WO2018141784A1 - Method for operating an electric machine - Google Patents

Abstract

The invention relates to a method for operating an electric machine (100) with a permanently and/or separately excited rotor (120) and a plurality of phase windings (111, 112, 113) for a stator (110), the electric machine (100) being operated in block commutation, in which one of the phase windings (111, 112, 113) at a time is energised for a block length and, after a commutation, another of the phase windings (111, 112, 113) is energised, and the block length is adapted according to a duration of the commutation between the phase windings (111, 112, 113) at a current operating point.

Description

 description

title

 Method for operating an electrical machine

The present invention relates to a method for operating an electrical machine as well as a computing unit and a computer program for its implementation.

State of the art

Electric machines with permanently or externally excited rotor and one or more windings for the stator, in particular synchronous machines, e.g. So-called brushless DC motors (BLDC, brushless DC) can be controlled, for example, via a microcontroller, with stator currents generally being set by means of a pulse-controlled inverter. The rotor position, whose knowledge of the control, in particular also for commutation, of the electrical machine is generally required, can be determined, for example, via the zero crossings of a so-called pole wheel voltage. Since, for example, in a block commutation, only two winding phases are energized outside the actual commutation process, the pole wheel voltage can be detected in a respective currentless winding strand.

For optimal operation of the electrical machine is usually required that sets a minimum possible current in the electric machine. For this, the internal voltage of the electrical machine and the associated motor fundamental current should be in phase. For this purpose, a time-advanced control of the winding strands is usually necessary due to the inductance of the electric machine. This correction, which is the lagging Behavior of the motor fundamental wave current compensated, is described by the so-called pre-commutation angle.

From EP 1 734 648 A1, for example, a method for commutating a brushless and sensorless direct current motor is known, in which the control of the winding phases takes place asynchronously.

Disclosure of the invention

According to the invention, a method for operating an electrical machine as well as a computing unit and a computer program for carrying it out with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

An inventive method is used to operate an electric machine with permanent and / or foreign-excited rotor and a plurality of winding strands for a stator, in particular a synchronous machine. It may in particular be a three-phase electric machine, but more phases (or winding phases), for example, five or seven, are conceivable.

In this case, the electric machine is operated in block commutation, in each of which one of the winding strands energized for a block length and after commutation another of the winding strands is energized. The block length is then adjusted taking into account a duration of the commutation between the winding phases at a current operating point. Particularly preferably, this adjustment can also be made continuously. Under a commutation here is a change in the current flows through the winding strands of the electric machine to understand (current application). Durations can be understood here to mean periods of time as well as angle durations or angular differences, which can be converted into one another taking account of a rotational speed or angular velocity of the electrical machine. A duration of such a commutation would mean that duration until the current in the winding strand from which it is switched off decays is. Thus can be regarded as the end of the commutation, a time or angle at which the current has subsided. Only when this current has subsided, then, for example, an induction voltage can be detected or determined, for example, to determine a position of the rotor.

A duration between two energizations of the winding strands (which lasts one block length in each case) would allow a constant gap length with a short duration of the commutation a larger gap, in which the induction voltage can be detected or determined, as necessary. However, a longer block length leads to a lower current in the winding strands and thus to a more efficient operation of the electrical machine. The adaptation of the block length taking into account a duration of the commutation thus allows a more efficient operation than when using a constant block length.

In this respect, it is also particularly expedient if the block length is adapted in such a way that a duration between two energizations of a winding strand complements the duration of the commutation by a fixed value or a value dependent on the duration of the commutation. In other words, the duration between two energisations can thus be made as small as possible in order to detect or determine, for example, the induction voltage just just reliably.

Advantageously, the duration of the commutation is determined on the basis of zero crossings of the voltage which occur due to the commutation. This is a particularly simple and accurate way to determine the current duration of the commutation.

Alternatively, it is preferred if the duration of the commutation is determined on the basis of a current in the phase windings at the current operating point and taking into account an inductance of the phase windings. To this

In this way, only a determination of the current is necessary, so that - with known inductance - determines the duration of the commutation very simple and thus the block length can be adjusted. Preferably, the block length is adjusted between a minimum value and a maximum value. In particular, the minimum value may be 120 ° and / or the maximum value 180 °. This represents the widest possible bandwidth for the block length, in which still reliable detection of the induction voltage is possible.

It is advantageous if, based on the voltage, a position of the rotor relative to the stator is also determined. Conveniently, the position of the rotor relative to the stator can be determined based on zero crossings of the voltage which occur due to the rotation of the rotor. In this way, very easily, for example, with a stored reference position, the position of the rotor can be determined. This allows a targeted commutation in the control of the electrical machine. Thus, for example, every 30 ° after a zero crossing, a switching operation in the course of commutation be made when, for example, a three-phase electric machine is used.

An arithmetic unit according to the invention, e.g. a control device of a motor vehicle is, in particular programmatically, configured to perform a method according to the invention.

Also, the implementation of the method in the form of a computer program is advantageous because this causes very low costs, especially if an executive controller is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as e.g. Hard drives, flash memory, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings. The invention is illustrated schematically with reference to an embodiment in the drawing and will be described below with reference to the drawing.

Brief description of the drawings

Figure 1 shows schematically and simplified an electrical machine, in which a method according to the invention can be carried out.

FIG. 2 shows an idealized energization of the winding strands of such an electric machine.

FIG. 3 shows an idealized course of a winding phase voltage during the operation of such an electrical machine.

FIG. 4 shows different block lengths when using a method according to the invention in a preferred embodiment.

Embodiment (s) of the invention

FIG. 1 schematically and simplified shows an electrical machine 100 in which a method according to the invention can be carried out. The electric machine 100 in the present case is a brushless DC motor.

The electric machine 100 has a stator 1 10, which in turn has three winding strands 1 1 1, 1 12, 1 13, for example. Furthermore, the electric machine 100 has a rotor 120 which, for example, has a permanent magnet. For each of the winding phases, which have an inductance, an unspecified resistance is plotted. Furthermore, by way of example, a winding phase voltage U _mo t and a winding phase current l _mot . located. Furthermore, a circuit arrangement 180 is shown, to which the three winding strands 1 1 1, 1 12, 1 13 are connected. The circuit arrangement has six switches, for example semiconductor switches such as transistors (eg MOSFETs, IGBTs), by means of which the three winding strands can be alternately connected to positive and negative voltage or ground, for example, and one of which is denoted by reference numeral 181 is.

Furthermore, an intermediate circuit voltage U _Z K is shown, which rests on the circuit arrangement. Furthermore, each of the switches is associated with a diode connected in parallel, one of which is denoted by the reference numeral 182 by way of example. This symbolizes, for example, an intrinsic body diode or a separate diode for a reverse conductivity (eg in the case of IGBTs). The circuit arrangement 180 and in particular the switches can be controlled for this purpose, for example by means of the arithmetic unit 190. Incidentally, the mode of operation of such an electrical machine is known per se and will therefore not be explained further here. FIG. 2 shows an idealized energization of the winding phases of an electrical machine, as shown in FIG. For this purpose, a current I is plotted over an angle φ of the rotor with respect to the stator for each of the three winding strands. The angle φ can also be seen as the product of the angular velocity ω of the rotor with the time t, ie φ = ωί.

The currents in the three winding phases are here designated by lu, lv and l _w for the three winding phases in the sense of phases. The energization, ie a block length Δφ, in each case lasts 120 ° and begins in each case 30 ° after a zero crossing of the respective phase voltage. This is a conventional energization ("block commutation"), which can take place by suitable actuation of the switches, as shown in FIG. It is assumed that the three winding phases or phases are arranged symmetrically distributed on the stator. FIG. 3 is a diagram of a profile of a winding phase voltage during operation of an electrical machine, as shown in FIG. For this purpose, a voltage U is plotted against the angle φ. With U ' _mo t while a Polradspannung is drawn, as it is caused by a rotation of the rotor and due to induction in the winding strands. In addition, an idealized winding _phase voltage U _mo t is shown, which corresponds to the actual voltage present.

The winding phase voltage U _mo t is composed here of the Polradspannung U'mot, the ohmic and inductive voltage drop across the winding strand and a superimposed voltage due to the commutation of the other phases. Thus, for example, at the angles φ of 30 °, 90 °, 150 ° and 210 °, a commutation (including both a beginning and an end of the current supply) takes place, as can also be seen from FIG.

During the duration μ of the commutation, ie until the current in the one winding strand from which is switched off, has decayed, depending on the winding strands, which are considered and switched, amount to one third or two thirds of the intermediate circuit voltage U _Z K, such as can be seen from the course U _mo t.

In a further diagram below the diagram with the voltage curve, a sign V of the winding phase voltage U _mo t is plotted against the angle φ. Based on the sign V, the zero crossings of the winding phase voltage U _mo t can be determined. In the present case occur at the angles φ-ι, φ ₂ , ψ3 and φ ₄ zero crossings.

The zero crossings φι and φ ₄ result from the course of the Polradspannung U'mot and thus from the rotation of the rotor. From this, the position of the rotor relative to the stator can be determined. The zero crossings φ ₂ and φ _3, on the other hand, result from the commutation process. It can be seen that the distance between the two zero crossings φ ₂ and φ ₃ corresponds exactly to the duration μ of the commutation. By determining the zero crossings of the winding phase voltage, the duration of the commutation that is determined in the Frame of the present invention is also referred to as a third duration and can be used for example as Vorsteuerwert.

FIG. 4 shows various block lengths when using a method according to the invention in a preferred embodiment. For this purpose, a current I is plotted over an angle φ of the rotor with respect to the stator for one of the three winding strands (similar to FIG. 2).

In addition to the block length Δφ = 120 °, the associated duration μ of the commutation, as explained in more detail with respect to FIG. 3, is shown. The duration

L between two energizations of the winding strand is, however, significantly greater than the duration μ of the commutation.

The block length can therefore be adjusted taking into account the duration μ of the commutation. In the present case, the block length is extended to

Δφ '= 150 °. This leads accordingly to a reduction in the duration between two energizations of the winding strand to L '. In this case, the duration L 'now corresponds to the duration μ of the commutation supplemented by a fixed value W. The duration corresponding to this fixed value W is sufficient in this case to detect or determine, for example, the induction voltage.

It should be noted that the adaptation of the block length can be carried out in particular (quasi) continuously, i. an increase of only a few degrees can also be made, so that only small changes in the operating point can be reacted. Furthermore, the adjustment from one to another

Value, for example, (quasi) continuously or in small steps over several block lengths away. In this way, speed jumps can be avoided. It is understood that the duration μ of the commutation can be calculated not only in accordance with the explanation of FIG. 3, but also, as mentioned above, from the winding phase current and the inductance. In both cases, however, the longest possible block length can be set, which leads to a more efficient operation of the electric machine.

Claims

claims 1 . Method for operating an electric machine (100) with a permanently and / or externally excited rotor (120) and a plurality of winding strands (1 1 1, 1 12, 1 13) for a stator (1 10),  wherein the electrical machine (100) is operated in block commutation, in each case one of the winding strands (1 1 1, 1 12, 1 13) energized for a block length (Δφ, Δφ ') and after commutation another of the winding strands (1 1 1, 1 12, 1 13) is energized, and  wherein the block length (Δφ, Δφ '), taking into account a duration (μ) of the commutation between the winding strands (1 1 1, 1 12, 1 13) is adjusted at a current operating point. 2. The method of claim 1, wherein the block length (Δφ, Δφ ') is adjusted such that a duration (μ) between two energizations of a winding strand, the duration (μ) of the commutation supplemented by a fixed or one of the duration (μ) commutation dependent value. 3. The method of claim 1 or 2, wherein the duration (μ) of the commutation based on zero crossings of the voltage, which occur due to the commutation, is determined. 4. The method according to any one of the preceding claims, wherein the duration (μ) of the commutation based on a current in the winding strands at the current operating point and taking into account an inductance of the winding strands (1 1 1, 1 12, 1 13) is determined. 5. The method according to any one of the preceding claims, wherein the block length (Δφ, Δφ ') is adjusted continuously. 6. The method according to any one of the preceding claims, wherein the block length (Δφ, Δφ ') is adjusted between a minimum value and a maximum value. 7. The method of claim 6, wherein the minimum value is 120 ° and / or the maximum value is 180 °. 8. The method according to any one of the preceding claims, wherein further based on the voltage (U _mo t), a position of the rotor (120) with respect to the stator (1 10) is determined. The method of claim 8, wherein the position of the rotor (120) with respect to the stator (110) is determined from zero crossings of the voltage (U _mo t) occurring due to the rotation of the rotor (120). 10. Computing unit (190), which is adapted to perform a method according to any one of the preceding claims. 1 1. A computer program that causes a computing unit (190) to perform a method according to any one of claims 1 to 9 when it is based on the Arithmetic unit (190) is executed. 12. A machine-readable storage medium having a computer program stored thereon as claimed in claim 1.