Method for non-invasive detection of motor temperature

Abstract

The invention discloses a non-invasive motor temperature detection method. A motor is connected with a control system. The method comprises the following steps that a, before a control system is started and a motor runs, the control system obtains a winding resistance initial value Rsinit and / or a back electromotive force constant initial value Kinit of the motor, and b, after the motor runs, the control system obtains a winding resistance value Rs and / or a back electromotive force constant value Ke in real time when the motor runs, c, the control system judges whether the temperature of the motor is overhigh or not by comparing the Rsinit with the Rs, or judges whether the temperature of the motor is overhigh or not by comparing the Kinit with the Ke, or judges whether the temperature of the motor is overhigh or not by comparing the Rsinit with the Rs and comparing the Kinit with the Ke at the same time. The method has the advantages that the motor cost can be reduced and the motor power is prevented from being reduced.

Description

Technical Field

[0001] The invention belongs to the field of motors, and in particular relates to a method for non-invasively detecting the temperature of a motor. Background Art

[0002] In motors, high temperatures may cause irreversible demagnetization of magnets and reduce the insulation life of motor windings, leading to premature failure of the motor. Although temperature sensors can be installed in motors to detect temperature-sensitive parts of the motor, installing temperature sensors will not only increase the cost of motor manufacturing, but may also affect the design of the motor, occupy space inside the motor, and thus reduce the power of the motor. Summary of the invention

[0003] The object of the present invention is to provide a method for non-invasively detecting the temperature of a motor. The present invention has the advantages of reducing the cost of the motor and avoiding the reduction of the motor power.

[0004] The technical solution of the present invention is: a method for non-invasively detecting the temperature of a motor, wherein the motor is connected to a control system, and the control system can control the start and stop of the motor, detect the speed of the motor, change the input voltage of the motor, and detect the current of the motor;

[0005] The method comprises the following steps,

[0006] a. Before the control system is turned on and the motor is running, the control system obtains the initial value Rs of the motor winding resistance init and / or the initial value of the back electromotive force constant Ke init ,

[0007] b. After the motor is running, the control system obtains the winding resistance value Rs and / or the back electromotive force constant value Ke of the motor in real time.

[0008] c. The control system compares Rs init and Rs to determine whether the motor temperature is overheated, or by comparing Ke init and Ke to determine whether the motor temperature is overheated, or compare Rs at the same time init and Rs and Ke init And Ke can be used to judge whether the motor temperature is overheated.

[0009] In the above-mentioned method for non-invasively detecting the motor temperature, in step a, the initial parameters of the winding resistance of the motor in the previous operation cycle are used as the initial value of the winding resistance Rs init , or use the initial parameters of the winding resistance of the motor in the current operating cycle as the initial value of the winding resistance Rs init .

[0010] In the aforementioned method for non-invasively detecting the motor temperature, the initial parameters of the winding resistance are calculated based on the input voltage, duty cycle and current of the motor after a small voltage is input when the motor is cooled and stationary. The motor remains stationary when the small voltage is connected.

[0011] In the above-mentioned non-invasive method for detecting the motor temperature, when the control system is turned on, if the motor has not completely cooled down, the initial parameters of the winding resistance of the motor in the previous operation cycle are used as the initial value of the winding resistance Rs. init .

[0012] In the above-mentioned method for non-invasively detecting the motor temperature, in step a, the initial parameters of the back electromotive force constant of the motor in the previous operation cycle are used as the initial value Ke of the back electromotive force constant init , or use the initial parameters of the back EMF constant of the motor's current operating cycle as the initial value of the back EMF constant Ke init .

[0013] In the aforementioned method for non-invasively detecting the motor temperature, the initial parameters of the back electromotive force constant are calculated based on the motor input voltage, duty cycle, current, total resistance and rotation speed.

[0014] Compared with the prior art, the present invention reduces the initial value of the winding resistance Rs init Compare it with the winding resistance value Rs when the motor is running, or by calculating the initial value Ke of the back electromotive force constant init By comparing the back electromotive force constant value Ke when the motor is running, it can be determined whether the motor is overheated, so that there is no need to set a temperature sensor inside the motor, which can reduce the cost of the motor and avoid the reduction of the motor power. Therefore, the present invention has the advantages of reducing the cost of the motor and avoiding the reduction of the motor power.

[0015] In many applications, the exact temperature value of the temperature-sensitive parts of the motor is not that important. Many users actually want to get an early warning when the motor temperature is overheated. Due to the design differences of each motor, the highest temperature may appear in different locations, mainly in the following two locations:

[0016] Winding: For every 10°C increase in temperature, the copper resistivity will increase by approximately 4%.

[0017] Magnets: For every 10°C increase in temperature, the magnetic field of a permanent magnet decreases by approximately 2%.

[0018] Both the winding and the magnet can withstand temperatures above 100°C. When they exceed the specified temperature, the changes in resistance and magnetic field will be more obvious. The present invention is designed based on this principle. In addition to being affected by temperature, the performance parameters of the winding and the magnet will also be affected by aging and manufacturing errors, which can easily lead to false alarms. Based on this, the present invention has also made corresponding optimizations.

[0019] Taking a brushed motor as an example, if the duty cycle, input voltage, and speed remain unchanged, when the temperature rises, the back EMF constant will decrease, thereby increasing the current, but the increase in total resistance will reduce the current, so both the total resistance and the back EMF constant need to be calculated separately.

[0020]

[0021] In the above formula, k e = back EMF constant, Vin = input voltage, D = duty cycle, I DC = Current, R Total = total resistance of the motor and circuit, ω m = motor speed, T = current temperature, init represents the initial state.

[0022] When the motor is at rest, a small voltage is injected and the resistance value can be directly obtained.

[0023]

[0024] When the motor is running, two sets of data are available, and then the substitution method can be used to find the two parameters (R Total and k e ).

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is an operation flow chart of Example 1 of the present invention.

[0027] Figure 2 This is a schematic diagram of the monitoring implementation of the control system of Example 1. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0029] Embodiment 1. A method for non-invasively detecting the temperature of a motor, wherein the motor is connected to a control system, and the control system can control the start and stop of the motor, detect the speed of the motor, change the input voltage of the motor, and detect the current of the motor. The non-invasive method means that when detecting the temperature of the motor, no temperature sensor that needs to invade the inside of the motor is used.

[0030] The method comprises the following steps,

[0031] a. Before the control system is turned on and the motor is running, the control system obtains the initial value Rs of the motor winding resistance init and the initial value of the back electromotive force constant Ke init .

[0032] There are two ways to obtain the above two initial values: 1) Use the initial parameters corresponding to the previous motor operation cycle; 2) Use the initial parameters corresponding to the current cycle (if the motor is already hot when it is turned on, it is still necessary to select the initial parameters of the previous cycle. If the motor is new, the initial parameters corresponding to the current cycle can be used by default).

[0033] Before the motor starts running, the control system starts measuring the winding resistance Rs.

[0034] The control system measures the winding resistance Rs by inputting a small voltage when the motor is stationary to obtain the total resistance Rtotal. Rs is the value obtained by subtracting the resistance of the circuit connected to the motor winding from Rtotal.

[0035] Formula 1:

[0036] In formula 1, R Total represents the total resistance of the motor winding and the connected circuit, Vin is the input voltage, D is the duty cycle, I DC is the current, and j represents the jth cycle (i.e. the current cycle).

[0037] When the initial value is obtained using the second method, the Rs used in the control system init This is the Rs measured when the motor just starts running, that is, Rs init =Rs.

[0038] When the initial value is obtained using the first method, the controller compares the Rs of the previous cycle. init And the Rs measured at this time, if the Rs of the previous cycle init If it is greater than or equal to the Rs measured at this time, the control system uses the Rs measured at this time as the Rs of the current cycle. init .

[0039] b. When the motor runs and reaches a constant speed, the control system obtains the winding resistance value Rs and the back electromotive force constant value Ke in real time. Rs is R Total Subtract the resistance of the circuit to which the motor windings are connected.

[0040] R in step b Total Calculated according to formula 2.

[0041] Formula 2:

[0042] ω m is the motor speed.

[0043] Ke in step b is calculated according to formula 3.

[0044] Formula 3:

[0045] R Total (T) and k e (T) is obtained in real time and will change with temperature.

[0046] When the initial value is obtained using the second method, the Ke used in the control system init It is the k measured when the motor just reaches constant speed. e (initial parameters), namely Ke init =k e .

[0047] When the initial value is obtained using the first method, the controller compares the Ke of the previous cycle. init and k measured when the motor just reaches constant speed e , if the Ke of the previous cycle init Less than or equal to k measured when the motor just reaches constant speed e , the control system uses the k measured when the motor just reaches constant speed e As the current cycle of Ke init .

[0048] c. The control system obtains Ke and Rs in real time and compares them with Ke init and Rs. init Compare, when comparing, in Rs init Increase coefficient K x , K x Greater than 1, in Ke init Increase coefficient K y , K y <1. K x and K y The user can set the value according to the internal material of the motor and the expected temperature difference, but ensure that the motor temperature rise does not exceed the rated temperature.

[0049] When Rs>K x Rs init , or Ke<K y Ke init , the control system considers the motor to be overheated and issues a preload and / or stops the motor from running; you can also set Rs and K x Rs init The relationship between Ke and K y Ke init The relationship between the control system and the motor is considered to be overheated by comprehensively considering the relationship between the control system and the motor to set the conditions under which the control system considers the motor to be overheated.

[0050] About K x and K yIn the control system, for example, when the motor uses copper wire windings and ceramic magnets, if the winding and magnet temperature is to be pre-tightened and the motor is to be paused after rising by 100°C, the parameters can be set as follows: kx=1.4, Ky=0.8.

[0051] If you want to give a warning when the temperature of the winding and magnet rises to 100℃, and then suspend operation after 125℃, kx can be divided into two: kx1 and kx2, Ky can be divided into two: ky1 and ky2, and the parameters can be set as follows:

[0052] kx1=1.4 (warning – temperature increased by 100℃), then kx2=1.5 (pause – temperature increased by 125℃); ky1=0.8 (warning – temperature increased by 100℃), then ky2=0.75 (pause – temperature increased by 125℃).

[0053] In actual use, the control system does not necessarily detect both Ke and Rs in real time at the same time. Single detection is also possible. When single detection is performed, the corresponding control system only needs to obtain Ke accordingly. init or Rs. init ; The present invention can detect the average temperature of motor components; The most suitable application scenario for the present invention is that the motor has more than two loads or runs at a constant speed, such as the motors on elevators or lifting tables, which run at a constant speed and have more than two loads.

Claims

1. A method for non-invasively detecting motor temperature, characterized in that: The motor is connected to a control system, which can control the start and stop of the motor, detect the speed of the motor, change the input voltage of the motor, and detect the current of the motor; The method comprises the following steps, a. Before the control system is turned on and the motor is running, the control system obtains the initial value Rsinit of the motor's winding resistance and / or the initial value Keinit of the back electromotive force constant. b. After the motor is running, the control system obtains the winding resistance value Rs and / or the back electromotive force constant value Ke of the motor in real time. c. The control system determines whether the motor temperature is overheated by comparing Rsinit and Rs, or by comparing Keinit and Ke, or by comparing Rsinit and Rs and Keinit and Ke at the same time.

2. The method for non-invasively detecting the motor temperature according to claim 1, characterized in that: In the step a, the initial parameters of the winding resistance in the previous operation cycle of the motor are used as the initial value of the winding resistance Rsinit, or the initial parameters of the winding resistance in the current operation cycle of the motor are used as the initial value of the winding resistance Rsinit.

3. The method for non-invasively detecting the motor temperature according to claim 2, characterized in that: The initial parameters of the winding resistance are calculated based on the input voltage, duty cycle and current of the motor after a small voltage is input when the motor is cooled and stationary. The motor remains stationary when the small voltage is connected.

4. The method for non-invasively detecting the motor temperature according to claim 3, characterized in that: When the control system is turned on, if the motor has not cooled down completely, the initial parameters of the winding resistance of the motor in the previous operation cycle are used as the initial value of the winding resistance Rsinit.

5. The method for non-invasively detecting the motor temperature according to claim 1, characterized in that: In the step a, the initial parameters of the back electromotive force constant of the previous operation cycle of the motor are used as the initial value Keinit of the back electromotive force constant, or the initial parameters of the back electromotive force constant of the current operation cycle of the motor are used as the initial value Keinit of the back electromotive force constant.

6. The method for non-invasively detecting the temperature of a motor according to claim 5, characterized in that: The initial parameters of the back electromotive force constant are calculated based on the motor input voltage, duty cycle, current, total resistance and rotation speed.

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