DE102019204934A1 - Method for controlling an electric motor, control device and corresponding systems - Google Patents

Abstract

A method for regulating an electric motor, in particular an electronically commutated electric motor, is disclosed, wherein a speed (n) of the electric motor (M) is regulated to a target speed by means of a speed controller (2), the target speed being specified by a target value and wherein the electric motor (M) is loaded with a load torque (M) during its operation. This method comprises the steps of: detecting an actual motor current (l) that flows at the load torque (M), detecting an actual speed (n) at which a rotor of the electric motor (M) rotates, calculating a parameter based on the actual motor current (l) and the actual speed (n), the parameter being representative of an operating point of the electric motor (M), determining a maximum speed (nmax) based on the parameter and a characteristic curve, the characteristic curve being a dependency of a maximum current strength (Imax) and a maximum speed (nmax), generating a scaled setpoint by scaling the setpoint based on the maximum speed (nmax) and inputting the scaled setpoint into the speed controller (2). Furthermore, a corresponding control device ( 1), as well as systems consisting of this control device (1) and an electric motor or a fan are disclosed.

Description

The invention relates to a method for controlling an electric motor, in particular an electronically commutated electric motor (EC motor). The invention also relates to a corresponding control device for an electric motor, a system comprising such a control device and an electric motor, and a system comprising such a control device and a fan.

Electric motors generate drive torque during their operation. This drive torque is usually opposed by a load torque, the load torque and the drive torque being directed in opposite directions. If the drive torque is greater than the load torque, the electric motor is accelerated. If the drive torque is less than the load torque, the electric motor is braked. If the load torque and drive torque are the same, the speed remains constant so that a stable operating point is present. The load torque is usually generated by the element that is driven by the electric motor.

If the electric motor is part of a fan and the electric motor drives an impeller of the fan, the load torque is generated by the impeller and the gaseous medium - usually air - moved by the impeller. The fan conveys the gaseous medium from an inflow side to an outflow side, thereby generating an increase in pressure. Depending on the technology of the fan and the basic structure, the pressure increase creates a volume flow of the gaseous medium moving through the fan. There is a mutual dependency of the volume flow and pressure increase, which can be described in a fan characteristic curve (also referred to as a fan characteristic curve and hereinafter also referred to as a pressure characteristic curve). The fan characteristic is given in data sheets and measured by a manufacturer of the fan on a fan test bench. The measured fan is usually operated as a free-standing fan so that the volume flow generated by the fan can flow unhindered. A real installation situation can influence this characteristic.

If a fan is installed in a system or a device, the fan must work against a flow resistance. The operating point (also referred to as the operating point) of such a fan results from the intersection of the fan characteristic with the system / device characteristic. If there is a system / device with a large flow resistance, the system / device characteristic curve rises steeply.

With a small flow resistance, the system / device characteristic is flatter. At the operating point, the fan generates a pressure increase that precisely compensates for the pressure loss in the device or system.

It turns out that depending on the pressure increase at a certain drive torque and - because of the proportionality between drive torque and motor current - at a certain motor current, different speeds are set. In this way, in different situations in which the fan is used, a pressure is set that determines the speed, depending on the flow resistance of the system in which the fan is installed. If a maximum possible motor current flows, this results in a maximum possible speed for the current installation situation. Since system resistances can change over time in practice, for example due to increasing contamination of filters, the maximum possible speed can also change during operation. As a result, the maximum possible speed for a specific fan or, more generally, for a specific electric motor cannot be determined without knowledge of the current operational situation. However, parameters of this installation situation can only be determined with considerable effort by, for example, pressure sensors determining the pressure difference.

When regulating the speed of a motor or a fan, it is common to assign a control signal specifying the speed setpoint (for example a voltage between 0 volts and 10 volts) to a range between minimum speed (for example 0 revolutions / minute) and maximum speed. However, since the maximum speed is unknown when the fan is manufactured, the difficulty arises in choosing a suitable setpoint. If the setpoint specification is scaled to the lowest possible maximum speed, a large part of the possible working area would not be used in most installation situations, since the electric motor then - regardless of the actual installation situation - cannot be controlled beyond this lowest possible maximum speed. If the greatest possible maximum speed were used to scale the setpoint specification, this maximum speed would never be reached in most installation situations, which is why part of the value range of the setpoint is not exhausted. This is undesirable for control reasons.

Because of these difficulties, speed control is usually dispensed with in practice and torque control is used instead. A speed is automatically set that corresponds to the system resistances and the motor current specifications via the control signal. This achieves the goal that, for example, with a control signal of 0 to 10 volts, the entire range up to the respective maximum speed can be covered.

However, dispensing with speed control leads to some disadvantages in practical operation. For example, start-up problems as a result of the electric motor getting stuck can be managed much better with a speed control, since the speed control - in contrast to the torque control - "pushes". In addition, many motor properties are based on speed values, such as step mode or the fading out of certain speeds to avoid resonances. In addition, in combination with upstream process controls, dispensing with speed control can lead to instabilities. This exemplary, but not exhaustive, list of possible disadvantages shows that speed control would be preferable to pure torque control.

The present invention is therefore based on the object of designing and developing a method, a control device and systems of the type mentioned at the outset in such a way that a flexible speed specification based on an operating situation of the electric motor is possible.

• Erfassen eines Ist-Motorstroms, der bei dem Lastmoment fließt,
• Erfassen einer Ist-Drehzahl, mit der sich ein Rotor des Elektromotors dreht,
• Berechnen einer Kenngröße basierend auf dem Ist-Motorstrom und der Ist-Drehzahl, wobei die Kenngröße repräsentativ für einen Arbeitspunkt des Elektromotors ist,
• Ermitteln einer maximalen Drehzahl basierend auf der Kenngröße und einer Kennlinie, wobei die Kennlinie eine Abhängigkeit von einer maximalen Stromstärke und einer maximalen Drehzahl angibt,
• Erzeugen eines skalierten Sollwerts durch Skalieren des Sollwerts basierend auf der maximalen Drehzahl und
• Eingaben des skalierten Sollwerts in den Drehzahlregler.

According to the invention, the above object is achieved by the features of claim 1. Thereafter, in the method in question, a speed of the electric motor is regulated to a target speed by means of a speed controller, the target speed being specified by a target value, the electric motor being loaded with a load torque during its operation. This procedure includes the steps:

• Acquisition of an actual motor current that flows at the load torque
• Acquisition of an actual speed at which a rotor of the electric motor rotates,
• Calculating a parameter based on the actual motor current and the actual speed, the parameter being representative of an operating point of the electric motor,
• Determining a maximum speed based on the parameter and a characteristic curve, the characteristic curve indicating a dependency on a maximum current intensity and a maximum speed,
• Generating a scaled setpoint by scaling the setpoint based on the maximum speed and
• Input of the scaled setpoint in the speed controller.

• einen Drehzahlregler,
• einen Sollwerteingang zum Eingeben eines Sollwerts,
• einen Stromeingang zum Eingeben eines Ist-Motorstroms, der bei dem Lastmoment in den Elektromotor fließt,
• einen Drehzahleingang zum Eingeben einer Ist-Drehzahl des Elektromotors, mit der sich ein Rotor des Elektromotors dreht,
• einen Speicher mit einer Kennlinie, die eine Abhängigkeit zwischen einer maximalen Stromstärke und einer maximalen Drehzahl angibt,
• eine Berechnungseinheit, die dazu ausgebildet ist, basierend auf dem Ist-Motorstrom, der Ist-Drehzahl und der Kennlinie eine maximale Drehzahl zu ermitteln, und
• eine Skalierungseinheit, die basierend auf der maximalen Drehzahl den Sollwert skaliert und als skalierten Sollwert an den Drehzahlregler ausgibt.

With regard to a regulating device, the above object is achieved by the features of claim 12. According to this, the control device for the electric motor loaded with a load torque during its operation comprises:

• a speed controller,
• a setpoint input for entering a setpoint,
• a current input for entering an actual motor current that flows into the electric motor at the load torque,
• a speed input for entering an actual speed of the electric motor at which a rotor of the electric motor rotates,
• a memory with a characteristic that indicates a dependency between a maximum current strength and a maximum speed,
• a calculation unit which is designed to determine a maximum speed based on the actual motor current, the actual speed and the characteristic curve, and
• a scaling unit that scales the setpoint based on the maximum speed and outputs it as a scaled setpoint to the speed controller.

With regard to the systems, the above object is achieved by the features of claims 16 and 18. According to this, these systems comprise a control device according to the invention and an electric motor or a fan.

In a manner according to the invention, it was first recognized that, based on an actual motor current and an actual speed, a parameter can be determined which is representative of an operating point of the electric motor in the current operating situation. This parameter can in turn be used to determine by means of a characteristic curve which indicates a dependency between a maximum current intensity and a maximum speed. By using this knowledge, a maximum speed of the current operating point can be determined and thus a scaled setpoint can be generated without this maximum speed actually being present and / or without the maximum motor current actually having to flow.

To use this knowledge, in the method according to the invention, an actual motor current is first recorded, which flows during operation of the electric motor when a load torque is applied. Furthermore, an actual speed at which a rotor of the electric motor rotates under the load with the load torque is recorded. Based on this actual motor current and this actual speed, a parameter is calculated in a next step which is representative of the current operating point of the electric motor. The operating point - as explained above - is dependent on the actual motor current flowing or the drive torque generated thereby and the load torque. Using a characteristic curve which indicates a dependency between a maximum current intensity and a maximum speed, a maximum speed is determined in a further step based on the parameter. The maximum speed is finally used to generate a scaled setpoint. This scaled setpoint is then entered into the speed controller. In this way, the originally entered setpoint value can be determined completely independently of the actual operating situation of the electric motor. For example, a value between 0 and 100% can generally be specified. Which speed this ultimately corresponds to is determined by scaling to the maximum speed. In this way, the speed controller is always subjected to a setpoint that is between a minimum speed value and the maximum speed value. This means that the range of values for the setpoint specification can always be fully utilized.

In principle, the parameter can be formed in the most varied of ways, as long as the parameter is dependent on the actual motor current and the actual speed and a maximum speed can be determined therefrom. The parameter must be representative of the operating point of the electric motor that is set when the load torque is applied. The parameter is preferably calculated as the quotient of the actual current strength and the square of the actual speed. Through this choice, a particularly favorable parameter can be obtained, particularly in the case of an electric motor that is part of a fan and drives an impeller of this fan. Because with fans the motor current is proportional to the square of the speed.

In principle, the load torque applied to the electric motor can be generated in the most varied of ways. As long as the rotor of the electric motor is loaded in a defined manner by the load torque, the prerequisites for using the method according to the invention exist in principle. In a preferred embodiment, however, the load torque is generated by an impeller of a fan, the electric motor driving this impeller. Since the impeller will move a stream of air, a load torque is created that is dependent on the speed. The load torque is preferably influenced by a flow resistance that opposes an air flow moving through the impeller. The higher the flow resistance, the higher the load torque.

If the electric motor is part of a fan, it is in principle irrelevant how the fan is constructed. The validity of the method according to the invention could be demonstrated for axial fans, for diagonal fans and for radial fans (with forward curved blades on the impeller), so that these represent preferred configurations.

The characteristic that is used to calculate the maximum speed can be defined in various ways. The characteristic curve can thus be determined via a mathematical relationship in the form of a formula, which means that any desired values of the characteristic curve can be calculated very easily by solving the formula. In a preferred embodiment, however, the characteristic curve is stored in a memory as a table of values (also known as a look-up table) and an interpolation is carried out when the maximum speed is determined. In this way, even mathematically complex relationships can be mapped with sufficient precision without the need for time-consuming calculations.

The setpoint is preferably scaled to a range between a minimum speed and the maximum speed. The minimum speed is particularly preferably zero revolutions per minute. In principle, it is irrelevant how the entered setpoint is scaled. Ultimately, relatively arbitrary behavior can be mapped via the scaling. Scaling with an exponential relationship is just as conceivable as quadratic or polynomial relationships. However, an essentially linear scaling is preferably carried out, ie a range of the entered setpoint value is mapped onto a range of the scaled setpoint value by means of a linear relationship. It is also conceivable that speeds to be omitted in the setpoint scaling are also taken into account, so that when a non-permissible setpoint speed is entered, a scaled speed is output that is a difference value Δn above or below the entered speed value, with Δn indicating a small speed difference and preferably based on the gap to be omitted and / or the maximum speed. Thus, in a preferred embodiment, Δn is a maximum of 10% of the maximum speed, particularly preferably a maximum of 5% of the maximum speed and very particularly preferably a maximum of 1% of the maximum speed. However, it should be ensured that the shifted, scaled setpoint is outside a correspondingly "forbidden" range.

In principle, the actual motor current and the actual speed can be determined in various ways. So it is conceivable that a dedicated current sensor is available for determining the actual motor current, which detects current values and - preferably in digitized form - provides them for further processing in the method according to the invention. To determine the actual speed, a dedicated speed sensor can be provided which detects the speed of the rotor or of an element connected to the rotor. Corresponding current or speed sensors are sufficiently known from practice. In the case of electronically commutated motors in particular, however, there is motor electronics that already contain information about the actual motor current and the actual speed. In this respect, in a preferred development, the step of determining an actual motor current includes the step of interrogating this value from the motor electronics of the electric motor and the step of determining the actual speed includes a step of interrogating this value from the motor electronics of the electric motor. In this way, the actual motor current and / or the actual speed can be determined in a particularly simple manner, without the need for additional sensors.

If the electric motor drives an impeller of a fan, the method according to the invention can additionally be used to determine a volume flow generated by the fan, a mass flow moved by the fan and / or a pressure increase generated by the fan. Since the parameter is representative of the operating point of the fan and the operating point is found in a pressure characteristic curve of the fan, a volume flow and / or a pressure increase can be determined in this way. If the pressure characteristic shows a relationship between mass flow and pressure increase, a mass flow moved by the fan and / or a pressure increase generated by the fan can be determined in this way. In this way the fan can also be used as a sensor.

The pressure characteristic can in turn be stored in various ways. Since the pressure characteristic is usually a complex to describe relationship, the pressure characteristic is preferably stored in the form of a value table (look-up table). A volume flow and / or a mass flow and / or a pressure increase in relation to a speed or a motor current is preferably specified in the table of values. The volume flow and / or the mass flow is preferably normalized to the speed and the pressure increase to the motor flow. To determine the volume flow, the mass flow and / or the pressure difference, a value would then be read out from the table of values or a value interpolated between two existing values in the table of values would be calculated. This read out or interpolated value would then - depending on the reference variable of the value - be multiplied by the actual speed or the actual motor current. In this way, an additional effect can be generated, namely that the electric motor becomes a sensor for volume flow, mass flow and / or pressure increase.

In a further development, another additional effect can be generated in that one or more values obtained during the method are passed on to a user or a higher-level system. For example, the user / higher-level system can be shown how high the current maximum speed is. If the method according to the invention is used to determine a volume flow, a mass flow and / or a pressure increase, these results can also be output to the user / higher-level system. The way in which these values are output depends on the particular application. It would be conceivable that the device executing the method, for example a microprocessor, is connected to a display device and that the values are displayed on this display device or can be displayed there. However, it is also conceivable that there is a communication unit via which the values obtained are output. The communication unit can be designed in the most varied of ways and the most varied of communication standards and technologies can be used for data transmission from and to this communication unit. Digital transmission technologies can be used as well as analog ones. The Transmission can be wired or wireless. Parallel or serial transmission interfaces can be used. The transmission can take place in packets or in direct connections. Merely by way of example, but not limited to these, reference is made to the use of Bluetooth, Bluetooth LE (Low Energy), NFC (Near Field Communication), Ethernet, RS485, Modbus, Profibus, CAN bus or USB (Universal Serial Bus). The communication unit particularly preferably provides a connection to an Industry 4.0 environment.

The characteristic curve, which indicates a dependency on a maximum current intensity and a maximum speed, can be obtained in the most varied of ways. In one embodiment, the electric motor in which the method according to the invention is carried out is measured in a test stand. This can be done, for example, as part of a final test of the electric motor after its manufacture. Since electric motors are usually subjected to a final test anyway, the characteristic curve can be determined without too much additional effort. Since identical models of an electric motor are very similar in terms of their behavior, it is also conceivable that an electric motor of the same type is measured and this characteristic curve is then distributed to other produced electric motors of the same type. If particular precision is required in the calculations, the characteristic curve can be used in a further development during commissioning of the electric motor in a system, i.e. in its later installation environment. This configuration offers the advantage that influences of the installation environment flow directly into the characteristic curve.

When the characteristic curve is determined, a maximum permissible motor current (and thus a maximum possible drive torque) can be impressed on the electric motor and the load torque can be increased in stages up to a maximum value. If the electric motor is part of a fan and drives its impeller, this can be achieved in that a flow resistance for an air flow conveyed by the fan is increased in stages, so that the pressure increases in stages.

In principle, only one characteristic curve can be used in the method according to the invention. This is particularly easy if the actual motor current and / or the actual speed can be determined relatively precisely. However, it is also conceivable to make the characteristic curve available as a characteristic curve field, the characteristic curve field consisting of several individual characteristic curves. In this case, between 5 and 50 individual characteristic curves, very preferably between 10 and 20 individual characteristic curves, are used. The family of characteristics can then be used when determining the maximum speed. The use of a family of characteristics is particularly recommended if, due to the characteristics of the fan, the system or the measuring device, there are deviations from the maximum characteristic at lower speeds or motor currents. The use of a family of characteristics increases the accuracy. In the application, the maximum power of a fan is often not used. For better accuracy in such cases, a family of characteristics can achieve improvements.

The control device according to the invention is designed for controlling an electric motor, in particular an electronically commutated motor, which is loaded with a load torque during its operation. The control device is preferably suitable for carrying out a method according to the invention. The control device according to the invention comprises a speed controller, a setpoint input, a current input, a speed input, a memory with a characteristic curve, a calculation unit and a scaling unit. The setpoint input is designed for entering a setpoint. The current input is designed to input an actual motor current that flows at the load torque. The speed input is designed to input an actual speed of the electric motor at which a rotor of the electric motor rotates. The memory stores a characteristic curve which indicates a relationship between a maximum current intensity and a maximum speed. The calculation unit is designed to determine a maximum speed based on the actual motor current, the actual speed and the characteristic curve. The scaling unit is designed to scale the setpoint entered in the setpoint input based on the maximum speed and to output it to the speed controller as a scaled setpoint.

The control device can be implemented in the most varied of ways. The functions can be implemented as software, as hardware or as a combination of software and hardware. In a preferred embodiment, the control device is implemented in a suitably programmed microprocessor with associated input interfaces.

The memory can also be implemented in the most varied of ways. However, the memory is preferably designed as a non-volatile memory. Such a non-volatile memory can be, for example, an EEPROM (Electronically Erasable Programmable Read-Only Memory), a flash memory, an NVRAM (Non-volatile Random Access Memory) or another semiconductor memory.

The speed controller can also be implemented in various ways. It is important that the speed controller acts on the electric motor in such a way that its speed comes as close as possible to an entered setpoint. How the controller is structured in detail depends on the expected control behavior. Appropriate approaches are known from practice.

To avoid or reduce undesirable fluctuations in the scaled speed over time, a smoothing unit for smoothing fluctuations over time can be coupled in between the calculation unit and the scaling unit. A value calculated by the calculation unit for a maximum speed would then be entered in this smoothing unit. The smoothing unit would smooth the entered value of the maximum speed over time and output the smoothed value of the maximum speed to the speed controller. The smoothing unit can be designed as an integrator.

In principle, the speed controller can output a manipulated variable directly to engine electronics, which then generate and output control signals for the electric motor based on this manipulated variable. In a preferred development, however, the manipulated variable output by the speed controller is input to a subordinate control device, the subordinate control device preferably performing a torque control of the electric motor. In this way, the electric motor can be regulated even more specifically.

In general, the inputs of the control device, i.e. in particular the setpoint input, the current input and / or the speed input can be designed differently. It is conceivable that the inputs are formed by memory cells of a memory, in which an “external” unit stores the values to be entered and from which the control device reads these values. The inputs can also be formed by (parallel or serial) bus lines into which the respective values are entered using logic levels. The individual inputs can also be designed differently. At the setpoint input, the setpoint can be entered as an analog voltage that assumes a value between a minimum voltage and a maximum voltage. In the field of regulating electric motors, a voltage between 0 volts and 10 volts has become established for entering setpoints. Therefore, in a preferred embodiment, the setpoint input is designed so that a setpoint can be input by means of such a control signal. The control signal can indicate a percentage of the maximum speed. For example, a voltage of 8.5 volts would correspond to a target value of 85% of the determined maximum speed.

The control device according to the invention can form a system according to the invention together with an electric motor or a fan. In a system with a fan, the electric motor would drive an impeller of the fan, the control device regulating the electric motor. In both cases, the electric motor can be designed as an electronically commutated electric motor and thus include motor electronics. In this case, the control device can be implemented in the engine electronics.

• 1 ein Blockdiagramm einer Drehmomentregelung gemäß Stand der Technik,
• 2 eine Tabelle mit Kenndaten eines aus dem Stand der Technik bekannten Ventilators,
• 3 ein Blockdiagramm eines Ausführungsbeispiels eines erfindungsgemäßen Systems mit einer Drehzahlregelung mit adaptivem Sollwertbereich und
• 4 ein Flussdiagramm für ein zweites Ausführungsbeispiel eines erfindungsgemäßen Verfahrens mit einer Bestimmung eines Volumenstroms und/ oder einer Druckerhöhung.

There are now various possibilities for designing and developing the teaching of the present invention in an advantageous manner. For this purpose, reference is made, on the one hand, to the claims subordinate to the independent claims and, on the other hand, to the following explanation of preferred exemplary embodiments of the invention based on the drawing. In connection with the explanation of the preferred exemplary embodiments of the invention with reference to the drawing, generally preferred embodiments and developments of the teaching are also explained. Show in the drawing

• 1 a block diagram of a torque control according to the prior art,
• 2 a table with characteristics of a fan known from the prior art,
• 3 a block diagram of an embodiment of a system according to the invention with a speed control with an adaptive setpoint range and
• 4th a flowchart for a second embodiment of a method according to the invention with a determination of a volume flow and / or a pressure increase.

1 shows a block diagram with a torque control of an electric motor known from the prior art. A torque regulator A. gives a manipulated variable to power electronics B. on the basis of which the power electronics generate and output control signals for an electric motor M, in particular an electronically commutated electric motor (EC motor). Between power electronics B. and electric motor M, an actual motor current I is detected, which is converted into a summing element C. is entered. The summing element C. forms a difference from a setpoint specification D. and the actual motor current I. This difference signal is used as a control difference in the torque controller A. entered. The torque controller A. is constructed in such a way that the control difference is brought to zero or at least close to zero. The setpoint specification D. can be done by means of a control signal that takes a value between 0 V and 10 V.

When the electric motor drives the impeller of a fan and the air moved by the fan experiences a flow resistance in a system in which the fan is installed, such a control device automatically sets a speed according to the system resistances and the current specification via the control signal and In the installation environment, the goal is achieved that the control signal 0-10V corresponds to the range from 0 to maximum speed.

In 2 an example of characteristic data of a fan is given which is known from the prior art and which can be regulated in such a torque control. The characteristics come from a centrifugal fan with forward curved blades of the impeller. In the individual columns of the table 2 the input current of the motor electronics I_L1, the power factor cos_phi_ed, the active power P, the speed n, the static pressure increase by the fan p_fs, the dynamic pressure p_f, the motor current and the volume flow q_V1 conveyed by the fan are specified, with one line each representing one measurement corresponds.

3 shows an embodiment of a system according to the invention with a control device according to the invention 1 and an electric motor M. This control device 1 includes a speed controller 2 , a setpoint input 3 , a power input 4th , a speed input 5 , a maximum speed determination 6th and a scaling unit 7th . The determination of the maximum speed 6th comprises a memory with a characteristic curve (symbolized by a table) and a calculation unit (not shown separately). The speed controller 2 outputs a control signal that is used in a subordinate torque control 8th that is entered in 1 corresponds. A determined actual motor current list is entered in the current input 4th is entered, a determined actual speed n _is in the speed input 5 . The actual motor current list and the actual speed n _ist can be obtained and output by the motor electronics of the electric motor M. The actual motor current list and the actual speed n _ist are included in the maximum speed determination 6th entered. There, based on the actual motor current list and the actual speed n _ist, a parameter is determined. This parameter is calculated as the quotient of the actual motor current I and the square of the actual speed n. This parameter is used to determine a maximum permissible speed nmax, a characteristic curve calculated with the same formula being used for this. The characteristic curve results from the characteristic data 2 as follows: n _max reference [1 / min] I _max [A] I _max / n _max ² 1 1529 0.71 3.04 E-07 2 1625 0.71 2.69 E-07 3 1677 0.71 2.52 E-07 4th 1743 0.71 2.34 E-07 5 1823 0.71 2.14 E-07 6th 1915 0.71 1.94 E-07 7th 2030 0.71 1.72 E-07 8th 2104 0.71 1.60 E-07 9 2198 0.71 1.47 E-07 10 2308 0.71 1.33 E-07 11 2391 0.71 1.24 E-07 12 2499 0.7 1.12 E-07

These values of the parameter l _max / n _max ^{2 together} with the associated speed and motor current values can be stored as a look-up table in the memory and form a characteristic curve in the sense of the method according to the invention. The parameter is constant for a stable operating point. Due to the quadratic relationship between current and speed in a fan, corresponding maximum speeds for other operating points can be calculated from the maximum values (max. Possible operating point).

Since the look-up table will only contain comparatively few values, an interpolation can be used. With the actual value of the parameter l / n ² one looks for the next larger and smaller value of the parameter l / n ² in the table of values. Assume the current value of the parameter l / n ² is 2.26 E-07. This current value is between the table entry 4th (Range start) and 5 (End of range), the maximum speed accordingly in the range between 1743 and 1823 rpm. A normalizing factor F can be calculated with these values: $$\text{F.}=1-\left(\left({\text{I.}}_{\text{is}}{\text{/ <figure-callout id="2" label="n" filenames="DE102019204934A1\_0005.png" state="{{state}}">n</figure-callout>}}^2{}_{\text{is}}-\text{End of range}\right)\text{/}\left(\text{Area start}-\text{End of range}\right)\right)\text{.}$$

This factor is in the range from 0 to 1. In this case, it should be noted that the parameter l / n ² behaves in the opposite direction to the maximum speed, which is already taken into account when calculating F. This factor F can then be used to interpolate between the speeds as follows: $${\text{n}}_{\text{Max}}-\text{reference}={\text{n}}_{\text{Max}}-\text{Range start + F *}\left({\text{n}}_{\text{Max}}-\text{End of range}-{\text{n}}_{\text{Max}}-\text{Area start}\right)$$

With the example value 2.26 E-07 a factor F = 0.4 is obtained, which results in an nmax reference of 1775 rpm.

One through the maximum value determination 6th The value obtained for the maximum speed nmax is sent to the scaling unit 7th to hand over. This uses the received value nmax to scale an in the setpoint input 3 entered setpoint. A scaled setpoint generated in this way is sent to a summing element 9 output that determines a difference between the scaled setpoint and the actual speed n _ist . The resulting difference is entered in the speed controller as a control difference.

During the execution of the method according to the present embodiment, after the determination of the actual motor current I _and the actual speed n _is a current characteristic value _is l / _n ² from the detected actual motor current _I, and the detected actual speed n _is calculated. From this parameter, an n _max reference value for the maximum speed of the current operating point of the fan is determined by means of interpolation from the characteristic. This n _max reference value can be smoothed by means of an integrator in order to be able to compensate for fluctuations over time. This (possibly smoothed) value for the maximum speed nmax is in the scaling unit 7th used to generate the setpoint input 3 to scale entered setpoint specification. The setpoint specification is a control signal that can assume a voltage between 0 and 10 volts.

The exemplary embodiment shown here uses the knowledge of the operating point to determine the maximum permissible speed nmax for the operating point. The reason for this is that an electronically commutated motor (EC motor) only has a certain maximum torque available. At low pressures i.e. For high volume flows, the speed must be set lower than for high pressures and low volume flows, as otherwise the fan will be overloaded or permanently operated within a limit, which has a negative effect on the control behavior. In this exemplary embodiment, the method is used to ideally design the control behavior at each operating point and always achieve the greatest possible volume flow at the respective operating point.

In an EC motor of the current type, a drive unit (power electronics) is integrated in a permanently excited synchronous motor (PMSM). In essence, the motor control works with a field-oriented current control. For this type of motor control, the exact motor currents and the position of the rotor and thus also the speed must be known. These two values can be used to determine the operating point by the method according to the invention.

4th shows a flow diagram of a second exemplary embodiment of a method according to the invention. In step 10 the parameter l / n ² _is calculated with current measured values for the actual motor current l _ist and the actual speed n _ist . In step 11 the area on the maximum fan curve is determined with the determined l / n ² . Since the fan characteristic in this embodiment is stored as a table of values with only a few parameters, the next larger or smaller value for the current parameter l / n ^{2 is determined} from the table for the following interpolation in this step. Between these two values, the following step 12 interpolated (see description of 3 ). In step 12 the operating point is determined from the characteristic by interpolation. In step 13 a Q _v / n, p / l or an nmax is determined for the determined operating point. In step 14th a current volume flow Q _v or a current pressure increase p is calculated from the values determined in this way by multiplying them by the actual speed or the actual motor current. These values can then be output to a user or communicated to a higher-level system.

With regard to further advantageous refinements, to avoid repetition, reference is made to the general part of the description and to the appended claims.

Finally, it should be expressly pointed out that the exemplary embodiments described above only serve to explain the teaching claimed, but do not restrict them to the exemplary embodiments.

List of reference symbols

A.

Torque control

B.

Power electronics

C.

Summing element

D.

Setpoint specification

M.

engine

1

Control device

2

Speed controller

3

Setpoint input

4th

Power input

5

Speed input

6th

Maximum speed determination

7th

Scaling unit

8th

Torque control

9

Summing element

10

step

11

step

12

step

13

step

14th

step

Claims (18)

Method for controlling an electric motor, in particular an electronically commutated electric motor, wherein a speed (n) of the electric motor (M) is controlled to a target speed by means of a speed controller (2), the target speed being specified by a target value, the electric motor (M) is loaded with a load torque (M _L ) during its operation, comprising the steps of: detecting an actual motor current (l _ist ) which flows at the load torque (M _L ), detecting an actual speed (n _ist ) at which a rotor of the electric motor (M) rotates, calculating a parameter based on the actual motor current (l _ist ) and the actual speed (n _ist ), the parameter being representative of an operating point of the electric motor (M), determining a maximum speed (nmax) based on the parameter and a characteristic curve, the characteristic curve indicating a dependency on a maximum current strength (Imax) and a maximum speed (nmax), generating a scaled setpoint dur ch Scaling of the setpoint based on the maximum speed (nmax) and input of the scaled setpoint in the speed controller (2). Procedure according to Claim 1 , Characterized in that the characteristic value the quotient of the actual current value _(l), and the square of the actual speed (n _ist) is calculated. Procedure according to Claim 1 or 2 , characterized in that the load torque (M _L ) is generated by an impeller of a fan which is driven by the electric motor (M), wherein the load torque (M _L ) is preferably influenced by a flow resistance caused by an air flow moving through the impeller opposes. Method according to one of the Claims 1 to 3 , characterized in that the characteristic is stored as a table of values in a memory and that the maximum speed (nmax) is determined by means of interpolation. Method according to one of the Claims 1 to 4th characterized in that the step of scaling comprises scaling the setpoint to a range between a minimum speed (nmin) and the maximum speed (nmax), the minimum speed (nmin) preferably being equal to 0. Method according to one of the Claims 1 to 5 , characterized in that the step of determining an actual motor current (l _ist ) and / or the step of determining an actual speed (n _ist ) comprises a step of requesting values from motor electronics of the electric motor (M). Method according to one of the Claims 1 to 6th , characterized in that the electric motor (M) drives an impeller of a fan and that from the parameter using a pressure characteristic curve of the fan, a volume flow (Q _v ) moved by the fan, a mass flow moved by the fan and / or a flow rate through the fan generated pressure difference (p) is determined. Procedure according to Claim 7 , characterized in that the pressure characteristic is stored in the form of a table of values, the table of values specifying a volume flow (Q _v ), a mass flow and / or a pressure difference (p) based on a speed (n) or on a motor current (I) is, and that when determining the volume flow (Q _v ), the mass flow and / or the pressure difference (p) a value read out from the table of values or a value interpolated between two values in the table of values with the actual speed (n _ist ) or the actual -Motorstrom _(l) is multiplied. Method according to one of the Claims 1 to 8th , characterized in that the maximum speed (nmax) and / or other values determined during the execution of the method are output to a user and / or to a higher-level system. Method according to one of the Claims 1 to 9 , characterized in that the characteristic curve is determined in a calibration measurement in a test bench and / or during commissioning of the electric motor in a system. Method according to one of the Claims 1 to 10 , characterized in that the characteristic curve is made available as a characteristic curve field, the characteristic curve field being formed from several individual characteristic curves, preferably between 5 and 50 individual characteristic curves, very particularly preferably between 10 and 20 individual characteristic curves, and that when the maximum speed is determined, the characteristic curve field is being used. Control device for an electric motor, in particular an electronically commutated motor, in particular for performing a method according to one of the Claims 1 to 11 , the electric motor being loaded with a load torque (M _L ) during its operation, comprising a speed controller (2), a setpoint input (3) for entering a setpoint, a current input (4) for entering an actual motor current (l _ist ), which flows at the load torque (M _L ), a speed input (5) for inputting an actual speed (n _ist ) of the electric motor (M) with which a rotor of the electric motor rotates, a memory with a characteristic curve that shows a dependency between indicates a maximum current strength (I _max ) and a maximum speed (nmax), a calculation unit which is designed, based on the actual motor current (l _ist ), the actual speed (n _ist ) and the characteristic curve, a maximum speed ( nmax), and a scaling unit (7) that scales the setpoint based on the maximum speed (nmax) and outputs it as a scaled setpoint to the speed controller (2). Control device according to Claim 12 , characterized in that a smoothing unit is coupled between the calculation unit and the scaling unit (7), wherein the smoothing unit is preferably designed as an integrator and wherein the smoothing unit is designed to carry one through the Calculation unit to smooth the value of the maximum speed (nmax) calculated over time and to output it to the speed controller as a smoothed value. Control device according to Claim 12 or 13 , characterized in that the speed controller (2) outputs a manipulated variable which is input into a subordinate control device, the subordinate control device preferably performing a torque control (8) of the electric motor (M). Control device according to one of the Claims 12 to 14th , characterized in that the setpoint input (3) is designed to receive the setpoint by means of a control signal, the control signal preferably lying between a minimum voltage and a maximum voltage, particularly preferably between 0 V and 10 V. System consisting of a control device (1) according to one of the Claims 12 to 15th and an electric motor (M). System according to Claim 16 , characterized in that the electric motor (M) has motor electronics and that the control device (1) is implemented in the motor electronics. System from a control device according to one of the Claims 12 to 15th and a fan, wherein the fan comprises an electric motor (M) and an impeller driven by the electric motor (M) and wherein the control device (1) controls the electric motor (M).

Images