Method for angle calculation, method for angle correction, and method for operating an electric motor

Abstract

The invention relates to a method for angle calculation (28) of an angle deviation value with respect to a rotor angle of an electric motor (18), the method comprising: providing (12) the electric motor (18), which has a rotor (14) that is rotatable with an associated change in the rotor angle, and which has at least one motor phase (16) and can be operated on the basis of at least one phase voltage and a phase current at at least the motor phase (16); calculating (32) an estimated current change in the phase current, at least on the basis of an estimated rotor angle value of the rotor angle; determining (36) an actual current change of the phase current; calculating (38) a current change difference between the estimated current change and the actual current change; calculating (26) an angle deviation value with respect to the estimated rotor angle value on the basis of the current change difference. The invention also relates to a method for angle correction (24) and to a method for operating (10) the electric motor (18).

Description

[0001] P250106 DE

[0002] -1-

[0003] Methods for calculating angles, methods for correcting angles, and methods for operating an electric motor.

[0004] Description introduction

[0005] The invention relates to a method for calculating angles according to claim 1. Furthermore, the invention relates to a method for angle correction and a method for operating an electric motor.

[0006] German patent application DE 10 2023 107 740 A1 describes a method for determining the angle of rotation and the rotational speed of an electric motor. In an iterative calculation algorithm, measured or estimated phase voltages and phase currents are compared with a voltage model. The angle of rotation and the rotational speed are calculated from the voltage errors between the measured and modeled voltages by reducing these errors. The iteratively calculated angle of rotation is output, and the output rotational speed is derived from the calculated angle of rotation.

[0007] The object of the present invention is to determine the rotor angle more accurately and quickly. The electric motor should then be operated more precisely and efficiently.

[0008] At least one of these tasks is solved by a method for calculating angles with the features according to claim 1. This allows the rotor angle to be determined more accurately and quickly. The electric motor can then be operated more efficiently and with less wear.

[0009] The following features, inserted in parentheses, possibly separated by commas and therefore to be understood separately from each other or in combination with each other, are to be understood as alternative, optional, supplementary, restrictive, clarifying, exemplary, expansive and / or explanatory information relating to the feature preceding the parentheses.

[0010] The electric motor can be located in a vehicle. The electric motor can provide drive power to move the vehicle. The electric motor can be a permanent magnet motor or a separately excited motor. The electric motor can have a stator. The rotor can rotate relative to the stator. The electric motor can be a synchronous motor.

[0011] INTERNALP250106 DE

[0012] -2- The electric motor can comprise at least two, in particular three, motor phases, to which a phase voltage and a phase current are applied for the operation of the electric motor.

[0013] The phase voltage and / or phase current can be output from an inverter to the electric motor.

[0014] The phase voltage can be an actual voltage (measured phase voltage) or a target voltage (specified phase voltage, phase voltage specified by a controller).

[0015] The phase current can be a phase current in the stator-fixed coordinate system, in particular I u , I v , I w in the case of three motor phases of the electric motor. The phase current can be a phase current in the rotor-fixed coordinate system, in particular I. d , I q in relation to the d-direction, the q-direction or, if applicable, a phase current of the e-direction (excitation direction, excitation coordinate) in a separately excited electric motor.

[0016] The angle calculation method can be combined with another method, particularly an injection method, especially at low speeds or in critical operating ranges of the electric motor. This can increase the reliability of the angle calculation in areas where the method described here, which is based on current change differences, is less reliable (less stable, less accurate).

[0017] The described angle estimator (for calculating the rotor angle value) can operate independently of a current controller or other control loops that at least regulate the phase current of the electric motor for its operation. The calculations for determining the rotor angle value can be performed in a separate routine or a separate signal path. These calculations can only utilize the available phase currents and phase voltages.

[0018] To initialize the estimation method (the estimated rotor angle value), an external angle value and / or an external angular velocity can be used, for example, from another angle determination method, such as during the start-up of the electric motor. This initialization can support the start-up phase or very low rotational speeds where the current change difference alone does not provide sufficient signal information.

[0019] The calculation of the angular deviation value can be performed independently of the actual current control of the electric motor and, in particular, directly...

[0020] INTERNALP250106 DE

[0021] -3- measured phase currents and the specified phase voltages are evaluated.

[0022] This allows the angle calculation method to be decoupled from the current controller and integrated into other control structures.

[0023] For motors with more than one phase, a current change difference can be calculated for each phase. Similarly, for motors with more than one phase, an angular deviation value can be calculated for each phase. The angular deviation value can be calculated by weighting and combining the individual angular deviation values. The angular deviation value can also be calculated by weighting and combining the individual current change differences.

[0024] The phase voltage and / or the phase current can be transformed into a rotor-fixed coordinate system to calculate the current change difference, taking into account the estimated rotor angle value.

[0025] The angular deviation value can be smoothed by applying a filter, taking into account at least one previously determined angular deviation value (an angular deviation value from a previous processing step). This can reduce the noise in the angular deviation value. The previous angular deviation value may have been calculated by the angle calculation method performed in a previous processing step. The previous angular deviation value may be stored and accessible. The filter can be an alpha / beta filter, a Kalman filter, and / or a PID control algorithm.

[0026] In a preferred embodiment of the invention, it is advantageous if the angular deviation value is proportional to the current change difference. The current change difference for a separately excited synchronous machine as an electric motor, particularly for small angular deviation values, can be calculated as follows.

[0027]

[0028] with

[0029] Δφ as the angular deviation value (between the estimated rotor angle and the actual rotor angle),

[0030] Δ dI / dt as the difference in current change between the estimated current change and the actual current change,

[0031] INTERNALP250106 DE

[0032] -4- K dd , K qq , K de , K ed as inverse elements of the inductance matrix, i.e. = -1 and

[0033] U d , U q , U e as phase voltages in the respective coordinate directions (U d , U qare phase voltages and U related to the coordinate direction of the rotor-fixed coordinate system e is the phase voltage related to the excitation direction).

[0034] In a permanent magnet synchronous machine (PMSM), the described quantities U d , U q as phase voltages in the dq coordinate system (rotor-fixed coordinate system). The e-axis (excitation axis) is omitted in PMSM, so the current change difference is reduced to two axes.

[0035] In an advantageous embodiment of the invention, the angular deviation value and the current change difference are mutually dependent via a proportionality factor, and the proportionality factor P is at least dependent on the phase voltage. The angular deviation value can be calculated as a function of the current change difference and the proportionality factor as follows: dl

[0036] Δφ = Δ dI / dt · P

[0037] An angular deviation value can be calculated for each coordinate direction as follows.

[0038]

[0039] Δφ d = Δ dI d / dt · 1 / K dd U q

[0040] Δφ q = Δ dI q / dt · 1 / (−K qq U d + K de U e )

[0041] dl e 1

[0042] Δφ e = Δ dI e / dt · 1 / (K ed U q )

[0043] with

[0044] Δφ d , Δφ q , Δφ e as coordinate-related angular deviation values ​​in the d-, q- and e-coordinate directions,

[0045]

[0046] Δ dI d / dt, Δ dI q / dt, Δ dI e / dt as the difference in current change in the d-, q- and e-coordinate directions,

[0047] ' a ' [ / d , U q , U eas phase voltages in the respective coordinate directions and

[0048] K dd , K qq , K de , K ed as inverse elements of the inductance matrix, i.e. = -1 .

[0049] INTERNALP250106 DE

[0050] -5- Instead of a coordinate-related calculation of the angular deviation value (Δφ d , Δφ q , Δφ e After considering the angular deviation value Δφ and possibly subsequent weighting, it is also possible to calculate it using a pseudoinverse of the relevant matrix quantities (for example, K). This can yield a least-squares solution that may be numerically stable, even if individual phase voltages become very small or individual components are close to zero.

[0051] The angular deviation value can be calculated as follows.

[0052]

[0053] with

[0054] K⃗ as the weight resulting from the inverse inductance elements and the associated phase voltages.

[0055] The same principle described above can be applied to a permanent magnet synchronous machine (PMSM), except that all terms relating to the excitation winding (e-coordinate direction) are omitted from the motor equations. The algorithm itself does not fundamentally change; it is simply performed without the e-axis.

[0056] A preferred embodiment of the invention is advantageous in which the change in actual current is determined as the difference between a current actual current and a previous actual current of the phase current. The previous actual current can be the actual current acquired (measured) in a preceding processing step. The current actual current can be a measured phase current. The previous actual current can be a previously measured phase current.

[0057] The change in actual current can be calculated from the current actual current and the preceding actual current as follows.

[0058]

[0059] with

[0060] as the actual current of the phase current in the processing step (time step) k,

[0061] INTERNALP250106 DE

[0062] -6- I (k-1) as the preceding actual current of the phase current (actual current of a preceding processing step k − 1, time step) and

[0063] At as sampling time (duration of a processing step, time between two measurements, control interrupt duration).

[0064] To achieve the best possible correlation between the current actual currents (measured phase currents) and the corresponding phase voltages, current and voltage values ​​from the current processing step k and from the preceding processing step k - 1 can be averaged. This can correspond to a delay of ½Δt (half the sampling interval) so that the current and voltage measurements remain synchronized.

[0065] In a specific embodiment of the invention, it is advantageous if the actual current is a measured phase current transformed into a rotor-fixed coordinate system depending on the estimated rotor angle value. The actual current can be transformed into the rotor-fixed coordinate system (reference system) depending on the estimated rotor angle value.

[0066] The phase current I u , I v , I wThe individual motor phases can be transformed into the rotor-fixed dq coordinate system and thus each represented as a transformed phase current I. d , I q present. The actual current I, if any, is present. e The phase current in the excitation direction (measured phase current with respect to the excitation direction) does not require a coordinate transformation.

[0067] In a preferred embodiment of the invention, the estimated change in current is determined by a motor model. This motor model can be an electrical motor model that, in particular, replicates (simulates, calculates, estimates) the electrical relationships.

[0068] The calculation of the estimated current change (with respect to the dq or dqe coordinate system) can be independent (time-independent) of the actual control loop (current controller) for the phase current. In particular, it is possible to perform the calculation without influencing the controller operation (operation of the current controller, operation of the torque controller).

[0069] In an advantageous embodiment of the invention, the motor model is provided to be dependent at least on the phase voltage. The estimated current change (current change with respect to the respective coordinate direction) can be determined by applying the

[0070] INTERNALP250106 DE

[0071] -7- Motor models can be calculated depending on the phase current and phase voltage, in particular as follows

[0072]

[0073] with

[0074] / d , I q , I eas phase currents (measured actual currents of the respective motor phase) in the respective coordinate directions,

[0075] [ / d , U q , U e as phase voltages in the respective coordinate directions,

[0076] R s the phase resistance (stator resistance),

[0077] R e the excitation resistance,

[0078] ω el the electric angular velocity,

[0079] Ψ d , Ψ q the magnetic flux linkage in the respective coordinate directions and

[0080] L dd , L qq , L ee , L de , L ed the differential inductances for the respective coordinate directions.

[0081] In particular, the denominator L dd L ee - L de L ed be the determinant of the L-matrix (inductance matrix).

[0082] In general, the transformation (of the phase current, the phase currents, the phase voltage, the phase voltages) into the rotor-fixed coordinate system with the coordinate directions d,q, assuming two motor phases u, v as an example, can be carried out as follows.

[0083] [I d ] = [cos φ sin φ][I u ][I q ] [−sin φ cos φ][I v ]

[0084] with

[0085] φ as the estimated rotor angle value (used here for coordinate transformation),

[0086] INTERNALP250106 DE

[0087] -8- I d , I q as transformed phase current (d- or q-component of the phase current) in the rotor-fixed coordinate system and

[0088] I u , I v as phase current (measured phase current).

[0089] In particular, the third engine phase I can also be used. w be included.

[0090] If necessary, the phase voltages can be further adjusted to account for non-linear switching losses or voltage drops in the power electronics before being used to determine the current change difference (in the motor model).

[0091] In a preferred embodiment of the invention, it is advantageous if the angular deviation value is calculated only when the phase voltage (at least one motor phase, at all motor phases) exceeds a predetermined minimum value (minimum value predetermined with respect to each motor phase, minimum value predetermined with respect to all motor phases). If the phase voltage is below the minimum value (equal to the minimum value), the calculation of the angular deviation value can be omitted or disregarded.

[0092] If, therefore, the following applies

[0093] \u d \ < I / lim or

[0094] |t / ^l < t / lim,

[0095] with the minimum value

[0096]

[0097] Then the calculation of the angular deviation value (the current use of the angular deviation value) can be suspended.

[0098] The specified minimum value [ / lim The phase voltage can be selected depending on the operating conditions, for example, based on a rated current or a DC link voltage of a power electronics system. This prevents incorrect attempts to calculate an angular deviation value at very low phase voltages, such as during no-load operation, when the measurement signal is too small and therefore too inaccurate.

[0099] If the phase voltage is below the minimum value, another method, such as speed estimation based on predefined ramps or an injection method, can be used, particularly until sufficient phase voltages are present to reliably perform the angle calculation method. Once the phase voltage exceeds the minimum threshold, the angle calculation method can be used.

[0100] INTERNALP250106 DE

[0101] -9- can be switched on or used as a priority. This enables reliable sensorless control across the entire speed range of the electric motor.

[0102] Furthermore, within the scope of the invention, a method for angle correction with the features of claim 9 is proposed to solve at least one of the aforementioned problems. The corrected rotor angle value can be the rotor angle value used in current control (torque control). The corrected rotor angle value can be calculated as the estimated rotor angle value minus the angle deviation value. The estimated rotor angle value can be determined by another angle estimation method, for example, for low rotational speeds. The estimated rotor angle value can be available as an external quantity (external rotor angle value, external rotational speed). The estimated rotor angle value can be an initial value used at least in the current processing step.

[0103] Furthermore, within the scope of the invention, a method for operation with the features of claim 10 is proposed to solve at least one of the aforementioned problems. The method for operation may include an injection method and / or a controlled speed ramp-up for low rotor speeds. The corrected rotor angle value can be used for current control, speed control, and / or torque control of the electric motor.

[0104] The electric motor can be operated in sensorless mode. At least one of the previously described methods can be performed during sensorless operation of the electric motor. The electric motor can be operated exclusively in sensorless mode. Sensorless operation can be understood as operation without the use of a sensor, such as a position sensor, to measure the rotation angle of the electric motor (rotor).

[0105] Further advantages and advantageous embodiments of the invention will become apparent from the description of the figures and the illustration.

[0106] Character description

[0107] The invention is described in detail below with reference to the figure. The figure shows a method for operating, a method for angle correction, and a method for angle calculation, each in a specific embodiment of the invention. The method for operating 10 of an electric motor comprises providing 12

[0108] INTERNALP250106 DE

[0109] -10- an electric motor 18 comprising a stator 13 and a rotor 14 rotatable relative to the stator 13 by changing a rotor angle φ and at least one motor phase 16, in particular three motor phases 16. Furthermore, a current control 20 of phase currents at the motor phases 16 is carried out depending on a corrected rotor angle value p cor, which is calculated by a method for angle correction 24 described below. The current control 20 of the phase currents at the three motor phases 16 of the electric motor 18 transforms, in particular, the phase currents I calculated in a rotor-fixed coordinate system. d , I q depending on the corrected rotor angle value p cor by a coordinate transformation into the phase currents to be applied, which are related to the stator-fixed coordinate system u , I v , I w If the electric motor 18 is designed as a separately excited synchronous machine, an additional excitation direction and, accordingly, a phase current in the excitation direction are present. A coordinate transformation is not required in this case.

[0110] Furthermore, the angle correction procedure 24 includes calculating 26 an angle deviation value Δφ according to a method for angle calculation 28 and calculating 30 the corrected rotor angle value φ.cor as the estimated rotor angle value φ adjusted for the angular deviation value Δφ. This adjusted estimated rotor angle value can be referred to as the corrected rotor angle value φ. cor output, in particular for the current control 20 of the phase currents of the electric motor 18 for the method for operating 10 of the electric motor 18, a speed control and / or a torque control of the electric motor 18. The estimated rotor angle value φ can be the previous corrected rotor angle value φ' applied in a previous processing step k-1, for example, for the previous current control. cor , an external angle value and / or an initial value.

[0111] The method for angle calculation 28 comprises providing 12 the electric motor 18, which can be operated depending on at least one phase voltage and the phase currents on the motor phases 16, and calculating 32 an estimated change in the phase currents at least depending on the estimated rotor angle value φ of the

[0112]

[0113] Rotor angle. The estimated change in current.

[0114]

[0115] is calculated in particular by a motor model 33. The motor model 33 depends at least on the estimated rotor angle value φ, the phase voltage U and motor parameters 35 as well as a previously determined rotational speed ω'.

[0116] The phase voltage U can be provided by a motor controller of the electric motor 18 and, depending on the estimated rotor angle value φ, after a correction 34,

[0117] INTERNALP250106 DE

[0118] -11- in which, in particular, the phase voltage is further adjusted to account for nonlinear switching losses or voltage drops in the power electronics, and is made available to motor model 33. The adjusted phase voltage U cor The motor model 33 is provided as a transformed phase voltage by a prior coordinate transformation 37 into the rotor-fixed coordinate system.

[0119] Furthermore, a determination of the actual change in phase current is carried out. d̃I / dtThe current is determined as the difference between a current actual current I and a previous actual current I' of the phase current. The current actual current I is preferably a measured phase current I* of the respective motor phase 16 at the current processing step k, and the previous actual current / ' is the phase current measured at a previous processing step k-1. The respective actual currents were transformed into the rotor-fixed coordinate system by a coordinate transformation 39, depending on the estimated rotor angle value p.

[0120] Using the calculated estimated current change and the calculated actual current change, a current change difference Δ is calculated between the estimated current change and the actual current change, and subsequently an angular deviation value Ap to the rotor angle value is calculated as a function of the current change difference.

[0121]

[0122] The angular deviation value Ap is proportional to the current change difference A^, and the angular deviation value Ap and the current change difference A^ are mutually dependent via a proportionality factor 41. The proportionality factor 41 depends at least on the phase voltage U. Specifically, the angular deviation value Ap is only calculated, or used to calculate, the corrected rotor angle value p. cor used when a test 22 shows that the phase voltage U is below a specified minimum value U lim exceeds this value. This can prevent the calculation of the angular deviation value Ap at very low phase voltages, for example during no-load operation, where the measurement signal is too small and therefore too inaccurate.

[0123] The angular deviation value Ap is smoothed by a filter 42 and used to calculate 30 the corrected rotor angle value p. corused, which is provided in particular for the operation of the electric motor 18, for example the current control 20.

[0124] INTERNALP250106 DE

[0125] -12-

[0126] Reference symbol list

[0127] 10 procedures for operation

[0128] 12. Provide

[0129] 14 Rotor

[0130] 16 Motor phase

[0131] 18 Electric motor

[0132] 20 Current control

[0133] 22nd exam

[0134] 24 methods for angle correction

[0135] 26 Calculate

[0136] 28 methods for calculating angles

[0137] Calculate 30

[0138] 32 Calculate

[0139] 33 Engine model

[0140] 34. Cleanup

[0141] 35 Engine parameters

[0142] 36 Investigation

[0143] 37 Coordinate transformation

[0144] 38 Calculate

[0145] 39 Coordinate transformation

[0146] 40 Calculate

[0147] 41 Proportionality factor

[0148] 42 filters

[0149] INTERNAL

Claims

P250106 DE -13- Patent claims 1. Method for calculating the angle (28) of an angular deviation value to a rotor angle of an electric motor (18), comprising Providing (12) the electric motor (18) which has a rotor (14) rotatable by changing the rotor angle and at least one motor phase (16) and which can be operated depending on at least one phase voltage and a phase current on at least the motor phase (16), Calculating (32) an estimated change in phase current at least as a function of an estimated rotor angle value, Determination (36) of an actual change in the phase current, Calculating (38) a current change difference between the estimated current change and the actual current change, Calculating (26) an angular deviation value to the estimated rotor angle value depending on the current change difference.

2. Method for calculating angles (28) according to claim 1, characterized in that the angle deviation value is proportional to the current change difference.

3. Method for calculating angles (28) according to claim 2, characterized in that the angle deviation value and the current change difference are dependent on each other via a proportionality factor (41) and the proportionality factor (41) is at least dependent on the phase voltage.

4. Method for calculating angles (28) according to one of the preceding claims, characterized in that the actual current change is determined as the difference between a current actual current and a previous actual current of the phase current.

5. Method for angle calculation (28) according to claim 4, characterized in that the respective actual current is a measured phase current transformed into a rotor-fixed coordinate system depending on the estimated rotor angle value.

6. Method for calculating angles (28) according to one of the preceding claims, characterized in that the estimated change in current is determined by a motor model (33). INTERNALP250106 DE -14- 7. Method for angle calculation (28) according to claim 6, characterized in that the motor model (33) is at least dependent on the phase voltage.

8. Method for calculating angles (28) according to one of the preceding claims, characterized in that the angle deviation value is only calculated if the phase voltage exceeds a predetermined minimum value.

9. Method for angle correction (24) of a rotor angle value of a rotor angle of an electric motor (18), comprising Providing (12) an electric motor (18) having a rotor (14) rotatable by changing the rotor angle value and having at least one motor phase (16), Providing (12) an estimated rotor angle value, calculating (26) an angle deviation value according to a method for angle calculation (28) according to any of the preceding claims and Calculating (30) a corrected rotor angle value as the estimated rotor angle value adjusted for the angle deviation value.

10. Method for operating (10) an electric motor (18), comprising Providing (12) an electric motor (18) rotatable by changing a rotor angle value of a rotor angle and having at least one motor phase (16) Setting at least one phase current on at least the motor phase (16) depending on a rotor angle value corrected by an angle correction method (24) according to claim 9. INTERNAL

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