Method for determining the motor temperature and / or ambient temperature for a rotating machine

Abstract

The invention relates to a method for determining the motor temperature and / or ambient temperature for a rotating machine, comprising an electric motor and at least one power module for controlling, in an open / closed-loop manner, the power consumption of the motor, wherein means for detecting the operating temperature of the power module and for detecting the motor current are provided and cooling is provided for the power module and the motor, the cooling effects of which generated during operation depend on one another in a defined manner, characterised in that the motor temperature and / or the ambient temperature is / are estimated on the basis of the detected operating temperature of the power module and of the detected motor current.

Description

[0001] Description

[0002] Method for determining the motor temperature and / or ambient temperature of a rotating machine

[0003] The invention relates to a method for determining the motor temperature and / or 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 system is provided for the power module and the motor, which cooling system generates a cooling effect for the motor and power module during operation, which cooling effect depends on one another in a defined manner.

[0004] Monitoring the ambient temperature and the motor temperature of a rotating machine during operation is important in order to, among other things, detect thermal overload situations in the motor in good time, as otherwise there is a risk of thermal destruction of the machine. Sensors for directly measuring the operating temperature of the motor and / or for measuring the ambient temperature are usually installed on the machine for monitoring purposes. However, providing separate sensors for temperature recording not only increases the production and maintenance costs of the machine, but can also lead to an increase in susceptibility to errors, as reliable monitoring is no longer possible if the sensors fail. A sensorless approach to thermal monitoring of the drive system is already known in the pump sector. Here, a dynamic (i.e. operating point-dependent) upper limit for the motor current is defined for the motor or electronics and monitored for compliance.If the current currently drawn by the motor exceeds this upper limit, the machine will shut down or at least reduce its motor power. For safety reasons, the upper limit is defined for a worst-case scenario, such as the highest conceivable ambient temperature. However, at lower ambient temperatures, this results in premature thermal shutdown or power reduction, and the motor's full permissible operating range cannot be utilized.

[0005] Furthermore, the above method cannot detect the ambient temperature and possible operation outside the permissible temperature range for the ambient temperature cannot be detected at all.

[0006] Based on the above considerations, it is therefore the object of the present invention to find a possibility for monitoring or determining the engine temperature or the ambient temperature without separate sensors, which can overcome the disadvantages mentioned above.

[0007] This object is achieved by a method according to the features of claim 1. Advantageous embodiments of the method are the subject of the dependent claims.

[0008] According to the invention, it is proposed to estimate the motor temperature and / or the ambient temperature of the machine on the basis of 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 on the power module. The inventive solution 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 on the current motor power. Assuming that both the motor and the power module assume at least a temperature corresponding to the ambient temperature, the temperature value exceeding the ambient temperature is referred to as the current operating temperature of the power module or the motor (also known as heating orOvertemperature (also known as overtemperature of the power module or motor) is primarily caused by the losses that occur during operation and the associated heat generation. The largest share, at least when the machine is in proper working order, is caused by electrical power loss, the magnitude of which depends largely on the current motor current.

[0009] Another factor influencing the operating temperature of the motor and power module is any active cooling of both components. Assuming that the cooling effect generated for the power module and the motor are interdependent or correlated in a defined manner, the measured operating temperature of the power module and the measured motor current can be used to draw conclusions about the ambient temperature and the motor operating temperature. Based on this knowledge, it is now possible to estimate sufficiently accurate temperature values ​​for the ambient temperature and / or the motor operating temperature.

[0010] An advantage of the method is that it is independent of the prevailing ambient temperature and the current operating point of the rotating machine. This enables a stable and reliable temperature estimation across the entire permissible operating range of the machine, avoiding the disadvantages of the prior art. In summary, the machine, and in particular the electric drive, can be operated and reliably monitored using the entire thermal operating range. The method preferably provides for determining the power component heating (power component overtemperature) generated in the power component based on the measured motor current.As already explained above, the heat loss generated internally in the power module is primarily caused by the electrical power loss, so that the measured motor current is a suitable indicator of the heat loss generated in the power module and thus of the heating of the power module compared to the ambient temperature. This relationship can be defined mathematically, in particular on the basis of a predefined correlation equation. Since the concrete correlation depends on the specific design of the machine and the choice of material, it must be determined in advance for each machine type or ideally for each individual machine using a training procedure. The term "machine" here includes not only the drive motor, but the entire system of the rotating machine, i.e., for example, a hydraulic pump unit driven by the motor.

[0011] Once the power module heating has been determined based on the motor current, the ambient temperature can be calculated in the next step. For this purpose, it is assumed that the operating temperature of the power module is equal to the sum of the ambient temperature and the generated power module heating. Since the operating temperature of the power module is also measured, the ambient temperature can be calculated by subtracting the estimated power module heating.

[0012] According to another preferred approach, the heat generated in the motor is also determined based on the measured 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 and thus the temperature increase caused by the motor relative to the ambient temperature can also be determined. The mathematical relationship between motor current and generated heat is also determined in advance for the individual machine type or machine and stored as a correlation equation in the control system.

[0013] When calculating the motor operating temperature, it is preferably assumed that it corresponds to the sum of the ambient temperature and the motor temperature rise. As already explained above, both variables can be determined from the measured motor current and the operating temperature of the power module. Of course, it is irrelevant whether the ambient temperature was actually determined beforehand or whether the mathematical relationship between the measured motor current and the operating temperature of the power module is used instead.

[0014] In the simplest case, the correlation equations used by the method correspond to a linear, time-invariant system, meaning that the power module heating and / or the motor heating develop proportionally to the motor current drawn. The linear relationship must be determined individually for different machine types, ideally for each individual machine.

[0015] However, experience has shown that the assumption of time invariance does not adequately reflect reality and instead represents a simplification. In practice, however, the operating temperature or heating of the power module and / or the motor will not change synchronously with the motor current; instead, there will be a time delay due to the specific heat capacity of the materials used. Since the simplification described above can lead to premature, unintentional shutdown of the machine or other control intervention, particularly in the case of only a brief current increase or fluctuation, it is preferable to also take the thermal inertia of the components into account accordingly. It is therefore preferable to supplement the corresponding correlation equations with a suitable time element in order to be able to adequately represent the thermal inertia of the power module and the motor.As a rule, the thermal inertia of the power module and the motor will differ considerably. Against this backdrop, it is recommended that the time delay for calculating the motor operating temperature or motor heating be significantly larger than any time delay in calculating the ambient temperature or power module heating. Due to the size of the power module, the thermal inertia of the power module can theoretically be neglected. The timing elements used are also determined individually for each machine or machine type in advance using a training procedure.

[0016] The training procedure in question is preferably carried out using at least one sensor for measuring the ambient temperature and one sensor for measuring the absolute engine operating temperature in order to be able to determine corresponding correlation equations and delay values ​​based on the measured values. Ideally, the training procedure is carried out at a high ambient temperature. A high ambient temperature, for example, is considered to be a temperature in the upper limit of the maximum permissible temperature operating range of the machine. Ideally, the training procedure is selected at an ambient temperature corresponding to the upper temperature limit of the permissible operating range of the machine.

[0017] As already explained above, it is an essential prerequisite for the implementation of the process that active cooling of the power module and the motor are dependent on one another in a defined manner. It can therefore be assumed that the influence of active cooling on the operating temperature of the power module and the motor is the same or at least predictable depending on the operating point. 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, a cooling flow is generated by a common fan, with the cooling air flows ideally running parallel. The common fan can be an externally driven fan. Ideally, however, the fan impeller is driven by the motor itself; in particular, the fan impeller is located on the motor shaft.Therefore, the cooling performance depends on the engine speed.

[0018] The power component used is, for example, a semiconductor element for current control or regulation, such as a semiconductor switch of an inverter, or the power component corresponds to the inverter component. The power component can be a transistor module, in particular an IGBT module. Ideally, such a module already includes an integral temperature measurement or integral measurement of the output current to be controlled, so that the corresponding measured values ​​can be tapped at the signal outputs of the module package.

[0019] The method design is particularly advantageous for machines which are characterized by a curve of the motor torque which is quadratic to the motor speed or by a curve of the electrical power which is cubic to the motor speed.

[0020] To monitor the engine temperature, it can be provided that the estimated engine temperature is compared with a limit value and, if this limit is exceeded, the engine power is reduced up to a complete stop of the machine.

[0021] The rotating machine can be a pump, in particular a centrifugal pump. Since pumps in particular are characterized by a torque curve that is quadratic with the speed, i.e. a curve of the electrical power consumption that is cubic with the speed, the application of the method leads to good estimation results, especially for pumps. Furthermore, pumps often use a common cooling system for the power electronics and the motor, which is also dependent on the speed of the motor, as a result of which the estimation accuracy is very high. Finally, the invention also relates to a rotating machine, in particular a pump, particularly preferably a centrifugal pump, having 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 further comprises means, in particular a sensor system, for detecting the operating temperature of the power module and for indirectly or directly measuring the motor current. The machine is further 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 machine operation are interdependent. According to the invention, the machine comprises a controller configured to carry out the method according to the invention. This results in the same advantages and properties for the machine as already explained above with reference to the method according to the invention. For this reason, a repetitive description is omitted.

[0022] Further advantages and features of the invention will be explained in more detail below using an exemplary embodiment illustrated in the figures. They show:

[0023] Figure 1: a sectional view of a pump according to the invention,

[0024] Figure 2: a flowchart of the method according to the invention using time-invariant correlation equations,

[0025] Figure 3: the embodiment according to Figure 2 with modification to

[0026] Consideration of thermal inertia,

[0027] Figure 4: a diagram illustrating the correlation between

[0028] Motor current and heating of the power module,

[0029] Figure 5: a diagram illustrating the correlation between

[0030] Motor heating and power module heating, Figure 6: a diagram to illustrate the power consumption of a

[0031] Pump depending on the current speed and

[0032] Figure 7: a diagram illustrating the correlation between motor current and loss-related motor heating.

[0033] The invention will be described in more detail below using a rotating machine in the form of a centrifugal pump as an example. Figure 1 shows a longitudinal section through the pump drive of a centrifugal pump. For simplicity, the hydraulic part of the pump is not shown. The electric motor 20 with the driven motor shaft 21 is visible. An electronics housing 10 is located on the periphery of the motor housing 22, which, among other things, includes the power electronics 11 of the 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 an inverter of the frequency converter. The transistor module corresponds to the claimed electronic power component.

[0034] Both the motor 20 and the power electronics 11 within the electronics housing 10 are cooled by air cooling. To generate the airflow, a fan impeller 30 is mounted on the shaft 21, which generates a cooling airflow 31 that flows circumferentially around the motor housing 22. This cooling airflow not only cools the motor housing 22 and thus the motor 20, but also flows past the heat-conducting underside of the electronics housing 10, ensuring sufficient heat dissipation of the heat loss generated by the power electronics 11, in particular by the transistor module, in the electronics housing 10.

[0035] To prevent thermal overload of the motor 20, the operating temperature of the motor 20 is continuously monitored during pump operation. Furthermore, the ambient temperature is continuously monitored to prevent pump operation during inadmissible external conditions. However, to monitor the operating temperature of the motor 20 and the ambient temperature, separate sensors for measuring these variables are dispensed with. Instead, the method according to the invention is implemented within the pump control system. This method estimates the motor operating temperature and the ambient temperature using correlations based on the operating temperature of the power component (hereinafter referred to as transistor temperature) and the set motor current (hereinafter referred to as transistor current) of the installed IGBT module in the electronics housing 10.The result of the estimation is independent of the operating point and external influences (ambient temperature, load, various disturbances).

[0036] Commercially available transistor modules (IGBT modules, etc.) have an integrated temperature sensor that measures the temperature inside the transistor and protects it from overheating. Such modules are also equipped with integrated current measurement. Therefore, the measured values ​​are already available at the modules' dedicated signal outputs.

[0037] In general, the following relationship applies to the estimation using the procedure, also known as the thermal correlation method:

[0038] • The transistor temperature is the sum of the ambient temperature and the transistor overtemperature. In the following, transistor overtemperature refers to the increase in temperature compared to the ambient temperature caused by losses in the power component or transistor module.

[0039] • The motor temperature is the sum of the ambient temperature and the motor overtemperature. In the following, the motor overtemperature is defined as the temperature increase in the motor caused by losses compared to the ambient temperature.

[0040] • Due to the direct electrical connection between the power electronics and the motor, the motor current absorbed by the stator corresponds to the transistor current.

[0041] • The transistor current causes the greatest losses in the transistor and thus the greatest increase in transistor overtemperature. The same applies to motor current and motor overtemperature. Based on this, the invention exploits the following correlations, which apply to the entire operating range of the pump:

[0042] • Correlation A): The transistor overtemperature is directly dependent on the transistor current, and both correlate across the entire operating range. This is clearly illustrated in Figure 4, where the transistor overtemperature exhibits an approximately linear (proportional) increase with increasing transistor current.

[0043] • Correlation B) Due to the shared cooling system and the transistor or motor current as the common main source of loss, the excess temperatures of the motor and transistor correlate (see Figure 5). Here, too, an approximately linear relationship can be seen.

[0044] • The two correlations A and B mentioned above apply to the entire operating range of the pump, as can be seen in Figure 6, which shows the torque curve over the motor's running speed. The diagram particularly shows the characteristics for pump applications, where power consumption typically increases quadratically with the speed.

[0045] The following values ​​can be derived from the above-mentioned correlations A) and B):

[0046] • Based on both correlations A), B), the motor overtemperature can be described as a function of the transistor current. Thus, the motor temperature can be estimated based on the transistor current and transistor temperature.

[0047] • Based on correlation A, the ambient temperature can also be estimated.

[0048] The basic process sequence is shown in Figure 2. During operation, the current transistor temperature and the current transistor current are tapped at the signal output of the IGBT module (blocks 40, 41). Based on these two direct measured values, the transistor overtemperature can then be estimated using the aforementioned correlation equation A (block 42), which is then kept ready for the further execution of the process to calculate the motor operating temperature (block 43). Subsequently, using correlation equation B, the transistor overtemperature and the measured transistor current, the motor overtemperature can be estimated (block 44), and based on this, the motor temperature can be calculated. The motor temperature is then output or used for monitoring, e.g., against a permissible limit value (block 46).

[0049] 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 a subsequent output or monitoring (block 47).

[0050] The method according to the invention therefore estimates the motor temperature independently of the ambient temperature. The motor 20 and optionally also the power electronics can thus be fully utilized across the entire operating range. Ambient temperatures above the permissible temperature range are detected, and the drive system can be protected. Furthermore, the method is independent of losses in the bearing and impeller. Deviations in bearing friction, for example, result in a change in the transistor current, which in turn leads to a change in the motor temperature. However, the method described above always assumes a thermally steady state. In practice, however, the motor 20 and power electronics 11 must run at a defined operating point for an extended period of time until the two components 11, 20 actually assume the correlated temperatures.This is due to the thermal inertia of the materials used, whereby the inertia of the motor 20 is of course significantly greater than the thermal inertia of the transistor module.

[0051] If thermal inertia is not taken into account, the estimated temperature value may be too high, especially if the current consumption only increases briefly. In this case, the permissible operating range of the machine may not be fully utilized if premature shutdown or a reduction in power occurs. However, utilization can be further optimized if the estimated motor temperature is compensated for over time. This modification is shown in Figure 3. The flow diagram corresponds to the embodiment shown in Figure 2, but here, when estimating the transistor overtemperature using correlation equation A, a time element 48 has been additionally introduced. This time element reflects the increase in the transistor overtemperature delayed by the increasing transistor current.Similarly, such a timer 49 is inserted when calculating the motor overtemperature based on correlation equation B to compensate for the motor's thermal inertia. Timer 49 is characterized by a significantly longer delay than timer 48.

[0052] The determination of the correlation equations A and B, as well as the time elements, must be determined in advance by measurement. For such a training procedure, preferably at high ambient temperatures, an external sensor is used to measure the absolute motor operating temperature and the ambient temperature. The other optionally required variables are already present in the drive control system (motor current and motor speed) and can be determined by measurement (thermal time constants of the motor and power electronics).

[0053] The temperature estimation performed using the method offers sufficient protection against possible motor overheating even in the event of a partial defect in the cooling system. If the function of the cooling system is impaired, e.g., due to contamination or a partial defect in the fan, this results in reduced cooling performance for the IGBT and motor, causing the temperature in the motor and IGBT to physically rise. In the first step, the method determines the ambient temperature based on correlation A between IGBT temperature and IGBT current. This ambient temperature is overestimated due to the higher measured value for the temperature in the IGBT. Based on this, the result is an estimated motor temperature (correlation B) that is higher than the actual physical motor temperature, at least for highly efficient motors. The thermal correlation method is therefore reliable because it estimates an excessively high motor temperature in the event of a fault.

Claims

Patent claims Method for determining the motor temperature and / or ambient temperature of a rotating machine 1. Method for determining the motor temperature and / or ambient temperature in a rotating machine, comprising an electric motor (20) and at least one electronic 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 system (30) is provided for the power module (11) and the motor (20), which cooling system produces a cooling effect for the motor (20) and the power module (11) during operation, which cooling effect is 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 of the power module (11) and the detected motor current.

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

3. Method according to claim 2, characterized in that the ambient temperature is determined on the basis of the operating temperature of the power module (11) less the power module temperature determined for the power module (11). warming is determined.

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

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

6. Method according to one of the preceding claims, characterized in that a linear correlation equation is used for determining the power module heating and / or for determining the motor heating.

7. Method according to one of the preceding claims, characterized in that a time delay is taken into account for the determination of the power module heating and / or for the determination of the motor heating in order to take into account the specific heat capacity of the power module (11) and the motor (20).

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

9. Method according to one of the preceding claims, characterized in that the correlation equations and / or the time delay values ​​are determined in advance during a training procedure, in particular using a sensor for measuring the ambient temperature and / or the engine temperature, wherein the training procedure is preferably carried out at a high ambient temperature.

10. Method according to one of the preceding claims, characterized in that the 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. Method according to one of the preceding claims, characterized in that the power module (11) is a transistor module which comprises an integral temperature measurement and / or integral current measurement.

12. Method according to one of the preceding claims, characterized in that the cooling effect generated for the power module (11) and the motor (20) is dependent on the motor speed, in particular increases in a defined manner with increasing speed.

13. Method according to one of the preceding claims, characterized in that the determined engine temperature is compared with a limit value and, if exceeded, a power reduction of the engine (20) is carried out.

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

15. Rotating machine, in particular a pump, particularly preferably a centrifugal pump, with an electric motor (20) for driving a rotating component of the machine, as well as 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 generated cooling power for the power module (11) and the motor (20) depends on one another in a defined manner, characterized in that the machine comprises a controller which is configured to carry out the method according to one of the preceding claims.

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