DE102019215854A1 - Method for operating a brushless and sensorless multiphase electric motor - Google Patents

Abstract

The invention relates to a method for operating a brushless and sensorless multiphase electric motor (4), a position signal (P) from a position observer (64) as a measure for a rotor position based on at least one motor variable (IU, IV, IW, UU, UV, UW , 40) of the electric motor (4) is determined, with a signal processor (66) calculating a rotation variable (θ, ω) on the basis of the position signal (P), the position signal (P) and / or the rotation variable (θ, ω) is generated with a stored minimum gradient (v) as a measure for a minimum speed (ω), and the electric motor (4) is controlled and / or regulated on the basis of the rotation variable (θ, ω).

Description

The invention relates to a method for operating a brushless and sensorless multiphase electric motor. The invention further relates to an electric drive, in particular for an adjusting element (adjusting system) of a motor vehicle, with an electric motor operated according to the method.

Adjustment systems driven or operated by electric motors as motor vehicle components, such as window lifters, seat adjustments, 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. For such electromotive drives, so-called brushless electric motors (brushless direct current motor, BLDC motor) are increasingly used, in which the wear-prone brush elements of a rigid (mechanical) commutator are replaced by electronic commutation of the motor current.

Electric motor drives for motor vehicles are usually fed by a (high-voltage) battery as the vehicle-internal energy storage device, from which the electric motor is supplied with electrical energy in the form of a direct current (direct voltage). To convert the direct current into the motor current, a power converter (inverter, inverter) is suitably connected between the energy store and the electric motor. The 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 pulse-width modulated (PWM) control or regulation of semiconductor switches in the bridge circuit. The semiconductor switches are switched between a conductive and a blocking state in a clocked manner using 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 then generates a rotating magnetic field that rotates with respect to the stator. The rotor of the electric motor here suitably has a number of permanent magnets, the interaction of the permanent magnets with the rotating field generating a resulting torque which sets the rotor in rotation.

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). The phases are connected to one another in a star point of a star connection, for example.

For efficient operation it is necessary that the phases are supplied with power at the right time. To do this, it is necessary to precisely determine the relative position of rotor and stator for motor control / regulation.

Here, for example, an observer-based control and / or regulation of the electric motor is conceivable. In such an observer or upper server method, a so-called state or position observer also runs based on the system equations of the electric motor or drive. From a comparison of the expected motor states from the observer with the measured values, the actual state and thus a rotation variable, that is to say the rotor position and / or the speed, can be determined.

An observer is to be understood here and in the following in particular as a system which, from known input variables (e.g. manipulated variables or measurable disturbance variables) and output variables (measured variables) of the observed electric motor, does not measure measurable variables (states), such as the rotor position in particular , reconstructed. For this purpose, the observer simulates the observed electric motor, for example as a model, and uses a controller to track the measurable state variables, which are therefore comparable to the electric motor.

The rotor position for determining the position is determined, for example, by means of additional rotation sensors, such as a Hall sensor. Rotation sensors or encoders of this type are, however, expensive, which is why a position determination should preferably be carried out without a sensor.

The sensorless position determination is based, for example, on the detection of induced current and / or voltage signals due to the back electromotive force (back EMF, back EMF) which the rotating permanent magnets induce in the phase windings. The induced back EMF signals are proportional to the rotor speed, which disadvantageously means that at low speeds or when the electric motor is at a standstill, only little or no information is available for determining the position for the motor controller. In particular, the signal-to-noise ratio is reduced at low speeds. Such a restriction also applies to flow-based sensorless measurement methods. As a result, a position determination or position recognition below a threshold speed is usually not possible, which means a safe and reliable operation of the electric motor, in particular when starting from standstill or during operation at low speed, is disadvantageously made more difficult.

To reach and / or exceed the threshold speed, it is possible, for example, to align the drive or the rotor without knowledge of the exact rotor position and then to accelerate it without regulation by means of a controller using an acceleration ramp. As a rule, a voltage vector is used for alignment, which rotates the rotor into a specified position (starting position). For this purpose, for example, one phase is connected to a reference potential, such as a ground, and the other phases are supplied with a pulse-width-modulated control signal. The magnetic field generated thereby aligns the rotor so that the rotor is transferred to a defined starting position.

After the alignment, the electric motor is run up or accelerated by means of an open-loop control, i.e. virtually blind. For this purpose, the electric motor or its rotor is accelerated step by step, for example by means of a ramp, up to a minimum speed from which a sensorless position detection is possible. For example, after the initial position alignment, the electric motor is supplied with a motor current with a constant amplitude, the frequency of which is increased step by step or successively.

Disadvantageously, this method requires comparatively high motor or phase currents. Furthermore, the electric motor or the rotor must first be aligned and is then accelerated comparatively slowly, so that there is a particularly long start or run-up time. There is also the risk of oscillations and the loss of the synchronous field. The oscillations and high motor currents disadvantageously also worsen the acoustics of such an operated drive.

Another possibility for position detection is the evaluation of anisotropic properties of the drive, such as, for example, an inductance of the phase windings that is dependent on the rotor position. This method for position detection also works advantageously at low speeds and when the rotor is at a standstill. Disadvantageously, however, the method can only be used in drives which have corresponding properties, such as, for example, a sufficiently high dependence of the inductance on the rotor position. Furthermore, a comparatively powerful measurement value acquisition is required. Furthermore, the acoustic properties of the electric motor are adversely affected during operation, as a result of which an increased noise level is generated.

The invention is based on the object of specifying a particularly suitable method for operating a brushless and sensorless multiphase electric motor. In particular, the method should enable effective and reliable operation of the electric motor even at low speeds or from a standstill. The invention is also based on the object of specifying an electric drive with an electric motor operated in this way.

With regard to the method, the object is achieved according to the invention with the features of claim 1 and with regard to the drive with the features of claim 10. Advantageous refinements and developments are the subject of the subclaims. The advantages and refinements cited with regard to the method can also be applied to the drive and vice versa.

The method according to the invention is suitable and set up for operating a brushless and sensorless multiphase, in particular three-phase, electric motor. The electric motor is in particular a synchronous machine, preferably a brushless direct current motor, of a motor vehicle, for example an adjusting motor.

According to the invention, a position signal is determined as a measure for a rotor position by a position observer. For this purpose, at least one motor variable of the electric motor is fed to the position observer, on the basis of which the position signal is determined.

The position signal is then fed to a signal processor, which calculates a rotation variable based on the position signal.

According to the invention, the position signal and / or the rotation variable are generated with a stored minimum gradient (minimum gradient) as a measure of a minimum speed. This means that the change in the position signal and / or the rotation variable over time is determined and / or calculated on the basis of the minimum gradient. The conjunction “and / or” is to be understood here and below 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 is controlled and / or regulated on the basis of the rotation variable. This is a implemented a particularly suitable method for operating an electric motor.

According to the method, the exact or exact position of the electric motor is therefore not determined. Instead of a classic position signal from an encoder or position sensor, the electric motor is controlled and / or regulated on the basis of the position signal from the position observer. This signal is processed, for example filtered, by a speed observer as signal processing, and the rotation variable is calculated or estimated. In other words, the position signal serves as an input for the signal processing, which filters the position substitute signal and determines the rotor position and / or the rotational speed or the speed for the control and / or regulation of the electric motor.

By means of the position detection system formed by the position observer and the signal processing, a regulating or control signal with a minimum slope or minimum slope is generated as a rotation variable, on the basis of which a rotating field is generated with a corresponding speed. In other words, the electric motor is operated at a minimum speed. This makes the method suitable even at low engine speeds or when starting from a standstill. In particular, the required speed from which a control method can be used for the operation of the electric motor is reduced. Furthermore, regulation and / or control at low speeds is thus made possible in a simple manner, without the electric motor having to have special motor properties for this, such as, for example, a sufficiently high dependence of the inductance on the rotor position.

A “minimum gradient” or minimum gradient is to be understood here as a change in the state of the position signal and / or the rotation variable, by means of which the minimum speed is implemented by the control and / or regulation. In other words, the minimum slope is preferably the smallest possible change in state that is required for realizing or converting a desired rotating field or the minimum speed.

A position observer is to be understood here and below in particular as an observer or status observer of the electric motor who uses the at least one motor variable to determine an estimated signal or an expected value for the current rotor position of a rotor of the electric motor.

Here and in the following, a motor variable is to be understood in particular as an (operating) state variable of the electric motor. The at least one motor variable is, for example, a measured variable, in particular a motor current or a motor voltage, for example a phase current or a phase voltage, or a (motor) temperature. Additionally or alternatively, for example, a motor resistance, a motor inductance, or a pulse duty factor of a PWM motor voltage is fed to the position observer as a motor variable.

Using the at least one motor variable, the position observer determines the position signal as the raw position of the electric motor or rotor. The position signal is then sent to the signal conditioning. The signal processing is carried out here, for example, as a speed observer, that is to say as an observer for the engine speed or engine speed. The signal processing or the speed observer is designed, for example, as a control system.

Using the position signal, the amount of rotation is calculated as a (filtered) rotor position and / or as speed information. RPM or speed, calculated. The rotation variable is then fed to a controller, for example a field-oriented controller, for example a current controller, which generates a rotating field and thus controls and / or regulates the movement of the electric motor or rotor.

Due to the minimal slope of the position signal and / or rotation signal, the electric motor is operated at the minimum or minimum speed. The movement of the rotor in turn generates an induced voltage as a back EMF, which can be used as a motor variable for sensorless position detection.

In contrast to a “blind” rotating field specification, the method according to the invention realizes a shorter start-up time for the electric motor. In particular, according to the method, prior alignment of the electric motor or rotor is dispensed with; the electric motor or rotor is operated directly at the minimum speed. As a result, a faster change to a regulated operating mode is made possible. Furthermore, the efficiency and the acoustics of the electric motor are improved. This significantly improves the robustness of the electric motor at low speeds.

In one possible embodiment, it is conceivable, for example, that the position observer from measured variables (e.g. from phase voltage, Phase current, temperature) and other variables (e.g. motor resistance, motor inductance, pulse duty factor of the PWM voltage) as motor variables, the position signal is determined as the raw position. During synchronization of the electric motor or at low (motor) speeds or (motor) speeds, it can be advantageous to deviate from this calculation. For example, a voltage drop across a (motor) inductance with the help of a derivative of the motor current is used as a motor variable. In order to improve the signal quality of the position signal, it is possible here, for example, for the calculated value of the inductance to be reduced or set to zero.

In contrast to classic or conventional sensorless position detection, the method according to the invention does not require any additional test pulses, which on the one hand does not result in any acoustic impairments and on the other hand ensures particularly simple integration. In comparison to classic sensorless methods, the method according to the invention is particularly robust with regard to measurement noise and tolerances. The method according to the invention is also particularly easy to implement and parameterize, so that a particularly low computing load is guaranteed.

The method according to the invention is particularly suitable for applications in which the inductances in the coordinate system are the same. This means that, for example, in a d / q coordinate system fixed to the rotor, the inductances are the same (Ld = Lq), in this case there is no magnetic asymmetry of the electric or synchronous motor and no reluctance contribution to the torque is generated. This means that the inductance is position-independent, so that, for example, conventional methods such as an INFORM method (indirect flow determination through online reactance measurement) cannot be used. In contrast to this, the method according to the invention can be used both for position-dependent (Ld ≠ Lq) and for position-independent (Ld = Lq) inductances.

The method according to the invention does not require any initial position detection. The control and / or regulation of the electric motor preferably synchronizes automatically.

Without specific initialization, the position signal and the rotor have essentially random positions with respect to one another. However, this can lead to the rotor being briefly accelerated in the opposite direction when it starts or starts up. This is uncritical and permissible for many applications. In order to avoid this start-up in the opposite direction and to generally improve the start-up behavior, the method according to the invention can, however, also be combined with an initial position or position detection method. This means that the method according to the invention is initialized with a detected rotor position.

When starting from a standstill, the initially unknown (initial) initial value can be determined at least approximately with the aid of position detection methods such as an INFORM method. This simplifies the synchronization of the electric motor at low speeds.

In a preferred development, the electric motor is driven at the minimum speed when starting from a standstill, that is to say in particular at the start of the process. In a suitable embodiment, the electric motor is limited in particular to the minimum speed. This means that the electric motor is controlled and / or regulated on the basis of the rotation variable in such a way that the gradient does not fall below the minimum.

According to the invention, when the electric motor is at a standstill or at low engine speeds, in particular starting or acceleration takes place at a minimum speed, that is to say at a minimum speed. In other words, in contrast to the prior art, there is no upstream or initial alignment of the rotor. Furthermore, in contrast to the prior art, the control and / or regulation based on the gradient or minimum speed realizes a closed-loop regulation when starting up. In particular, by limiting to the minimum gradient or to the minimum speed or minimum rotational speed, a “downward” limitation is implemented, which enables the electric motor to accelerate or start up particularly quickly. As a result, the start-up time of the electric motor is reduced and, as a result, the acoustics of the electric motor are improved and its energy consumption is advantageously reduced during a start-up.

In a conceivable further development, the rotation variable is calculated and limited on the basis of the position signal and the stored gradient or minimum speed (minimum speed). A minimum speed is to be understood here as a minimum speed or minimum rotation of the rotor, for example 10 revolutions per minute (rounds per minute, RPM).

This additional functionality is integrated in the signal processing, for example. This essentially means that the speed of the signal processing for the calculation of the rotation size is limited to the minimum speed. As a result, the calculated rotation size increases with a minimum gradient, even if that Position signal at the input of the signal conditioning remains constant. In other words, the amount of rotation increases even with a constant position signal.

If the minimum speed is too low, for example at one revolution per minute (1 RPM, rounds per minute), the rotor will follow in most applications, but the position detection or the position observer will not receive sufficiently good signals. Correspondingly, if the minimum speed is too high, for example at 1000 revolutions per minute (1000 RPM), the signal quality would be sufficient, but the drive or the electric motor would not synchronize and would therefore stop.

In a particularly preferred embodiment, the minimum gradient and / or the minimum speed are preferably designed so that on the one hand a stationary rotor of the electric motor is carried along and on the other hand, a motor variable for position detection is generated by the movement of the rotor. The minimum speed is to be understood in particular as a certain speed or rotational speed range of the rotor.

The upper limit of the minimum speed is selected in such a way that a stationary rotor is carried along, that is to say that the rotor does not slip.

The lower limit for the minimum speed is a speed at which a sufficient effect for a back EMF or a flux determination for determining a corresponding motor variable is brought about. If the rotor speed is below the lower limit, then the minimum speed in the calculation of the rotation variable results in an acceleration of the electric motor or rotor in order to increase the back EMF or flux determination. This also ensures that the electric motor does not start or run in the wrong direction (opposite direction).

With a suitable choice of the start and minimum speed, it is thus ensured that the method is automatically synchronized and thus an initial position detection is essentially not necessary. This enables a reliable and safe start of the electric motor.

The permissible range of the minimum speed depends on the application or application and can also be influenced, for example, by controller settings.

The electric motor is operated, for example, at a constant minimum speed during the process. However, the minimum speed is preferably adapted or varied at least as a function of an operating point or an operating situation of the electric motor. In a suitable embodiment, the value of the minimum speed is adapted in particular as a function of temperature. In other words, the value of the minimum speed is preferably varied as a function of the operating temperature. As a result, a particularly flexible method is implemented which adapts to the respective operating situation or operating temperature of the electric motor.

In an expedient dimensioning, a rotational speed of less than or equal to 300 revolutions per minute (300 RPM), in particular less than or equal to 20 revolutions per minute (20 RPM), is used as the minimum speed. In a preferred dimensioning, in particular a minimum speed in the range between 5 RPM and 20 RPM is used. This enables, on the one hand, a reliable entrainment or synchronization of the rotor and, on the other hand, a sufficiently high signal quality of the back EMF or flux determination, so that a particularly reliable start-up of the electric motor is ensured.

Additionally or alternatively, it is conceivable, for example, that the minimum speed is varied or changed during a period of time, for example during the starting process. For example, it is advantageous to select the minimum speed to be small or equal to zero in order to better capture the rotor with the generated rotating field, and then to increase the value in order to bring about a sufficient speed or acceleration of the rotor.

In an expedient embodiment, the minimum speed is increased continuously after a predetermined period of time. In particular, in a suitable development, the minimum speed is increased from a first speed value to a second speed value which is approximately 25% to 100% larger than the first speed value. In other words, the minimum speed is increased from a low (first) speed value, for example 5 RPM to 20 RPM, to a (second) speed value that is increased in comparison, for example 10 RPM to 40 RPM.

In a preferred embodiment of the method, a flow observer is used as the position observer. This means that the motor variable for determining the position signal is recorded in particular on the basis of a flux determination. Thereby a particularly useful observation with regard to the rotor position is implemented.

The electric drive according to the invention is designed, for example, as an adjusting drive of a motor vehicle. For this purpose, the drive has a brushless and sensorless multiphase electric motor and a sensor unit z for detecting the at least one motor variable as well as a position observer for sensorless determination of the position signal. The drive also has signal processing for the sensorless determination of the rotation variable based on the position signal and a current regulator for controlling and / or regulating the electric motor, in particular by means of pulse width or space vector modulation.

The position observer and the signal processing are in this case designed, for example, as controllers, that is to say as control devices, and are generally suitable and set up here - in terms of programs and / or circuitry - for carrying out the method described above. The position observer is thus specifically set up to determine the position signal on the basis of the motor variable, for example on the basis of measured or calculated phase voltages and / or phase currents. The position signal is fed to the signal processing unit, which determines the amount of rotation, for example on the basis of a speed observation and the stored minimum gradient.

The position signal is fed to the signal processing unit, which filters and evaluates the position signal, for example, and thus calculates or estimates the rotation variable, that is to say the rotor position and / or the (rotor) speed. This calculated or estimated rotation variable is fed to the current controller as a manipulated variable.

In a preferred embodiment, the position observer and / or the signal processing and / or the current regulator are at least essentially formed by a microcontroller with a processor and a data memory, in which the functionality for carrying out the method according to the invention, or the respective method steps, is in the form of operating software ( Firmware) is implemented in a program, so that the method or the method steps - possibly in interaction with a user - is carried out automatically when the operating software is executed in the microcontroller.

The position observer and / or the signal conditioning and / or the current regulator can alternatively also be formed in the context of the invention by a non-programmable electronic component, for example an ASIC (application-specific integrated circuit) or an FPGA (field programmable gate array), in which the functionality for performing the method is implemented with circuitry.

The drive or the electric motor operated with the method thus has an improved behavior with regard to starting or starting from a standstill and with regard to permanent or continuous operation at low speeds.

In a conceivable embodiment, the electric motor is connected in particular to a bridge circuit of a converter, which converts a direct voltage from an intermediate circuit into an alternating voltage for driving or operating the electric motor. The drive thus has a DC voltage input or DC voltage connection. The bridge circuit is controlled and / or regulated by the current regulator, for example, in terms of signaling.

Depending on the switching states of the power semiconductor switches in the bridge circuit, a phase current flows through a shunt. The voltage drop across the shunt is, for example, amplified and evaluated. The phase currents are reconstructed using measurements and knowledge of the switching states of the power semiconductor switches. Alternatively, it is also conceivable, for example, for the phase currents to be measured directly or immediately. Together with the measured and / or calculated phase voltages, the position observer thus has the phase voltages and phase currents available as motor variables for determining the position signal.

In a conceivable embodiment, the position observer and the signal processing are designed, for example, as a common component.

• 1 einen elektrischen (elektromotorischen) Antrieb mit einer Stromquelle und mit einem Elektromotor sowie mit einem dazwischen verschalteten Stromrichter,
• 2 einen phasenspannungsgeregelten Antrieb,
• 3 drei Phasenwicklungen eines dreiphasigen Elektromotors in Sternschaltung,
• 4 ein Brückenmodul einer Brückenschaltung des Stromrichters zur Ansteuerung einer Phasenwicklung des Elektromotors,
• 5 ein Ersatzschaltbild der Stromquelle,
• 6 einen Positionsbeobachter und eine Signalaufbereitung des Antriebs,
• 7 ein Zeit-Winkel-Diagramm bei einem Startvorgang aus dem Stillstand gemäß dem Stand der Technik, und
• 8, 9 ein Zeit-Geschwindigkeits-Diagramm bei einem Startvorgang aus dem Stillstand gemäß dem erfindungsgemäßen Verfahren.

Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. It shows in schematic and simplified representations:

• 1 an electric (electromotive) drive with a power source and with an electric motor as well as with a converter connected in between,
• 2 a phase voltage controlled drive,
• 3 three phase windings of a three-phase electric motor in star connection,
• 4th a bridge module of a bridge circuit of the converter for controlling a phase winding of the electric motor,
• 5 an equivalent circuit diagram of the power source,
• 6th a position observer and a signal processing of the drive,
• 7th a time-angle diagram for a starting process from standstill according to the prior art, and
• 8th , 9 a time-speed diagram for a starting process from standstill according to the method according to the invention.

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

The 1 shows an electric or electromotive drive 2 for an adjustment system of a motor vehicle, not shown in detail, for example a window regulator or a seat adjustment. The drive 2 includes a brushless and sensorless three-phase electric motor 4th , which by means of a converter 6th to a power source (power supply) 8th connected. The power source 8th In this exemplary embodiment, it comprises an energy store inside the vehicle 10 , for example in the form of a (motor vehicle) battery, and an associated (DC) intermediate circuit 12, which is at least partially in the converter 6th extends.

The intermediate circuit 12th is essentially through an outgoing line 12a and a return line 12b formed, by means of which the converter 6th to the energy storage 10 connected. The lines 12a and 12b are at least partially in the converter 6th out, in which between these an intermediate circuit capacitor 14th as well as a bridge circuit 16 are interconnected.

During operation of the drive 2 becomes one of the bridge circuit 16 supplied input current IE ( 5 ) 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 4th changed. The output currents also referred to below as phase currents IU , IV , IW are connected to the corresponding motor phases or phases (windings) U , V , W. ( 3 ) out of a stator not shown in detail.

In 3 is a star connection 18th of the three phase windings U , V , W. shown. The phase windings U , V and W. are each with a (phase) end 20th , 22nd , 24 to a respective bridge module 26th ( 3 ) the bridge circuit 16 out, and with the opposite end in a star point 28 interconnected as a common connection terminal.

In the representation of the 3 are the phase windings U , V and W. each by means of an equivalent circuit diagram in the form of an inductance 30th and an ohmic resistor 32 as well as a respective voltage drop 34 , 36 , 38 shown. Each via the phase winding U , V , W. falling voltage 34 , 36 , 38 is represented schematically by arrows and results from the sum of the voltage drops across the inductance 30th and the ohmic resistance 32 as well as the induced voltage or the induced phase current 40 . That by a movement of a rotor of the electric motor 4th induced phase current 40 (Back-EMF, back-EMF) is in the 3 shown schematically on the basis of a circle.

The control of the star connection 18th takes place by means of the bridge circuit 16 . The bridge circuit 16 is with the bridge modules 26th in particular designed as a B6 circuit. In this embodiment, each of the phase windings is in operation U , V , W. clocked at a high switching frequency between a high (direct) voltage level of the outgoing line 12a and a low return line voltage level 12b switched. The high voltage level is in particular an intermediate circuit voltage UCC of the intermediate circuit 12th , the low voltage level preferably being a ground potential Basement is. This clocked control is available as an - in 1 represented by arrows - PWM control by a device 42 designed as a controller with which a control and / or regulation of the speed, the power and the direction of rotation of the electric motor 4th is possible.

The bridge modules 20th each include two semiconductor switches 44 and 46 , what a 3 only schematic and exemplary for the phase W. are shown. The bridge module 26th is on the one hand with a potential connection 48 to the supply line 12a and thus to the intermediate circuit voltage UCC connected. On the other hand is the bridge module 26th with a second potential connection 50 to the return line 12b and thus to the earth potential Basement contacted. About the semiconductor switch 44 , 46 is the respective end of the phase 20th , 22nd , 24 the phase U , V , W. either with the intermediate circuit voltage UCC or with the earth potential Basement connectable. Will the semiconductor switch 44 closed (conductive) and the semiconductor switch 46 open (not conductive), then the end of the phase 20th , 22nd , 24 with the potential of the intermediate circuit voltage UCC connected. The same applies when the semiconductor switch is opened 44 and closing the semiconductor switch 46 the phase U , V , W. with the earth potential Basement contacted. Thereby it is by means of the PWM control of the device 42 possible any phase winding U , V , W. to apply two different voltage levels.

In 4th is a single bridge module 26th shown in simplified form. In this embodiment, the semiconductor switches 44 and 46 realized as MOSFETs (metal-oxide semiconductor field-effect transistor), which switch between a switched-through state and a blocking state by means of the PWM control. For this purpose, the respective gate connections are connected to the corresponding control voltage inputs 52 , 54 out, by means of which the signals of the control 42 be transmitted.

The 5 shows an equivalent circuit diagram for the current source 8th . The energy store generates during operation 10 a battery voltage UBat as well as a corresponding battery current IBat to operate the converter 6th . In 5 is the internal resistance of the energy store 10 as an ohmic resistor 56 and a self-inductance of the energy store 10 as an inductor 58 shown. In the return line 12b is a shunt resistor 60 switched to which the intermediate circuit voltage UCC falls off.

In the embodiment of 1 are the phase currents IU , IV , IW by means of an ammeter 62 detected and to the device 42 guided. A position observer 64 determined on the basis of motor variables, in particular on the basis of the recorded phase currents IU , IV , IW and calculated phase voltages UU , UV , UW , as well as a position signal based on other variables (e.g. motor resistance, motor inductance, pulse duty factor of the PWM voltage) P. as a raw position as a measure of the rotor position of the electric motor 4th .

The position signal or the raw position P. is sent to signal processing 66 transmitted. In addition to the position signal P. becomes, for example, a minimum slope or minimum slope v as a measure of a minimum speed or as a raw speed for signal processing 66 sent. The signal processing 66 is preferably designed as a speed observer, with the position signal P. and / or the slope v filtered, and a rotation size 0 , ω , i.e. the rotor position 0 and / or the (rotor) speed ω , calculates or estimates. This calculated or estimated amount of rotation θ , ω is used as a manipulated variable for a current controller 68 supplied, which generates the PWM control signals.

The position observer trained in particular as a river observer 64 and the signal processing especially designed as a speed observer 66 form a position detection system 70 the device 42 . The position detection system 70 gives the rotation size θ as a position control signal to the current controller 68 with a minimal slope in the form of the rotation size ω as speed or speed control signal.

In 2 is a version of the drive in a comparatively simple representation 2 shown in which a phase-voltage-controlled operation of the electric motor 4th is made possible. In this embodiment, the phase disturbances IU , IV , IW and the phase voltages UU , UV , UW directly measured or recorded and used as motor variables in the 6th individually represented position detection system 70 fed.

The method according to the invention is described below with reference to FIG 7th and 8th explained in more detail.

The 7th shows a schematic time-angle diagram, the time being horizontal, that is to say along the respective abscissa axis (X-axis) t , and an angle or position along the vertical ordinate axis (Y-axis) W. is applied. There are two curves in the diagram 72 and 74 shown. The course of the curve 72 shows the time course of the angle of a current regulator 70 generated voltage vector, the curve progression 74 represents the rotor position or the angular position of the rotor. The 7th shows a starting process of the electric motor 4th , i.e. starting from a standstill.

In the 7th a starting process according to the prior art is shown. Since there are usually no signals or motor variables for a sensorless position determination at standstill or at low speeds, the rotor is switched off for a first period of time t1 aligned and then for a period of time t2 for example accelerated with a fixed acceleration ramp. As a rule, a constant voltage vector is used for alignment, which rotates the rotor into a specified position (starting position). For example, a phase U , V , W. with a reference potential Basement connected, and the remaining phases are supplied with a pulse-width modulated control signal. The magnetic field generated thereby aligns the rotor so that the rotor at the end of the period t1 is transferred to a defined starting position.

After aligning the electric motor 4th by means of an open-loop control, i.e. virtually blind, started up or accelerated. This is done by the electric motor 4th or its rotor is accelerated, for example, by means of a fixed acceleration ramp up to a minimum speed from which a sensorless position detection is possible.

Disadvantageously, this method requires comparatively high motor or phase currents IU , IV , IW . Furthermore, the electric motor 4th or the rotor accelerates comparatively slowly, so that a long start or run-up time given is. There is also the risk of oscillations and the loss of the synchronous field. The oscillations and high motor currents disadvantageously also worsen the acoustics of such an operated drive.

In the 8th and 9 a starting process according to the method according to the invention is shown in each case. The 8th and the 9 each show a schematic time-speed diagram or time-speed diagram, the time being horizontal, that is to say along the respective abscissa axis (X-axis) t , and along the vertical ordinate axis (Y-axis) an angular velocity or a rotational speed D. is applied. There are two curves in each case in the diagram 76 , 76 ' and 78 , 78 ' shown. The course of the curve 76 , 76 ' shows the time course of the angle of an actual speed, the course of the curve 78 , 78 ' represents the system speed. In this context, an actual speed is to be understood in particular as the actual angular speed or rotation speed of the rotor, the system speed being the calculated or determined rotation variable ω is.

According to the invention, the electric motor 4th when starting from a standstill, in particular at the start of the process, with a gradient due to the minimal incline v characterized rotation or manipulated variable ω driven at a minimum speed or minimum speed. In particular, the operation of the electric motor 4th here to the minimum speed ω limited. This means the electric motor 4th based on the rotation size ω is controlled and / or regulated in such a way that the minimum slope v is not fallen below.

According to the invention, it takes place when the electric motor is at a standstill 4th or at low engine speeds, in particular, starting at the minimum speed, that is to say at the minimum speed ω . In other words, in contrast to the prior art, there is no upstream or initial alignment of the rotor. Furthermore, the control and / or regulation based on the slope v or minimum speed ω In contrast to the state of the art, a closed-loop control is implemented when starting up.

Because of the minimal incline v of the position signal P. and / or the rotation size 0 , ω the electric motor is operated at the minimum or minimum speed. The resulting movement of the rotor in turn generates an induced voltage as a back EMF or a (magnetic) flux, which can be used as a motor variable for sensorless position detection.

The minimum slope v and / or the minimum speed ω are designed in such a way that, on the one hand, a stationary rotor of the electric motor is taken along and, on the other hand, a motor variable for position detection is generated by the movement of the rotor. The minimum speed is to be understood in particular as a certain speed or rotational speed range of the rotor. As a result, the curves show 78 , 78 essentially has a linear curve with a constant value.

The upper limit of the minimum speed is selected in such a way that a stationary rotor is carried along, that is to say that the rotor does not slip.

The lower limit for the minimum speed is a speed at which a sufficient effect for a flux determination to determine a corresponding motor variable is brought about. With a suitable choice of the start and minimum speed, it is thus ensured that the method is automatically synchronized and thus an initial position detection is essentially not necessary. This enables a reliable and safe start of the electric motor 4th .

In the embodiments of 8th and the 9 becomes the minimum speed ω after a predetermined period of time t1 ' continuously increased. In particular, the minimum speed becomes during a period of time t2 ' increased or accelerated from a low (first) speed value, for example 5 RPM to 20 RPM, to a (second) speed value increased in comparison, for example 10 RPM to 40 RPM. This enables, on the one hand, a reliable entrainment or synchronization of the rotor and, on the other hand, a sufficiently high signal quality of the back EMF or flux determination, so that a particularly reliable start-up of the electric motor 4th is guaranteed. In particular takes place during the period t2 ' a transition to an ordinary sensorless control and / or regulation method.

In the embodiment of 9 no initial position detection of the rotor position is provided, so that the rotor is first driven in the opposite direction and then taken along in the correct direction.

In one conceivable embodiment, the electric motor is 4th during the periods t1 ' , t2 ' for example each operated at a constant minimum speed. However, the minimum speed is preferably at least dependent on an operating point or an operating situation of the electric motor 4th customized or varied. In particular, the value of the minimum speed becomes during the time periods t1 ' , t2 ' adjusted depending on the temperature.

The invention is not restricted to the exemplary embodiments described above. Rather, other variants of the invention can also be derived therefrom by the person skilled in the art without departing from the subject matter of the invention. In particular, all of the individual features described in connection with the exemplary embodiments can also be combined with one another in other ways without departing from the subject matter of the invention.

The control and / or regulation method or the device 42 can be combined with an initial position or position detection method in order to avoid a start-up or acceleration in the opposite direction.

In the 8th and 9 there is a constant increase in speed or acceleration during the period t2 ' . However, a ramp-shaped or curved acceleration, that is to say a non-constant acceleration, is also conceivable.

List of reference symbols

2

drive

4th

Electric motor

6th

Power converter

8th

Power source

10

Energy storage

12th

Intermediate circuit

12a

Forwarding

12b

Return line

14th

DC link capacitor

16

Bridge circuit

18th

Star connection

20,22,24

End of phase

26th

Bridge module

28

Star point

30th

Inductance

32

resistance

34, 36, 38

Voltage drop

40

Phase current / motor size

42

Device / regulator

44, 46

Semiconductor switch

48, 50

Potential connection

52, 54

Control voltage input

56

resistance

58

Inductance

60

Shunt resistance

62

Ammeter

64

Position observer

66

Signal conditioning

68

Current regulator

70

Position detection system

72, 74

Curve progression

76, 76 ', 78, 78'

Curve progression

IE

Input current

IU, IV, IW

Phase current / motor size

AND MANY MORE

phase

UCC

Intermediate circuit voltage

Basement

Earth potential

IBat

Battery power

UBat

Battery voltage

UU, UV, UW

Phase voltage / motor size

P

Position signal / raw position

v

Minimum gradient / raw speed

0

Rotation size / rotor position

ω

Rotation size / speed / minimum speed

W.

Angle / position

t

time

t1, t2, t1 ', t2'

Duration

D.

Angular velocity / speed

Claims (10)

Method for operating a brushless and sensorless multiphase electric motor (4), - with a position signal (P) from a position observer (64) as a measure of a rotor position is determined based on at least one motor variable (IU, IV, IW, UU, UV, UW, 40) of the electric motor (4), - a rotation variable (θ, ω) is calculated by a signal processor (66) on the basis of the position signal (P) - where the position signal (P) and / or the rotation variable (θ, ω) is generated with a stored minimum gradient (v) as a measure for a minimum speed (ω), and - where the electric motor (4) is based on the rotation variable (θ, ω) is controlled and / or regulated. Procedure according to Claim 1 , characterized in that the electric motor (4) is driven at the minimum speed (ω) when starting from a standstill. Procedure according to Claim 1 or 2 , characterized in that a starting speed of the electric motor (4) when starting from a standstill is limited to the minimum speed (ω). Method according to one of the Claims 1 to 3 , characterized in that the slope (v) and / or the minimum speed (ω) is designed so that on the one hand a stationary rotor of the electric motor (4) is carried along, and on the other hand, a motor variable (40) for position detection due to the movement of the rotor is produced. Method according to one of the Claims 1 to 4th , characterized in that the value of the minimum speed (ω) is adapted as a function of the temperature. Method according to one of the Claims 1 to 5 , characterized in that a speed of less than or equal to 300 revolutions per minute, in particular less than or equal to 20 revolutions per minute, is used as the minimum speed (ω). Method according to one of the Claims 1 to 6th , characterized in that the minimum speed (ω) is continuously increased after a predetermined period of time (t1 '). Procedure according to Claim 7 , characterized in that the minimum speed (ω) is increased from a first speed value to a second speed value which is 25% to 100% larger than the first speed value. Method according to one of the Claims 1 to 8th , characterized in that a river observer is used as the position observer (64). Electric drive (2) for carrying out a method according to one of the Claims 1 to 9 , having - a brushless and sensorless multiphase electric motor (4), - a sensor unit (62) for detecting the at least one motor variable (IU, IV, IW, 40), - a position observer (64) for determining the position signal (P) without a sensor, - a signal processor (66) for calculating the rotation variable (θ, ω), and - a current regulator (68) for controlling and / or regulating the electric motor (4).

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