Method and control module for calculating rotor flux linkage position of electric motor

Abstract

The invention relates to a method for calculating the rotor flux linkage position of an electric motor, wherein a formula based on current, voltage, resistance, starting value and inductance value is used. The invention also relates to an associated control module.

Description

Technical Field

[0001] The present invention relates to a method for calculating the rotor flux position of an electric motor and a related control module for executing such a method. Background Art

[0002] For example, electric motors can be used to drive a vehicle or generate hydraulic pressure in a braking system. Information about the rotor flux position at a specific time has proven to be beneficial for the operation of certain types of electric motors, particularly AC motors, in order to improve the control of the motor. Summary of the Invention

[0003] Therefore, the object of the present invention is to provide a method for calculating the rotor flux position of an electric motor. Furthermore, the object of the present invention is to provide a related control module. According to the present invention, this is achieved by the method and control module described in the respective independent claims. Advantageous embodiments can be derived, for example, from the respective dependent claims. The content of the claims is expressly incorporated into the description by reference.

[0004] The present invention relates to a method for calculating the rotor flux position of an electric motor.

[0005] Rotor flux position It can also be referred to as the electrical position and is calculated in particular using the following formula, more precisely in particular from the flux linkage:

[0006] (1)

[0007] - in is the second component of the flux linkage, and

[0008] - in is the first component of the magnetic flux.

[0009] This formula allows to calculate the rotor flux position in a simple way given the known flux.

[0010] Preferably, the flux linkage at time t Calculated using the following formula:

[0011] (2)

[0012] - in is the stator voltage space vector in the stationary reference frame,

[0013] - in is the stator current space vector in the stationary reference frame,

[0014] - where R sis the resistance of the motor,

[0015] - in is the starting value, and

[0016] - where L eq is the inductance value, which depends on the type of motor.

[0017] Motor flux This method can be used to calculate the inductance in a simple and reliable manner. For example, the starting value can be calculated as explained below. Currents and voltages, in particular, can be measured in a suitable manner and, if necessary, converted into a suitable coordinate system. The vector representation of the variables can take into account their vector nature. The resistance of a particular motor is generally known. The inductance value depends on the type of motor, and, for example, can be implemented so that the programming or control module can be adapted to a certain type. Typical assignments will be described in detail below.

[0018] Here, the vector is a complex vector, where is its real part, is its imaginary part. The corresponding divisions and names apply to other vectors as well.

[0019] The electric motor is in particular an electric motor which is operated with alternating current. Typical embodiments will be described further below.

[0020] According to one embodiment, the stator voltage space vector is calculated using the following formula:

[0021] (3)

[0022] - in It's a magnetic link.

[0023] This allows for a simple calculation of the stator voltage space vector using measured and known variables. Equation (3) is a variation of Equation (2).

[0024] Therefore, in addition to information about the flux, information about the rotor flux position or electrical position is also available. Stated another way, information about the motor angle is obtained. This motor angle can also be used for control. The two components refer to: The flux is a vector quantity. This can particularly be the active flux.

[0025] According to one embodiment, the flux is calculated in a time-discrete form. Similarly, the rotor flux position can also be calculated in a time-discrete form. Therefore, a time-discrete calculation can be used, which can be implemented numerically in a typical control device.

[0026] For example, the following formula can be used for this purpose:

[0027] (4)

[0028] (5)

[0029] - Where T s is the sampling period of the obtained discrete signal,

[0030] - where t k = k·T S is the value of the sampling time of the obtained discrete signal,

[0031] - in is the starting value of the flux linkage of the direct-axis AC motor in the stationary reference frame, and

[0032] - in It is the starting value of the flux linkage of the quadrature-axis AC motor in the stationary reference frame.

[0033] The starting value can be calculated, for example, using the following formula:

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041] These differential equations are obtained by discretizing the following continuous-time dependent differential equations:

[0042]

[0043]

[0044]

[0045] (6)

[0046] - where α > 0 is the parameter of the continuous differentiator,

[0047] - where β > 0 is the parameter of the continuous low-pass filter,

[0048] - where γ1 > 0, γ2 > 0 are the gains of the gradient estimator,

[0049] - is the continuous derivative operator.

[0050] These equations can be used to calculate starting values. If the derivative operator is present in the denominator, the equation can be understood in particular as follows: the equation is multiplied by the denominator so that the equation has the form in which the derivative operator acts directly on the corresponding variable.

[0051] In particular, when the motor is a surface-mounted permanent magnet synchronous machine (SMS), L eq It can be the phase inductance L of the motor S (Synchronous Inductor).

[0052] In particular, when the motor is an interior permanent magnet synchronous motor (interior permanent magnet synchronous motor), L eq It can be the inductance L of the motor on the q axis q .

[0053] In particular, when the motor is a DC-excited synchronous machine, L eq It can be the inductance L of the motor on the q axis q .

[0054] In particular, when the motor is a hybrid-excited synchronous machine, L eq It can be the inductance L of the motor on the q axis q .

[0055] In particular, when the motor is a reluctance synchronous machine, L eq It can be the inductance L of the motor on the q axis q .

[0056] In particular, when the motor is a rotor field oriented asynchronous machine (rotor field oriented asynchronous machine), Leq It can be the stator inductance L of the motor S Multiply by the overall loss factor σ.

[0057] In particular, the motor can be independent of the definition of the inductance of one of the given types.

[0058] The present invention further relates to a control module for an electric motor, the control module being configured to execute the method described herein. Furthermore, the present invention relates to a non-volatile computer-readable storage medium containing program code, which, when executed, causes a processor to execute the method described herein. With respect to the method, all embodiments and variants described herein may be used.

[0059] For example, the relevant variable can be measured at sampling time points n. These sampling time points can be separated from each other by a time T, for example. s . Thus, a number of discrete measurements can be performed. In particular, these measurements can be performed at evenly spaced times. However, in principle, measurements can also be performed at irregular intervals. In this case, the time T s For example, it can be determined as the average value of the time intervals between corresponding consecutive sampling time points.

[0060] An inductance value can be predefined for a particular type of motor, as described above. Multiple inductance values ​​can also be stored in the unit executing the method (e.g., a control device or a control module) to allow for use with different types of motors. This selection can be performed manually or automatically, for example.

[0061] The method described here can be carried out in particular in an electronic unit (eg a control module).

[0062] When referring to the d-axis or q-axis, this is usually referring to the axis after a d / q transform, Park transform, or other transformation that converts a three-phase variable into a two-dimensional variable. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The present invention will now be described with reference to an embodiment. In the accompanying drawings:

[0064] Figure 1 An electric motor with a control module is shown, and

[0065] Figure 2 Shows a block diagram. DETAILED DESCRIPTION

[0066] Figure 1 The electric motor 10 and the associated control module 20 are shown purely schematically.

[0067] The control module 20 has a measuring unit 22. This measuring unit is designed to measure operating data of the electric motor 10. The operating data include, in particular, at least two voltages u and at least two currents i. The processed variables described here are formed from these.

[0068] In general, particularly advantageous control of such an electric motor 10 can be achieved by means of field-oriented control techniques. For this purpose, accurate knowledge of the rotor flux linkage and / or angular position is often helpful.

[0069] For example, in conventional field-oriented control techniques, two current control loops are implemented, specifically in a synchronously rotating dq reference frame. This allows for better performance compared to static reference controllers, which are based on DC variables. The d component of the stator current contributes to the stator flux, while the q component contributes to the torque. A position controller provides a reference speed, while a speed controller controls the reference torque. For permanent magnet synchronous motors with surface-mount magnets, the direct-axis current can be set to zero, below the base speed, to control the torque generated by the quadrature-axis current.

[0070] Controlling an AC motor often requires precise rotor position and speed. In this case, these variables can be obtained, for example, from a position sensor mounted on the rotor shaft. Rotor position can be used for Parker conversion and position control, and speed can be used for speed control, torque control, and current control.

[0071] One challenge in this area is so-called sensorless (or self-sensing) control, which aims to replace mechanical sensors with estimators or observers by leveraging available information about machine currents and voltages. Sensorless control, in particular, offers significant cost savings. Furthermore, it reduces space requirements and eliminates electromagnetic compatibility issues.

[0072] Sensorless control methods can be divided into passive and active methods. In particular, passive methods include techniques using flux observers and estimating the back electromotive force (BEMF). In this case, no test signal is used. Instead, the rotor flux is estimated by an observer, or the BEMF information is extracted from the voltage and current ratio based on the motor model. Active methods use high-frequency signals to observe the changes in rotor statistics during rotor movement. In passive methods, the relationship between stator current and voltage is used to estimate the rotor position and speed. This can be achieved in particular in a stationary α-β coordinate system, where the values ​​in this coordinate system can be calculated from the measured stator current and the measured or estimated stator voltage.

[0073] For isotropic AC motors, such as synchronous motors with permanent magnets and / or surface-mount magnets, BEMF methods are commonly used to estimate rotor position and speed. To increase accuracy and improve dynamic estimation, observers can be used. Observers are complex estimation algorithms that can incorporate correction terms based on the measured and estimated signals.

[0074] For the BEMF observer, the correction term can be based on the measured and estimated currents in the α-β stationary reference frame.

[0075] One possibility to estimate the rotor flux is to estimate the flux in the stator to derive the rotor flux angle, in particular by integrating the back EMF equation:

[0076] (7)

[0077] The flux linkage of a permanent magnet synchronous motor with surface mounted magnets can be estimated, for example, as follows:

[0078] (8)

[0079] Unlike BEMF, the magnitude of the rotor flux remains constant at zero speed. Based on this information, the angle The following relationship:

[0080] (9)

[0081] In this case, these two components of the flux linkage vector are used.

[0082] On the other hand, the angular velocity It can be estimated as follows:

[0083] (10)

[0084] The approach described further above for calculating the flux linkage has proven to be advantageous, notably because it is compatible with existing solutions for calculating certain variables (such as angles) and is easy to use.

[0085] This is for example Figure 2 In the α-β coordinate system, the stator current (i) or two currents (i) and voltage (u) or two voltages (u) are input variables at the corresponding discrete time point t k Used as input variable and calculate the angle or its tangent. Here, the variable "L eq ” is calculated as described above and participates in the calculation of the angle. The further details of this approach will not be discussed in more detail here.

[0086] The above-mentioned steps of the method according to the present invention can be performed in the order given. However, if technically reasonable, these steps can also be performed in a different order. The method according to the present invention can be performed in one of its embodiments, for example, with a specific combination of steps, in such a way that no further steps are performed. However, in principle, further steps can also be performed, even those not mentioned.

[0087] It should be noted that in the claims and the description, features may be described in combination, for example to facilitate understanding, although these features can also be used separately from each other. Those skilled in the art recognize that such features can also be combined independently of each other with other features or combinations of features.

[0088] The references in the dependent claims may characterize preferred combinations of individual features, but do not exclude other combinations of features.

[0089] List of reference numerals:

[0090] 10 electric motors

[0091] 20 control modules

[0092] 22 measuring units.

Claims

1. A method for calculating the rotor flux position of an electric motor (10), in, The rotor flux position is calculated using the following formula : - in, is the second component of the magnetic linkage, - is the first component of the magnetic flux.

2. The method according to claim 1, in, Calculate the flux linkage at time t using the following formula: - in, is the stator voltage space vector in the stationary reference frame, - is the stator current space vector in the stationary reference frame, - R s is the resistance of the motor (10), - is the starting value, -L eq is the inductance value, which depends on the type of motor (10).

3. The method according to claim 1 or 2, wherein: The flux is calculated in a time-discrete form, and / or the rotor flux position is calculated in a time-discrete form.

4. The method according to claim 1, wherein: When the motor (10) is a permanent magnet synchronous motor with surface mounted magnets, i.e., a surface mounted permanent magnet synchronous motor, L eq is the phase inductance L of the motor (10) S .

5. The method according to claim 1, wherein: When the motor (10) is a permanent magnet synchronous motor with internally mounted magnets, i.e., an internal permanent magnet synchronous motor, L eq is the q-axis inductance of the motor (10).

6. The method according to claim 1, wherein: When the motor (10) is a DC-excited synchronous motor, that is, a DC-excited synchronous motor, L eq is the q-axis inductance of the motor (10).

7. The method according to claim 1, wherein: When the motor (10) is a hybrid excitation synchronous motor, that is, a hybrid excitation synchronous motor, L eq is the q-axis inductance L of the motor (10) q .

8. The method according to claim 1, wherein: When the motor (10) is a reluctance motor, that is, a reluctance synchronous motor, L eq is the q-axis inductance L of the motor (10) q .

9. The method according to claim 1, wherein: When the electric motor (10) is an asynchronous motor with rotor field orientation, i.e., a rotor field orientation type asynchronous motor, L eq is the phase inductance L of the motor (10) S Multiply by the overall loss factor σ.

10. A control module (20) for an electric motor (10), the control module being configured to carry out the method according to one of the preceding claims.

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