EP2338223A2

EP2338223A2 - D.c. motor and method for operating said d.c. motor

Info

Publication number: EP2338223A2
Application number: EP09736594A
Authority: EP
Inventors: David Fricker; Gerhard Knecht
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2008-10-23
Filing date: 2009-10-13
Publication date: 2011-06-29
Also published as: JP5535226B2; WO2010046266A2; CN102197582B; CN102197582A; JP2012506684A; DE102008043134A1; WO2010046266A3

Abstract

The invention relates to a D.C. motor (1) comprising a rotor (26) having at least one permanent magnet (27), and a stator (16) having at least three stator coils (u, u', v, v', w, w'). The D.C. motor also comprises a control device which is adapted to determine a rotational position of the rotor (26) and to initiate the supply of power to the stator coils (u, u', v, v', w, w') depending on the rotational position of the rotor (26). The control device is also adapted to determine the rotational position in a high speed range based on a voltage which is induced in one of the stator coils (u, u', v, v', w, w'). In order for the D.C. motor (1) to be controllable in a low speed range depending on the rotational position of the rotor, the control device (6) is adapted to determine the rotational position in a low speed range based on a current which flows when a voltage is applied to one of the stator coils (u, u', v, v', w, w').

Description

ROBERT BOSCH GMBH, 70442 Stuttgart

DC MOTOR AND METHOD OF OPERATING THE DC CURRENT MOTOR

State of the art

The present invention relates to a DC motor according to the preamble of claim 1 and a method for operating the DC motor according to the preamble of claim 2.

Such a so-called brushless sensorless DC motor comprises a rotor having at least one permanent magnet, and a stator having at least three stator coils, wherein a control device is provided, which is adapted to determine a rotational position of the rotor and an energization of the stator coils from the rotational position of the rotor, and wherein the control means is arranged to determine the rotational position in a high speed range based on a voltage induced in one of the stator coils.

A disadvantage, however, is that at low speeds no sufficient voltages are induced in the stator coils. Therefore, the rotational position of the rotor can not be determined. The stator coils are therefore switched blind during startup of the engine in the low speed range. This can lead to the fact that the energization of the stator coils does not lead to an acceleration of the motor, but to a deceleration of the rotor. The rotor then reaches the high speed range only after a long time or not at all.

Disclosure of the invention The present invention has for its object to provide a DC motor of the type mentioned and a method for operating the DC motor, wherein the DC motor is controlled by the method in a low speed range depending on a rotational position of the rotor.

The object underlying the invention is achieved by a DC motor having the features of the characterizing part of patent claim 1 and a method for operating the DC motor having the features of the characterizing part of patent claim 2.

The present invention relates to a DC motor, wherein the control means is arranged to determine the rotational position in a low speed range based on a current when a voltage is applied to one of the stator coils. A low speed range is generally a speed range that is below a high speed range in which sufficient voltages are not induced in the stator coils to determine the rotational position, and in which the rotor speed is typically less than 500 rpm, while in the high Speed range the

Rotor speed is typically more than 500 U / min. Advantageously, no further sensor is required to determine the speed in the low speed range. In the ideal case, the DC motor is a follow-up pole motor (English: consequent pole motor).

The present invention further relates to a method of operating the DC motor with the following steps in a low speed range: applying a voltage to one of the stator coils; Determining a current at the one of the stator coils; Determining the rotor position based on the course of the current; and energizing the stator coils in dependence on the detected rotational position. The determination of the current in connection with the invention does not mean that the current is determined numerically exactly. It can also be determined only a size that is proportional to the current. In a preferred embodiment, a voltage is applied to the at least one further stator coil, a further current is determined at the at least one further stator coil, and the rotational position is determined based on the course of the further current. This makes it possible to determine if the rotor is in one of several different rotational positions.

In a development of the preferred embodiment, the applied voltages are voltage pulses. These voltage pulses typically have a duration of several 100 μs. This allows the rotational position of the

Accurately determine the rotor. In addition, only a short time interval is required to determine the rotational position in which the normal operation of the DC motor must be interrupted.

In a further development of the preferred embodiment, the voltage pulses are applied repeatedly, and the time interval between the repeated application of the voltage pulses decreases. Thus, the time interval between the repeated application of the voltage pulses is adapted to the increasing speed of the rotor.

In a further development of the preferred embodiment, the applied voltages are reversed, currents are determined on the stator coils for the polarity reversed voltages, and the rotational position is determined based on the course of the currents for the polarity reversed voltages. The reversed voltages are preferably also voltage pulses and have the same duration as the aforementioned voltage pulses. By two opposite voltage pulses, the speed of the rotor is hardly affected.

In yet another embodiment of the preferred embodiment, the amounts of current increases at each voltage and reverse voltage stator coil are added together to form a summed current increase, the maximum summed current increase is compared to the other current increases to determine the rotational position. Offset errors of the streams can thus be extracted. By a suitable Tolerance in the determination of the comparison criterion, an angular range can be set, in which the rotational position of the rotor.

In a further development of the preferred embodiment, in the high speed range to determine the speed identical

Voltage values of the voltage induced in one of the stator coils are determined to be a multiple (at least twice) of the electrical angle of 360 °. These are voltage values for the same rotor position. This ensures that deviations between the poles of the rotor do not affect the determination of the rotational position.

Brief description of the drawings

The invention will be described in more detail below with reference to the drawings. Show it:

FIG. 1 is a schematic view of a DC motor with an associated power supply;

FIG. 2 is a detail view of the DC motor and its associated

Switching device of FIG. 1 ; FIG. 3 is a view of the voltage comparator circuit of FIG. 1 ;

FIG. 4 is a view of the voltage amplifier of FIG. 1 ;

FIG. Fig. 5A is a view of the electric angle motor αel = 0 °;

FIG. Fig. 5B is a view of the electric angle motor αel = 120 °;

FIG. 5C is a view of the electric angle motor αel = 240 °; and FIG. 6 shows the amplitude of the induced voltage as a function of the electrical

Angle.

FIG. 1 shows a schematic view of a DC motor 1 with an associated energizing device 2. Such a DC motor is used, for example, for a coolant pump of a motor vehicle.

The energizing device 2 provides a current to the DC motor 1 via the power lines 3, 4 and 5. The energizing device 2 comprises a control circuit 6, a driver circuit 7 with a charge pump, a switching device 8 with a plurality of switching transistors, a voltage comparator circuit 9 and a voltage amplifier circuit 10. In addition For example, a voltage regulation circuit 1 1, a polarity reversal protection circuit 12, an overvoltage protection circuit 13, a capacitor 14 and a resistor 15 are provided. The capacitor 14 buffers the recovered energy due to the inductive load of the stator coils (see FIG.2). The resistor 15 has a low value and ensures that the current flowing through the resistor 15 to the ground terminal can be amplified by the voltage amplifier circuit 10. The polarity reversal protection circuit 12 ensures that an incorrectly polarized supply voltage Vref does not damage the lighting device 2. The voltage regulation circuit 1 1 controls the voltage applied to the control circuit 6 to a certain value. The

Overvoltage protection circuit 13 ensures that the driver circuit 7 is not damaged by overvoltages. The control circuit 6 controls the driver circuit 7 depending on the signals from the voltage comparator circuit 9 or the voltage amplifier circuit 10. The driver circuit 7 applies voltages to the switching transistors of the switching device 9 to open or close the switching transistors.

FIG. 2 shows a detailed view of the DC motor 1 and the associated switching device 8 from FIG. 1. The DC motor includes an iron core

16 with six core projections 17, which are each offset by 60 ° and about each one of the stator coils u, v, w, u ', v' or w 'is wound. The stator coils u and u ', v and v', w and w 'respectively form stator coil pairs uu', vv 'and ww' of two stator coils connected in series. The two stator coils of a stator coil pair uu ', vv' and ww 'are each offset by 180 °. The one end of each stator coil pair uu ', vv' and ww 'is connected to two switching transistors T1 and T2, T3 and T4 and T5 and T6, respectively, which are closed or opened by the driver circuit 7. The switching transistors T1, T3 and T5 respectively connect or disconnect the stator coil pairs uu ', vv' and ww 'with a high voltage potential Vref. The switching transistors T2, T4 and T6 respectively connect or disconnect the stator coil pairs uu ', vv' and ww 'with a low voltage potential at a node 25. The other ends of each stator coil pair uu ', vv' and ww 'are connected to each other. A rotor 26 with two permanent magnets 27 is in the rotational position αel = 0 °. At this

Arrangement corresponds to an electrical angle αel = 360 ° mechanical Angle αmec = 180 °, that is, each of the stator coils u, u \ v, v ', w and w' is exactly twice twice magnetic poles with a certain polarity in a full rotation of the rotor 26. While the magnetic poles having the one polarity S are formed on the outside of the permanent magnets 27, the magnetic poles of the opposite polarity N are between them

Permanent magnet 27 is formed. Such a DC motor is known by the name "consequent pole motor." The switching transistor T1 is intended to be switched on for an electrical angle of αel = 30 ° to 150 ° C. The switching transistor T2 is intended for an electrical angle of αel = 210 The switching transistor T3 is intended to be switched on for an electrical angle of αel = 150 ° to 270 ° The switching transistor T4 is to be switched on for an electrical angle of αel = 330 ° to 90 ° The switching transistor T6 should be switched on for an electrical angle of αel = 90 ° to 210 °, so there should always be exactly two

Transistors are turned on, so that the current flows through two pairs of stator coils.

FIG. 3 shows a view of the voltage comparator circuit 9 of FIG. 1. The voltage comparator circuit 9 comprises three identically formed

Comparator circuits 18, 19 and 20, wherein each of the comparator circuits 18, 19 and 20 compares the voltage applied to the power line 3, 4 and 5, respectively, of one of the stator coil pairs uu ', vv' and ww ', to a voltage applied to one Star point 21 is applied and depends on all voltages that are applied to the power lines 3, 4 and 5 respectively. Each of the comparator circuits comprises a plurality of resistors R1, R2, R3, R4 and R5, a plurality of capacitors C1, C2 and C3 and an operational amplifier OP1. As already noted, in normal operation only two pairs of stator coils are alternately energized. The voltage across the two energized stator coils are opposite and equal in magnitude, when the induced voltage at the third non-energized stator coil has its zero crossing. Therefore, at a node 21 at zero crossing, an internal voltage of 0 V is applied (the internal voltage of 0 V is here defined as Vref / 2). At zero crossing, the voltage also changes sign. Accordingly, the sign of the voltage at the output 22, 23, or 24 of the respective changes

Operational amplifier OP1, which belongs to the third non-energized coil. The Voltages at the nodes 22, 23 and 24 are supplied to the control circuit 6.

FIG. 4 shows a view of the voltage amplifier circuit 10 of FIG. 1 . The voltage amplifier circuit 10 comprises a plurality of resistors R6, R7, R8,

R9, R10 and R1 1, a capacitor C4 and two operational amplifiers OP2 and OP3. The resistors R8 and R1 1 and R10 and R9 are each the same size. Nodes 25, 28 and 29 are also shown in FIG. 1 drawn. The resistors R6 and R7 are also the same size, so that at the non-inverting input of the operational amplifier OP2 and at the output of the

Operational amplifier OP2 voltage Vref / 2 (internal voltage of 0 V) is applied. When an identical voltage is applied to the node 25 and the node, no current flows through the resistor 15 (see Fig. 1), and there is also an internal voltage of 0V at the node 28. The operational amplifier OP3 is connected as an inverting amplifier, so that at the output of the operational amplifier OP3 (node 28) a proportional voltage corresponding to the current direction across R15 is applied, as is necessary for the operation of the control circuit 6.

During startup, the normal operation of the DC motor 1 is interrupted at a low speed by test pauses. In the test pauses, two opposite voltage pulses are applied to each of the pairs of stator coils uu ', vv' and ww 'shortly after one another. The voltage pulses are all the same length and have the same amplitude. By applying two opposite voltage pulses possible offset errors are compensated. In addition, the movement of the rotor 26 is hardly affected. For the stator coil pair uu ', the transistors T1, T4 and T6 are turned on during the first voltage pulse and the transistors T2, T3 and T5 are switched on during the second voltage pulse. Each of the voltage pulses has a duration of a few 100 μs. The rotor 26 is therefore almost in the same rotational position during the entire test break. For the stator coil pair vv ', the transistors T3, T2 and T6 are turned on during the first voltage pulse and the transistors T4, T1 and T5 are turned on during the second voltage pulse. For the stator coil pair ww 'during the first voltage pulse, the

Transistors T5, T2 and T4 are switched on and during the second voltage pulses, the transistors T6, T1 and T3 turned on. It therefore flows through a Statorspulenpaar each of the entire current, which then splits to the two other Statorspulenpaare. FIG. 5A, FIG. 5B and FIG. 5C show views of the DC motor 1 for the electrical angle αel = 0 °, for the electrical angle αel = 120 ° and for the electrical angle αel = 240 °, the magnetic field line course of the magnetic field being drawn from the energized stator coil pair uu ' is produced. Depending on the rotational position of the rotor 26, the magnetic field lines penetrate the permanent magnets 27 more or less. As a result, the inductance of the stator coil pair uu 'changes. For the rotational position αel = 0 °, the current increases in the

Statorspulenpaar uu 'for the voltage pulse quickly on, while the current for the rotational positions αel = 120 ° and αel = 240 ° less rapidly increases. A voltage value proportional to the current value is supplied to the control circuit 6. The control circuit 6 determines whether or not the rotor 26 is at the rotational position αel = 0 °. Analog can the

Control circuit 6 also determine whether the rotor 26 is at the rotational position αel = 120 ° or αel = 240 ° or not. To determine the rotational position, the control circuit 6 first determines the magnitudes of the current increases for the first voltage pulse and the second voltage pulse of each stator coil pair uu ', vv' and ww '. The control circuit 6 then sums the two amounts for each stator coil pair to a summing current increase. The control circuit 6 then determines the maximum summed current increase of the three summed current increases and the average of the other two summed current increases. The control circuit 6 subtracts the average of the two other summed current increases from the maximum summed current increase and compares the subtraction result with a threshold value. If the subtraction result is greater than the threshold, this indicates that the rotor 26 is in the rotational position in which the stator coils through which the currents flow at the maximum summed current increase are located. By a suitable selection of the threshold value, the angular range of this rotational position can be restricted or increased. From the detected rotational position (s), the control circuit 6 calculates when the rotor 26 is at a rotational position at which one of the transistors T1 to T6 is to be turned on or off. The control circuit 6 now causes the driver circuit 7, the

Transistors T1 to T6 turn on or off as desired at certain rotational positions off. The test pauses are repeated continuously in the low speed range. The time interval of the test pauses is thereby continuously reduced in order to adapt the determination of the rotational position to the increased rotational speed. After a certain time, the DC motor 2 has reached a high speed (> 500 rpm). The fast rotating magnetic field of the

Rotor 26 can now induce a measurable voltage in the stator coil pairs uu \ vv 'or ww'. The zero crossings of these induced voltages are recognized by control circuit 6 as changing the sign of the voltages at outputs 22, 23, and 24, respectively. Interrupting the normal operation of the DC motor to detect the rotational position of the rotor is not required. These zero crossings each correspond to a certain electrical angle αel. FIG. 6 shows the amplitude of the induced voltage as a function of the electrical angle. From the continuously detected zero crossings, the control circuit 6 calculates the rotational speed and concludes from the rotational speed and the determined electrical angles αel when the rotor 26 is at a rotational position at which one of the transistors T1 to T6 is to be turned on or off. In this case, the control circuit 6 uses only sharply defined magnetic poles as formed in front of the permanent magnets 27 (poles S in FIG.2) but not between the permanent magnets 27 (poles N in FIG.2). To determine the speed, the control circuit 6 also preferably compares zero crossings, each corresponding to a complete rotation of the rotor 26 by 360 ° and thus belong to a particular magnetic pole. In this case, the control circuit analyzes the zero crossings, which belong to both sharply defined magnetic poles, to determine from as many data as possible a functional dependence of the rotational position of the rotor 26 on time. These two sharply defined magnetic poles are offset by one turn of the rotor by 180 °. The control circuit 6 now causes the driver circuit to turn on or off the transistors T1 to T6 as desired at certain rotational positions.

Claims

claims

A DC motor having a rotor (26) having at least one permanent magnet (27) and a stator (16) having at least three stator coils (u, u ', v, v', w, w '), wherein a Control device (6) is provided, which is adapted to determine a rotational position of the rotor (26) and an energization of the stator coils (u, u ', v, v', w, w ') depending on the rotational position of the rotor (26) and wherein the control device (6) is arranged to determine the rotational position in a high speed range based on a voltage in one of the

Stators (u, u ', v, v', w, w ') is induced, characterized in that the control device (6) is arranged, the rotational position in a low speed range based on a current when applying a voltage to one of the stator coils ( u, u ', v, v', w, w ').

2. A method of operating a DC motor having a rotor (26) having at least one permanent magnet (27), and a stator (16) having at least three stator coils (u, u ', v, v', w, w ') wherein the energization of the stator coils (u, u ', v, v', w, w ') is switched in response to a rotational position of the rotor (26) to drive the rotor (26), the DC motor being of a low speed range goes to a high speed range, wherein the rotational position of the rotor (26) is determined in the high speed range by means of a voltage which is induced in one of the stator coils (u, u ', v, v', w, w '), characterized by the following steps in a low speed range:

- applying a voltage to one of the stator coils (u, u ', v, v', w, w ');

Determining a current at the one of the stator coils (u, u ', v, v', w, w ');

- Determining the rotor position based on the course of the current; and

- energizing the stator coils (u, u ', v, v', w, w ') as a function of the detected rotational position.

3. The method according to claim 2, characterized in that at the at least one further stator coil (u, u ', v, v', w, w '), a voltage is applied, that a further current to the at least one further stator coil (u , u ', v, v', w, w ') is determined, and that the rotational position is determined by the course of the further current.

4. The method according to claim 3, characterized in that the applied voltages are voltage pulses.

5. The method according to any one of claims 4, characterized in that the

Voltage pulses are applied repeatedly, and that the time interval between the repeated application of the voltage pulses decreases.

6. The method according to any one of claims 3 to 5, characterized in that the applied voltages are reversed, that currents at the stator coils

(u, u ', v, v', w, w ') are determined for the polarity reversed voltages, and that determines the rotational position based on the course of the currents for the polarity reversed voltages.

7. The method according to any one of claims 3 to 6, characterized in that the amounts of the current increases at each stator coil (u, u ', v, v', w, w ') for the voltage and for the polarized voltage in each case to a summed current increase, the maximum summed current increase is compared with the other current rises to determine the rotational position.

8. The method according to any one of claims 2 to 7, characterized in that in the high speed range for determining the speed identical voltage values of the voltage in the one of the stator coils (u, u ', v, v', w, w ') can be determined for a multiple of the electrical angle of 360 °.