DE102022208234A1 - Method for operating an electric machine of a rotary drive - Google Patents

Abstract

The invention relates to a method for operating an electric machine (4) of a rotary drive with a gearbox (2) which has a gear unit, wherein the electric machine (4) is regulated in accordance with a target value (n_EMsoll) of a controlled variable, wherein the Control includes a proportional controller, and wherein a proportional gain factor (K_P) of the proportional controller is varied depending on a size that indicates a force-free state of the transmission (2).

Description

The present invention relates to a method for operating an electrical machine of a rotary drive as well as a computing unit and a computer program for carrying it out.

Background of the invention

In mechanical gears in rotary drives, gear play or backlash can occur, i.e. there can be play in the gear between the drive and the output. The gear backlash can be described, for example, as an angular interval in which a drive can rotate without the output moving. Gear looseness occurs at approximately every gear pairing in a transmission. In the case of a multi-stage gearbox, the gearless angle intervals are multiplied by the respective gear ratios. Gearless problems can occur, for example, in steering systems as steering play, in vehicle drives as play between thrust and drive, in machine tools, for example on spindles, or in rotary drives such as slewing gears of excavators or cranes.

Disclosure of the invention

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

The invention uses the measure of varying the gain of a P controller in the control of an electric machine of a rotary drive with a gearbox that has a gearless unit, depending on a variable that indicates a power state, in particular a powerless state . Vibrations and high mechanical loads, which can occur particularly with high control gain when the drive motor or the electrical machine accelerates strongly in the angular range within the gear unit compared to the output and tooth flanks collide with a high differential speed, can be avoided. The transmission can have one or more gear stages, each with a gear unit, which together form the entire gear unit.

It is assumed that the proportional gain factor and, if applicable, the integral gain factor (see below) are positive.

In one embodiment, the method is used for rotary drives with a gearbox that has a gear range of at least 10°, at least 20° or at least 30° and/or that has a ratio (between the drive axle and the output axle) of at least 20:1, at least 50: 1 or at least 100:1. Here, gearless is intended to refer to the size of the (maximum) angular range in which the drive axle of the gearbox or the associated output axis of the electric machine can be rotated back and forth without a corresponding (corresponding to the gear ratio) rotation of the output axis of the gearbox occurring.

In one embodiment, the variable that indicates a force-free state of the transmission is a control deviation of the controlled variable (e.g. difference between the target value and the actual value of the controlled variable). In one embodiment, the proportional gain factor increases as the magnitude increases. The control deviation is determined as part of the control anyway, so no additional calculations are necessary. The control deviation indicates to what extent the electrical machine can follow the target value of the controlled variable and is therefore a measure of how heavily the electrical machine is loaded, with only a small load due to the moment of inertia of the electrical machine in the force-free state, so that the control deviation remains small.

In one embodiment, the controlled variable is a speed of the electrical machine. Likewise, in one embodiment, the controlled variable can be given as the torque of the electric machine.

In one embodiment, a gradient of the proportional gain factor is limited upwards. The speed at which the proportional gain factor increases or is built up is therefore limited. A downward limitation, i.e. a limitation of the speed at which the proportional amplification factor decreases or is reduced, can also optionally be provided, but the amount of the limit with which the structure is limited should be significantly smaller than the limit with which the reduction is limited (e.g. by at least a factor of 10). It can be provided that the barrier with which the gradient of the proportional amplification factor is limited upwards is dependent on the proportional amplification factor, in particular increasing as the proportional amplification factor increases.

In one embodiment, a torque requirement is determined (in the control system) with which a Inverter of the electric machine is controlled, wherein a gradient of the amount of the torque request is limited asymmetrically, and further in one embodiment the amount of a lower limit for the gradient of the torque request is greater than an upper limit for the gradient of the torque request. This asymmetrical restriction makes it possible to avoid vibrations in particular, for example due to latencies in the system.

In one embodiment, an output speed is determined, a corresponding speed of the electric machine being determined from the output speed, taking into account the gear ratio of the transmission, and a speed difference being determined as the difference between the actual speed of the electric machine and the corresponding speed of the electric machine becomes. The output speed is the speed of an output axle of the transmission or a load that is driven by the rotary drive via the transmission. Between the output axis of the transmission and a drive axle of the transmission, which corresponds to the output axis of the electric machine, there is a speed ratio corresponding to the gear ratio of the transmission, as long as the transmission is not within the gear range.

The speed difference represents a measure or quantity that indicates the extent to which the gearbox is in a force-free state (i.e. whether the rotary drive is within the gearbox). Accordingly, in one embodiment, the variable that indicates a force-free state of the transmission is the speed difference, with the proportional amplification factor decreasing as the amount of the variable increases.

Likewise, in one embodiment, the target value of the controlled variable is formed or filtered in such a way that a gradient of the target value of the controlled variable is limited in accordance with a limit that is dependent on the speed difference; wherein in one embodiment the amount of the barrier of the gradient of the setpoint value of the controlled variable decreases as the speed difference increases. This makes it possible to avoid high torque stops, for example from tooth flanks in the gearbox.

A computing unit according to the invention, for example a control device of a rotary drive or a machine with a rotary drive, is set up, in particular in terms of programming, to carry out a method according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous because this causes particularly low costs, especially if an executing control device is used for additional tasks and is therefore present anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and refinements of the invention result from the description and the accompanying drawing.

It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the present invention.

The invention is shown schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing.

Character description

• 1 shows an exemplary topology of an electric rotary drive with a gear.
• 2 shows a controller structure according to an embodiment of the invention.
• 3 shows, as an example of a machine in which the invention can be applied, an excavator which has an electrically driven slewing gear.

Detailed description of the drawing

1 shows an exemplary topology of an electric rotary drive with a gear 2. The electric rotary drive has an electric machine 4, which drives a load 6, ie a driven element of a machine in which the electric rotary drive is used, via the gear 2. The transmission 2 has, for example, a drive axle, which is coupled to an output axle of the electric machine 4, and an output axle, which is coupled to the load 6 or the driven element. The drive axle and the output axle can be coupled to one another in the transmission via gears, toothed belts or the like. This can result in gear looseness or backlash, ie the drive axle can move rotate in an angular interval without there being a corresponding rotation of the output axis, taking into account the gear ratio of the gearbox.

The electrical machine 4 is controlled via an inverter 8, which typically has an inverter control that is in particular set up to control (semiconductor) switching elements of the inverter according to a control variable 14. The control variable 14 can in particular be a requested torque (torque request) or a requested speed (speed request). In the case of control according to a requested speed or speed request, the inverter 8 or the inverter control can have a speed control. The inverter 8 is typically set up to determine an actual speed or actual speed of the electrical machine 4. For example, by means of a resolver provided in the electrical machine, a corresponding signal from the resolver, i.e. a speed feedback from the resolver, being shown as arrow 9 in the figure.

The control variable 14 is determined by a control device 10, for example a control device. For this purpose, the control device 10 implements in particular a regulation, approximately accordingly 2 . As input variables, the control device 10 uses, on the one hand, a control signal 16, which indicates a desired speed of the electrical machine or the load and which is generated, for example, by a control element 12 (eg a joystick) that detects a user input. Alternatively or additionally, the control signal 16 could also be generated at least partially by a (partially) autonomous machine control. On the other hand, the control device 10 uses actual or actual variables. The actual variables include the actual speed n_EMist of the electrical machine 4 and/or an actual torque M_EMist of the electrical machine 4. Both can be determined, for example, by the inverter 8 and transmitted to the control device 10. Optionally, an actual speed n_Abtrieb of the output, ie the load 6 or the output axle of the transmission 2, can also be used as an input variable of the control device 10. If there is no sensor that detects the actual speed of the output, an observer can be used (not shown) that models the real controlled system in order to use the control variable and the actual speed of the electrical machine 4 and/or the actual Torque of the electric machine 4 to reconstruct the actual speed n_Abtrieb of the output. The control variable 14 and the actual variables are transmitted, for example, via a signal bus (e.g. CAN: Controller Area Network). Latencies can occur in the range of, for example, 0.5 to 5 ms.

In the embodiment shown, the control variable 14 is a target torque that is transferred to the inverter 8. According to another embodiment (not shown here), the control device 10 or the functionality implemented by it (for example by executing at least one corresponding computer program) can be at least partially part of the inverter 8 or the functionality of the control device can be at least partially implemented by the inverter 8 (e.g. by executing at least one corresponding computer program by the inverter control). In this case, for example, a pre-filtering 60 of the target speed remains (see 2 ) still part of the control device 10.

2 shows a controller structure according to an embodiment, as used, for example, in the control device 10 of FIG 1 electric rotary drive shown can be used.

Essentially, the controller structure shown comprises a proportional controller in which a speed difference Δn_EM of the electrical machine between a target speed n_EMsoll of the electrical machine and the actual speed n_EMist of the electrical machine (Δn_EM = n_EMsoll - n_EMist) with a proportional amplification factor K_P is multiplied (proportional element 24) to determine a torque request M_Anf to the electrical machine. In this example, the speed difference Δn_EM represents the control deviation. The speed of the electric machine is an example of a controlled variable, the target speed is an example of a target value of the controlled variable and the actual speed is an example of an actual value the controlled variable.

The proportional gain factor K_P is not constant, but variable depending on the control deviation, ie the speed difference Δn_EM. The control deviation, ie the speed difference Δn_EM in the example shown, is a quantity that indicates whether or not the gear is in the force-free state or within the gear slack, ie a state in which no torque is transmitted to the load. Since no torque is transmitted to the load, only the moment of inertia of the electric machine itself (and possibly of axles and/or gears directly connected to it) acts on the electric machine in the power-free state or within the gearbox. However, even taking the gear ratio into account, the moment of inertia of the electric machine is much smaller (e.g. by a factor of 100) than the moment of inertia of the load acting on the electric Machine works when there is no power-free state or outside the gearbox. Within the gear unit, the control deviation (e.g. speed difference Δn_EM) can also be kept small with a relatively small proportional amplification factor K_P, since the electric machine only has to apply a relatively small torque in order to overcome the moment of inertia of only the electric machine, and thus the controlled variable can be regulated quickly. In addition, the maximum speed gradient of the target variable (n_EMsoll) can be greatly limited by optional pre-filtering (see below) of the target speed, so that no large accelerations of the electrical machine are required.

A progressive proportional gain factor K_Pprog is determined (element 22), which varies or is changed depending on the speed difference Δn_EM (control deviation) between a minimum proportional gain factor and a maximum proportional gain factor. In one embodiment it is provided that the progressively determined proportional amplification factor K_Pprog increases monotonically as the speed difference Δn_EM increases. This can in particular be done symmetrically, i.e. the progressively determined proportional amplification factor K_Pprog is a function of the amount of the speed difference Δn_EM (as shown as an example). Correspondingly (with a monotonic increase), with a control deviation of zero, the progressively determined proportional gain factor K_Pprog is equal to the minimum proportional gain factor and with a high control deviation it is equal to the maximum proportional gain factor. This design prevents the controller from oscillating, even if the speed feedback is slightly delayed (latency). A very high P gain, together with the small inertia of the machine, could lead to oscillation (or a jitter of speed and torque) even with a small latency time (e.g. 5 ms), which would be clearly noticeable and lead to high wear on the gearbox can. For example, there may be a ratio of at least 5 or at least 10 between the maximum and the minimum proportional gain factor. The minimum proportional amplification factor should be non-zero or chosen so large that the free-running electric machine can largely follow the desired speed dynamics. However, it should be chosen so small that speed oscillations within the gearbox are avoided.

The progressively determined proportional gain factor K_Pprog can be used directly as the proportional gain factor K_P. Optionally (deviating from direct use) a gradient limitation (block 30) of the proportional gain factor K_P can be provided. The implementation of this gradient restriction shown is intended to be exemplary; Of course, other implementations are also conceivable.

With the (exemplary) gradient limitation, the gradient (rate of change) of the proportional gain factor is limited upwards. The corresponding upper limit is dependent on the progressively determined proportional amplification factor K_Pprog, e.g. corresponding to a gradient limitation function (term 32), which increases monotonically, in particular strictly monotonically, with the progressively determined proportional amplification factor K_Pprog (in particular not constantly over the entire range of values is). The upper bound is positive, corresponding to an increasing proportional gain factor, i.e. positive gradient. In the minimum element 34, the smaller value is, on the one hand, the (limitation) value obtained by means of the gradient limitation function and, on the other hand, the deviation ΔK, which is the difference between the desired, progressively determined proportional gain factor K_Pprog and the currently used value of the proportional gain factor K_P is determined (ΔK = K_Pprog - K_P), selected to realize the upward restriction. As shown, scaling (element 36) or normalization of the deviation ΔK can also take place. The scaling in term 36 can be viewed as a control gain of the feedback loop formed in block 30. This can also be achieved by appropriate choice of parameters in other members of the gradient constraint. The dynamics of the gradient limitation (block 30) can be adjusted by suitably selected values of the parameters of link 32, link 36 and barrier 38.

Additionally, with gradient limiting, the gradient of the proportional gain factor can be limited downwards as shown. For this purpose, a lower (negative) limit 38 is provided, the amount of which is (significantly) larger than any value assumed by the gradient limitation function (in the possible range of values of the progressively determined proportional amplification factor K_Pprog, element 32). Compared to the upward gradient restriction, the downward gradient restriction is weaker. Here a maximum term 40 is used to implement the downward restriction.

Overall, a limited gradient ΔK_lim of the proportional amplification factor is obtained upwards and, if necessary, downwards, which is integrated in an integral element 42 in order to achieve this To determine the proportional gain factor K_P.

Furthermore, an integral controller 50 can optionally be provided, which has a variable integral amplification factor K_I and which determines an additive integral component for the torque request M_Anf. As shown, the integral amplification factor K_I is particularly dependent on the magnitude of the actual speed n_EMist of the electrical machine, which is formed in the magnitude element 52. The integral amplification factor K_I is formed as a function (element 54) of the amount of the actual speed, with the integral amplification factor K_I decreasing monotonically as the amount of the actual speed increases. This function can include constant sections (like here for small magnitude values), but should not be constant. The speed difference Δn_EM is integrated in an integral element 56 in accordance with the integral amplification factor K_I (e.g. multiplied by this).

As shown, the integral controller 50 can optionally have a maximum value (Max) and a minimum value (Min), i.e. the integration is limited to the value range from the minimum to the maximum value. The maximum and minimum values can be variable. The maximum and minimum values, similar to the integral amplification factor K_I, can be dependent on the amount of the actual speed n_EMist of the electrical machine, with the amount of the maximum and minimum value in particular decreasing monotonically as the amount of the actual speed increases. For example, one can start from the variable integral amplification factor K_I, which already has a corresponding functional dependency. The variable integral gain factor K_I can be multiplied by an integral limit factor (term 57). The obtained value can be used immediately as the maximum value and additionally multiplied by -1 to obtain the minimum value.

Likewise, a differential controller, in particular with a variable gain factor (variable differential component), can optionally be provided (in addition to or instead of the integral controller; not shown).

The setpoint of the controlled variable, ie the setpoint speed n_EMsoll of the electrical machine in 2 , can be obtained from the control signal 16, which can be a desired speed n_w (eg a speed desired by a user of the machine in which the rotary drive is used) of the electric machine. It can be provided that the desired speed n_w or the control signal 16 (eg corresponding to a deflection of a joystick) is used directly as the target speed n_EMsoll. Alternatively, pre-processing of the desired speed n_w or the control signal 16 can optionally be provided, for example a progressive mapping of the deflection of a joystick to the target speed n_EMsoll as well as a first pre-filtering and gradient limitation of the joystick signal in order to enable sensitive operation.

According to an optional embodiment, a (second) pre-filtering 60 of the target speed n_EMsoll of the electrical machine is provided as preprocessing, in which a gradient (or a rate of change) of the target speed n_EMsoll depends on the amount of a difference speed n_diff between the Actual speed n_EMist of the electrical machine and an (expected) speed i · n_Abtrieb of the electrical machine which correlates to the actual speed n_Abtrieb of the output is limited, where i is the gear ratio of the transmission (n_diff = n_EMist - i · n_Abtrieb). The correlating (expected) speed i · n_Abtrieb is the speed at which the electric machine would have to rotate at a given actual speed n_Abtrieb of the output if the gearbox is outside the gearbox or if there is adhesion in the gearbox. If the differential speed n_diff is not equal to zero, it must be assumed that the gearbox is in gearless position. The differential speed n_diff is also a quantity that indicates whether or not the transmission is in the power-free state or within the gear range. In principle, differential speed n_diff could be used instead of or in addition to the control deviation when determining the progressive proportional gain factor.

In the pre-filtering 60 it is provided that the target speed n_EMsoll of the electric machine is determined from the desired speed n_w such that the gradient of the target speed n_EMsoll is limited depending on the amount of the difference speed n_diff, in particular the amount of the gradient the target speed n_EMsoll is smaller than a limit dependent on the amount of the difference speed n_diff. In one embodiment, the barrier decreases monotonically (in particular strictly monotonically) as the difference speed n_diff increases up to a minimum value, which should be non-zero (the barrier should not be constant over the entire range).

By limiting the gradient of the target speed, excessive acceleration of the electric machine within the gear unit is prevented, so that high torque surcharges in the gear unit are avoided. A concrete implementation of pre-filtering 60 can For example, similar to the gradient limitation (block 30) of the proportional gain factor K_P can be implemented.

The electric machine or the inverter can be controlled directly with the torque request M_Anf (i.e. used as control variable 14). Optionally, a torque limitation (block 70) can be provided, in which a limited torque request M_Anflim is determined from the torque request M_Anf (which is used as control variable 14).

In the torque limitation (block 70), a gradient (rate of change) of the amount (if a distinction is made between positive and negative torque depending on the direction of rotation) of the torque request is limited, i.e. in areas of the torque request M_Anf in which the gradient is above or below is a lower limit, the torque request is adjusted according to these limits to determine the limited torque request M_Anflim. In one embodiment, the amount of the lower limit is greater than the upper limit, for example by at least a factor of 5 or at least a factor of 10. This means that the gradient of the amount of the torque request is limited asymmetrically. In this way, vibrations in particular can be avoided.

In 2 For example, the speed of the electrical machine is used as a controlled variable. Alternatively or additionally, another controlled variable could also be used, for example the angle of rotation of the electrical machine or possibly the torque of the electrical machine.

As an example of a machine in which the invention can be applied, shows 3 an excavator 130, in which electric drives, in particular electric rotary drives, which can be controlled according to the invention, can be provided. The excavator 130 comprises a chassis 132 and a structure 134 rotatably mounted thereon. Wheels 136 mounted on the chassis can be driven via an electric driving machine operated according to the invention and not shown in detail; at least one wheel axle, to which at least one of the wheels is attached is coupled to the electric driving machine directly or via a transmission. The electric driving machine, possibly the gearbox and wheels together form a travel drive that enables the excavator to move. A rotation of the structure relative to the chassis is made possible by a slewing gear 138, which can be viewed as a gear or as part of a gear, which is driven by an electric machine which is operated according to the invention. The slewing gear 138 or its drive is shown enlarged in the figure, with an output shaft of an electrical machine 4 being coupled to a gear 137, which interacts with a ring gear 139. The gear 137 is coupled, for example, via a planetary gear 149 with one or more planetary gear sets (not shown in detail) to the electrical machine 4 or its output shaft. A gearless action occurs here as play between the electrical machine 4 or the movement of its output shaft and the movement of the structure. The gear unit in particular includes a portion of the play of the planetary gear 149 and a portion of the play between the gear 137 and the ring gear 139. A boom or excavator arm 140 is attached to the structure 134, at the end of which there is a shovel 142. The boom, arm and shovel are moved here, for example, via electro-hydraulics 144 using hydraulic cylinders 146. A battery 148 supplies the traction motor, the electric slewing machine and/or the electro-hydraulics with electrical energy.

Claims (16)

Method for operating an electric machine (4) of a rotary drive with a gear (2) which has a gear unit, wherein the electrical machine (4) is regulated in accordance with a target value (n_EMsoll) of a controlled variable, the regulation including a proportional controller; wherein a proportional amplification factor (K_P) of the proportional controller is varied depending on a variable that indicates a force-free state of the transmission (2). Procedure according to Claim 1 , whereby the variable that indicates a force-free state of the transmission (2) is a control deviation (Δn_EM) of the controlled variable. Procedure according to Claim 2 , where the proportional gain factor (K_P) increases as the magnitude increases. Method according to one of the preceding claims, wherein the controlled variable is a speed of the electrical machine. Method according to one of the preceding claims, wherein a gradient of the proportional gain factor (K_P) is limited upwards Procedure according to Claim 5 , where a barrier with the gradient of the proportional ver amplification factor is limited upwards, depends on the proportional amplification factor, in particular increases as the proportional amplification factor increases. Method according to one of the preceding claims, wherein a torque request (M_Anf, M_Anflim) is determined, with which an inverter of the electrical machine is controlled; wherein a gradient of the magnitude of the torque request is limited asymmetrically; wherein in particular the amount of a lower limit for the gradient of the torque request is greater than an upper limit for the gradient of the torque request. A method according to any one of the preceding claims, wherein the control includes an integral controller (50); wherein an integral amplification factor (K_I) of the integral controller is varied depending on the amount of an actual value (n_EMist) of the controlled variable; whereby the integral amplification factor (K_I) decreases monotonically, particularly as the amount of the controlled variable increases. Procedure according to Claim 8 , wherein the integral controller (50) has a maximum and a minimum value; wherein the amount of the maximum and the amount of the minimum value of the integral controller (50) are varied depending on the amount of the actual value (n_E-Mist) of the controlled variable; whereby the amount of the maximum and the amount of the minimum value of the integral controller decrease monotonically, in particular as the amount of the controlled variable increases. Method according to one of the preceding claims, wherein the control includes a differential controller. Method according to one of the preceding claims, wherein an output speed (n_Abtrieb) is determined; wherein a corresponding speed of the electric machine is determined from the output speed, taking into account the gear ratio of the transmission; and wherein a speed difference is determined as the difference between the actual speed (n_EMist) of the electric machine and the corresponding speed of the electric machine; whereby the output speed (n_Abtrieb) is determined in particular by an observer. Procedure according to Claim 11 , whereby the target value of the controlled variable is formed or filtered in such a way that a gradient of the target value of the controlled variable is limited in accordance with a limit which is dependent on the speed difference; in particular, the amount of the barrier of the gradient of the setpoint value (n_EMsoll) of the controlled variable decreases as the speed difference increases. Procedure according to Claim 11 or 12 , where the quantity that indicates a power-free state of the transmission is the speed difference; in particular, the proportional amplification factor decreases as the magnitude increases. Computing unit comprising a processor which is configured to carry out the method according to one of the preceding claims. Computer program comprising commands which, when the program is executed by a computer, cause it to follow the method Claim 1 until 13 to carry out. Computer-readable data carrier on which the computer program is written Claim 15 is stored.

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