Method and device for controlling an electric motor

Abstract

Method for controlling an electric motor (1), comprising the steps - Specification of an initial target value (T ref ) for an engine characteristic (T); - Input of the first target value (T ref ) into a motor control (4); - Determination of a motor current (I 123 ) and / or a rotor angle of the motor (φ), where the motor current (I) 123 ) and / or the rotor angle of the motor (φ) is incorporated into the motor control (4); - Supplying the motor control (4) with a supply current (I Batt ); - Analysis of the supply current for variable components, whereby a quantity of a given nth harmonic oscillation of a speed of the motor is determined taking into account a rotor angular velocity of the motor (φ); - Comparison of the determined magnitude of the nth harmonic oscillation with a target value for the magnitude of the nth harmonic oscillation, wherein a correction value is determined from the comparison to influence the magnitude of the nth harmonic oscillation in the direction of the target value, wherein the correction value is used by the motor control (4) to determine a second setpoint (U 123 ) to form a curve for the motor voltage in order to influence the magnitude of the nth harmonic oscillation in the direction of the target value, - Output of the second setpoint (U 123 ) to regulate the voltage of the motor (1).

Description

[0001] The invention relates to a method for controlling an electric motor and a corresponding control device. In particular, this method can counteract unwanted noise generation. State of the art

[0002] The demands placed on electric machines, such as those used for steering and traction drives, or as pump or fan motors, are constantly increasing. On the one hand, the electric machines or the corresponding motors should deliver, for example, a constant torque without harmonics, a target speed, or a target position; on the other hand, the drives should be acoustically unobtrusive.

[0003] However, electric drive systems often exhibit negative acoustic characteristics, also known as "Noise, Vibration, Harshness" (NVH). NVH refers to the audible and / or perceptible vibrations in machines, often caused by stick-slip effects or by harmonics of a rotating machine and their transmission via a shaft to adjacent mechanical structures. Such noises are often perceived as disturbing and detract from the overall quality. Therefore, it is desirable to be able to influence and optimize the noise of electric machines.

[0004] In the prior art, sound sensors are often used to influence the noise generated by an electric machine, as described, for example, in DE 10 2021 115 749 B4. Depending on a signal from the sound sensor, a mapping is determined with which at least one operating parameter of the electric machine is influenced or adapted. The use of additional sensors, such as MEM sensors for structure-borne sound detection, microphones for airborne sound detection, or torque sensors, has the disadvantage of generating additional installation space requirements and further costs. Disclosure of the invention

[0005] The invention is based on the objective of positively influencing the noise and torque ripple caused by electric machines without having to provide special, additional sensors.

[0006] This problem is solved by a method for controlling an electric motor and a corresponding control device with the features of the independent claims. Advantageous embodiments are specified in the dependent claims.

[0007] A method for controlling an electric motor powered by a supply current, particularly from a battery, comprises the following steps: A first setpoint for a motor parameter is specified. This motor parameter could be, for example, a desired speed or torque of the motor. This first setpoint is then input into a motor control system. The motor control system could, for example, be a field-oriented control system that uses a space vector representation, particularly in (rotationally fixed) dq coordinates. A motor current and / or a rotor angle of the motor are determined, and these values ​​are then incorporated into the motor control system. Depending on the control method used, either the motor current or the rotor angle, or both, may be incorporated into the motor control system.It is also possible to determine the rotor's angle using appropriate algorithms, without having to measure the rotor angle. Depending on the motor used, the motor current may also consist of three phase currents.

[0008] Measurements have demonstrated a strong correlation between negative acoustic characteristics (NVH) and harmonics in the power supply for many electric drives. These harmonics are typically nth harmonics of an oscillation that correlate with the motor's rotational speed. However, harmonics at the desired torque (torque ripple) and / or at the motor's rotational speed can also be undesirable and can have repercussions on the power supply, where they can be detected.

[0009] The method according to the invention therefore determines the supply current with which the motor is driven and analyzes it for variable components, whereby a quantity, in particular a quantity pair or a quantity vector, of a predetermined nth harmonic oscillation of a rotational speed of the motor is determined, taking into account the rotor angle of the motor. The quantity pair or the quantity vector can represent an amplitude and a phase angle of an oscillation, in particular a sine and / or cosine oscillation. In addition, other quantities that uniquely describe the oscillation, such as an xy representation of sine-cosine weightings, can also be used instead of the amplitude and the phase angle.

[0010] The measured magnitude of the nth harmonic oscillation of the motor's speed at the given supply current is compared to a target value for this nth harmonic oscillation. By comparing this measured nth harmonic oscillation with the target value, a correction value is determined to influence the nth harmonic oscillation in the direction of the target value. This can be achieved using classical controller approaches or more complex optimization algorithms for minimizing an objective function, such as H. ∞-Control or model predictive control. In this method, the correction value from the motor control is used to generate a second setpoint for the motor voltage. This second setpoint is preferably output to a voltage regulator of the motor. In other words, the output second setpoint represents a setpoint adjusted by the correction value, minimizing undesirable negative effects on acoustics and / or harmonics at the desired torque and / or speed of the motor.

[0011] After receiving the second setpoint, the voltage divider outputs a motor voltage, so that the motor operates with a motor characteristic, for example with a desired speed or a desired torque.

[0012] An advantage of the method according to the invention is that no further, additional sensors are required for optimizing the acoustics. The supply current is measured directly or indirectly (e.g., via the motor phase currents) in most control systems anyway, and this measurement can be performed with a very high bandwidth. Since the verification of the adjustment by the correction value can again be observed via the supply current, a cost-effective control loop is created that is more robust against manufacturing variations and therefore does not require each motor to be individually measured for calibration.

[0013] In one embodiment, the correction value is a voltage value that the motor control takes into account when determining the second setpoint for the motor voltage. Specifically, a motor control—without considering harmonics—can output a voltage value so that the voltage regulator outputs a motor voltage that causes the motor to operate with a desired motor characteristic. To account for and minimize the magnitude of the nth harmonic oscillation on the supply current, for example, an additional control unit can determine a correction value that is output as a correction voltage value and then added to the voltage value from the motor control.In this case, a "corrected" second target value for the motor voltage is formed by addition, which takes into account the minimization of the size of the nth harmonic oscillation and thus achieves the desired improvement with regard to acoustics and / or harmonics on the desired torque and / or on the speed of the motor.

[0014] In one embodiment, the correction value is a torque value that is taken into account when specifying the first setpoint for the motor parameter. Specifically, in a motor control system with sufficient frequency bandwidth, the correction value can be incorporated into the calculation of the first setpoint for the motor parameter.

[0015] In one embodiment, the magnitude of an nth harmonic oscillation of the motor's rotational speed on the supply current is determined by demodulating the supply current, taking into account the motor's rotor angle (φ), particularly by Fourier analysis. The demodulation represents the transition from the carrier frequency range to the baseband. For example, Fourier analysis can be used to determine the amplitude and phase of the relevant harmonic oscillation. In a subsequent step, the magnitude of an nth harmonic oscillation can be controlled to a target value. Typically, the target value of the nth harmonic oscillation can be set to "zero". Alternatively, the target value can be chosen to be different from "zero", thus optimizing desired NVH (noise, vibration, and harshness) behavior. In particular, the target value can also be state-dependent, for example, depending on the torque or rotational speed of the drive.

[0016] In one embodiment, the nth harmonic oscillation of the motor's speed on the supply current is selected by measuring a motor on a motor test bench. The nth harmonic oscillation selected is the one that reduces the motor's noise during operation. One or more motors from a series or model can be examined to determine a correlation between acoustic and / or harmonic anomalies at the desired torque and / or speed of the motor and the intensity of different harmonic oscillations on the supply current.

[0017] In one embodiment, during exemplary measurements of the engine on the engine test bench, the target value for the magnitude of the nth harmonic vibration is determined, at which an optimum noise reduction of the engine occurs during operation. This target value can be "zero" or can be chosen to be different from "zero", so that the desired NVH behavior is optimized.

[0018] In one embodiment, the motor is measured under various operating conditions, for example, at different speeds or torques. Specifically, there may be several relevant harmonic vibrations that affect the acoustics, so that several harmonic vibrations are determined, for example, an nth and an mth harmonic vibration, which may be relevant for different speed ranges. Target values ​​are defined for each of these relevant harmonic vibrations during the measurement.

[0019] Depending on the chosen configuration, the motor can be powered via a DC inverter. In this configuration, the inverter's DC power supply can be used to analyze fluctuations in the supply current.

[0020] In one version, the supply current is an alternating voltage source current of a drive system supplied, for example, from the power grid (utility grid), consisting of a rectifier stage with a downstream motor-inverter unit.

[0021] A control device according to the invention for an electric motor, which is supplied with supply current, in particular from a battery, is configured to process a first setpoint for a motor characteristic, a motor current, a rotor angle of the motor, a supply current, and a target value for a predetermined nth harmonic oscillation of the motor's speed on the supply current. The control device is configured to analyze the supply current for variable components and to determine a predetermined nth harmonic oscillation of the motor's speed on the supply current, taking into account the motor's rotor angle (φ).The control device is further configured to compare the magnitude of the nth harmonic oscillation with the target value for the magnitude of the nth harmonic oscillation and to determine a correction value from this comparison, which influences the magnitude of the nth harmonic oscillation in the direction of a target value. Furthermore, the control device is configured to use the correction value to establish a second setpoint for the motor voltage and to output this second setpoint to a voltage regulator of the motor.

[0022] In one embodiment, the control device is configured to consider a voltage value as a correction value when determining the second setpoint for the motor voltage. Specifically, the control device may include a motor control circuit—without considering harmonics—that is configured to output a voltage value to the voltage regulator, so that the voltage regulator outputs a motor voltage that causes the motor to operate with a desired motor characteristic. Furthermore, the control device may include an additional controller configured to output a voltage value as a correction value. The control device may then be configured to add the voltage value from the motor control circuit to the correction value to determine the second setpoint for the motor voltage.

[0023] Classical controller approaches can be used for the additional controller, or more complex optimization algorithms for minimizing an objective function, such as H. ∞ -Regulation or a model predictive regulation.

[0024] In one embodiment, the control device is configured to determine the magnitude of an nth harmonic oscillation of the motor's rotational speed by demodulating the supply current, taking into account the motor's rotor angle, in particular by Fourier analysis.

[0025] In one embodiment, the control device is configured to take a torque value into account as a correction value when specifying the first setpoint for the motor characteristic.

[0026] Exemplary embodiments of the invention are explained with reference to the following drawings. The schematic drawing shows: Fig. 1 a schematic representation of a system with an electrically operated motor and a control device according to the invention; Fig. 2 a schematic representation of an embodiment of the control device; Fig. 3 a schematic representation of a circuit arrangement for regulating the motor voltage based on the value of the nth harmonic oscillation of the battery current; Fig. 4. Another embodiment of the control or regulation method, wherein a target value for the torque is determined on the basis of a setpoint for the torque, the rotor angle of the motor, and the battery current; and Fig. 5 a schematic representation of a further embodiment of the proposed control device and the proposed method in which correlation methods are used.

[0027] The following describes an embodiment of an electric drive system that is powered by a battery. The invention also relates to embodiments in which other power sources are used to provide the power supply.

[0028] Fig. Figure 1 shows an electric drive system with an electrically operated motor 1 and a control device 4 according to the invention. The motor 1 draws supply current from a battery 2, which is converted by a voltage regulator 3 accordingly for the motor 1. The voltage regulator 3 is controlled by the control device 4. A predetermined first setpoint T ref A motor parameter T is entered into the control device 4; this motor parameter T could, for example, be a desired torque. The motor current I 123The current is measured by an ammeter 5, the rotor angle of the motor φ by a rotor angle measuring device 6, and the values ​​are entered into the control device 4. In the simplest case, both measuring devices can be sensors that can be read directly by the control device. Depending on the control method used, the motor current I can be 123 or the rotor angle φ of the motor can be incorporated into the motor control, or both. It is also possible to determine rotor angle information using appropriate algorithms without having to measure the rotor angle φ. Depending on the motor used, the motor current I can vary. 123 It also involves three phase currents.

[0029] The battery current I Batt The battery current is measured by a battery current meter 7, which may also be a suitable sensor. The battery current I may be measured. BattIt can also be determined or calculated via the phase current measurement of the motor. The determined battery current I Batt is entered into control device 4.

[0030] In the control device 4, a setpoint U is calculated from the aforementioned inputs according to the described procedure. 123 The signal is generated and passed on to the voltage regulator 3, which then sets the appropriate voltage for motor 1. 123 This corresponds to the three phase voltages "U1", "U2", "U3" in a three-phase electric motor. That is, U 123 is actually a voltage vector consisting of three individual voltages, one for each phase.

[0031] I 123 This corresponds to the three phase currents "I1", "I2", "I3" in a three-phase electric motor. That is, I 123 is actually a current vector consisting of three individual currents, one for each phase.

[0032] Fig. Figure 2 shows an embodiment of the control device 4 according to the invention, in which a motor control 8 is supplemented by an additional control 9 according to the invention. The motor current I 123 and / or the rotor angle of the motor φ is fed into the motor control unit 8, which, however, does not yet take harmonics into account. The motor control unit 8 outputs a voltage value U. The battery current I goes into the auxiliary control unit 9. Batt The motor speed is analyzed for the magnitude of the nth harmonic oscillation. In the additional control 9, a target value for the magnitude of the nth harmonic oscillation is specified. To influence the magnitude of the nth harmonic oscillation towards the target value, a correction value, in this embodiment a correction value U, is applied. korr output for the voltage. The voltage value U and the correction value U korrThe voltage values ​​are linked together, for example by adding the two values. This linkage results in the second setpoint U. 123 , which - as in Fig. 1 explained - output to the voltage regulator 3.

[0033] Fig. Figure 3 shows a schematic representation providing a detailed description of supplementary regulation 9 of the Fig. 2 The battery current I BattThe signal is fed to a demodulator 11. The rotor angle φ of the motor is also fed to the demodulator 11. Based on the motor angle φ, the demodulator 11 determines a quantity, in particular a quantity pair or a quantity vector, for the given nth harmonic oscillation 12 of the battery current, for example, for the 6th harmonic oscillation, and transmits the quantity, in particular the quantity pair or the quantity vector of the given nth harmonic oscillation 12, to a control unit 13. The control unit 13 also receives a target value 14 for the quantity, in particular the quantity pair or the quantity vector, of the nth harmonic oscillation from a data storage device 15. The target value can be a predetermined value, in particular a constant value. For example, the target value can be 0.

[0034] The control unit 13 compares the target value 14 with the quantity, in particular the quantity pair or quantity vector, of the nth harmonic oscillation 12, which was determined by the demodulator 11. From this comparison, the control unit 13 determines a control value 16, depending on predefined procedures, which is fed to a modulator 17. The modulator 17 transforms the control value 16 from the nth harmonic oscillation into the frequency range of the motor using the rotor angle φ of the motor.

[0035] The control value 16 output by the control unit 13 is converted into the correction value U using the modulator 17 and the rotor angle φ of the motor. korr converted. The voltage value U and the correction value U korr for the tension are linked together ( Fig. 2), for example by adding the two values, and thus a second target value U 123The motor voltage is calculated and supplied to the motor 1 (both not shown here) by the voltage controller 3. The control unit 13 determines the control value 16 such that the quantity, in particular the quantity pair or quantity vector, of the nth harmonic oscillation 12 approaches or reaches the target value 14. This type of control ensures that the specified nth harmonic oscillation of the battery current I is maintained. Batt approximated or adjusted to the desired target value.

[0036] Fig. Figure 4 shows another embodiment of the control method. In this method, the motor voltage is controlled based on a setpoint for the torque T. ref , the rotor motor angle φ and based on the battery current I Batt a correction value or a correction oscillation T hThe torque is determined by a calculation block 18 using predefined procedures based on the rotor motor angle φ and the battery current I. Batt the correction value or correction oscillation T h for the torque in such a way that a desired target value is achieved for the specified nth harmonic oscillation of the battery current. The correction oscillation T h For example, a corrective oscillation with amplitude and phase in the nth order of the harmonic oscillation.

[0037] The correction value or correction oscillation T h The torque is fed to an adder 19, to which the first setpoint T is also fed. ref The torque T is supplied. The adder 19 adds the two values ​​and passes the added torque value 20 to the motor controller 8. The motor controller 8 determines the torque based on the added torque value 20 and optionally depending on the motor current I. 123and / or, depending on the rotor angle of the motor, a control value for the voltage U 123 , which is output to the voltage regulator.

[0038] Fig. Figure 5 shows a schematic representation providing a detailed description of supplementary regulation 9 of the Fig. 2 with a second further circuit arrangement 23 or a control method in which a correlation method is used. A correlation unit 21 is provided, to which the battery current I Batt and the rotor angle φ, that is, the phase angle of the motor's rotor, is supplied. The correlation unit 21 determines a quantity, in particular a pair of quantities or a quantity vector, for the given nth harmonic oscillation 12 of the battery current and supplies the quantity, in particular a pair of quantities or a quantity vector, of the nth harmonic oscillation 12 of the battery current to the control unit 13.

[0039] Furthermore, the control unit 13 receives a target value 14 for the quantity, in particular a quantity pair or a quantity vector, of the nth harmonic oscillation from a data storage device 15. The target value 14 can, for example, be the value 0.

[0040] The control unit 13 compares the target value 14 with the quantity, in particular a quantity pair or a quantity vector, of the nth harmonic oscillation 12 determined by the correlation unit 21. From this comparison, the control unit 13 determines a control value 16, depending on predefined procedures, which is fed to a synthesis block 22. The control value 16 output by the control unit 13 is transformed into the motor's frequency domain using the synthesis block 22 and the rotor angle φ of the motor, and converted into a correction value U. korr converted. The voltage value U and the correction value U korr The tension is linked together, as in Fig.Figure 2 is shown. For example, the voltage value U and the correction value U are shown. korr by adding the two values ​​together, thus creating a second target value U 123 calculated for the motor voltage, which is provided to the motor 1 by the voltage controller 3.

[0041] With the second setpoint U 123 The motor is controlled based on the motor voltage. The control unit 13 determines the control value 16 such that the nth harmonic oscillation of the battery current approaches or reaches the target value. This type of control ensures that the specified nth harmonic oscillation of the battery current I is maintained. Batt approximated or adjusted to the desired target value.

[0042] Depending on the chosen configuration, the motor can be powered via a DC inverter. In this configuration, the inverter's DC power supply can be used to analyze fluctuations in the supply current. All described methods and devices can be used analogously. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 115 749 B4

[0004]

Claims

[1] Method for controlling an electric motor (1), comprising the steps - Specification of an initial target value (T ref ) for an engine characteristic (T); - Input of the first target value (T ref ) into a motor control (4); - Determination of a motor current (I 123 ) and / or a rotor angle of the motor (φ), where the motor current (I) 123 ) and / or the rotor angle of the motor (φ) is incorporated into the motor control (4); - Supplying the motor control (4) with a supply current (I Batt ); - Analysis of the supply current for variable components, whereby a value of a given nth harmonic oscillation of a speed of the motor is determined taking into account the rotor angle of the motor (φ); - Comparison of the determined magnitude of the nth harmonic oscillation with a target value for the magnitude of the nth harmonic oscillation, wherein a correction value is determined from the comparison to influence the magnitude of the nth harmonic oscillation in the direction of the target value, wherein the correction value is used by the motor control (4) to determine a second setpoint (U 123 ) to form a curve for the motor voltage in order to influence the magnitude of the nth harmonic oscillation in the direction of the target value, - Output of the second setpoint (U 123 ) to regulate the voltage of the motor (1). [2] Method according to claim 1, wherein the correction value is a stress value (U) korr ) is, which is used by the motor control (4) when determining the second setpoint (U) 123 ) is taken into account for the motor voltage. [3] Method according to claim 1, wherein the correction value is a torque value which is determined when specifying the first setpoint (Tref ) is taken into account for the engine characteristic. [4] Method according to claim 1, wherein the magnitude of an nth harmonic oscillation of the rotational speed of the motor on the supply current is determined by demodulation of the supply current taking into account the rotor angle of the motor (φ), in particular by Fourier analysis. [5] Method according to claim 1, wherein a selection of the nth harmonic oscillation of the speed of the motor on the supply current is carried out by an exemplary measurement of a motor (1) on a motor test bench, wherein the nth harmonic oscillation is selected which has an influence on a reduction of noise generation of the motor (1) during operation. [6] Method according to claim 5, wherein, in the exemplary measurement of the motor (1) on the motor test bench, the target value for the size of the nth harmonic oscillation is determined at which an optimum noise reduction of the motor (1) occurs during operation. [7] Method according to claim 5 or 6, wherein the exemplary measurement of the motor (1) is carried out under different operating conditions. [8] Method according to one of the preceding claims, wherein the quantity of the nth harmonic oscillation is a pair of quantities or a quantity vector, wherein the quantity in particular has an amplitude and a phase angle of the oscillation. [9] Method according to any of the preceding claims, wherein the supply current is a current from a battery. [10] Method according to any one of claims 1 to 8, wherein the supply current is a DC voltage source current of a DC inverter. [11] Method according to any one of claims 1 to 8, wherein the supply current is an AC voltage source current of a drive system consisting of a rectifier stage with a downstream motor inverter unit supplied, for example, from the power grid (utility grid). [12] Control device for an electric motor (1), configured for processing ◯ of a first setpoint (T ref ) for an engine characteristic (T), ◯ of a motor current (I 123 ), ◯ of a rotor angle of the motor (φ), ◯ of a supply current (I Batt ) the control device, ◯ and a target value for a quantity of a given nth harmonic oscillation of the motor's rotational speed, - wherein the control device is set up, ◯ the supply current (I Batt) to analyze variable components and to determine a magnitude of the given nth harmonic oscillation of the motor speed on the supply current, taking into account the rotor angle of the motor (φ), ◯ to compare the magnitude of the nth harmonic oscillation with the target value for the magnitude of the nth harmonic oscillation ◯ to determine a correction value from the comparison that influences the magnitude of the nth harmonic oscillation in the direction of a target value, to use the correction value to determine a second setpoint (U) 123 ) to form the motor voltage, ◯ the second setpoint (U 123 ) to output a voltage of the motor (1). [13] Control device according to claim 12, wherein the control device is configured to set a voltage value (U korr ) as a correction value when determining the second target value (U) 123) to take into account the motor voltage. [14] Control device according to claim 12 or 13, wherein the control device is configured to provide a torque value as a correction value when specifying the first setpoint (T ref ) to be taken into account for the engine characteristic. [15] Control device according to one of claims 12 to 14, wherein the control device is configured to determine the magnitude of an nth harmonic oscillation of the rotational speed of the motor by demodulation of the supply current taking into account the rotor angle of the motor (φ), in particular by Fourier analysis.

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