DE102008027720A1 - Method for sensorless position detection of electrical adjusting or positioning drive, involves determining position of rotor of direct current motor based on specific equation by comparing inductance stored in storage unit - Google Patents

Abstract

The method involves determining inductance of motor strands of a direct current motor (1) i.e. switched reluctance motor, based on a rotary angle of a rotor (3) at switching times of a hysteresis current controller. The inductance is stored in a storage unit in form of a look-up table. Voltage and current of the motor strands are detected. Position of the rotor of the direct current-motor is determined based on a specific equation by comparing the position with the stored inductance. The motor strands of the direct current motor are supplied via a hysteresis current controller.

Description

The The present invention relates to a method for sensorless position detection an electric positioning or positioning drive with a DC motor, the number of independently energisable motor strings and a rotor.

Out The prior art are actuating or positioning drives with DC motors already in many different embodiments known. Frequently, such drives are permanently excited DC motors, brushless DC motors or Also called switched reluctance motors (Engl.: Switched Reluctance Motor, SRM). An important aspect of such Actuators is the location detection, often with the help suitable position sensor means and signal processing means performed becomes.

The DE 198 34 108 C2 discloses a method of determining the number of engine revolutions of an electric motor from current ripples, wherein the motor current comprises a DC component and an AC component. The motor current signal passes through a low-pass filter in this method and is then differentiated. The method disclosed in the cited document is characterized in that a time interval is determined and that the difference values between successive minimum and maximum values of the differentiated, low-pass filtered motor current are calculated within the time interval. The difference values within the time interval are stored and the ripple are determined from the stored difference values. Finally, the length of the time interval is adjusted in dependence on the previous detected ripples.

Around the manufacture and operation of a positioning or positioning drive It is common to simplify with a DC motor desirable to a position sensor for detecting the position waive the positioning or positioning drive to Kings NEN. Then both the commutation time as well the position signal of the positioning or positioning drive from the motor string sizes of the DC motor can be determined. Even at high speeds a continuous situation survey is carried out, increases the power requirement of signal processing relatively strong. When the speed increases, the drive instead of the regulated Operation with position detection operated as a controlled stepper motor, There is a risk that a step is not reliable is executed, but not registered by the controller becomes.

Here uses the present invention.

Of the The present invention is based on the object, a method for sensorless position detection of an electric actuator or Positioning drive of the type mentioned above available to provide, which allows a reliable position detection and is particularly suitable for drives in which the DC motor rotor-dependent strand inductance having.

These Task is by a method of the type mentioned with the features of claim 1 solved. The dependent claims relate to advantageous developments of the invention.

• – die Induktivität L(φ, I) der Motorstränge in Abhängigkeit vom Drehwinkel φ des Rotors bestimmt und in einem Speichermittel gespeichert wird,
• – die Spannung U(t) und der Strom I(t) mindestens eines der Motorstränge erfasst werden,
• – die Position des Rotors des Gleichstrommotors anhand der Gleichung L(φ, I) = (U(t) – R·I(t)): dI(t) / dt durch einen Vergleich mit der im Speichermittel gespeicherten Induktivität L(φ, I) bestimmt wird.

According to claim 1, an inventive method for sensorless position detection of an electric positioning or positioning drive with a DC motor, which has a number of independently energisable motor strands and a rotor, characterized in that

• The inductance L (φ, I) of the motor strands is determined as a function of the angle of rotation φ of the rotor and stored in a storage means,
• The voltage U (t) and the current I (t) of at least one of the motor strings are detected,
• The position of the rotor of the DC motor is determined by the equation L (φ, I) = (U (t) -R * I (t)): dI (t) / dt by comparison with the inductance L (φ, I) is determined.

The method presented here is suitable for an accurate detection of the position of the positioning or positioning drive. It can be used in particular in positioning or positioning drives, in which the DC motor has a rotor position-dependent strand inductance. The motor strings of the DC motor are energized in operation in succession to effect the desired movement of the rotor within the stator. In the method according to the invention, the position detection of the positioning or positioning drive takes place on the basis of the differential equation of a motor train which, assuming that the mutual inductance of the stator coils of the DC motor is low, initially has the following shape:

In In this equation, U (t) denotes the voltage, I (t) the current, R the resistance and L (φ, I) the inductance of a Motor strand, where φ is the angle of rotation of the rotor of the DC motor and t is the time. From this equation it becomes clear that the applied voltage U (t) is divided into a total of four parts. there ensures the effective resistance of the winding for a voltage drop, if it is traversed by a stream. If the rotor of the DC motor rotates, the inductance of the affected changes Engine train.

The equation simplifies on the assumption that the inductance L (φ, I) changes only slightly by avoiding saturation effects in the motor parts (∂L (φ, I) / ∂I ≈ 0) and the process only at standstill or at low speeds (preferably below the basic speed of the DC motor) relationship, or low angular velocities ω = dφ / dt ≈ 0 of the DC motor is executed, to:

In this equation, the inductance L (φ, I) is thus the only angle-dependent variable, so that the position of the positioning or positioning drive by determining the remaining terms of the equation by measuring the voltage U (t) and the current I (t) a motor string can be determined. The following applies:

Consequently it becomes clear that the position of the rotor of the DC motor with the help of the method presented here with knowledge of the resistance R by measuring the voltage U (t) and the current I (t) and determined by a determination of the temporal change of the current dI (t) / dt can be. The calculated inductance L (φ, I) can with the predetermined and stored in a storage means Inductance L (φ, I) are compared to thereby to reliably determine the position of the rotor.

In a particularly preferred embodiment is provided that during standstill of the DC motor all Motor strands of the DC motor simultaneously with a DC voltage are excited and then one of the Motor strands for determining the initial position of the rotor is selected. The excitement of the motor strands preferably takes place over a comparatively short time Period that is small enough to no significant torque to create. In doing so, the current passing through each of the motor strands becomes flows, measured and that engine train determined by the largest current flows. One to this Engine train adjacent engine train can then be used for position detection of the rotor used according to the principle explained above become. In an advantageous embodiment, it is provided that during the rotation of the rotor always one of the motor strands of the DC motor is selected to determine the position of the rotor becomes.

There the position of the positioning or positioning drive with the aid of here explained method in a simple and accurate manner can determine a position-controlled operation of the drive be performed. To the effort for the signal processing kept as low as possible, the regulated operation takes place the positioning or positioning preferably only during the initial orientation and when reaching the final position. Travels that exceed a full step, are advantageously carried out in controlled operation.

So that a step loss can be detected reliably, the position-dependent inductance of the motor strands is evaluated in a stepping operation of the DC motor in a particularly preferred embodiment at the beginning and at the end of each step. A simplification of this measurement results from the fact that the energization of the motor strands of a DC motor is usually block-shaped. This can advantageously be achieved with a hysteresis current regulator. A hysteresis current controller switches the current in a motor string in case of deviations from the setpoint by a certain preset or presettable amount on or off. When the inductance changes as the rotor of the DC motor rotates, so do the times between the individual switching operations of the hysteresis current regulator, since a large inductance increases the current more slowly and decreases than a small inductance and vice versa. The time between two switching operations at the beginning and at the end of a step must therefore change by a value to be determined. Otherwise, it can be assumed that the step is not completed was led. In a particularly preferred embodiment, it is proposed that the position-dependent inductance L (φ, I) is determined via the switching times of the hysteresis current regulator. The evaluation of the switching times of the Hysteresestromreglers can be used in a particularly advantageous embodiment for a continuous position determination of the positioning or positioning who the. This embodiment requires a relatively small amount of logic and is easy to integrate. The limit may be obtained at a high step frequency, so that the method described above can be used in addition.

Around the method for position detection of the positioning and positioning drive Making it more efficient will result in a particularly advantageous Embodiment proposed that the position-dependent Inductance L (φ, I) in the form of a look-up table is stored in the storage means.

Based In the accompanying drawings, the invention will be described below explained in more detail.

there shows:

1 a schematic representation of a DC motor, which is designed as a switched reluctance motor;

2 a graph of the inductance of the stator windings as a function of the rotor position of the switched reluctance motor according to 1 ,

With reference to 1 and 2 is a method for sensorless position detection of an electric positioning or positioning drive with a DC motor 1 according to a preferred embodiment of the present invention will be explained in more detail. In 1 is first a DC motor 1 schematically shown greatly simplified, which is suitable for carrying out such a method and in this embodiment is a so-called switched reluctance motor (SRM).

The DC motor 1 has a stand 2 and a rotor (runner) 3 on that inside the stand 2 is rotatably mounted. Both the stand 2 as well as the rotor 3 are relatively strongly grooved in a switched reluctance motor. In the embodiment shown here, the stand comprises 2 a total of six teeth 20 . 20 ' . 21 . 21 ' . 22 . 22 ' , each with a coil 4 are wrapped. Two diagonally opposite teeth 20 . 20 ' . 21 . 21 ' . 22 . 22 ' and the associated coils 4 each form an energisable motor train of the DC motor 1 , The DC motor 1 thus has a total of three motor strings, which during operation of the DC motor 1 can be energized independently of each other.

The rotor 3 of the DC motor 1 has no coils and no permanent magnets and has in this embodiment a total of four teeth 30 . 31 . 32 . 33 on. Based on the illustration in 1 it becomes clear that the numbers of teeth of the stand 2 and the rotor 3 are different in a switched reluctance motor. It depends on the ratio of the number of teeth of the stand 2 to the number of teeth of the rotor 3 from, which in the embodiment shown here is six to four, in which direction the rotor 3 rotates relative to the direction of movement of the rotating stator field. Is the ratio of the number of teeth of the stand 3 to the number of teeth of the rotor 3 as in the embodiment shown here is greater than one, so the rotor moves 3 opposite to the direction of movement of the rotating stator field. The in 1 illustrated DC motor 1 thus rotates clockwise (indicated by an arrow) when the stator field rotates counterclockwise. The three motor strings each generate a torque pulse when one of the teeth 30 . 31 . 32 . 33 of the rotor 3 during operation of the DC motor 1 passed them.

When carrying out the method presented here for sensorless position detection of the electric positioning or positioning drive with the in 1 illustrated DC motor 1 In advance, the inductance L (φ, I) of the motor strands of the DC motor 1 in dependence on the angle of rotation φ of the rotor 3 determined and stored in a storage means - preferably in the form of a look-up table - stored. The position-dependent inductance L (φ, I) is in 2 depending on the angle of rotation of the rotor 3 shown. It can be seen that the inductance L (φ, I) has a rising edge and a falling edge. Preferably, the falling edge of the inductance L (φ, I) for the position determination of the rotor 3 used.

For determining the angle of rotation of the rotor 3 the voltage U (t) and the current I (t) are detected. Based on the following equation, but only during standstill or at low speeds (preferably below the basic speed of the DC motor 1 ) is valid, the position of the rotor 3 of the DC motor 1 be determined with knowledge of the resistance R.

In the above-mentioned equation, the inductance L (φ, I) is the only angle-dependent variable, so that the position of the positioning or positioning drive by determining the remaining terms of the equation by measuring the voltage U (t) and the current I ( t) can be determined. The following applies:

The position of the rotor 3 of the DC motor 1 can therefore be determined by measuring the voltage U (t) and the current I (t) and by determining the change over time of the current dI (t) / dt. In this case, by means of the above-mentioned equation, the inductance L (φ, I) is calculated and compared with the inductance L (φ, I) stored in the storage means, so that the position of the rotor 3 can be determined with high accuracy.

To find the optimal engine train for determining the position of the rotor 3 during the standstill of the DC motor 1 First, select all three motor strands of the stator 2 over a comparatively short period of time, small enough to produce no appreciable torque, simultaneously energized with a DC voltage. The current I (t) flowing through each of the three motor strings is measured. In this case, the one of the three motor strings is determined, through which the largest current I (t) flows. In the in 1 illustrated position of the rotor 3 inside the stand 2 this is the one through the two diagonally opposite teeth 20 . 20 ' formed first engine train, there none of the four teeth 30 . 31 . 32 . 33 of the rotor 3 with one of the teeth 20 . 20 ' of the motor string is aligned. A motor train adjacent to this engine train (in the in 1 shown position of the rotor 3 for example, by the two opposite teeth 21 . 21 ' formed second Mo torstrang) can then for position detection of the rotor 1 be used according to the principle explained above.

Once the initial position of the rotor 3 is known, by a controlled energizing the coils 4 of the stand 2 the rotor 3 be set in motion. To avoid step loss due to the mechanical inertia of the engine, transmission and load, both when starting and when braking the DC motor 1 a ramp function are traversed. For continuous torque generation in the in 1 illustrated DC motor 1 With a total of three motor strings, one of the three motor strings is energized, while the other two motor strings are not energized.

To find the optimal engine train for determining the position of the rotor 3 during rotation, first that one of the three motor strings is determined which carries the largest current I (t). This is the engine train that is responsible for the operation of the DC motor 1 was energized. Then, an adjacent engine train is selected to determine the position of the rotor 3 to determine. For example, the one through the teeth 22 . 22 ' formed third motor string energized to the rotation of the rotor 3 The effect of the teeth 21 . 21 ' formed second motor train for determining the position of the rotor 3 be used during the rotation.

So that a step loss can be detected reliably, the position-dependent inductance of the motor strands in a stepping operation of the DC motor 1 preferably evaluated at the beginning and at the end of each step. A simplification of this measurement results from the fact that the energization of the motor strands of a DC motor 1 mostly block-shaped. This can advantageously be achieved with a hysteresis current regulator. A hysteresis current controller switches the current in a motor string in case of deviations from the setpoint by a certain preset or presettable amount on or off. If the inductance during rotation of the rotor 3 inside the stand 2 changes, so also change the times between the individual switching operations of the hysteresis, since a large inductance increases the current slower and can sink than a small inductance and vice versa. The time between two switching operations at the beginning and at the end of a step must therefore change by a value to be determined. Otherwise, it can be assumed that the step was not executed. It can be provided that the position-dependent inductance L (φ, I) is determined via the switching times of the hysteresis current controller. The evaluation of the switching times of the hysteresis current regulator can also be advantageously used for a continuous position determination of the positioning or positioning drive. This embodiment requires a relative low logic overhead and can be easily integrated.

1

DC motor

2

stand

3

rotor

4

Kitchen sink

20 20 '

teeth a first motor train of the stator

21 21 '

teeth a second engine train of the stator

22 22 '

teeth a third motor train of the stator

30 31, 32, 33

teeth of the rotor

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 19834108 C2 [0003]

Claims (7)

Method for sensorless position detection of an electric positioning or positioning drive with a DC motor ( 1 ), a number of independently energisable motor strings and a rotor ( 3 ), characterized in that - the inductance L (φ, I) of the motor strands in dependence on the rotational angle φ of the rotor ( 3 ) and stored in a memory means, - the voltage U (t) and the current I (t) of at least one of the motor strands are detected, - the position of the rotor ( 3 ) of the DC motor ( 1 ) is determined by means of the equation L (φ, I) = (U (t) -R * I (t)): dI (t) / dt by comparison with the inductance L (φ, I) stored in the storage means. A method according to claim 1, characterized in that during the standstill of the DC motor ( 1 ) all motor strands are energized simultaneously with a DC voltage and then one of the motor strands for determining the initial position of the rotor ( 3 ) is selected. Method according to claim 1 or 2, characterized in that during the rotation of the rotor ( 3 ) always one of the motor strings of the DC motor ( 1 ) for determining the position of the rotor ( 3 ) is selected. Method according to one of claims 1 to 3, characterized in that the position-dependent inductance L (φ, I) of the motor strings in a step mode of the DC motor at the beginning and at the end of each step is evaluated. Method according to one of claims 1 to 4, characterized in that the motor strands of the DC motor ( 1 ) are energized by means of a hysteresis current regulator. Method according to claim 5, characterized in that that the position-dependent inductance L (φ, I) determined by the switching times of the hysteresis current controller becomes. Method according to one of claims 1 to 6, characterized in that the position-dependent inductance L (φ, I) in the form of a look-up table in the memory means is stored.