Method for determining maximum operating speed of electric motor

Abstract

The disclosed method involves determining the maximum operating speed of the electric motor (M) under varying torque conditions, in particular at speeds exceeding its nominal speed. Initially, the electric motor is operated at its maximum speed over different torque values, thereby establishing a data set of actual measurement points. These points show the relationship between the maximum motor speed and the applied torque. A coefficient (COF) that is in the range of 0 to 1 and is dependent on motor characteristics is selected. Two curves are then established: a first for a lower maximum speed, represented by # imgabs0 #, and a second for a torque below a defined limit torque Tlim, represented by # imgabs1 # wherein f is a polynomial function derived from the measurement point. Then, based on whether the torque is greater than or less than Tlim, an appropriate profile is used to determine the maximum motor speed for the given torque.

Description

Technical Field

[0001] The present disclosure relates to a method for determining the maximum operating speed of an electric motor that withstands a defined torque at a speed above the motor's rated speed. More specifically, the present disclosure relates to the field of high-speed lifting. Background Art

[0002] Mechanical and electromechanical lifting devices, including cranes and lifting gears, must be able to lift loads at high speed. This feature is particularly important in situations where time efficiency of materials and rapid movement are critical, such as in industrial environments or construction sites. Conventional high-speed lifting systems rely heavily on electric motors to generate the power required for the lifting process. The performance of these motors, especially their output at different speeds, plays a central role in the overall efficiency of the lifting system.

[0003] Motor manufacturers typically provide information about the rated power and rated speed of the motor. This information is usually given on the electric motor nameplate.

[0004] The rated speed is the speed at which the motor or device is designed to operate optimally and efficiently under a standard load. The rated speed reflects the speed at which the device achieves its expected performance, especially in terms of efficiency and durability. On the other hand, the rated power is the maximum power that the motor or device can continuously deliver during normal operation without the risk of damage or reduced lifespan.

[0005] Conventional systems assume that the motor can deliver its rated power regardless of speed. However, in practice, the motor may not be able to maintain its rated power beyond the rated speed. Therefore, the actual speed of the motor under load does not match the speed calculated using this assumption.

[0006] Therefore, it is necessary to be able to accurately determine the maximum speed that can be achieved when the motor is subjected to a defined load (i.e., defined torque), even at high operating speeds (i.e., especially when the motor speed is above its rated speed). Summary of the Invention

[0007] To this end, the present disclosure relates to a method for determining the maximum operating speed of an electric motor that withstands a defined torque at a speed above the motor's rated speed, the method comprising:

[0008] operating the motor at its maximum speed for different torque values and determining the corresponding maximum motor speed for each torque value to obtain a set of actual measurement points that represent the evolution of the maximum motor speed as a function of the torque applied to the motor,

[0009] - selecting, for example according to the motor characteristics, a coefficient COF between 0 and 1,

[0010] - For low maximum speeds, determine the torque T corresponding to the actual measurement point meas The maximum speed of the function Ω ref The first curve of the evolution is

[0011] Definition, where Ω ref is the maximum speed, P nom is the rated power, and T meas is the measured torque of the motor,

[0012] - defining a limit torque corresponding to the torque at the intersection of the first curve and a set of measurement points

[0013] T lim ,

[0014] -For below T lim The measured torque T meas , determine the measured torque T corresponding to the actual measurement point meas The maximum speed of the function Ω ref The second curve of the evolution of Definition, where f is a polynomial function, the function f is determined according to the measurement points,

[0015] -For a limited torque T, if T ≥ T lim , then determine the corresponding maximum motor speed from the equation of the first curve, if T≤T lim , then determine the corresponding maximum motor speed from the equation of the second curve.

[0016] The maximum operating speed of an electric motor is the highest speed at which the motor can operate safely and efficiently under specific circumstances, including varying loads or torques. Unlike the rated speed, which is the optimal speed of the motor under standard load conditions, the maximum operating speed can vary depending on factors such as the applied load, motor design, and operating conditions. In practical applications, especially in scenarios such as high-speed lifting, this speed is critical because it determines the motor's ability to handle higher-than-normal speeds and loads, directly affecting the efficiency and effectiveness of performance in demanding situations.

[0017] The limited torque of an electric motor refers to the specific amount or value of rotational force that the motor is expected to produce or handle under certain conditions. Torque refers to a characteristic of motor performance that refers to the force that the motor can apply to a rotating object or system.

[0018] The relationship between torque, speed, and power can be expressed by the equation: Power = Torque * Speed. The classical unit of torque is Newton-meter (Nm). Speed is usually measured in revolutions per minute (RPM). The classical unit of power is watt (W). The formula for calculating power in an electric motor, considering these units: Factor is used to convert the rotational speed from RPM to radians per second, which aligns with the units used to calculate power in watts.

[0019] In the above equation the speed Ω ref is expressed in radians per second (rad / s), the power P nom is expressed in watts (W), and the torque T meas is expressed in Newton-meters (Nm).

[0020] Actual measurement points refer to specific data points collected from real-world tests or the operation of an electric motor. The actual measurement points show how the maximum speed of the motor changes in response to different levels of the applied torque. These measurement points are collected by subjecting the electric motor to varying torque conditions and observing the corresponding speeds obtained. This data is used to understand the performance characteristics, particularly its ability to maintain or reach a specific speed under varying loads. The relationship between torque and speed captured through these measurements helps to construct a detailed and practical performance profile of the motor, which can be used to design effective and reliable motor drive systems, especially in applications where precise control of speed and torque is required.

[0021] Motor characteristics refer to the specific attributes and performance parameters of an electric motor that define its operating capabilities and efficiency. Among other things, these characteristics can include the rated power and speed of the motor, torque-speed curve, efficiency, power factor, starting torque, and thermal limits, etc. They determine how the motor behaves under various load conditions, its power consumption, and its overall suitability for a particular application. Motor characteristics can be provided by the manufacturer of the motor.

[0022] The determination of the first curve can consider the actual measurement points for low maximum speeds, i.e., for maximum speeds Ω ref .

[0023] Once the first curve is determined, the limit torque T corresponding to the torque at the intersection of the first curve and this set of measurement points is defined lim .

[0024] This can be achieved, for example, by interpolating or regressing the measurement points to obtain a curve, called the descriptive curve, that describes the evolution of the actual measurement points and by determining the intersection of the first curve and the descriptive curve.

[0025] Interpolation involves creating a curve or function that passes exactly through all given data points. This assumes that the data is precise enough and seeks to produce values consistent with the given set.

[0026] Such interpolation can be, for example, linear or polynomial. Linear interpolation is the simplest form of interpolation and involves drawing a straight line between two known data points and using that line to estimate values between those points. Polynomial interpolation is a more complex method where a polynomial (of order 2 or higher) is fitted to the data, enabling better estimation in cases where the relationship between the points is not linear.

[0027] In regression analysis, the fitted line or curve represents the best estimate of the relationship between variables, minimizing the overall error or distance between the data points and the line or curve. For example, the regression can be linear or polynomial.

[0028] Alternatively, the intersection point can be estimated from the unique measurement points, for example, by choosing one of the actual measurement points as the intersection point, without determining the descriptive curve that fits these points. This implies an acceptable approximation in this process.

[0029] The function f can be a polynomial function, such as a first-order polynomial function or a second-order polynomial function.

[0030] The function f can be a function that defines a Bézier curve.

[0031] The function that defines a Bézier curve is a mathematical representation used to model smooth curves that can be easily scaled and manipulated. The basic idea behind a Bézier curve is to use a set of control points to define the shape of the curve. This function uses these control points to produce a smooth and continuous parametric curve. The function of a Bézier curve is a polynomial function, where the order of the polynomial is one less than the number of control points. For example, a cubic Bézier curve has a third-order polynomial.

[0032] In a Bézier curve, the curve itself generally does not pass through the intermediate control points. The role of these points is more similar to that of magnets pulling the curve in certain directions to shape it.

[0033] The method may further include:

[0034] - Determining an initial torque T0, the maximum speed Ω of the motor ref Starting from this initial torque and decreasing, when the torque applied to the motor is less than the initial torque, the maximum speed is constant.

[0035] - If the defined torque T ≤ T0, defining the maximum motor speed Ω that can withstand the defined torque ref Equal to the constant maximum value Ω max .

[0036] In other words, for a defined torque T, the corresponding maximum speed can be determined by the following equation:

[0037] If T ≥ T lim , then

[0038] If T0 ≤ T ≤ T lim , with the above function f (first-order polynomial function), then

[0039] If T ≤ T0, then Ω = Ω max .

[0040] In any case, Ω can be bounded by Ω max (i.e., it can not exceed Ω max ).

[0041] The present disclosure also relates to a computer program comprising instructions for implementing the above method when the program is executed by a processor.

[0042] The present disclosure also relates to a non-transitory computer-readable recording medium having recorded thereon a program which, when used, implements the above method when executed by a processor. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Further features, details and advantages will become clear from the following detailed description and from the analysis of the drawings, in which:

[0044] Figure 1 A lifting device comprising an electric motor supporting a load is schematically shown,

[0045] Figure 2 The various stages of the process described herein are schematically shown,

[0046] Figure 3 is a graph showing the evolution of the maximum speed of an electric motor as a function of the torque supported by the motor. DETAILED DESCRIPTION

[0047] Figure 1 A lifting device for a crane, for example, comprising a load-bearing electric motor is shown. The motor includes a stator and a rotor coupled to a shaft, and the rotational movement of the shaft moves the load. The speed at which the load is moved is linked to the rotational speed of the motor shaft, also known as the motor speed. Thus, during operation, the motor supports a torque, the value of which depends on the load to be moved.

[0048] Figure 2 A method for determining the maximum operating speed of an electric motor supporting a defined torque at a speed above the rated speed of the motor is schematically shown.

[0049] Figure 3Shows the evolution of the maximum speed of a motor as a function of the torque applied to the motor. More specifically, this evolution is represented by a series of measurement points collected from experiments conducted on a lifting device or a test bench, both including motors to which a load has been applied. The graph provides a detailed view of how the maximum speed of the motor varies in response to different torque levels.

[0050] This variation in the maximum speed reveals three different regions, a first region where the maximum speed is substantially constant and equal to Ω max (T meas ≤ T0), a second region where the speed decreases with torque (T0 ≤ T meas ≤ T lim ), and a third region where the speed also decreases with torque but faster than in the second region (T meas ≥ T lim ).

[0051] In the proposed method, for different torque values (i.e., with different loads), the motor runs at its maximum speed ( Figure 3 S1 in

[0052] ), and for each torque value, the corresponding maximum motor speed is determined to obtain a set of actual measurement points representing the evolution of the maximum motor speed as a function of the torque applied to the motor.

[0053] To this end, the load can be gradually increased or decreased incrementally, for example. The torque applied to the motor and the maximum speed can be measured or determined directly or indirectly, for example by calculation from another measurement.

[0054] Then, a coefficient COF (S2) between 0 and 1 is selected, for example, based on the motor characteristics. meas For low maximum speeds (S3), a first curve C1 representing the evolution of the maximum speed Ω ref as a function of the measured torque T corresponding to the actual measurement points can then be determined. The first curve can be defined by ref where Ω nom is the maximum speed, P meas is the rated power, and T

[0055] Then, the limit torque T iim corresponding to the torque at the intersection of the first curve and the set of measurement points can be determined (S4).

[0056] Then, a second curve C2 can be determined (S5), which represents the evolution of the maximum speed Ω meas as a function of the measured torque T ref corresponding to the actual measurement points, the measured torque T meas including values between T0 and Tlim between which the second curve is defined by where f is a polynomial function, and the function f is determined from measurement points.

[0057] The function f is a polynomial function, for example, a first-order polynomial function.

[0058] In this case, the equation can be changed to where a and b are scalars. In this case, in order to determine the second curve, the values of the scalars a and b need to be determined first.

[0059] To this end, one option can be to solve a system of two equations with two unknowns by selecting two measurement points defined by the coordinates (Ω ref1 ; T meas1 ) and (Ω ref2 ; T meas2 ), and then the equation can be defined as follows:

[0060] (Equation 1):

[0061] (Equation 2):

[0062] The values of Ω ref1 , T meas1 , Ω ref2 , T meas2 , COF, and P nom are known, and a and b can be determined.

[0063] Alternatively, a and b can be determined by the following equation:

[0064]

[0065] where FRS is the rated frequency of the motor. The rated frequency of the motor refers to the specific frequency at which the motor is designed to operate most efficiently and effectively. This frequency is usually specified by the manufacturer (e.g., on the nameplate of the motor) and is closely related to the power supply standard of the area where the electric motor is intended to be used.

[0066] Then, for a defined torque T, if T ≥ T lim , the corresponding maximum motor speed can be determined from the equation of the first curve (S6), and if T0 ≤ T ≤ T lim , the corresponding maximum motor speed can be determined from the equation of the second curve.

[0067] In other words, for a defined torque T, the corresponding maximum speed can be determined by the following equation:

[0068] If T ≥ Tlim , then If T0 ≤ T ≤ T lim , with the above function f (first-order polynomial function), then If T ≤ T0, then Ω = Ω max .

Claims

1. A method of determining a maximum operating speed of an electric motor (M) subjected to a limited torque at a speed higher than the rated speed of the motor (M), comprising: - operating (S1) the motor at its maximum speed for different torque values ​​and determining for each torque value the corresponding maximum motor speed in order to obtain a set of actual measurement points representing the evolution of the maximum motor speed as a function of the torque applied to the motor, - selecting ( S2 ) a coefficient COF between 0 and 1, for example depending on the characteristics of the motor, - For low maximum speeds, determine (S3) the measured torque T corresponding to the actual measurement point ,eas The maximum speed of the function Ω ref The first curve of the evolution is Definition, where Ω ref is the maximum speed, P nom is the rated power, T meas is the measured torque of the motor, - defining (S4) a limit torque T corresponding to the torque at the intersection of said first curve and said set of measurement points li, , -For measuring torque T meas Lower than T lim , determining (S5) represents the measured torque T corresponding to the actual measurement point meas The maximum speed of the function Ω ref The second curve of the evolution of the first curve is Definition, where f is a polynomial function, the function f is determined according to the measurement points, -For limited torque T, if T ≥ T lim , then determine (S6) the corresponding maximum motor speed from the equation of the first curve, and if T≤T lim , then determine the corresponding maximum motor speed from the equation of the second curve. The method according to claim 1 , wherein the function f is a polynomial function. The method according to claim 2 , wherein the function f is a function defining a Bezier curve.

4. The method according to any one of the preceding claims, wherein the method further comprises: - Determine the initial torque T0, the maximum speed Ω of the motor ref decreasing from the initial torque, when the torque applied to the motor is less than the initial torque, the maximum speed is constant, - If the limited torque T≤T0, then the maximum motor speed Ω that can withstand the limited torque is limited ref Equal to a constant maximum value Ω max .

5. A computer program comprising instructions for implementing the method according to any one of the preceding claims when the program is executed by a processor. 6 . A non-transitory computer-readable recording medium having recorded thereon a program for implementing the method according to claim 1 when executed by a processor.

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