DE102020104384A1 - Method for starting an electric motor - Google Patents

Abstract

The invention, which relates to a method for starting an electric motor, is based on the object of specifying a solution which ensures a safe starting process, for example in an electric refrigerant compressor, is easy to implement and with which a reduction in noise when starting or starting an electric motor is achieved . Furthermore, an overshoot of the speed of the electric motor during the transition from the operating state (5) with an open control loop to the operating state (6) with a closed control loop should be reduced or avoided. This object is achieved in that a table is provided with at least two values for amplitudes of phase currents to be selected, that in a first method step a first attempt to start the electric motor in the first operating state (5) is carried out by selecting a first and smallest value in the table, that in a second process step the transition from the first operating state (5) to a second operating state (6) takes place, that in a third process step after a predetermined period of time Δt in the second operating state (6) a test (17) of the functionality of the electric motor takes place, that if the check is successful, the starting process of the electric motor has been successfully completed, that if the check is unsuccessful, a further attempt to start the electric motor is carried out in the first process step in the first operating state (5) by selecting a second value in the table, that the second and third process steps are repeated t until the electric motor has started successfully or a termination criterion has been reached.

Description

The invention relates to a method for starting an electric motor, in which phase currents with a predetermined amplitude and an increasing frequency are generated in a first operating state with an open control loop and a transition from the first operating state to a second operating state with a closed control loop takes place subsequently , in which the electric motor is operated with speed control.

Electric motors for driving various arrangements or units, such as an electric refrigerant compressor in a vehicle, are known.

Such an electric motor can be, for example, a brushless direct current motor, also referred to as a BLDC motor (BLDC; brushless direct current motor), or a permanent magnet synchronous motor (PMSM). In the following, only the term electric motor will be used for these explanations.

A speed control, alternatively also a current control or a torque control, of a brushless direct current motor or a permanent magnet synchronous motor can take place via a position sensor, which supplies a sufficiently precise position of the rotor based on its magnetic poles as a reference variable.

Alternatively, such a regulation can take place in a so-called sensorless operation by means of a sufficiently accurately estimated rotor position.

The following statements relate to the case of a sufficiently accurately estimated rotor position of an electric motor, in which a sensorless method for determining the position or for estimating the position of the rotor position according to the prior art is used.

• - Erkennung eines Nulldurchgangs der elektromotorischen Gegenkraft (BEMF; back-electro-motive-force), auch als „zero-crossingdetection“ bezeichnet,
• - Beobachterbasierte Verfahren (observer; observer pattern) vergleichen eine erwartete elektrische Motorgröße, wie beispielsweise einen Phasenstrom, mit einem gemessenen Wert und ermitteln anhand des festgestellten Unterschiedes eine geschätzte Ist-Position des Rotors, über die dann die Drehzahl und der Drehwinkel bestimmt wird.
• - Messung von Induktivitäten beziehungsweise Induktivitätsänderungen bei unterschiedlichen Motorstellungen.

According to the known state of the art, there are various sensorless methods for regulating the speed by means of a rotor position estimated without a sensor:

• - Detection of a zero crossing of the counter electromotive force (BEMF; back-electro-motive-force), also referred to as "zero-crossingdetection",
• - Observer-based methods (observer pattern) compare an expected electrical motor variable, such as a phase current, with a measured value and, based on the determined difference, determine an estimated actual position of the rotor, which is then used to determine the speed and the angle of rotation.
• - Measurement of inductances or changes in inductance with different motor positions.

It is known that the counter electromotive force (BEMF, back-electro-motive-force) is a force or voltage that is generated in the coils or windings of the stator of an electric motor when a rotor equipped with permanent magnets is can rotate. Here, the motor can be designed as a so-called internal rotor, in which the rotor revolves inside the stator, or it can be designed as a so-called external rotor, in which the rotor rotates around the outside of the stator.

The changing magnetic field generates a current in the coils of the electric motor, so that a changing voltage can be tapped or measured at the winding ends or at the motor terminals. The amplitude and frequency of this voltage change depending on the speed of the rotor. If you now apply a voltage to a motor that generates a flow of current, the beginning of the rotation of the rotor in the motor phases, as previously described, also creates a counter-electromotive force (BEMF), which can then be used to determine the position of the rotor.

It is known from the prior art that when a BLDC or PMS motor is started up, the rotor is initially set in rotation in an operating state with an open control loop by the application of an electric field. This is usually done by impressing a sinusoidal electrical current or phase current with a corresponding angular offset in all motor phases of the motor. For optimal control, it is helpful to determine the current rotor position as precisely as possible in advance. This can be done with various methods known from the prior art, such as one from US Pat US 2008/0067961 A1 known procedures.

Known methods of this type are able to estimate a rotor position of an electric motor, for example when the electric motor is in an idle state, before it is started. By means of such a position determination for the rotor position of the electric motor, the start-up or the start of the electric motor is controlled in the best possible way.

The sinusoidal phase current that is applied to the start-up or the start of the electric motor has an increasing frequency applied, with the aim of accelerating the rotor to a speed at which a sufficiently large counter electromotive force (BEMF) is induced in the stator coils, so that with their help a position determination or position estimation of the rotor position and thus a regulated motor operation in an operating state a closed control loop is made possible.

In an operating state with an open control loop, in which the phase current is impressed with a fixed amplitude and increasing frequency, the motor is not regulated, but rather controlled. In this range, a reported or estimated speed is initially not taken into account for a change in current. Operation in the open control loop without feedback of the controlled variable ("open loop operation") is used here. Therefore, this phase current in the operating state with an open control loop is referred to in the following as “open loop current”.

For example, when an electric motor is used in an electric refrigerant compressor, movable components or assemblies are attached to the shaft of the electric motor. These can be, for example, balancing weights or an orbiting disk which, together with a stationary disk, ensures the actual compression of the refrigerant. These components can be accelerated differently relative to the shaft when starting or starting the electric motor. The reasons for this are a mass inertia and an existing mechanical play to the shaft.

Depending on the amplitude with which the phase currents are applied and depending on the size of the load to be overcome when starting or starting the electric motor, the shaft and the aforementioned other components are accelerated to different degrees. The load to be overcome depends, for example, on the pressure levels and temperatures that prevail in the refrigeration circuit of the electric refrigerant compressor.

With a correspondingly high acceleration and large relative displacement of the components with respect to one another, it can happen, for example, that components hit one another and thus cause an undesirable noise when the electric motor is started or started.

The higher the open-loop current and the lower the load that the motor has to overcome when starting up, the higher the initial acceleration experienced by the shaft and the components connected to it. Thus, in the present case, increasing the open-loop current worsens the so-called NVH characteristic of the electric refrigerant compressor.

The NVH characteristic (noise, vibration, harshness), which includes noises, vibrations or a roughness, is known as a designation for the audible and perceptible vibrations and the associated disturbing noises emanating from components or assemblies in a vehicle. The aim in the development of vehicles and assemblies for vehicles is to achieve good NVH characteristics, i.e. the avoidance of noises and vibrations which are perceived as annoying by the occupants of a vehicle.

Since the load applied to its shaft when starting or starting the electric motor is generally not known, when applying a fixed open-loop current, if the amplitude is selected too small, the selected amplitude is too small in relation to a large applied load, the refrigerant compressor cannot or does not start. In the case of applying a fixed open-loop current with an amplitude that is too large, disruptive start-up noises occur in the form of an audible overshoot when entering the operating state with a closed control loop (closed-loop operation), in which now the speed controller is part of the control loop.

The choice of the open-loop current when starting or starting the electric motor thus has a direct influence on the NVH characteristics of the assembly, such as an electric refrigerant compressor, although there is no restriction to such assemblies.

If the motor has been accelerated by the open loop current in the operating state with an open control loop, then the transition to the operating state with a closed control loop takes place, that is, in a regulated operation.

In this regulated operation, a determined speed is transferred to a motor controller as a feedback variable and a current amplitude and a frequency are set for the electric motor through a comparison with a specified target speed, with which the required target speed is to be achieved. The speed can be determined, for example, by means of one of the aforementioned methods, which detects the counter electromotive force (BEMF).

The operating state with a closed control loop or the regulated one Operation is also referred to as "closed loop operation".

In practice, the transition from an operating state with an open control loop to an operating state with a closed control loop often results in a rapid and strong change in the current amplitude of the phase currents. One reason for this can be that with a low load applied to the electric motor, a high current amplitude of the phase currents was specified during open-loop operation, which is not required at all when starting or starting the electric motor. In this case, during the transition to an operating state with a closed control loop, there is a mostly brief but strong increase in the speed of the electric motor, which then has to be regulated down by the motor controller.

The higher the amplitude of the open-loop current and the lower the load applied, the greater the increase in speed, which in turn contributes to a deterioration in the NVH characteristic. This can be seen, for example, in the form of a so-called “roar” of the engine.

In the case of an electric refrigerant compressor in a vehicle, depending on the operating state, different load conditions can arise during the start-up or starting of the electric motor. The load conditions are usually not necessarily known in the converter, which is used to control the electric motor, which is, for example, a BLDC motor or a PMS motor, so that a load-related selection of the open-loop current cannot be made in a targeted manner.

As a result, with a low load and a high open-loop current, the motor can start to accelerate rapidly, and thus also the components coupled to the motor shaft, which are used to compress the refrigerant. This, in turn, is associated with undesirable noises, which are generated when various components touch each other due to the high initial acceleration or are excited to excessively strong vibrations.

Furthermore, in the case described above, there may be a strong increase in the speed, especially during the transition from the operating state with an open control loop to the operating state with a closed control loop, since the high amplitude of the selected open-loop current through the motor controller only reaches the determined Power demand must be adjusted if it is too large for the load case described above.

If the motor has to start up against an unexpectedly high load, which in the case of a refrigeration circuit is determined by the existing pressure conditions and the temperature, if too low an open-loop current is selected, the situation may arise that the current is not sufficient to to accelerate or start the engine. This can have the consequence that the refrigerant compressor either does not start at all or the rotor is at least temporarily not detected synchronously by the generated magnetic field and this also leads to undesirable noises during the start-up or starting of the electric motor.

There is thus a need to improve the known methods of starting an electric motor.

The object of the invention is to provide a method for starting an electric motor which is easy to implement and with which a reduction in the generation of noise when starting or starting an electric motor is achieved, provided that the rotor position is not detected by a sensor and is closed no information is available on the applied load torques at any time.

In addition, overshooting of the speed of the electric motor during the transition from an operating state with an open control loop to an operating state with a closed control loop is to be reduced or avoided.

Furthermore, it should be ensured that the start-up or the start of an electric motor, for example in an electric refrigerant compressor, takes place safely and thus the function of a connected assembly, such as an electric refrigerant compressor, is guaranteed.

The object is achieved by a method with the features according to claim 1 of the independent claims. Further developments are given in the dependent claims.

It is intended to store a table which provides at least two values for the amplitudes of the phase currents to be selected. The values for the amplitudes of the phase currents to be selected in the table can be the same. Alternatively, the values for the amplitudes of the phase currents to be selected are of different sizes. In this case, these are stored with their consecutive numbering in the table in their value of the amplitude increasing in the table. For example, the first and smallest value for the amplitudes of the phase currents to be selected can be 10 A, the second value is 20 A and the third value is 30 A.

It is provided that in a first method step a first attempt to start the electric motor is carried out in the first operating state by selecting a first and smallest value in the table. In the above example, the first attempt to start would be made with phase currents with an amplitude of 10 A.

In a second method step, which is carried out after the first method step, the transition from the first operating state with an open control loop to a second operating state with a closed control loop takes place. In this second operating state, the speed of the electric motor is controlled using a setpoint value for the speed.

It is also provided that, in a third method step, after a predetermined period of time Δt has elapsed in the second operating state, a test of the functionality of the electric motor takes place, the starting process of the electric motor being successfully completed if the test is successful.

If the test is unsuccessful, that is, in the event that the electric motor could not be started successfully in the first start attempt, a further start attempt of the electric motor is carried out again in the first method step in the first operating state. This further start attempt is carried out by selecting a second value in the table. In the above example, this would be the value of 20 A for the amplitude of the phase currents in the second start attempt. The process is then run through again in the form of a loop and the second and third process steps are repeated. This loop continues with the next value from the table until the electric motor has started successfully or a termination criterion has been met.

A termination criterion is, for example, reaching a specified number of maximum permissible start attempts. If the number of maximum permissible start attempts is limited to three attempts, for example, the third start attempt is the last in the process sequence.

It is also provided that, if the functionality of the electric motor is successfully checked, the starting process of the electric motor in the third method step involves a reset of variables used in the method sequence to their initial values before the method is ended with a successful start of the electric motor. This resetting has the effect that a subsequent first start attempt, for example after the vehicle has come to a standstill, is started with the first and smallest value in the table.

It is provided that when the functionality of the electric motor is checked in the third method step, it is checked whether the electric motor is working in the operating state with a closed control loop after the time difference Δt has elapsed since the start of the method for starting an electric motor. If, for whatever reason, after the time difference Δt has elapsed, the electric motor no longer works in the operating state with a closed control loop, the next start is carried out with the next current. A possible reason for the motor leaving the operating state with closed loop control is, for example, the deviation of the (estimated) speed from the target speed by more than a previously defined tolerance value. However, if the electric motor is still in the operating state with closed control loop after Δt, the starting process is assessed as successful.

It is also provided that before each further start attempt it is checked whether the next start attempt is the last possible or permitted start attempt. In the event of the last possible start attempt, the highest permitted or defined value for the amplitudes of the phase currents is selected from the table and the next and last start attempt is carried out with this value. This ensures that the electric motor is started even under high load conditions.

In the event that it is determined that the further or next start attempt is not the last possible start attempt, a counter of the start attempts is increased by the value one. This counter shows in the table the next value in the table when the next start attempt is carried out.

If the procedure is not completed with a successful start attempt, it is intended to generate and output corresponding error messages. Such error messages are transmitted, for example, to a central control unit or an associated control device, which decides on the further method strategy.

Provision is made for the time duration Δt to be in a range between 1 second and 10 seconds and, in particular, to be 6 seconds.

• 1: zeigt exemplarisch zwei Phasenströme während des Anlaufens beziehungsweise Startens eines Elektromotors nach dem Stand der Technik,
• 2: zeigt exemplarisch den Zusammenhang zwischen Phasenströmen und Drehzahl des Rotors im Bereich des Übergangs in den Betriebszustand mit einem geschlossenen Regelkreis,
• 3: zwei Diagramme mit Beschleunigungsmessungen während des Anlaufens beziehungsweise Startens eines Elektromotors mit unterschiedlichen Phasenströmen,
• 4: ein Ablaufdiagramm des Anlaufens beziehungsweise Startens eines Elektromotors nach dem Stand der Technik,
• 5: ein Ablaufdiagramm des erfindungsgemäßen Verfahrens zum Starten eines Elektromotors,
• 6a - 6i: zeigen in den Darstellungen Beschleunigungsmessungen für mehrere Startvorgänge mit verschiedenen Phasenströmen unter verschiedenen Lastbedingungen,
• 7: ein erfindungsgemäßes Ausführungsbeispiel für die Phasenströme während drei Startvorgängen und
• 8: ein Schaltbild einer Anordnung zur Umsetzung des erfindungsgemäßen Verfahrens zum Starten eines Elektromotors.

Further details, features and advantages of embodiments of the invention emerge from the following description of FIG Embodiments with reference to the accompanying drawings. Show it:

• 1 : shows an example of two phase currents during the start-up or starting of an electric motor according to the state of the art,
• 2 : shows an example of the relationship between phase currents and the speed of the rotor in the area of transition to the operating state with a closed control loop,
• 3 : two diagrams with acceleration measurements during the start-up or starting of an electric motor with different phase currents,
• 4th : a flow chart of the startup or starting of an electric motor according to the prior art,
• 5 : a flow chart of the method according to the invention for starting an electric motor,
• 6a - 6i : show acceleration measurements for several starting processes with different phase currents under different load conditions,
• 7th : an embodiment according to the invention for the phase currents during three starting processes and
• 8th : a circuit diagram of an arrangement for implementing the method according to the invention for starting an electric motor.

the 1 shows an example of two phase currents during the start-up or starting of an electric motor, such as a BLDC or PMS motor. For a better overview, the current-time diagram shows the 1 only a first phase current 1 and a second phase current 2 of, for example, three phase currents of an electric motor shown, which are applied with a phase shift of 120 ° to each other.

Like in the 1 can be seen, after a rest phase, in which the amplitudes of the phase currents 1 and 2 Are zero, the act of determining your position 3 the rotor position of the electric motor. Once the rotor position of the electric motor has been determined using a suitable method, generation begins 4th the sinusoidal phase currents in, for example, three phases of the electric motor with a respective phase shift of 120 ° to one another. As in the example of phase currents 1 and 2 in the 1 is shown, this generation occurs 4th of the sinusoidal phase currents with a constant amplitude and a rising frequency. This generation 4th the phase currents take place in a first operating state 5 with an open loop.

the 2 shows the relationship between the phase currents shown as an example 1 , 2 and a speed 7th of the rotor of the electric motor in the area of the transition from a first operating state 5 with an open control loop in the second operating state 6th with a closed loop.

The speed 7th shows an overshoot 8th in the transition area of the operating states 5 and 6th in the example to more than twice the initial value of the speed 7th . This too high speed 7th must subsequently be in the second operating state 6th be corrected with a closed control loop by a speed controller again over a more or less long period of time until the specified target speed has been regulated.

In the 3 two diagrams each with two acceleration measurements are shown over a time axis with time t. These measurements were carried out during the start-up or starting of the electric motor by means of appropriate sensors with different phase currents. These acceleration sensors were installed at different positions on the housing of the compressor for the measurements. These acceleration measurements are directly related to the NVH characteristics of the compressor. High acceleration results in poor NVH characteristics with corresponding vibrations and noises.

An example is in the 3 in the upper diagram, during the first operating state 5 with an open control circuit, a start-up or starting of the electric motor with phase currents with an amplitude of 12.5 A.

In the lower diagram of the 3 is shown, assuming an identical load condition in a starting phase, a start-up or starting of the electric motor with phase currents with an amplitude of 10 A.

Like in the 3 As can be clearly seen in the lower diagram with phase currents of only 10 A, accelerations in m / s ² occur in the range between 1.5 s and 3 s, which cause vibrations and thus also noise. These vibrations and noises are many times higher than in the upper diagram with phase currents of 12.5 A. These are due to the fact that the electromagnetic field with phase currents of only 10 A in the given load case is not able to affect the rotor of the BLDC motor or to accelerate the PMS motor synchronously.

Although the two acceleration measurements per diagram differ slightly from one another, they confirm the essential statements or differences when the electric motor is started or started with phase currents with different amplitudes. In the upper diagram of the 3 the differences in the acceleration measurements are so small that they cannot be represented with function graphs that differ from one another. Only in the lower diagram of the 3 the deviation of the function graphs from one another can be seen.

In the 4th is a flow chart of the startup or starting of an electric motor according to the prior art.

At the start of the procedure, step 9 the start of the electric motor operation is triggered. This electric motor is provided, for example, to drive an electric refrigerant compressor. This start in step 9 can be initiated, for example, by a starting process or starting the vehicle.

In step 10 a program initialization or the start of the program controlling the electric refrigerant compressor takes place. After the program is initialized, step 11 a determination of the position of the rotor position of the electric motor in a resting state of the rotor of the electric motor.

In the next step 12th the generation takes place 4th the sinusoidal phase currents in, for example, three phases of the electric motor with a respective phase shift of 120 ° to one another. This process takes place using the information of the specific position of the rotor, with a fixed amplitude and an increasing frequency of the phase currents in the first operating state 5 with an open loop.

For example, after reaching a predetermined speed of the rotor of the electric motor in the first operating state 5 the transition from the first operating state takes place 5 with an open control loop to the second operating state 6th with a closed loop in step 13th . The information on the speed can be derived from the frequency of the generated phase currents, in which case it is assumed that the rotor is accelerated to a speed synchronous to the frequency by the magnetic field generated by the phase currents. In this case, too, there is no feedback on the actual speed (for example via a speed sensor).

Alternatively, the transition from the first operating state 5 with an open control loop to the second operating state 6th with a closed loop in step 13th take place after a specified time.

Below is in step 14th in the second operating state 6th a closed-loop control of the engine speed is carried out in accordance with a predetermined target speed.

In step 15th the flowchart ends with a successful start-up or start of the electric motor, its operation in the second operating state 6th is continued.

In the 5 a flow chart of a startup or starting of an electric motor according to the invention is shown.

At the start of the procedure, step 9 the start of the electric motor operation is triggered. This electric motor is intended, for example, to drive an electric refrigerant compressor and can be designed as a BLDC motor or PMS motor. This start in step 9 can be initiated, for example, by switching on the air conditioning of the vehicle.

In step 10 a program initialization or the start of the program controlling the electric refrigerant compressor takes place. After the program is initialized, step 11 a determination of the position of the rotor position of the electric motor in a resting state of the rotor of the electric motor.

In the next step 16 the generation takes place 4th the sinusoidal phase currents in, for example, three phases of the electric motor with a respective phase shift of 120 ° to one another. This process takes place using the information of the specific position of the rotor, with a fixed amplitude and an increasing frequency of the phase currents in the first operating state 5 with an open loop. In contrast to the prior art, the amplitude or the value for the phase currents to be generated is stepped 16 read from a table.

Such a table contains at least two values for the magnitude of the phase currents. Here, these two values can be the same. In many cases these two or more values will be different. In one example, the first value in the table can be 10A and the second value can be 10A. In another example, the first value in the table is 10 A and the second value is 12 A. In another example with three values stored in the table, the first value in the table can be 10 A, the second value is 12 A and the third value is 34 A.

Such a table with at least two values can be stored, for example, within an electronic control unit which also implements the program initialization and the further control according to the method. Such a control unit is, for example, a microprocessor or a motor controller arranged in an inverter for an electric refrigerant compressor.

In one embodiment of the invention it is provided that the amplitudes of the phase currents of the values stored in the table become larger or remain the same with their consecutive numbering.

According to the invention, for the first start-up or the first start of the electric motor, hereinafter referred to as the first starting process, after the program initialization in step 10 the first value is read from the table and the first starting process is started with the amplitude for the phase currents given by the first value. The phase currents are generated in the first operating state 5 with the amplitude given by the first value and with increasing frequency. As a rule, the maximum possible or maximum permissible phase current is not used for this first starting process, which is intended to prevent high accelerations of the mechanical assemblies and overshoot of the speed during the transition to the second operating state in order to reduce the disturbing noise generation.

For example, after reaching a predetermined speed of the rotor of the electric motor in the first operating state 5 the transition from the first operating state takes place 5 with an open control loop to the second operating state 6th with a closed loop within the step 16 . The electric motor is now in a regulated mode in the second operating state 6th operated.

In the next step 17th the functioning of the electric motor is checked in such a way that it is queried whether the electric motor is still in the second operating mode after a minimum predetermined period of time Δt has elapsed 6th is operated with a closed control loop or whether the electric motor is no longer in the operating mode 6th is located.

Does the motor run in step when checking 17th after the time period Δt has elapsed, it is still in the second operating mode 6th with a closed control loop within a specified tolerance threshold, the first start process was successful. In this case the procedure in step 18th continued. In step 17th Alternatively, a determined or estimated speed of the electric motor can be compared with a setpoint speed and a decision about a successful first starting process can be made as a function of this comparison.

In step 18th the variables used in the process sequence are reset to their initial or initial values. For example, the variable for the value to be read from the table is reset to the first value, so that it can be used for the first start process in step 16 the first value is read from the table again.

In the next step 19th the starting process has been successfully completed and the electric motor continues to operate in the second operating mode 6th operated with a closed control loop, i.e. in regulated operation. Thus, for example, the start of an assembly such as an electric refrigerant compressor has been successfully completed. In this case, for example, corresponding information about the successful start process can be transmitted to a central control unit and evaluated, passed on or displayed.

Does the motor run in step when checking 17th after the expiry of the time period Δt no longer in the second operating mode 6th with a closed loop, the first start process was unsuccessful. Alternatively, a determined or estimated speed of the electric motor can be compared with a setpoint speed and a decision about a successful first starting process can be made as a function of this comparison. In the event that the determined speed deviates from the target speed by more than a permissible tolerance range, the starting process is assessed as unsuccessful.

In this case the procedure in step 20th continued. In this step 20th it is checked whether the maximum permitted number of start attempts has already been reached. Depending on the specification, this maximum permissible number of start attempts can be, for example, 2, 3 or 4 attempts. If this maximum number of start attempts has already been reached, the method in step 21 terminated, the startup process being terminated as unsuccessful. In this case, for example, corresponding information about the unsuccessful starting process can be transmitted to a central control unit or a control unit in the vehicle. The central control unit or the control unit evaluates the information accordingly out, forwards this information or displays the information.

If this maximum number of start attempts has not yet been reached, for example after the first start process with two permissible start processes, the method in step 22nd continued.

In this step 22nd there is another query in which it is checked whether the next or following start attempt will be the last possible or permissible start attempt.

If this is not the case, step 23 the variable or the counter, which or which counts the number of start attempts and with the help of which an associated value for the phase current is read from the table, increased by one and the method in step 11 continued. In step 11 the position determination of the rotor position is now carried out again in a next pass and on this basis in step 16 Phase currents are generated which have the amplitude specified by the next value in the table. For example, if the first attempt at starting was carried out with a phase current of 10 A, the second attempt at starting is carried out with a value of 12.5 A, for example.

When asked in step 22nd it is determined that the next start attempt is the last possible in step 24 the selection of the value for the phase currents is carried out in such a way that the last value in the table which has the largest amount for the phase current is selected for the next and last run in the method. The procedure is again in step 11 and in the following steps 16 and 17th continued.

With the selection of the largest amount for the phase current, it is ensured that at the latest in the last possible start attempt, the starting process takes place with the maximum possible value for the phase current in order to achieve a safe start of the electric motor. The highest possible phase current is selected in order to start the electric motor with the maximum torque in this high load case. No or only a slight reduction in the generation of noise when starting or starting an electric motor is possibly achieved here. In this case, it is more important to start the electric motor safely in order to ensure the function of the assembly, such as an electric refrigerant compressor, for example. In the event that the compressor could not start with lower phase currents and a start attempt is now being made with the highest possible phase current, the case of a high load is likely and thus the acceleration on the components in the starting process is not so great, whereby in this case the Noise should not be that high.

In the event that this start attempt with the largest phase current could not start the electric motor successfully, for example, an error message can be transmitted to a central control unit or a control unit, depending on the requirement.

In many operating cases, the electric motor of an electric refrigerant compressor in a vehicle can be started under low load conditions, since a so-called “balanced system” represents low load requirements during a start process, for example after the vehicle has been idle for a long time. Thus, in the majority of cases, only a small current amplitude is necessary for the open-loop currents or phase currents.

If the maximum possible current amplitude were applied in each of these low-load cases, this would result in undesirable noises and vibrations, i.e. undesirable NVH behavior, as well as a large overshoot of the speed during the transition to the regulated operation of the second operating state 6th come, which would also worsen the NVH characteristics.

Therefore, according to the method, an attempt is made to start the electric motor with the lowest possible current amplitude of the phase currents in order to avoid these undesirable effects.

In those cases in which the load conditions are higher when starting or starting the electric motor, the electric motor should ideally also be able to start, so the current amplitude of the phase currents is increased in these cases after a faulty start attempt.

the 6th 6a to 6i shows several starting processes of an electric motor with different phase currents under different load conditions. In the diagrams 6a to 6i, measured accelerations a, which represent vibrations of the assembly, are shown in m / s ² over a time axis with time in seconds. To record the acceleration, two acceleration sensors were attached to an assembly such as an electric refrigerant compressor at two different points. Thus, two function graphs are shown in each of the diagrams 6a to 6i.

In the left column of the 6th are with the , and three exemplary Starting processes of an electric motor are shown, which have been carried out with a low load or under low load conditions.

The one in the middle column of the 6th The three exemplary starting processes shown in diagrams 6b, 6e and 6h were under medium load conditions and those in the right-hand column of FIG 6th The three exemplary starting processes shown in diagrams 6c, 6f and 6i were carried out under high load conditions.

During these start-ups, the in the bottom line of the 6th Start processes shown in diagrams 6g, 6h and 6i each with a current of 10 A, which is shown in the middle line of the 6th Start processes shown in diagrams 6d, 6e and 6f each with a current of 12.5 A and that in the top line of the 6th The starting processes shown in diagrams 6a, 6b and 6c are each carried out with a current of 34 A.

It can be seen, for example, that in the event of a low load or under low load conditions, a high acceleration of the assemblies involved in the compression occurs, in particular with a phase current of 34 A. There is a first peak at around 0.5 s and a second peak at 1.2 s. In addition, there is a large overshoot of the speed during the transition to the second operating state at a time of around 2.5 s. These disruptive phenomena are already significantly reduced with a phase current of 12.5 A and further with a phase current of 10 A. The start attempt is successful in all three cases, so choosing a phase current of 10 A offers the best reduction in noise for this load case when starting or starting the electric motor.

In the middle load case in diagram 6b, a significantly reduced amplitude of the accelerations at 34 A can be seen compared to the same amplitude of the phase current in diagram 6a, which suggests a reduced acceleration due to the higher load applied. The same can be seen for a phase current of 12.5 A in diagrams 6e and 6d. In both cases, the electric motor starts successfully under the given load conditions.

The acceleration at a phase current of 10 A is shown in diagram 6h. In this case it can be seen that this phase current is not sufficient to accelerate the rotor correctly and that in this case an incorrect start attempt occurs. In this case, the second starting attempt carried out according to the method according to the invention would thus start the electric motor successfully.

Diagrams 6c, 6f and 6i show the cases with the highest applied load or the highest load conditions. In these cases, only a selection of a phase current of 34 A ensures that the electric motor will start successfully. In this case, the third attempt to start carried out according to the method according to the invention would start the electric motor successfully. In the event that the maximum number of start attempts allowed in the present method is limited to two, after the first start attempt with a phase current of 10 A, the second and thus last allowed start attempt is carried out with the highest phase current of 34 A and the electric motor is started successfully.

Due to the load situation, the reduced acceleration amplitude can also be seen in diagram 6c in comparison with the same cases of medium or low load.

the 7th shows an embodiment according to the invention with three starting processes of an electric motor. A diagram shows three phase currents of an electric motor with their amplitudes of the currents in A for three starting processes over a time axis with time t.

According to the present method, for the first start-up 25th a first value for the phase currents is selected from the table. In the example, the first value is 10 A. The first start process 25th starts with the first operating state 5 with an open control loop and the generation of phase currents with an amplitude of 10 A and an increasing frequency to set the rotor in accelerated motion. After this first operating state 5 the transition to the second operating state takes place 6th with a closed control loop in which the speed of the rotor is regulated to a predetermined target speed. This first startup process 25th ends after a period of 5 s as an unsuccessful start process 21 because the electric motor is in the second operating state 6th does not work correctly for longer than a specified time, which in this case is> 5 s.

The second start-up process begins after a time of around 7 s 26th . According to the present method, a further value for the phase currents is selected from the table for the second starting process. In the example, the second value is 20 A. The second start process 26th starts with the first operating state 5 with an open control loop and the generation of phase currents with an amplitude of 20 A and an increasing frequency in order to set the rotor in accelerated motion. After this first operating state 5 the transition to the second operating state takes place 6th with a closed control loop in which the speed of the rotor is regulated to a predetermined target speed. This second startup process 26th ends after a time of 12 s, based on the beginning of the recording and not based on the beginning of the second start attempt, also as an unsuccessful start process 21 because the electric motor is in the second operating state 6th no longer than a specified time in the second operating state 6th works with a closed control loop.

According to the present method, for the subsequent third start-up process 27 a third or highest value for the phase currents selected from the table. In the example, the selected value is 30 A.

The third start-up process 27 starts at about 14 s with the first operating state 5 with an open control loop and the generation of phase currents with an amplitude of 30 A and an increasing frequency in order to set the rotor in accelerated motion. After this first operating state 5 the transition to the second operating state takes place 6th with a closed control loop in which the speed of the rotor is regulated to a predetermined target speed. This third start-up process 27 ends successfully because the electric motor is in the second operating state 6th in this case works correctly for longer than a specified time. The electric motor is in the second operating state 6th continued to operate. At this point it should be mentioned that during the start-up attempts the pressure situation in the refrigeration circuit will even out further, which could simplify the starting of the electric motor.

the 8th shows a circuit diagram of an arrangement for implementing the method according to the invention for starting an electric motor.

Such an arrangement is, for example, a B6 bridge in an inverter from the prior art. The inverter includes, for example, three half bridges 28 , in each of which a high-side circuit breaker 29 and a low-side power switch 30th is arranged. The half bridges 28 are arranged, for example, between the input-side potentials HV + and HV-.

The half bridges 28 are constructed in such a way that between the respective high-side power switch 29 and the associated low-side power switch 30th the output of the respective phase U, V and W is connected, which is connected to the windings of the electric motor 33 are connected.

In the 8th are the freewheeling diodes on the circuit breakers known from the prior art 29 and 30th not shown.

For controlling the circuit breakers 29 and 30th is a control unit 32 , a driver unit 31 , an evaluation unit 34 for evaluating the measured currents i1, i2, i3 and a unit for determining the rotor position 35 intended. The control unit 32 controls the operating sequence in the inverter, in particular in the first and second operating states 5 and 6th . The control unit 32 also controls the sequence of the method according to the invention for starting an electric motor and contains the table with the values of the phase currents for the individual starting attempts.

The control unit 32 is usually designed as a microcontroller or microprocessor and provides, in particular, the control of the electric motor 33 associated PWM voltage values (Pulse Width Modulation, Pulse Width Modulation).

The control unit 32 is not able to provide the necessary current at the outputs to control the electronic circuit breakers, high-side circuit breakers 29 and low-side circuit breakers 30th , which can be implemented as MOSFET or IGBT, to be adequately controlled. For this purpose there is a driver unit 31 provided, which based on the input signals of the control unit 32 the currents required for the circuit breakers 29 and 30th provides.

Using the evaluation unit 34 are the voltages across the measuring resistors 36 (Shunt) were measured to determine the phase currents i1, i2 and i3, processed. The measurement of the voltages across the measuring resistors 36 is not shown here and takes place according to methods known from the prior art or by means of known arrangements.

The processing includes, for example, an analog-to-digital conversion of the voltage values or filtering, which can be implemented using components (e.g. RC filters) or software filters using calculations in the microcontroller or microprocessor.

The unit 35 to determine the rotor position is usually implemented as a microcontroller or microprocessor or implemented as a program sequence which is executed in the microcontroller or microprocessor. In this determination of the rotor position, the processed, measured phase currents i1, i2, i3 or total currents are evaluated and the currents based on their amplitudes and associated Sorted angles and from this the rotor position of the electric motor 33 definitely.

Such a total current is the sum of the measured individual phase or so-called base point currents, which either flow through the motor phases U, V and W and are measured or as in 8th indicated by measurements of the voltages across the measuring resistors 36 (Shunt resistors R1, R2 and R3) and the currents derived therefrom (i1, i2 and i3) can be determined.

List of reference symbols

1

first phase current

2

second phase current

3

Determination of the rotor position

4th

Generation of phase current with constant amplitude and increasing frequency

5

first operating state with an open control loop; first operating mode with an open loop

6th

second operating state with a closed control loop; second operating mode with an open loop

7th

rotational speed

8th

Overshoot

9

Start electric motor operation; Step 9

10

Program initialization; Step 10

11

Determining the position of the rotor position of the electric motor; Step 11

12th

Generation of sinusoidal phase currents; Step 12

13th

Transition between the operating states; Step 13

14th

regulated operation in the second operating state; Step 14

15th

successful start; Step 15

16

Generation of phase current according to table value; Step 16

17th

Test engine speed; Step 17

18th

Reset; Step 18

19th

Startup completed successfully; Step 19

20th

Check maximum number of start attempts; Step 20

21

Start process ended unsuccessfully; Step 21

22nd

Check of the last possible start attempt; Step 22

23

Increase the number of start attempts; Step 23

24

Selection of maximum value phase current; Step 24

25th

first attempt to start; first start process; Step 25

26th

second start attempt; first start process; Step 26

27

third attempt to start; first start process; Step 27

28

Half bridge

29

High-side circuit breaker

30th

Low-side circuit breaker

31

Driver unit

32

Control unit

33

Electric motor

34

Evaluation unit

35

Unit for determining a rotor position

36

Measuring resistor

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 2008/0067961 A1 [0010]

Claims (10)

Method for starting an electric motor, in which, in a first operating state (5) with an open control loop, phase currents with a predetermined amplitude and an increasing frequency are generated and with a subsequent transition from the first operating state (5) to a second operating state (6). takes place with a closed control loop in which the electric motor is operated with speed control, characterized in that a table with at least two values for amplitudes of phase currents to be selected is provided, that in a first method step a first attempt to start the electric motor in the first operating state (5) is selected of a first and smallest value in the table is carried out, that in a second process step the transition from the first operating state (5) to a second operating state (6) takes place, that in a third process step after a predetermined period of time Δt in the second operating mode stand (6) a test (17) of the functionality of the electric motor is carried out, that if the test is successful, the starting process of the electric motor is successfully completed, that if the test is unsuccessful, a further attempt to start the electric motor in the first process step in the first operating state (5) with selection of a second value it is carried out in the table that the second and the third method step are repeated until the electric motor has started successfully or a termination criterion has been reached. Procedure according to Claim 1 , characterized in that a termination criterion is reaching a predetermined number of maximum permissible start attempts. Procedure according to Claim 1 or 2 , characterized in that the table contains two or more values, wherein the values for amplitudes of phase currents to be selected can be the same or the values for amplitudes of phase currents to be selected are different and with their consecutive numbering in the table in their value of the amplitude increase. Method according to one of the Claims 1 until 3 , characterized in that in the event of a successful check of the starting process of the electric motor in the third method step, variables used in the method sequence are reset (18) to their initial values before the method is ended in step (19) with a successful start of the electric motor . Method according to one of the Claims 1 until 4th , characterized in that the check (17) of the functioning of the electric motor in the third process step is carried out in such a way that it is checked whether the electric motor in the second operating state (6) works with a closed control loop or whether a speed of the electric motor is within a predetermined speed range. Method according to one of the Claims 1 until 5 , characterized in that before the further start attempt it is checked in a step (22) whether the next start attempt is the last possible or permitted start attempt, that for the case of the last possible start attempt a highest value for the amplitudes of the phase currents is selected from the table and the start attempt is carried out with this value. Method according to one of the Claims 1 until 6th , characterized in that in the event that it is determined in step (22) that the next start attempt is not the last possible start attempt and in a step (23) a counter of the start attempts is increased by the value one. Method according to one of the Claims 1 until 7th , characterized in that in the event of an unsuccessful start attempt in a step (21) an error message is generated and output. Method according to one of the Claims 1 until 8th , characterized in that in the second operating state (6) the speed of the electric motor is controlled using a default value. Method according to one of the Claims 1 until 9 , characterized in that the predetermined time period Δt is less than 10 seconds, in particular 6 seconds.

Images