Self-adaptive demagnetization control strategy for variable-speed pumped storage unit under low penetration

Abstract

The invention discloses a self-adaptive demagnetization control strategy for a variable-speed pumped storage unit under low penetration, and the strategy comprises the steps: building a doubly-fed induction motor mathematical model of a variable-speed pumped storage system, and building an exponential decay function of a stator flux linkage based on the doubly-fed induction motor mathematical model, a vector control system of the doubly-fed induction motor is established based on the mathematical model of the doubly-fed induction motor and the exponential decay function, a stator flux linkage reference value and a rotor reference current are dynamically adjusted based on the vector control system, a rotor target voltage is output, and adaptive control is performed on a rotor side converter RSC based on the rotor target voltage. Through fault depth adaptive parameter adjustment, dynamic flux linkage trajectory reconstruction and torque prediction feedback control, rapid clearing and accurate regulation and control of electromagnetic energy during a fault period are realized, rotor current and torque fluctuation are significantly reduced, transition response of a natural flux linkage can be effectively suppressed, electromagnetic oscillation time is shortened, and the fault diagnosis efficiency is improved. And the rotor voltage and current are ensured to operate in an RSC capacity range.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel power system energy storage, and in particular relates to an adaptive demagnetization control strategy under low-speed wear of a variable-speed pumped storage unit. Background Art

[0002] Variable-speed pumped storage (VSPS) systems are highly efficient, long-term energy storage and frequency regulation technologies designed to address power fluctuations caused by the integration of large-scale renewable energy sources into the grid. Variable-speed systems typically utilize a doubly-fed induction motor (DFIM) as the core drive device. The rotor-side converter (RSC) controls its excitation current, enabling flexible power regulation and efficient operation. Low voltage ride-through (LVRT) requires that generators remain connected to the grid during voltage sags or short-term faults while providing a certain amount of reactive power support to restore voltage. Traditional generators rely on synchronous generators, which offer strong voltage support capabilities. However, the limited capacity of the rotor-side converter (RSC) in DFIM systems prevents them from providing a rotor voltage that matches the stator voltage during voltage sags. This results in a sharp increase in rotor current, DC-side voltage overshoot, and even triggering crowbar protection, which can cause the system to lose reactive power support and further deteriorate grid stability. At the same time, DC-side voltage stability and rotor-side converter overcurrent protection issues in DFIGs also pose challenges to the system's sustained and stable operation. Voltage sags caused by grid faults can trigger severe stator flux disturbances, generating transient back electromotive force (EMF) and overcurrent peaks on the rotor side, threatening the safe operation of the rotor-side converter (RSC). To address these issues, various LVRT control strategies have been proposed. Current LVRT control schemes primarily rely on temporary hardware protection and fixed control strategies, but these have significant limitations in addressing varying fault types and depths. On the one hand, they cannot dynamically adjust control parameters based on fault severity, leading to overprotection and wasted control potential during minor faults. On the other hand, under severe fault conditions, the response lag system cannot effectively suppress transient shocks to the rotor current and stator flux. Therefore, the DFIG, which is tightly coupled to the grid on the stator side, faces the problem of air gap flux not being able to dissipate instantaneously. Because the stator flux remains high for a very short period of time, excessive transient currents are generated on the rotor side, accompanied by torque fluctuations and even excessive equipment stress. Therefore, in the context of a high proportion of renewable energy connected to the grid, the shortcomings of traditional solutions make it difficult for DFI M to meet the stringent requirements of the power system for fast, precise, economical and efficient dynamic regulation. Summary of the Invention

[0003] To solve the above problems, the present invention provides an adaptive demagnetization control strategy for a variable-speed pumped storage unit under low-breakdown conditions, so as to address the significant limitations of traditional LVRT control strategies in dealing with different fault types and depths. On the one hand, the control parameters cannot be dynamically adjusted according to the severity of the fault, resulting in over-protection and waste of regulation potential in the case of mild faults. On the other hand, under deep fault conditions, due to the response lag, the system cannot effectively suppress the transient impact of the rotor current and stator flux, and the DFI G, which is tightly coupled to the power grid on the stator side, faces the problem that the air gap flux cannot disappear instantaneously.

[0004] An adaptive demagnetization control strategy for a variable-speed pumped storage unit under low-speed wear-through conditions includes:

[0005] Establish a mathematical model of the doubly-fed induction motor for a variable-speed pumped storage system;

[0006] An exponential decay function of the stator flux is established based on the mathematical model of the doubly-fed induction motor;

[0007] Build a vector control system for a doubly fed induction motor based on its mathematical model and exponential decay function;

[0008] Based on the vector control system, the stator flux reference value and the rotor reference current are dynamically adjusted and the rotor target voltage is output;

[0009] The rotor-side converter (RSC) is adaptively controlled based on the rotor target voltage.

[0010] According to a specific embodiment of the present invention, establishing a mathematical model of a doubly-fed induction motor of a variable-speed pumped-storage system includes:

[0011] The mathematical model of the doubly-fed induction motor of the variable-speed pumped storage system is established using the dq-axis synchronous rotating coordinate system with stator flux orientation.

[0012] According to a specific embodiment of the present invention, the mathematical model of the doubly-fed induction motor includes:

[0013] Stator voltage equation:

[0014]

[0015] Among them, v s,d is the d-axis component of the stator voltage, v s,q is the q-axis component of the stator voltage, i s,d is the d-axis component of the stator current, i s,q is the q-axis component of the stator current, ψ s,d is the d-axis component of the stator flux, ψ s,q is the q-axis component of the stator flux, R s is the stator winding resistance, ω s is the synchronous angular velocity;

[0016] Rotor voltage equation:

[0017]

[0018] Among them, v r,d is the d-axis component of the rotor voltage, v r,q is the q-axis component of the rotor voltage, i r,d is the d-axis component of the rotor current, i r,q is the q-axis component of the rotor current, ψ r,d is the d-axis component of the rotor flux, ψ r,q is the q-axis component of the rotor flux, R r is the rotor winding resistance, ω r is the rotor mechanical angular velocity;

[0019] Rotor flux state equation:

[0020]

[0021] Where, L s is the stator self-inductance, L r is the rotor self-inductance, L m is the mutual inductance, σ is the leakage coefficient, and s is;

[0022] Electromagnetic torque equation:

[0023]

[0024] Where, T e is the electromagnetic torque, and p is the number of pole pairs.

[0025] According to a specific embodiment of the present invention, establishing an exponential decay function of the stator flux based on a doubly-fed induction motor mathematical model includes:

[0026] During LVRT, the voltage dip depth ΔV is defined as:

[0027]

[0028] Where V nom is the steady-state voltage, V fault is the fault voltage;

[0029] The decay rate factor λ(ΔV) is defined based on the voltage drop depth as:

[0030]

[0031] Where λ0 is the minimum decay rate, λ1 is the deep fault decay rate;

[0032] The exponential decay function of the stator flux is established based on the decay rate factor λ(ΔV) and the mathematical model of the doubly fed induction motor. for:

[0033]

[0034] Where, ψ s0 is the stator flux reference value, k ψ is the gain coefficient, is the real-time reactive power feedback signal after first-order filtering, t fault is the time when the fault occurs, and t is the time variable.

[0035] According to a specific embodiment of the present invention, a vector control system for a doubly-fed induction motor is constructed based on a mathematical model of the doubly-fed induction motor and an exponential decay function, including:

[0036] Based on the mathematical model of the doubly fed induction motor and the exponential decay function, a stator flux given value is constructed. and Rotor current setpoint and Rotor voltage setpoint and As the input signal, the actual measured value of stator flux ψ s,d and ψ s,q , Actual measured value of rotor current i r,d and i r,q , Actual measured value of rotor voltage u r,d and u r,q A vector control system with RSC modulation signal as the output signal and RSC modulation signal as the feedback signal.

[0037] According to a specific embodiment of the present invention, the stator flux given value and The calculation formula is:

[0038]

[0039] Rotor current setpoint and The calculation formula is:

[0040]

[0041] in, is the stator flux d-axis current, is the stator flux q-axis current;

[0042] Rotor voltage setpoint and The calculation formula is:

[0043]

[0044] Among them, e rd is the rotor d-axis error signal, e rq is the rotor q-axis error signal.

[0045] According to a specific embodiment of the present invention, a vector control system includes:

[0046] The first signal input terminal, the second signal input terminal, the first PI controller, the second PI controller, the third PI controller, the fourth PI controller, the dq-abc coordinate converter and the space vector pulse width modulator, the first signal input terminal, the first PI controller, the second PI controller and the dq-abc coordinate converter are connected in sequence, the second signal input terminal, the third PI controller, the fourth PI controller and the dq-abc coordinate converter are connected in sequence, and the dq-abc coordinate converter is connected to the space vector pulse width modulator.

[0047] According to a specific embodiment of the present invention, dynamically adjusting the stator flux reference value and the rotor reference current based on the vector control system and outputting the rotor target voltage includes:

[0048] Determine the operating status of the vector control system based on the voltage drop depth ΔV;

[0049] When ΔV=0, it is determined that the vector control system is operating in a normal state, and the stator flux reference value ψ is controlled by reactive power droop. s0 Perform ±5% regulation and output rotor target voltage;

[0050] When ΔV>0, the vector control system is judged to be operating in the low voltage ride-through state. The reference current of the rotor in the d and q axes is dynamically adjusted according to the actual feedback value of the rotor current in the vector control system. At the same time, the stator flux reference value ψ is adaptively adjusted according to the actual feedback value of the voltage drop depth. s0 , and output the rotor target voltage.

[0051] According to a specific embodiment of the present invention, adaptively controlling the rotor-side converter RSC based on the rotor target voltage includes:

[0052] The rotor target voltage is converted into a PWM signal based on the space vector pulse width modulation technology, and the switching state of the rotor-side converter RSC is adaptively controlled according to the PWM signal.

[0053] According to a specific embodiment of the present invention, the method further includes:

[0054] The adaptive demagnetization control strategy of the variable-speed pumped storage unit under low-load condition is simulated and analyzed, and a simulation benefit diagram of the implementation effect is obtained.

[0055] According to a specific embodiment of the present invention, a simulation analysis is performed on the adaptive demagnetization control strategy of a variable-speed pumped storage unit under low-speed wear, and a simulation benefit diagram of the implementation effect is obtained, including:

[0056] Use MATLAB or Simu link to build a simulation model of the variable-speed pumped storage unit under low-power wear, and perform simulation analysis based on the adaptive demagnetization strategy, and output simulation benefit diagrams of the implementation effect, including simulation diagrams of stator current, DC side voltage, and grid voltage.

[0057] Compared with the prior art, the adaptive demagnetization control strategy for variable-speed pumped storage units under low wear-through provided by the present invention has the following advantages:

[0058] 1. The present invention utilizes the rapid initial decline characteristic of the exponential function and adopts an exponential decay strategy of the flux reference value related to the fault depth within the first millisecond of the fault, which rapidly reduces the stator flux electromagnetic energy inventory, greatly reducing the induced current on the rotor side and fundamentally reducing the risk of rotor overcurrent.

[0059] 2. By dynamically adjusting the stator flux reference value, the present invention can not only effectively relieve the torque spike caused by transient excess flux, but also smooth the electromagnetic torque curve during the fault period, significantly reduce mechanical oscillation and fatigue load, and create favorable conditions for the long-term safe operation of the unit.

[0060] 3. The present invention integrates reactive power droop control into adaptive demagnetization control. During a fault, exponential decay is used to scale the entire reference value. The system still maintains a certain degree of reactive power flexibility, which helps the grid voltage recover during a fault.

[0061] 4. The present invention can maintain the autonomous control capability of the RSC in a low voltage fault by quickly releasing the air gap flux and constraining the rotor current without resorting to Crowbar hardware short-circuiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0063] Figure 1 The flowchart of the adaptive demagnetization control strategy under low-speed wear of a variable-speed pumped storage unit is provided according to one embodiment of the present invention.

[0064] Figure 2 4 is a flow chart of a method for establishing a stator flux exponential decay function according to an embodiment of the present invention.

[0065] Figure 3 2 is a schematic structural diagram of a variable-speed pumped storage unit according to an embodiment of the present invention.

[0066] Figure 4 1 is a schematic diagram of the adaptive demagnetization control principle of a variable-speed pumped storage unit according to an embodiment of the present invention.

[0067] Figure 5 This is a simulation effect diagram of a variable-speed pumped storage unit under low wear according to an embodiment of the present invention.

[0068] Reference numerals:

[0069] 1-first signal input terminal; 2-first PI controller; 3-second PI controller; 4-dq-abc coordinate converter; 5-second signal input terminal; 6-third PI controller; 7-fourth PI controller; 8-space vector pulse width modulator. DETAILED DESCRIPTION

[0070] In order to make those skilled in the art understand the concept and thought of the present invention more clearly, the present invention is described in detail below in conjunction with specific embodiment.It should be understood that the embodiment provided herein is only a part of all possible embodiments of the present invention.After reading the specification of the application, those skilled in the art have the ability to make improvements, transformations, or replacements to part or all of the following embodiments, and these improvements, transformations, or replacements are also included in the scope of protection claimed in the present invention.

[0071] In this document, the terms "advance", "entry" and other similar words are not intended to imply any order, quantity and importance, but are merely used to distinguish different elements. In this document, the terms "one", "an" and other similar words are not intended to indicate that there is only one thing, but rather that the relevant description is only for one of the things, and the thing may have one or more. In this document, the terms "comprise", "include" and other similar words are intended to indicate logical relationships, and cannot be regarded as indicating relationships in spatial structure. For example, "A includes B" is intended to indicate that B logically belongs to A, and does not mean that B is spatially located inside A. In addition, the meanings of the terms "comprise", "include" and other similar words should be regarded as open, not closed. For example, "A includes B" is intended to indicate that B belongs to A, but B does not necessarily constitute the whole of A, and A may also include other elements such as C, D, and E.

[0072] In this document, the terms "embodiment," "this embodiment," "one embodiment," and "an embodiment" do not indicate that the description applies only to a specific embodiment, but rather indicate that the description may also apply to one or more other embodiments. Those skilled in the art should understand that any description of a particular embodiment herein may be substituted, combined, or otherwise combined with the description of one or more other embodiments. New embodiments resulting from such substitution, combination, or other combination are readily conceivable by those skilled in the art and fall within the scope of protection of this invention.

[0073] Example 1

[0074] Additional aspects and advantages of embodiments of the present invention will be given in part in the following description and will become apparent from the following description or learned through practice of embodiments of the present invention. Figure 1-Figure 5 The embodiment of the present invention provides an adaptive demagnetization control strategy for a variable-speed pumped storage unit under low wear, including:

[0075] S1: Establish a mathematical model of the doubly-fed induction motor for a variable-speed pumped storage system.

[0076] S2: Establish the exponential decay function of the stator flux based on the mathematical model of the doubly fed induction motor.

[0077] S3: Build a vector control system for the doubly fed induction motor based on its mathematical model and exponential decay function.

[0078] S4: Based on the vector control system, the stator flux reference value and the rotor reference current are dynamically adjusted and the rotor target voltage is output.

[0079] S5: Adaptively control the rotor-side converter RSC based on the rotor target voltage.

[0080] like Figure 3As shown in the figure, the variable-speed pumped storage system includes a hydro turbine, a doubly-fed induction generator (DFIG), and a back-to-back converter. The stator side of the DFIG is directly connected to the grid, while the rotor side of the DFIG is connected to the grid DC bus via the back-to-back converter. The back-to-back converter includes a rotor-side converter (RSC) and a grid-side converter (GSC). The RSC and GSC work together to control the rotor current of the DFIG. The RSC adjusts the rotor current frequency, amplitude, and phase to control the output power and torque of the DFIG. The GSC controls the DC link voltage, ensuring effective connection to the grid and enabling bidirectional energy flow. When a grid fault causes a voltage sag, the stator-terminal voltage drop in a doubly-fed induction motor (DFIM) is directly connected to the grid. This stator-terminal voltage drop prevents the stator flux from dissipating instantly, and the electromagnetic energy stored in the air gap must be released within a very short period of time. This causes a large transient current surge on the rotor side, which in turn triggers RSC overcurrent, rotor winding overstress, and even damage to the converter and electromechanical components. At the same time, grid faults require the generator set to provide support to the grid to help voltage recovery. During a low-voltage ride-through (LVRT) fault, the RSC must quickly enter fault mode. This invention aims to ensure reliable operation of the rotor-side converter. By introducing an exponential decay function associated with the fault depth, the stator flux reference value is adaptively adjusted based on the voltage drop, thereby rapidly reducing the air gap flux inventory at the initial stage of the fault. Furthermore, a reactive power regulation strategy is embedded in the calculation of the stator flux reference value. This allows the RSC in the fault state to not only effectively suppress rotor overcurrent and electromagnetic torque fluctuations, but also provide appropriate voltage support. This invention, without the need for complex predictive control or additional hardware, can adaptively control the RSC during LVRT, achieving highly reliable and flexible LVRT performance.

[0081] Specifically, step S1 of establishing a mathematical model of a doubly-fed induction motor of a variable-speed pumped storage system includes:

[0082] The mathematical model of the doubly-fed induction motor of the variable-speed pumped storage system is established using the dq-axis synchronous rotating coordinate system with stator flux orientation.

[0083] The embodiment of the present invention uses a dq-axis synchronous rotating coordinate system with stator flux orientation to establish a mathematical model of a doubly fed induction motor, which can achieve decoupling control of flux and torque, making the control more linear. By orienting the stator flux vector along a specific direction, the control model of the motor is simplified, and the dynamic response speed and control accuracy of the system are improved. In addition, the use of stator flux orientation technology can effectively suppress system disturbances and output stable power.

[0084] In the embodiment of the present invention, iron loss and nonlinear saturation are ignored, and the mathematical model of the doubly-fed induction motor established includes:

[0085] Stator voltage equation:

[0086]

[0087] Among them, v s,d is the d-axis component of the stator voltage, v s,q is the q-axis component of the stator voltage, i s,d is the d-axis component of the stator current, i s,q is the q-axis component of the stator current, ψ s,d is the d-axis component of the stator flux, ψ s,q is the q-axis component of the stator flux, R s is the stator winding resistance, ω s is the synchronous angular velocity.

[0088] Rotor voltage equation:

[0089]

[0090] Among them, v r,d is the d-axis component of the rotor voltage, v r,q is the q-axis component of the rotor voltage, i r,d is the d-axis component of the rotor current, i r,q is the q-axis component of the rotor current, ψ r,d is the d-axis component of the rotor flux, ψ r,q is the q-axis component of the rotor flux, R r is the rotor winding resistance, ω r is the rotor mechanical angular velocity.

[0091] Among them, the relationship between magnetic flux and stator and rotor current is:

[0092] ψ s,d =L s i s,d +L m i r,d (5)

[0093] ψ s,q =L s i s,q +L m i r,q (6)

[0094] ψ r,d =L m i s,d +L r i r,d (7)

[0095] ψ r,q =L m i s,q +L r i r,q (8)

[0096] Among them, L s is the stator self-inductance, L r is the rotor self-inductance, L m For mutual induction.

[0097] Substituting formulas (5)-(8) into formulas (1)-(4) can derive the rotor flux state equation:

[0098]

[0099]

[0100] Where σ is the magnetic leakage coefficient and s is.

[0101] Electromagnetic torque equation:

[0102]

[0103] Where, T e is the electromagnetic torque, and p is the number of pole pairs.

[0104] Specifically, step S2 establishes an exponential decay function of the stator flux based on the mathematical model of the doubly-fed induction motor, including:

[0105] S21: During LVRT, the voltage dip depth ΔV is defined as:

[0106]

[0107] Where V nom is the steady-state voltage, V fault is the fault voltage. When ΔV is 0, it means there is no fault. The larger the value, the more serious the fault.

[0108] S22: Based on the voltage drop depth, the decay rate factor λ(ΔV) is defined as:

[0109]

[0110] Where λ0 is the minimum attenuation rate, and λ1 is the attenuation rate for deep faults. In the embodiment of the present invention, λ0 and λ1 are parameters to be adjusted, where λ0 is used to provide a gentle flux attenuation for lighter faults, and λ1 is used to determine the enhanced flux attenuation amplitude for deep faults. When ΔV>50%, λ1 can make the stator flux reference value ψ s0 It decreases rapidly within 10 to 20 ms to create a safe range for RSC.

[0111] S23: Establishing an exponential decay function for the stator flux based on the decay rate factor λ(ΔV) and the mathematical model of the doubly-fed induction motor for:

[0112]

[0113] Where, ψ s0 is the stator flux reference value, k ψ is the gain coefficient, which is designed as the ratio of the flux change to the reactive change to avoid the flux reference being too low. is the real-time reactive power feedback signal after first-order filtering, t fault is the time when the fault occurs, and t is the time variable.

[0114] When ΔV=0, it means the system has no fault. When ΔV>0, it means the system is in low voltage ride-through state. The larger ΔV is, the higher the value of λ(ΔV) is, so the stator flux reference value ψ s0 The current rapidly decreases at the initial moment of the fault, thereby quickly releasing the air gap flux energy. The stator flux reference value ψ s0 Adaptive regulation is performed to improve voltage support and reactive power distribution during low voltage ride-through.

[0115] Specifically, step S3 of building a vector control system of the doubly-fed induction motor based on the mathematical model of the doubly-fed induction motor and the exponential decay function includes:

[0116] Based on the mathematical model of the doubly fed induction motor and the exponential decay function, a stator flux given value is constructed. and Rotor current setpoint and Rotor voltage setpoint and As the input signal, the actual measured value of stator flux ψ s,d and ψ s,q , Actual measured value of rotor current i r,d and i r,q , Actual measured value of rotor voltage u r,d and u r,q The vector control system with RSC modulation signal as the output signal is as the feedback signal, such as Figure 4As shown, the vector control system of the doubly fed induction motor includes: a first signal input terminal 1, a second signal input terminal 5, a first PI controller 2, a second PI controller 3, a third PI controller 6, a fourth PI controller 7, a dq-abc coordinate converter 4 and a space vector pulse width modulator 8. The first signal input terminal 1, the first PI controller 2, the second PI controller 3 and the dq-abc coordinate converter 4 are connected in sequence, the second signal input terminal 5, the third PI controller 6, the fourth PI controller 7 and the dq-abc coordinate converter 4 are connected in sequence, and the dq-abc coordinate converter 4 is connected to the space vector pulse width modulator 8. Among them, the first signal input terminal 1 is used to input the d-axis component of the stator flux set value The second signal input terminal 5 is used to input the q-axis component of the stator flux set value In order to realize the decoupling control of rotor current and simplify the control system design, the present invention will Set to 0, based on the actual measured value of the stator flux fed back by the system ψ s,d Given value of stator flux Perform dynamic adjustment and input the adjustment result into the first PI controller 2, which outputs the rotor current given value. And use it as the input of the second PI controller 3, according to the actual measurement value of the rotor current i fed back by the system r,d The rotor current is given Perform dynamic adjustment and input the adjustment result to the second PI controller 3, which outputs the rotor voltage set value. According to the actual measured value of voltage u fed back by the system r,d The rotor voltage is given Dynamic adjustment is performed, and the adjustment result is input into the dq-abc coordinate converter 4, which outputs the rotor target voltage. The rotor target voltage is input into the space vector pulse width modulator 8 to output the RSC modulation signal to achieve adaptive control of RSC.

[0117] Among them, the stator flux given value and The calculation formula is:

[0118]

[0119] Rotor current setpoint and The calculation formula is:

[0120]

[0121] in, is the stator flux d-axis current, is the stator flux q-axis current.

[0122] Rotor voltage setpoint and The calculation formula is:

[0123]

[0124] Among them, e rd is the rotor d-axis error signal, e rq is the rotor q-axis error signal.

[0125] In the embodiment of the present invention, when ΔV>0 is detected, it indicates that the system is in a low voltage ride-through state, and the d-axis flux After a fault occurs, the voltage drop decays exponentially, and the decay rate changes with the fault depth. By introducing the voltage drop depth ΔV into the exponential decay function, the deceleration slope of the flux reference value can be accurately set according to the fault severity. By using the exponential decay function, the rotor current and torque can be effectively suppressed within a few milliseconds after the fault occurs, maintaining stability within the safety margin of the equipment under low voltage ride-through conditions. In addition, the exponential decay function The reactive power droop control is deeply coupled with the dynamic adjustment of the stator flux reference value, so that the system can suppress rotor overcurrent and torque oscillation without sacrificing the voltage support function under fault conditions, thereby taking into account both the safety of the power generation unit itself and the overall steady-state recovery of the power grid during the low voltage ride-through process.

[0126] Traditional demagnetization control is typically based on direct attenuation of the stator flux. During rapid demagnetization, changes in the stator flux affect the dynamic behavior of the rotor side through electromagnetic coupling. Directly controlling the stator flux can cause drastic fluctuations in the rotor current and voltage, and does not consider the optimal transition trajectory for the system to recover from the fault state to the normal state, which may lead to suboptimal control performance. Unlike traditional solutions, the present invention achieves rapid clearance and precise regulation of electromagnetic energy during faults through fault depth adaptive parameter adjustment, dynamic flux trajectory reconstruction, and torque prediction feedback control, significantly reducing rotor current and torque fluctuations. At the same time, it weakens the dependence on Crowbar hardware, ensuring the system's active adjustment capabilities during faults.

[0127] Specifically, step S4 dynamically adjusts the stator flux reference value and the rotor reference current based on the vector control system and outputs the rotor target voltage, including:

[0128] The operating status of the vector control system is determined based on the voltage drop depth ΔV.

[0129] When ΔV=0, it is determined that the vector control system is operating in a normal state, and the stator flux reference value ψ is controlled by reactive power droop. s0 Perform ±5% regulation and output the rotor target voltage.

[0130] When ΔV>0, it is determined that the vector control system is operating in the low voltage ride-through state. At this time, it is necessary to fault Rapidly reduce the stator flux reference value ψ s0 In the embodiment of the present invention, the reference current of the rotor in the d and q axes is dynamically adjusted according to the actual feedback value of the rotor current in the vector control system, and the stator flux reference value ψ is adaptively adjusted according to the actual feedback value of the voltage drop depth. s0 , and output the rotor target voltage.

[0131] Specifically, step S5 of adaptively controlling the rotor-side converter RSC based on the rotor target voltage includes:

[0132] The rotor target voltage is converted into a PWM signal based on the space vector pulse width modulation technology, and the switching state of the rotor-side converter RSC is adaptively controlled according to the PWM signal.

[0133] like Figure 4 As shown, the output target voltage and The dq-abc coordinate converter converts the three-phase AC power into a, b, and c, and inputs it into the space vector pulse width modulator for signal processing, which outputs the PWM signal to control the switching state of the rotor-side converter RSC.

[0134] Specifically, the method further includes:

[0135] The adaptive demagnetization control strategy of the variable-speed pumped storage unit under low-speed wear is simulated and analyzed, and a simulation benefit diagram of the implementation effect is obtained, including:

[0136] Use MATLAB or Simu link to build a simulation model of the variable-speed pumped storage unit under low-power wear, and perform simulation analysis based on the adaptive demagnetization strategy, and output simulation benefit diagrams of the implementation effect, including simulation diagrams of stator current, DC side voltage, and grid voltage.

[0137] like Figure 5 As shown in the simulation results, an embodiment of the present invention utilizes a 300MW variable-speed pumped storage system connected to the grid. When the grid voltage drops to 0.3 pu, this embodiment rapidly guides the rotor flux to a new reference trajectory, effectively suppressing the stator current surge, which rapidly decays and stabilizes within 0.05 seconds. The DC side voltage responds quickly to the voltage drop, rising to a maximum of approximately 1.04 pu and recovering to 1 pu after approximately 0.1 seconds. 0.2 seconds after the fault is cleared, the grid voltage recovers, and the control system is able to rapidly track voltage changes, enabling low-voltage ride-through of the pumped storage unit.

[0138] In summary, the adaptive demagnetization control strategy for a variable-speed pumped storage unit under low wear-through conditions described in the present invention has the following advantages:

[0139] 1. The present invention utilizes the rapid initial decline characteristic of the exponential function and adopts an exponential decay strategy of the flux reference value related to the fault depth within the first millisecond of the fault, which rapidly reduces the stator flux electromagnetic energy inventory, greatly reducing the induced current on the rotor side and fundamentally reducing the risk of rotor overcurrent.

[0140] 2. By dynamically adjusting the stator flux reference value, the present invention can not only effectively relieve the torque spike caused by transient excess flux, but also smooth the electromagnetic torque curve during the fault period, significantly reduce mechanical oscillation and fatigue load, and create favorable conditions for the long-term safe operation of the unit.

[0141] 3. The present invention integrates reactive power droop control into adaptive demagnetization control. During a fault, exponential decay is used to scale the entire reference value. The system still maintains a certain degree of reactive power flexibility, which helps the grid voltage recover during a fault.

[0142] 4. The present invention can maintain the autonomous control capability of the RSC in a low voltage fault by quickly releasing the air gap flux and constraining the rotor current without resorting to Crowbar hardware short-circuiting.

[0143] The concepts, principles, and ideas of the present invention are described in detail above in conjunction with specific implementation methods (including embodiments and examples). Those skilled in the art should understand that the implementation methods of the present invention are not limited to the forms given above. After reading this application document, those skilled in the art can make any possible improvements, replacements, and equivalent forms to the steps, methods, systems, and components in the above-mentioned implementation methods. These improvements, replacements, and equivalent forms should be deemed to fall within the scope of the present invention, and the scope of protection of the present invention shall be subject only to the claims.

Claims

1. An adaptive demagnetization control strategy for variable-speed pumped storage units under low-power wear, characterized in that: include: Establish a mathematical model of the doubly-fed induction motor for a variable-speed pumped storage system; Establishing an exponential decay function of the stator flux based on the doubly-fed induction motor mathematical model; Building a vector control system for the doubly-fed induction motor based on the doubly-fed induction motor mathematical model and the exponential decay function; Based on the vector control system, the stator flux reference value and the rotor reference current are dynamically adjusted and the rotor target voltage is output; The rotor-side converter RSC is adaptively controlled based on the rotor target voltage.

2. The adaptive demagnetization control strategy under low wear of the variable speed pumped storage unit according to claim 1 is characterized in that: The mathematical model of the double-fed induction motor for the variable-speed pumped storage system is established as follows: The mathematical model of the doubly-fed induction motor of the variable-speed pumped storage system is established using the dq-axis synchronous rotating coordinate system with stator flux orientation.

3. The adaptive demagnetization control strategy under low wear of the variable speed pumped storage unit according to claim 2, characterized in that: The doubly-fed induction motor mathematical model includes: Stator voltage equation: Among them, v s,d is the d-axis component of the stator voltage, v s,q is the q-axis component of the stator voltage, i s,d is the d-axis component of the stator current, i s,q is the q-axis component of the stator current, ψ s,d is the d-axis component of the stator flux, ψ s,q is the q-axis component of the stator flux, R s is the stator winding resistance, ω s is the synchronous angular velocity; Rotor voltage equation: Among them, v r,d is the d-axis component of the rotor voltage, v r,q is the q-axis component of the rotor voltage, i r,d is the d-axis component of the rotor current, i r,q is the q-axis component of the rotor current, ψ r,d is the d-axis component of the rotor flux, ψ r,q is the q-axis component of the rotor flux, R r is the rotor winding resistance, ω r is the rotor mechanical angular velocity; Rotor flux state equation: Where, L s is the stator self-inductance, L r is the rotor self-inductance, L m is the mutual inductance, σ is the leakage coefficient, and s is; Electromagnetic torque equation: Where, T e is the electromagnetic torque, and p is the number of pole pairs.

4. The adaptive demagnetization control strategy under low wear of the variable speed pumped storage unit according to claim 3 is characterized in that: The exponential decay function of the stator flux linkage established based on the doubly-fed induction motor mathematical model includes: During LVRT, the voltage dip depth ΔV is defined as: Where V nom is the steady-state voltage, V fault is the fault voltage; The decay rate factor λ(ΔV) is defined based on the voltage drop depth as: Where λ0 is the minimum decay rate, λ1 is the deep fault decay rate; An exponential decay function of the stator flux is established based on the decay rate factor λ(ΔV) and the mathematical model of the doubly fed induction motor. for: Where, ψ s0 is the stator flux reference value, k ψ is the gain coefficient, is the real-time reactive power feedback signal after first-order filtering, t fault is the time when the fault occurs, and t is the time variable.

5. The adaptive demagnetization control strategy under low wear of the variable speed pumped storage unit according to claim 4 is characterized in that: The vector control system of the doubly-fed induction motor based on the mathematical model of the doubly-fed induction motor and the exponential decay function includes: Based on the mathematical model of the doubly fed induction motor and the exponential decay function, a stator flux given value is constructed. and Rotor current setpoint and Rotor voltage setpoint and As the input signal, the actual measured value of stator flux ψ s,d and ψ s,q , Actual measured value of rotor current i r,d and i r,q , Actual measured value of rotor voltage u r,d and u r,q A vector control system with RSC modulation signal as the output signal and RSC modulation signal as the feedback signal.

6. The adaptive demagnetization control strategy under low wear of the variable speed pumped storage unit according to claim 5, characterized in that: The stator flux set value and The calculation formula is: The rotor current set value and The calculation formula is: in, is the stator flux d-axis current, is the stator flux q-axis current; Rotor voltage setpoint and The calculation formula is: Among them, e rd is the rotor d-axis error signal, e rq is the rotor q-axis error signal.

7. The adaptive demagnetization control strategy under low wear of the variable speed pumped storage unit according to claim 5, characterized in that: The vector control system comprises: A first signal input terminal, a second signal input terminal, a first PI controller, a second PI controller, a third PI controller, a fourth PI controller, a dq-abc coordinate converter and a space vector pulse width modulator, wherein the first signal input terminal, the first PI controller, the second PI controller and the dq-abc coordinate converter are connected in sequence, the second signal input terminal, the third PI controller, the fourth PI controller and the dq-abc coordinate converter are connected in sequence, and the dq-abc coordinate converter is connected to the space vector pulse width modulator.

8. The adaptive demagnetization control strategy under low wear of the variable speed pumped storage unit according to claim 7, characterized in that: The step of dynamically adjusting the stator flux reference value and the rotor reference current based on the vector control system and outputting the rotor target voltage includes: Determining the operating state of the vector control system based on the voltage drop depth ΔV; When ΔV=0, it is determined that the vector control system is operating in a normal state, and the stator flux reference value ψ is adjusted by reactive power droop control. s0 Perform ±5% regulation and output rotor target voltage; When ΔV>0, it is determined that the vector control system is operating in the low voltage ride-through state, and the reference current of the rotor in the d and q axes is dynamically adjusted according to the actual feedback value of the rotor current in the vector control system, and the stator flux reference value ψ is adaptively adjusted according to the actual feedback value of the voltage drop depth. s0 , and output the rotor target voltage.

9. The adaptive demagnetization control strategy under low wear of the variable speed pumped storage unit according to claim 8, characterized in that: The adaptively controlling the rotor-side converter RSC based on the rotor target voltage includes: The rotor target voltage is converted into a PWM signal based on a space vector pulse width modulation technology, and the switching state of the rotor-side converter RSC is adaptively controlled according to the PWM signal.

10. The adaptive demagnetization control strategy under low wear of the variable speed pumped storage unit according to claim 9, characterized in that: The method further comprises: The adaptive demagnetization control strategy of the variable-speed pumped storage unit under low-load condition is simulated and analyzed, and a simulation benefit diagram of the implementation effect is obtained.

11. The adaptive demagnetization control strategy under low wear of a variable speed pumped storage unit according to claim 10, characterized in that: The simulation analysis of the adaptive demagnetization control strategy under low-speed wear of the variable-speed pumped storage unit is performed, and the simulation benefit diagram of the implementation effect is obtained, including: Use MATLAB or Simulink to build a simulation model of the variable-speed pumped storage unit under low-power wear, and perform simulation analysis based on the adaptive demagnetization strategy, and output simulation benefit diagrams of the implementation effect, including simulation diagrams of stator current, DC side voltage, and grid voltage.

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