Method for measuring mechanical losses of an electric machine

Abstract

The application discloses a kind of motor mechanical loss measurement methods, comprising: S1.motor is made from the set speed to carry out no-load free running;S2.collection motor in no-load free running state under the speed and speed corresponding time;S3.to speed and speed corresponding time are data fitting, obtain the function of speed and time;S4.to the function of speed and time is time derivation, obtain the change relation of acceleration and time;S5.according to the change relation of acceleration and time, construct the function of friction resistance moment and speed;S6.speed is substituted into the function of friction resistance moment and speed, obtain the friction resistance moment corresponding to speed;Speed and friction resistance moment corresponding to speed are substituted into motor mechanical loss power calculation formula as parameter, obtain the mechanical loss power of motor.The application can realize low cost, simple, high-precision motor mechanical loss measurement.

Description

Technical Field

[0001] This invention relates to the field of electric motors for new energy vehicles, and specifically to a method for measuring the mechanical losses of electric motors. Background Technology

[0002] As the energy conversion device in new energy vehicles, the electric motor plays a crucial role in the conversion between electrical energy and mechanical energy. Motor efficiency is one of the key indicators for evaluating its performance. Motor efficiency losses mainly originate from various losses during motor operation. Among these, mechanical losses have a significant impact on optimizing motor performance and improving efficiency. Motor mechanical losses primarily include wind friction loss, oil friction loss, bearing loss, and other frictional losses. These losses are typically reduced through measures such as lubrication, selecting high-quality, low-friction bearings, improving the motor's dimensional and positional tolerances, and ensuring assembly quality.

[0003] The current main method for measuring the mechanical losses of electric motors is as follows: First, the overall loss of the motor is measured. Then, electrical losses, stray losses, and other losses are subtracted from the overall loss, and the remaining part is the mechanical loss. This test method inputs a stable electrical power to the motor and simultaneously uses a high-precision torque sensor to measure the output mechanical power of the motor shaft. The difference between the two is the total loss of the motor. Then, other losses besides mechanical losses are calculated theoretically or empirically. Subtracting the calculated other losses from the total loss completely isolates the mechanical loss. This common approach has the following problems: 1. It can only obtain the loss at discrete speed points; 2. The calculation of other losses relies on theoretical or empirical formulas, which differ from the actual product conditions, and the accuracy and precision of the calculation cannot be guaranteed, resulting in a large error in the isolated mechanical loss.

[0004] Therefore, a method for measuring the mechanical losses of motors is needed to solve the above problems. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to overcome the defects in the prior art and provide a method for measuring the mechanical loss of motors, which can achieve low-cost, simple and high-precision measurement of motor mechanical loss.

[0006] The method for measuring the mechanical loss of an electric motor according to the present invention includes the following steps:

[0007] S1. This allows the motor to coast freely under no-load starting from the set speed;

[0008] S2. Collect the motor speed and the corresponding time when the motor is in a no-load free-slip state;

[0009] S3. Perform data fitting on the rotational speed and the corresponding time to obtain the relationship function between rotational speed and time;

[0010] S4. Take the time derivative of the function relating rotational speed and time to obtain the relationship between acceleration and time;

[0011] S5. Based on the relationship between acceleration and time, construct a function relating frictional resistance torque to rotational speed;

[0012] S6. Substitute the rotational speed into the relationship function between frictional resistance torque and rotational speed to obtain the frictional resistance torque corresponding to the rotational speed; substitute the rotational speed and the frictional resistance torque corresponding to the rotational speed as parameters into the motor mechanical loss power calculation formula to obtain the motor mechanical loss power.

[0013] Furthermore, before the motor is allowed to coast freely under no-load conditions, the rotor magnets of the motor are treated to be demagnetized.

[0014] Furthermore, the relationship between rotational speed and time is determined using the following formula:

[0015] w = A + B*t + C*t 2 +D*t 3 ;

[0016] Where w is the rotational speed, A, B, C, and D are all fitting coefficients, and t is time.

[0017] Furthermore, the relationship between acceleration and time is determined using the following formula:

[0018] a=dw / dt=B+2C*t+3D*t 2 ;

[0019] Where a is acceleration, w is rotational speed, and t is time.

[0020] Furthermore, based on the relationship between acceleration and time, a function relating frictional resistance torque and rotational speed is constructed, specifically including:

[0021] S51. Construct the dynamic differential equations for the motor's no-load coasting:

[0022] T d =-J*dw / dt=K0+K1*w+K2*w 2 ;

[0023] Among them, T d , where is the frictional resistance torque, J is the moment of inertia of the motor, K0, K1 and K2 are all undetermined coefficients, w is the rotational speed and t is the time;

[0024] S52. The dynamic differential equation of the motor during unloaded coasting is derived to obtain the acceleration a′ of the motor during unloaded free coasting:

[0025] a′=dw / dt=-(K0+K1*w+K2*w 2 ) / J;

[0026] S53. Substituting the acceleration a′ into the relationship between acceleration and time, we obtain the following equation:

[0027] a=a′=B+2C*t+3D*t 2 =-(K0+K1*w+K2*w) 2 ) / J;

[0028] S54. Substitute the rotation speed and the time corresponding to the rotation speed collected in step S2 into the formula described in step S53, and solve to obtain the coefficient value K′0 corresponding to K0, the coefficient value K′1 corresponding to K1, and the coefficient value K′2 corresponding to K2;

[0029] S55. Substituting K′0, K′1, and K′2 into the dynamic differential equation for the motor's no-load coasting, we obtain the relationship function between the frictional resistance torque and the rotational speed:

[0030] T d =K′0+K′1*w+K′2*w 2 .

[0031] Furthermore, the formula for calculating the mechanical loss power of the motor is determined based on the following formula:

[0032] P = T d *w / τ;

[0033] Where P is the mechanical loss power of the motor, and T d Let w be the frictional resistance torque, w be the rotational speed, and τ be a constant.

[0034] Furthermore, a tow-and-rotor assembly is used to enable the motor to reach the set speed;

[0035] The towing assembly includes a test bench for towing the motor to a set speed; the output shaft of the test bench is connected to the motor shaft of the motor.

[0036] Furthermore, the output shaft of the test bench is connected to the motor shaft of the motor via a coupling disconnection device.

[0037] The beneficial effects of this invention are as follows: The method for measuring the mechanical loss of a motor disclosed in this invention has a simple experimental data processing process. The mechanical loss of the motor under different speed conditions can be obtained through a single test. Only the mechanical loss of the motor is involved in the test; there are no other losses such as electrical losses or stray losses. Specifically, the beneficial effects are: 1. No high-precision torque sensors or other testing equipment are required, and the testing method is simple; 2. The mechanical loss of the motor is calculated based on the motor's speed decay, and normal speed fluctuations have little impact on data processing; 3. The mechanical loss at any speed point within the test speed range can be obtained through testing, eliminating the need for data fitting; 4. No other losses are involved in the testing process, preventing calculation errors in mechanical loss due to theoretical calculation errors. Attached Figure Description

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0039] Figure 1 This is a schematic diagram of the measurement method of the present invention;

[0040] Figure 2 This is a schematic diagram showing the connection between the test bench and the motor of the present invention;

[0041] Figure 3 This is a schematic diagram of the fitting curve of the relationship between rotational speed and time according to the present invention. Detailed Implementation

[0042] The present invention will be further described below with reference to the accompanying drawings, as shown in the figures:

[0043] The method for measuring the mechanical loss of an electric motor according to the present invention includes the following steps:

[0044] S1. This allows the motor to coast freely under no-load starting from the set speed;

[0045] S2. Collect the motor speed and the corresponding time when the motor is in a no-load free-slip state;

[0046] S3. Perform data fitting on the rotational speed and the corresponding time to obtain the relationship function between rotational speed and time;

[0047] S4. Take the time derivative of the function relating rotational speed and time to obtain the relationship between acceleration and time;

[0048] S5. Based on the relationship between acceleration and time, construct a function relating frictional resistance torque to rotational speed;

[0049] S6. Substitute the rotational speed into the relationship function between frictional resistance torque and rotational speed to obtain the frictional resistance torque corresponding to the rotational speed; substitute the rotational speed and the frictional resistance torque corresponding to the rotational speed as parameters into the motor mechanical loss power calculation formula to obtain the motor mechanical loss power.

[0050] In this embodiment, in step S1, a towing assembly is used to make the motor reach a set speed; such as Figure 2 As shown, the towing assembly includes a test bench for towing a motor to a set speed; the output shaft of the test bench is connected to the motor shaft of the motor. The output shaft of the test bench is connected to the motor shaft of the motor via a coupling disconnection device. The test bench uses existing equipment with torque transmission capabilities, such as a servo motor or electric motor; the coupling disconnection device uses existing disconnection equipment with detachable functionality, which will not be described in detail here.

[0051] The motor under test is towed to a set speed by a test bench. This set speed is the maximum speed that meets the actual operating conditions for measuring mechanical losses. The connection between the test bench and the motor is then disconnected, allowing the motor to glide freely under no-load.

[0052] In this embodiment, the rotor magnets of the motor are demagnetized before the motor coasts freely under no-load conditions. This ensures that the motor does not generate electromagnetic torque during the no-load coasting process, thereby avoiding the additional losses caused by electromagnetic torque.

[0053] In this embodiment, in step S2, the motor rotor speed and the corresponding time are recorded by the motor resolver sensor until the motor rotor speed decays to 0; thus providing data support for data fitting of the speed and the corresponding time.

[0054] In this embodiment, in step S3, as follows: Figure 3 As shown, data fitting was performed on the rotational speed and the corresponding time to obtain the relationship curve between rotational speed and time;

[0055] The relationship between rotational speed and time is determined using the following formula:

[0056] w = A + B*t + C*t 2 +D*t 3 ;

[0057] Where w is the rotational speed, A, B, C, and D are all fitting coefficients, and t is time.

[0058] In this embodiment, in step S4, the time derivative of the function relating rotational speed and time is calculated to obtain the relationship between acceleration and time.

[0059] The relationship between acceleration and time can be determined using the following formula:

[0060] a=dw / dt=B+2C*t+3D*t 2 ;

[0061] Where a is the motor's acceleration under no-load free gliding, w is the rotational speed, and t is the time.

[0062] In this embodiment, step S5 involves constructing a function relating frictional resistance torque to rotational speed based on the relationship between acceleration and time. Specifically, this includes:

[0063] S51. Based on the force analysis of the motor during the no-load free coasting process, construct the dynamic differential equation of the motor during no-load coasting:

[0064] T d =-J*dw / dt=K0+K1*w+K2*w 2 ;

[0065] Among them, T d , where is the frictional resistance torque, J is the moment of inertia of the motor, K0, K1 and K2 are all undetermined coefficients, w is the rotational speed and t is the time;

[0066] S52. The dynamic differential equation of the motor during unloaded coasting is derived to obtain the acceleration a′ of the motor during unloaded free coasting:

[0067] a′=dw / dt=-(K0+K1*w+K2*w 2 ) / J;

[0068] S53. Combining the dynamic differential equations of the motor under no-load coasting and the relationship between acceleration and time, substituting the acceleration a′ into the relationship between acceleration and time, we obtain the following equation:

[0069] a=a′=B+2C*t+3D*t 2 =-(K0+K1*w+K2*w) 2 ) / J;

[0070] S54. Substitute the rotation speed and the time corresponding to the rotation speed collected in step S2 into the formula described in step S53, and solve to obtain the coefficient value K′0 corresponding to the undetermined coefficient K0, the coefficient value K′1 corresponding to the undetermined coefficient K1, and the coefficient value K′2 corresponding to the undetermined coefficient K2.

[0071] S55. Substituting K′0, K′1, and K′2 into the dynamic differential equation for the motor's no-load coasting, we obtain the relationship function between the frictional resistance torque and the rotational speed:

[0072] T d =K′0+K′1*w+K′2*w 2 .

[0073] In this embodiment, in step S6, by substituting different rotational speeds into the relationship function between frictional resistance torque and rotational speed, the frictional resistance torque at different rotational speeds can be obtained.

[0074] By substituting the rotational speed and the corresponding frictional resistance torque into the formula for calculating the mechanical loss power of the motor, the mechanical loss power of the motor can be obtained.

[0075] The formula for calculating the mechanical loss power of a motor is determined based on the following formula:

[0076] P = T d *w / τ;

[0077] Where P is the mechanical loss power of the motor, and T d Let w be the frictional resistance torque, w be the rotational speed, and τ be a constant. In this embodiment, τ is taken as 9550. By substituting different rotational speeds and the frictional resistance torques at different rotational speeds into the above mechanical loss power calculation formula, the motor mechanical loss power at different rotational speeds can be obtained.

[0078] The method for measuring the mechanical loss of a motor according to the present invention does not require additional high-precision sensors or other equipment. The testing method is simple and easy to use, and the testing equipment is low in cost. No other losses are involved in the testing process, so there is no need to consider the separation of other losses, resulting in small calculation errors for mechanical loss. The mechanical loss value at any speed point can be obtained through testing, without the need to adjust the speed and repeatedly test the loss at different points.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for measuring the mechanical loss of an electric motor, characterized in that: Includes the following steps: S1. This allows the motor to coast freely under no-load starting from the set speed; S2. Collect the motor speed and the corresponding time when the motor is in a no-load free-slip state; S3. Perform data fitting on the rotational speed and the corresponding time to obtain the relationship function between rotational speed and time; S4. Take the time derivative of the function relating rotational speed and time to obtain the relationship between acceleration and time; S5. Based on the relationship between acceleration and time, construct a function relating frictional resistance torque to rotational speed, specifically including: S51. Construct the dynamic differential equations for the motor's no-load coasting: T d =-J*dw / dt=K0+K1*w+K2*w 2 ; Among them, T d , where is the frictional resistance torque, J is the moment of inertia of the motor, K0, K1 and K2 are all undetermined coefficients, w is the rotational speed and t is the time; S52. The dynamic differential equation of the motor during unloaded coasting is derived to obtain the acceleration of the motor during unloaded free coasting. : =dw / dt=-(K0+K1*w+K2*w 2 ) / J; S53. Acceleration Substituting the equations into the relationship between acceleration and time, we obtain the following formula: a= =B+2C*t+3D*t 2 =-(K0+K1*w+K2*w 2 ) / J; S54. Substitute the rotational speed and the corresponding time collected in step S2 into the formula described in step S53, and solve for the coefficient value corresponding to K0. The coefficient value corresponding to K1 and the coefficient value corresponding to K2 ; S55. Will , as well as Substituting into the dynamic differential equation of the motor's no-load coasting, we obtain the relationship function between the frictional resistance torque and the rotational speed: T d = + *w+ *w 2 ; S6. Substitute the rotational speed into the relationship function between frictional resistance torque and rotational speed to obtain the frictional resistance torque corresponding to the rotational speed; substitute the rotational speed and the frictional resistance torque corresponding to the rotational speed as parameters into the motor mechanical loss power calculation formula to obtain the motor mechanical loss power.

2. The method for measuring the mechanical loss of a motor according to claim 1, characterized in that: Before the motor is allowed to coast freely under no-load conditions, the rotor magnets of the motor are treated to be demagnetized.

3. The method for measuring the mechanical loss of a motor according to claim 1, characterized in that: The relationship between rotational speed and time is determined using the following formula: w=A+B*t+C*t 2 +D*t 3 ; Where w is the rotational speed, A, B, C, and D are all fitting coefficients, and t is time.

4. The method for measuring the mechanical loss of an electric motor according to claim 3, characterized in that: The relationship between acceleration and time can be determined using the following formula: a=dw / dt=B+2C*t+3D*t 2 ; Where a is acceleration, w is rotational speed, and t is time.

5. The method for measuring the mechanical loss of an electric motor according to claim 1, characterized in that: The formula for calculating the mechanical loss power of a motor is determined based on the following formula: P=T d *w / ; Where P is the mechanical loss power of the motor, and T d The frictional resistance torque is denoted by ω, and the rotational speed is ω. It is a constant.

6. The method for measuring the mechanical loss of an electric motor according to claim 1, characterized in that: A towing assembly is used to enable the motor to reach the set speed; The towing assembly includes a test bench for towing the motor to a set speed; the output shaft of the test bench is connected to the motor shaft of the motor.

7. The method for measuring the mechanical loss of an electric motor according to claim 6, characterized in that: The output shaft of the test bench is connected to the motor shaft of the motor via a coupling disconnection device.

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