METHOD AND DEVICE FOR CALIBRINGING A CONTROL SYSTEM OF AN ELECTRIC MACHINE

Description

[0001] The invention relates to a method and a device for calibrating the control system of an electric machine for a predefinable torque value. Furthermore, the invention relates to an electric drive system with a corresponding device, a vehicle with an electric drive system, a computer program, and a computer-readable storage medium. State of the art

[0002] Documents DE 10 2007 003874 A1, DE 10 2016 201746 A1 and US 2014 / 145655 A1 disclose methods and devices for calibrating a control system of an electrical machine.

[0003] Electric rotating field machines, especially permanent magnet synchronous machines, are controlled to generate a desired torque by means of a suitable combination of direct torque and reluctance torque. In field-oriented control, the direct torque and the reluctance torque are set by appropriately selecting the d- and q-current operating points ((id,iq)) in the rotor-fixed coordinate system. For current control in field-oriented control (FOC), especially in the base speed range, the corresponding current for a desired torque is determined from a locus curve, the so-called MTPC (maximum torque per current). These MTPC loci can be determined analytically, assuming an ideal machine with known inductances Ld and Lq. For real machines with saturation effects, a preferred approach is to numerically determine the MTPC locus from simulation data (e.g.,...Finite element simulations) are used to generate the MTPC (Maximum Power Consumption) locus curve. Further dependencies, such as temperature dependencies, internal losses of the electric machine, variations in material parameters and fluxes, often make experimental determination of the MTPC locus curve on a test bench the most feasible approach, preferably using a golden sample machine. In this process, variations between individual machines, tolerances, etc., are neglected. For example, a characteristic map of the torque is scanned via id / iq, currents and torques are measured, and the points for the shortest current phasor for the desired torques are determined and appropriately stored. This procedure is often complex and slow, and therefore costly.

[0004] Therefore, there is a need for alternative methods and devices for calibrating the control system of an electric machine for a predefinable torque value. Disclosure of the invention

[0005] The invention is defined by the features of the independent claims.

[0006] A method for calibrating a control system, preferably a current control system, of an electric machine for a predefinable torque value is provided. The electric machine is operated with field-oriented control. The method comprises the following steps: a.) Specifying a current vector to generate the specified torque value using a connectable electric machine. The current vector has a length and a direction as parameters. b.) Specifying a test signal and superimposing the current vector with the test signal. c.) Capturing a response signal resulting from the superposition, preferably the amplitude of the resulting response signal, using a sensor. d.) Evaluating the response signal. e.) Determining a calibrated current vector as a function of the evaluation of the response signal. f.) Operating the control system of the electric machine for the specified torque value by specifying the calibrated current vector.

[0007] The operation of electrical machines using field-oriented control is well known. In this process, the alternating quantities of the phase currents are each converted into a value corresponding to the

[0008] The frequency of the alternating quantities is transferred to a rotating coordinate system. Within this rotating coordinate system, during steady-state operation of the electric machine, the alternating quantities become DC quantities to which all standard control engineering methods can be applied. Due to the multiphase, phase-shifted alternating currents impressed into the stator, a rotating magnetic field is generated during operation of the electric machine, consisting of a stator flux and a rotor flux. The control system of the electric machine specifies a stator current as a function of a predefined torque value. Within the rotating coordinate system, the d / q coordinate system, which rotates synchronously with the rotor flux and whose d-axis points in the direction of the rotor flux, a stator current is represented as a stator current phasor or stator current vector, which is characterized by its length and direction.This current vector rotates synchronously with the rotating stator or rotor flux of the electric machine. In the d / q coordinate system, the current vector can be represented according to its length and direction by two mutually perpendicular components, Id and Iq, which are equivalent quantities in the steady state. Machine-specific lines, along which the electric machine delivers a constant torque, so-called iso-torque lines, can be plotted in this coordinate system. A control system for an electric machine can access desired operating points on these iso-torque lines using characteristic maps. However, these parameters can change for each machine (individual variations), the rotor temperature, and over the machine's operating time due to the dependencies mentioned above, and therefore should be calibrated.For current vectors of equal length, there is only one specific direction in which the maximum torque is generated by a connected electric machine. In one step of the process, a current vector is specified to generate a predefined torque value. To verify that this is the correct direction for generating the maximum torque, a test signal is applied and superimposed on the current vector. This superposition causes an oscillation in the output torque of a connected electric machine. Due to the mechanical coupling of the electric machine to the housing, this oscillation in the torque leads to a mechanical and / or acoustic vibration of the housing and connected components. The mechanical transmission behavior of the mechanical system results in noise excitation of a connected electric machine and / or the power electronics, which can be detected with a suitable sensor, e.g., a noise meter.The torque oscillation, or resulting oscillations, are measured acoustically. A sensor captures the response signal resulting from the superposition of the current vector and the test signal. This response signal is evaluated, and based on this evaluation, the calibrated current vector, preferably its direction, is determined. The parameter of the current vector's direction for delivering a predefined torque value is thus calibrated and stored in a characteristic map. Subsequently, the electric machine is controlled for the predefined torque value by specifying the calibrated current vector.

[0009] Advantageously, a method for calibrating a control system, preferably a current control system, of an electric machine for a predefinable torque value is provided. The method is preferably provided for an integrated electric axis, consisting of the rotating field machine and power electronics mechanically attached to the machine, preferably with strong or rigid mechanical coupling, or integrated into the machine. The method allows it to be carried out for each individual electric machine. It can be performed at the end of the production line and / or at any time during the service life of the electric drive, including during regular operation. Preferably, a drive component (e.g., an e-axis) includes the sensor and the method. A means is provided to run the method during commissioning, end-of-line testing, or during operation.This allows calibration parameters to be determined and readjusted or relearned on a sample-specific, temperature-dependent, and / or age-dependent basis. A method is created that provides a self-learning / self-calibrating control system for an electric drive. Self-calibration for the MTPC locus curve is enabled, which occurs independently of a test bench and external sensors.

[0010] The test signal has a length and a direction, the direction being orthogonal to the current vector, the test signal oscillating on both sides of the current vector, and preferably being vectorially added to the current vector.

[0011] The test signal has a length and a direction corresponding to the specified current vector as a parameter. The superposition is vectorial. In the rotating coordinate system, this results in a vector addition of the current vector and the test signal. The test signal is oriented orthogonally to the current vector and oscillates, preferably at a predefined frequency. Due to the oscillation of the test signal, a connected electrical machine generates a different torque, particularly the harmonically oscillating component, depending on the current length and direction of the test signal. This results in two distinct types of response signals. The amplitude of the torque oscillation increases as the direction of the specified current vector deviates from the maximum torque achievable with its length. The oscillation of the torque and the test signal share a common phase and frequency.The amplitude of the torque oscillation decreases as the deviation of the direction of the given current vector from the maximum torque achievable with its length decreases. The torque oscillation contains a frequency component at twice the frequency of the test signal precisely when the direction of the current vector is very close to that corresponding to the torque achievable with that length. This double-frequency component occurs because, due to the typical curvature of the isotorque lines, an oscillation tangential to the isotorque line to the right and left of the initial current vector results in a torque minimum at twice the frequency.The minimized oscillation of the torque, the disappearance of torque ripple, or even the occurrence of double the frequency can be acoustically detected using suitable harmonic frequencies, i.e., when the corresponding frequency disappears or appears in the measured noise. Particularly favorable frequencies for the oscillation of the test signal should be those at which the connected machine exhibits no or only minimal intrinsic electromagnetic excitations. For example, for a three-phase electric machine, these could preferably be order 5 or 7 in the torque, since intrinsic excitations are expected at orders 6 and 12. A favorable excitation order relative to the set electrical frequency for this method is preferably chosen such that, without a predefined test signal, no or hardly any intrinsic electromagnetic orders are generated in the torque oscillation at this order.This would mean that the expected response signal would be coupled solely with the procedure, and the vanishing response signal could be used as the target variable.

[0012] Furthermore, when choosing the excitation frequency or order, it is preferable to select a frequency / order that is easily detectable by the sensor, with regard to the sensor sensitivity and, above all, the transfer behavior of this frequency of a torque ripple to the sensor.

[0013] Advantageously, a possible test signal is provided, which allows an assessment of the direction of the specified current vector with regard to the achievable maximum torque.

[0014] In another embodiment of the invention, steps a) to d) are repeated at least twice, with the direction of the current vector being changed by a predefinable amount each time. When evaluating the response signals according to step d), the detected response signals are compared. A gradient or a minimum of the detected response signals is then determined.

[0015] The application of the current vector and the test signal are repeated at least twice with different current vector directions. The response signals are evaluated by comparing them, preferably their amplitudes. Preferably, based on the magnitude and change of the response signal's amplitude, preferably as a function of the gradient and / or minimum, it is determined whether the applied current vector generates the maximum torque in a connected electric machine, or in which direction the current vector must be changed in further repetitions to more closely approximate the direction in which a connected electric machine generates the maximum torque. With a greater length or magnitude of the test signal, the amplitude of the resulting torque oscillation increases. Therefore, if the amplitude becomes too large, the length of the test signal must be reduced.

[0016] Advantageously, a method is provided for iteratively approximating the direction of the current vector in which a connected electrical machine generates the maximum torque.

[0017] In another embodiment of the invention, the direction of the current vector is specified by a predefinable amount, preferably anew in each iteration step, in the positive and negative direction of the last specified current vector, or in the positive or negative direction of the last specified current vector. The repetition of the steps is preferably carried out until the gradient between the, preferably approximately last three, response signals falls below a first predefinable threshold or the response signal falls below a second predefinable threshold.

[0018] Advantageously, different variants are provided for iteratively approximating the direction of the current vector in which a connected electrical machine generates the maximum torque.

[0019] In another embodiment of the invention, according to step e.) the calibrated current vector is specified by specifying the parameters of the specified current vector, whose detected response signal is minimal, for the calibrated current vector.

[0020] When the current vector reaches the direction at which a connected electric machine would generate maximum torque, a minimal response signal results, preferably with a minimal amplitude. The current vector parameters present at that time—its length and direction—are then specified as parameters for the calibrated current vector.

[0021] Advantageously, a method for determining the calibrated current vector is specified.

[0022] Furthermore, the invention relates to a computer program which includes instructions which, when executed by a computer, cause it to perform the steps of the method described so far.

[0023] Furthermore, the invention relates to a computer-readable storage medium comprising instructions which, when executed by a computer, cause it to perform the steps of the method described so far.

[0024] Furthermore, the invention relates to a device for calibrating the control system of an electric machine. The device comprises a sensor, preferably a mechanical one. The device also comprises a circuit carrier, the circuit carrier having a test signal generator and a processing unit. The device is configured to perform the steps of the described method.

[0025] Advantageously, a device for calibrating the control system of an electric machine is provided. This device comprises a sensor, preferably mechanical, for detecting the response signal resulting from the superposition of the current vector and the test signal. The device further comprises a test signal generator for specifying the test signal and a processing unit for carrying out the described procedure.

[0026] In another embodiment of the invention, the sensor is mechanically fixed or essentially rigidly connected to the electric machine. Alternatively, the sensor is fixedly mounted on the circuit carrier and the circuit carrier is fixedly integrated on or in the electric machine.

[0027] For high-resolution and undisturbed acquisition of the response signal, a mechanically rigid connection to the electric machine or via a circuit carrier attached to or within the electric machine is provided. Alternatively, it can of course also be carried out with a sensor outside the device or power electronics, e.g., a microphone on or next to the electric machine, or by means of a structure-borne sound sensor, for example, implemented as an accelerometer mounted on a surface, preferably of the electric machine or a control unit or inverter.

[0028] Advantageously, a position is provided for mounting the sensor to ensure good signal transmission.

[0029] In another embodiment of the invention, the mechanical sensor is a microphone, an accelerometer, a structure-borne sound sensor, or a speed sensor.

[0030] Advantageously, sensors are provided to detect the response signal resulting from the torque oscillation. These oscillations can be detected acoustically, by means of acceleration measurement (preferably on a mechanically fixed unit with the electric machine), or by structure-borne sound. The torque oscillations also result in a change in the rotational speed of the electric machine, so the response signals can also be detected using a speed sensor.

[0031] Furthermore, the invention relates to an electric drive system comprising an electric machine and a described device. Such an electric drive system serves, for example, to power an electric vehicle. The method and the device enable a sensibly controlled operation of the drive train.

[0032] Furthermore, the invention relates to a vehicle with a described drive system. Advantageously, a vehicle is thus provided which includes a device with which the control system of an electric machine can be calibrated.

[0033] It is understood that the features, properties and advantages of the method according to the invention apply accordingly to the device or drive system and the vehicle and vice versa.

[0034] Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings. Brief description of the drawing

[0035] The invention will be explained in more detail below using some figures, including: Figure 1 a schematic representation of a device for calibrating the control system of an electric machine Figure 2a diagram of the dq current plane with plotted isotorque lines for the application of field-oriented control. Figure 3 a schematically represented vehicle with a drivetrain, Figure 4 A schematically represented flowchart for a procedure for calibrating an offset angle of a field-oriented control of an electric machine. Embodiments of the invention

[0036] The Figure 1Figure 100 shows a device 100 for calibrating a control unit 110 of an electric machine 120. The device comprises a sensor 130, preferably a mechanical sensor with a mechanically rigid or fixed direct or indirect connection to the electric machine 120. The device further comprises a circuit carrier 150, wherein the circuit carrier has a test signal generator 160 and a processing unit 170. Preferably, the control unit 110 is integrated into an inverter 140, wherein the inverter comprises power electronics 145, preferably a B6 bridge, for supplying the connectable machine 120 from a battery 155. Furthermore, the device includes a circuit carrier 150, which has a test signal generator 160 and a processing unit 170. Fig. 1 The electric drive system 200 is shown with the device 100 and the electric machine 120.

[0037] Figure 2Figure 1 shows a diagram of the dq current plane with plotted isotorque lines for the application of field-oriented control. Within the rotating coordinate system, DC quantities result from the alternating quantities, such as the phase currents, during steady-state operation of the electric machine. In the d / q coordinate system, which rotates synchronously with the rotor flux and whose d-axis points in the direction of the rotor flux, a stator current is represented as a current vector Ix_v, characterized by its magnitude or length I_s and its direction Ix_a. This current vector Ix_v rotates synchronously with the rotating stator or rotor flux of the electric machine. In this coordinate system, machine-specific lines T1, T2, T3, T_Des can be plotted, along which the electric machine delivers a constant torque.An electric machine's control system can access the parameters of these lines using characteristic maps or configurable data. By varying the direction Ix_a of the current vector, and thus different id and iq components, the different operating points on these lines can be set. Three current vectors of equal length Is are represented by I1_v, I2_v, and I3_v, whose directions Ix_a differ by a predefined amount Ix_a_Delta. The predefined test signals S1_Test, S2_Test, and S3_Test are shown orthogonal to these current vectors. The diagram shows that the oscillating test signals S1_Test and S3_Test intersect more isotorque lines than the test signal S2_Test.Therefore, the superposition of the current vectors and the test signals S1_Test and S3_Test results in larger torque fluctuations than the superposition of the current vector I2_v and the test signal S2_Test with a connected electric machine. Accordingly, in this example, the parameters, preferably the direction, of the current vector I2_v are adopted for the calibrated current vector I_Vk.

[0038] The Figure 3 Figure 1 shows a schematic representation of a vehicle 300 with an electric drive system 200. The drive system 200 comprises the device 100 for calibrating the control 110 of the electric machine 120 in the inverter 140 and the electric machine 210. Preferably, the electric drive system includes the battery 150.

[0039] The Figure 4Figure 400 shows a schematic sequence of a procedure for calibrating the control system of an electric machine 120 for a predefinable torque value T_Des. The procedure starts with step 405. The electric machine 120 is operated with a field-oriented control system. The procedure comprises the following steps: a.) Specifying a current vector Ix_v, 410 to generate the specified torque value T_Des using a connectable electric machine 120, wherein the current vector Ix_v has a length I_s and a direction Ix_a as parameters; b.) Specifying a test signal Sx_Test, 420 and superimposing the current vector Ix_v with the test signal Sx_Test; c.) Capturing 430 a response signal Sx_Antw resulting from the superposition using a sensor 130; d.) Evaluating 440 the response signal Sx_Antw; e.) Determining 450 a calibrated current vector I_Vk as a function of the evaluation of the response signal Sx_Antw; f.) Operating 460 the control of the electric machine 120 for the specified torque value T_Des by specifying the calibrated current vector I_Vk. Steps a.) to d.Steps 410-440 are preferably repeated at least twice for iterative approximation to the direction of the current vector Ix_v in which a connected electric machine 120 generates the maximum torque. The procedure ends with step 470.

Claims

1. Method (400) for calibrating a control of an electrical machine (120) for a specifiable torque value (T_Des), wherein the electrical machine (120) is operated using a field-oriented control, having the following steps: a.) specifying a current vector (Ix_V) (410) to generate the specifiable torque value (T_Des) by means of a connectable electrical machine (120), wherein the current vector (Ix_V) has a length (I_s) and a direction (Ix_a) as parameters, b.) specifying a test signal (Sx_Test) (420) and superimposing the current vector (Ix_V) with the test signal (Sx_Test), c.) capturing (430) a response signal (Sx_Antw) resulting from the superposition by means of a sensor (130), d.) evaluating (440) the response signal (Sx_Antw), e.) determining (450) a calibrated current vector (I_Vk) as a function of the evaluation of the response signal (Sx_Antw), f.) operating (460) the control of the electrical machine (120) for the specifiable torque value (T_Des) by means of specifying the calibrated current vector (I_Vk), characterized in that the test signal (Sx_Test) has a length (S_s) and a direction (Sx_a), wherein the direction (Sx_a) is aligned orthogonally to the current vector (Ix_V), and the test signal (Sx_Test) oscillates on both sides of the current vector (Ix_V).

2. Method according to Claim 1, wherein steps a.) to d.) are repeated at least twice, wherein the direction (Ix_a) of the current vector (Ix_V) is specified changed in each case by a specifiable absolute value (lx_a_Delta), wherein upon the evaluation of the response signals (Sx_Antw) according to step d.), the captured response signals (Sx_Antw) are compared and a gradient or a minimum of the captured response signals (Sx_Antw) is ascertained.

3. Method according to Claim 2, wherein the direction (Ix_a) of the current vector (Ix_V) is specified in each case by a predefinable absolute value (Ix_a_Delta) in the positive and negative direction of the last specified current vector (Ix_V) or is specified in each case in the positive or negative direction of the last specified current vector (Ix_V).

4. Method according to Claim 3, wherein according to step e.), the calibrated current vector (I_Vk) is specified in that the parameters of the specified current vector (Ix_V), the captured response signal (Sx_Antw) of which is minimal, are specified for the calibrated current vector (I_Vk).

5. Computer program, comprising commands which, upon the execution of the program by a computer, cause it to carry out the method / the steps of the method (400) according to Claims 1 to 4.

6. Computer-readable storage medium, comprising commands which, upon the execution by a computer, cause it to carry out the method / the steps of the method (400) according to Claims 1 to 4.

7. Device (100) for calibrating a control (110) of an electrical machine (120), having a sensor (130), having a circuit carrier (150), wherein the circuit carrier has a test signal generator (160) and a computing unit (170), wherein the device is configured to carry out the steps of the method according to any one of Claims 1-4.

8. Device according to Claim 7, wherein the sensor (130) is mechanically fixedly connected to the electrical machine (120) or the sensor (130) is fixedly attached to the circuit carrier (150) and the circuit carrier (150) is fixedly integrated on or in the electrical machine (120).

9. Device according to Claim 8, wherein the sensor (130) is a microphone, an acceleration sensor or structure-borne sound sensor or a speed sensor.

10. Electrical drive system (200) having an electrical machine (120) and a device (100) according to any one of Claims 7 to 9.

11. Vehicle (300) having an electrical drive system (200) according to Claim 10.