Method for calculating initial rotating speed of cooling fan of new energy automobile

Abstract

The invention relates to a new energy automobile cooling fan initial rotating speed calculation method. The method comprises the steps that a critical line counter electromotive force peak value is set; and whether the line counter electromotive force peak value is larger than or equal to the critical line counter electromotive force peak value for the first time is determined, if yes, each half-cycle time t is obtained from the second half cycle, and the initial rotating speed of the cooling fan is calculated according to the half-cycle time t. According to the method for calculating the initial rotating speed of the cooling fan of the new energy automobile, the rotating speed is calculated through the period of the line counter electromotive force and the number of pole pairs of the motor and is not affected by temperature; according to the new energy automobile cooling fan initial rotating speed calculation method, the rotating speed is calculated in each half cycle, the rotating speed of the motor is fed back in real time, the correct rotating speed can be calculated in time after the rotating speed fluctuates, and an alarm can be given in time when the rotating speed is too high.

Description

Technical Field

[0001] The present invention relates to the field of fan technology, and in particular to a method for calculating the initial rotational speed of a cooling fan of a new energy vehicle. Background Art

[0002] In new energy vehicles, the cooling fan is one of the core components of the thermal management system. It is mainly used to regulate the temperature of the battery pack, motor and other core components to ensure that the vehicle runs efficiently while avoiding the risk of overheating.

[0003] For fan motors with sinusoidal back EMF waveforms, when the fan rotation is controlled using position-free control, it is necessary to estimate the motor speed and rotor position to accurately control the fan motor. This control strategy requires the fan rotor to be stationary when the fan starts, otherwise it will easily fail to start. When the vehicle is in operation, the fan can easily reach an initial speed before being controlled due to airflow or mechanical vibration. Therefore, the fan needs to be stationary before controlling the fan to start. There are currently two common ways to stationary the fan:

[0004] 1. Before starting, a static magnetic field of a specific amplitude (usually requiring a high current) is injected into the fan motor windings, using electromagnetic torque to suppress rotor motion. This static magnetic field requires a high current and is suitable for low speeds. However, this solution's parameters (current amplitude, duration, etc.) are fixed values ​​and cannot adapt to varying initial speeds, making the motor prone to startup failure.

[0005] 2. Before starting, the speed is determined and different static strategies are adopted according to the speed. When the speed is low, the ASC short-circuit shutdown is used. By short-circuiting the three upper bridge power devices or the three lower bridge power devices of the inverter simultaneously, a static magnetic field is formed to stop the fan. When the speed is high, the fan is stopped by free stop.

[0006] There are currently two common methods for calculating the fan speed before startup:

[0007] 1. For non-position control strategies, the opposite potential peak method is usually used to calculate the fan speed before startup. E is the peak value of the opposite electromotive force, ω represents the electrical angular velocity of the motor, represents the motor flux. This method requires the peak value of the reverse EMF for each cycle. Furthermore, when the motor temperature is high, the flux will also change, requiring proportional adjustment of the flux. The flux is significantly affected by changes in ambient temperature. When the ambient temperature is high, the flux will decrease. Given the same reverse EMF peak, the higher the temperature, the higher the calculated speed will be, and this will not match the actual situation. Furthermore, since many motors are star-connected and lack a neutral point, the reverse EMF cannot be measured and must be calculated using the line back EMF, which is a complex calculation process.

[0008] 2. Use the position sensor to calculate the speed, and you can get the speed position θ in real time. Calculate the current speed. However, using a position sensor to calculate speed does not constitute a position-free control strategy. Using a position sensor to calculate speed has many drawbacks. Installing the position sensor in the controller increases the size of the controller, taking up space, and increasing space is difficult when the controller is compact. Installing the position sensor in the motor also takes up additional space and increases the size of the motor. Furthermore, excessive motor speeds can burn out the position sensor, and installing a position sensor also increases costs. Summary of the Invention

[0009] To solve at least some of the above problems in the prior art, the present invention provides a method for calculating the initial speed of a cooling fan of a new energy vehicle, comprising:

[0010] Setting the critical line back EMF peak value; and

[0011] Check whether the line back EMF peak value is greater than or equal to the critical line back EMF peak value for the first time. If so, obtain each half cycle time t starting from the second half cycle and calculate the initial speed of the cooling fan based on the half cycle time t.

[0012] Furthermore, a critical line back electromotive force peak value is set according to a critical speed value, and the critical line back electromotive force peak value is greater than zero.

[0013] Furthermore, the critical speed value is set, and the critical line back EMF peak value is calculated according to the following formula:

[0014] ω=2πnp / 60,

[0015] Where E is the peak value of the opposite electromotive force, ω represents the electrical angular velocity of the motor, Represents the motor flux, E 线 is the line back EMF peak value, n is the speed, and p is the number of motor pole pairs.

[0016] Furthermore, if the absolute value of the line back EMF peak value is less than the critical line back EMF peak value, the rotation speed is determined to be 0.

[0017] Furthermore, if the line back EMF peak value is greater than or equal to the critical line back EMF peak value for the first time, the second half cycle time is the time it takes for the line back EMF to decrease from 0 and then increase back to 0.

[0018] Furthermore, a counter is used to calculate each half cycle time t, including:

[0019] When each half cycle starts, the counter count value increases by 1, and when the line back EMF exceeds 0, the counter stops counting;

[0020] The count value is multiplied by the unit time to obtain the half-cycle time t, and the initial speed of the cooling fan is calculated according to the half-cycle time t. Then the counter is reset to zero and the next round of counting begins.

[0021] Furthermore, the unit time is 125 us.

[0022] Furthermore, the initial speed of the cooling fan is calculated based on the half-cycle time t:

[0023] Period T = 2t, frequency f = 1 / T, speed n = 60f / p, where p is the number of motor pole pairs.

[0024] The present invention has at least the following beneficial effects:

[0025] (1) The method for calculating the initial speed of the cooling fan of a new energy vehicle of the present invention uses the period of the line back electromotive force and the number of pole pairs of the motor to calculate the speed, which is not affected by temperature;

[0026] (2) The method for calculating the initial speed of the cooling fan of a new energy vehicle of the present invention calculates the speed every half cycle, and provides real-time feedback on the motor speed. The correct speed can be calculated promptly after the speed fluctuates, and a warning can be given in time when the speed is too high.

[0027] (3) This method can quickly estimate the motor speed of the fan caused by the vehicle's movement, so as to select the appropriate fan static mode and prevent the ASC mode from being used when the speed is too high, which may burn out the power devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention shows a process of calculating the initial speed of a cooling fan of a new energy vehicle.

[0029] Figure 2 The back EMF waveform at a fixed speed is shown.

[0030] Figure 3 The waveform of the line back electromotive force at a rotation speed of 50 rpm when the controller is powered by low voltage according to one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0031] It should be noted that components in the drawings may be shown exaggerated for illustrative purposes and are not necessarily true to scale.

[0032] In the present invention, each embodiment is only intended to illustrate the aspects of the present invention and should not be construed as limiting.

[0033] In the present invention, unless otherwise specified, the quantifiers "a" and "an" do not exclude the presence of multiple elements.

[0034] It should also be pointed out that in the embodiments of the present invention, for the sake of clarity and simplicity, only a portion of the parts or components may be shown, but a person skilled in the art will understand that under the teachings of the present invention, the required parts or components may be added according to the needs of the specific scenario.

[0035] It should also be pointed out that within the scope of the present invention, the terms "same", "equal", "equal to" and the like do not mean that the two values ​​are absolutely equal, but allow a certain reasonable error, that is, the terms also cover "substantially the same", "substantially equal", and "substantially equal to".

[0036] It should also be noted that in the description of the present invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate description and simplify the present invention. They do not explicitly or implicitly state that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0037] In addition, the embodiments of the present invention describe the process steps in a specific order, but this is only for the convenience of distinguishing the steps, and does not limit the order of the steps. In different embodiments of the present invention, the order of the steps can be adjusted according to the adjustment of the process.

[0038] Controlling the cooling fan using a position-free control strategy requires the fan motor to be stationary before starting. However, when the vehicle is in motion, the fan can easily reach an initial speed before control is achieved due to airflow or mechanical vibration. Therefore, the fan must be stationary before starting.

[0039] Before the fan is started, the speed must be determined and different stopping strategies are adopted according to the speed. When the speed is low, the ASC short-circuit shutdown is used to stop the fan. When the speed is high, the fan is stopped by free stop.

[0040] The present invention provides a method for calculating the initial speed of a new energy vehicle cooling fan, which is suitable for estimating the initial speed of a fan motor without position control. A force is required to keep the rotor stationary, and this force depends on the speed. If the speed is high, the ASC short-circuit shutdown method is likely to burn out the power components, so it is necessary to observe the speed in advance so that a suitable stationary method can be adopted.

[0041] For a motor with a sinusoidal back EMF waveform, within each cycle T, the positive half-cycle duration = the negative half-cycle duration = half the cycle duration. Simply calculating the positive or negative half-cycle duration will yield the rotational speed. The relationship between cycle and frequency is: f = 1 / T, where f is the frequency and T is the cycle duration; n = 60f / p, where n is the motor speed and p is the number of motor pole pairs. Assuming the cooling fan motor has 8 pole pairs, n = 60f / 8.

[0042] When the vehicle is in operation, the fan has an initial speed before it starts, affected by airflow or mechanical vibration. When the fan speed is too low, the back EMF peak may be small and unstable, and there may also be external interference. In this case, calculating the speed when the back EMF crosses zero (either greater than or less than 0) can result in a very large speed n. The reason is as follows: Due to interference, the back EMF amplitude (back EMF peak) may fluctuate around 0, resulting in a very short period T and a high frequency f. Therefore, the speed calculated based on n = 60f / p is very large. Therefore, when designing, the positive half-cycle time should not be calculated solely based on the time when the back EMF peak (y-axis) is greater than 0. Cycle time calculation should start from the time when the back EMF peak (y-axis) is greater than or equal to a set threshold value, which is the first positive half-cycle. The negative half-cycle time occurs when the back EMF amplitude is less than a set threshold value. The time from when the back EMF decreases from below 0 and then increases back to 0 is the half-cycle time.

[0043] This threshold is set by Determine, E is the peak value of the opposite potential, When it is detected that the back electromotive force is too small, the feedback speed can be equal to 0.

[0044] When the controller is powered on and off (low-voltage power is used to turn power devices on and off), the software is reset. Therefore, the first half-cycle time calculated is likely inaccurate. Therefore, when the controller is initially powered on, the first half-cycle is not calculated. Cycle time calculation begins with the second half-cycle, and then frequency and speed calculations are made. Similarly, when the controller switches from "Not calculating speed when back EMF is low" to "Start calculating," the first half-cycle time is not calculated.

[0045] Figure 1 The present invention shows a process of calculating the initial speed of a cooling fan of a new energy vehicle.

[0046] like Figure 1 As shown, a method for calculating the initial speed of a cooling fan of a new energy vehicle includes the following steps:

[0047] Step 1: setting a critical line back electromotive force peak value according to a critical speed value, wherein the critical line back electromotive force peak value is greater than 0.

[0048] Determine, where E is the peak value of the opposite potential, the unit is V (volts); ω represents the motor electrical angular velocity, the unit is rad / s (radians per second); represents the motor flux, measured in Weber (Wb); ω = 2πnp / 60, where n is the speed (rpm); and p is the number of motor pole pairs. Based on the relationship between speed n and the motor's electrical angular velocity ω, the motor's electrical angular velocity corresponding to the critical speed can be calculated, and thus the critical line back EMF peak value.

[0049] You can select a critical speed value based on actual conditions, and then set a theoretical critical line back EMF peak value based on the critical speed value. Use the critical line back EMF peak value as a reference to determine whether to start speed calculation.

[0050] Step 2: confirm whether the line back EMF peak value is greater than or equal to the critical line back EMF peak value for the first time. If so, obtain each half cycle time t starting from the second half cycle, and calculate the initial speed of the cooling fan based on the half cycle time t.

[0051] If the absolute value of the line back EMF peak value is less than the critical line back EMF peak value, the speed is 0. If the line back EMF peak value is greater than or equal to the critical line back EMF peak value, the cycle time is obtained and the speed is calculated.

[0052] Since the start of cycle time calculation is determined by whether the line back EMF peak is greater than or equal to the critical line back EMF peak, the first half cycle usually does not start completely from 0. Therefore, the first half cycle time is incomplete and the calculated speed is incorrect. Therefore, the half cycle time is usually calculated starting from the second half cycle, and the speed is calculated based on the half cycle time.

[0053] Generally speaking, the first half cycle belongs to the positive half cycle, and its line back EMF peak value belongs to the positive peak value; the second half cycle belongs to the negative half cycle, and its line back EMF peak value belongs to the negative peak value.

[0054] The second half cycle time refers to the time it takes for the line back EMF to gradually decrease from 0 to the line back EMF peak value (negative peak value), and then gradually increase back to 0.

[0055] The counter is used to calculate the time t of each half cycle, including:

[0056] When each half cycle starts, the counter count value increases by 1, and when the line back EMF exceeds 0, the counter stops counting;

[0057] Multiply the count value by the unit time to obtain the half-cycle time t. The initial speed of the cooling fan is calculated based on this half-cycle time t. The counter is then reset to zero and the next counting cycle begins. The system is a discrete model. After calculating the speed of one cycle, the counter is reset and starts counting again for the next half-cycle speed calculation.

[0058] In one embodiment, the unit time is 125 us.

[0059] Positive half-cycle time = negative half-cycle time = half of a cycle, cycle T = 2t, frequency f = 1 / T, speed n = 60f / p, n = 60 / Tp, n = 60 / 2tp, T is the cycle time, t is half the cycle time, and p is the number of motor pole pairs.

[0060] Since the strategy currently adopted is to calculate the frequency and speed in half a cycle, when the speed fluctuates, the correct speed after the speed fluctuation can be calculated in time.

[0061] The following is a specific example to illustrate the method for calculating the initial speed of the cooling fan of a new energy vehicle.

[0062] Figure 2 The back EMF waveform at a fixed speed is shown. Figure 3 The waveform of the line back electromotive force at a rotation speed of 50 rpm when the controller is powered by low voltage according to one embodiment of the present invention is shown.

[0063] The cooling fan on a new energy vehicle can reach several thousand rpm when in operation. The initial speed of the cooling fan caused by the vehicle's operation is extremely low compared to the normal operating speed.

[0064] When the fan speed is too low, the line back EMF peak may be very small and unstable. There are also external interference effects, and the back EMF may fluctuate around 0. The cycle time is very short, and the speed calculated based on n = 60f / p is too high. A critical speed value and a critical line back EMF peak value corresponding to the critical speed value can be set. In this embodiment, the critical speed value can be set to 50rpm. The critical line back EMF peak value is also related to the magnetic flux, which varies for different motors. For some motors, the corresponding critical line back EMF peak value is 5V.

[0065] In this embodiment, when the peak value of the motor's line back EMF is less than 5V, it is considered that the fan is not rotating at this time, and the feedback speed is 0. When the peak value of the motor's line back EMF is greater than 5V, it belongs to the first half cycle, such as Figure 3 As shown, the first half cycle is incomplete and the speed is not calculated. When it is less than -5V, it belongs to the second half cycle. The speed calculated in the second half cycle is the actual speed of the fan.

[0066] When the line back EMF peak = 5V, V. The peak value of the line back EMF is Calculation shows that the rotation speed is 50 rpm, p = 8, and the corresponding electrical frequency of 50 rpm is: f = 50*p / 60 = 6.667 Hz.

[0067] When the line back EMF peak = 5V, you can start calculating the speed and use the counter to calculate the time corresponding to half a cycle: t = (1 / f) / 2 = 0.075s; this is the maximum half-cycle time at this time. Since the system is a discrete model, each increase of the counter by 1 is equivalent to an increase of 125us; so when the counter is greater than the maximum time of the corresponding half cycle, the fan speed should be 0 at this time; the maximum count value of the counter calculated according to the half-cycle time is: 0.075 / 0.000125 = 600.

[0068] Since this calculation method requires a certain amount of time to complete each time the controller is powered back on, provided the fan is rotating and the speed meets the calculation criteria, the first half-cycle is not calculated, and the second half-cycle begins calculation. Therefore, the entire system operation is delayed by the time corresponding to the minimum observable speed. During this time, the motor is rotating, and the delay is the time from the start of line back EMF detection to the line back EMF crossing zero and then zero again. In this embodiment, the delay is: 0.075 * 2 = 0.15s; therefore, the entire system should delay operation by 150ms.

[0069] This solution is only suitable for the case where all power devices are turned off. Because when the power devices are turned on, without considering hardware filtering, the line voltage is equal to 0, so the line back EMF = 0, and the calculated result must be 0; when the motor fails, all power devices are turned off, and this solution can be used to calculate the motor speed at this time.

[0070] The communication method between the host computer and the motor controller is CANFD communication to prevent interference.

[0071] Although certain embodiments of the present invention have been described in this application, those skilled in the art will appreciate that these embodiments are provided by way of example only. Numerous variations, alternatives, and modifications will be contemplated by those skilled in the art in light of the teachings of this disclosure without departing from the scope of the present invention. The appended claims are intended to define the scope of the present invention and are intended to encompass methods and structures within the scope of these claims and their equivalents.

Claims

1. A method for calculating the initial speed of a cooling fan of a new energy vehicle, characterized in that: include: Set the critical line back EMF peak value; as well as Check whether the line back EMF peak value is greater than or equal to the critical line back EMF peak value for the first time. If so, obtain each half cycle time t starting from the second half cycle and calculate the initial speed of the cooling fan based on the half cycle time t.

2. The method according to claim 1, characterized in that The critical line back electromotive force peak value is set according to the critical speed value, and the critical line back electromotive force peak value is greater than 0.

3. The method according to claim 2, characterized in that Set the critical speed value and calculate the critical line back EMF peak value according to the following formula: ω=2πnp / 60, Where E is the peak value of the opposite electromotive force, ω represents the electrical angular velocity of the motor, Represents the motor flux, E 线 is the line back EMF peak value, n is the speed, and p is the number of motor pole pairs.

4. The method according to claim 2, characterized in that If the absolute value of the line back EMF peak value is less than the critical line back EMF peak value, the rotational speed is determined to be 0.

5. The method according to claim 2, characterized in that If the line back EMF peak value is greater than or equal to the critical line back EMF peak value for the first time, the second half cycle time is the time it takes for the line back EMF to decrease from 0 and then increase back to 0.

6. The method according to claim 1, wherein The counter is used to calculate the time t of each half cycle, including: When each half cycle starts, the counter count value increases by 1, and when the line back EMF exceeds 0, the counter stops counting; The count value is multiplied by the unit time to obtain the half-cycle time t, and the initial speed of the cooling fan is calculated according to the half-cycle time t. Then the counter is reset to zero and the next round of counting begins.

7. The method according to claim 6, characterized in that The unit time is 125us.

8. The method according to claim 1, characterized in that Calculate the initial speed of the cooling fan according to the half-cycle time t: Period T = 2t, frequency f = 1 / T, speed n = 60f / p, where p is the number of motor pole pairs.

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