DE102021203591A1 - Process for field-oriented control of an electric motor - Google Patents

Abstract

The invention relates to a method for field-oriented control of an electric motor (4), in which an operating state of the electric motor (4) is set via a current control (64) in the d-q reference system with a direct component (Id) and a quadrature current (Iq), with a Target value (Id_set) of the direct component (Id) to bring about an operating state of the electric motor (4) with maximum torque per ampere is estimated, with the reference value (Id_set) at least one reference variable (IMTPAControl) for controlling the direct component (Id) of the current control (64 ) is determined by means of which the electric motor (4) is operated at a first operating point and a second operating point that differs therefrom, with at least one optimization variable (I1, I2) as a reaction of the electric motor (4) to operation at the first operating point and at the second Operating point is detected, the at least one optimization variable (I1, I2) with regard to the operating state de s electric motor is evaluated with maximum torque per ampere, and the setpoint (Id_set) of the direct component (Id) is set based on the evaluation.

Description

The invention relates to a method for field-oriented control of an electric motor, in which an operating state of the electric motor is set via current control in the d-q reference system with a direct component and a quadrature current. The invention also relates to an electric motor and software on a data carrier.

Adjustment systems powered or operated by electric motors as motor vehicle components, such as window lifters, seat adjusters, door and sunroof drives or radiator fan drives, as well as pumps and interior fans, typically have an electric drive with a controlled electric motor. So-called brushless electric motors (brushless DC motors, BLDC motors) are increasingly being used for such electromotive drives, in which the wear-prone brush elements of a rigid (mechanical) commutator are replaced by electronic commutation of the motor current.

Electromotive drives for motor vehicles are usually fed by a (high-voltage) battery as an on-board energy store, from which the electric motor is supplied with electrical energy in the form of a direct current (direct current). In order to convert the direct current into the motor current, a power converter (inverter) is suitably connected between the energy store and the electric motor. The power converter has a bridge circuit, which is supplied with the direct current or direct voltage of the energy store via an electrical intermediate circuit. The motor current is generated as a multi-phase output current by a pulse width modulated (PWM) control or regulation of semiconductor switches of the bridge circuit. The semiconductor switches are switched between a conducting and a blocking state in a clocked manner by the pulses of the PWM signals.

During operation, the bridge circuit feeds the electric motor current (three-phase current) into the stator coils of the electric motor, which subsequently generates a rotating magnetic field with respect to the stator. In this case, the rotor of the electric motor suitably has a number of permanent magnets, the interaction of the permanent magnets with the rotary field producing a resulting torque which causes the rotor to rotate.

The phases of the three-phase current generated by the bridge circuit and the associated rotating field are referred to as (motor) phases. In a figurative sense, this also includes the stator coils (phase winding) assigned to such a phase with the associated connecting lines (phase end). In this case, the phases are connected to one another, for example, in a star point of a star connection.

For efficient operation, it is necessary that the phases are supplied with power at the right time. Vector control, also known as field-oriented control (FOC), is possible for this purpose. With such a field-oriented control or FOC, the three-phase current is identified as two orthogonal components that can be visualized with a current space vector. One component (direct component) defines the magnetic flux of the motor, the other the torque (quadrature current).

The field-oriented control regulates the three-phase current in a d-q reference system (reference system) of the electric motor. In the ideal case, the current space vector is fixed in magnitude and direction (quadrature) with respect to the rotor, independent of the rotation. Since the current space vector is static in the d-q reference system, the current control is based on direct current signals. This isolates the regulators from the time varying winding currents and voltages and therefore eliminates the limitation of regulator frequency response and phase shift on motor torque and speed.

In this case, the electric motor has an associated motor controller, which determines the corresponding current component setpoint values from the flux and torque setpoint values, which are specified by a speed controller. The motor or phase currents are transformed into the d-q reference system. The current control typically has two proportional-integral (PI) controllers; one for the direct component (direct current) and one for the quadrature current, in order to keep the measured current components at the preset setpoints.

The outputs of the two PI controllers represent a voltage space vector with respect to the rotor. Mirroring the transformation performed on the motor currents, these static sig nale is processed through a series of reference system transforms to generate voltage control signals for the PWM drive.

The amount of torque depends on the current amplitude and the current angle of the three-phase current. If the current angle is selected in such a way that the electric motor generates the maximum torque at a given current amplitude, the electric motor is said to be in an operating state with maximum torque per ampere (Max Torque Per Ampere, MTPA). The MTPA operating point has the best efficiency for electric motor operation. This MTPA operating point depends on many influencing factors, so that it is desirable to determine and, if necessary, to correct it during operation of the electric motor, that is to say when the electric motor is running.

Conventionally, a torque controller specifies the desired value or the command variable for the quadrature current, with a field weakening controller generating the command variable for the direct component. If field weakening is not necessary (basic speed range), the reference variable of the direct component has the value zero (0). This drives the direct component to zero and thus forces the current space vector to run exclusively in the quadrature direction. Since only the quadrature current produces useful torque, this maximizes the torque efficiency of the electric motor. An improved field-oriented control can be implemented, for example, by using the reluctance torque and setting the command variable of the direct component to a value not equal to zero. Depending on the system knowledge and the tolerances, the MTPA operating point and thus the best efficiency of the electric motor is more or less achieved.

The invention is based on the object of specifying a particularly suitable method for field-oriented control of an electric motor. In particular, a reliable determination and, if necessary, correction of the MTPA operating point should be made possible during the runtime. The invention also relates to an electric motor and software on a data carrier.

With regard to the method, the object is achieved with the features of claim 1 and with regard to the electric motor with the features of claim 9 and with regard to the software with the features of claim 10. Advantageous refinements and developments are the subject of the respective dependent claims.

Insofar as method steps are described below, advantageous configurations for the electric motor result in particular from the fact that it is designed to carry out one or more of these method steps.

The method according to the invention is intended for the field-oriented control of an electric motor and is suitable and designed for this. In other words, a field-oriented controlled operation of the electric motor (motor operation) is provided according to the method. The method is therefore suitable for operating the electric motor and is provided and designed for this purpose.

With field-oriented control (FOC), an operating state of the electric motor is controlled via a current control loop (CCL) in a d-q reference system with a direct voltage component and a quadrature current.

The current control of the electric motor preferably has two (current) controllers, in particular in the form of PI controllers, with which the direct component (direct current) on the one hand and the quadrature current on the other hand are regulated and/or controlled. The conjunction “and/or” is to be understood here and in the following in such a way that the features linked by means of this conjunction can be designed both together and as alternatives to one another.

The electric motor can also have a speed control loop (SCL), for example a speed or torque control, with a controller, in particular a PI controller, which generates a setpoint for the quadrature current controller.

According to the method, a target value of the direct component to bring about an operating state of the electric motor with maximum torque per ampere is first estimated. In other words, a target value of the direct component for the MTPA operating point is determined. Here and in the following, "estimate" or "estimate" means an approximate determination of the MTPA operating point, for example by evaluating the phase voltages and/or phase currents, or by pre-characterized measurements tables or characteristic curves, or by means of (statistical) mathematical methods. In particular at the beginning of the method, an initial (start) estimate of the target operating point can also consist, for example, in setting the target value to zero or, taking into account a reluctance torque, to a value not equal to zero.

A command variable for the current control, in particular for the controller of the direct component, is then determined on the basis of the setpoint value. The reference variable thus leads the direct component in the current control. The electric motor is operated at a first operating point and at a second operating point, which differs therefrom, by means of the reference variable. The first or second operating point can be the estimated MTPA operating point, for example. In other words, the reference variable for the first or second operating point can correspond to the setpoint.

According to the method, at least one optimization variable is then recorded as a reaction of the electric motor to operation at the first operating point and at the second operating point. In other words, the optimization variable is a measure of the operation of the electric motor; in particular, the optimization variable enables conclusions to be drawn about the degree of efficiency present at the respective operating point. The at least one optimization variable is evaluated here with regard to the operating state of the electric motor with maximum torque per ampere. In other words, the first and second operating point are evaluated with regard to the MTPA operating point. The setpoint or the reference variable for the current control is set on the basis of the evaluation. The target value is therefore set in such a way that the efficiency of the electric motor is maximized.

According to the method, the electric motor is operated at the first and/or second operating point that deviates from the estimated MTPA operating point. This results in an operating point that differs from the MTPA operating point. This change in the operating point or operating state makes it possible to use the detected optimization variable to draw a conclusion as to whether the reference variable—and thus the setpoint value of the direct component—is approaching or moving away from the MTPA operating point. By setting the setpoint based on this evaluation, it is thus possible to determine the MTPA operating point during engine operation and to approach it successively or iteratively.

According to the invention, regulation of the setpoint of the direct component to the MTPA operating point is therefore provided, which is regulated using the optimization variable as the input variable.

With the method according to the invention, deviations from the MTPA operating point can be detected and corrected or reported over the lifetime of the electric motor. Furthermore, the method reduces the requirement for the (calibration) accuracy of a positioning system of the electric motor, since any inaccuracies in the determination of the position or attitude are eliminated by controlling the setpoint.

The optimization according to the method can take place during the entire life cycle of the electric motor. Alternatively, it can also only take place at certain times. For example, the operating situation after the production of the electric motor, i.e. at the end of production (End of Line, EOL), is very well known, so that a targeted and reliable estimate for the setpoint is made possible. This enables a particularly effective optimization.

The method is particularly suitable for static operation of the electric motor. It can therefore make sense to suspend the adjustment of the setpoint according to the invention or to reduce the adjustment speed in the event of changes in the operating state (e.g. speed or load). If the system is already at the control limit, the optimization can also be stopped or halted.

If the controller is (deliberately) outside the MTPA (e.g. in the event of field weakening), the optimization or the process is also stopped, paused or interrupted.

The target value for the MTPA operating point (optimization value) determined using the method can be saved or stored when the method is terminated or interrupted, and can thus be reused as a new starting point (estimated point) when the method is started or restarted.

As an alternative or in addition to the above-described hiding (termination, interruption) of the method, the adjustment to the MTPA can also be limited. This means that, for example, a control factor with which the setpoint is adjusted is reduced or limited.

In a preferred application or use of the method, the method is used to determine an individual, unknown or imprecise system variable. A position offset of the position of the motor shaft or the rotor is preferably determined here. With position detection systems, there may be deviations in the position detection. In order to determine and eliminate this deviation, the electric motor can be operated at the presumed or estimated MTPA operating point. Instead of the direct component, an offset is varied in the actual position. Here, too, the target is reaching the MTPA operating point. However, this is achieved by correcting the position.

In an expedient embodiment of the method, the first and/or second operating point is brought about by a test value of the reference variable. In this case, the command variable is composed in particular of a sum or difference between the desired value and the test value. The test value is a known deviation or disturbance which is added to (or subtracted from) the (estimated) target value in order to realize two different operating points.

In a conceivable embodiment, after the start of the method, the estimated setpoint is used in a first method step as the (first) reference variable. This means that the controller of the direct component first sets the estimated MTPA operating point and operates the electric motor at this (first) operating point. In a second method step, the reaction of the electric motor to this operating point is recorded using a first optimization variable. In this case, the optimization variable is, for example, a phase current of the electric motor. The optimization variable is stored and then, in a third method step, a (second) reference variable is used, which is made up of the estimated target value and the test value. A second operating point, which differs from the first operating point, is set by the additional test value in the reference variable. In a fourth method step, the reaction of the electric motor to this second operating point is recorded using a second optimization variable, and the second optimization variable is stored. In a fifth method step, a comparison is carried out as an evaluation as to whether the first or second optimization variable has better engine operation. If the second optimization variable is better, the target value of the direct component is readjusted. If the first optimization variable is better, method steps one to five are repeated, with the test value being used in the third method step to deviate alternately in one direction and then the other.

In an equally conceivable alternative embodiment, a reference variable with a test value or deviation in one direction is used in the first method step and a reference variable with a test value or deviation in the other (opposite) direction is used in the third method step.

The test value can be chosen in different ways. For example, the test value has a constant value, for example 0.5 A (ampere). The test value may alternatively have an alternating value, for example ±0.5 A, or variations in amplitude. It is also possible to select the amplitude of the test value depending on the operating status or the change in operating status (e.g. acceleration).

wobei I_Delta der Testwert, I₀ die Testwertamplitude, t die Zeit, und ω die Testwertfrequenz ist. Zusätzlich ist beispielsweise eine Frequenzvariation, also eine variable Testwertfrequenz möglich. Ebenso denkbar ist beispielsweise ein Testwert zur Multifrequenzanregung, bei welchem mehrere sinusförmige Werte addiert sind.The test value is preferably varied over time with a test value frequency. For example, the test value has a sinusoidal value: $${\text{I}}_{\text{delta}}={\text{I}}_0\text{sin}\left(\mathrm{\omega }\text{t}\right),$$

where I _Delta is the test value, I ₀ is the test value amplitude, t is the time, and ω is the test value frequency. In addition, for example, a frequency variation, ie a variable test value frequency, is possible. Also conceivable is, for example, a test value for multi-frequency excitation, in which several sinusoidal values are added.

The test value can also be in the form of a sawtooth, trapezoidal shape, or a shape similar to a trapezoidal shape. In this context, “similar to a trapezoidal shape” is to be understood in particular as an excitation shape similar to a trapezoidal shape, with the corner regions being rounded in order, for example, to improve the (engine) acoustics.

Random values can also be used as a test value, in particular as a time-varying test value. Distributions without high frequencies are preferably used here.

The controllers (e.g. CCL & SCL) influence the influence of the test value on the reaction of the electric motor at the respective operating point. For example, a certain settling time is necessary, or there is a phase shift. This influence is therefore preferably taken into account in the method, in particular when determining the optimization variable, for example by means of a waiting time.

wobei I_MTPAControl die Führungsgröße, k₁ ∫Optimierungsgröße sin(ωt + α) dt der Sollwert, und k₂ sin(ωt) der Testwert sind. k1 und k2 sind die Regel- oder Lernfaktoren, t die Zeit, ω die Testwertfrequenz, und α berücksichtigt den Phasenversatz aufgrund der Regelverzögerung. Ist die Frequenz ω klein genug, so kann der Wert für α beispielsweise auf null gesetzt werden. Die Korrelationsfunktion ist somit im Wesentlichen das Integral aus dem was man bisher bei der Optimierung gelernt hat. Alternativ zu dem Integral kann auch ein Tiefpass verwendet werden.In addition to the step-by-step optimization described above, continuous optimization of the setpoint is also possible using the method. In this case, the reference variable is preferably varied continuously, so that a continuous transition between two or more different operating points is implemented. In this case, the correlation between the reference variable and the optimization variable is expediently determined and used. For example, a correlation function of the optimization variable and the reaction of the electric motor to the test value is used as a target value, which represents the correlation between the change in the control variable and the optimization variable: $${\text{I}}_{\text{MTPAControl}}={\text{k}}_1{\displaystyle \int \text{optimization gr}\ddot{\text{O}}\text{ß}}\text{sin}\left(\mathrm{\omega }\text{t}+\mathrm{a}\right)\text{German}+{\text{k}}_2\text{sin}\left(\mathrm{\omega }\text{t}\right),$$

where I _{MTPAControl is} the reference variable, k ₁ ∫Optimization variable sin(ωt + α) dt is the target value, and k ₂ sin(ωt) is the test value. k1 and k2 are the control or learning factors, t is the time, ω is the test value frequency, and α accounts for the phase offset due to the control delay. If the frequency ω is small enough, the value for α can be set to zero, for example. The correlation function is thus essentially the integral of what has been learned so far in the optimization. As an alternative to the integral, a low-pass filter can also be used.

An additional or further aspect of the invention provides that the command variable also leads or influences the quadrature current of the current control in addition to the direct component. If the direct component changes, the other controllers in the system (e.g. the SCL) regulate the system. In order to accelerate this, the command variable can optionally also influence the regulation of the quadrature current. So both the direct component and the quadrature current are adjusted using the command variable. The value should preferably be selected in such a way that the optimization variable, for example the square root of the sum of the squares of the actual direct component and the actual quadrature current, remains unchanged.

Particularly noteworthy are field-oriented controls of electric motors whose systems do not have SCL. If the direct component changes, the amplitude of the motor current remains the same. The resulting speed can be used here as an optimization parameter (the ohmic losses remain constant, but the speed varies).

In order to accelerate adjustment, the reference variable can also be used to change other variables, particularly in the course of pre-control. For example, the reference variable changes the direct component. The direct component also changes the phase voltage assigned to the direct component via the current controller (CCL). This adjustment can be accelerated by a suitable pre-control. This is also possible for other variables, for example for the quadrature current and/or its associated phase voltage.

Depending on the control (e.g. with and without SCL), different optimization variables can be used. For example, a battery current or an intermediate circuit current of the motor electronics is used as an optimization parameter. In one possible embodiment of the method, a motor current, in particular an actual value for the motor current, is used as the optimization variable. In addition to the actual values for the motor current, the setpoints can also be used as an optimization parameter to reduce the influence of measurement noise. Expediently including the setpoint value regulated according to the procedure. The target values have filtered properties, since the determination of the target values already results in a certain filtering or suppression of the measurement noise.

The electric motor according to the invention is, for example, part of an (actuating) drive of a motor vehicle. In this case, the electric motor has motor electronics with a controller for field-oriented regulation of the electric motor operation. In this case, the controller has a current control and optionally a torque or speed control. The controller also has an optimal regulator.

In this case, the optimum controller is generally set up--in terms of program and/or circuitry--to carry out the method according to the invention described above. The optimal controller is thus specifically set up to operate the electric motor deviating from an estimated MTPA operating point and, based on the change that occurs, to draw a conclusion as to whether the actual MTPA operating point is approaching or moving away.

In a preferred embodiment, the optimum controller is formed, at least in its core, by a microcontroller with a processor and a data memory, in which the functionality for carrying out the method according to the invention is implemented programmatically in the form of operating software (firmware), so that the method - optionally in interaction with a device user - is performed automatically upon execution of the operating software in the microcontroller. Alternatively, within the scope of the invention, the optimum controller can also be formed by a non-programmable electronic component, such as an application-specific integrated circuit (ASIC), in which the functionality for carrying out the method according to the invention is implemented with circuitry means.

The advantages and configurations given with regard to the method can also be transferred to the electric motor and vice versa.

The method according to the invention is implemented as a control concept for current control. For example, the optimum controller initially outputs a zero current (I _MTPAControl =0 A) as an estimate for the MTPA operating point. This zero current is initially supplied as a reference variable for controlling the current controller of the direct component, and the electric motor is operated at the estimated (first) operating point. The optimal controller then records and stores a first optimization variable 11, the root of the sum of the squares of the actual direct component Id and the actual quadrature current Iq, for example, being used as the optimization variable I ₁ (l ₁ = √(Id ² + Iq ² ) ). The optimal controller then changes the Id setpoint at its output by the test value I _Delta , for example by increasing the Id setpoint by a value of 0.5 A. Then there is a waiting period until the regulators of the controller have adjusted. The second optimization variable I ₂ (I ₂ =√(Id ² +Iq ² )) is then recorded and stored. Finally, the reference variable or the target value I _MTPAControl is adjusted depending on the optimization variable. For example, a difference in the optimization variables (target variable difference) weighted with a control factor k is used as the new target value: I _MTPAControl = k (12 - 11).

A variable adjustment of the learning or control factor k can be advantageous here. For example, the factor can be set higher in particularly suitable (e.g. static) operating situations than less in suitable operating situations.

A learning success can also be accelerated depending on the past learning steps. If, for example, a current learning direction is recognizable (e.g. several learning steps in succession in the same direction), the learning factor can be increased. Instead of an increment that is proportional to the target variable difference, a non-linear function can also be used, for example the product of k and a sign factor and the difference in the optimization variables.

An additional or further aspect of the invention provides software on a medium or data carrier for carrying out or executing the method described above when the software runs on a computer. The explanations in connection with the method and/or the electric motor also apply to the software and vice versa.

A computer is to be understood here as a device which processes data using programmable calculation rules. The computer is, for example, a calculator, controller, or microcontroller.

The software is stored on a data carrier and is intended to carry out the method described above, and is suitable and designed for this. As a result, particularly suitable software for the operation of an electric motor is implemented, with which the functionality for carrying out the method according to the invention is implemented in terms of programming. The software is thus, in particular, operating software (firmware), with the data medium being, for example, a data memory of the controller.

• 1 eine elektrische Maschine mit einer Stromquelle und mit einem Elektromotor sowie mit einem dazwischen verschalteten Stromrichter,
• 2 drei Phasenwicklungen eines dreiphasigen Elektromotors der Maschine in Sternschaltung,
• 3 ein Brückenmodul einer Brückenschaltung des Stromrichters zur Ansteuerung einer Phasenwicklung des Elektromotors,
• 5 eine feldorientierte Regelung des Elektromotors,
• 6 ein Flussdiagramm eines erfindungsgemäßen Verfahrens zur feldorientierten Regelung eines Elektromotors, und
• 7 ein Flussdiagramm des erfindungsgemäßen Verfahrens in einer zweiten Ausführungsform.

An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. It shows in schematic and simplified representations:

• 1 an electrical machine with a power source and with an electric motor and with a power converter connected in between,
• 2 three phase windings of a three-phase machine electric motor in star connection,
• 3 a bridge module of a bridge circuit of the power converter for controlling a phase winding of the electric motor,
• 5 a field-oriented control of the electric motor,
• 6 a flowchart of a method according to the invention for field-oriented control of an electric motor, and
• 7 a flowchart of the method according to the invention in a second embodiment.

Corresponding parts and sizes are always provided with the same reference symbols in all figures.

the 1 shows an electric machine 2 for an electromotive adjustment system of a motor vehicle, not shown in detail, for example a window winder or a seat adjustment. For this purpose, the machine 2 comprises a three-phase electric motor 4 which is connected to a current source (voltage supply) 8 by means of a converter 6 . In this exemplary embodiment, the power source 8 comprises a vehicle-internal energy store 10 , for example in the form of a (vehicle) battery, and a (DC) intermediate circuit 12 connected thereto, which extends at least partially into the power converter 6 .

The intermediate circuit 12 is essentially formed by a forward line 12a and a return line 12b, by means of which the power converter 6 is connected to the energy store 10. The lines 12a and 12b are at least partially routed into the power converter 6, in which an intermediate circuit capacitor 14 and a bridge circuit 16 are connected between them.

When the machine 2 is in operation, an input current IE supplied to the bridge circuit 16 is converted into a three-phase output current (motor current, three-phase current) IU, IV, IW for the three phases U, V, W of the electric motor 4 . The output currents IU, IV, IW, also referred to below as phase currents, are fed to the corresponding phase (windings) U, V, W ( 2 ) out of a stator, not shown.

In the 2 a star connection 18 of the three phase windings U, V, W is shown. The phase windings U, V and W are each connected to a (phase) end 22, 24, 26 to a respective bridge module 20 ( 3 ) of the bridge circuit 16 out, and connected to each other with the respective opposite end in a star point 28 as a common connection terminal. In the representation of 2 the phase windings U, V and W are each shown by means of an equivalent circuit diagram in the form of an inductance 30 and an ohmic resistance 32 and a respective voltage drop 34, 36, 38. The respectively across the phase winding U, V, W dropping voltage 34, 36, 38 is represented schematically by arrows and results from the sum of the voltage drops across the inductance 30 and the ohmic resistance 32 and the induced voltage 40. The movement of a Rotor of the electric motor 4 induced voltage 40 (electromagnetic force, EMF, EMF) is in the 2 represented by a circle.

The star circuit 18 is controlled by means of the bridge circuit 16. The bridge circuit 16 is designed with the bridge modules 20 in particular as a B6 circuit. In this embodiment, during operation, each of the phase windings U, V, W is switched at a high switching frequency between a high (DC) voltage level of the supply line 12a and a low voltage level of the return line 12b. In this case, the high voltage level is in particular an intermediate circuit voltage UZK of the intermediate circuit 12, the low voltage level preferably being a ground potential UG. This clocked control is available as a - in 1 PWM control, illustrated by arrows, is carried out by a controller 42, with which control and/or regulation of the speed, the power and the direction of rotation of the electric motor 4 is possible.

The bridge modules 20 each include two semiconductor switches 44 and 46, which in the 2 are shown only schematically and as an example for the W phase. The bridge module 20 is connected on the one hand with a potential connection 48 to the supply line 12a and thus to the intermediate circuit voltage UZK. On the other hand, the bridge module 20 is contacted with a second potential connection 50 to the return line 12b and thus to the ground potential UG. About the semiconductor switches 44, 46 is the respective Phase end 22, 24, 26 of the phase U, V, W can be connected either to the intermediate circuit voltage UZK or to the ground potential UG. If the semiconductor switch 44 is closed (conductive) and the semiconductor switch 46 is opened (nonconductive, blocking), then the phase end 22, 24, 26 is connected to the potential of the intermediate circuit voltage UZK. Correspondingly, when the semiconductor switch 44 opens and the semiconductor switch 46 closes, the phase U, V, W is in contact with the ground potential UG. This makes it possible to apply two different voltage levels to each phase winding U, V, W using PWM control.

In the 3 a single bridge module 20 is shown in simplified form. In this exemplary embodiment, the semiconductor switches 44 and 46 are implemented as MOSFETs (metal-oxide semiconductor field-effect transistors), which each switch clocked by means of PWM control between an on state and an off state. For this purpose, the respective gate connections are routed to corresponding control voltage inputs 52, 54, by means of which the signals of the PWM control of the controller 42 are transmitted.

the 4 shows an equivalent circuit diagram for the current source 8. During operation, the energy store 10 generates a battery voltage U _Bat and a corresponding battery current I _Bat for operating the converter 6. In FIG 4 the internal resistance of the energy store 10 is shown as an ohmic resistance 56 and an inherent inductance of the energy store 10 as an inductance 58 . A shunt resistor 60, across which the intermediate circuit voltage U _ZK drops, is connected in the return line 12b.

Depending on the switching states of the (power) semiconductor switches 44, 46, the phase current I _U , I _V , I _W flows through the shunt resistor 60. The voltage drop across the shunt resistor 60 is amplified and evaluated. The phase currents Iu, Iv, Iw are reconstructed by the controller 42 using measurements and the state of knowledge of the switching states of the semiconductor switches 44, 46. Other measurement methods can also be used to determine the motor currents (e.g. direct phase current measurement). The phase voltages (Uu, Uv, Uw) and the phase currents Iu, Iv, Iw are available to the controller 42 together with the measured and/or calculated phase voltages (Uu, Uv, Uw).

The controller 42 is provided for field-oriented control (FOC) of the electric motor 2 and is suitable and set up for this. For this purpose, the (actual) phase currents Iu, Iv, Iw are transformed into a d/q reference system by means of a Park or d/q transformation. In this case, the three phase currents Iu, Iv, Iw are transformed into two orthogonal components, which are referred to below as the direct component _Id and as the quadrature current _Iq .

The controller 42 here - as in particular in the 5 visible - a FOC controller 62 with a current control 64 on. The current control 64 has two controllers 66, 68; the regulator 66 being provided for the direct component I _d and the regulator 68 for the quadrature current I _q . The outputs of the two controllers 66, 68 represent a voltage space vector with components U _d and U _q . Mirroring the transformation performed on the motor currents, these static signals are processed through a series of reference system transformations to provide voltage control signals 70 for the PWM generate control.

In this case, the current control 64 essentially has four sections 72 , 74 , 76 , 78 . Sections 72 and 74 are designed to regulate the quadrature current I _q , and sections 76 and 78 to regulate the direct component I _d . The setpoint values are determined in sections 72 and 76, on the basis of which a control difference for controllers 66, 68 is generated in sections 74 and 78.

In section 72, the FOC target value for the quadrature current I _q is determined. A speed controller 80 is provided for this purpose. The speed controller 80 is designed, for example, as a speed or torque controller. A desired or adjusted target speed SetSpeed and a current actual speed Speed are supplied to the speed controller 80 . The speed controller 80 uses the speed signals to generate a setpoint value I _{q_set} as a reference variable for controlling the quadrature current I _q .

Section 74 includes controller 68 . In section 74, a control difference I _{q_Error is} determined based on the current actual value of the quadrature current I _q and the desired value I _{q_set} and is supplied to the controller 68 as an input signal. From this, the controller 68 generates the quadrature voltage U _q as a manipulated variable.

Sections 76 and 78 have an optimal controller 82 for determining and, if necessary, correcting the MTPA operating point during the runtime. The optimum controller 82 is provided and set up to carry out a method according to the invention.

In this case, the current actual values of the quadrature current I _q and the direct component I _d are supplied to the optimum controller 82 . From this, the optimum controller 82 determines an optimization variable, which is used to generate a reference variable I _MTPAControl as an output signal. In section 78, a system deviation I _{d_Error is} determined based on the current actual value of the direct component I _d and the reference variable I _MTPAControl generated by the optimal controller 82, and is supplied to the controller 66 as an input signal. From this, the controller 66 generates the DC voltage component U _d as a manipulated variable.

The optimal controller 82 has, for example, a setpoint unit 84 and a control unit 86 . In this case, setpoint unit 84 is assigned to section 76 and control unit 86 to section 78 , for example. The setpoint unit 84 generates a setpoint I _{d_set} , with the control unit 86 generating a test value I _Delta . In this case, the current actual values of the quadrature current I _q and the direct component I _d are supplied to the control unit 86 . The setpoint I _{d_set} and the test value I _Delta are combined to form the reference variable I _MTPAControl .

The method carried out by the optimal controller 82 is described below with reference to FIG 6 explained in more detail.

The method is started in a method step 88 and ended in a method step not shown in detail.

In a first method step 90, the optimal controller 82 initially outputs a zero current as a reference variable (I _MTPAControl =0 A), which is used as an initial estimate for the MTPA operating point. This zero current is realized in particular by a setpoint value I _{d_set} of 0 A and by a test value I _Delta of 0 A. This zero-sequence current is initially used as reference variable I _MTPAControl for determining the control deviation I _{d_Error} . As a result, controller 66 initially regulates to the estimated MTPA operating point, as a result of which electric motor 4 or machine 2 is operated at this (first) operating point.

After the electric motor 4 or the machine 2 has adjusted itself, in a second method step 92 the reaction of the electric motor 4 or the machine 2 to this operating point is recorded with a first optimization variable I ₁ . In this case, the optimization variable I ₁ is determined by the optimal controller 82 or the control unit 86 on the basis of the actual values of the quadrature current I _q and the direct component I _d . For example, the square root of the sum of the squares of the actual direct component I _d and the actual quadrature current I _q is used as the optimization variable I ₁ : I ₁ =√(I _d +I _q ). The optimization variable I ₁ is stored in a memory of the optimal controller 82 .

In a third method step 94, a (second) reference variable I _MTPAControl is generated, which differs from the reference variable I _MTPAControl of method step 90. As a result of the changed reference variable I _MTPAControl , the control deviation I _{d_Error is} changed, so that the controller 66 regulates to a new (second) operating point. To do this, the optimum controller 82 changes the setpoint I _{d_set} by a test value I _Delta which is not equal to 0A. For example, the test value I _Delta has a current value of 0.5 A here, so that the setpoint I _{d_set} —and thus the command variable I _MTPAControl —is increased by a value of 0.5 A.

After the electric motor 4 or the machine 2 has adjusted to the new operating point, the reaction of the electric motor 4 or the machine 2 to this second operating point is recorded with a second optimization variable I ₂ in method step 96 . The optimization variable I ₂ is determined analogously to the optimization variable I ₁ from the current actual values of the quadrature current I _q and the direct component I _d . For example, the square root of the sum of the squares of the actual direct component I _d and the actual quadrature current I _q is used as the optimization variable I ₂ : I ₂ =√(I _d +I _q ).

In a method step 98, the optimization variables I ₁ and I ₂ are evaluated. A comparison is carried out for this purpose, for example. If the first optimization variable I ₁ shows better engine operation, ie engine operation with higher efficiency, method steps 90 to 98 are repeated, with the sign of the test value I _Delta being changed in method step 94 .

If the second operating point has the higher efficiency, i.e. the second optimization variable I ₂ has better engine operation, the setpoint I _{d_set} is adjusted in a method step 100, which means that when method steps 90 to 98 are subsequently carried out, there is no zero current for the setpoint I _{d_set} is used. The setpoint I _d Set is thus gradually or iteratively approximated to the actual MTPA operating point. For example, a difference in the optimization variables (target variable difference) weighted with a control factor k is used as the new setpoint value I _{d_set} : I _{d_set} = k (I ₂ -I ₁ ).

the 7 shows an alternative embodiment of the method. In this case, in the first method step 90', a test value I _Delta not equal to 0 A is added to the desired value I _{d_set} . This means that the reference variable I _MTPAControl has a test value I _delta in one direction. Correspondingly, in the third method step 94′, the test value I _Delta is subtracted from the target value I _d Set , ie a reference variable I _MTPAControl with a test value I _Delta in the other (opposite) direction is used.

If the operating point of method step 94' has the higher efficiency, that is to say the second optimization variable I ₂ has better engine operation, then the setpoint value I _{d_set} is adjusted in a method step 100a. If the operating point of method step 90' has the higher efficiency, that is to say the first optimization variable I ₁ has better engine operation, then the setpoint value I _{d_set} is adjusted in a method step 100b.

The claimed invention is not limited to the embodiments described above. Rather, other variants of the invention can also be derived from this by the person skilled in the art within the scope of the disclosed claims without departing from the subject matter of the claimed invention. In particular, all of the individual features described in connection with the various exemplary embodiments can also be combined in other ways within the scope of the disclosed claims, without departing from the subject matter of the claimed invention.

For example, it is conceivable that the command variable I _MTPAControl also leads or influences the quadrature current I _q in addition to the direct component I _d . In order to accelerate the adjustment, the reference variable I _MTPAControl can also be used to change other variables, particularly in the course of a pre-control.

Depending on the control (e.g. with and without speed controller 80), different optimization variables can be used. For example, the battery current I _Bat is used as an optimization variable. In addition to the actual values for the motor current, the setpoint values I _{d_Set} , I _{q_set} can also be used as an optimization variable or as a basis for determining the optimization variable.

Reference List

2

machine

4

electric motor

6

power converter

8th

power source

10

energy storage

12

intermediate circuit

12a

direction

12b

return line

14

intermediate circuit capacitor

16

bridge circuit

18

star connection

20

bridge module

22,24,26

phase end

28

star point

30

inductance

32

Resistance

34, 36, 38

voltage drop

40

tension

42

controllers

44, 46

semiconductor switch

48, 50

potential connection

52, 54

control voltage input

56

Resistance

58

inductance

60

shunt resistance

62

field-oriented regulation

64

current control

66, 68

controller

70

voltage control signal

72, 74, 76, 78

section

80

speed controller

82

optimal controller

84

setpoint unit

86

control unit

88... 100

process step

90', 94'

process step

100a, 100b

process step

AND MANY MORE

phase/phase winding

lu, Iv, Iw

phase current/output current

ie

input current

UCC

intermediate circuit voltage

UG

earth potential

IBat

battery power

UBat

battery voltage

id

direct component

Iq

quadrature current

SetSpeed

target speed

speed

Is speed

Iq_set

setpoint

Iq_Error

deviation

Uq

quadrature voltage

id_set

setpoint

IMTPAControl

benchmark

Id_Error

deviation

Ud

DC component

11, 12

optimization size

Claims (10)

Method for field-oriented control of an electric motor (4), in which an operating state of the electric motor (4) is set via a current control (64) in the dq reference system with a direct component (I _d ) and a quadrature current (I _q ), - with a setpoint (I _{d_set} ) of the direct component (I _d ) to bring about an operating state of the electric motor (4) with maximum torque per ampere is estimated, - with the reference value (I _{d_set} ) at least one command variable (I _MT - _PAControl ) for guiding the direct component ( I _d ) of the current control (64), by means of which the electric motor (4) is operated at a first operating point and a second operating point that differs therefrom, - with at least one optimization variable (11, 12) as a reaction of the electric motor (4) to operation at the first operating point and at the second operating point is recorded, - the at least one optimization variable (11, 12) with regard to the operating state of the E lektromotors is evaluated with maximum torque per ampere, and - the setpoint (I _{d_set} ) of the direct component (I _d ) is set based on the evaluation. procedure after claim 1 , characterized in that the first and/or second operating points are brought about by a test value (I _Detla ) of the reference variable (I _MTPAControl ). procedure after claim 2 , characterized in that the reference variable (I _MTPAControl ) is composed of a sum of the desired value (I _{d_Set} ) and the test value (I _Delta ). procedure after claim 3 , characterized in that a correlation function of the optimization variable (11, 12) and the reaction of the electric motor (4) to the test value (I _Delta ) is used as the desired value (I _{d_set} ). Procedure according to one of claims 2 until 4 , characterized in that the test value (I _Delta ) is varied over time with a test value frequency. Procedure according to one of Claims 1 until 5 , characterized in that the command variable (I _MTPAControl ) is varied continuously. Procedure according to one of Claims 1 until 6 , characterized in that the reference variable (I _MTPAControl ) leads the quadrature current (I _q ) of the current control (64) in addition to the direct component (I _d ). Procedure according to one of Claims 1 until 7 , characterized in that a motor current is used as the optimization variable (I ₁ , I ₂ ). Electric motor (4) with motor electronics having a controller (42) for field-oriented regulation (62) of the electric motor (4), the controller (42) having a current regulator (64) and an optimal regulator (82) for carrying out a method according to one of the Claims 1 until 8th having. Software on a data carrier for carrying out a method according to one of Claims 1 until 8th , if the software runs on a computer.

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