Method for temperature monitoring of an electrical system

Abstract

The invention relates to a method for monitoring a component temperature in an electrical system (1) with several components (21, 22, 23, 25, 26), comprising the following steps: - When starting an operating phase of the electrical system (S1), measuring (S2) a reference temperature representing a temperature at a location in the electrical system (1); - Continuous modeling (S3, S4) of component temperatures of at least one component (21, 22, 23, 25, 26) in the electrical system (1) starting from the reference temperature as a starting value using a heat balance model modeled as a state model with a differential equation; - Continuously monitoring (s6) the component temperatures of the at least one component (21, 22, 23, 25, 26) based on a threshold temperature predetermined for the at least one component (21, 22, 23, 25, 26); characterized in that monitoring continues to be subject to temperature uncertainty, wherein the temperature uncertainty is determined depending on a final reference temperature as a reference temperature at an end time of the previous operating phase and the measured reference temperature.

Description

Technical FieldThe invention relates to the thermal management of electrical systems, particularly electrical systems with sources of high power dissipation, such as drive systems with electric machines and the like. The invention further relates to the execution of a temperature monitoring of component temperatures after an activation or switching on of a power supply if the time duration since the last switching off is not known.Background ArtElectrical systems, such as drive systems with electric motors, convert a significant proportion of the electrical energy into heat during operation, which can lead to unequal heating of individual components of the system. For reasons of component protection, it is necessary to monitor the temperature of the individual components of the electrical system in order to detect and avoid overheating of the components.Since, owing to the high outlay, not each of the warm components can be provided with a temperature sensor, the temperature is frequently modeled with the aid of a heat balance model. This makes possible, based on energy inputs, energy outputs taking into account heat transfer resistances, a thermal modelling with which the component temperatures can be continuously modeled and estimated. The modeled component temperatures can be monitored with respect to a temperature by a threshold value comparison. However, the modeling requires the specification of an initial state of the component temperatures.However, in electrical systems that are not permanently switched on or supplied with energy, for example electrical systems that are only switched on for a short time in response to a user's request, the component temperatures are not known at the switch-on time, since it cannot be determined whether the components of the electrical system have assumed ambient temperature or are still in an operationally warm state. Therefore, the initial state of the electrical system is not available for modeling the component temperatures. Examples of such electrical systems include, for example, drive systems in a power window system, a sunroof electrical system, a seat recliner electrical system, and the like.It is an object of the present invention to provide a method for temperature monitoring of at least one component in an electrical system which ensures robust and reliable temperature monitoring of the at least one component independently of the time duration since the last switching off and independently of the operating intensity in a preceding operating phase.Disclosure of the InventionThis object is achieved by the method for temperature monitoring of a component of an electrical system according to Claim 1, and by a device and an electrical system according to the subordinate claims.Further embodiments are given in the dependent claims.According to a first aspect, a method, in particular a computer-implemented method, for monitoring a component temperature in an electrical system having a plurality of components is provided, having the following steps:upon start of an operating phase of the electrical system, measuring a reference temperature representing a temperature at a location in the electrical system;continuously modelling component temperatures of at least one component in the electrical system starting from the reference temperature as a respective starting value with the aid of a heat balance model which is modeled as a state model with a differential equation;continuously monitoring the component temperatures of the at least one component based on a threshold temperature predetermined for the at least one component;wherein the monitoring is furthermore carried out as a function of a temperature uncertainty, wherein the temperature uncertainty is determined as a function of a final reference temperature as a reference temperature at an end time of the preceding operating phase and the measured reference temperature.The temperature uncertainty can furthermore be determined as a function of a final component temperature of the at least one component as a modeled component temperature at a final time of a preceding operating phase and / or as a function of a temperature spread as a difference between a maximum and minimum component temperature.Electrical systems, in particular drive systems with an electric machine and integrated motor electronics, are of compact construction. During operation, some components of the systems, such as coils contained therein, stator and rotor components, and bearings, develop power losses due to energy inputs, which leads to local heating. The heating of individual components brings about a heat transfer to adjacent components due to the compact construction. The heat inputs from one or more components, the heat transfer between components, and the dissipation of heat from the electrical system via, e.g., a heat sink into the environment may be modeled using a heat balance model. This heat balance model corresponds to a state model and is based on a linear differential equation.In electrical systems, such as are used, for example, in drive systems in devices that can be operated by a driver of a motor vehicle, operation is frequently carried out by manual input or controlled by a superordinate system, with the result that the time intervals between the operating phases are different and are generally not known. For example, time periods of frequent activation of the electrical system may occur, as a result of which the individual components of the electrical system may heat up correspondingly strongly. In addition, the ambient temperature in summer can likewise lead to heating of the components or of the entire electrical system.Since the time duration since the end of the preceding operating phase or the time period between the switching off and the renewed switching on of a control device, for example a control unit / microcontroller, is generally not known, there are generally no initial values for the modeling of the component temperatures, starting from which the further temperature modeling can be carried out with the aid of the state model. In particular, at high ambient temperatures or at a short period of time since the previous operating phase, this may result in component temperatures being close to the threshold temperatures for monitoring when the electrical system is switched on, without this being able to be detected by the state model.It is therefore provided to perform the temperature monitoring of a component temperature of at least one component based on a temperature uncertainty that takes into account the possibility of a high component temperature, in order to reduce the risk of not detecting an exceeding of a threshold temperature.For this purpose, the above method proposes measuring a reference temperature at a position in the electrical system at the start time of a new operating phase of the electrical system. This is generally carried out with the aid of a temperature sensor, which may preferably be provided in a control unit of the electrical system. An operating phase is understood herein to mean the period of time during which the tracking or modelling of the component temperatures can be carried out by the electrical system.With the aid of the heat balance model, starting from an initial component temperature, which is assumed to be the reference temperature, modeling of the component temperatures is continuously performed by discretely calculating the heat balance model corresponding to a linear differential equation in successive time steps.During starting, i.e. at a starting time of the current operating phase, the component temperatures of the at least one component are therefore set to the measured reference temperature for the duration of time that has elapsed since the end of the last operating phase, for lack of other information. This reference temperature is measured by at least one temperature sensor in the electrical system. As a result of the modeling, modeled component temperatures are then available during the course of the operating phase.It can be provided that the temperature uncertainty is still taken into account only for a predetermined period of time after the start of the operating phase. In particular, the temperature uncertainty can be taken into account in a reducing manner starting from a basic value at the start time of the operating phase. In particular, the temperature uncertainty can be taken into account in a linearly decreasing manner or in a decreasing manner exponentially over the predetermined time duration after the start of the operating phase.Furthermore, a temperature uncertainty for the at least one component is determined at a respective point in time after the start point in time, which temperature uncertainty results from a basic value of the temperature uncertainty assigned to the component and in particular from a temporal factor function which, starting from the time duration since the start point in time of the current operating phase, provides a variation of the temperature uncertainty which decreases to in particular zero.It can be provided that after the lapse of the predetermined period of time a predetermined value for the temperature uncertainty is continuously assumed.The basic value of the temperature uncertainty can be determined as a function of a reference temperature at the end time of the preceding operating phase (end reference temperature), a modeled component temperature of the at least one component at the end time of the preceding operating phase (end component temperature) and, if appropriate, based on a temperature spread of the component temperature of the at least one component during the preceding operating phase.Thus, the higher the final reference temperature, the higher the basic value of the temperature uncertainty can be selected. Furthermore, the lower the temperature spread during the last operating cycle, the lower the basic value of the temperature uncertainty can be selected. Furthermore, the higher the final component temperature, the higher the base value of the temperature uncertainty can be selected. Furthermore, a smaller degree of uncertainty can be selected the smaller the temperature difference between the currently measured reference temperature and the final reference temperature with simultaneously a small temperature spread (e.g. a temperature spread below a predefined threshold value) during the preceding operating phase. Alternatively, a lower basic value of the temperature uncertainty can be selected, the lower the product of the temperature difference between the currently measured reference temperature and the final reference temperature and the temperature spread during the preceding operating phase.The basic value of the temperature uncertainty determined in this way can now be taken into account in the temperature monitoring based on a threshold temperature predefined for the at least one component and the current temperature uncertainty can be taken into account with the aid of the temporal factor function. Thus, the temperature uncertainty can be added to the modeled component temperature and the threshold value comparison with the threshold temperature can subsequently be carried out. Alternatively, the temperature uncertainty may be subtracted from the threshold temperature determined for the at least one component before performing the threshold comparison with the reduced threshold temperature. In this way, different threshold values for the monitoring can result at a plurality of modeled component temperatures.It may be provided that a plurality of component temperatures for a plurality of components are determined using the thermal balance model, wherein one or more corresponding threshold temperatures are provided for each of the components.Furthermore, the fault response can comprise a throttling or interruption of the power supply or a shutdown of the electrical system.According to a further aspect, an apparatus is provided which is configured to carry out the above method.According to a further aspect, an electrical system is provided, comprising:a plurality of components arranged in an assembly such that heat transfers occur between at least two of the components;the above device.Brief Description of the DrawingsEmbodiments are explained in more detail below with reference to the attached drawings. The following are shown: FIG. 1 is a schematic diagram of a drive system as an example of an electric system; and FIG. 2 illustrates a method for monitoring a component temperature in the electric drive system of FIG. 1.DESCRIPTION OF EMBODIMENTSFIG. 1 shows a drive system 1 as an example of an electrical system having an electric machine 2 and a control unit 3 for the electric machine 2.The control unit 3 and the electric machine 2 are arranged compactly in one structural unit.The electric machine 2 may have a stator 21 and a rotor 22. The rotor 22 has a rotor shaft 23, which is mounted in a housing 24 of the electric machine 2 via a suitable bearing 25. The electric machine 2 is supplied with electrical energy via drive lines 26.The activation is carried out with the aid of a driver circuit 31 in the control device 3. The driver circuit 31 is driven by control signals from a control unit 32. The control unit can contain a microprocessor or microcontroller, which adjusts the control signals according to a predetermined rotational speed or load specification in a manner known per se with the aid of a regulation or control and thus operates the electric machine 2.Sensors 33 are provided in the drive system, for example, in order to determine or model the motor current, in particular phase currents, to measure the motor voltage, to measure the rotational speed of the motor (e.g. Hall sensor), to measure or determine the supply voltage present for the drive circuit and to measure a reference temperature with the aid of a temperature sensor 34 arranged at a suitable point in the drive system.Based on the possibly estimated motor current and the rotational speed, the electrical power loss of the electric machine 2 can be determined. Based on the rotational speed and estimated motor current (or torque), a mechanical power loss can also be determined, for example, in the bearing 25 of the rotor shaft 23 in a manner known per se.The start of operation of the drive system 1 can be activated manually via an operating unit (not shown) or by activation of a superordinate system. When using such a drive system for user comfort applications in motor vehicles, such as, for example, electric window lifter systems, electric sliding roof systems or electric seat adjustment systems, the use takes place irregularly, so that during certain time phases, the electric machine is operated frequently and the electric machine 2 is not operated at all during other time phases.In principle, in the control device 3 at an operation start, no information is available about how long the end of the operating phase of the last operating phase has elapsed.Temperature monitoring is carried out in the control unit 32 which ensures that no component 21, 22, 23, 25, 26 of the electric machine 2 experiences heating above a predefined threshold temperature. This temperature monitoring is carried out with the aid of a temperature model which can be designed in the form of a heat balance model. The heat balance model takes into account heat sources and heat sinks in the components and heat transfer resistances between the individual components in the form of a linear differential equation of a state model. For this purpose, the electrical and mechanical operating variables, through which energy inputs or outputs into or from the electrical system take place, are monitored and the energy input is calculated according to physical model equations.The temperatures of the components in the electric drive system 1 may be modeled based on the heat balance model indicated by a state model of the shape. The vector T corresponds to the estimated state of the system, which is determined by the component temperatures T1...Tn, A and B, to the system matrices, which on the one hand represent the reaction to thermal gradients (A) and on the other hand represent the reaction to power losses u (B) which are coupled into the components on account of the contact with adjacent components.Due to the shape of the state model, it is necessary to define an initial state which is present at the start, i.e. at the start time, of an operating phase. However, since it is not known how long the last operating phase has elapsed and the component temperatures can therefore possibly deviate considerably from the ambient temperature, the uncertainty of the temperature determination of the component temperatures which arises as a result is taken into account by the subsequent method in order to carry out temperature monitoring for all components 21, 22, 23, 25.The method for temperature monitoring is illustrated in the flow chart of FIG. 2. The method is preferably carried out in the control unit and can be implemented there as software and / or hardware.In step S 1, it is first checked whether an operating phase is to be started. The operating phase is characterized in that the electric machine 2 is actively operated. The operating phase can be carried out, for example, by manual operation of a corresponding operating element or by external control by a superordinate system. The operating phase is generally characterized by a starting time and an ending time, wherein between the ending time and the subsequent starting time the system is passive and has no activity, in particular no powers are converted.If a start of an operating phase is detected (alternative: yes), the method continues with step S 2, otherwise the method jumps back to step S 1. The operating phase begins as soon as the control device is switched on, regardless of whether an operation of the electric machine already takes place.In step S 2, a reference temperature at the start time is determined with the aid of the temperature sensor 34.In step S 3, this reference temperature is assumed as the starting temperature for all components 21, 22, 23, 25 of the electric drive system 1 to be monitored. This is correct in particular when the components have cooled to an ambient temperature.Furthermore, in step S 4, the temperature is determined continuously, i.e. cyclically, starting from the reference temperatures of the components using the above-mentioned state model taking into account the detected or modeled operating variables, in order thus to determine the component temperatures for each component cyclically, i.e. at associated time steps.In a subsequent step S5, the reference temperature at the end time of the preceding operating phase is called the end reference temperature, the component temperature at the end time of the preceding operating phase is called the end component temperature and / or a temperature spread during the preceding operating phase, i.e. a difference between a maximum component temperature and a minimum component temperature, is called up from a nonvolatile memory and a temperature uncertainty value is determined accordingly. The temperature uncertainty value T un-sicher for the various components can be determined, for example, by a weighted sum of the reference temperature at the start time of the current operating phase, the final reference temperature, the final component temperature of the relevant component and the temperature spread of the relevant component, wherein g1, g2, g3, g4represent predefined weighting factors.Immediately after the start time of an operating phase, however, there is an increased uncertainty in the determination of the component temperature, which decreases with increasing time duration from the start time, since the component temperatures at the start time of the current operating phase have an ever less weight in the modeled component temperatures.In particular, it is provided that the temperature uncertainty is only taken into account during the monitoring for a specific period of time, since it can be assumed that after a specific period of time the temperature model correctly determines the component temperatures, since the influence of the component temperature at the start time becomes increasingly smaller. It can therefore be provided that, on the one hand, the temperature uncertainty is taken into account only for a predetermined period of time. After the predetermined period of time has elapsed, the temperature uncertainty may have the value 0 or a predefined value with which fundamental measurement uncertainties can be taken into account.Alternatively, it is provided that the temperature uncertainty decreases with increasing time duration since the start time of the current operating phase, preferably linearly, or is determined by an e-function as followsIn this case, the time constants τ 1... τ n for the various components which are to be monitored with the aid of the temperature monitoring can be chosen differently. T unsicher_1... T unsicher_n correspond to the temperature uncertainties for the various components, t corresponds to the evaluation times determined by the time steps.It is now also provided in step S 6 to perform a threshold value comparison, in which the modeled component temperature of each of the monitored components is compared with a threshold temperature predefined for the relevant component at each time step. In this case, the component temperature must always be below the predefined threshold temperature for the relevant component.In principle, in the method presented here, the uncertainty is not explicitly included in the temperature estimation, but rather is taken into account separately with its own dynamics. Therefore, the temperature uncertainty is taken into account accordingly in the threshold value comparison. This can be done by adding the temperature uncertainty to the component temperature determined before the threshold value comparison or subtracting it from the respective threshold temperature of the temperature uncertainty.If an exceedance of the corresponding threshold temperature is determined in step S 6 (alternative: yes), an error response is carried out in step S 10. Otherwise, the method continues with step S 7.In step S 7, it is checked whether the operating phase is to be ended. If this is the case (alternative: yes), the method continues with step S 8, otherwise the method jumps back to step S 4. It can be established that the operating phase is ended, when the manual operation is ended, or when a corresponding signal is received from the higher-level system.At the end time, in step S 8, the reference temperature is then measured with the temperature sensor, a temperature spread that can be determined for a temperature difference between the maximum reference temperature and the minimum reference temperature during the current operating phase just ended, and a component temperature of the monitored components are stored in a nonvolatile memory in order to use these for determining the temperature uncertainty when activating a next operating phase.According to another embodiment, multiple threshold temperatures may be predetermined for a component. These are taken into account in a corresponding threshold value comparison, as described above. For example, the temperature uncertainty can be acted upon by a threshold value factor between 0.1 and 1, which is taken into account in the threshold value comparison during the temperature monitoring, so that, in stages, an operating state is initially restricted when a lower threshold temperature is exceeded, while the operation of the electric drive system 1 is completely stopped when a higher threshold temperature is exceeded.

Claims

Method for monitoring a component temperature in an electrical system (1) having a plurality of components (21, 22, 23, 25, 26), having the following steps: - at the start of an operating phase of the electrical system (S1), measuring (S2) a reference temperature which represents a temperature at a location in the electrical system (1); - continuously modelling (S3, S4) component temperatures of at least one component (21, 22, 23, 25, 26) in the electrical system (1) starting from the reference temperature as starting value using a heat balance model which is modeled as a state model using a differential equation; - continuously monitoring (s6) the component temperatures of the at least one component (21, 22, 23, 25, 26) on the basis of a threshold temperature which is predefined for the at least one component (21, 22, 23, 25, 26); characterized in that the monitoring is furthermore carried out as a function of a temperature uncertainty, wherein the temperature uncertainty is determined as a function of a final reference temperature as a reference temperature at an end time of the preceding operating phase and the measured reference temperature.Method according to claim 1, wherein the temperature uncertainty is further determined depending on a final component temperature of the at least one component as a modeled component temperature at a final time of a previous operating phase and / or depending on a temperature spread as a difference between a maximum and minimum component temperature.Method according to claim 1 or 2, wherein the temperature uncertainty is further taken into account only for a predetermined period of time after the start of the operating phase.Method according to Claim 3, in which the temperature uncertainty is taken into account in a decreasing manner starting from the value at the starting time of the operating phase.The method of claim 4, wherein the temperature uncertainty is taken into account in a linearly decreasing or exponentially decreasing manner over the predetermined time period after the start of the operating phase.Method according to one of Claims 3 to 5, wherein a predefined value for the temperature uncertainty is assumed continuously after the predetermined period of time has elapsed.The method of any of claims 1 to 6, wherein a plurality of component temperatures for a plurality of components (21, 22, 23, 25, 26) are determined using the thermal balance model, wherein one or more corresponding threshold temperatures are provided for each of the components (21, 22, 23, 25, 26).Method according to one of Claims 1 to 7, wherein the fault response (S10) comprises a power supply restriction or a shutdown of the electrical system (1).An apparatus configured to perform the method of any one of claims 1 to 8.An electrical system (1) comprising: - a plurality of components (21, 22, 23, 25, 26) arranged in an assembly such that heat transfers take place between at least two of the components (21, 22, 23, 25, 26); - an apparatus according to claim 9.A computer program product comprising instructions which, when the program is executed by at least one data processing device, cause the program to carry out the steps of the method according to any one of claims 1 to 8.A machine readable storage medium comprising instructions which, when executed by at least one data processing device, cause the at least one data processing device to carry out the steps of the method according to any one of claims 1 to 8.

Images