closed-loop control unit 6 is here coupled to the voltage transformer 7 by means of signal lines 8, the voltage transformer 7 being actuatable by the open- and/or closed-loop control unit 6. In the example the open- and/or closed-loop control unit 6 takes the form of a microcontroller or microprocessor. Moreover, the voltage transformer 7 takes the form of a three-phase regulator and comprises in the present example a bridge circuit including a plurality of transistors, in particular field effect transistors (MOSFET), such that the three coil strands 3a, 3b, 3c of the stator winding 3 of the stator 2 are commutated via the bridge circuit with the transistors. The voltage transformer 7 has the task of transforming a DC voltage or a rectified voltage into a three- phase current, with which the electric machine 1 is supplied via the three coil strands 3a, 3b, 3c. To this end, the voltage transformer 7 is coupled to a DC voltage source 9, which may for example be a vehicle battery. Moreover, the open- and/or closed-loop control unit 6 is likewise coupled to the DC voltage source 9 for power supply.

It should be mentioned at this point that in the present example the electric machine 1 is provided as a drive for a fuel cell unit of a motor vehicle, here an automobile.

In the present case interest focuses primarily on recognition of a rotor position during a start process of the electric machine 1 operated without a sensor with regard to subsequent operation. In the case in particular of a start/stop strategy for a motor vehicle hybrid drive, the rotor position has to be known during the start process, in order to ensure closed-loop controlled and not open-loop controlled startup of the electric machine 1. To this end it is proposed according to the invention that the open- and/or closed-loop control unit 6 be constructed in such a way that, when the electric machine 1 is at a standstill, one of the coil strands 3a, 3b, 3c of the stator winding 3 is energized, such that the rotor is held in a neutral angular position other than a dead center position as a result of said energization. Alternatively, provision may also be made for two or three coil strands 3a, 3b, 3c to be energized simultaneously, the rotor likewise being fixed in a known neutral angular position. This ensures that the neutral angular position adopted by the rotor when the electric machine 1 is at a standstill is known by the open- and/or closed-loop control unit 6, such that upon startup of the electric machine 1 the speed characteristics of the electric machine 1 may be closed-loop controlled, without having to actuate the electric machine 1 during an initialization process. This ensures considerable ride comfort. List of reference signs

1 Permanent-magnet-excited electric machine

2 Stator

3 Stator winding 3a, 3b, 3c Coil strands

4a, 4b, 4c Connection poles

5 Open- and/or closed-loop control means

6 Open- and/or closed-loop control unit

7 Voltage transformer

8 Signal lines

9 DC voltage source

Claims

Patent Claims

1. A permanent-magnet-excited electric machine (1 ) operated without a sensor, in particular for a fuel cell unit of a motor vehicle, having a stator (2) comprising a stator winding (3) and a rotor mounted rotationally movably relative to the stator (2), which rotor comprises at least one permanent magnet with a north pole region and a south pole region, and having an open- and/or closed-loop control means (5), which is coupled to the stator winding (3) and is designed to energize the stator winding (3), characterized in that the open- and/or closed-loop control means (5) is designed to energize the stator winding (3) when the electric machine (1) is at a standstill and the rotor may be fixed in a neutral angular position other than a dead center position as a result of said energization when at a standstill.

2. The electric machine (1) as claimed in claim 1 , characterized in that the stator winding (3) comprises three coil strands (3a, 3b, 3c), and the electric machine (1) is designed for operation with three-phase current.

3. The electric machine (1) as claimed in claim 1 or 2, characterized in that the open- and/or closed-loop control means (5) comprises an open- and/or closed loop control unit (6), in particular a microprocessor, which is designed for open- and/or closed- loop control of the speed characteristics of the electric machine (1).

4. The electric machine (1) as claimed in one of the preceding claims, characterized in that the open- and/or closed-loop control means (5) comprises a voltage transformer (7), in particular a three phase regulator, by means of which a DC voltage may be transformed into a three-phase current for operating the electric machine (1).

5. The electric machine (1) as claimed in one of the preceding claims, characterized in that the open- and/or closed-loop control means (5) is designed to energize just one coil strand (3a, 3b, 3c) of the stator winding (3) when the electric machine (1) is at a standstill.

6. The electric machine (1) as claimed in one of claims 1 to 4, characterized in that the open- and/or closed-loop control means (5) is designed to energize at least two coil strands (3a, 3b, 3c) of the stator winding (3) when the electric machine (1) is at a standstill.

7. A method of operating a permanent-magnet-excited electric machine (1) operated without a sensor, in particular for a fuel cell unit of a motor vehicle, the electric machine (1) having a stator (2) comprising a stator winding (3) and a rotor mounted rotationally movably relative to the stator (2), which rotor comprises at least one permanent magnet with a north pole region and a south pole region, the stator winding (3) being energized by means of an open- and/or closed-loop control means (5) coupled to the stator winding (3), characterized in that the stator winding (3) is energized by means of the open- and/or closed-loop control means (5) when the electric machine (1) is at a standstill and the rotor is held in a neutral angular position other than a dead center position as a result of said energization when at a standstill.

8. The method as claimed in claim 7, characterized in that the stator winding (3) comprises three coil strands (3a, 3b, 3c), which are energized with three-phase current by means of the open- and/or closed-loop control means (5).

9. The method as claimed in claim 7 or 8, characterized in that the speed characteristics of the electric machine (1) are open- and/or closed-loop controlled by means of an open- and/or closed-loop control unit (6), in particular a microprocessor, of the open- and/or closed-loop control means (5).

10. The method as claimed in one of claims 7 to 9, characterized in that a DC voltage is transformed by means of a voltage transformer, in particular a three-phase regulator, of the open- and/or closed-loop control means (5) into a three-phase current for operating the electric machine (1).

11. The method as claimed in one of claims 7 to 10, characterized in that just one coil strand of the stator winding (3) is energized by means of the open- and/or closed-loop control means (5) when the electric machine (1) is at a standstill.

12. The method as claimed in one of claims 7 to 10, characterized in that at least two coil strands (3a, 3b, 3c) of the stator winding (3) are energized by means of the open- and/or closed-loop control means (5) when the electric machine (1) is at a standstill.