Motor starting method based on position sensorless algorithm and smooth switching closed-loop strategy

Abstract

This invention discloses a motor starting method based on a position sensorless algorithm and a smooth switching closed-loop strategy. This method analyzes the motor startup process, controlling the motor's startup by changing the given current amplitude and position angle. To ensure that the given position angle matches the actual rotor position angle, the reference current amplitude is gradually reduced during the closed-loop switching process until there is essentially no phase difference between the two. The closed-loop is then switched to ensure smooth motor operation. The proposed algorithm achieves a higher slope in the early stages of the switching process and a lower slope in the later stages, clearly meeting the performance requirements of a switching speed closed-loop.

Description

Technical Field

[0001] The present invention belongs to the technical field of permanent magnet brushless motor control, and in particular relates to a motor starting method based on a position sensorless algorithm and a smooth switching closed-loop strategy. Background Art

[0002] Brushless DC motors (BLDCs), a product of the rapid development of semiconductor electronics, combine modern electronics, control theory, and motor technology to offer excellent controllability, a wide speed range, high starting torque, and high efficiency. Early DC power, which passed through brushes and a commutator to the armature winding, suffered from brush wear, electromagnetic interference, high noise, and a short lifespan. These motors were a significant source of system instability in many critical applications.

[0003] In recent years, due to the advancement of power electronics and vector control technology, brushless DC motors have entered the application stage and have been widely used due to their high reliability. Initially, brushless DC motors used open-loop U / f constant control, and later a current loop was added, called slip frequency control, which improved performance and has been put into practical use.

[0004] However, the system only uses average value control derived from steady-state equations, resulting in poor startup stability. Position sensors were subsequently used to replace brushes, improving this stability. However, these sensors are prone to failure in certain environments (such as high humidity, inside fuel tanks, and in environments with magnetic fields). Innovations in new permanent magnet materials, microelectronics, automatic control, and power electronics have led to the emergence of a new generation of sinusoidal brushless permanent magnet synchronous motors (PMSMs). These PMSMs synthesize the voltage and current vectors by sampling phase voltages and currents, calculate the rotor angle, and control the rotating magnetic field to always lead the rotor magnetic field by a specific angle, thereby driving the rotor.

[0005] Since the position sensorless algorithm is generally inaccurate at low speeds, it is usually necessary to accelerate the motor rotor to a certain speed, and then use the control model as follows: Figure 1 As shown in (a), the speed and position are detected using a position sensorless algorithm and a complete speed closed loop is entered. The control model is as follows: Figure 1 As shown in (b), high-performance vector control of the motor is achieved.

[0006] During the system switching process, since the reference current amplitude i and position angle θ in the acceleration start-up phase are both given, but after entering the speed closed loop, the reference current amplitude i* in the speed closed loop phase is determined by the speed control module, and the rotor position angle θ* is determined by the non-position detection module, it is necessary to design a switching strategy. f is the feedback current amplitude during the acceleration start-up phase, i f* is the feedback current amplitude in the speed closed loop stage, v is the reference speed amplitude in the acceleration start stage, v f It is the feedback speed amplitude in the speed closed loop stage. After the system acceleration start-up phase is completed, there is a phase difference α between the given position angle and the actual rotor position angle (i.e. the angle detected by no position sensor). At the same time, the given current amplitude is also inconsistent with the current amplitude generated by the speed loop (such as PI controller). Figure 2 As shown in the figure, if the closed loop is switched directly at this time, it will inevitably cause oscillation of the rotor current and speed, which may cause the motor to fail to start normally; therefore, in order to ensure high-performance operation of the motor, it is necessary to achieve smooth switching of the position angle and current amplitude. Summary of the Invention

[0007] In view of the above, the present invention provides a motor starting method based on a position sensorless algorithm and a smooth switching closed-loop strategy to achieve stable operation of the motor and avoid motor jitter during the switching process.

[0008] A motor starting method based on a position sensorless algorithm and a smooth switching closed-loop strategy includes the following steps:

[0009] (1) Given the motor current amplitude i and rotor position angle θ;

[0010] (2) Implementing I / F acceleration start on the motor to make it reach a given speed; during the motor acceleration process, the position sensorless algorithm module is used to detect the motor speed v and rotor position angle θ* in real time. When the detected speed v reaches the given speed, the phase angle difference α = θ - θ* is calculated;

[0011] (3) Adjusting the given rotor position angle θ or current amplitude i to make the phase angle difference approach 0;

[0012] (4) Switch the motor into speed closed-loop control mode.

[0013] Furthermore, the specific implementation of adjusting the given rotor position angle θ in step (3) is as follows:

[0014] 3.1 Calculate the phase angle difference change rate after the kth adjustment using the following formula:

[0015]

[0016] Where: d1 and d2 are given coefficients used to control the rate of change of the power function, α k is the phase angle difference calculated by step (2) after the kth adjustment, where k is a natural number;

[0017] 3.2 According to the rate of change of phase angle difference The phase angle difference reference value for the next adjustment is calculated using the following formula:

[0018]

[0019] Where: Δt is the time step;

[0020] 3.3 According to the phase angle difference reference value Adjust the given rotor position angle θ, re-execute step (2) and calculate the phase angle difference α after the k+1th adjustment k+1 , if α k+1 If it is less than the precision threshold ε, then execute step (4); otherwise, let k+1→k and return to execute step 3.1.

[0021] Furthermore, the specific implementation of adjusting the given current amplitude i in step (3) is as follows:

[0022] 3.1 Calculate the current change rate after the kth adjustment using the following formula:

[0023]

[0024] Where: d2 and d3 are given coefficients used to control the rate of change of the power function, α k is the phase angle difference calculated by step (2) after the kth adjustment, where k is a natural number;

[0025] 3.2 According to the current change rate The current reference value i for the next adjustment is calculated by the following formula: k+1 ;

[0026]

[0027] 3.3 According to the current reference value i k+1 Adjust the given current amplitude i, re-execute step (2) and calculate the phase angle difference α after the k+1th adjustment k+1 , if α k+1 If it is less than the precision threshold ε, then execute step (4); otherwise, let k+1→k and return to execute step 3.1.

[0028] Furthermore, in step 3.3, when the number of adjustments reaches the set maximum number of iterations, no further adjustments are made and the process directly proceeds to step (4).

[0029] Furthermore, in step (4), the motor is switched into the speed closed-loop control mode, and the current amplitude i given in the acceleration start-up phase is assigned as the reference current initial amplitude in the speed closed-loop phase.

[0030] Furthermore, when the phase angle difference approaches 0 by adjusting the given current amplitude i in step (3), if the phase angle difference meets the accuracy requirement, the step (4) first uses the position sensorless algorithm module to detect the current speed v of the detection motor. f , and assign it as the reference speed of the speed control module. At the same time, the current amplitude i given in the acceleration start-up phase is assigned as the reference current initial amplitude in the speed closed-loop phase. Then, the motor working state can be adjusted directly by changing the reference speed, realizing high-performance vector control and making the motor run smoothly and stably.

[0031] Furthermore, the motor starting method of the present invention is based on the d-axis current i d =0 motor vector control mode.

[0032] Furthermore, the rate of change of the phase angle difference is c α And c α =Δα / Δt, the rate of change of current is c i And c i =Δi / Δt, where Δα is the phase angle difference change, Δi is the given current change, and Δt is the time step. In order to ensure the switching speed, it is necessary to increase the phase angle difference change rate c. α However, when the phase angle difference is close to zero, the motor needs to be able to run stably, and the current change rate c needs to be reduced. i Otherwise, the phase angle difference may become negative due to rapid changes, and the motor may be at risk of losing step. Therefore, the present invention introduces a power function to dynamically control the change of the phase angle difference, i.e., c α =d1α d2 , d1 and d2 are given coefficients used to control the rate of change of the power function.

[0033] This paper analyzes how the motor's startup process is controlled by changes in a given current amplitude and position angle. To ensure that the given position angle matches the actual rotor position angle, the reference current amplitude should be gradually reduced during the closed-loop switching process until there is essentially no phase difference between the two. This closed-loop switching ensures smooth motor operation. The proposed algorithm achieves a higher slope in the early stages of the switching process and a lower slope in the later stages, clearly meeting the performance requirements for a speed-switching closed-loop. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 (a) is a schematic diagram of the motor control model during the acceleration start-up phase.

[0035] Figure 1 (b) is a schematic diagram of the motor control model in the speed closed-loop stage.

[0036] Figure 2 Schematic diagram of the relationship between the reference current amplitude and the phase angle difference α in the dq coordinate system.

[0037] Figure 3 This is a schematic diagram of a first embodiment of the present invention.

[0038] Figure 4 Schematic diagram of the dq coordinate system under the initial rotor position angle.

[0039] Figure 5 is the initial phase angle difference α in the coordinate system 0 Schematic diagram of .

[0040] Figure 6 is the phase angle difference α in the coordinate system after adjustment k times k Schematic diagram of .

[0041] Figure 7 This is a flow chart of a second embodiment of the present invention.

[0042] Figure 8 Schematic diagram of current and position angle in the coordinate system after adjusting the current amplitude k times.

[0043] Figure 9 Schematic diagram of the current and position angle in the coordinate system at the end of the current amplitude iteration.

[0044] Figure 10 This is a schematic diagram of a third embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] like Figure 3 As shown, the specific control process of this embodiment is as follows:

[0048] (1) Determine the initial position of the motor rotor, thereby establishing the initial D rotor Q rotor Axis coordinate system, such as Figure 4 shown.

[0049] (2) Based on the initial position angle, the current amplitude i and angle θ are given to realize I / F acceleration start, and the speed v = Δθ / Δt, where Δθ is the change in position angle.

[0050] (3) Continuously accelerate until the speed detected by the position sensorless algorithm module substantially matches the given speed v = Δθ / Δt. The minimum speed value for substantially matching the speed depends on the selected position sensorless algorithm.

[0051] (4) Use the position sensorless algorithm module to detect the actual rotor angle and obtain the initial phase angle difference α 0 ,like Figure 5 shown.

[0052] (5) Adjust the position angle and adjust the phase angle difference α k times k like Figure 6 As shown, α k <α 0 .

[0053] During the switching process, the rate of change of the phase angle difference α is c α , since motor control is generally implemented in digital control, it is expressed as discrete variables:

[0054]

[0055] Where: Δα represents the change in phase angle difference, and Δt represents the change in time.

[0056] The phase angle difference α changes continuously until its value approaches 0, that is, there is basically no phase angle difference between the two, and then the closed loop is switched. Therefore, in order to ensure the speed of switching, it is necessary to increase the angle change rate c α However, in order to ensure stable operation when the angle difference is close to zero, that is, stable operation when close to the critical stable state, it is necessary to reduce the rate of change of current. Otherwise, the phase angle difference may change to a negative value due to excessive change, and the motor will be at risk of losing step. Therefore, a power function is introduced to dynamically control the change of angle:

[0057]

[0058] Where: d1 and d2 represent the coefficients that control the rate of change of the power function.

[0059] If α k >ε, then the following iterative process is performed until there is basically no phase angle difference between the two.

[0060]

[0061]

[0062] k←k+1

[0063] Where: Indicates the phase angle difference reference value, α k It represents the phase angle difference after k iterations, ε represents the accuracy threshold, i.e. the error range, and k represents the number of iterations. The maximum number of iterations k can be set. max As another sufficient condition to end the cycle, that is, k>k max , ending the loop.

[0064] (6) When the phase angle difference αk When <ε, assign i * (0) =i and enter speed closed loop control, i * (0) Indicates the initial amplitude of the reference current in the speed closed loop stage.

[0065] (7) Change the reference speed amplitude v and realize the speed closed loop by feedback speed amplitude vf, see Figure 1 (b).

[0066] Example 2

[0067] like Figure 7 As shown, the specific control process of this embodiment is as follows:

[0068] (1) Determine the initial position of the motor rotor, thereby establishing the initial D rotor Q rotor Axis coordinate system, such as Figure 4 shown.

[0069] (2) Based on the initial position angle, the current amplitude i and angle θ are given to realize I / F acceleration start, and the speed v = Δθ / Δt, where Δθ is the change in position angle.

[0070] (3) Continuously accelerate until the speed detected by the position sensorless algorithm module substantially matches the given speed v = Δθ / Δt. The minimum speed value for substantially matching the speed depends on the selected position sensorless algorithm.

[0071] (4) Use the position sensorless algorithm module to detect the actual rotor angle and obtain the initial phase angle difference α 0 ,like Figure 5 The position sensorless algorithm module can calculate the motor back electromotive force based on the output voltage of the motor controller and the detected current, and further calculate the rotor position angle θ.

[0072] (5) Adjust the current amplitude i, adjust the current amplitude k times as follows Figure 8 shown.

[0073] The phase angle difference α can be controlled by changing the reference current amplitude. In order to make the given position angle match the actual rotor position angle, the reference current amplitude should be gradually reduced during the closed loop switching process until there is basically no phase angle difference between the two, and then the closed loop is switched; therefore, the given current change rate c i It can be expressed as:

[0074]

[0075] So:

[0076]

[0077] Where: d2, d3 and d4 represent the coefficients that control the rate of change of the power function.

[0078] If α k >ε, then the following iterative process is performed until there is basically no phase difference between the two, such as Figure 9 shown.

[0079]

[0080] i k+1 =i k -c i k Δt

[0081] k←k+1

[0082] Where: c i k Indicates the current change rate after iteration k times, i k It represents the current amplitude after k iterations, where ε and d values ​​(including d2 and d4) depend on the characteristics and requirements of the actual system. Obviously, the algorithm proposed in the present invention can make the slope of the switching process larger in the early stage and smaller in the later stage, which obviously meets the performance requirements of the switching speed closed loop.

[0083] (6) When the phase angle difference α k When <ε, assign i * (0) =i and enter speed closed-loop control.

[0084] Example 3

[0085] like Figure 10 As shown, the specific control process of this embodiment is as follows:

[0086] (1) Determine the initial position of the motor rotor, thereby establishing the initial D rotor Q rotor Axis coordinate system, such as Figure 4 shown.

[0087] (2) Based on the initial position angle, the current amplitude i and angle θ are given to realize I / F acceleration start, and the speed v = Δθ / Δt, where Δθ is the change in position angle.

[0088] (3) Continuously accelerate until the speed detected by the position sensorless algorithm module substantially matches the given speed v = Δθ / Δt. The minimum speed value for substantially matching the speed depends on the selected position sensorless algorithm.

[0089] (4) Use the position sensorless algorithm module to detect the actual rotor angle and obtain the initial phase angle difference α 0 ,like Figure 5 shown.

[0090] (5) Adjust the given current amplitude i, and adjust the current amplitude k times as follows Figure 8 shown.

[0091] (6) When the phase angle difference α k When ε<ε, the position sensor-free algorithm module detects the motor speed v f As the speed feedback value in the closed loop stage, the current speed v f Input the reference speed v assigned to the speed control module; when the current amplitude does not match, it can be solved by setting the initial value of the speed loop. For example, if the speed control module uses a commonly used PID controller, the initial integral value can be set.

[0092] (7) Assign i * (0) =i and enters speed closed-loop control. At this time, the entire control system smoothly enters the speed closed-loop, and then the motor working state can be adjusted directly by changing the reference speed to achieve high-performance vector control and make the motor run smoothly and stably.

[0093] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It is apparent that those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without requiring creative effort. Therefore, the present invention is not limited to the above embodiments. Any improvements or modifications made by those skilled in the art based on the disclosure of the present invention should fall within the scope of protection of the present invention.

Claims

1. A motor starting method based on a position sensorless algorithm and a smooth switching closed-loop strategy, comprising the following steps: (1) Given the motor current amplitude i and rotor position angle θ; (2) Implementing I / F acceleration start on the motor to make it reach a given speed; during the motor acceleration process, the position sensorless module is used to detect the motor speed v and rotor position angle θ* in real time. When the detected speed v reaches the given speed, the phase angle difference α = θ - θ* is calculated; (3) Adjusting the given rotor position angle θ or current amplitude i to make the phase angle difference approach 0; The specific implementation of adjusting the given rotor position angle θ is as follows: A1 calculates the phase angle difference change rate after the kth adjustment using the following formula in: d1 and d2 are given coefficients used to control the rate of change of the power function, α k is the phase angle difference calculated by step (2) after the kth adjustment, where k is a natural number; A2 is based on the rate of change of phase angle difference The phase angle difference reference value for the next adjustment is calculated using the following formula: Where: Δt is the time step; A3 based on the phase angle difference reference value Adjust the given rotor position angle θ, re-execute step (2) and calculate the phase angle difference α after the k+1th adjustment k+1 , if α k+1 If it is less than the precision threshold ε, then execute step (4), otherwise let k+1→k and return to execute step A1; The specific implementation of adjusting the current amplitude i is as follows: B1 calculates the current change rate after the kth adjustment using the following formula Where: d3 is a given coefficient used to control the rate of change of the power function; B2 according to the current change rate The current reference value i for the next adjustment is calculated by the following formula: k+1 ; B3 is based on the current reference value i k+1 Adjust the current amplitude i, re-execute step (2) and calculate the phase angle difference α after the k+1th adjustment k+1 , if α k+1 If it is less than the precision threshold ε, then execute step (4), otherwise let k+1→k and return to execute step B1; (4) Switch the motor into speed closed-loop control mode.

2. The motor starting method according to claim 1, wherein: In step 3.3, when the number of adjustments reaches the set maximum number of iterations, no further adjustments are made and the process directly proceeds to step (4).

3. The motor starting method according to claim 1, wherein: In the step (4), the motor is switched into the speed closed-loop control mode, and the current amplitude i given in the acceleration start-up phase is assigned as the reference current initial amplitude in the speed closed-loop phase.

4. The motor starting method according to claim 1, wherein: When the phase angle difference approaches 0 by adjusting the current amplitude i in step (3), if the phase angle difference meets the accuracy requirement, the step (4) first uses the position sensorless algorithm module to detect the current speed v of the motor. f The speed control module uses the current amplitude i given in the acceleration start-up phase as the reference current initial amplitude in the speed closed-loop phase. The motor working state is then adjusted directly by changing the reference speed to achieve high-performance vector control and make the motor run smoothly and stably.

5. The motor starting method according to claim 1, wherein: The motor starting method is based on the d-axis current i d =0 motor vector control mode.

6. The motor starting method according to claim 1, wherein: The rate of change of the phase angle difference is c α And c α =Δα / Δt, the rate of change of current is c i And c i =Δi / Δt, where Δα is the change in phase angle difference and Δi is the change in given current. To ensure the switching speed, the rate of change of phase angle difference c needs to be increased. α However, when the phase angle difference is close to zero, the motor needs to be able to run stably, and the current change rate c needs to be reduced. i Otherwise, the phase angle difference may become negative due to rapid changes, and the motor may be at risk of losing step. Therefore, this method introduces a power function to dynamically control the change of the phase angle difference, namely c α =d1α d2 .

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