DE102017012208A1 - A method of minimizing torque of an electrical machine during an energy transfer process - Google Patents

Abstract

A method for minimizing a torque of an electric machine of a vehicle electric drive during an energy transmission operation by the electric machine will be described. The energy transfer process comprises: conducting electrical energy through at least one stator winding of a stator of the electric machine for charging an energy storage device of the vehicle drive train or for feeding energy back from the energy store, while a rotor of the electric machine is mechanically locked relative to the stator. Further, the torque between the at least one stator winding and a rotor of the electric machine is minimized by minimizing the angular amount (W) between a magnetic stator flux (1-3) resulting from the passage of electrical energy through the at least one stator winding Direction (5), which is opposite to the rotor flux, which prevails during the conduction of electrical energy. The angular amount (W) is minimized at the beginning or before the step of directing energy by subdividing the windings into subgroups, applying a hill start assist or by using a separately excited machine and minimizing the excitation.

Description

The method described here relates to the field of energy transfer from or to an electric drive train, in particular to its energy storage. It is known, when charging an energy storage device of an electric drive of a vehicle, to transmit current through windings of an electric machine in order to achieve a filtering effect. In particular, in the case of a permanent-magnet electric machine, torques arise which are undesirable, since in this state the vehicle is at a standstill. It is also known to use a locking mechanism to prevent movement of the rotor of the electric machine.

It is an object of the invention to provide a way to reduce the mechanical stress on such a mechanical interlock.

This object is achieved by the method according to claim 1. Further advantages, features, properties and embodiments will become apparent from the dependent claims, the description and the figures.

It is proposed to minimize a deviation of the mutual orientation of rotor flux and stator flux against an anti-parallel alignment of the flows. This minimizes the torque created by the transfer of energy through the electric machine. There are proposed ways by which the torque can be minimized, or a torque of substantially zero can be achieved. Consider an angle between rotor flux and stator flux that is zero when the rotor flux and stator flux are exactly antiparallel so that there is no torque-producing interaction in this position. The deviation of the angle (or angle) between stator flux and rotor flux from an angle of 180 ° is minimized.

A method is proposed for minimizing a torque of an electrical machine, in particular the torque between the rotor and the stator. The electric machine is associated with an electric vehicle powertrain, which may be the sole drive, such as in an electric vehicle, or which may be one of multiple drives, such as an electric vehicle. The vehicle powertrain is a plug-in powertrain or is configured to receive electrical energy from a stationary device (such as for charging) or backfeed through a line-based electrical connection (especially during a regenerative process).

The torque to be minimized referred to here refers to an energy transfer process in which energy is transmitted through the electric machine, in particular through a winding of the electric machine or through a plurality of windings of the electric machine. During energy transfer, at least one of the windings is disconnected from the other windings, i. During the energy transfer process, the electric machine is not in a complete drive configuration, i. not in a complete (symmetric) star configuration, nor in a complete (symmetric) triangle configuration.

The energy transfer process comprises conducting electrical energy through at least one stator winding of a stator of the electric machine for charging an energy store of the vehicle drive train or for feeding energy back from the energy store. During the energy transfer process, the rotor of the electric machine is mechanically locked to the stator, either by a direct locking connection between the rotor and stator, or by the rotor to the stator via a locked connection.

As electrical energy, preferably a direct current (constant or pulsating) is transmitted. In other words, the signal by which the electrical energy is transmitted is a DC signal (as a constant voltage or as a pulsating voltage).

It is intended to minimize the torque between the at least one stator winding (or stator) and a rotor of the electric machine. This can be accomplished by minimizing the angular amount between a magnetic stator flux resulting from the passage of electrical energy through the at least one stator winding and a direction opposite the rotor flux prevailing during the conduction of electrical energy , The minimization corresponds to the alignment of stator and rotor in an anti-parallel as possible alignment with each other. The angular amount is minimized at the beginning or before the step of conducting energy.

As a result, during the energy transfer process only a minimal torque, so that the mechanical stress of the lock (and also the electric machine) is minimized. The considerations of the magnetic fluxes relate in particular to the interior of the stator, in particular to flows that arise within the rotor or result in the gap between rotor and stator.

The minimization can be realized by determining different current values and resulting individual flows for a subgroup of stator windings in a step I. The vector sum of the individual fluxes has a minimized angle to a direction opposite to the direction of the stator flux. The electrical energy is passed through the subgroup of stator windings according to the different current values.

The minimization can be realized by locking the rotor in a step II by means of a Hill Start Assist. The hill start assist is active while conducting electrical energy through at least one stator winding. The Hill Start Assist is also active in a drive mode of the powertrain on slopes.

The minimization can be realized by using a third-excited electric machine as the electric machine in a step III. The torque is minimized by minimizing the magnetic interaction between the rotor flux and the stator flux by modulating an excitation current flowing through the rotor.

Steps I, II and III can be carried out individually or in any combination as part of the process. Only step I can be executed. Furthermore, in the context of the method only step II can be carried out. In addition, only step III can be carried out in the context of the method. Within the scope of the process, steps I and II (without step III), steps I and III (without step II) or steps II and III (without step I) can be carried out. Finally, in the context of the method, steps I, II and III can be carried out. In particular, the designation of the steps is not a definition of the sequence of execution, but only a pure short name that serves as a reference. Among other things, further possibilities are mentioned below which are helpful in understanding the invention with regard to the minimization of the torque.

The torque can be minimized by aligning the stator flux. In this case, at least one stator winding can be selected. The one stator winding is chosen which leads at the given current direction of the (later) energy transfer process through this stator winding to the lowest of all possible torques, i. leads to a stator flux, which deviates only by a minimum angle (incl. 0 °) of an anti-parallel alignment with the rotor flux. Further, that subgroup of stator windings may be chosen which at the given current direction of the (later) energy transfer operation through these stator windings leads to the lowest of all possible torques, i. leads to a (total) stator flux, which differs only by a minimum angle (incl. 0 °) from an anti-parallel alignment with the rotor flux.

Since the normal of the stator winding determines the direction of the stator flux, the normal can also be considered for selecting the stator winding or the subgroup. Here, the alignment of the normals is crucial, especially their unit vector. If a given current direction (for the subsequent energy transfer) is given, the half space adjacent to the stator winding, into which the stator flux points, is taken into account. In particular, the ambiguity of the normals is resolved by the given current direction.

It is therefore possible to select that stator winding whose normal (possibly taking into account a predetermined current direction of the energy transmission) has the smallest angle with respect to the rotor flux. The electrical energy is then passed only through this stator winding. As mentioned, the ambiguity of the normals of the stator winding is resolved by a given (later) current flow. In other words, the stator winding that generates a (magnetic) stator flux at a given current flow direction that has the smallest angle to a direction opposite to the rotor flux (i.e., smallest angle to complete anti-parallelism) can be selected.

Instead of a single winding and several stator windings can be considered. Their flux results from the vector sum, so that stator flux alignments are possible, which lie between the orientations of the stator fluxes of individual stator windings. If the energy flow of a single stator winding promises the least angular deviation from the rotor flux, it can be used for energy transfer. However, if the least angular deviation lies between the orientations of the stator windings, for example, substantially at a vector sum of two (generally several) stator windings, then these are selected for power transmission.

It is therefore selected that subgroup of stator windings whose normal in sum have the smallest angle to the rotor flux. The smallest angle refers to all tuples of a subgroup of the stator windings. The electrical energy is only passed through this subgroup of stator windings.

Again, the ambiguity of the normals of the stator windings can each resolve resolved by a respective, predetermined ( later) current flow. In other words, those stator windings of a subgroup may be selected which together produce at the respective predetermined current flow directions a (magnetic) stator flux having the smallest angle to a direction opposite to the rotor flux (ie smallest angle to complete anti-parallelism). It is envisaged that when transferring energy across a subset of stator windings, the amount of current through all the stator windings (through which energy is transferred) is the same. In this case, the resultant direction of the resulting common stator flux can be determined by a vector sum of the orientations of the stator windings. Since the amount of current through the respective stator windings is the same, the resulting stator flux orientation can be adjusted by connecting or disconnecting windings, such as by selecting by means of a switching device.

In the following there is shown a possibility in which the common stator flux of a subset of stator windings does not have discrete orientations as in the aforementioned possibilities, but the alignment can be substantially continuously adjusted (i.e., as close to antiparallel to the rotor flux as possible). This is possible by setting different RMS currents through multiple stator windings. One possible implementation of the adjustment is the modulation of the current, the RMS value being set by (at least) one modulation parameter. As a result, angle-continuous alignments of the (total) stator flux are possible.

Minimizing the torque may therefore provide that different (effective) current values and preferably also (different) resulting individual flows are determined for a subset of stator windings. These current values are determined such that the vector sum (which, in addition to the direction, also represents the strength of the individual magnetic fluxes) of the individual flows has a minimized angle with respect to a direction which is opposite to the stator flux. The electrical energy is passed through the subgroup of stator windings according to the different current values. As a result of the different current values, stator flux directions (of the common stator flux) which lie between orientations of normals of individual stator windings and which lie between alignments of vector sums of normals of the stator windings result.

In addition to the above-described minimization by selecting a stator winding or a subset of stator windings, a finer (and in principle angular continuous) alignment of the (total) stator flux can thus be achieved by different (adjustable) current values flowing through the stator windings when energy is transferred. The different current values can be achieved in particular by modulation, for example by a phase control or by a pulse width modulation.

The different current values are realized by different modulation parameters for the subgroup of stator windings as modulation parameters are the sizes pulse width, frequency, phase and others into consideration. Differently high modulation parameters (i.e., different modulation parameters in their value) are associated with different RMS currents. The RMS currents determine the individual flows, i. the individual stator fluxes of the individual stator windings.

Different current values can be combined with determining a subset of stator windings to achieve the lowest possible angle and thus the lowest possible torque.

A subgroup is a group of stator windings of all stator windings, which does not include all stator windings. The subset preferably includes at least two stator windings (but not all stator windings of the electrical machine). For example, two stator windings form a subgroup.

Another way of locking the rotor with respect to the stator at an angle associated with a minimum torque (depending on the or for the energy transfer provided stator windings). While previously adjusting the resulting stator flux in its (angular) position to the rotor flux, it is therefore proposed to adjust the position of the rotor to a (predetermined) stator flux by locking the rotor in a minimum torque position. This may also include moving the rotor to one of these positions to lock the rotor in that position.

Therefore, minimizing the torque may provide that the rotor is locked to the stator in a position in which an angle between the normal of one of the stator windings and a direction opposite the rotor flux is minimized. Energy is then passed through this stator winding. Further, if the current direction associated with the transfer of energy is given, then that one of the two normals associated with the minimum torque is used. If the current direction is not specified, then the current direction depends on the normal.

Further, this may involve not only a stator winding but also a plurality of stator windings (or a subset of stator windings). The rotor is locked relative to the stator in a position where an angle between a vector sum of the (ie all) normal of a subset of stator windings and a direction opposite to the rotor flux is minimized. In other words, the rotor is locked in a position where the total stator flux is only a minimum angle (or not at all) away from an antiparallel alignment between the stator flux and the rotor flux. The energy is passed through this subgroup of stator windings in equal parts. As a result, the vector sum of the normals of the respective stator windings also indicates the direction of the total stator flux.

For locking, a mechanical lock adapted to lock the rotor (i.e., to lock a rotation) may be used. The rotor can thus be locked by means of a mechanical lock. The lock has multiple lock positions. In at least one of these lock positions, the angle of a direction opposite to the rotor flux from a normal of a stator winding (when transferring energy only through this stator winding) or to a vector sum of normals of a subset of stator windings (when transferring energy through that subgroup) is minimized. The positions or blocking positions are preferably angularly discrete and in particular determined by structural features of the mechanical barrier. The lock is in particular an electrically controllable lock.

The lock, by means of which the rotor is locked, can have recesses, claws or grooves. These define the angle-discrete locking positions. The barrier may have two opposing sections that can be controlledly engaged with each other. A section may have at least one recess or a protrusion, while the other section has at least one structure complementary thereto or at least engageable with it. A section may have a plurality of structures that are distributed circumferentially and whose angular position defines the locking positions. The number of blocking positions may correspond to the number of stator windings or may correspond to an integer multiple of the number of stator windings, the latter approximately in the transmission of energy across a subset of stator windings.

Instead of a dedicated lock, the rotor can be locked by means of a Hill Start Assist. This is active during conduction of electrical energy through at least one stator winding, i. generates a holding torque. The hill start assist may be active on a ride mode (of the vehicle or vehicle powertrain) on slopes, such as when the vehicle is on a grade. In a parking mode, i. If the vehicle drive train is not kept ready for traction, the hill start assist is used in accordance with the method described herein. It results in a double use.

The electric machine can be a permanent-magnet electric machine. The rotor may have a permanent magnet. The rotor flux results from the permanent magnet or from the permanent excitation and thus from the remanence in the rotor. The electric machine may further be a foreign-excited electric machine. In this case, the rotor comprises an exciter coil. When transmitting energy, an excitation current can be impressed into the exciter coil. The exciter current flows through the rotor (where it generates the magnetic rotor flux). The current direction of the exciting current can be selected to reduce the angle or the torque; In particular, a current direction is selected that is associated with a rotor flux which is substantially opposite to the stator flux (or at least has an angle greater than 180 ° to the stator flux).

If the electric machine is a foreign-excited electric machine, then the torque can be minimized by modulating the excitation current. In general, the current can be set by at least one winding to a value of less than 100% of the current supply of another stator winding; In particular, all stator windings which are energized can also be adjusted with regard to the current supply. One way of adjusting the current is modulating.

By adjusting the current (in particular by modulating), in particular the magnetic interaction between the rotor flux and the stator flux is minimized. It can be provided that, by means of the modulation, a voltage induced in the stator windings is below a predetermined maximum value. This is especially true for windings through which no power is transmitted when transmitting energy. The maximum value may be based on a voltage maximum value of power electronics defined by the design that is connected to the windings.

• Die 1 - 4 dienen zur näheren Erläuterung des hier beschriebenen Verfahrens.

Furthermore, an electric vehicle drive train with an electric machine will be described. The electric machine is provided between a power converter (in particular an inverter) and an electrical connection designed to connect the vehicle drive train. The vehicle drive train is therefore set up for an energy transmission process between the vehicle drive train and a connection station (in particular a charging station). The power converter and the electric machine are configured to carry energy from the connection to an energy store of the vehicle drive train and / or in the opposite direction (ie to charge the vehicle drive train and / or to regenerate energy from it). The power converter is further adapted to carry out the method described herein, in particular by driving the windings of the electric machine and may have an output which is drivingly connected to an electrically controllable lock (as described herein). For this purpose, the power converter may have a controller which controls switches of the power converter according to the method.

• The 1 - 4 serve for a more detailed explanation of the method described here.

The 1 symbolically shows the possible stator fluxes 1 . 2 and 3 of three stator windings of a stator of an electric machine. It can be seen that these 120 ° are offset from each other, as it is in the 2 - 4 the case is. The individual stator fluxes are represented by double arrows, with the fraction of the hatched area in a double arrow representing the strength of the magnetic flux generated by the individual stator windings.

In the 1 - 4 is the (single) stator flux 1 at 100% (one for the 1 - 4 valid standard strength). In the 1 - 4 is also the stator flux 3 (the relevant single stator winding) 0% (the same standard). In the 1 and 2 This also applies to the single stator flux 2 to, being in the 3 the single stator flux 2 100%, and in the 4 the single stator flux 2 about 40% of the mentioned standard thickness. The strength data are purely exemplary, it being relevant for understanding whether the strength amounts to 0%, 100% or a part thereof (here by way of example 40%), and how this results in the (total) stator flux. At the arrows 1 - 3 the direction and the corresponding strength are relevant (represented by the hatched area). The length of the double arrows themselves indicates a flow that will result at a flow strength of 100%. It can be seen that the individual fluxes of the stator windings would be the same for an assumed same current supply.

The arrow 5 is in the 1 - 4 assigned to the direction of the rotor flux, and corresponds to the opposite direction of the rotor flux. Thus, if the stator flux is aligned antiparallel to the rotor flux as a whole, the arrow representing the total stator flux (shown as a double arrow) and the rotor direction arrow, which represents the opposite direction of rotor flow (single arrow) are superimposed. In this case results in a torque of zero. The opposite direction of the rotor flux is shown to be easily seen in the figures as to how far the stator flux and the rotor flux are from antiparallel alignment. The arrow 5 Specifically, only indicates the direction.

In the 1 is shown that at a given orientation of the stator flux (see arrow 1 - 3 ) to the rotor direction arrow 5 the one rotor winding is selected which has the lowest angle W to the rotor directional arrow 5 having. This is as shown in the 1 the one rotor winding that drives the rotor 1 generated. Usually, the respective winding is perpendicular to the rotor direction arrow 1 , It can be seen that, for example, during current supply only for generating the rotor flux 2 or only to generate a rotor flux 3 the angle W to the rotor direction arrow 5 larger than with the exclusive generation of a single rotor flux 1 , so that the torque would be greater than in the energization of the rotor winding, the rotor flux 1 generated. The 1 serves therefore to illustrate a method in which the stator winding is formed whose normal has the smallest angle to the rotor flux, in which case electrical energy is passed only through this stator winding. This corresponds in the case of 1 the generation of a rotor flux 1 (but not a rotor flux 2 or 3 ) by passing the electrical energy only through the respective stator winding.

The 2 shows six different possible locking positions P, wherein one of the positions P of the direction of the rotor arrow 5 equivalent. It is based on the 2 to recognize that here the rotor is locked relative to the stator in a position in which the rotor direction arrow (opposite to the rotor flux) parallel to the (single) stator flux 1 lies. As mentioned, the rotor is locked in a position P and it is determined which (single) stator flux or which associated stator winding would be the most suitable to generate the lowest possible torque. In a lock, in which the rotor direction arrow 5 along the stator flux of a single rotor winding, only this stator winding is energized, as indicated by the fully hatched arrow 1 is shown.

If locked in another position, for example in position P, lies between the individual stator fluxes 1 and 3 is located, then both associated stator windings (the rivers 1 and 3 generate) energized. It is preferred that in this case both associated stator windings produce the same current, so that the vectorial addition of the individual stator fluxes results in the direction in which the rotor directional arrow points, so that the torque is minimized. In principle, a stator winding can be energized to 100%, while another stator winding is energized with only a part thereof (<100% and> 0%), such as by modulation, so as to achieve a total stator flux whose direction is not more than a predetermined Angular difference of the rotor flux and in particular deviates from one of the locking positions P, preferably an angular difference of substantially 0 °. A corresponding variant is in the 4 represented in which by modulation (at least) a stator winding, a direction can be generated angle-continuous; the angle is set by the modulation or by adjusting the current through at least one winding. In combination with 2 the flux can be adjusted so that the direction of the stator flux is one which gives one of the positions P.

The 3 shows an energization of two stator windings, so that two individual stator flows result (in the 3 the rivers 1 and 2 ), so as shown (by the arrow 1 and the arrow 2 ' ) by vector addition (approximately) gives the direction of the rotor direction arrow.

The 3 also serves to explain a case where the rotor is not locked in one of the positions P but in a position defined by the rotor direction arrow 5 is reproduced. It is determined here that in sum the stator fluxes 1 and 2 the smallest angle W to the rotor direction arrow 5 to have. Since the individual rotor flows 1 and 2 are equally strong (corresponding to an equal power of the associated stator windings) results in an addition of the unit vectors of the individual stator fluxes. For graphical representation of the arrow 2 ' who the arrow 2 corresponds to the end of the arrow 1 pushed, so that the rivers are added graphically, and the direction of the total stator flux is the direction R, according to the illustrated dotted line. It can be seen that in this selection, the angle W between the rotor directional arrow 5 and the direction R of the total stator flow from all possible selections of the rivers 1 . 2 and 3 the minimum angle results. The rivers 1 and 2 are generated by a subset of stator windings, with the resulting stator flux being the smallest possible angle (from all possible selections) to the rotor directional arrow 5 having. It can be seen that approximately in the selection of the individual flows 1 and 3 at the same rotor direction arrow 5 a significantly larger angle W would result; The same applies to a potentially possible selection of the individual stator fluxes 2 and 3 ,

While in the 3 is based on a selection of stator windings, which are energized to 100%, ie the same power, the serves 4 to explain the method when using different current values.

The 4 shows a rotor direction arrow 5 whose direction corresponds to the direction of the total stator flux. The direction R of the total stator flux results as in the 3 by the addition of several single stator fluxes. It can be seen that the stator flux 1 100% of a standard thickness while the stator flux 2 , see dotted arrow, about 40% of the standard thickness. For a better illustration, the arrow 1 an empty double arrow is deposited, which represents the length of the arrow at a standard thickness of 100%. The rivers 1 and 2 are generated by different current values flowing through the windings, which are the stator fluxes 1 and 2 produce. Here, too, results in a vectorial addition, represented by the arrow shifted to the addition 2 ' which is at the end of the stator flux 1 appends. The result is the overall direction R for the total stator flux, that of the direction of the rotor direction arrow 5 equivalent. This results in an angle of substantially zero between the stator flux and opposite to the rotor flux (corresponding to the rotor direction arrow), so that the torque is substantially zero.

It should be noted again that the rotor direction arrow 5 represents the opposite direction of the rotor flux, so as to easily detect when the rotor flux and the stator flux are as anti-parallel to each other and thus the torque is minimized.

Claims (6)

A method of minimizing torque of an electrical machine of an electric vehicle powertrain during an energy transfer operation by the electrical machine, the energy transfer process comprising: passing electrical energy through at least one stator winding of a stator of the electrical machine to charge or regenerate energy from the vehicle powertrain Energy storage, while a rotor of the electric machine is mechanically locked relative to the stator, the method further comprising: minimizing the torque between the at least one stator winding and a rotor of the electric machine by minimizing the angular amount (W) between a magnetic stator flux (1-3 ) resulting from the passing of electrical energy through the at least one stator winding, and a direction (5) that governs the rotor flux that occurs during the conduction of electrical energy. is opposite, the Angle amount (W) at the beginning or before the step of conducting energy is minimized, wherein according to a step I different current values and resulting individual flows (1; 2; 3) are determined for a subset of stator windings, wherein the vector sum of the individual flows (1; 2, 3) has a minimized angle to a direction opposite to the direction of the stator flux (1-3) and the electrical energy is passed through the subgroup of stator windings according to the different current values, or according to a step II the rotor by means of a Hill start assist is locked, which is active during the passage of electrical energy through at least one stator winding, and which is also active in a drive mode of the drive train on slopes, or in a step III, the electric machine is a foreign-excited electric machine, wherein the torque is minimized by modulating an excitation current through the rotor flows, the magnetic interaction between the rotor flux and the stator flux (1 - 3) is minimized. Method according to Claim 1 wherein minimizing the torque comprises: aligning the stator flux (1-3) with the rotor of the electric machine by (a) selecting that stator winding whose normal has the smallest angle to the rotor flux and passing the electrical energy only through that stator winding, or (b) Selection of that subgroup of stator windings whose normal sum in total has the smallest angle to the rotor flux, from all stator windings, and passing the electrical energy only through this subset of stator windings. Method according to Claim 1 wherein, according to step I, the different current values and the resulting individual flows (1; 2; 3) are determined for a subset of stator windings, and further wherein the different current values are determined by determining different modulation parameters for the subset of stator windings, different modulation parameters having different effective currents are assigned, which determine the individual flows. Method according to Claim 1 or 2 wherein (a) minimizing torque comprises: locking the rotor to the stator in a position where an angle between the normal of one of the stator windings and a direction opposite the rotor flux is minimized, and wherein the energy through that stator winding or (b) locking the rotor to the stator in a position where an angle between a vector sum of the normals of a subset of stator windings and a direction (5) opposite to the rotor flux is minimized and wherein the energy passes through this subgroup of stator windings is passed in equal parts. Method according to Claim 4 wherein the rotor is locked by means of a mechanical lock having a plurality of locking positions (P), wherein in at least one of these locking positions (P) the angle of a direction opposite to the rotor flux relative to a normal of a stator winding or against a vector sum of normals of a subset of stator windings is minimized. Method according to Claim 5 wherein the barrier by which the rotor is locked has recesses, jaws or grooves defining the angularly discrete locking positions (P).

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