DE102022213330A1 - Method for controlling an operation of an electrical machine - Google Patents

Abstract

Method for controlling an operation of an electrical machine, in particular an electrical machine of a motor vehicle, wherein an operating variable of the electrical machine is limited in an overload range as a function of at least one measured control parameter, in particular the temperature and/or the current, wherein a first limiting factor (1) is determined as a function of the at least one measured control parameter and a second limiting factor (2) is determined based on a model of the electrical machine and the operating variable of the electrical machine is set based on the first limiting factor (1) and the second limiting factor (2).

Description

The invention relates to a method for controlling an operation of an electrical machine, in particular an electrical machine of a motor vehicle, wherein an operating variable of the electrical machine is limited in an overload range depending on at least one measured control parameter, in particular the temperature and/or the current.

Methods for controlling the operation of electrical machines in overload ranges, in which an operating variable of the electrical machine is limited depending on a measured control parameter, are generally known from the prior art. Such a limitation of the operating variable, in particular the power of the electrical machine, is also referred to in the prior art as "derating". For example, the temperature of the electrical machine can be measured as a control parameter and, if a certain limit temperature is exceeded or exceeded, the power of the electrical machine can be limited in order to reduce further temperature control and prevent the electrical machine from overheating.

It is also known that the resulting control loop must be designed to be stable enough to prevent instabilities from occurring. It is particularly important to take into account that, especially when temperature is used as a control variable or control parameter, there is a delay between the set operating variable and the measured temperature. The delay is caused on the one hand by the temperature input and on the other by heat conduction, i.e. the time delay until the temperature change can actually be measured by the temperature sensor. There is also a delay in the opposite case, i.e. the operating variable of the electrical machine may already be reduced, i.e. no further thermal input above the limit temperature is to be expected, while the measured temperature nevertheless makes derating seem necessary due to the slower cooling.

In the state of the art, approaches are known that influence the proportional factor. In other words, the course of the derating or a derating factor, which can also be referred to as a limiting factor, can be designed differently using the reference variable or the reference parameter. A compromise must always be found here, since if the derating curve or the derating factor is set too flat, the operating variable of the electrical machine is already limited in areas of the reference parameter that do not require any limitation, i.e. the derating would already start below the actual limit temperature.

If the proportional factor is set too steeply, i.e. the change in the limiting factor occurs over too small a range of change in the control parameter, the control loop can become unstable. The compromise described therefore leads to a limitation of the operating variable in selected operating states, although this is not necessary. For example, the power of the electrical machine is limited, although no limitation is required in the operating state, since the temperature input into the electrical machine is already reduced, but this cannot yet be detected by the assigned temperature sensor due to delays in the measuring chain.

The invention is based on the object of specifying an improved method for controlling the operation of an electrical machine.

The object is achieved by a method having the features of claim 1. Advantageous embodiments are the subject of the subclaims.

As described, the invention relates to a method for controlling the operation of an electrical machine, in particular an electrical machine of a motor vehicle, which electrical machine can represent a traction drive of the motor vehicle or a part thereof. The method can be carried out on a control device of the motor vehicle, which is designed to specify the operating variable of the electrical machine or to limit it. The operating variable of the electrical machine can in particular be calculated with the limiting factor, for example multiplied, so that the operating variable can be adjusted according to the current operating state of the electrical machine in order to prevent an overload of the electrical machine, for example too high a current or too high a temperature. If the electrical machine reaches an overload range during operation of the electrical machine, for example too high a current or too high a temperature, the operating variable is limited accordingly. An operating variable can be understood to be, for example, an electrical parameter of the electrical machine, for example the current, or a performance parameter of the electrical machine, for example a target torque.

The invention is based on the finding that depending on the at least one measured control parameter, a first limiting factor is determined and a second limiting factor is determined based on a model of the electrical machine and the operating variable of the electrical machine is set based on the first limiting factor and the second limiting factor. In other words, instead of a pure measurement of a control parameter and a corresponding selection of a limiting factor, as is usual in the prior art, a second limiting factor is determined in addition to the first limiting factor, which is determined based on the measured control parameter.

The second limiting factor is determined based on a model of the electrical machine. The model of the electrical machine models the behavior of the real electrical machine at the respective operating point or, based on the current operating point, the behavior of the electrical machine in the future is modeled or simulated. In this way, corresponding operating parameters of the electrical machine or the current operating state can be fed into the model and the behavior of the electrical machine under these operating conditions can be simulated. Accordingly, the model can predict the behavior of the electrical machine, in particular a change in the control parameter. The first limiting factor is thus determined based on the measured control parameter and reflects the state of the electrical machine based on sensor values, for example based on values from a current sensor or a temperature sensor. The second limiting factor, which is determined based on the model, takes into account the further behavior of the electrical machine in the future or in the current operating state, so that this can be taken into account in an improved manner.

The operating variable is then set taking into account the first limiting factor and the second limiting factor. This means that both the first limiting factor and the second limiting factor, possibly weighted differently, can be included in the setting of the operating variable and thus in the limitation of the performance of the electrical machine. The second limiting factor can advantageously introduce a change in the limitation of the operating variable into the control of the operation of the electrical machine, independent of delays. Since the second limiting factor is determined based on the model of the electrical machine, it can be taken into account, for example, whether the current operation of the electrical machine leads to a further increase in the temperature or current at all, or whether this already causes a reduction in the temperature, so that a further limitation of the operating variable may no longer be necessary. This allows boundary conditions of the current operating state to be taken into account better than a pure measurement of a control parameter.

As already described, the second limiting factor is determined based on the model of the electrical machine. According to one embodiment of the method, it can be provided that the second limiting factor is determined based on a modeled change in the control parameter within a look-ahead time. The model of the electrical machine thus models the real system of the electrical machine. At least one operating parameter of the electrical machine can be fed to the model as an input variable, wherein the model can output at least the change in the control parameter as an output variable. In other words, one or more input variables can be fed to the model so that the model can model the change in the operating state of the electrical machine and thus output the change in the control parameter.

The second limiting factor can be determined in particular within a look-ahead time, i.e. for a change in the control parameter that will occur within the specific look-ahead time. This means that the limiting factor is not determined purely based on measured values of the control parameter, as is usual in the prior art, but a current change in the control parameter or a change in the control parameter that occurs within the look-ahead time is also taken into account. Since both the first limiting factor and the second limiting factor are used to set the operating variable of the electrical machine, the approach described here is based on both the measurement and the modeling of the control parameter.

The joint use of the model and the measured control parameter offers the advantage over pure modelling that deviations of the model and the real system are not used in full to limit the operating variable, but are only taken into account proportionally and can therefore be corrected if necessary by the first limiting factor, which is determined on the basis of the measured control parameter. The model can, for example, be operated on the assumption that the current control, for example the engine torque, is maintained over the look-ahead time. The defined look-ahead time can can basically be chosen arbitrarily. This can be selected depending on which parameter is used as the control parameter.

The look-ahead time described above can generally be determined depending on the specific boundary conditions of the system, for example the motor vehicle or the electrical machine. For example, the look-ahead time can be determined depending on a dead time of the control parameter. Dead time is the time that must be spent to register a change in the control parameter or the time that passes until a change in the operating variable leads to a detectable change in the control parameter. The dead time can therefore also be referred to as delay time.

By setting the look-ahead time as a function of the dead time of the control parameter, it is possible, for example, to take into account how a change in the operating variable influences a change in the temperature or current, which can be used as a control parameter. If, for example, the temperature as the control parameter has a comparatively long dead time, this means that a change in the operating variable can only be measured comparatively late using the control parameter. In this case, it is advisable to choose the look-ahead time as long as possible so that longer-term changes in the control parameter due to changes in the operating variable can be modeled and taken into account when determining the second limiting factor. The look-ahead time can be defined, for example for a specifically intended system, and can be specified for a control parameter. It is also possible to set the look-ahead time based on a measurement of the dead time, for example to measure after which dead time from a change in the operating variable a change in the control parameter can be measured.

As already described, the look-ahead time is fundamentally dependent on how long it can take for a change in the operating variable to cause a measurable or detectable change in the control parameter. Different control parameters can therefore result in different look-ahead times. The look-ahead time can therefore be set depending on the parameter according to one design of the method. For example, a first look-ahead time can be set for a first control parameter and a second look-ahead time for a second control parameter. For the respective parameters, for example, delays or modeled retarders defined in the system can be used. For example, with temperature as a control parameter, various retarders can be taken into account that take into account the heat input or heat transfer or heat storage and the like. Likewise, with current as a control parameter, the current conduction, the electrical resistance and the like can be taken into account.

As already explained at the beginning, the operating variable is set based on the first limiting factor and the second limiting factor. According to one embodiment of the method, the operating variable of the electric machine can be set based on a mixed factor which is formed from a weighted first limiting factor and a weighted second limiting factor, in particular based on $$D=a\ast d_{mess}+\left(1-a\right)\ast d_{mOdell}.$$

Here, “D” indicates the mixing factor, which can ultimately be made up of the two limiting factors, which can be weighted differently. The factor “a” refers to a weighting factor that can be selected differently for different operating states of the electrical machine or for different control parameters. The parameter “d _mess ” refers to the first limiting factor, which, as described above, is determined based on the measured control parameter. The parameter “d _model ” refers to the second limiting factor, which, as also described above, is determined based on the model of the electrical machine. Depending on the current operating state and the control parameter currently being used, the weighting factor can be used to determine whether the first limiting factor or the second limiting factor plays a greater role in determining the mixing factor. The mixing factor is then used to set or limit the operating size of the electrical machine, for example by multiplying it by the operating size of the electrical machine.

According to a further development of the method, it can be provided that a weighting factor is determined based on a volatility of the control parameter. Depending on how much the control parameter fluctuates over the operation of the electrical machine or how quickly it can change, the weighting factor can be selected differently in order to take such volatile changes in the control parameter into account. This ensures, on the one hand, that the control loop for limiting the operating size of the electrical machine does not become unstable and, on the other hand, other unnecessary limitations on the size of the company can be avoided.

According to one embodiment of the method, the weighting factor, in particular when a current is used as a control parameter, can be determined based on a past control value, in particular a target torque. The control value can in particular relate to the operating variable to be limited or be identical to it. The weighting factor can be determined depending on the value of the past control value, i.e. the control value in the last period of the method. The variant described is particularly suitable for current derating. The weighting factor can be determined in particular by dividing the past control value from the previous time interval by the current control value. The control value can, for example, be the target torque or the desired torque of the electrical machine. By setting or limiting the target torque, the current made available to the electrical machine is also indirectly limited.

According to a further embodiment of the method, the weighting factor, in particular with a temperature as a control parameter, can be determined based on an average value of a past control value, in particular the current. For this purpose, the average value or the moving average value of the control value, for example the current in the previous period of the method, can be formed and this can be divided by the current control value. The control value can here be, for example, the current that is provided to the electrical machine for operation.

In addition to the method, the invention relates to a control device for controlling the operation of an electrical machine, in particular an electrical machine of a motor vehicle, wherein the control device is designed to limit an operating variable of the electrical machine in an overload range as a function of a control parameter, in particular the temperature and/or the current, wherein the control device is designed to determine a first limiting factor as a function of at least one measured control parameter and to determine a second limiting factor based on a model of the electrical machine and to set the operating variable of the electrical machine based on the first limiting factor and the second limiting factor. The invention further relates to a motor vehicle comprising such a control device. The control device is designed in particular to carry out the method described above.

All advantages, details and features described with regard to the method are fully transferable to the control device and the motor vehicle.

• 1 ein beispielhaftes Diagramm einer Bestimmung eines Begrenzungsfaktor; und
• 2 ein Beispiel des Ablaufdiagramm eines Verfahrens zur Steuerung eines Betriebs einer elektrischen Maschine.

The invention is explained below using embodiments with reference to the figures. The figures are schematic representations and show:

• 1 an exemplary diagram of a determination of a limiting factor; and
• 2 an example of a flow chart of a method for controlling an operation of an electrical machine.

1 shows a schematic diagram in which the course of a limiting factor, for example a first limiting factor 1 or a second limiting factor 2, is plotted against a control parameter, for example a current or a temperature, by way of example only. The course between a value of the limiting factor 1, 2 of "1" in a regular operating state of the electrical machine to a value of the limiting factor 1, 2 of "0" is shown by way of example only. The shape of the course of the limiting factor 1, 2 is to be understood as an example only and can be selected differently as desired, for example with a course other than a linear one.

The diagram also shows a limit value 3 of the control parameter, which represents the transition from a normal operating state to an overload range of the electrical machine. In other words, the electrical machine reaches an overload range when the control parameter rises above the limit value. If, for example, a temperature is considered as the control parameter, the limit value can represent a limit temperature. If the electrical machine is operated below the limit temperature, it can be operated at its maximum performance, i.e. a limiting factor of 1.2 of 1 is selected so that the performance of the electrical machine is not limited, i.e. no "derating" is carried out.

However, if the control parameter exceeds the limit value, for example if the electrical machine is operated above the limit temperature, this leads to a corresponding limiting factor of 1.2, depending on how far the limit value was exceeded. The limiting factor of 1.2 can then be offset against an operating variable of the electrical machine, for example This means that in an overload range the operating size is reduced, for example a target torque or a current of the electrical machine is limited accordingly.

2 shows a schematic flow diagram of a method for controlling the operation of an electrical machine. The electrical machine or the system controlled or regulated by the method is shown abstractly in a block 4. Block 4 is connected to a block 5, which can represent a controller of a control device for controlling the electrical machine. The controller is supplied with a control value, as indicated by an arrow 6, which can be the operating variable, for example, or is connected to it. For example, a target torque can be set as the control value, which is required by a user of the motor vehicle and is to be provided by the electrical machine. It is also possible to consider a current that is to be supplied to the electrical machine as the control value.

2 further shows a block 7 which is connected to the block 4. In block 7, in the method, a control parameter of the controlled system in block 4 can be detected, ie in particular measured, and based on the measured control parameter, a first limiting factor 1, such as in 1 For example, a temperature or a current of the system is measured as a control parameter and thus passed from block 4 to block 7, in which a first limiting factor 1 matching the control parameter is determined. The first limiting factor 1 determined or determined in block 7 can then be fed to block 8.

How to continue in 2 As shown, the operating variable can not only be fed to the controlled system shown in block 4, but also to a block 9 in which a model of the controlled system shown abstractly in block 4 is operated. Block 9 can, for example, represent a model of the electrical machine. By feeding the operating variable and, if necessary, knowing other parameters of the controlled system from block 4, the change in the control parameter can be modeled in block 9. In other words, block 9 is not fed with a currently measured control parameter, but the change that the control parameter will make is determined, i.e. modeled or simulated, depending on the operating parameters of the electrical machine.

Block 9 can thus model a behavior of the electrical machine and pass an expected control parameter to a block 10 or pass an expected change in the control parameter to block 10. Analogous to block 7, in block 10, as for example with regard to 1 explained, based on the expected control parameter transmitted by block 9, a second limiting factor 2 is determined, which can also be fed to block 8. For example, based on the operating variables and/or operating parameters of the electrical machine received from block 5, the model in block 9 can be used to determine how the control parameter, for example the temperature, will change. This control parameter expected in the future is then made available to block 10, in which a suitable second limiting factor 2 is determined for this control parameter.

In block 8, a mixing factor is formed, namely from the first limiting factor 1 from block 7 and the second limiting factor 2 from block 10. The mixing factor is then transferred to block 5, in which the control value according to arrow 6 is offset against the mixing factor in order to set the operating variable, which is then transferred from block 5 to block 4. In particular, the operating variable can be limited if necessary. For example, the mixing factor "D" is calculated according to the following formula: $$D=a\ast d_{mess}+\left(1-a\right)\ast d_{mOdell}.$$

Here, “a” denotes a weighting factor, “d _meas “ the first limiting factor 1, which is determined based on the measured control parameter, and “d _model “ the second limiting factor 2, which is determined based on the expected control parameter determined from the model in block 9. The mixing factor can then be offset against the control value, for example multiplied by it. If the electrical machine is therefore operated in an overload range or if it is expected that the current operating state of the electrical machine from model 9 will result in a control parameter that requires derating, the mixing factor will assume a corresponding value and thus reduce the control value or operating variable, for example reduce a target torque set by the driver so that a corresponding reduced current is generated in block 5 and passed on to block 4.

The weighting factor described above can be adjusted depending on the type of control parameter, for example whether the control parameter is a current of the electrical machine or a temperature of the electrical machine. Accordingly, the weighting factor can be determined differently, for example depending on a previous control value. In particular, the value of a previous control value divided by the current control value. Such a determination of the weighting factor is particularly suitable if the current of the electrical machine is considered as the control parameter. If the temperature is considered as the control parameter, the weighting factor can, for example, be determined depending on an average value of a previous control value divided by the current control value.

Reference symbols

1

first limiting factor

2

second limiting factor

3

limit

4, 5

block

6

Arrow

7-10

block

Claims (10)

Method for controlling an operation of an electrical machine, in particular an electrical machine of a motor vehicle, wherein an operating variable of the electrical machine is limited in an overload range as a function of at least one measured control parameter, in particular the temperature and/or the current, characterized in that a first limiting factor (1) is determined as a function of the at least one measured control parameter and a second limiting factor (2) is determined based on a model of the electrical machine and the operating variable of the electrical machine is set based on the first limiting factor (1) and the second limiting factor (2). Procedure according to Claim 1 , characterized in that the second limiting factor (2) is determined based on a modelled change in the control parameter within a look-ahead time. Procedure according to Claim 2 , characterized in that the look-ahead time is determined as a function of a dead time of the control parameter. Procedure according to Claim 3 , characterized in that the look-ahead time is determined depending on the parameters. Method according to one of the preceding claims, characterized in that the operating variable of the electrical machine is set based on a mixing factor which is formed from a weighted first limiting factor (1) and a weighted second limiting factor (2), in particular based on D = a ∗ d _mess + (1 - a) ∗ d _model . Procedure according to Claim 5 , characterized in that a weighting factor is determined based on a volatility of the control parameter. Procedure according to Claim 5 or 6 , characterized in that the weighting factor, in particular in the case of a current as a control parameter, is determined based on a past control value, in particular a target torque. Procedure according to Claim 5 or 6 , characterized in that the weighting factor, in particular with a temperature as a control parameter, is determined based on an average value of a past control value, in particular the current. Control device for controlling the operation of an electrical machine, in particular an electrical machine of a motor vehicle, wherein the control device is designed to limit an operating variable of the electrical machine as a function of a control parameter, in particular the temperature and/or the current, in an overload range, characterized in that the control device is designed to determine a first limiting factor (1) as a function of at least one measured control parameter and to determine a second limiting factor (2) based on a model of the electrical machine and to set the operating variable of the electrical machine based on the first limiting factor (1) and the second limiting factor (2). Motor vehicle comprising a control device according to the preceding claim.

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