Sensorless block commutation

Abstract

A method for sensorless block commutation of a brushless DC motor is disclosed in which, within the scope of the method, a current sensor for detecting a current flowing through the DC motor, a detection circuit for detecting a zero crossing of a back electromotive force, and a control unit are used, the control unit is adapted to provide block control signals and position detection signals for a motor inverter assigned to the DC motor based on the detected current and / or zero crossing of the back electromotive force, where the block control signals are used to generate a propulsive force in order to drive a rotor of the DC motor in rotation, and where the position detection signals are used to detect the position of the motor inverter assigned to the DC motor. The position detection signals are used to detect the rotor position of the rotor, and wherein the DC motor passes through a plurality of rotor position sectors in a start-up phase before reaching a normal operating phase, and the control unit outputs only the position detection signals to the motor inverter in the start-up phase.

Description

Technical Field

[0001] The invention relates to a method for sensorless block commutation of a brushless DC motor. Within the scope of the method, a current sensor for detecting a current flowing through the DC motor, a detection circuit for detecting a zero crossing of a back electromotive force, and a control unit are used, wherein the control unit is suitable for providing a block control signal and a position detection signal for a motor inverter assigned to the DC motor based on the detected zero crossing of the current and / or the back electromotive force. The block control signal is typically used to generate a propulsion force in order to drive the rotor of the DC motor so that it rotates. The position detection signal is typically used to detect the rotor position of the rotor. Within the scope of the method, the DC motor undergoes a startup phase before reaching a normal operating phase. In practice, it has been shown that during the startup phase, the determination of the zero crossing of the back electromotive force (BEMF zero crossing recognition) as the basis for sensorless block commutation cannot be reliably achieved. Background Art

[0002] Devices and methods for sensorless mass commutation are known in principle from the prior art.

[0003] US 9,819,290 B2 describes an electric tool having a motor and a control unit designed to output detection signals and control signals for an inverter. The control unit determines these block control signals for mode control in the starting phase of the motor based on the position detection current component of the motor current.

[0004] US 11,171,586 B2 discloses an electric tool having a control unit designed to identify an incorrect direction of rotor rotation by applying a plurality of first voltage pulses at the current motor sector and a plurality of second voltage pulses at the previous sector. Summary of the invention

[0005] The object of the present invention is to specify a method for sensorless mass commutation of a DC motor, which method forms the basis for a more accurate tracking of the rotor position of the DC motor.

[0006] This purpose is achieved by the control unit only outputting the position detection signal in the startup phase. In other words, the DC motor rotates only by the position detection current triggered by the position detection signal in the startup phase.

[0007] The present invention comprises the discovery that, with previously known commutation methods, the current signal detected by the current sensor during the start-up phase contains both a control current component and a position detection current component. While this enables high starting torque, it does reduce the accuracy during tracking of the rotor position.

[0008] The invention also includes the finding that changes in the stator inductance can be used in sensorless motor regulation in order to be able to detect and track rotor positions below a limit at which tracking is possible on the basis of BEMF-based methods. In this case, two fundamental physical properties of the motor can be used, namely the saturation effect and / or the saliency effect of the stator. Changes in the current signal detected by the current sensor that are affected by these properties preferably form the basis for the method according to the invention.

[0009] In a particularly preferred configuration, the position detection signal has a plurality of main pulses and a plurality of secondary pulses. It has been found that it is advantageous that the main pulses and the secondary pulses alternate. The main pulses and the secondary pulses may have the same pulse duration. Alternatively, the main pulses and the secondary pulses may have different pulse durations. It has been found that it is advantageous that the same pause times are provided between the transitions from the main pulse to the secondary pulse or from the secondary pulse to the main pulse. Alternatively, correspondingly different pause times may be provided between the transitions from the main pulse to the secondary pulse or from the secondary pulse to the main pulse. An alternating sequence of main pulses and secondary pulses is defined as a pulse sequence.

[0010] In a particularly preferred configuration, the control state assigned to the current rotor position sector is used for the main pulse, and the control state assigned to the rotor position sector following the current rotor position sector in the direction of rotor rotation is used for the secondary pulse.

[0011] In a further particularly preferred configuration, an effective change in the rotor position sector is detected when the absolute value of the main pulse current response to the main pulse detected by the current sensor is greater than the absolute value of the secondary pulse current response to the secondary pulse detected by the current sensor. It has been found to be advantageous that the main pulse current response to the main pulse detected by the current sensor has a commutation current hysteresis compared to the secondary pulse current response to the secondary pulse detected by the current sensor. An effective change in the rotor position sector is only detected when the absolute value of the main pulse current response is greater than the secondary pulse current response caused by the commutation current hysteresis. This commutation current hysteresis can be adjustable. In a particularly preferred configuration of the method, it is provided that a preferably adjustable pause time is waited after the detection of the effective change in the rotor position sector, during which the motor phase current completely decays. After the pause time, the next pulse sequence is started.

[0012] It has been found to be advantageous that, upon detection of an effective change in the rotor position sector, the control state of the main pulses and the auxiliary pulses is incremented or decremented, i.e. switched to the corresponding next rotor position sector. It has been found to be advantageous that the switchover only occurs when a minimum number of main pulses and / or auxiliary pulses per pulse sequence has been input. Alternatively or additionally, it can be provided that the switchover only occurs when a maximum number of pulse inputs of the main pulses and / or auxiliary pulses per pulse sequence has not been exceeded. In a further particularly preferred configuration, the current rotor speed itself is determined in each case over the input time period of the pulse sequence. Each pulse sequence can be valid for a rotor position sector (preferably 60°). From these two pieces of information, the mechanical speed can be uniquely determined knowing the number of pole pairs of the motor.

[0013] In a further particularly preferred configuration, it is provided that a direction detection pulse is output once as the position detection signal if a valid change in the rotor position sector is detected, wherein the control state assigned to the rotor position sector directly preceding the current rotor position sector in the direction of rotor rotation is used for the direction detection pulse.

[0014] In a particularly preferred arrangement, at the beginning of the start-up phase, when the rotor is stationary, an initial rotor position detection occurs which produces no resultant rotor torque.

[0015] It has been found that, advantageously, the normal operation phase begins as soon as the rotor speed reaches a value in the range of 1000 rpm to 3000 rpm. In a particularly preferred configuration, commutation of the brushless DC motor in the normal operation phase takes place exclusively by block commutation. In another particularly preferred configuration, commutation of the DC motor in the normal operation phase takes place based on determining a zero crossing of the back electromotive force.

[0016] This object is also achieved by an electric handheld power tool, which has a brushless DC motor, a current sensor for detecting the current flowing through the DC motor, a detection circuit for detecting the zero crossing of the back electromotive force, and a control unit. The control unit is designed to provide a block control signal and a position detection signal to a motor inverter assigned to the DC motor based on the detected zero crossing of the current and / or the back electromotive force, wherein these block control signals are used to generate a propulsion force so as to drive the rotor of the DC motor to rotate, and these position detection signals are used to detect the rotor position of the rotor. The DC motor is also designed to pass through multiple rotor position sectors in the startup phase before reaching the normal operation phase. According to the present invention, the control unit is designed to output only the position detection signal to the motor inverter in the startup phase.

[0017] An electric handheld power tool can be developed in a corresponding manner by referring to the features described for the method.The method according to the invention can also be implemented in other devices equipped with a brushless DC motor, such as a vacuum cleaner or a chipping hammer.

[0018] In a particularly preferred configuration, the brushless DC motor has a three-phase design and has six sectors in the electrical reference system, each with 60°. Correspondingly, the motor inverter is configured for commutation of the three-phase DC motor. This motor inverter therefore has three half-bridges, each with two power semiconductors. It has been found that it is advantageous that the brushless DC motor is connected in a delta. Alternatively, the brushless DC motor can be connected in a star. Further advantages arise from the following description of the drawings. Different exemplary embodiments of the invention are shown in the drawings. The drawings, the description and the claims contain many combined features. Those skilled in the art will also conveniently consider these features individually and combine them to form reasonable further combinations. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the figures, identical and functionally identical parts are denoted by the same reference numerals. In the figures:

[0020] Figure 1 A first exemplary embodiment of a handheld power tool according to the present invention is shown;

[0021] Figure 2 A first exemplary embodiment of a method according to the invention is shown;

[0022] Figure 3 A second exemplary embodiment of a method according to the invention is shown;

[0023] Figure 4 Shows Figure 2 Initial rotor position detection in the method of; and

[0024] Figure 5 An alternative method for initial rotor position detection is shown. DETAILED DESCRIPTION

[0025] Figure 1 An electric hand-held power tool 100 is shown in highly schematic form. The hand-held power tool 100 is equipped with a brushless DC motor 90. The brushless DC motor 90 has a three-phase design and has a rotor 95 with six rotor position sectors I, II, III, IV, V, VI, each with 60°. A current sensor 80 for detecting the current flowing through the DC motor 90 is assigned to the DC motor 90. In addition, a circuit 70 for zero crossing recognition of the back electromotive force is provided.

[0026] The motor inverter 20 is connected upstream of the DC motor 90 and has six FETs (field effect transistors) in this case, wherein two FETs are provided per phase U, V, W in each case. The electric handheld power tool 100 also has a control unit 10, which is designed to provide a block control signal and a position detection signal to the motor inverter 20 based on the zero crossing of the current and / or the back electromotive force detected by means of the current sensor 80. The block control signal is used to generate a propulsion force (in a manner known in the prior art) in order to drive the rotor 95 to rotate. The position detection signal is used to detect the rotor position of the rotor 95. According to the invention, the control unit 10 is designed to output only the position detection signal to the motor inverter 20 during the starting phase (i.e., for example, the speed of the DC motor is up to 2000 rpm), which will be explained more precisely with reference to the following figures.

[0027] Figure 2 The phase currents A, B, and C (corresponding to Figure 1 The characteristic diagram of the phase U, V, W in the rotor changing with time. The diagram is divided into the initial position detection / stationary phase IPD / RPH, the startup phase APH and the normal operation phase NPH. During the initial position detection / stationary phase IPD / RPH, the rotor is at rest. This will be referred to later Figure 4 and Figure 5 Explain the initial rotor position detection more precisely.

[0028] In the startup phase APH, which follows the initial position detection and lasts up to about 30 milliseconds, for example, the determination of the zero crossing of the back electromotive force (BEMF zero crossing detection) cannot be reliably achieved as the basis for the sensorless block commutation of the DC motor 90. The present invention starts from this and provides that the control unit outputs only the position detection signal to the motor inverter in the startup phase APH.

[0029] Within the scope of this method, two voltage pulses (i.e., a main pulse and a secondary pulse) are alternately input to the motor inverter 20 as position detection signals, and the resultant current amplitude is detected and compared. Therefore, this method can also be called a "2-pulse acceleration method." With the help of the input main pulse and secondary pulse, a resultant torque is generated to mobilize the rotor to rotate.

[0030] Correspondingly, Figure 2The figure in shows that the main pulse current response I (P1) alternates with the auxiliary pulse current response I (P2). The control state of the motor inverter assigned to the current rotor position sector is used for the main pulse. The control state assigned to the next rotor position sector immediately following the current rotor position sector in the direction of rotor rotation is used for the auxiliary pulse. The main pulse current response I (P1) and the auxiliary pulse current response I (P2) vary with the rotor position, which can be attributed to the saturation effect or salient pole effect mentioned at the beginning.

[0031] If the main pulse current response I(P1) of the main pulse has a larger amplitude than the secondary pulse current response I(P2) of the secondary pulse, the rotor is in the next rotor position sector. Here, for reasons of robustness, an adjustable commutation current hysteresis IHys is additionally used and applied to the secondary pulse current response I(P2). Accordingly, when the condition that main pulse current response I(P1)>secondary pulse current response I(P2)+commutation current hysteresis IHys is met, a valid change in the rotor position sector is detected. If such a valid change in the rotor position sector is detected, the control state of the main pulse and the secondary pulse is incremented or decremented. A first pulse sequence PS1 is obtained. Then, an adjustable pause time TPS is waited. In this pause time TPS, the motor phase current needs to be completely decayed, such as Figure 2 If the pause time TPS has elapsed, the next pulse sequence, in this case the second pulse sequence PS2, begins. Figure 2 In the start-up phase (APH) shown, there are eight pulse trains. At the end of the eighth pulse train PS8, there is a switching time (UP) at which the normal operation phase (NPH) of the DC motor begins. From this switching time (UP), the commutation of the brushless DC motor is performed only by block commutation. The commutation of the DC motor in the normal operation phase occurs based on determining the zero crossing of the back EMF.

[0032] Figure 3 shows the so-called "3-pulse acceleration method", in which, in addition to the reference Figure 2 In addition to the method described, a direction detection pulse is output to the motor inverter once per pulse train (PS) as a position detection signal. This direction detection pulse affects in each case Figure 3 The direction detection pulse current response I(P3) shown in FIG. In each case, a control state is assigned to the rotor position sector directly preceding the current rotor position sector in the direction of rotor rotation for the direction detection pulse. Figure 2 Description, a direction detection pulse is input in each case when a valid change of the rotor position sector is detected.

[0033] If the direction detection pulse current response I(P3) of the direction detection pulse has a larger amplitude than the main pulse current response I(P1) of the last measured main pulse, the rotor rotates in the desired direction. Here, for reasons of robustness, an adjustable directional current hysteresis IHysRi is additionally used and applied to the main pulse current response I(P1). Accordingly, when the condition of direction detection pulse current response I(P3)>main pulse current response I(P1)+directional current hysteresis IHysRi is met, the rotation of the rotor in the desired rotation direction is detected. Otherwise, the rotor rotates in an undesired rotation direction.

[0034] refer to Figure 2 and Figure 3 The described method can be supplemented in each case by an initial rotor position detection. Figure 4 and Figure 5 Give a more precise explanation of this.

[0035] Figure 4 and Figure 5 Each shows the phase currents A, B, C (corresponding to Figure 1 The initial rotor position detection occurs in the stationary phase RPH, which precedes the starting phase APH in time (see Figure 2 and Figure 3 ). In the stationary phase RPH, the rotor is at rest.

[0036] Initial rotor position detection preferably occurs in such a way that in each case pairs of opposite control states are input so that no resultant torque is produced on average.After a pulse is input, a pause time is provided so that the induced current can decay completely before the next pulse is input.

[0037] In the case of the initial rotor position detection, the same physical characteristics are preferably used, which also appear in the startup phase APH. In the case of the initial rotor position detection, it can be said that the difference in the current response of the input voltage pulse is used in order to be able to draw conclusions about the initial rotor position. However, in the case of a specific rotor position, more precisely in the case of the sector limit of the detection, there is an angular uncertainty of 60° (rotor position sector). At these positions, the measurement noise of the current measurement may have led to an erroneous detection of the initial rotor position by the rotor position sector. It has been found to be advantageous that, in order to minimize the frequency of erroneous determination of the initial rotor position, the stationary position of the brushless DC motor does not correspond to the detection sector limit of the method. This may be because the magnetic system of the DC motor strives to obtain the lowest magnetic resistance (reluctance), and this is met at the magnetic stationary position of the motor. Therefore, the stationary position represents the most frequent rotor position during the initial rotor position detection. In addition, the orientation of the voltage phasors of these inputs is determined by the (star or triangle) connection of the motor. The orientation of the input voltage phasors differs by 30° between the star connection and the triangle connection.

[0038] The method according to the invention and / or the device according to the invention can envisage the use of 3-FET block commutation or 2-FET block commutation, depending on the electrical connection (star or triangle) of the brushless DC motor. The two control systems differ from each other in that they have different control states and therefore input voltage pulses that differ by 30°. As a result, the differences in the connection can be compensated. The detection limit can therefore always be separated from the magnetic rest position. This provides the advantage that the above-mentioned detection algorithm can remain unchanged. In this regard, the invention includes the discovery that different control states are used in order to separate the detection limit of the method from the magnetic rest position of the motor, depending on the connection.

[0039] Figure 4 The initial rotor position detection for a star-connected brushless DC motor with a three-phase design and 6 sectors with 60° each in the electrical reference system is shown. For this motor connection, it is advantageous if the motor inverter has three active power semiconductors (3-FET) during the position detection pulse in the case of the initial rotor position detection.

[0040] Figure 5 The initial rotor position detection for a delta-connected brushless DC motor with a three-phase design and 6 sectors with 60° each in the electrical reference system is shown. For this motor connection, it is advantageous if the motor inverter has two active power semiconductors (2-FET) during the position detection pulse in the case of the initial rotor position detection.

[0041] List of Reference Numerals

[0042] 10Control Unit

[0043] 20 Motor Inverter

[0044] 70BEMF zero-crossing detection circuit

[0045] 80 Current Sensor

[0046] 90 Brushless DC Motor (BLDC Motor)

[0047] 95 rotor

[0048] 100 Electric Handheld Power Tools

[0049] I, II…VI rotor position sectors

[0050] IPD Initial Rotor Position Detection

[0051] APH startup phase

[0052] I(P1) Main pulse current response

[0053] I(P2) secondary pulse current response

[0054] I (P3) direction detection pulse current response

[0055] IHys commutation current hysteresis

[0056] IHysRi Directional Current Hysteresis

[0057] NPH normal operation stage

[0058] RPH static phase

[0059] PS1, PS2 pulse sequences

[0060] Phase of U, V, WDC motor

[0061] UP switching time

[0062] TPs pause time

Claims

1. A method for sensorless block commutation of a brushless DC motor (90), wherein: Within the scope of the method, a current sensor (80) for detecting a current flowing through the DC motor (90), a detection circuit (70) for detecting a zero crossing of a back electromotive force, and a control unit (10) are used, wherein the control unit (10) is suitable for providing a block control signal and a position detection signal to a motor inverter (20) assigned to the DC motor (90) based on the detected current and / or the zero crossing of the back electromotive force, wherein the block control signals are used to generate a propulsion force in order to drive a rotor (95) of the DC motor (90) to rotate, and the position detection signals are used to detect the rotor position of the rotor (95), and wherein the DC motor (90) passes through a plurality of rotor position sectors in a starting phase (APH) before reaching a normal operating phase (NPH), The invention is characterized in that the control unit (10) only outputs the position detection signal to the motor inverter (20) during the startup phase (APH).

2. The method according to claim 1, It is characterized in that These position detection signals have a single or multiple main pulses and a single or multiple sub-pulses.

3. The method according to claim 2, It is characterized in that The main pulse and the sub-pulse alternate.

4. The method according to claim 2 or 3, It is characterized in that The control state assigned to the current rotor position sector is used for the main pulse, and the control state assigned to the next rotor position sector following the current rotor position sector in the direction of rotor rotation is used for the secondary pulse.

5. The method according to any one of claims 2 to 4, It is characterized in that When the absolute value of the main pulse current response I(P1) to the main pulse detected by the current sensor (80) is greater than the absolute value of the auxiliary pulse current response I(P2) to the auxiliary pulse detected by the current sensor (80), a valid change of the rotor position sector is detected.

6. The method according to claim 5, It is characterized in that If a valid change in the rotor position sector is detected, the control states of the main pulse and the auxiliary pulse are incremented or decremented.

7. The method according to claim 5 or 6, It is characterized in that If a valid change in the rotor position sector is detected, a direction detection pulse (P3) is output once as a position detection signal, wherein the control state assigned to the rotor position sector directly preceding the current rotor position sector in the direction of rotor rotation is used for the direction detection pulse.

8. The method according to at least one of the preceding claims, It is characterized in that At the beginning of the start-up phase (APH), when the rotor (95) is stationary, an initial rotor position detection (IPD) occurs which produces no resultant rotor torque.

9. The method according to at least one of the preceding claims, It is characterized in that Once the rotor speed reaches a value in the range of 1000 rpm to 3000 rpm, the normal operation phase (NPH) begins.

10. The method according to at least one of the preceding claims, It is characterized in that The commutation of the brushless DC motor (90) in the normal operating phase (NPH) is performed only by block commutation.

11. The method according to at least one of the preceding claims, It is characterized in that Commutation of the DC motor (90) in the normal operating phase (NPH) occurs based on detecting the zero crossing of the back electromotive force.

12. An electric handheld power tool (100), comprising a brushless DC motor (90), a current sensor (80) for detecting a current flowing through the DC motor (90), a detection circuit (70) for detecting a zero crossing of a back electromotive force, and a control unit (10), wherein: The control unit (10) is designed to provide a block control signal and a position detection signal to a motor inverter (20) assigned to the DC motor (90) based on the detected zero crossing of the current and / or the back electromotive force, wherein the block control signals are used to generate a propulsion force so as to drive a rotor (95) of the DC motor (90) to rotate, and the position detection signals are used to detect the rotor position of the rotor (95), and wherein the DC motor (90) is designed to pass through a plurality of rotor position sectors (I, II ... VI) in a starting phase (APH) before reaching a normal operating phase (NPH), The invention is characterized in that the control unit (10) is designed to output only the position detection signal to the motor inverter (20) during the startup phase (APH).

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