Smooth transition method and system for sensorless field-oriented control

Abstract

The invention discloses a smooth transition method and system for sensorless field directional control, and relates to the technical field of permanent magnet synchronous motor sensorless control. According to the method, an error between an I-f starting virtual synchronous reference coordinate system and a sensorless observer estimation coordinate system is eliminated through a dual-core mechanism of a robust transition strategy and a position error compensation strategy, and then rotor position deviation caused by non-ideal factors is corrected through an exclusive compensation module; the system constructs a multi-stage switching control framework based on the method, and seamless transition from I-f open-loop starting to sensorless FOC closed-loop control is achieved. Complex parameter adjustment is not needed, transition is fast and stable, torque magnetic flux control precision can be optimized, copper loss is reduced, system efficiency and robustness are improved, and the method is suitable for industrial driving scenes such as air conditioner compressors.

Description

Technical Field

[0001] This invention belongs to the field of sensorless control technology for permanent magnet synchronous motors, and in particular relates to a smooth transition method and system for sensorless magnetic field orientation control. Background Technology

[0002] Permanent magnet synchronous motors, with their advantages of high efficiency and high power density, are widely used in industrial drive systems such as air conditioning compressors. In the operation of air conditioning compressors, due to installation space limitations and cost control requirements, sensorless control methods have become the mainstream choice.

[0003] In existing technologies, the If synchronous starting method is commonly used during the low-speed phase of motor startup. This method, based on open-loop position control, provides a stable startup process. However, once the motor enters the high-speed operation phase, it needs to switch to sensorless FOC control based on back electromotive force (Back-EMF). This control method relies on an observer to achieve closed-loop position estimation. However, the control logic of If starting and sensorless FOC differs fundamentally, and the switching process between the two control methods faces key technical challenges.

[0004] Coordinate system inconsistency issue: If the startup is based on a virtual synchronous reference coordinate system, while the sensorless FOC is based on the actual rotor coordinate system estimated by the observer, if the two coordinate systems are not aligned during the switch, it can easily cause speed and current oscillations;

[0005] Non-ideal factors: Inverter dead time, control delay, motor parameter deviation and other non-ideal factors will increase the deviation between the position estimate and the actual value, further exacerbating the switching difficulty;

[0006] The shortcomings of traditional transition methods: Existing transition schemes (such as the method of gradually reducing the deviation angle based on the first-order compensator) are highly dependent on the compensator parameters, and the parameters need to be repeatedly adjusted to adapt to different operating conditions; some schemes have problems such as long start-up time and large torque pulsation during the switching process, which affect the operating stability and energy efficiency of the air conditioning compressor.

[0007] Therefore, there is an urgent need for a robust, fast and stable transition method for sensorless FOC smooth transition that can adapt to complex working conditions, in order to solve the pain points of existing technologies. Summary of the Invention

[0008] The purpose of this invention is to provide a smooth transition method and system for sensorless magnetic field orientation control, which solves problems such as coordinate system deviation and interference from non-ideal factors when switching from If start to sensorless FOC, and achieves fast, stable and low-fluctuation control mode switching, while optimizing system efficiency and stability.

[0009] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0010] This invention relates to a sensorless magnetic field orientation control smooth transition method and system, comprising the following steps:

[0011] Step 1: If Synchronous Start-up Phase: The If method is used to start the permanent magnet synchronous motor from a standstill with low acceleration until it reaches a stable desired speed, and the motor back EMF satisfies the observer position estimation conditions; during the start-up process, the q-axis current is kept constant, and the d-axis current is set to zero. In the initial stage, the rotor is positioned to zero using DC current; the rotor position calculation formula at time k is:

[0012]

[0013] in Given the rotor position at time k-1, ω r0 (k) represents the given speed at time k, and Δt represents the motor current loop control period;

[0014] Step 2: Coordinate System Error Elimination Phase: After the startup phase, activate the PI compensator to eliminate the position estimation error from the sensorless observer. If start reference location The error between them; only the position signal is switched, keeping the reference current constant; the PI compensator execution process includes:

[0015] Calculate reference position With compensator output θ o The difference Input the difference into the PI controller;

[0016] The proportional output of the PI controller is u p (k)=k p u err (k),

[0017] The integral output is u i (k)=u i (k-1)+k i Tu err (k),

[0018] Where k p k is the proportionality coefficient. i The integral coefficient is T, and the PWM execution period is T.

[0019] The total output of the PI controller is θ o1 (k)=u p (k)+u i (k),

[0020] The final output position of the compensator is Make estimation Align the coordinate system with the virtual synchronous reference coordinate system;

[0021] Step 3: Position Error Compensation and FOC Switching Stage: Switch the control switch to sensorless FOC mode, and eliminate the deviation between the actual rotor position and the observer's estimated position based on the position error compensation strategy;

[0022] The compensation strategy is based on the voltage equation:

[0023]

[0024] in These represent the estimated voltages along the dq axes of the rotating coordinate system, respectively. They represent the estimated rotating coordinate system, respectively. Current of the shaft; ω e ψ represents the electric speed of the motor rotor. f Represents the magnetic flux linkage of the motor. Is the actual position θ e With estimated location The error between;

[0025] By initializing the compensation factor θ c With a variable step size dθ, set the number of control cycles k, and calculate... and Amplitude; if If the value is increased, dθ[k] remains unchanged; otherwise, the sign of dθ[k] is reversed (i.e., -dθ is taken) and the calculation is repeated. Maintain the maximum value (satisfy) This completes position error compensation and enables a seamless switch to sensorless FOC.

[0026] In one embodiment, the position error compensation strategy in step 3 is characterized in that it is used to correct the rotor position estimation error caused by inverter dead time, control delay, and changes in motor parameters. It does not require complex modeling, and the initial output of the speed PI controller and the superimposed value of the compensated position remain consistent with the previous stage during the compensation process.

[0027] A sensorless magnetic field orientation control smooth transition system, comprising:

[0028] If Start Control Module: Used to execute the If synchronous start logic in step 1, outputting the given speed ω. r0 (k) Reference position With a constant q-axis current, the motor can start at low acceleration and the rotor can be initially positioned.

[0029] Coordinate transformation and current regulation module: including CLARK transformation unit, PARK transformation unit, d / q axis PI regulator and SVPWM unit, used to realize coordinate transformation and closed-loop control of three-phase current, and output inverter drive signal;

[0030] PI compensation module: Used to execute the coordinate system error elimination logic in step 2, with the reference position θ as input. e Position estimated by the observer Output the compensated position signal to align the estimated coordinate system with the virtual synchronous reference coordinate system;

[0031] Position error compensation module: Used to execute the error compensation strategy in step 3, based on the voltage equation and Amplitude feedback, dynamically adjusting the compensation factor θ c With step size dθ, the deviation between the actual position and the estimated position is eliminated;

[0032] Switching control module: contains multiple sets of control switches to realize the stage switching of "If start → coordinate system error elimination → sensorless FOC". When the control switches are switched, the reference current and control parameters are kept continuous.

[0033] Sensorless observer module: Used to estimate rotor position after the motor reaches the desired speed. With rotational speed ω e This provides position feedback for subsequent compensation and FOC control.

[0034] In one embodiment, the system is applied to the permanent magnet synchronous motor drive scenario of an air conditioning compressor, and can adapt to load changes and driving condition fluctuations without the need for precise adjustment of parameters such as the first-order compensator.

[0035] The present invention has the following beneficial effects:

[0036] 1. Solve the core switching challenges and achieve a seamless and stable transition.

[0037] Overcoming the pain point of coordinate system inconsistency: Through the dual mechanism of "PI compensation module + position error compensation module", the deviation between the virtual synchronous reference coordinate system and the estimated coordinate system of the sensorless observer is first eliminated during If startup, and then the error between the actual position and the estimated position is corrected. This completely avoids the speed oscillation and current fluctuation problems caused by coordinate system misalignment in traditional switching, ensuring a smooth switching from If open-loop startup to sensorless FOC closed-loop control, especially suitable for scenarios with high requirements for operational stability, such as air conditioning compressors.

[0038] Resisting interference from non-ideal factors: Without complex modeling, the rotor position estimation deviation caused by non-ideal factors such as inverter dead time, control delay, and changes in motor parameters can be automatically corrected through position error compensation strategy. Compared with traditional solutions, it is more adaptable to operating condition fluctuations and reduces compressor start-up and shutdown failures or efficiency reduction caused by external interference.

[0039] 2. Simplify operating costs and reduce debugging difficulty.

[0040] Eliminates complex parameter adjustment: It abandons the strong dependence on parameters of traditional transition schemes (such as first-order compensators), eliminates the need to repeatedly adjust the compensator coefficients to adapt to different loads or driving conditions, lowers the debugging threshold for engineers, and shortens the equipment installation and maintenance cycle. It is especially suitable for the standardized deployment of batch equipment in industrial scenarios.

[0041] Control logic continuity assurance: When switching control modules switch stages, they maintain consistency between the initial output of the reference current and speed PI controller and the superimposed value of the compensation position in the previous stage, without the need for additional parameter reset, reducing system debugging and potential operational errors.

[0042] 3. Optimize motor control performance and improve system energy efficiency.

[0043] Precise control of torque and flux: Through a dual-core error compensation mechanism, the accuracy of rotor position estimation is greatly improved, ensuring more precise control of d / q axis current, effectively optimizing torque and flux control accuracy, reducing torque pulsation during motor operation, and improving the smoothness and comfort of air conditioning compressor operation.

[0044] Reduced energy consumption and copper loss: Precise current control can avoid ineffective current loss and significantly reduce motor copper loss; at the same time, the combination of stable transition process and efficient FOC control mode further improves the operating efficiency of the entire drive system, which meets the development needs of energy conservation and consumption reduction in industrial equipment.

[0045] 4. Enhance system robustness and adapt to complex operating conditions.

[0046] Adapting to load and environmental fluctuations: The system can dynamically respond to load changes (such as load fluctuations when switching between cooling and heating modes) and drive condition fluctuations (such as voltage fluctuations) during the operation of the air conditioning compressor, maintaining stable operation without manual intervention and improving the reliability of the equipment under complex operating conditions.

[0047] Expanding the scope of applicable scenarios: In addition to air conditioning compressors, this method and system can be extended to other industrial drive scenarios that use permanent magnet synchronous motors (such as water pumps, fans, etc.). Its fast and stable transition characteristics and strong robustness can meet the core requirements of different equipment for sensorless control and have broad application value.

[0048] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a control architecture diagram of the system of the present invention;

[0051] Figure 2 This is a flowchart of the position error compensation algorithm in this invention. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] In the description of this invention, it should be understood that the terms "upper," "middle," "outer," "inner," etc., which indicate orientation or positional relationship, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this invention.

[0054] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0055] Example 1

[0056] This embodiment further explains the open-loop operation process of the air conditioner compressor If. The execution period of this control strategy is the PWM period T, and the value of any variable u at time kT is denoted as u(k). It includes the following steps:

[0057] Step 1: Based on the speed setpoint, the speed is gradually increased from 0 to the switching speed. The speed setpoint value at time k is ω. r0 (k), the given angle value at time k can be obtained through the integrator:

[0058] Step 2: Analyze the three-phase current i of the motor. a i b i c Perform CLARK coordinate transformation to obtain the components i in the two-phase stationary coordinate system. α and i β .in

[0059] Step 3: Utilize the component i in the two-phase stationary coordinate system α and i β Calculate the component i in the two-phase rotating coordinate system d and i q ,in

[0060] Step 4: Transfer the i obtained in Step 3 q With a given value The difference is calculated, and the difference is used as the input to the q-axis current PI regulator. The i obtained in step three is then used to... d The difference is calculated from the given value of 0, and the difference is used as the input of the d-axis current PI regulator.

[0061] Step 5: The output of the d-axis PI controller is The output of the q-axis PI controller is and angle As input to the inverse PARK transform, obtain and in and The inverter duty cycle is calculated by the SVPWM module.

[0062] Example 2

[0063] This embodiment describes a smooth transition method for sensorless magnetic field orientation control, comprising the following steps:

[0064] Step 1: Use the If method to start the motor from a standstill with low acceleration until it reaches a stable desired speed. At this point, the back electromotive force is large enough to estimate the position using an observer. Both switches are connected to terminal 1. During acceleration, the q-axis current is kept constant, and the d-axis current is set to zero. In the initial stage, the rotor is positioned to zero using DC current.

[0065] The formula for calculating the rotor position at this stage is:

[0066] in The rotor position is given at time k-1, ω r0 (k) is the given speed at time k, and Δt is the motor current loop control period.

[0067] Step 2: The PI compensator will adjust the estimated position. Reference position The error between terminals is reduced to zero, preparing the system to switch to terminal 2.

[0068] During this process, only the position signal is switched, while the reference current remains constant. The specific execution process of the PI compensator: reference position... With the output θ of the compensator o The difference is calculated and used as the input to the PI controller. The input difference at time kT is... The proportional output of the PI controller is u p (k)=k p u err (k), k p This is the proportionality coefficient;

[0069] The integral output of the PI controller is: u i (k)=u i (k-1)+k i Tu err (k), where k i The integral coefficient is θ, and T is the PWM execution period. The output θ of the PI regulator... o1 (k)=u p (k)+u i (k). The PI compensator output is calculated as follows: Due to estimation Coordinate system and virtual synchronous reference coordinate system d * q * The alignment is maintained, so switching from terminal 1 to terminal 2 does not cause significant speed or current fluctuations.

[0070] Step 3: Switch the switch to terminal 3. At this time, the rotor position and speed observer output will initially show the same error as calculated by the compensator, but this position error will be eliminated based on the error compensation strategy proposed by the following formula.

[0071]

[0072] These represent the estimated voltages along the dq axes of the rotating coordinate system, respectively. They represent the estimated rotating coordinate system, respectively. Current of the shaft; ω e ψ represents the electric speed of the motor rotor. f Represents the magnetic flux linkage of the motor. Is the actual position θ e With estimated location The error between them. The flowchart of the proposed position error compensation algorithm is shown in [link to algorithm]. Figure 2 To completely correct the positional error after switching to terminal 3, It must reach its maximum value (i.e., satisfy) By adjusting the estimated position using the proposed method, Maintain the maximum value and ensure that the position error is compensated. (Set) The θ is used as a compensation factor to correct the position error estimation unit. The algorithm first initializes θ. c And set the variable step size dθ. Calculate the number of control cycles "k" by setting the control cycle number. and The amplitude. If If the value increases, dθ[k] remains unchanged; otherwise, the sign of dθ[k] is reversed (i.e., -dθ is taken) and the voltage amplitude is recalculated. This method can ensure that position error compensation is completed in a short time without complex modeling. Since the initial output of the speed PI controller and the compensation position superimposed on the estimated position are consistent with the previous stage, and the error between the actual position and the estimated position will be gradually eliminated after the terminal switching, switching from terminal 2 to terminal 3 will not cause any speed or current fluctuations.

[0073] In the description of this specification, references to terms such as "an embodiment," "example," and "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0074] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A smooth transition method for sensorless magnetic field orientation control, characterized in that, Includes the following steps: Step 1: If Synchronous Start-up Stage: The If method is used to start the permanent magnet synchronous motor from a standstill with low acceleration until it reaches a stable desired speed, and the back electromotive force of the motor satisfies the position estimation conditions of the observer. During startup, the q-axis current is kept constant, and the d-axis current is set to zero. In the initial stage, the rotor is positioned to zero using DC current. The rotor position at time k is calculated using the following formula: in Given the rotor position at time k-1, ω r0 (k) represents the given speed at time k, and Δt represents the motor current loop control period; Step 2: Coordinate System Error Elimination Phase: After the startup phase, activate the PI compensator to eliminate the position estimation error from the sensorless observer. If start reference location The error between them; only the position signal is switched, keeping the reference current constant; The PI compensator execution process includes: Calculate reference position With compensator output θ o The difference Input the difference into the PI controller; The proportional output of the PI controller is u p (k)=k p u err (k), The integral output is u i (k)=u i (k-1)+k i Tu err (k), Where k p k is the proportionality coefficient. i The integral coefficient is T, and the PWM execution period is T. The total output of the PI controller is θ o1 (k)=u p (k)+u i (k), The final output position of the compensator is Make estimation Align the coordinate system with the virtual synchronous reference coordinate system; Step 3: Position Error Compensation and FOC Switching Stage: Switch the control switch to sensorless FOC mode, and eliminate the deviation between the actual rotor position and the observer's estimated position based on the position error compensation strategy; The compensation strategy is based on the voltage equation: in These represent the estimated voltages along the dq axes of the rotating coordinate system, respectively. They represent the estimated rotating coordinate system, respectively. Current of the shaft; ω e ψ represents the electric speed of the motor rotor. f Represents the magnetic flux linkage of the motor. Is the actual position θ e With estimated location The error between; By initializing the compensation factor θ c With a variable step size dθ, set the number of control cycles k, and calculate... and Amplitude; if If the value is increased, dθ[k] remains unchanged; otherwise, the sign of dθ[k] is reversed (i.e., -dθ is taken) and the calculation is repeated. Maintain the maximum value (satisfy) This completes position error compensation and enables a seamless switch to sensorless FOC.

2. The smooth transition method for sensorless magnetic field orientation control according to claim 1, characterized in that, The position error compensation strategy in step 3 is used to correct the rotor position estimation error caused by inverter dead time, control delay, and changes in motor parameters. It does not require complex modeling, and the initial output of the speed PI controller and the superimposed value of the compensated position remain consistent with the previous stage during the compensation process.

3. A sensorless magnetic field orientation control smooth transition system, characterized in that, include: If Start Control Module: Used to execute the If synchronous start logic in step 1, outputting the given speed ω. r0 (k) Reference position With a constant q-axis current, the motor can start at low acceleration and the rotor can be initially positioned. Coordinate transformation and current regulation module: including CLARK transformation unit, PARK transformation unit, d / q axis PI regulator and SVPWM unit, used to realize coordinate transformation and closed-loop control of three-phase current, and output inverter drive signal; PI compensation module: Used to execute the coordinate system error elimination logic in step 2, with the reference position θ as input. e Position estimated by the observer Output the compensated position signal to align the estimated coordinate system with the virtual synchronous reference coordinate system; Position error compensation module: Used to execute the error compensation strategy in step 3, based on the voltage equation and Amplitude feedback, dynamically adjusting the compensation factor θ c With step size dθ, the deviation between the actual position and the estimated position is eliminated; Switching control module: contains multiple sets of control switches to realize the stage switching of "If start → coordinate system error elimination → sensorless FOC". When the control switch switches are switched, the reference current and control parameters are kept continuous. Sensorless observer module: Used to estimate rotor position after the motor reaches the desired speed. With rotational speed ω e This provides position feedback for subsequent compensation and FOC control.

4. The sensorless magnetic field orientation control smooth transition system according to claim 3, characterized in that, The system is applied to the permanent magnet synchronous motor drive scenario of air conditioner compressors. It can adapt to load changes and driving condition fluctuations without the need for precise adjustment of parameters such as the first-order compensator.

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