A control method and system for indirectly obtaining commutation signals based on BLDC terminal voltage

Abstract

This invention discloses a control method and system for indirectly obtaining commutation signals based on BLDC terminal voltage, belonging to the field of brushless DC motor positionless control. The method includes: sampling the voltage of the floating phase at the current commutation point after a set electrical angle; sampling the voltage of the floating phase at the next detected zero-crossing point after the current commutation point; calculating the actual zero-crossing time using the linear relationship between the back electromotive force of the first and second sampling points; obtaining the lag compensation time from the zero-crossing point to the commutation point by combining the difference between the actual and detected zero-crossing times and the commutation reference time delay; sampling the same floating phase at an electrical angle interval of α after the current commutation point and at an electrical angle interval of (60°-α) after the turn-off point, summing the two samples, and determining whether the commutation is leading or lagging based on the result; and using a PI regulator to correct the lag compensation time in a closed loop. This invention is simple, practical, and can accurately obtain the commutation signal.

Description

Technical Field

[0001] This invention belongs to the field of positionless control technology for brushless DC motors, and more specifically, relates to a control method and system for indirectly obtaining commutation signals based on BLDC terminal voltage. Background Technology

[0002] Brushless DC motors are widely used in the automotive and aerospace industries due to their simple structure, high reliability, wide speed range, and ease of maintenance. Commutation is a major research topic in brushless DC motors. Traditional commutation methods directly obtain commutation signals using Hall effect sensors, but this increases hardware costs and reduces system reliability. Therefore, the research focus for brushless DC motors is primarily on sensorless control methods. The basic idea of ​​sensorless rotor position detection control methods is to process characteristic quantities such as the three-phase terminal voltage and three-phase current of the motor through software or hardware to obtain the commutation signal. These methods can be categorized into back EMF methods, inductive methods, and state observer methods, among which the back EMF method is the most mature and effective. The back EMF method detects the zero-crossing point of the back EMF of the suspended phase and then delays it by 30° electrical angle to obtain the commutation point. However, the back EMF signal is susceptible to PWM noise interference. To filter out noise and avoid obtaining erroneous commutation signals, traditional methods use low-pass filters to remove high-frequency interference. However, low-pass filters cause phase lag, which is difficult to accurately compensate for. Therefore, accurately obtaining the zero-crossing point of the back electromotive force to achieve accurate commutation is a key issue in BLDC sensorless control. Summary of the Invention

[0003] To address the above-mentioned deficiencies or improvement needs of existing technologies, this invention provides a control method and system for indirectly obtaining commutation signals based on BLDC terminal voltage. Its purpose is to accurately obtain the zero-crossing point of the back electromotive force, thereby achieving accurate commutation of the brushless DC motor.

[0004] To achieve the above objectives, according to one aspect of the present invention, a control method for indirectly obtaining a commutation signal based on the BLDC terminal voltage is provided, comprising:

[0005] S1. The voltage of the floating phase is sampled for the first time after a set electrical angle lags the current commutation point, and the voltage of the floating phase is sampled for the second time at the next detected zero crossing point at the current commutation point;

[0006] S2. Calculate the actual zero-crossing time using the linear relationship between the back electromotive force between the first and second sampling points;

[0007] S3. By combining the difference between the actual zero-crossing time and the detected zero-crossing time, and the delayed commutation reference time, the lag compensation time from the zero-crossing point to the commutation point is obtained.

[0008] S4. Sample the same suspended phase at an electrical angle interval of α after the current commutation point and at an electrical angle interval of (60°-α) after the turn-off point. Sum the two results and determine whether it is a leading or lagging commutation based on the results. Use a PI regulator to correct the lag compensation time in a closed loop.

[0009] Furthermore, the first sampling time is the time corresponding to an electrical angle 24° behind the current commutation point.

[0010] Furthermore, the formula for calculating the actual zero-crossing time is as follows:

[0011]

[0012] t1 is the first sampling time, y1 is the floating phase terminal voltage obtained from the first sampling; t2 is the first sampling time, y2 is the floating phase terminal voltage obtained from the first sampling, u d This indicates the bus voltage.

[0013] Furthermore, the lag compensation time from the zero crossing point to the commutation point is:

[0014]

[0015] t delta This is the time interval between every three zero crossings.

[0016] Furthermore, the sampling times in step S4 are the intervals after the current commutation point.

[0017] The present invention also provides a control system for indirectly obtaining commutation signals based on BLDC terminal voltage, comprising:

[0018] The sampling module is used to perform the first sampling of the floating phase voltage after a set electrical angle lag at the current commutation point, and the second sampling of the floating phase voltage at the next detected zero crossing point at the current commutation point;

[0019] The actual zero-crossing point calculation module is used to calculate the actual zero-crossing point time by utilizing the linear relationship between the back electromotive force between the first and second sampling points.

[0020] The lag compensation time calculation module is used to combine the difference between the actual zero-crossing time and the detected zero-crossing time, as well as the delayed commutation reference time, to obtain the lag compensation time from the zero-crossing point to the commutation point.

[0021] The closed-loop correction module is used to sample the same suspended phase at an electrical angle interval of α after the commutation point and at an electrical angle interval of (60°-α) after the turn-off point. The two samples are then summed, and the result is used to determine whether the commutation is ahead or behind. The PI regulator is used to correct the lag compensation time in a closed loop.

[0022] Furthermore, the formula for calculating the actual zero-crossing time is as follows:

[0023]

[0024] t1 is the first sampling time, y1 is the floating phase terminal voltage obtained from the first sampling; t2 is the first sampling time, y2 is the floating phase terminal voltage obtained from the first sampling, u d This indicates the bus voltage.

[0025] Overall, the above-described technical solutions conceived by this invention can achieve the following beneficial effects compared with the prior art.

[0026] The zero-crossing signal of the present invention can be calculated by a simple algebraic equation without the need for an additional low-pass filter and comparator, thus avoiding the inconvenience of mechanical installation. Furthermore, there is no delay in the zero-crossing signal (ZCP) caused by low-pass filtering, reducing hardware costs. The method is simple, practical, and can accurately obtain the commutation signal.

[0027] The closed-loop phase correction introduced in this invention can compensate for the deviation of the commutation signal in real time, thereby realizing high-precision control of the commutation of the brushless DC motor. Attached Figure Description

[0028] Figure 1 This is a structural block diagram of the present invention;

[0029] Figure 2 This diagram illustrates the sampling of terminal voltage.

[0030] Figure 3 This represents the zero-crossing signal waveform considering factors such as bias voltage and impedance asymmetry.

[0031] Figure 4 This is a schematic diagram of the back electromotive force in this invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0033] The main idea of ​​this invention is to obtain a zero-crossing signal through a zero-crossing detection circuit and compensate for the delay angle based on the zero-crossing signal. First, a more accurate time reference is obtained by using three consecutive zero-crossing intervals with an electrical angle of 180°. Then, the voltage of the floating phase is sampled before and at the zero-crossing point. Using the linear relationship between the sampling point and the ideal zero-crossing point, the actual zero-crossing point time can be derived. Finally, based on the symmetry of the back electromotive force, the same floating phase is sampled at the same electrical angle time after turn-off and before turn-on, and the two samples are summed. Based on the summation result, a PI regulator is used to correct the lag compensation time in a closed loop, thereby reducing commutation error.

[0034] refer to Figure 1 The method of the present invention specifically includes the following steps:

[0035] S1. The voltage of the floating phase is sampled for the first time after a set electrical angle lags the current commutation point, and the voltage of the floating phase is sampled for the second time at the next detected zero crossing point at the current commutation point;

[0036] Specifically, sampling is first performed one moment before the zero-crossing point. In order to get closer to the commutation point and to facilitate sampling, the voltage of the floating phase is sampled at 6° electrical angle before the zero-crossing point, that is, 24° electrical angle after the commutation point. The sampling time is recorded as t1 and the voltage of the floating phase terminal is recorded as y1. Then, when the zero-crossing point of the floating phase is actually sampled, another sampling is performed. The sampling time is recorded as t2 and the voltage of the floating phase terminal is recorded as y2.

[0037] S2. Calculate the actual zero-crossing time using the linear relationship between the back electromotive force between the first and second sampling points;

[0038] Because the two sampling points are close together, even if the back EMF waveform is not ideal, the back EMF between the two sampling intervals can be considered linear. The sampling time interval between sampling point 1 and sampling point 2 is t2-t1, and the sampling voltage difference is y2-y1, as shown in the attached figure. Figure 2 Sampling point 1 is denoted as S(1), sampling point (2) is denoted as S(2), and the ideal zero-crossing point is denoted as Z. A perpendicular line is drawn from S(2) downwards, and a line is drawn from S(1) parallel to the horizontal coordinate, intersecting the perpendicular line at point B. A line is drawn from Z parallel to the horizontal coordinate, intersecting the perpendicular line at point A. Then, triangle S(2)ZA and triangle S(2)S(1)B are similar triangles. According to the properties of similar triangles, the actual zero-crossing time can be calculated as follows:

[0039]

[0040] u d Indicates the bus voltage;

[0041] S3. By combining the difference between the actual zero-crossing time and the detected zero-crossing time, and the delayed commutation reference time, the lag compensation time from the zero-crossing point to the commutation point is obtained.

[0042] First, the commutation compensation time reference used in this invention will be explained:

[0043] In the ideal case where there is no back EMF zero-crossing position error, each zero-crossing interval should be 60°, and the commutation point is 30° after the zero-crossing. In traditional methods, the zero-crossing interval is usually used as the 60° standard angle reference, and other angles, such as the 30° delay angle and the commutation compensation angle, are further determined using the 60° standard angle reference.

[0044] Based on actual engineering conditions, this invention analyzes the parameters of the motor driver and the motor, and finds that the size of the zero-crossing interval is affected not only by the motor parameters, but also by DC voltage drop, bias voltage, and asymmetric back EMF. When these irrational factors exist, the zero-crossing interval will repeatedly shorten or lengthen, no longer being a fixed 60°. If other angles are still determined by the interval of the zero-crossing interval, commutation errors will inevitably occur.

[0045] To address the impact of the aforementioned non-ideal factors on commutation, this invention improves the time reference for motor commutation compensation:

[0046] As attached Figure 3 The waveform represents the zero-crossing signal, where the ideal zero-crossing signal, denoted as point Z, is represented by a black dot. The ideal zero-crossing signal is uniformly distributed within one electrical cycle, with a 60° interval between each adjacent zero-crossing signal. When factors such as DC voltage drop exist and the motor's three-phase impedance is asymmetrical, the resulting zero-crossing signal is the zero-crossing pulse shown in the figure. In this case, the distance between the ideal commutation point and the zero-crossing point is no longer 30° electrical angle, but contains an error. When a brushless DC motor operates, it divides the 360° electrical angle into 6 sectors, commutating every 60°. Assuming that when the motor operates in sector I, the upper bridge arm of phase A is conducting, the lower bridge arm of phase B is conducting, and phase C is floating, then when the motor operates in sector IV, the upper bridge arm of phase B is conducting, the lower bridge arm of phase A is conducting, and phase C is floating. Therefore, the DC voltage drop and the inconsistent three-phase impedance of the motor have the same impact on sectors I and IV, meaning that the error angle magnitudes of sectors I and IV are the same. Similarly, the error angle magnitudes of sectors II and V, as well as sectors III and VI, are the same. (See Appendix) Figure 3 We can obtain:

[0047]

[0048] θ1, θ2, θ3, and θ4 represent the angular positions of the first, second, third, and fourth actual zero-crossing signals, respectively, Δθ A , △θ B , △θC These represent the deviations of the first, second, and third zero-crossing intervals, respectively.

[0049] Simplifying the above equation, we get:

[0050] θ2-θ1+θ3-θ2+θ4-θ3=180

[0051] The above equation shows that even with DC voltage drop, bias voltage, unbalanced back electromotive force, and unbalanced three-phase impedance of the motor, the three consecutive zero-crossing intervals remain 180°. This invention uses the 180° electrical angle of each three zero-crossing intervals as the standard angular reference, and denotes the time interval of each three zero-crossing intervals as t. delta .

[0052] Once an accurate standard angle reference is determined, the delay angle and compensation angle during motor commutation can be determined.

[0053] From the appendix Figure 4 It can be seen that the lag compensation time from the zero crossing point to the commutation point is the time corresponding to a 30° electrical angle delay minus (t2-t3). Using the time corresponding to the above angle reference, the time corresponding to 30° can be obtained as follows: Therefore, the commutation lag compensation time is:

[0054] S4. Sample the same suspended phase at the interval α electrical angle and at the (60°-α) electrical angle after the switch-off, then sum the two samples. Based on the result, determine whether it is a leading or lagging commutation, and use a PI regulator to correct the lag compensation time in a closed loop.

[0055] The commutation error calculated in the first two steps is relatively small, but a certain error still exists. To further reduce the commutation error, this invention adopts a closed-loop correction scheme based on the symmetry of the terminal voltage. During accurate commutation, the back electromotive force (EMF) at any time after each phase disconnection and before the same time interval is turned on is symmetrical about the zero-crossing point of the back EMF. That is, during accurate commutation, the back EMF at any time after each phase disconnection and before the same time interval is turned on is symmetrical about the zero-crossing point of the back EMF, and the terminal voltage at the zero-crossing point is... The sum of the voltages at the points symmetrical before and after the zero-crossing point is u. d Considering the follow-through period after shutdown, to avoid the influence of the follow-through on the sampling results, the same suspended phase is sampled at 15° electrical angle after shutdown and 45° electrical angle after shutdown (i.e., 15° electrical angle before turn-on). The time corresponding to the electrical angle here is also the time t corresponding to the aforementioned standard angle reference. delta Therefore, the sampling times are the intervals after the commutation point.

[0056] Then sum the two sampled values, and compare the sum with u.d The difference is calculated and input into the PI controller. Based on this, the PI controller is used in a closed-loop correction to compensate for the lag time and reduce commutation error.

[0057] The present invention uses a closed-loop correction method to compensate for commutation deviation in real time, eliminates unpredictable or uncertain factors, and has strong anti-interference ability.

[0058] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A control method for indirectly obtaining commutation signals based on BLDC terminal voltage, characterized in that, include: S1. The voltage of the floating phase is sampled for the first time after a set electrical angle lags the current commutation point, and the voltage of the floating phase is sampled for the second time at the next detected zero crossing point at the current commutation point; S2. Calculate the actual zero-crossing time using the linear relationship between the back electromotive force between the first and second sampling points; the formula for calculating the actual zero-crossing time is: For the first sampling time, This refers to the voltage at the floating phase terminal obtained from the first sampling. For the first sampling time, The voltage at the floating phase terminal obtained from the first sampling. Indicates the bus voltage; S3. Combining the difference between the actual zero-crossing time and the detected zero-crossing time, and the delayed commutation reference time, the lag compensation time from the zero-crossing point to the commutation point is obtained; the lag compensation time from the zero-crossing point to the commutation point is: The time interval between every three zero crossings; S4. Sample the same suspended phase at an electrical angle interval of α after the current commutation point and at an electrical angle interval of (60°-α) after the turn-off point. Sum the two results and determine whether it is a leading or lagging commutation based on the results. Use a PI regulator to correct the lag compensation time in a closed loop.

2. The control method for indirectly obtaining commutation signals based on BLDC terminal voltage according to claim 1, characterized in that, The first sampling time is the time corresponding to the electrical angle lag of 24° after the current commutation point.

3. The control method for indirectly obtaining commutation signals based on BLDC terminal voltage according to claim 1, characterized in that, Step S4 sampling times are the intervals after the current commutation point. , .

4. A control system for indirectly obtaining commutation signals based on BLDC terminal voltage, characterized in that, include: The sampling module is used to perform the first sampling of the floating phase voltage after a set electrical angle lag at the current commutation point, and the second sampling of the floating phase voltage at the next detected zero crossing point at the current commutation point; The actual zero-crossing point calculation module is used to calculate the actual zero-crossing point time by utilizing the linear relationship between the back electromotive force between the first and second sampling points; the formula for calculating the actual zero-crossing point time is: For the first sampling time, This refers to the voltage at the floating phase terminal obtained from the first sampling. For the first sampling time, The voltage at the floating phase terminal obtained from the first sampling. Indicates the bus voltage; The lag compensation time calculation module is used to calculate the lag compensation time from the zero-crossing point to the commutation point by combining the difference between the actual zero-crossing time and the detected zero-crossing time, as well as the delayed commutation reference time. The lag compensation time from the zero-crossing point to the commutation point is: The time interval between every three zero crossings; The closed-loop correction module is used to sample the same suspended phase at an electrical angle interval of α after the commutation point and at an electrical angle interval of (60°-α) after the turn-off point. The two samples are then summed, and the result is used to determine whether the commutation is ahead or behind. The PI regulator is used to correct the lag compensation time in a closed loop.

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