Method for observing mixed air gap flux linkage of synchronous motor of high-power pumped storage system

Abstract

The invention relates to the technical field of power electronics and motor control, in particular to a high-power pumped storage system synchronous motor mixed air gap flux linkage observation method, which comprises the following steps of: establishing an air gap flux linkage voltage observation model and an air gap flux linkage current observation model influenced by a damping winding; adding a nonlinear link of a magnetization curve into a feedback channel of the current observation model, comparing the deviation of the air gap flux linkage calculated by the air gap flux linkage voltage observation model and the new air gap flux linkage current observation model, and taking the deviation as an input signal of a sliding mode controller; an output signal of the sliding mode controller is smoothed through a low-pass filter, and a stator voltage correction value is obtained; the hybrid air gap flux linkage observation technology and the sliding mode controller are combined, the influence of the damping winding and the magnetic circuit saturation effect are deeply considered at the same time, and the control precision and stability of the electro-magnetic synchronous motor in a high-power pumped storage power generation system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics and motor control, and particularly to a method for observing the mixed air-gap magnetic flux of a synchronous motor in a high-power pumped-storage system. Background Art

[0002] As an important energy storage device in the power system, the pumped-storage power generation system effectively regulates the grid load and improves the flexibility and stability of the power system by means of pumping energy storage and discharging power generation. In a high-power pumped-storage power generation system, an electrically excited synchronous motor is widely used due to its high efficiency, high stability and good speed regulation performance. However, traditional magnetic flux observation methods have problems of insufficient observation accuracy when facing complex working conditions, such as high-speed operation of the motor, magnetic circuit saturation and the influence of damping windings, which affect the control performance of the motor and the stability of the system. Summary of the Invention

[0003] The present invention provides a method for observing the mixed air-gap magnetic flux of a synchronous motor in a high-power pumped-storage system, which combines the mixed air-gap magnetic flux observation technology and a sliding mode controller, and deeply considers the influence of the damping winding and the magnetic circuit saturation effect. The aim is to improve the control accuracy and stability of an electrically excited synchronous motor in a high-power pumped-storage power generation system. Without adding additional equipment, a better air-gap magnetic flux observation effect can be obtained through this method.

[0004] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0005] A method for observing the mixed air-gap magnetic flux of a synchronous motor in a high-power pumped-storage system, which establishes an air-gap magnetic flux voltage observation model and an air-gap magnetic flux current observation model considering the influence of the damping winding, and adds a non-linear link of the magnetization curve to the feedback channel of the air-gap magnetic flux current observation model to form a new air-gap magnetic flux current observation model. The inputs of the air-gap magnetic flux voltage observation model and the new air-gap magnetic flux current observation model are the stator voltage feedback value and the current feedback value. Compare the air-gap magnetic flux values calculated by the air-gap magnetic flux voltage observation model and the new air-gap magnetic flux current observation model, obtain the deviation between them, and use this deviation as the input signal of the sliding mode controller after being processed by a saturation function. The output signal of the sliding mode controller is smoothed by a low-pass filter to obtain a stator voltage correction value, and this stator voltage correction value is used to correct the sampled value of the stator voltage.

[0006] Further, the air-gap magnetic flux voltage observation model is calculated based on the stator voltage and current in the static coordinate system αβ0 axis system, and the model inputs are the stator voltages u mA 、u mB 、u mC , the currents i mA 、i mB 、i mC, the output is the air-gap flux linkage ψ in the αβ0 axis system mα , ψ mβ , the air-gap flux linkage voltage observation model based on the stationary coordinate αβ0 axis system is as follows:

[0007]

[0008] Among them, R s is the resistance of the stator winding, L sl is the leakage inductance of the stator winding, ψ mα is the α-axis stator air-gap flux linkage, ψ mβ is the β-axis stator air-gap flux linkage, u mα is the α-axis stator voltage, u mβ is the β-axis stator voltage, i mα is the α-axis stator current, i mβ is the β-axis stator current.

[0009] Furthermore, the air-gap flux linkage current observation model considering the influence of the damper winding includes the d-axis air-gap flux linkage current observation model and the q-axis air-gap flux linkage current observation model;

[0010] The d-axis air-gap flux linkage current observation model is:

[0011]

[0012] Among them, ψ Ddl is the leakage flux linkage of the d-axis damper winding, i Dd is the d-axis damper winding current, L Ddl is the leakage inductance of the d-axis damper winding, ψ md is the d-axis air-gap flux linkage, L md is the d-axis armature reaction inductance, i md is the d-axis stator current, i f is the field winding current;

[0013] The d-axis damper current is:

[0014]

[0015] Among them, ψ Dd is the d-axis damper winding flux linkage;

[0016] The q-axis air-gap flux linkage current observation model is:

[0017]

[0018] Among them, ψ Dq is the q-axis damper winding flux linkage, ψ mq is the q-axis air-gap flux linkage, ψ Dql is the leakage flux linkage of the q-axis damper winding, L mqis the q-axis armature reaction inductance, and i mq is the q-axis stator current, and i Dq is the q-axis damper winding current;

[0019] The q-axis damper current is:

[0020]

[0021] Among them, L Dql is the leakage inductance of the q-axis damper winding.

[0022] Furthermore, adding a non-linear link of the magnetization curve to the feedback channel of the air-gap flux current observation model to form a new air-gap flux current observation model. The inverse magnetization curve of the motor is obtained according to the no-load characteristic curve of the motor. This non-linear relationship only exists in the d-axis. Therefore, the influence of the q-axis magnetic saturation effect is negligible, and an air-gap flux current observation model that meets the actual engineering application is obtained.

[0023] Furthermore, the deviation is processed by a saturation function and used as the input signal of the sliding mode controller, as shown in the following formula:

[0024]

[0025] Among them, sign is the sign function, taking 1 for positive numbers and -1 for negative numbers; h is the sliding mode gain; is the corrected value of the α-axis of the stator voltage; is the corrected value of the β-axis of the stator voltage, is the α-axis air-gap flux value observed by the voltage model, is the α-axis air-gap flux value observed by the current model, is the β-axis air-gap flux value observed by the voltage model, is the β-axis air-gap flux value observed by the current model.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1) Improve the observation accuracy: Through the design of the hybrid air-gap flux observation method and the application of the sliding mode controller, the accurate observation of the motor air-gap flux is realized, and the accuracy and robustness of the observation are improved;

[0028] 2) Enhance the system stability: By considering the influence of the damper winding and the compensation strategy for the magnetic circuit saturation effect, the stability and reliability of the system are improved, and the failure rate is reduced;

[0029] 3) Improve control performance: Accurate flux linkage observation provides a reliable basis for motor control, contributing to more precise motor control and higher system efficiency. A non-linear link of the magnetization curve is added to the feedback channel of the air-gap flux current observation model to improve calculation accuracy, enhance system disturbance resistance, and improve response speed. At the same time, the application of a sliding mode controller improves the robustness of the system to non-linear characteristics and external disturbances, ensuring stable performance under various operating conditions and enhancing system adaptability. Description of the Drawings

[0030] Figure 1 is the structural diagram of the air-gap flux voltage observation model described in the present invention.

[0031] Figure 2 is the schematic diagram of the observation structure of the d-axis air-gap flux current observation model considering the influence of the damper winding in the present invention.

[0032] Figure 3 is the schematic diagram of the observation structure of the q-axis air-gap flux current observation model considering the influence of the damper winding in the present invention.

[0033] Figure 4 is the schematic diagram of the no-load characteristic curve of the electric-excitation synchronous motor in the present invention.

[0034] Figure 5 is the schematic diagram of the inverse magnetization curve of the electric-excitation synchronous motor in the present invention.

[0035] Figure 6 is the schematic diagram of the observation structure of the air-gap flux current observation model considering the non-linear saturation of the magnetic circuit of the electric-excitation synchronous motor in the present invention.

[0036] Figure 7 is the schematic diagram of the observation of the air-gap flux current observation model comprehensively considering the influence of the damper winding and the non-linear saturation of the magnetic circuit in the present invention.

[0037] Figure 8 is the hybrid air-gap flux observation control block diagram based on the sliding mode controller in the present invention.

[0038] Figure 9 is the schematic diagram of the simulation comparison result curve considering the damper winding and ignoring the damper winding in the present invention.

[0039] Figure 10 is the schematic diagram of the simulation comparison result curve considering the influence of the flux saturation effect in the present invention.

[0040] Figure 11 is the schematic diagram of the comparison result curve of the air-gap flux modulus value of the method described in the present invention with other methods. Detailed Embodiments

[0041] The following further describes the detailed embodiments of the present invention with reference to the drawings:

[0042] A method for observing the mixed air-gap magnetic flux of a synchronous motor in a high-power pumped storage system according to the present invention establishes an air-gap magnetic flux voltage observation model and an air-gap magnetic flux current observation model considering the influence of the damper winding. A new air-gap magnetic flux current observation model is formed by adding a non-linear link of the magnetization curve to the feedback channel of the air-gap magnetic flux current observation model. The inputs of the air-gap magnetic flux voltage observation model and the new air-gap magnetic flux current observation model are the stator voltage feedback value and the current feedback value. The air-gap magnetic flux values calculated by comparing the air-gap magnetic flux voltage observation model and the new air-gap magnetic flux current observation model are obtained, and the deviation between them is obtained. After processing this deviation through a saturation function, it is used as the input signal of the sliding mode controller. The output signal of the sliding mode controller is smoothed through a low-pass filter to obtain a corrected value of the stator voltage, and this corrected value of the stator voltage is used to correct the sampled value of the stator voltage.

[0043] See Figure 1 , which is the structural diagram of the air-gap magnetic flux voltage observation model. It is calculated based on the stator voltage and current in the static coordinate system αβ0 axis system. The model inputs are the stator voltages u mA , u mB , u mC , the currents i mA , i mB , i mC , and the outputs are the air-gap magnetic fluxes ψ mα , ψ mβ ;

[0044] According to the voltage equation of the synchronous motor in the αβ0 axis system, the relationship of the air-gap magnetic flux in the αβ0 axis system can be deduced, that is, the air-gap magnetic flux voltage observation model based on the static coordinate system αβ0 axis system:

[0045]

[0046] Among them, R s is the resistance of the stator winding, L sl is the leakage inductance of the stator winding, ψ mα is the stator air-gap magnetic flux on the α axis, ψ mβ is the stator air-gap magnetic flux on the β axis, u mα is the stator voltage on the α axis, u mβ is the stator voltage on the β axis, i mα is the stator current on the α axis, i mβ is the stator current on the β axis;

[0047] The magnetic flux identification method of the air-gap magnetic flux voltage observation model is mainly obtained by integrating the induced electromotive force of the electrically excited synchronous motor. Relatively speaking, the calculation of the air-gap magnetic flux is relatively easy. However, at low frequencies of the motor, the voltage is small, and at this time, the accuracy of obtaining the air-gap magnetic flux is low, which has a greater impact on the control accuracy and stability performance during the low-speed operation of the motor.

[0048] By performing a rotation transformation using the geometric axis of the motor rotor, a conventional mathematical model of the dq0 axis system of an electrically excited synchronous motor can be obtained. Considering the influence of the damper winding, the relationship between current and air-gap flux linkage is derived from the mathematical model of the dq0 axis system of the synchronous motor, that is, an air-gap flux linkage current observation model considering the influence of the damper winding. The air-gap flux linkage current observation model considering the influence of the damper winding includes a d-axis air-gap flux linkage current observation model and a q-axis air-gap flux linkage current observation model;

[0049] The d-axis air-gap flux linkage current observation model is as follows:

[0050]

[0051] where, ψ Ddl is the leakage flux linkage of the d-axis damper winding, i Dd is the current of the d-axis damper winding, L Ddl is the leakage inductance of the d-axis damper winding, ψ md is the d-axis air-gap flux linkage, L md is the d-axis armature reaction inductance, i md is the d-axis stator current, i f is the field winding current;

[0052]

[0053] where, ψ Dd is the flux linkage of the d-axis damper winding;

[0054] The q-axis air-gap flux linkage current observation model is as follows:

[0055]

[0056] where, is the flux linkage of the q-axis damper winding, ψ mq is the q-axis air-gap flux linkage, ψ Dql is the leakage flux linkage of the q-axis damper winding, L mq is the q-axis armature reaction inductance, i mq is the q-axis stator current, i Dq is the current of the q-axis damper winding;

[0057] The q-axis damper current is:

[0058]

[0059] where, L Dql is the leakage inductance of the q-axis damper winding.

[0060] Because the damper winding currents i Dd 、i DqIt is immeasurable. Therefore, in general engineering applications, the leakage reactance of the damper winding is directly ignored when observing the air-gap flux linkage, and the damper current is eliminated. Thus, the air-gap flux linkage equation is:

[0061]

[0062] Among them, is the time constant of the d-axis damper winding of the synchronous machine; is the time constant of the q-axis damper winding of the synchronous machine; in the context of flux linkage changes, the damper winding will generate a damper current, whose function is to oppose and slow down this change in flux linkage. Therefore, if the effect brought by the damper current is ignored, then during the dynamic process, the observation of the air-gap flux linkage will lose accuracy. And the present invention fully considers the influence of the damper winding and modifies the motor model to ensure that the observer can accurately reflect the actual operating state of the motor when observing the air-gap flux linkage;

[0063] In the present invention, the damper current expression is derived from the aforementioned relationship between the air-gap flux linkage and the current, and then the observation method of the air-gap flux linkage current observation model considering the influence of the damper current is obtained, as Figure 2 the schematic diagram of the observation structure of the d-axis air-gap flux linkage current observation model considering the influence of the damper winding, Figure 3 the schematic diagram of the observation structure of the q-axis air-gap flux linkage current observation model considering the influence of the damper winding; the simulation comparison results of considering the damper winding and ignoring the damper winding are as Figure 9 shown. The three curves in the figure are respectively the magnitude of the air-gap flux linkage of the motor provided by the simulation model, the magnitude of the air-gap flux linkage observed by the current observation model considering the damper winding, and the magnitude of the air-gap flux linkage observed by the current observation model ignoring the influence of the damper winding. It can be seen from the simulation results that if the influence of the damper winding is ignored, then the deviation between the observed magnitude of the air-gap flux linkage and the actual value is relatively large, especially in the dynamic adjustment stage of the motor.

[0064] Through the above analysis, there is a linear relationship between the current and the flux linkage, but in an actual motor, the relationship between the magnetic flux density and the magnetomotive force is non-linear, that is, the relationship between the flux linkage and the current is non-linear. Figure 4 is the no-load characteristic curve of the synchronous motor, that is, the magnetization curve of the electrically excited synchronous motor. It can be clearly seen from Figure 4 the magnetic saturation effect. When the excitation current increases, due to the saturation of the magnetic material, the magnetic resistance of the motor magnetic circuit increases, thus weakening the effect of the excitation current. Therefore, the curve will bend downward;

[0065] When the magnetization current of the motor is inversely calculated from the known motor flux linkage, the magnetization current of the motor conforms to the inverse magnetization curve shown in Figure 5 ;

[0066] To improve the calculation accuracy, enhance the system's anti-interference ability, and improve the response speed, the present invention designs a scheme considering the nonlinear influence of the magnetization curve as follows Figure 6 shown. A nonlinear link of the magnetization curve is added to the feedback channel of the air-gap flux current observation model considering the influence of the damping winding. Before the magnetization curve, for the magnetization current i μ , the stator current i m , and the rotor excitation current i f , the mathematical models for calculating the flux are all linear. Denote the flux calculated by the linear model as ψ δi , expressed as a current quantity. After the nonlinear transformation, the observed flux value ψ δi becomes the magnetic flux ψ δ , which forms a closed-loop control with the given value to realize a new air-gap flux current observation model considering the magnetization curve;

[0067] In summary, according to the no-load characteristic curve of the motor, the inverse magnetization curve of the motor can be obtained. Also, since this nonlinear relationship only exists in the d-axis and the influence of the q-axis can be ignored, an air-gap flux-current observation model that conforms to practical engineering applications is obtained as Figure 7 shown; The simulation comparison results considering the influence of flux saturation effect are as Figure 10 shown. The three curves in the figure are respectively the magnitude of the air-gap flux of the motor provided by the simulation model, the magnitude of the air-gap flux observed by the current observation model considering the influence of the flux saturation effect, and the magnitude of the air-gap flux observed by the current observation model without the influence of the flux saturation effect. From the simulation results, it can be seen that if the influence of the damping winding is ignored, the deviation between the observed magnitude of the air-gap flux and the actual value is relatively large, especially in the dynamic adjustment stage of the motor.

[0068] Introduce a compensation strategy for the magnetic circuit saturation effect. By real-time monitoring of the motor current and voltage, and using the magnetic circuit saturation characteristic curve, dynamically adjust the observation parameters to reduce the influence of the magnetic circuit saturation on the observation accuracy of the air-gap flux;

[0069] The flux identification method of the air-gap flux voltage observation model mainly obtains it by integrating the induced electromotive force of the synchronous motor. Relatively speaking, the calculation of the air-gap flux is relatively easy, but at low frequencies of the motor, the voltage is small, and at this time, the accuracy of obtaining the air-gap flux is low; To obtain accurate air-gap flux information, the present invention adopts a hybrid flux calculation method using a sliding mode controller to correct the voltage observation model and the current observation model. The control block diagram is as Figure 8 shown;

[0070] Figure 8 shown. The observer built combines the advantages of the voltage observation model and the current observation model in calculating the air-gap flux, can automatically switch the observation mode according to different working conditions, and realizes the accurate observation of the motor air-gap flux; First, by comparing the air-gap flux values calculated by the voltage observation model and the current observation model, that is and Calculate the deviation between them, and use this deviation as the input signal of the sliding mode controller SMC. To suppress the excessive jitter that may exist in the input signal, this deviation signal is first processed by a saturation function to ensure that the signal input to the sliding mode controller SMC is within the set deviation;

[0071] Subsequently, the signal processed by the saturation function is sent into the sliding mode controller SMC, as shown in the following formula, where sign is the sign function, taking 1 for positive numbers and -1 for negative numbers, and h is the sliding mode gain,

[0072]

[0073] where, is the correction value of the α-axis of the stator voltage; is the correction value of the β-axis of the stator voltage, is the α-axis air-gap flux linkage value observed by the voltage model, is the α-axis air-gap flux linkage value observed by the current model, is the β-axis air-gap flux linkage value observed by the voltage model, is the β-axis air-gap flux linkage value observed by the current model;

[0074] The sliding mode controller is known for its strong robustness and anti-interference ability, but its output may contain high-frequency jitter noise. To eliminate these high-frequency components, the output signal of the sliding mode controller SMC is smoothed by a low-pass filter LPF to obtain the correction value of the stator voltage;

[0075] This correction value is used to correct the sampled value of the stator voltage, so as to observe a more accurate and standard air-gap flux linkage value through the stator voltage observation model. This process not only improves the accuracy of air-gap flux linkage observation, but also realizes the smooth transition between the voltage observation model and the current observation model in air-gap flux linkage observation, enhancing the stability and performance of the entire motor control system;

[0076] Figure 11 Compared the magnitude of the air-gap flux linkage provided by the motor model, the magnitude of the hybrid observed air-gap flux linkage based on the sliding mode controller SMC, and the magnitude of the hybrid observed air-gap flux linkage based on the conventional PI. It can be seen that during the dynamic regulation process, the magnitude of the hybrid observed air-gap flux linkage based on the sliding mode controller SMC can quickly respond to the change of the flux linkage and accurately observe the air-gap flux linkage.

[0077] The above embodiments are implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are all conventional methods unless otherwise specified.

Claims

1. A method for observing the mixed air gap flux of a synchronous motor in a high-power pumped storage system, characterized in that: An air-gap flux voltage observation model and an air-gap flux current observation model with the influence of damping winding are established, and the nonlinear link of the magnetization curve is added to the feedback channel of the air-gap flux current observation model to form a new air-gap flux current observation model. The inputs of the air-gap flux voltage observation model and the new air-gap flux current observation model are the stator voltage feedback value and the current feedback value. The air-gap flux values ​​calculated by the air-gap flux voltage observation model and the new air-gap flux current observation model are compared to obtain the deviation between them. This deviation is processed by a saturation function and used as the input signal of the sliding mode controller. The output signal of the sliding mode controller is smoothed by a low-pass filter to obtain a stator voltage correction value, which is used to correct the sampling value of the stator voltage.

2. The method for observing the hybrid air gap flux of a synchronous motor in a high-power pumped storage system according to claim 1 is characterized in that: The air gap flux voltage observation model is based on the stator voltage and current calculation of the stationary coordinate system αβ0 axis system. The model input is the stator voltage u mA 、u mB 、u mC , current i mA 、i mB 、i mC , the output is αβ0 axis air gap flux ψ mα , mβ , the air gap flux voltage observation model based on the stationary coordinate system αβ0 axis system is as follows: Among them, R s is the resistance of the stator winding, L sl is the leakage inductance of the stator winding, ψ mα is the stator air gap flux on the α axis, ψ mβ is the β-axis stator air gap flux, u mα is the α-axis stator voltage, u mβ is the β-axis stator voltage, i mα is the α-axis stator current, i mβ is the β-axis stator current.

3. The method for observing the mixed air gap flux of a synchronous motor in a high-power pumped storage system according to claim 1 is characterized in that: The air gap flux current observation model with the damping winding effect added includes a d-axis air gap flux current observation model and a q-axis air gap flux current observation model; The d-axis air gap flux current observation model is: Among them, ψ Ddl is the leakage flux of the d-axis damping winding, i Dd is the d-axis damping winding current, L Ddl is the leakage inductance of the d-axis damping winding, ψ md is the d-axis air gap flux, L md is the d-axis armature reaction inductance, i md is the d-axis stator current, i f is the exciting winding current; The d-axis damping current is: Among them, ψ Dd is the d-axis damping winding flux; The q-axis air gap flux current observation model is: Among them, ψ Dq is the q-axis damping winding flux, ψ mq is the q-axis air gap flux, ψ Dql is the leakage flux of the q-axis damping winding, L mq is the q-axis armature reaction inductance, i mq is the q-axis stator current, i Dq is the q-axis damping winding current; The q-axis damping current is: Among them, L Dql is the leakage inductance of the q-axis damping winding.

4. The method for observing the hybrid air gap flux of a synchronous motor in a high-power pumped storage system according to claim 1 is characterized in that: The nonlinear link of the magnetization curve is added to the feedback channel of the air gap flux current observation model to form a new air gap flux current observation model. The reverse magnetization curve of the motor is obtained according to the no-load characteristic curve of the motor. This nonlinear relationship only exists in the d-axis, so the influence of the q-axis magnetic saturation effect is negligible, and the air gap flux current observation model that meets the actual engineering application is obtained.

5. The method for observing the mixed air gap flux of a synchronous motor in a high-power pumped storage system according to claim 1 is characterized in that: The deviation is processed by the saturation function and used as the input signal of the sliding mode controller, as shown in the following formula: Where, sign is the sign function, which takes 1 for positive numbers and -1 for negative numbers; h is the sliding mode gain; is the stator voltage α-axis correction value; is the stator voltage β-axis correction value, is the α-axis air gap flux value observed by the voltage model, is the α-axis air gap flux value observed by the current model, is the β-axis air gap flux value observed by the voltage model, is the β-axis air gap flux value observed by the current model.

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