Sensorless control method and system for electrically excited synchronous motor

Abstract

The invention discloses a sensorless control method and system for an electrically excited synchronous motor, and relates to the technical field of motor control, and the technical scheme is characterized in that the air gap flux linkage of the electrically excited synchronous motor is observed through a closed-loop air gap flux linkage observer, and the closed-loop air gap flux linkage observer is composed of a voltage model and a current model; the voltage model and the current model are connected through a PI regulator; extracting rotating speed and position information in the air gap flux linkage through an orthogonal phase-locked loop model; detecting the voltage of the power grid by using a three-phase phase-locked loop; and selecting a corresponding control strategy according to the voltage drop depth of the power grid voltage so as to realize sensorless control of the electrically excited synchronous motor. The closed-loop air gap flux linkage observer is composed of a voltage model and a current model, the voltage model and the current model are connected through a PI regulator, the influence of direct current bias in a sampling signal on a flux linkage observation result can be restrained, and the performance of the models at a low speed is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and more particularly to a sensorless control method and system for an electrically excited synchronous motor. Background Art

[0002] With the gradual completion of compressor stations along the West-East Gas Pipeline, the number of compressor units is increasing, and their cumulative operating time is growing. Compressors are key equipment in natural gas pipeline compressor stations and can be categorized by drive type: fuel-driven or electric-driven. Electric-driven compressor units are more environmentally friendly and economical, offering significant advantages over fuel-driven systems, and are widely used in compressor stations along the West-East Gas Pipeline. In compressor control systems, mechanical sensors are typically used to detect the motor's rotor position in real time for closed-loop control. However, the presence of mechanical sensors significantly increases system cost and reduces reliability, and they are susceptible to issues such as assembly, signal transmission, and environmental conditions. Furthermore, in western my country, power is primarily supplied by wind and photovoltaic power generation, resulting in low-quality grid-connected power. This is particularly prone to short-term line voltage drops, particularly during periods of severe weather. Voltage drops in inverters can cause a sudden increase in stator current and overvoltage on the DC-side capacitors, leading to motor shutdown and production losses. In severe cases, equipment burnout can occur. Therefore, to improve the reliability of compressor control systems, sensorless motor control and low-voltage ride-through technologies are attracting significant attention.

[0003] Sensorless control technologies can generally be divided into two categories: those based on high-frequency signal injection and those based on motor models. While the former accurately identifies motor speed without being affected by changes in motor parameters, the accuracy is low. This method also generates additional electromagnetic torque, which can affect normal operation. Therefore, motor model-based speed estimation schemes have become increasingly popular due to their ease of implementation and versatility. These schemes typically employ a phase-locked loop (PLL) to extract position and speed information from the flux or back EMF. However, traditional flux observers based on single voltage or current models are unable to effectively measure the motor's flux. The former, due to the pure integrator effect, can lead to increasing errors due to DC offsets in the sampled signal. The latter, however, can be affected by changes in motor parameters during operation, leading to increased observation errors.

[0004] Therefore, how to research and design a sensorless control method and system for an electrically excited synchronous motor that can overcome the above-mentioned defects is a problem that we urgently need to solve. Summary of the Invention

[0005] In order to address the deficiencies in the prior art, the purpose of the present invention is to provide a sensorless control method and system for an electrically excited synchronous motor, which can suppress the influence of the DC bias in the sampling signal on the flux observation results and improve the performance of the model at low speeds.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] In a first aspect, a sensorless control method for an electrically excited synchronous motor is provided, comprising the following steps:

[0008] The air gap flux of the electrically excited synchronous motor is observed by a closed-loop air gap flux observer, which consists of a voltage model and a current model, and the voltage model and the current model are connected through a PI regulator;

[0009] Extract the speed and position information in the air gap flux through the orthogonal phase-locked loop model;

[0010] Utilize a three-phase phase-locked loop to detect grid voltage;

[0011] The corresponding control strategy is selected according to the voltage drop depth of the grid voltage to realize sensorless control of the electrically excited synchronous motor.

[0012] Furthermore, if the motor speed is less than or equal to the speed threshold, the current model is used to observe the air gap flux of the electrically excited synchronous motor;

[0013] If the motor speed is greater than the speed threshold, the voltage model is used to observe the air gap flux of the electrically excited synchronous motor.

[0014] Furthermore, the method further comprises:

[0015] Improve the motor position and speed estimation by adjusting the parameters of the PI regulator;

[0016] Furthermore, the estimated rotation speed and position are used as feedback to form a closed-loop control.

[0017] Furthermore, the voltage sag depth of the grid voltage includes mild sag, moderate sag and severe sag;

[0018] When the grid voltage drops to more than 83% of the rated voltage, it is considered a slight drop;

[0019] When the grid voltage drops to 65%-83% of the rated voltage, it is considered a moderate drop;

[0020] When the grid voltage drops below 65% of the rated voltage, it is considered a severe drop.

[0021] Furthermore, if the voltage drop depth of the grid voltage is a slight drop, the control strategy is:

[0022] By increasing the inverter margin and injecting the third harmonic into the PWM modulation wave, the DC side voltage utilization rate is improved, allowing the system to smoothly pass through the low voltage stage.

[0023] Furthermore, if the voltage drop depth of the grid voltage is a moderate drop, the control strategy is:

[0024] Considering the extreme working conditions and leaving a set margin, the air gap magnetic field is reduced to 50% of the rated value;

[0025] At the same time, the speed loop is abandoned and the motor torque is reduced to zero, and then increased to 50% of the rated value after a set time;

[0026] Also, after the voltage is restored, the speed loop is switched back to enable the motor to achieve low voltage ride-through.

[0027] Furthermore, if the voltage drop depth of the grid voltage is a severe drop, the control strategy is:

[0028] When the grid voltage drops, the PWM wave is blocked, the speed loop and current loop PI regulators are reset to zero, and no-load excitation current is applied to the motor to make it idle.

[0029] After the voltage is restored, the angle and speed information extracted by the phase-locked loop are used as feedback to make the speed loop PI regulator start working from zero, and the current loop PI regulator is assigned an initial value, and the wave is generated and the rated excitation is added. After the preset time, the motor is accelerated to the rated speed.

[0030] In a second aspect, a sensorless control system for an electrically excited synchronous motor is provided. The system is used to implement a sensorless control method for an electrically excited synchronous motor as described in any one of the first aspects, comprising:

[0031] The flux observation module is used to observe the air gap flux of the electrically excited synchronous motor through a closed-loop air gap flux observer. The closed-loop air gap flux observer consists of a voltage model and a current model, and the voltage model and the current model are connected through a PI regulator.

[0032] An information extraction module is used to extract the speed and position information in the air gap flux through an orthogonal phase-locked loop model;

[0033] A voltage detection module is used to detect the grid voltage using a three-phase phase-locked loop;

[0034] The motor control module is used to select a corresponding control strategy according to the voltage drop depth of the grid voltage to achieve sensorless control of the electrically excited synchronous motor.

[0035] In a third aspect, a computer terminal is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, a sensorless control method for an electrically excited synchronous motor as described in any one of the first aspects is implemented.

[0036] In a fourth aspect, a computer-readable medium is provided, on which a computer program is stored. The computer program is executed by a processor to implement a sensorless control method for an electrically excited synchronous motor as described in any one of the first aspects.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention provides a sensorless control method for an electrically excited synchronous motor. The closed-loop air gap flux observer comprises a voltage model and a current model, which are connected via a PI regulator. Appropriate parameters are set to achieve smooth switching between the two models, using the current model at low speeds and the voltage model at high speeds. This allows the two models to calibrate each other, suppressing the impact of DC bias in the sampled signal on the flux observation results and improving the model's performance at low speeds.

[0039] 2. The present invention improves the motor position and speed estimation effect by adjusting the parameters of the PI regulator, and finally uses the estimated speed and position as feedback to form a closed-loop control. The error of the motor angle and speed estimation result is small, thereby improving the performance of the control system.

[0040] 3. The present invention can achieve smooth transition under different voltage drop conditions. During moderate drops, the motor can output a certain torque. During low voltage processes, the stator side current of the motor does not overcurrent, and the torque does not fluctuate violently. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0042] Figure 1 This is a principle block diagram of a closed-loop air gap flux observer used in an embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of a phase-locked loop in an embodiment of the present invention, used to extract the angle and position information contained in the air gap flux of the motor;

[0044] Figure 3 1 is a structural diagram of a voltage detection module in an embodiment of the present invention;

[0045] Figure 4 1 is a waveform diagram of the stator current of phase A of the motor when the voltage slightly drops in an embodiment of the present invention;

[0046] Figure 5 This is a waveform diagram of the motor speed when the voltage slightly drops in an embodiment of the present invention;

[0047] Figure 6 This is a torque waveform diagram of the motor when the voltage slightly drops in an embodiment of the present invention;

[0048] Figure 7 This is a schematic diagram of the low voltage ride-through control strategy for a motor during a moderate voltage sag in an embodiment of the present invention;

[0049] Figure 8 1 is a waveform diagram of the A-phase stator current of the motor when the voltage drops moderately in an embodiment of the present invention;

[0050] Figure 9 This is a waveform diagram of the motor speed when the voltage drops moderately in an embodiment of the present invention;

[0051] Figure 10 1 is a torque waveform diagram of a motor when a moderate voltage drop occurs in an embodiment of the present invention;

[0052] Figure 11 This is a schematic diagram of the low voltage ride-through control strategy for a motor when the voltage drops severely in an embodiment of the present invention;

[0053] Figure 12 1 is a waveform diagram of the A-phase stator current of the motor when the voltage drops severely in an embodiment of the present invention;

[0054] Figure 13 This is a waveform diagram of the motor speed when the voltage drops severely in an embodiment of the present invention;

[0055] Figure 14 This is a torque waveform diagram of the motor when the voltage drops severely in an embodiment of the present invention;

[0056] Figure 15 is a system block diagram in an embodiment of the present invention;

[0057] Figure 16 It is a traditional voltage and current observation model. DETAILED DESCRIPTION

[0058] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0059] Example 1: A sensorless control method for an electrically excited synchronous motor is implemented by the following steps.

[0060] Step S1: observing the air gap flux of the electrically excited synchronous motor through a closed-loop air gap flux observer, wherein the closed-loop air gap flux observer is composed of a voltage model and a current model, and the voltage model and the current model are connected through a PI regulator.

[0061] The traditional voltage model and current model flux observers are both open-loop models. Figure 16 (a) It can be seen that the voltage model obtains the motor's magnetic flux information by directly integrating the back electromotive force, which has the advantages of simplicity and convenience. However, a pure integrator is introduced into the model. In practical applications, sensors generally have a certain DC bias, which will produce cumulative errors after passing through the integrator. In addition, the voltage model is easily affected by the stator resistance, which is particularly obvious at low speeds. Figure 16 (b) It can be seen that the current model uses stator current, coordinate transformation and many motor parameters to calculate the motor's flux information. During the operation of the motor, the parameters will inevitably change, resulting in poor robustness. In addition, the traditional voltage model and current model are both open-loop models, which have poor stability and are easily affected by disturbances such as DC bias and parameter changes. They are less effective in practical applications. Therefore, the present invention adopts a closed-loop rotor flux observer to combine the two. The current model is used at low speed and the voltage model is used at high speed. The bandwidth of the current loop and voltage loop is adjusted by the PI regulator. The current mode is mainly used in the low-frequency band and the voltage mode is mainly used in the high-frequency band. At the same time, the current model can suppress the influence of DC bias on the system. Finally, a phase-locked loop is used to extract the position and speed information in the flux.

[0062] The specific implementation block diagram of the closed-loop flux observer is as follows: Figure 1 As shown in the figure: u α 、u β is the component of the stator voltage on the α-axis and β-axis, i α 、i β are the components of the stator current in the α-axis and β-axis. is the component of the air gap flux in the α-axis and β-axis, is the component of the air gap flux in the d-axis and q-axis, i fd is the excitation current of the motor, L md , L mq is the stator mutual inductance of the motor, T Dd and T Dq is the damping winding time constant, and T Dd =(L md +L Dd ) / R Dd , T Dq =(L mq +L Dq ) / R Dq , where R Dd and R Dqis the damping winding resistance, L Dd and L Dq is the damping winding inductance, L ls is the stator leakage inductance, R s is the stator resistance.

[0063] Specifically, if the motor speed is less than or equal to the speed threshold, the current model is used to observe the air gap flux of the electrically excited synchronous motor; if the motor speed is greater than the speed threshold, the voltage model is used to observe the air gap flux of the electrically excited synchronous motor.

[0064] Step S2: extracting the speed and position information in the air gap flux through the orthogonal phase-locked loop model.

[0065] like Figure 2 As shown, the air gap flux obtained in step S1 is used as the input of the orthogonal phase-locked loop to extract the motor speed and position information in the flux observed by the air gap flux observer, and the motor position and speed estimation effect is improved by adjusting the parameters of the PI regulator. Finally, the estimated speed and position are used as feedback to form a closed-loop control.

[0066] Step S3: Detecting the grid voltage using a three-phase phase-locked loop.

[0067] like Figure 3 As shown in the figure, a three-phase phase-locked loop is used to detect the grid voltage. First, the three-phase line voltage of the grid is transformed into the dq0 coordinate system, and then converted into a DC quantity for control. The PI regulator is used to make the q-axis component 0. At this time, the component of the grid voltage on the d-axis is the grid voltage amplitude, and the integral link is used to calculate the angle of rotation of the d-axis.

[0068] Step S4: selecting a corresponding control strategy according to the voltage drop depth of the grid voltage to achieve sensorless control of the electrically excited synchronous motor.

[0069] Low-voltage ride-through technology typically involves blocking the inverter output to allow the motor to survive the low-voltage phase. Because the motor speed is high and no-load excitation is applied when the PWM pulses are blocked, the motor's back EMF is high for a period of time. This back EMF can be used to extract motor position information, allowing the motor to restart after voltage is restored. While this method ensures a quick motor start after the low-voltage phase ends, it is a limited approach. When the grid voltage dip is minor, it wastes the motor's torque output capacity.

[0070] The voltage sag depth of the grid voltage includes mild sag, moderate sag and severe sag.

[0071] (1) When the grid voltage drops slightly (drops to more than 83% of the rated voltage), by increasing the inverter margin and injecting the third harmonic into the PWM modulation wave, the DC side voltage utilization rate is improved, allowing the system to smoothly pass through the low voltage stage.

[0072] Using MATLAB / Simulink simulation, the grid voltage is set to drop to 83% of the rated value at 27-29 seconds. Figure 4-Figure 6 The following are the waveforms of the motor's phase A stator current, speed, and torque under this operating condition. As can be seen from the figure, due to the high inverter margin, the motor can basically operate normally under this condition, with no stator current overcurrent, the speed reaching the rated value, and no significant torque fluctuations.

[0073] (2) Moderate grid voltage drop

[0074] When the grid voltage experiences a moderate dip (to 65%-83% of rated voltage), the DC-side voltage drop is excessive. If the inverter doesn't promptly lock out its output, the output power will remain unchanged, but the output current will inevitably increase. Furthermore, the air gap magnetic field and motor speed remain high during the voltage drop, potentially causing the back EMF to exceed the DC-bus voltage, leading to induced current. Consequently, under these conditions, the motor's stator current experiences a significant surge, torque fluctuates violently, and the DC-bus voltage also experiences a significant surge. In severe cases, this can damage the equipment and cause significant losses.

[0075] In the MT coordinate system, the flux equation and voltage equation of the electromagnetic motor are:

[0076]

[0077] Among them, ψ δm , ψ δt is the component of the air gap flux on the M axis and T axis; u sm 、u st is the component of the stator voltage on the M axis and T axis; i sm 、i st is the component of the stator current on the M axis and T axis; ψ δ is the air gap flux; L sσ is the stator leakage inductance; p is the differential operator; ω e is the motor electrical angular velocity.

[0078] Under the air gap flux oriented vector control, the stator current in the m-axis component i sm = 0, when the motor is running in steady state, ignore the current differential in the voltage equation and set i sm =0, we can get the stator phase voltage amplitude u spmax for:

[0079]

[0080] Ignoring the stator resistance and leakage inductance of the motor, we can get:

[0081] u spmax ≈ω e ψ δ .

[0082] Using PWM modulation with third harmonic injection, the DC side voltage U dc The relationship with the phase voltage amplitude is:

[0083]

[0084] Combining the above two formulas, we can get:

[0085]

[0086] If the speed remains unchanged at the moment of voltage drop, it can be seen from the above formula that when the DC side voltage drops, the value of the air gap magnetic field needs to be reduced so as to maintain the balance between the DC side voltage and the back electromotive force.

[0087] Under the vector control of air gap flux orientation, due to i sm =0, then the stator current expression is:

[0088]

[0089] in, is the torque given value, i s is the stator current, u spmax is the stator phase voltage amplitude, i sm is the m-axis component of the stator current.

[0090] From the above formula, we can see that if only the air gap magnetic field is reduced at low voltage, the stator current will increase, triggering the protection action and failing to achieve low voltage ride through. Therefore, when reducing the air gap flux in the low voltage stage, the torque set value must also be reduced to ensure that the current on the stator side of the motor does not flow. In addition, the magnitude of the torque reduction should be equal to the magnitude of the flux reduction, otherwise it will cause i s Larger or smaller than the rated value. If i s A value larger than the rated value may cause overcurrent; a value smaller than the rated value will not fully utilize the maximum torque that the motor can currently output.

[0091] Reducing the air gap magnetic field simply requires lowering the air gap magnetic field setpoint, and using the PI regulator to make the actual value track the setpoint. However, the PI regulator takes some time for the actual air gap magnetic field to reach the setpoint. For safety reasons, the motor torque is first controlled to zero during this stage and then increased to the current maximum torque output.

[0092] Based on the above analysis, during a moderate voltage drop, the extreme operating condition (voltage drops to 65% of the rated value) is considered and a certain margin is left. The air gap magnetic field is reduced to 50% of the rated value. At the same time, the speed loop is abandoned and the motor torque is reduced to zero. After a short period of time, it is increased to 50% of the rated value. After the voltage recovers, the speed loop is switched back to achieve low voltage ride-through.

[0093] Figure 7 The control block diagram for this working condition is shown in the following figure. Using MATLAB / Simulink simulation, the grid voltage is set to drop to 65% of the rated value at 27-29 seconds. Figures 8-10 The following waveforms show the motor's phase A stator current, speed, and torque under this operating condition. As can be seen from the figure, under this condition, there is no overcurrent on the motor's stator side, and it can output a certain torque, minimizing speed drops. The speed drops to 2500 rpm in 29 seconds, and then quickly returns to the rated value after voltage recovery.

[0094] (3) Severe voltage drop in the power grid

[0095] When the grid voltage drops severely (drops below 65% of the rated voltage), the voltage drop is too large and the motor cannot output a large torque. The blocking method is used to allow the motor to pass through the low voltage stage. The specific strategy is as follows:

[0096] When the grid voltage drops, the PWM waveform is blocked, the speed loop and current loop PI regulators are reset, and no-load excitation current is applied to the motor, causing it to coast. After the voltage recovers, the angle and speed information extracted by the phase-locked loop is used as feedback to restart the speed loop PI regulator from zero. The current loop PI regulator is initialized, and the waveform is generated and rated excitation is applied. After a period of time, the motor speed is increased to the rated speed.

[0097] Figure 11 The control block diagram for this working condition is shown in the following figure. Using MATLAB / Simulink simulation, the grid voltage is set to drop to 50% of the rated value at 27-29 seconds. Figure 12-14 The following waveforms show the motor's phase A stator current, speed, and torque under this operating condition. As can be seen, under this condition, the motor torque is controlled to zero, there is no stator current overcurrent, and the speed drops to 2000 rpm in 29 seconds. Once the voltage is restored, the speed quickly returns to the rated value.

[0098] Example 2: A sensorless control system for an electrically excited synchronous motor, the system is used to implement the sensorless control method for an electrically excited synchronous motor described in Example 1, such as Figure 15 As shown, it includes a flux observation module, an information extraction module, a voltage detection module and a motor control module.

[0099] Among them, the flux observation module is used to observe the air gap flux of the electrically excited synchronous motor through a closed-loop air gap flux observer. The closed-loop air gap flux observer consists of a voltage model and a current model, and the voltage model and the current model are connected through a PI regulator; the information extraction module is used to extract the speed and position information in the air gap flux through an orthogonal phase-locked loop model; the voltage detection module is used to detect the grid voltage using a three-phase phase-locked loop; the motor control module is used to select the corresponding control strategy according to the voltage drop depth of the grid voltage to realize sensorless control of the electrically excited synchronous motor.

[0100] The present invention also describes a computer terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, a sensorless control method for an electrically excited synchronous motor as described in Example 1 is implemented.

[0101] The present invention also describes a computer-readable medium on which a computer program is stored. The computer program is executed by a processor to implement a sensorless control method for an electrically excited synchronous motor as described in Example 1.

[0102] Working principle: The closed-loop air gap flux observer in the present invention is composed of a voltage model and a current model, which are connected by a PI regulator. Appropriate parameters are set according to the current model used at low speed and the voltage model used at high speed to achieve smooth switching of the two models, so that the two models can be corrected to each other, which can suppress the influence of the DC bias in the sampling signal on the flux observation results and improve the performance of the model at low speed; in addition, the present invention can achieve smooth transition under different voltage drop conditions, and can make the motor output a certain torque in the case of moderate drop, and there is no overcurrent on the stator side of the motor during the low-voltage process, and the torque does not fluctuate violently.

[0103] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0104] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0105] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0106] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0107] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A sensorless control method for an electrically excited synchronous motor, characterized in that: The following steps are involved: The air gap flux of the electrically excited synchronous motor is observed by a closed-loop air gap flux observer, which is composed of a voltage model and a current model, and the voltage model and the current model are connected through a PI regulator; The speed and position information in the air gap flux are extracted through the orthogonal phase-locked loop model; Utilize a three-phase phase-locked loop to detect the grid voltage; The corresponding control strategy is selected according to the voltage drop depth of the grid voltage to realize sensorless control of the electrically excited synchronous motor.

2. The sensorless control method of an electrically excited synchronous motor according to claim 1, characterized in that: If the motor speed is less than or equal to the speed threshold, the current model is used to observe the air gap flux of the electrically excited synchronous motor; If the motor speed is greater than the speed threshold, the voltage model is used to observe the air gap flux of the electrically excited synchronous motor.

3. The sensorless control method of an electrically excited synchronous motor according to claim 1, characterized in that: The method further includes: Improve the motor position and speed estimation by adjusting the parameters of the PI regulator; Furthermore, the estimated rotation speed and position are used as feedback to form a closed-loop control.

4. The sensorless control method of an electrically excited synchronous motor according to claim 1, characterized in that: The voltage drop depth of the grid voltage includes a slight drop, a moderate drop and a severe drop; When the grid voltage drops to more than 83% of the rated voltage, it is considered a slight drop; When the grid voltage drops to 65%-83% of the rated voltage, it is considered a moderate drop; When the grid voltage drops below 65% of the rated voltage, it is considered a severe drop.

5. The sensorless control method of an electrically excited synchronous motor according to claim 1, characterized in that: If the voltage drop depth of the grid voltage is a slight drop, the control strategy is: By increasing the inverter margin and injecting the third harmonic into the PWM modulation wave, the DC side voltage utilization rate is improved and the system can smoothly pass through the low voltage stage.

6. The sensorless control method of an electrically excited synchronous motor according to claim 1, characterized in that: If the voltage drop depth of the grid voltage is a moderate drop, the control strategy is: Considering the extreme working conditions and leaving a set margin, the air gap magnetic field is reduced to 50% of the rated value; At the same time, the speed loop is abandoned and the motor torque is reduced to zero, and then increased to 50% of the rated value after a set time; And, after the voltage is restored, the speed loop is switched back to enable the motor to achieve low voltage ride-through.

7. The sensorless control method of an electrically excited synchronous motor according to claim 1, characterized in that: If the voltage drop depth of the grid voltage is a severe drop, the control strategy is: When the grid voltage decreases, the PWM wave is blocked, the speed loop and current loop PI regulators are cleared, and no-load excitation current is added to the motor to make the motor idle; After the voltage is restored, the angle and speed information extracted by the phase-locked loop is used as feedback to make the speed loop PI regulator start working from zero, and the current loop PI regulator is assigned an initial value, and the wave is generated and rated excitation is added. After a preset time, the motor is accelerated to the rated speed.

8. A sensorless control system for an electrically excited synchronous motor, characterized in that: The system is used to implement a sensorless control method for an electrically excited synchronous motor as claimed in any one of claims 1 to 7, comprising: A flux observation module is used to observe the air gap flux of the electrically excited synchronous motor through a closed-loop air gap flux observer. The closed-loop air gap flux observer is composed of a voltage model and a current model, and the voltage model and the current model are connected through a PI regulator. An information extraction module is used to extract the speed and position information in the air gap flux through an orthogonal phase-locked loop model; A voltage detection module is used to detect the grid voltage using a three-phase phase-locked loop; The motor control module is used to select a corresponding control strategy according to the voltage drop depth of the grid voltage to achieve sensorless control of the electrically excited synchronous motor.

9. A computer terminal comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, a sensorless control method for an electrically excited synchronous motor as described in any one of claims 1 to 7 is implemented.

10. A computer readable medium having a computer program stored thereon, characterized in that: The computer program is executed by a processor to implement a sensorless control method for an electrically excited synchronous motor as described in any one of claims 1 to 7.

Images