Fractional order PID (Proportion Integration Differentiation) additional frequency control method and system for doubly-fed variable-speed pumped storage unit

Abstract

The invention relates to a doubly-fed variable-speed pumped storage unit fractional order PID additional frequency control method and system, and the method comprises the steps: building an electrical mathematical model of a doubly-fed induction motor based on a synchronous rotating coordinate system, enabling a stator flux linkage to be aligned with the d-axis direction through employing a stator flux linkage directional control strategy, and enabling the stator flux linkage to be aligned with the d-axis direction; therefore, decoupling adjustment of active power and reactive power output by the unit is realized. The frequency deviation between the power grid common connection point frequency and the rated frequency is obtained and serves as an input signal of the fractional order PID additional controller, the frequency deviation can be effectively restrained under various working conditions, the system stability and the inertia supporting capacity are enhanced, and the method is suitable for auxiliary frequency control of a variable speed pumped storage unit in a high-proportion new energy power grid.

Description

Technical Field

[0001] This application relates to the field of control technology for variable speed pumped storage units, specifically to a fractional-order PID additional frequency control method and system for doubly-fed variable speed pumped storage units. Background Technology

[0002] As the proportion of intermittent renewable energy sources such as wind and solar power in the power system continues to increase, the power grid faces challenges such as increased frequency fluctuations and weakened system inertia. Against this backdrop, pumped storage, as a large-capacity energy storage method with fast response and a wide regulation range, is increasingly becoming a key technology for supporting frequency stability in new power systems. In particular, variable-speed pumped storage units based on doubly-fed induction generators have significant advantages in system frequency regulation, power balance, and inertia support due to their high energy regulation accuracy and flexible decoupling control of active and reactive power.

[0003] However, in variable frequency operation mode, the rotor speed of traditional doubly-fed induction generator (DFIG) units is decoupled from the grid frequency, resulting in a significant decrease in their inertial response to frequency disturbances and a weakening of the equivalent moment of inertia. This makes it difficult to effectively provide the required "virtual inertia," a problem particularly prominent in scenarios with high penetration rates of renewable energy. To compensate for this deficiency, existing research proposes introducing an additional frequency control strategy into the DFIG unit control loop. This strategy adjusts the rotor excitation current to quickly respond to frequency changes, thereby achieving auxiliary inertial support. However, most existing additional control methods employ integer-order PID controllers, which struggle to balance system dynamic performance and robustness. Furthermore, the control parameter tuning relies heavily on experience, making it difficult to adapt to complex operating conditions.

[0004] In recent years, fractional-order control theory, due to its inherent memory and heritability, has gradually gained widespread application in nonlinear modeling and control of power systems. Fractional-order PID controllers outperform traditional PID controllers in both parameter tuning freedom and dynamic response sensitivity, and are expected to provide better performance guarantees for additional frequency control in generating units. However, due to the large number of parameters and complex structure of fractional-order controllers, how to efficiently tune the control parameters under multi-objective constraints has become a key challenge in their practical engineering applications.

[0005] Therefore, there is an urgent need for a new frequency control strategy that integrates fractional-order PID control mechanism and advanced intelligent optimization algorithm to improve the dynamic adjustment capability and system stability of doubly-fed variable-speed pumped storage units under frequency disturbance conditions, and to achieve more efficient and flexible auxiliary service response. Summary of the Invention

[0006] The purpose of this application is to provide a fractional-order PID additional frequency control method and system for doubly-fed variable-speed pumped storage units, which solves the problems of insufficient inertial support capability in frequency disturbance response, poor adjustment flexibility of traditional controllers, and difficulty in parameter tuning of existing doubly-fed variable-speed pumped storage units.

[0007] To achieve the above objectives, this application provides the following technical solution:

[0008] In a first aspect, embodiments of this application provide a fractional-order PID additional frequency control method for a doubly-fed variable-speed pumped storage unit, comprising the following specific steps:

[0009] An electrical mathematical model of a doubly fed induction motor is established based on a synchronous rotating coordinate system, and a stator flux orientation control strategy is adopted to align the stator flux with the d-axis direction, thereby achieving decoupled regulation of the unit's output active and reactive power.

[0010] Obtain the frequency deviation between the power grid point of common coupling frequency and the rated frequency. As the input signal to the fractional-order PID additional controller, the fractional-order PID controller outputs an additional q-axis current component. Its expression is:

[0011] in, , , For controller gain parameters, , Let be the fractional orders of the integral and the differential, respectively, satisfying... The fractional-order calculus operator D is approximated in the frequency domain using an Oustaloup hierarchical filter, which... This is superimposed on the original rotor current reference signal to form a new q-axis shaft current command. The frequency deviation is controlled by the converter to adjust the active power output of the unit, thereby achieving dynamic response and stable control to system frequency disturbances. Obtained by the frequency measurement module, it is defined as the difference between the unit's current real-time frequency and the rated frequency.

[0012] The approximation band of the Oustaloup filter is set to to A 5th-order hierarchical approximation is used for the digital implementation of fractional operators.

[0013] The controller parameters , , , and Global optimization is performed using the improved Grey Wolf Optimization Algorithm (GGWO), with the objective function being the minimum integral of the absolute error of frequency deviation (IAE). This algorithm improves the accuracy and robustness of controller parameter optimization by combining grouped collaborative search with a random reconnaissance strategy.

[0014] The initial search range for the controller parameters in the GGWO algorithm is: .

[0015] Secondly, this application provides a fractional-order PID-assisted frequency control system for a doubly-fed variable-speed pumped storage unit. This system comprises the following functional modules: a frequency signal detection module, a fractional-order proportional-integral-derivative (FOPID) control module, an Oustaloup approximate digital filter module, a improved grey wolf optimization (GGWO) parameter tuning module, and a control signal injection execution module. During system operation, the frequency detection module monitors the grid frequency deviation in real time and transmits it as input to the FOPID control module. This controller module outputs an initial control signal, which is processed by the Oustaloup filter to generate a precise control quantity. The controller parameters are globally optimized by the GGWO optimization module to ensure optimal control performance. Finally, the control signal is injected into the current command channel of the unit's rotor-side converter through the injection module, achieving rapid adjustment and dynamic stability control of the unit's response characteristics under frequency disturbances, thereby enhancing the system's frequency support capability and frequency regulation effect.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1. It adopts a fractional-order PID control structure, which has stronger adjustment flexibility and memory, and can better adapt to complex power grid frequency disturbance scenarios;

[0018] 2. The introduction of the Oustaloup approximation method facilitates engineering implementation and deployment of digital control systems;

[0019] 3. By combining the improved gray wolf optimization algorithm, intelligent tuning of control parameters is achieved, thereby improving the robustness and adaptability of the controller;

[0020] 4. Higher frequency response accuracy and smoother adjustment process, effectively enhancing the virtual inertial response capability of the variable speed unit.

[0021] In summary, the doubly-fed variable-speed pumped storage unit additional fractional-order PID frequency control method and system proposed in this invention can effectively enhance the frequency regulation performance of the unit, and provide an efficient and reliable auxiliary frequency regulation technology solution for building a new power system under the condition of high proportion of new energy grid connection. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 Block diagram of the stator flux orientation control strategy for the rotor side of the variable speed pumped storage unit;

[0024] Figure 2 Block diagram of fractional-order PID with added frequency control;

[0025] Figure 3 Parameter optimization process and framework for fractional-order PID with added frequency control;

[0026] Figure 4 Simulation model of variable speed pumped storage unit;

[0027] Figure 5 Simulink block diagram of rotor-side control for a variable-speed pumped storage unit;

[0028] Figure 6 Comparison of different methods for subsynchronization of variable speed pumped storage units under sudden load increases;

[0029] Figure 7 Comparison of different methods and frequencies for synchronizing variable speed pumped storage units under sudden load increases;

[0030] Figure 8 Comparison of different methods for frequency response to supersynchronization of variable speed pumped storage units under sudden load increases. Detailed Implementation

[0031] The technical solutions of the embodiments of this application will now be described with reference to the accompanying drawings. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0032] The terms “comprising,” “including,” or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase “comprising one…” does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0033] The terms “first,” “second,” etc., are used only to distinguish one entity or operation from another, and should not be construed as indicating or implying relative importance, nor as requiring or implying any such actual relationship or order between these entities or operations.

[0034] This invention relates to a frequency regulation method for doubly fed variable speed pumped storage units based on fractional-order PID control and an improved Grey Wolf Optimization (GGWO) algorithm, aiming to improve their dynamic performance and robustness in power system frequency control.

[0035] 1. Unit modeling and electrical control structure

[0036] To accurately characterize the control characteristics of a doubly-fed variable-speed pumped storage unit during frequency regulation, this embodiment models its electrical characteristics in a synchronous rotating coordinate system (dq coordinate system). The model includes the voltage equations and flux linkage equations for the stator and rotor, and further derives the expressions for active and reactive power to facilitate subsequent controller design.

[0037] The voltage equation is as follows:

[0038] in, Representing the stator and rotor respectively shaft and Voltage component along the axial direction; These are the current components along the corresponding axes; Indicates the magnetic flux linkage component; and These are the resistances of the stator and rotor, respectively; Given the synchronous electrical angular frequency, the slip angular velocity is defined as follows: ,in ω is the electric angular velocity of the rotor.

[0039] Furthermore, the relationship between magnetic flux and electric current is as follows:

[0040] The equivalent inductances of the stator and rotor are respectively and ,in This represents the mutual inductance between the stator and rotor. and These represent the leakage inductance parameters of the stator and rotor, respectively.

[0041] To achieve independent regulation of the unit's active and reactive power, this paper introduces a stator flux orientation control method on the rotor side, namely, making... At this point, the relationship between the stator and rotor currents and the magnetic flux is as follows:

[0042]

[0043] in Let be the leakage flux coefficient. Substituting the above expression for rotor flux linkage into the voltage model, the voltage equation on the rotor side can be expressed as:

[0044]

[0045] Under steady-state operation, the effect of stator resistance on phase can be ignored. Assuming the stator voltage vector is orthogonal to the stator flux linkage, the unit's output active and reactive power can be expressed as:

[0046]

[0047] in, These represent the active and reactive power outputs of the stator, respectively. This indicates the magnitude of the stator-side voltage.

[0048] In summary, as Figure 1 As shown. Under the stator flux orientation control strategy, the doubly-fed variable-speed pumped storage unit can achieve control over the rotor current component. This allows for independent adjustment, thereby achieving decoupled control of the unit's active and reactive power outputs. This control structure provides a sound modeling foundation and control interface for the introduction of additional frequency control strategies.

[0049] 2. Design of an Additional Fractional-Order PID Frequency Controller

[0050] To compensate for the insufficient inertial response of variable speed units and improve their performance in frequency control, this invention designs a fractional-order PID auxiliary controller based on the original dual-loop current control structure, the structure of which is as follows: Figure 2 As shown. The controller uses the system frequency deviation. As input signal, output additional current command quantity Superimposed on q-axis reference value The formula is as follows:

[0051]

[0052] in, For controller gain parameters, These represent the fractional integral and differential orders, respectively. Since fractional operators cannot be directly implemented, this paper employs an Oustaloup hierarchical filter in the frequency range... A fifth-order approximation is performed internally to achieve its digital realization.

[0053] 3. Parameter optimization and tuning: Implementation of the GGWO algorithm

[0054] This invention employs an improved Grouped Grey Wolf Optimizer (GGWO) algorithm to optimize controller parameters. Tuning is performed. This method introduces "group cooperative hunting" and "random reconnaissance" mechanisms on the basis of traditional GWO, improving the diversity and convergence speed of the algorithm, and optimizing the process as follows: Figure 3 As shown. This algorithm achieves a better balance between local exploration and global search by improving the gray wolf pack grouping mechanism, thus obtaining better quality search results. GGWO is an improved algorithm of the conventional gray wolf optimizer (GWO). It introduces a grouping mechanism to achieve broader and deeper cooperative hunting among gray wolves, thereby significantly improving the global optimal search performance. Its prey encirclement strategy is as follows:

[0055]

[0056] In the formula: Indicates the current iteration number; and These are the position vectors of the prey and the gray wolf, respectively. and It is a coefficient vector; It is the encirclement coefficient vector, whose value decreases linearly from 2 to 1 during the iteration process. and They represent in Random vectors in.

[0057] The hunting strategy is described as follows:

[0058]

[0059] in, and They represent and The position vectors of the three levels of gray wolves; the corresponding guiding parameters are denoted as follows: and This is used to measure their guiding role in the search direction.

[0060] The random reconnaissance strategy is as follows:

[0061]

[0062] in, It is a random reconnaissance vector with an arbitrary range, limited only by the upper and lower bounds of controllable variables. Figure 3 middle, To determine the convergence criterion, we select [the following] here. ; and They represent the first time. The second iteration and the first The fitness function value at the next iteration.

[0063] The algorithm's objective function is the absolute integral (IAE) of the frequency deviation:

[0064]

[0065] To improve parameter tuning efficiency, the initial parameter range is first set based on the frequency response characteristics of the variable-speed pumped storage unit. Referring to existing literature and engineering experience, the recommended initial range is as follows: ; ; ; ; ;in, This avoids excessively strong low-frequency gain. It can prevent high-frequency noise amplification and form a stable response bandwidth.

[0066] Ultimately, the GGWO search yields the optimal parameter set for controller deployment, enhancing frequency regulation performance and robustness.

[0067] 4. Simulation System and Performance Verification

[0068] To verify the effectiveness of the controller, a system was built based on Simulink, such as... Figure 4 The doubly-fed variable-speed pumped storage unit grid-connected simulation system shown is illustrated in the rotor-side control block diagram of the variable-speed unit as follows: Figure 5 As shown, a system frequency disturbance scenario is simulated. A 336MW doubly-fed variable-speed pumped-storage unit is connected to the system and further connected to the 500kV main grid. A complex power load is set at the point of common coupling (PCC). It is used to simulate load conditions in actual operation.

[0069] The main electrical parameters of the unit are as follows: The rated capacity is 336 MVA, the rated stator voltage is 15.75 kV, and the corresponding rated stator current is 12317 A; the rotor-side rated voltage is 3.3 kV, and the rated current is 6400 A. Regarding impedance parameters, the stator resistance is... The rotor resistance is also The stator leakage inductance is 0.3267 mH, and the rotor leakage inductance is 0.4442 mH; the mutual inductance between the stator and rotor is 8.2 mH. These parameters provide basic data support for subsequent modeling and simulation analysis.

[0070] To verify the robustness and regulation performance of the proposed fractional-order PID frequency control method under different operating conditions, system frequency disturbance simulations were conducted on the doubly-fed variable-speed pumped storage unit under three typical operating conditions: subsynchronous, synchronous, and supersynchronous. The operating condition was set as a sudden increase of 500MW in system load, and the frequency response effect under different control strategies was observed. Simulation results are shown below. Figures 6-8 .

[0071] like Figure 6 As shown, in subsynchronous operation, compared to traditional control methods without additional control, the proposed method responds to frequency disturbances more quickly, effectively suppresses the initial frequency drop, and significantly shortens the frequency recovery time. Especially in the initial stage, the proposed method's controller exhibits stronger dynamic response capabilities, enabling the system frequency to quickly approach the steady-state value and avoiding excessive frequency sags. Furthermore, Figure 7 The simulation results are shown for synchronous operation. It can be seen that although both control methods can achieve a certain degree of frequency recovery, the proposed method has a significant advantage in controlling steady-state error. Its frequency response is smoother, overshoot is minimal, and the system can enter the stable region more quickly. Furthermore, as... Figure 8 As shown, under supersynchronous operation, the system frequency fluctuation response is further aggravated, posing a greater challenge to controller regulation. In this case, the proposed method achieves a good balance between rapid adjustment and steady-state maintenance, not only reducing the maximum frequency drop amplitude but also significantly reducing the oscillation duration, demonstrating its good nonlinear adaptability and anti-interference capability.

[0072] In summary, the simulation results show that the fractional-order PID additional frequency control method for doubly fed variable speed pumped storage units based on GGWO proposed in this invention has excellent dynamic regulation performance and steady-state robustness under different synchronization states. In particular, it exhibits higher frequency control accuracy and system stability under load disturbance conditions, which is superior to traditional control strategies and is suitable for the wide frequency regulation requirements in grid-connected systems of high-proportion variable speed units.

[0073] This application also provides a fractional-order PID-assisted frequency control system for a doubly-fed variable-speed pumped storage unit. This system comprises the following functional modules: a frequency signal detection module, a fractional-order proportional-integral-derivative (FOPID) control module, an Oustaloup approximate digital filter module, a improved grey wolf optimization (GGWO) parameter tuning module, and a control signal injection execution module. During system operation, the frequency detection module monitors the grid frequency deviation in real time and transmits it as input to the FOPID control module. This controller module outputs an initial control signal, which is processed by the Oustaloup filter to generate a precise control quantity. The controller parameters are globally optimized by the GGWO optimization module to ensure optimal control performance. Finally, the control signal is injected into the current command channel of the unit's rotor-side converter through the injection module, achieving rapid adjustment and dynamic stability control of the unit's response characteristics under frequency disturbances, thereby enhancing the system's frequency support capability and frequency regulation effect.

[0074] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A fractional-order PID additional frequency control method for a doubly-fed variable-speed pumped storage unit, characterized in that, The specific steps include the following: An electrical mathematical model of a doubly fed induction motor is established based on a synchronous rotating coordinate system, and a stator flux orientation control strategy is adopted to align the stator flux with the d-axis direction, thereby achieving decoupled regulation of the unit's output active and reactive power. Obtain the frequency deviation between the power grid point of common coupling frequency and the rated frequency. As the input signal to the fractional-order PID additional controller, the fractional-order PID controller outputs an additional q-axis current component. Its expression is: ， in, , , For controller gain parameters, , Let be the fractional orders of the integral and the differential, respectively, satisfying... The fractional-order calculus operator D is approximated in the frequency domain using an Oustaloup hierarchical filter, which... This is superimposed on the original rotor current reference signal to form a new q-axis current command. The converter then regulates the active power output of the unit, thereby achieving dynamic response and stable control to system frequency disturbances.

2. The fractional-order PID additional frequency control method for doubly-fed variable-speed pumped storage units according to claim 1, characterized in that, The frequency deviation Obtained by the frequency measurement module, it is defined as the difference between the unit's current real-time frequency and the rated frequency.

3. The fractional-order PID additional frequency control method for doubly-fed variable-speed pumped storage units according to claim 1, characterized in that, The approximation band of the Oustaloup filter is set to to A fifth-order hierarchical approximation is used for the digital implementation of fractional operators.

4. The fractional-order PID additional frequency control method for doubly-fed variable-speed pumped storage units according to claim 1, characterized in that, The controller parameters , , , and Global optimization is performed using the improved Grey Wolf Optimization Algorithm (GGWO), with the objective function being the minimum integral of the absolute error of frequency deviation (IAE). This algorithm improves the accuracy and robustness of controller parameter optimization by combining grouped collaborative search with a random reconnaissance strategy.

5. The fractional-order PID additional frequency control method for doubly-fed variable-speed pumped storage units according to claim 4, characterized in that, The initial search range for the controller parameters in the GGWO algorithm is: .

6. A fractional-order PID-assisted frequency control system for a doubly-fed variable-speed pumped storage unit, characterized in that, The system consists of the following functional modules: a frequency signal detection module, a fractional-order proportional-integral-derivative (FID) control module, an Oustaloup approximate digital filter module, an improved gray wolf (GGWO) optimization parameter tuning module, and a control signal injection execution module. During system operation, the frequency detection module monitors the grid frequency deviation in real time and transmits it as input to the FOPID control module. The controller module outputs an initial control signal, which is processed by the Oustaloup filter to generate a precise control quantity. The controller parameters are globally optimized by the GGWO optimization module to ensure optimal control performance. Finally, the control signal is connected to the current command channel of the unit's rotor-side converter through the injection module, realizing rapid adjustment and dynamic stability control of the unit's response characteristics under frequency disturbances, thereby enhancing the system's frequency support capability and frequency regulation effect.

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