Motor overload detection method capable of adjusting curve shape based on heat accumulation

Abstract

The invention relates to the field of motor overload protection, in particular to a heat accumulation-based motor overload detection method with an adjustable curve shape, which comprises the following specific steps of: S1, calculating overload coefficients In and MCA; s2, adjusting a coefficient; s3, judging the size relationship between I and Ir; s4, accumulative or subtractive calculation is carried out; and S5, judging whether the motor is overloaded or not. Compared with a mechanical overload relay, the method has the advantages that the implementation process is simple, corresponding hardware does not need to be additionally purchased, and a motor overload protection function can be realized without increasing hardware cost; compared with a traditional manufacturer overload curve method, the method has the advantages that corresponding functions can be achieved without storing more data points, the overload curve can better meet the actual condition by adjusting the coefficient, and the adjusting mode is convenient and visual.

Description

Technical Field

[0001] The invention relates to the technical field of motor overload protection, and in particular to a motor overload detection method with an adjustable curve shape based on heat accumulation. Background Art

[0002] With the continuous development of the robotics industry, faster beats have become an important reference. Robot motors often need to work under heavier loads or higher speeds. At this time, the heat generated by the motor in a short period of time is much greater than the rated operating conditions. If the overload condition cannot be detected in time, the motor is likely to be directly burned due to the excessive temperature rise caused by the heat, causing the rotor to demagnetize more seriously. Therefore, accurate detection of motor overload conditions is of great significance to improving the working capacity of the motor.

[0003] At present, in practical applications, there are generally two ways to protect motors from overload. One is to use a mechanical overload relay, that is, to disconnect the motor power supply to protect the motor when an overload is detected. The other is to use software detection, that is, to protect the motor from overload by looking up the overload curve based on the inverse time characteristics of current and temperature. However, both methods have defects. The first method has the problem of mechanical failure and increases hardware costs, while the second method stores an overload curve for each motor, which takes up a lot of storage space, and the stored overload curve is not smooth in sections, which will cause large local errors. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a motor overload detection method with an adjustable curve shape based on heat accumulation.

[0005] The motor overload detection method with adjustable curve shape based on heat accumulation has the following specific steps:

[0006] S1. Calculate the overload factor In and MCA: Calculate the overload factor In and MCA based on the two overload points P1 (I1, T1) and P2 (I2, T2). The calculation formula used is:

[0007] [(I1^2-Ir^2) / (I1^2-In^2)]^(T2 / T1)=[(I2^2-Ir^2) / (I2^2-In^2)],

[0008] MCA=T1 / ln[(I1^2-Ir^2) / (I1^2-In^2)];

[0009] Where Ir is the rated current of the motor, ln(x) is the logarithmic function of the exponent e;

[0010] S2. Adjustment Coefficients: After calculating the coefficients In and MCA in step S1, set two adjustment coefficients In_Coef and MCA_Coef to further adjust the coefficients to obtain more realistic values;

[0011] S3. Determine the size relationship between I and Ir;

[0012] S4. Cumulative or subtractive calculation: Perform cumulative addition or subtraction on ΔM until M(k) = 0, where M is the continuous cumulative value of the motor overload;

[0013] S5. Determine whether the motor is overloaded: When M(k) > MCAc, report a motor overload fault; otherwise, continue to accumulate the overload cumulative amount or subtract the load elimination cumulative amount.

[0014] I1 and I2 in step S1 are the currents of the motor in the overload state, and T1 and T2 are the times maintained by the motor under the overload currents respectively.

[0015] The further adjustment in step S2 is obtained through calculation, and the calculation formula is Inc = In * In_Coef, MCAc = MCA * MCA_Coef.

[0016] In step S3, when the motor current I > Ir, the overload cumulative amount of the motor in Δt time is calculated as: ΔM = Δt / ln[(I^2 - Ir^2) / (I^2 - Inc^2)].

[0017] In step S3, when the motor current I < Ir, the load elimination cumulative amount of the motor in Δt time is calculated as: ΔR = Δt / ln[(I^2 - Inc^2) / (I^2 - Ir^2)].

[0018] In step S4, perform cumulative addition on ΔM: M(k + 1) = M(k) + ΔM.

[0019] In step S4, perform subtractive calculation on ΔR: M(k + 1) = M(k) - ΔR.

[0020] The beneficial effects of the present invention are as follows: Compared with using a mechanical overload relay, the implementation process of the present invention is simple, without the need to purchase additional corresponding hardware, and the motor overload protection function can be achieved without increasing the hardware cost; compared with the traditional manufacturer's overload curve method, the corresponding function can be achieved without storing a large number of data points, and the overload curve can be made more in line with the actual situation by adjusting the coefficients, and the adjustment method is convenient and intuitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the drawings and embodiments.

[0022] Figure 1 It is a schematic diagram of the process structure of the present invention;

[0023] Figure 2 It is a schematic diagram of heat accumulation of the motor of the present invention. DETAILED DESCRIPTION

[0024] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below.

[0025] like Figure 1 and Figure 2 As shown, the motor overload detection method with adjustable curve shape based on heat accumulation has the following specific steps:

[0026] S1. Calculate the overload factor In and MCA: Calculate the overload factor In and MCA based on the two overload points P1 (I1, T1) and P2 (I2, T2). The calculation formula used is:

[0027] [(I1^2-Ir^2) / (I1^2-In^2)]^(T2 / T1)=[(I2^2-Ir^2) / (I2^2-In^2)],

[0028] MCA=T1 / ln[(I1^2-Ir^2) / (I1^2-In^2)];

[0029] Where Ir is the rated current of the motor, ln(x) is the logarithmic function of the exponent e;

[0030] exist Figure 2 In the equation, let the mass of the motor be M, the specific heat capacity be C, the heat dissipation coefficient be A, the ambient temperature be T0, and the initial temperature of the motor be T1. When the current I flows through the motor coil, part of the heat generated by the current is absorbed by the motor to increase its own temperature, and the other part of the heat is dissipated into the environment.

[0031] In a short period of time Δt, the heat generated by the current in the motor coil is: Δh1 = I^2*R*Δt, and the heat dissipated by the motor to the environment is: Δh2 = A*(T(k)-T0)*Δt, so the temperature rise of the motor can be calculated as: ΔT(k) = (Δh1-Δh2) / (M*C) = (I^2*R*Δt-A*(T(k)-T0)*Δt) / (M*C). The temperature of the motor at time k is: T(k) = T1+∑ΔT(k-1). Let the total temperature rise of the motor before time k be y = ∑ΔT(k-1), then the equation for temperature rise can be described as: dy / dt+A*y / (M*C) = [A*(T0-T1)+I^2*R] / (M*C). Substituting the initial conditions of the motor into the general solution of temperature change can be obtained as:

[0032] y(t) = [(T0 - T1) + I^2 * R / A] * [1 - e^(-A * t / (M * C)]

[0033] And the final temperature equation of the motor is:

[0034] T(t) = T1 + [(T0 - T1) + I^2 * R / A] * [1 - e^(-A * t / (M * C)]

[0035] It can be seen from the above formula that when the initial temperature of the motor is the same as the ambient temperature, i.e., T0 = T1, the value of the motor temperature when it reaches stability under the rated current Ir is: Tr = T0 + Ir^2 * R / A. Similarly, for the maximum temperature Tn of the motor, there is: Tn = T0 + In^2 * R / A, where In is the current when the motor operates stably at the maximum temperature.

[0036] Define the overload curve as: at the ambient temperature of T0 and the initial temperature of the motor as Tr, when the motor current I > Ir, the time required for the motor temperature to reach the maximum value Tn. Therefore, there is:

[0037] Tn = Tr + [(T0 - Tr) + I^2 * R / A] * [1 - e^(-A * t / (M * C)]

[0038] After substituting the values of Tn and Tr, there is:

[0039] t = MC / A * ln[(I^2 - Ir^2) / (I^2 - In^2)]

[0040] Define the load shedding curve as: at the ambient temperature of T0 and the initial temperature of the motor as Tm, when the motor current I < Ir, the time required for the motor temperature to reach the rated value Tr, that is, Tr = Tn + [(T0 - Tn) + I^2 * R / A] * [1 - e^(-A * t / (M * C)]. After simplification, there is:

[0041] t = MC / A * ln[(I^2 - In^2) / (I^2 - Ir^2)];

[0042] S2. Adjustment coefficients: After calculating the coefficients In and MCA in step S1, set two adjustment coefficients In_Coef and MCA_Coef to further adjust the coefficients to obtain more realistic values;

[0043] S3. Judge the size relationship between I and Ir;

[0044] S4. Cumulative or subtractive calculation; perform cumulative addition or subtraction calculation on ΔM until M(k) = 0, where M is the continuous cumulative value of the motor overload;

[0045] In order to adjust the overload curve conveniently, let MCA = MC / A, and set the adjustment coefficients In_Coef and MCA_Coef to adjust the values ​​of parameters In and MCA respectively, so that the overload curve is more in line with the actual situation, Inc = In*In_Coef, MCAc = MCA*MCA_Coef;

[0046] In actual applications, the motor current I changes all the time, so it is not easy to directly determine whether it is overloaded by directly applying the above formula. Therefore, the above formula can be transformed accordingly:

[0047] MCAc=t / ln[(I^2-Ir^2) / (I^2-Inc^2)]

[0048] Then, within the time Δt, ΔMCAc=Δt / ln[(I^2-Ir^2) / (I^2-Inc^2)], and when ∑ΔMCAc>MCAc, it can be determined that the motor is in an overload state;

[0049] S5. Determine whether the motor is overloaded: when M(k)>MCAc, report a motor overload fault; otherwise, continue to accumulate the overload accumulation or reduce the load elimination accumulation.

[0050] Compared with the use of mechanical overload relays, the present invention has a simple implementation process, does not require the purchase of corresponding hardware, and can achieve the motor overload protection function without increasing hardware costs; compared with the traditional manufacturer's overload curve method, it does not need to store more data points to achieve the corresponding function, and the overload curve can be made more in line with the actual situation by adjusting the coefficient, and the adjustment method is convenient and intuitive.

[0051] I1 and I2 of step S1 are the currents of the motor under the overload state, T1 and T2 are the time the motor maintains under the overload current respectively, and according to the heat accumulation characteristics of the motor overload, a model is established and two overload points are used to determine the overload curve of the motor. There is no need to use a hardware overload relay or store more overload points. The parameter setting is simple and convenient, the overload curve can be flexibly adjusted, the usability is good, and the accuracy of the overload curve is also high.

[0052] The further adjustment of step S2 is obtained by calculation, and the calculation formula is Inc=In*In_Coef, MCAc=MCA*MCA_Coef.

[0053] In the step S3, when the motor current I>Ir, the accumulated overload of the motor in the Δt time is calculated as: ΔM=Δt / ln[(I^2-Ir^2) / (I^2-Inc^2)].

[0054] In the described step S3, when the motor current I < Ir, the cumulative load shedding amount of the motor in Δt time is calculated as: ΔR = Δt / ln[(I^2 - Inc^2) / (I^2 - Ir^2)].

[0055] In the described step S4, ΔM is cumulatively calculated as M(k + 1) = M(k) + ΔM.

[0056] In the described step S4, ΔR is subtracted cumulatively as M(k + 1) = M(k) - ΔR.

[0057] After analyzing the motor heat model of the present invention, it is found that the motor overload and load shedding curves can be determined by the overload coefficients calculated from two overload points. Therefore, the present invention first proposes a method for calculating the overload curve coefficient. By adjusting the overload coefficient using the adjustment parameters, the shape of the overload curve can be conveniently adjusted, so as to design an overload curve that more meets the actual requirements.

[0058] Correspondingly, after calculating the overload coefficient, the present invention proposes a new calculation method for judging motor overload based on heat accumulation. Using this solution, there is no need for a mechanical relay or to look up a table according to the manufacturer's curve. Only by performing corresponding calculations based on the motor current can it be determined in real time whether the motor is in an overload state, which has the characteristics of being simple and easy to use.

[0059] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art of this industry should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A motor overload detection method with an adjustable curve shape based on heat accumulation, characterized in that: The specific steps are as follows: S1. Calculate the overload coefficient In and MCA: Calculate the overload coefficient In and MCA based on two overload points P1(I1, T1) and P2(I2, T2). The formulas used for calculation are: [(I1^2 - Ir^2) / (I1^2 - In^2)]^(T2 / T1) = [(I2^2 - Ir^2) / (I2^2 - In^2)], MCA = T1 / ln[(I1^2 - Ir^2) / (I1^2 - In^2)]; where Ir is the rated current of the motor, and ln(x) is the logarithmic function of the exponential e; S2. Adjustment coefficients: After calculating the coefficients In and MCA in step S1, set two adjustment coefficients In_Coef and MCA_Coef to further adjust the coefficients to obtain more practical values; S3. Judge the size relationship between I and Ir; S4. Cumulative addition or subtraction calculation: Perform cumulative addition or subtraction calculation on ΔM until M(k) = 0, where M is the continuous cumulative value of the motor overload amount; S5. Judge whether the motor is overloaded: When M(k) > MCAc, report the motor overload fault; otherwise, continue to accumulate the overload cumulative amount or subtract the load elimination cumulative amount.

2. The motor overload detection method with adjustable curve shape based on heat accumulation according to claim 1, characterized in that: In step S1, I1 and I2 are the currents of the motor in the overload state, and T1 and T2 are the times maintained by the motor under the overload currents respectively.

3. The motor overload detection method with adjustable curve shape based on heat accumulation according to claim 1, characterized in that: The further adjustment in step S2 is obtained through calculation. The calculation formulas are Inc = In * In_Coef and MCAc = MCA * MCA_Coef.

4. The motor overload detection method with adjustable curve shape based on heat accumulation according to claim 1, characterized in that: In step S3, when the motor current I > Ir, the overload cumulative amount of the motor in Δt time is calculated as: ΔM = Δt / ln[(I^2 - Ir^2) / (I^2 - Inc^2)].

5. The motor overload detection method with adjustable curve shape based on heat accumulation according to claim 1, characterized in that: In step S3, when the motor current I < Ir, the load elimination cumulative amount of the motor in Δt time is calculated as: ΔR = Δt / ln[(I^2 - Inc^2) / (I^2 - Ir^2)].

6. The motor overload detection method with adjustable curve shape based on heat accumulation according to claim 1, characterized in that: In step S4, perform cumulative addition calculation on ΔM: M(k + 1) = M(k) + ΔM.

7. The motor overload detection method with adjustable curve shape based on heat accumulation according to claim 1, characterized in that: In step S4, perform subtraction calculation on ΔR: M(k + 1) = M(k) - ΔR.

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