Method for determining motor temperature and / or ambient temperature in rotary machine

Abstract

The invention relates to a method for determining a motor temperature and / or an ambient temperature in a rotary machine comprising an electric motor and at least one power module for controlling / regulating the current consumption of the motor, in which means are provided for detecting the operating temperature of the power module and for detecting the motor current, cooling devices for the power module and the motor are provided, the cooling effects generated during operation of the cooling devices being dependent on one another in a defined manner, characterized in that the motor temperature and / or the ambient temperature is estimated on the basis of the detected operating temperature and the detected motor current of the power module.

Description

Technical Field

[0001] The invention relates to a method for determining the motor temperature and / or the ambient temperature in a rotating machine comprising an electric motor for driving a rotating component of the machine and at least one power module for controlling / regulating the current consumption of the motor, wherein means are provided for detecting the operating temperature of the power module and for detecting the motor current, and a cooling device for the power module and the motor is provided, which cooling device, during operation, produces a cooling effect for the motor and the power module, which are related to one another in a defined manner. Background Art

[0002] Monitoring the ambient and motor temperatures of rotating machinery during continuous operation is crucial to promptly identify thermal overloads in the motor, potentially leading to thermal damage to the machine. Typically, sensors are incorporated into the machine to directly measure the motor's operating temperature and / or the ambient temperature for this purpose. However, the use of separate temperature sensors not only increases the production and maintenance costs of the machine but also increases the potential for errors, as reliable monitoring is no longer possible in the event of sensor failure.

[0003] In the pump sector, a sensorless approach for thermal monitoring of drive systems is already known. Here, a dynamic, operating-point-dependent, upper motor current limit is defined for the motor or electronics, and compliance with this limit is monitored. If the current motor current consumed by the motor exceeds this upper limit, a mechanical shutdown or at least a reduction in motor power occurs. For safety reasons, the upper limit is defined for the worst-case scenario, for example, the highest conceivable ambient temperature. However, this results in premature thermal shutdown or power reduction at lower ambient temperatures, and prevents full utilization of the motor's full permissible operating range.

[0004] Furthermore, the ambient temperature cannot be detected with the above-described method, and any operation possible outside the permissible temperature range of the ambient temperature cannot be detected at all. Summary of the Invention

[0005] Based on the above considerations, the object of the present invention is therefore to find a possibility for monitoring or determining the motor temperature or the ambient temperature without separate sensor devices, which overcomes the above disadvantages.

[0006] This object is achieved by a method according to the features of claim 1. Advantageous embodiments of the method are the subject matter of the dependent claims.

[0007] According to the present invention, it is proposed to estimate the motor temperature and / or ambient temperature of the machine based on the detected operating temperature of the electronic power module and the detected motor current. The motor current is understood to be the motor current present at the output of the power module and supplied to the motor. The motor current is preferably measured in or at the power module.

[0008] The solution according to the present invention is based on the premise that the motor current controlled or regulated by the power module corresponds to the motor current consumed by the electric motor and thus provides information about the current motor power. Assuming that both the motor and the power module have at least one temperature that is a function of the ambient temperature, the current operating temperature of the power module or motor exceeding the ambient temperature (also referred to as heating or overheating of the power module or motor) is primarily caused by losses occurring during operation and the resulting heat generation. At least in the normal mechanical state, the largest contribution is caused by lost electrical power, the magnitude of which is primarily dependent on the current motor current.

[0009] Another factor influencing the operating temperatures of the motor and power module is the possible active cooling of both components. Assuming that the cooling effects on the power module, on the one hand, and the motor, on the other, are related or correlated in a defined manner, it is possible to infer the current ambient temperature and the motor operating temperature based on the detected power module operating temperature and the detected motor current. Based on this knowledge, sufficiently accurate temperature values ​​for the ambient temperature and / or the motor operating temperature can now be estimated.

[0010] One advantage of this method is that it is independent of the current ambient temperature and the current operating point of the rotating machine. This enables stable and reliable temperature estimation across the entire permissible operating range of the machine, avoiding the disadvantages of the prior art. Overall, the machine, and in particular the electric drive, can be operated and reliably monitored using the entire thermal operating range.

[0011] Preferably, the method proposes that the power module heating (power module overtemperature) generated in the power component is determined based on the detected motor current. As described above, the heat loss generated inside the power module is mainly caused by electrical power loss, so that the measured motor current is a suitable indicator of the heat loss generated in the power module and thus the heat generated by the power module relative to the ambient temperature. This relationship can be defined mathematically, in particular based on a predefined correlation equation. Since the specific correlation depends on the specific configuration and material selection of the machine, the correlation must be determined in advance for each machine type or ideally for each individual machine through a training process. Here, the term "machine" refers not only to the drive motor, but also to the entire system of the rotating working machine, that is, for example, also the hydraulic pump unit to be driven by the motor.

[0012] If the power module heating is determined based on the motor current, the ambient temperature can be calculated in the next step. This is based on the fact that the operating temperature of the power module corresponds to the sum of the ambient temperature and the generated power module heating. Since the power module operating temperature is also measured, the ambient temperature can be calculated by subtracting the estimated power module heating.

[0013] According to another preferred procedure, the motor heating generated in the motor is also determined based on the detected motor current. Since the motor current generated by the power module corresponds to the motor current consumed by the stator, the waste heat generated in the motor due to electrical losses can also be determined, and thus the temperature rise relative to the ambient temperature. The mathematical relationship between the motor current and the generated heating is also determined in advance for the individual machine type or machine and stored as a correlation equation in the control device.

[0014] To calculate the motor operating temperature, it is preferably assumed that the motor operating temperature corresponds to the sum of the ambient temperature and motor heating. As described above, both variables can be determined from measured values ​​of the motor current and the operating temperature of the power module. Of course, it is not important whether the ambient temperature is actually determined in advance or, instead, a mathematical relationship between the measured motor current and the operating temperature of the power module is used.

[0015] In the simplest case, the correlation equations used in this method correspond to linear, time-invariant systems, i.e., the power module heating and / or motor heating, respectively, develop proportionally to the consumed motor current. For different machine types, ideally for each individual machine, the linear relationship must be determined individually.

[0016] However, empirically, the assumption of time invariance is merely an inadequate reflection of reality and, in other words, a simplification. In practice, however, the operating temperature or heating of the power module and / or motor does not change synchronously with the motor current; rather, a time delay occurs due to the specific heat capacity of the materials used. Since this simplification can lead to premature or unintended mechanical shutdowns or other control interventions, especially in the case of only brief current increases or fluctuations, it is preferable to instead take the thermal inertia of the components into account. Therefore, it is preferably provided that the corresponding correlation equations are supplemented with adapted time components to adequately reflect the thermal inertia of the power module and motor.

[0017] Typically, the thermal inertia of power modules and motors differs significantly. Therefore, in this context, it is proposed that the time delay for calculating the motor operating temperature or motor heating be significantly greater than the possible time delay for calculating the ambient temperature or power module heating. Due to the size of the power module, the thermal inertia is theoretically negligible in the power module. The time elements used are also determined separately in advance in a machine- or machine-type-dependent manner through a training process.

[0018] The training process is preferably performed using at least one sensor for measuring the ambient temperature and a sensor for measuring the absolute operating temperature of the motor, so that corresponding correlation equations and delay values ​​can be determined based on the measured values. Ideally, the training process is performed at a high ambient temperature. For example, a temperature within the upper limit of the maximum permissible operating temperature range of the machine is suitable as the high ambient temperature. Ideally, the training process is performed at an ambient temperature selected based on the upper temperature limit of the permissible operating range of the machine.

[0019] As described above, the main prerequisite for implementing the method is that the active cooling of the power module and the motor are interconnected in a defined manner. Therefore, it can be assumed that the influence of active cooling on the operating temperature of the power module and the motor is the same depending on the operating point, or at least predictable. From a design perspective, this prerequisite is met, for example, if the active cooling of the power module and the motor is provided by a common cooling system. For example, in the case of air cooling, the cooling flow is generated by a common fan, wherein ideally, the cooling air flows in parallel. The common fan can be an externally driven fan. However, ideally, the fan impeller is driven by the motor itself, in particular, the fan impeller is located on the motor shaft. As a result, the cooling power depends on the motor speed.

[0020] The power modules used are, for example, semiconductor components used for current control or current regulation. Thus, for example, the semiconductor switches or power modules of an inverter correspond to inverter modules. Power modules can be transistor modules, in particular IGBT modules. Ideally, such modules already include an integrated temperature measurement or integrated measurement of the output current to be controlled, so that corresponding measured values ​​can be tapped at the signal output of the module package.

[0021] This embodiment of the method is particularly advantageous for machines that are characterized by a motor torque curve that is a quadratic function of the motor speed or by an electrical power curve that is a cubic function of the motor speed.

[0022] For monitoring the motor temperature, it can be provided that the estimated motor temperature is compared with a limit value and, if exceeded, the power of the motor is reduced until the machine comes to a complete standstill.

[0023] The rotating machine may be a pump, in particular a centrifugal pump. Since pumps are characterized by a torque curve that is a quadratic function of the rotational speed, i.e., an electrical power consumption curve that is a cubic function of the rotational speed, the application of this method yields good estimation results specifically for pumps. Furthermore, pumps typically use a common cooling system for the power electronics and the motor, which also depends on the motor's running speed, resulting in very high estimation accuracy.

[0024] Finally, the present invention also relates to a rotating machine, in particular a pump, particularly preferably a centrifugal pump, which has an electric motor for driving a rotating component of the machine, in particular a pump impeller, and at least one power module for controlling or regulating the current consumption of the motor. The machine also includes means, in particular a sensor device, for detecting the operating temperature of the power module and for directly or indirectly measuring the motor current. The machine is also equipped with a cooling system for cooling the power module and the motor. The cooling power actively generated for the power module and the motor during operation of the machine is related to each other. According to the invention, the machine includes a control device configured to carry out the method according to the invention. This provides the machine with the same advantages and characteristics as explained above in relation to the method according to the invention. For this reason, a detailed description is not given here. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other advantages and features of the present invention will be explained in more detail below based on the embodiments shown in the accompanying drawings, in which: Figure 1 shows a cross-sectional view of a pump according to the invention, Figure 2 A flow chart showing a method using a time-invariant correlation equation according to the present invention is shown. Figure 3 Show the basis Figure 2 An embodiment with a modification taking into account thermal inertia, Figure 4 A diagram illustrating the relationship between the motor current and the heat generation of the power module is shown. Figure 5 A diagram illustrating the relationship between motor heat generation and power module heat generation is shown. Figure 6 shows a graphical representation of the power consumption of the pump as a function of the current rotational speed, and Figure 7 A graphical view illustrating the relationship between motor current and loss-dependent motor heating is shown. DETAILED DESCRIPTION

[0026] The invention will be described in more detail below by way of example with reference to a rotary machine in the form of a centrifugal pump. Figure 1 A longitudinal section through the pump drive of a centrifugal pump is shown. For simplicity, the hydraulic part of the pump is not shown. An electric motor 20 with a driven motor shaft 21 is visible. An electronics housing 10 is situated circumferentially on the motor housing 22. This electronics housing contains, in particular, the power electronics 11 of a frequency converter for controlling / regulating the electric motor 20. The power electronics 11 includes at least one transistor module (e.g., an IGBT module) for implementing the inverter of the frequency converter. This transistor module corresponds to the electronic power module required by the present invention.

[0027] Both the motor 20 and the power electronics 11 within the electronics housing 10 are cooled by air cooling. To generate the air flow, a fan wheel 30 is mounted on the shaft 21. This fan wheel generates a cooling air flow 31 that flows around the motor housing 22. This cooling air flow not only cools the motor housing 22 and thus the motor 20, but also flows over the heat-conducting underside of the electronics housing 10, thereby ensuring sufficient heat dissipation of the heat losses generated within the electronics housing 10 by the power electronics 11, in particular by the transistor modules.

[0028] In order to avoid thermal overload of the motor 20, the operating temperature of the motor 20 is continuously monitored during continuous pump operation. In addition, the ambient temperature is also continuously monitored to avoid running the pump during periods when external conditions do not allow it.

[0029] However, to monitor the operating temperature of motor 20 and the ambient temperature, separate sensors are not used to measure these variables. Instead, a method according to the present invention is implemented within the pump control system. This method estimates the motor operating temperature and the ambient temperature using a correlation between the operating temperature of the power module (hereinafter referred to as transistor temperature) and the set motor current (hereinafter referred to as transistor current) of the IGBT module installed in electronics housing 10. The estimation result is independent of the operating point and external influences (ambient temperature, load, various disturbance variables).

[0030] Commercially available transistor modules (IGBT modules, etc.) have integrated temperature sensors that measure the temperature within the transistors and protect them from overheating. These modules are also often equipped with integrated current measurement. Therefore, in commercially available transistor modules, the measured values ​​are already available at the module's associated signal outputs.

[0031] In general, the following relationships apply to estimates using this method (also known as the thermal correlation method): • The transistor temperature is derived from the sum of the ambient temperature and the transistor overtemperature. In the following, the heating caused by losses in the power module or transistor module relative to the ambient temperature is referred to as the transistor overtemperature.

[0032] • The motor temperature is derived from the sum of the ambient temperature and the motor overtemperature. In the following, the motor overtemperature is understood to mean the temperature increase in the motor relative to the ambient temperature caused by losses.

[0033] • Through the direct electrical connection between the power electronics and the motor, the motor current consumed by the stator corresponds to the transistor current.

[0034] • The transistor current causes the greatest losses in the transistor and thus the greatest rise in transistor overtemperature. The same applies to the motor current and motor overtemperature.

[0035] Based on this, the present invention utilizes the following relationship which applies to the entire operating range of the pump: • Correlation A): Transistor overtemperature is directly related to transistor current and the two are correlated over the entire operating range. Figure 4 This is clearly illustrated in Figure 1, where the transistor overtemperature rises approximately linearly (proportional) with increasing transistor current.

[0036] • Correlation B) Correlation of motor and transistor overtemperature via a common cooling system and transistor current or motor current as a common main source of losses (see Figure 5 ). Here too, an approximately linear relationship can be identified.

[0037] • The two relationships A and B mentioned above apply to the entire operating range of the pump, which can be determined according to Figure 6 It is concluded that Figure 6 The curve of the torque over the running speed of the motor is depicted as an example. This diagram particularly illustrates the characteristics of pump applications, in which the power consumption generally increases quadratically with the speed.

[0038] From the above associations A) and B) the following values ​​can be derived: • Based on the two relationships A) and B), the motor overtemperature can be described in terms of the transistor current. Therefore, the motor temperature can be estimated based on the transistor current and the transistor temperature.

[0039] •Based on correlation A, the ambient temperature can also be estimated.

[0040] The basic method flow is Figure 2 . During continuous operation, the current transistor temperature and the current transistor current are tapped off at the signal output of the IGBT module (blocks 40, 41). Based on these two directly measured values, the transistor overtemperature can then be estimated using the aforementioned correlation equation A (block 42). This overtemperature is then provided for further method execution to calculate the motor operating temperature (block 43). Subsequently, the motor overtemperature can be estimated using correlation equation B, the transistor overtemperature, and the measured transistor current (block 44), and the motor temperature can be calculated accordingly. The motor temperature is then output or used for further monitoring, for example, against permitted limit values ​​(block 46).

[0041] At the same time, the ambient temperature can be calculated by subtracting the transistor overtemperature from the measured transistor temperature (block 42 ) and fed to subsequent output or monitoring (block 47 ).

[0042] The method according to the invention therefore estimates the motor temperature independently of the ambient temperature. As a result, the motor 20 and optionally also the power electronics can be fully utilized throughout the entire operating range. Ambient temperatures outside the permissible temperature range are identified and the drive system can be protected. Furthermore, the method is independent of losses in the bearings and impellers. For example, deviations in bearing friction lead to changes in the transistor current, which in turn lead to changes in the motor temperature. However, the above-described method is always based on a thermally stable state. In practice, however, the motor 20 and the power electronics 11 must be operated for a longer time in a defined operating point until the two components 11, 20 actually reach the associated temperature. This is due to the thermal inertia of the materials of construction, wherein the inertia of the motor 20 is naturally significantly greater than the thermal inertia of the transistor module.

[0043] If thermal inertia is not taken into account, the estimated temperature value will be too high, especially if the current consumption increases only briefly. In this case, if premature shutdown or power reduction occurs, the permissible operating range of the machine may not be fully utilized. However, if the estimated motor temperature is time-compensated, the utilization can be further optimized. This modification is in Figure 3 This flow chart is shown in Figure 2 , except that, when estimating the transistor overtemperature using correlation equation A, a time element 48 is additionally introduced, which reflects the delayed rise in transistor overtemperature relative to the increasing transistor current. Similarly, when calculating the motor overtemperature based on correlation equation B, a time element 49 is inserted to compensate for the thermal inertia of the motor. Time element 49 is characterized by a significantly longer delay compared to time element 48.

[0044] The coupling equations A and B and the determination of the time components must be determined in advance using measurements. For this training process, external sensors are used to detect the absolute motor operating temperature and the ambient temperature, preferably at high ambient temperatures. Other variables that may be required are already present in the drive control (motor current and motor speed) and can be determined using measurements (thermal time constants of the motor and power electronics).

[0045] The temperature estimation performed using this method provides adequate protection against possible motor overheating even in the event of a partial failure of the cooling system. If the cooling system's functionality is impaired, for example due to contamination or a partial fan failure, this is reflected in a decrease in the cooling power provided to the IGBTs and motor, resulting in a physical increase in the temperature in the motor and IGBTs. In a first step, the method determines the ambient temperature based on a correlation A between the IGBT temperature and the IGBT current. This ambient temperature is overestimated due to the high measured temperature values ​​in the IGBTs. Consequently, at least in the case of high-efficiency motors, the resulting estimated motor temperature is higher than the actual physically existing motor temperature (correlation B). Therefore, the thermal correlation method is reliable because it estimates an excessively high motor temperature even in the event of a failure.

Claims

1. A method for determining the motor temperature and / or the ambient temperature in a rotating machine, the rotating machine comprising an electric motor (20) and at least one power module (11) for controlling / regulating the current consumption of the motor (20), wherein means are provided for detecting the operating temperature of the power module and for detecting the motor current, and a cooling device (30) is provided for the power module (11) and the motor (20), which cooling device generates a cooling effect for the motor (20) and the power module (11) during operation, the cooling effects being related to one another in a defined manner, It is characterized by: The motor temperature and / or the ambient temperature are estimated based on the detected operating temperature of the power module (11) and the detected motor current.

2. The method according to claim 1, characterized in that Based on the detected motor current, the heating of the power module caused by electrical losses in the power module (11) is determined, in particular based on the previously determined correlation equation.

3. The method according to claim 2, characterized in that The ambient temperature is determined based on the operating temperature of the power module (11) minus the power module heat generated by the power module (11).

4. The method according to any one of the preceding claims, characterized in that The motor heating caused by the electrical losses in the motor (20) is determined based on the detected motor current, in particular based on a predetermined correlation equation.

5. The method according to claim 4, characterized in that The motor temperature is determined by adding the motor heating to the ambient temperature previously determined based on the detected motor current and the operating temperature of the power module (11).

6. The method according to any one of the preceding claims, characterized in that The linear correlation equation is used to determine the power module heating and / or to determine the motor heating.

7. The method according to any one of the preceding claims, characterized in that A time delay is taken into account for determining the power module heating and / or determining the motor heating in order to take into account the specific heat capacities of the power module (11) and the motor (20).

8. The method according to claim 7, characterized in that The time delay for determining heating of the motor is selected to be greater than the time delay for determining heating of the power module.

9. The method according to any one of the preceding claims, characterized in that The correlation equation and / or the time delay value are predetermined during a training process, in particular using sensors for measuring the ambient temperature and / or the motor temperature, wherein the training process is preferably performed at a high ambient temperature.

10. The method according to any one of the preceding claims, characterized in that Cooling for the power module (11) and the motor (20) is provided by a common cooling system, for example by an externally driven fan or by a fan (30) driven by the motor (20).

11. The method according to any one of the preceding claims, characterized in that The power module (11) is a transistor module comprising an integrated temperature measurement and / or an integrated current measurement.

12. The method according to any one of the preceding claims, characterized in that The cooling effect produced for the power module (11) and the motor (20) depends on the motor speed and, in particular, increases in a defined manner with increasing speed.

13. The method according to any one of the preceding claims, characterized in that The determined motor temperature is compared with a limit value and, if exceeded, the power of the motor (20) is reduced.

14. The method according to any one of the preceding claims, characterized in that The rotating machine is a pump, in particular a centrifugal pump.

15. A rotating machine, in particular a pump, particularly preferably a centrifugal pump, having an electric motor (20) for driving a rotating component of the machine, and at least one power module (11) for controlling / regulating the current consumption of the motor (20), and means for detecting the operating temperature of the power module (11) and for detecting the motor current, wherein a cooling system (30) is provided for cooling the power module (11) and the motor (20), the cooling power generated by the cooling system for the power module (11) and the electric motor (20) being related to one another in a defined manner during operation, characterized in that The machine comprises a control device configured to carry out the method according to any one of the preceding claims.

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