Systems and methods for monitoring motor temperature

Abstract

The present invention relates to a system (1) and method for monitoring the temperature of a motor (M) having an electromechanically driveable motor shaft, the system comprising a sensor (10), a measuring mechanism for determining the electrical input power (P) of the motor (M), and a measuring mechanism for detecting the shaft rotational speed n of the motor shaft, the sensor being based on a thermal model (MOD) describing the thermal characteristics of the motor (M), wherein an evaluation device is further provided, configured to determine the temperature of the motor (M) based on the input power (P), a reference temperature T, and other parameters. Ref The current motor temperature of the motor (M) is determined by using the obtained shaft speed n and the thermal model (MOD).

Description

Technical Field

[0001] This invention relates to a system and method for determining or estimating the temperature of a motor, and particularly for preventing motor overheating. Furthermore, this invention relates to a motor constructed with such a system. Background Technology

[0002] Known methods for detecting motor temperature include, for example, installing sensors into the windings, determining the winding temperature from the motor differential equations using a state estimator (Kalman filter, gradient method), directly measuring the winding resistance during operation by coupling in a measurement voltage, or calculating the motor temperature based on the motor's thermal network model.

[0003] Recently, there have been increasing attempts to determine the temperature inside electric motors, but this does not necessarily require installing temperature sensors or similar measuring devices in the motor itself, that is, in the electromechanical parts of the motor.

[0004] For example, DE 10 2008 040 725 A1 discloses a method for determining the rotor temperature of a permanent magnet synchronous motor, in which an estimate of the rotor temperature is obtained by means of a Kalman filter incorporating a thermal model of the synchronous motor.

[0005] EP 2977733 A1 discloses another method for determining the winding temperature of the excitation winding of a separately excited synchronous motor using a Kalman filter. Here, a first temperature estimate of the winding temperature is given in advance for a start time point. At different measurement time points following the start time point, the excitation voltage applied to the excitation winding and the excitation current flowing through the excitation winding are detected respectively. For each measurement time point, an updated temperature estimate is recursively formed based on the excitation voltage detected at the measurement time point, the excitation current detected at the measurement time point, and the previous temperature estimate.

[0006] DE 102019105081 A1 discloses an apparatus for determining the temperature of the windings of a rotating magnetic field motor having a stator and a rotor. The apparatus includes at least one first Kalman filter (K1) for calculating the temperature and a rotating magnetic field adjustment unit for adjusting the rotating magnetic field motor with at least one id current regulator vector. The id current regulator is configured to apply a high-frequency voltage signal (HF) to the winding voltage to obtain a winding current having a current component with high-frequency superposition for the winding. The current component is fed to the Kalman filter (K1), which has a high-frequency model of the motor to determine the high-frequency resistance of the winding and, by means of calculation, the winding temperature.

[0007] However, the methods known in the prior art also have specific drawbacks in implementation or application, thus there is a need for reliable monitoring of the motor temperature inside the electric motor, without having to install temperature sensors or similar measuring devices in the motor, i.e., in the electromechanical part of the motor. Summary of the Invention

[0008] Therefore, the objective of this invention is to overcome the above-mentioned disadvantages and to provide an effective system and method for detecting the motor temperature of a motor, and in particular for preventing the motor from overheating.

[0009] Here, the basic concept of the present invention is to design a sensor such that it can determine the temperature inside the motor based on a thermal model of the characteristics of a mapped thermomotor, electrical input power, preferably shaft speed, and reference temperature.

[0010] Therefore, according to the present invention, a system for monitoring the temperature of a motor having an electromechanically driveable motor shaft is proposed, comprising a "virtual" sensor based on a thermal model describing the thermal characteristics of the motor, a measuring mechanism for determining the electrical input power of the motor, and a measuring mechanism for detecting the shaft rotational speed of the motor shaft, wherein an evaluation device is further provided, configured to consider the input power, a reference temperature T, and other parameters. Ref The current motor temperature is determined by using the obtained shaft speed n and the thermal model.

[0011] In a particularly advantageous embodiment of the invention, the thermal model (MOD) is specified as a system of differential equations simulating the thermal characteristics of a motor. Therefore, by solving the system of differential equations, given the required input values, the motor temperature can be calculated. In this regard, the sensor based on the system of differential equations can also be understood as a virtual sensor.

[0012] Preferably, the system of differential equations used is characterized by a specific property that allows for a variety of alternative solution methods for determining the temperature, particularly through numerical integration, simulation calculations implemented using analog computers, or simulation calculations implemented using models including passive components. Other solution methods may also be considered in principle.

[0013] Another aspect of the present invention relates to a method for monitoring temperature, in addition to a system for monitoring temperature. According to the invention, a method is provided for this purpose, particularly utilizing a system described above using a set of differential equations (DGLs) describing the thermal characteristics of a motor, the method comprising the following steps:

[0014] a. Detect the electrical input power of the motor;

[0015] b. Calculate the mechanical shaft power and obtain the corresponding torque of the motor based on the detected motor speed;

[0016] c. In particular, the heat loss power that causes the motor temperature to rise is calculated by subtracting the mechanical shaft power from the electrical input power;

[0017] d. The calculated heat loss power is provided as an input parameter to the system of differential equations to solve the system and thereby calculate the temperature rise, especially when using an additional reference temperature T. Ref In this case, the additional reference temperature T Ref It is added to the temperature rise so that the motor temperature can be determined.

[0018] In a first advantageous embodiment of the invention, the method is characterized by determining the motor temperature by solving a system of differential equations through numerical integration (e.g., according to the Euler method, ..., Runge-Kutta method, etc.).

[0019] In both alternative implementations, the solutions to the system of differential equations used to determine the motor temperature are calculated analogously, either using circuitry corresponding to an analog computer type with appropriate computer modules or alternatively based on suitable RC modules and passive components. When using a passive RC system, current and / or voltage sources can be used in conjunction with operating circuits or transistor circuits.

[0020] In the described embodiment, it is advantageous if the detection of the motor's electrical input power is performed by measuring the intermediate circuit voltage and intermediate circuit current and by multiplying the two measurements (preferably using a microcomputer), or by obtaining the power from the intermediate circuit voltage. Possible implementations for this purpose are described in detail in the embodiments mentioned later.

[0021] The rotational speed can be determined, for example, by measuring the frequency of the line voltage and obtaining the corresponding torque from the corresponding stored characteristic curve, or by using the q component of the current iq or by using a strain gauge, especially in the case of implementations in numerical integration.

[0022] In principle, a voltage proportional to the motor speed can be generated from the measured line voltage of the motor using a simulated frequency-to-voltage converter, thereby allowing the shaft power to be determined. Alternative methods for determining shaft power can also be considered. Attached Figure Description

[0023] Other advantageous improvements of the invention are shown above or below in detail with reference to the accompanying drawings, together with the description of preferred embodiments of the invention. Wherein shown:

[0024] Figure 1 A schematic illustration of one embodiment of the present invention is shown;

[0025] Figure 2 An exemplary implementation of a computational method for automatic code generation using the software Matlab Simulink (without real data acquisition) is shown.

[0026] Figure 3 An exemplary implementation of a computational method for automatic code generation using the software Matlab Simulink (with specific data acquisition capabilities) is presented.

[0027] Figure 4 An RC link is shown to illustrate an implementation design using differential equations.

[0028] Figure 5 An implementation scheme of a CRCR network with a voltage source is shown, and

[0029] Figure 6 An implementation scheme of a CRCR network with a voltage source is shown. Detailed Implementation

[0030] The following description refers to an exemplary implementation method. Figures 1 to 3 The invention will be described in more detail, wherein the same reference numerals denote the same functional and / or structural features.

[0031] First refer to Figure 1 Describe three alternative implementation variations. Figure 1 The following method steps for determining motor temperature are shown in the figure:

[0032] Step a: Detect the motor's electrical input power;

[0033] Step b: Calculate the mechanical shaft power and obtain the corresponding torque of the motor based on the detected motor speed;

[0034] Step c: Specifically, calculate the heat loss power that causes the motor temperature to rise by subtracting the mechanical shaft power from the electrical input power, and

[0035] Step d: Input the calculated heat loss power as an input parameter into the system of differential equations to solve the system and thereby calculate the temperature rise, especially when using an additional reference temperature T. Ref In this case, the additional reference temperature T Ref It is added to the temperature rise so that the motor temperature can be determined.

[0036] In the first embodiment, when numerical integration is used to solve the differential equation, steps a) to d) are characterized as follows.

[0037] The following will describe according to Figure 4An example implementation of an RC link concept. In the RC link, three parallel RC grids are connected by resistors R1, R2, R3, and R4. L This is achieved using capacitors C1, C2, and C3. Additionally, nodes K1, K2, and K3, and currents i1, i2, and i3 or i... c1 i c2 and i c3 The current i1 flows to the first node K1 and then splits into currents i2 and i... c1 .from Figure 4 This shows how the flow is distributed to the network accordingly. A voltage U is applied between the connectors. R The voltage drop across capacitors C1, C2, and C3 is represented by U. C1 U C2 and U C3 Represented by U e The voltage at the input terminal is represented by U. a This represents the voltage at the output terminal.

[0038] The following relationship applies here:

[0039] U R =i1 R1+U C1

[0040] K1: i1 = i c1 +i2→(i1-i2)·1 / C1=dU C1 / dt

[0041] K2: i2 = i c2 +i3→(i2-i3)·1 / C2=dU C2 / dt

[0042] K2: i3 = i c3 +i4→(i3-i4)·1 / C3=dU C3 / dt

[0043] For i4, apply: i4 = 0 (no load)

[0044] i4 = U C3 / R L (With load)

[0045] Current represents heat power and voltage represents temperature. Therefore, the thermal model is calculated similarly to the electrical model shown. Thus, resistance is analogous to thermal resistance, and capacitance represents heat capacity.

[0046] Additional conditions exist:

[0047] M1: (U e -U C1 )·1 / R1=i1

[0048] M2: (U C1 -U C2 )·1 / R2=i2

[0049] M3: (U C2 -U C3 )·1 / R3=i3.

[0050] When feeding with a current source, i1 is predetermined or introduced, thereby disregarding equation M1 (as observed in a manner similar to calculation).

[0051] The following relation applies to the state space:

[0052]

[0053] in,

[0054]

[0055] The detection of electrical input power (used to power the thermal DGL system) can be performed, for example, by measuring the intermediate loop voltage and intermediate loop current (two AD channels) and by multiplying the two values ​​in a microcomputer implemented for this purpose.

[0056] The power of the mechanical shaft can be calculated from the rotational speed (measured by measuring the frequency of the line voltage using a timer) and the corresponding torque calculated from the stored characteristic curve. Alternatively, the torque can be calculated from the current iq (which can be calculated using the rotor position and the three-phase line current or provided by a rectifier program). Alternatively, the torque can also be measured using a strain gauge.

[0057] The mechanical shaft power is subtracted from the electrical input power, and this difference generates the thermal power (i.e., loss power) that causes the motor to heat up. The magnetic power (which represents reversible reactive power) in the input power exists only when the line current (RMS value) changes and can be detected as needed, for example, via relevant constants, characteristic curves, or as an input value from a calculation circuit used for accurate power balance calculations, under frequent speed and load variations. However, heating caused by the current (through winding resistance) used to store the magnetic power (reactive power) is automatically taken into account.

[0058] The calculated thermal power (loss power) is now fed into the system of differential equations as an input parameter, from which the temperature rise caused by this power is calculated. The temperature rise calculated using the system of differential equations and the input power is then added to the measured reference temperature to obtain an estimated temperature within the motor's internal space.

[0059] The temperature output can then be given as an analog signal via a DA converter of any implementation, via a data bus, or as a binary threshold and alarm value on a pin.

[0060] In the second embodiment, simulation calculation is used. The system of differential equations is thus calculated analogously, that is, by constructing the corresponding circuitry on a printed circuit board (PCB) according to the type of analog computer. This requires the necessary operational amplifiers, adders, subtractors, constant potentiometers (for multiplication by a constant), function generators (for torque characteristic curves), and integrators. Then, steps a) through d) are performed as follows:

[0061] Preferably, the electrical input power is detected from the intermediate loop using a suitable voltage divider for the intermediate loop voltage, a shunt for current measurement, and an operational amplifier (OP) for signal amplification. Then, multiplication for calculating the input power occurs using a suitable operational circuit (multiplier) or a dedicated (analog or digital) multiplication module (modulation method or calculation). If the intermediate loop voltage is to be constant and its constantness is monitored, then it is sufficient to transmit the measured current to the input power with a constant gain.

[0062] Using an analog frequency-to-voltage converter, a voltage proportional to the motor's rotational speed can be generated from the motor's line voltage. This voltage is then multiplied by a torque-proportional voltage using an analog multiplier or a controlled amplifier (with gain control) to obtain the shaft power.

[0063] This voltage, which is proportional to torque, can be obtained, for example, using an analog or digital function generator (with rotational speed as the input parameter). For this purpose, the characteristic curve of a fan wheel driven by a motor, for example, is stored in the function generator.

[0064] Subtracting the mechanical shaft power from the electrical input power also yields the thermal power (loss power) that causes the motor to heat up. This thermal power is now fed as an input parameter to the system of differential equations, as in the above embodiment, for calculating the motor temperature.

[0065] If a voltage corresponding to the heat loss power is fed into the system of differential equations, the system of differential equations provides the desired temperature rise at its final capacitor. If the heat loss power is fed into the system of differential equations as a current source, the voltage at the first capacitor provides the desired temperature rise.

[0066] The temperature rise calculated using the analog differential equations and input power is now added to the measured reference temperature to obtain an "estimated" temperature within the motor's internal space. The aforementioned adder circuit now provides an analog output voltage proportional to the motor temperature, which can be simply displayed and / or transmitted, or used to shut off the motor using a comparator.

[0067] exist Figure 1 In the third embodiment, a similar calculation is used. For this purpose, the solution for developing electronic analog computers is to solve the problem by forming a direct (electrical) simulation using passive components such as resistors, capacitors, and inductors. The underlying path can be modeled using a resistive network. If, for example, an AC voltage is fed or a voltage is applied between the input and / or capacitors and inductors and the output during pulsed operation, the shortest path is found by following the maximum current flow at each node. The basic principle of this solution is based on current distribution through a resistive network with parallel and series components. Such a system is also called an analog cellular automaton. Therefore, with the help of this adapted RC network (resistors and capacitors), the actual temperature characteristics of the motor can be simulated after calibration (i.e., determining the R and C values). The cellular automaton used can also be a simple RC link.

[0068] In this embodiment, steps a) to d) are then performed as follows:

[0069] The electrical input power is detected using a voltage divider appropriately designed for the intermediate loop voltage, a shunt for current measurement, and an operational amplifier (OP) for signal amplification. Then, multiplication for calculating the input power occurs using a suitable operational circuit (multiplier) or a dedicated (analog or digital) multiplication module (modulation method or calculation).

[0070] The shaft power is determined similarly to the steps described for the second embodiment. Subtracting the mechanical shaft power from the electrical input power yields the thermal power (loss power) that causes the motor to heat up. Operational amplifier circuitry is used for subtraction and feeding the controlled source into the RC network, as well as for other mathematical operations and / or transistor circuitry as described in this scheme. The actual RC network is configured to be passive here. If the RC network is fed with a voltage source ( Figure 6 If the voltage source value corresponds to the heat dissipation power, then the end of the corresponding RC chain (the voltage across the load resistor or the voltage across the final capacitor) provides the desired temperature rise. Conversely, if the RC network feeds the heat dissipation power as a current source ( Figure 5 Then the start of the RC chain (the voltage at the current source or the first capacitor) provides the desired temperature rise.

[0071] exist Figure 5 The diagram illustrates the CRCR network and the feeding of a controlled current source. The control signal for the current source forms the calculated heat loss power. For example, the current source can be designed as a Tietze branch with an operational amplifier.

[0072] exist Figure 6The diagram illustrates the CRCR network and the power supply of a controlled voltage source. The control signal for the voltage source forms the calculated heat loss power. The R and C components are determined using parameter fitting based on values ​​measured on an actual motor. For example, the voltage source could be designed as a Tietze branch with an operational amplifier.

[0073] Measuring the corresponding voltage across the RC network (OP circuit) when it is fed with a voltage or current source now provides a temperature rise. To further increase the temperature (analog voltage), the measured ambient temperature is also added as an analog voltage.

[0074] The thermal model can be implemented and calculated in any implementation, depending on the specific requirements. This idea is consistent with the modular system or modular solution according to the present invention.

[0075] The embodiments of the present invention are not limited to the preferred embodiments of the parameter selection type described above. Instead, multiple variations are possible, and these variations can also use the illustrated solution in substantially different types of embodiments.

Claims

1. A system for monitoring the temperature of a motor having an electromechanically driven motor shaft, the system comprising a sensor, a measuring mechanism for determining the electrical input power of the motor, and a measuring mechanism for detecting the rotational speed of the motor shaft, the sensor being based on a thermal model describing the thermal characteristics of the motor, wherein an evaluation device is further provided, the evaluation device being configured to consider the electrical input power, a reference temperature T... Ref The current motor temperature is determined by measuring the detected rotational speed and using a thermal model. in, The rotational speed can be determined by measuring the frequency of the line voltage and obtaining the corresponding torque from the stored characteristic curve, or by using the q-component of the current iq or by using a strain gauge. The thermal model includes a set of differential equations simulating the thermal characteristics of a motor.

2. The system according to claim 1, characterized in that, The system of differential equations, as a modular system, allows for a variety of alternative solution methods for determining temperature.

3. The system according to claim 2, characterized in that, The alternative solution methods are numerical integration, simulation calculations implemented using analog computers, or simulation calculations implemented using models that include passive components.

4. A method for monitoring the temperature of a motor, the method comprising the steps of: using a system according to any one of claims 1 to 3, wherein the motor temperature is monitored with the aid of a set of differential equations describing the thermal characteristics of the motor; a. Detect the electrical input power of the motor; b. Calculate the mechanical shaft power and obtain the corresponding torque of the motor based on the detected motor speed; c. Calculate the heat loss power that causes the motor temperature to rise by subtracting the mechanical shaft power from the electrical input power; d. The calculated heat loss power is provided as an input parameter to the system of differential equations to solve the system, and the temperature rise is calculated from this, using an additional reference temperature T. Ref In this case, the additional reference temperature T Ref Add to the temperature rise so as to determine the motor temperature.

5. The method according to claim 4, characterized in that, The solution to the system of differential equations used to determine the motor temperature is achieved through numerical integration.

6. The method according to claim 4, characterized in that, The solution to the system of differential equations used to determine the motor temperature is calculated by analogy, using circuits corresponding to the type of analog computer with appropriate computer modules, or based on freely programmable circuits or with the aid of suitable RC modules and passive components.

7. The method according to claim 4 or 5, characterized in that, The electrical input power of the motor is detected by measuring the intermediate circuit voltage and current and multiplying the two measurements.

8. The method according to claim 4 or 5, wherein, The shaft power is determined by using a simulated frequency-to-voltage converter to generate a voltage proportional to the motor speed from the measured line voltage.

9. The method according to claim 7, wherein, The electrical input power of a motor can be detected using a microcomputer or programmable circuit.

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