Two-stage frequency modulation method, device and equipment of variable speed pumped storage unit and medium

Abstract

The application discloses a two-stage frequency modulation method, device, equipment and medium of a variable-speed pumped storage unit, and belongs to the field of power system operation control, and comprises the following steps: dividing a primary frequency modulation process of the unit into first-stage frequency modulation control and second-stage frequency modulation control; when the frequency of a power system deviates and triggers a primary frequency modulation response of the unit, the first-stage frequency modulation control is performed; the electromagnetic torque is adjusted under operation constraints through coordinated control of a rotor-side converter and guide vanes; the switching condition is determined according to the frequency variation characteristics of the system, and the first-stage frequency modulation control is switched to the second-stage frequency modulation control; the frequency support of the unit to the power system is maintained, the rotor speed is adjusted, and the rotor speed is restored to the rated speed or a stable operation interval. The application can coordinate the improvement of the frequency regulation performance of the power system and the operation safety of the variable-speed pumped storage unit without relying on additional energy storage devices, and is suitable for a power system with a high proportion of new energy access.

Description

Technical Field

[0001] This invention relates to the field of power system operation control technology, and in particular to a two-stage frequency regulation method, apparatus, equipment and medium for a variable speed pumped storage unit. Background Technology

[0002] During the operation of a power system, when the load changes or the power output fluctuates, the system frequency will deviate from the rated value. In order to suppress frequency deviation and maintain the safe and stable operation of the power system, it is usually necessary to rely on primary frequency regulation control to quickly adjust the power output at the initial stage of the disturbance.

[0003] With the continuous growth of installed capacity of new energy power generation, the proportion of synchronous generators in the power system is gradually decreasing, the equivalent inertia of the system is declining, and the frequency change rate is accelerating, which places higher demands on the response speed and support capacity of primary frequency regulation resources. Against this backdrop, pumped storage units, especially variable-speed pumped storage (VSPS) units, are gradually becoming important frequency regulation resources in the power system due to their large regulation capacity and fast power regulation capability.

[0004] Variable-speed pumped-storage hydroelectric units typically adjust the rotor-side electromagnetic torque via a converter to achieve rapid regulation of the unit's active power, thus participating in primary frequency regulation when the system frequency deviates. Existing technologies for primary frequency regulation control of variable-speed pumped-storage hydroelectric units often employ a single control mode, directly adjusting the unit's electromagnetic power output based on the system frequency deviation to support the system frequency. However, under this control method, to achieve strong frequency support, the unit often needs to rapidly increase its electromagnetic power output in the initial stages of frequency disturbances. This leads to a significant release of rotor kinetic energy and a rapid decrease in unit speed. When the speed approaches the lower operating limit, this can easily cause instability in unit operation, converter protection activation, or limited regulation capability, which is detrimental to the safe operation of the unit.

[0005] On the other hand, to avoid excessive speed drop, some existing technologies protect the unit by limiting the electromagnetic power adjustment range or reducing the frequency modulation control gain. However, this method weakens the unit's frequency modulation capability in the early stage of frequency disturbance, resulting in a lower minimum system frequency and a longer frequency recovery process, making it difficult to meet the demand for fast frequency support under the condition of high proportion of new energy access.

[0006] In addition, existing frequency regulation control methods usually do not clearly distinguish between the frequency support phase and the speed recovery phase in the frequency regulation process, and lack a phased control design for the entire frequency regulation process. This makes it difficult to coordinate the frequency support performance and the unit speed recovery process, and can easily introduce additional power fluctuations or operational risks in the later stages of frequency regulation.

[0007] Therefore, how to fully utilize the rapid adjustment capability of variable speed pumped storage units in the early stage of system frequency disturbance, while effectively controlling the changes in unit speed during frequency regulation, and achieving coordination between frequency support performance and unit operation safety, remains a problem to be solved in the existing technology. Summary of the Invention

[0008] The purpose of this application is to overcome the deficiencies of the prior art and provide a two-stage frequency regulation method, device, equipment and medium for variable speed pumped storage units, so as to balance frequency support capability and unit operation safety.

[0009] In a first aspect, this application provides a two-stage frequency regulation method for a variable-speed pumped storage unit, comprising the following steps:

[0010] The motor's state parameters are collected, and the primary frequency regulation process of the variable speed pumped storage unit is divided into the first stage frequency regulation control and the second stage frequency regulation control. When the power system frequency deviates and triggers the primary frequency regulation response of the variable speed pumped storage unit, the first stage frequency regulation control is performed.

[0011] In the first stage of frequency regulation control, the electromagnetic torque is adjusted and the rotor kinetic energy is released under operating constraints through the coordinated control of the rotor-side converter and guide vanes.

[0012] The system frequency change rate is monitored in real time. Based on the relationship between the system frequency change rate and the pull-back threshold, the lower limit of the rotational speed is calculated. The switching conditions are determined based on the system frequency change characteristics. When the switching conditions are met, the system switches from the first stage frequency modulation control to the second stage frequency modulation control.

[0013] In the second stage of frequency regulation control, the variable speed pumped storage unit maintains frequency support for the power system, and the rotor speed of the variable speed pumped storage unit is adjusted until the rotor speed returns to the rated speed or stable operating range, the system frequency tends to stabilize, and the entire frequency regulation process is completed.

[0014] Optionally, in the first stage of frequency regulation control, the electromagnetic torque is adjusted under operating constraints through coordinated control of the rotor-side converter and guide vanes to release rotor kinetic energy, including:

[0015] Construct the electromagnetic equations for a variable-speed pumped storage unit;

[0016] The power boundary is determined based on the electromagnetic equation of the variable speed pumped storage unit. Under the premise of satisfying the power boundary, the power command value when the frequency of the variable speed pumped storage unit is disturbed is set as the maximum value of the stator power.

[0017] Under the premise of meeting the dynamic constraints of the hydraulic system and the limit of the guide vane opening change rate, the guide vane opening is driven to the maximum allowable value.

[0018] Optionally, the power boundary expression is:

[0019]

[0020]

[0021]

[0022] in, Indicates the maximum allowable value of stator current; Indicates the maximum allowable rotor current; , These represent the q-axis and d-axis components of the rotor current, respectively. , Indicates the active power coefficient. Indicates the reactive power coefficient. Indicates the grid voltage after orientation. Indicates the mutual inductance between the stator and rotor. Indicates electronic-side inductance; Indicates stator flux linkage; Indicates the stator active power; Indicates the stator reactive power; Indicates the maximum allowable rotor voltage; , These represent the d-axis and q-axis components of the rotor voltage, respectively. Indicates the rotor-side inductance; Indicates the rotor speed; , representing the leakage inductance coefficient.

[0023] Optionally, the system frequency change rate is monitored in real time, and a lower speed limit is calculated based on the relationship between the system frequency change rate and the pull-back threshold. Switching conditions are determined based on the system frequency change characteristics. When the switching conditions are met, the system switches from the first stage frequency modulation control to the second stage frequency modulation control, including:

[0024] Based on the operating mode of the variable speed pumped storage unit and the rotor-side power limit, the maximum and minimum lower speed limits are determined to obtain the pull-back threshold.

[0025] The system frequency change rate is monitored in real time. When the rotor speed reaches the lower limit of the speed or the system frequency change rate meets the switching adaptive threshold, the system switches from the first stage frequency regulation control to the second stage frequency regulation control.

[0026] Optionally, when rotor-side power is limited Equal to the rated power of the continuous rotor-side converter ,Right now At that time, the maximum lower limit of the rotational speed is obtained. for:

[0027] ;

[0028] When rotor-side power limitation Equal to 1.2 times the rated power of the continuous rotor-side converter ,Right now At that time, the minimum lower limit of the rotational speed is obtained. for:

[0029] ;

[0030] Pullback threshold The expression is:

[0031]

[0032] in, Indicates synchronous speed. Indicates the total effective power. This represents the amplitude of the system's rate of change of frequency.

[0033] Optionally, in the second stage of frequency regulation control, the variable-speed pumped storage unit maintains frequency support for the power system, and the rotor speed of the variable-speed pumped storage unit is adjusted until the rotor speed returns to the rated speed or stable operating range, and the system frequency tends to stabilize, completing the entire primary frequency regulation process, including:

[0034] The target speed recovery of the variable speed pumped storage unit in the second stage frequency regulation control is determined based on dynamic adaptation logic.

[0035] Based on the deviation between the actual rotor speed and the speed recovery target, an electromagnetic torque reference value or an active power reference value for the second-stage frequency modulation control is generated.

[0036] By adjusting the rotor current through the rotor-side converter, the rotor speed is driven to gradually converge toward the speed recovery target.

[0037] Switch the guide vane control mode to power tracking mode, input the frequency deviation into the power PI controller to obtain an additional power command, and superimpose the additional power command on the reference power set value to obtain the total power reference value of the guide vane.

[0038] Based on the reference value of the total power of the guide vanes and the speed recovery target, the guide vane opening is coordinated and adjusted to match the turbine input power with the electromagnetic power demand. The rotor speed and system frequency are continuously monitored until the rotor speed recovers to the rated speed or its stable operating range, and the system frequency tends to stabilize. The second stage of frequency regulation control is then terminated, and the entire frequency regulation process is completed.

[0039] Secondly, this application also provides a two-stage frequency regulation device for a variable-speed pumped-storage unit, used to execute the two-stage frequency regulation method for a variable-speed pumped-storage unit as described in any one of the first aspects, and to control the variable-speed pumped-storage unit. The variable-speed pumped-storage unit includes hydraulic machinery, a gearbox, a motor, and a converter module. The hydraulic machinery converts water flow into mechanical energy and outputs it to the gearbox, or converts mechanical energy into high-pressure water flow. The gearbox transmits the mechanical energy output by the hydraulic machinery to the motor. The motor converts mechanical energy into electrical energy and outputs it to the converter module. The converter module adjusts the electrical energy of the motor to adapt to the power grid.

[0040] The two-stage frequency regulation device of the variable-speed pumped storage unit includes a frequency observation module, a staged frequency regulation control module, a rotor-side converter control module, a guide vane control module, and a speed protection module. The frequency observation module collects the frequency signal of the power grid and outputs the system frequency change rate. The staged frequency regulation control module determines the switching time of the frequency regulation stage based on the system frequency change rate and outputs electrical frequency regulation commands and hydraulic frequency regulation commands. The rotor-side converter control module adjusts the power of the variable-speed pumped storage unit according to the electrical frequency regulation commands. The guide vane control module receives the hydraulic frequency regulation commands and outputs guide vane opening control signals to adjust the water flow power. The speed protection module protects the speed of the rotor-side converter control module and the guide vane control module respectively based on the system frequency change rate.

[0041] Optionally, the speed protection module includes a speed lower limit calculation unit, a pullback threshold generation unit, and a control correction unit. The speed lower limit calculation unit determines the speed lower limit based on the operating constraints of the variable speed pumped storage unit and the system frequency change rate. The pullback threshold generation unit receives the speed lower limit and obtains the speed pullback threshold based on the system frequency change rate. The control correction unit corrects the current frequency regulation control quantity based on the real-time rotor speed and the speed pullback threshold to obtain the corrected frequency regulation control quantity.

[0042] Thirdly, this application also provides a computer device, including one or more processors; a storage device for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the two-stage frequency regulation method for a variable speed pumped storage unit as described in any of the first aspects.

[0043] Fourthly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the two-stage frequency regulation method for a variable-speed pumped storage unit as described in the first aspect.

[0044] This application provides a two-stage frequency regulation method, apparatus, equipment, and medium for variable-speed pumped-storage (PSH) units. The method divides the primary frequency regulation process of the PSH unit into a first-stage frequency regulation control and a second-stage frequency regulation control. In the first stage, through the coordinated control of the rotor-side converter and guide vanes, the active power output of the unit is rapidly increased while meeting the operating constraints of the converter and the PSH unit, releasing rotor kinetic energy to suppress a rapid drop in system frequency. In the second stage, while continuously providing necessary frequency support, the rotor speed of the PSH unit is adjusted to smoothly recover to the rated speed or a target range near it. The switching time between the first and second stages is determined based on the frequency dynamic characteristics represented by the system frequency change rate, thereby achieving adaptive switching of the frequency regulation control stages. By using a lower speed limit constraint, operational risks caused by excessive speed drops can be avoided. This method can coordinate and improve the frequency regulation performance of the power system and the operational safety of the PSH unit without relying on additional energy storage devices, and is suitable for power systems with a high proportion of renewable energy integration.

[0045] To make the above-mentioned features and advantages of the invention more apparent and understandable, specific embodiments are described below, and detailed descriptions are provided in conjunction with the accompanying drawings. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of the two-stage frequency regulation device of a variable speed pumped storage unit provided in one embodiment of this application.

[0048] Figure 2 This is a flowchart of a two-stage frequency regulation method for a variable-speed pumped storage unit provided in one embodiment of this application.

[0049] Figure 3 This is a flowchart of step S2 in a two-stage frequency regulation method for a variable-speed pumped storage unit provided in one embodiment of this application.

[0050] Figure 4 This is a flowchart of step S3 in a two-stage frequency regulation method for a variable-speed pumped storage unit provided in one embodiment of this application.

[0051] Figure 5 This is a flowchart of step S4 in a two-stage frequency regulation method for a variable-speed pumped storage unit provided in one embodiment of this application.

[0052] Figure 6 The waveform diagram shows the frequency deviation and system frequency change rate of the strategy proposed in this application.

[0053] Figure 7 The waveforms of torque and rotor speed under the traditional strategy are shown.

[0054] Figure 8 The waveform diagram shows the torque and rotor speed under the strategy proposed in this application.

[0055] Figure 9 An improved IEEE 39-node topology diagram.

[0056] Figure 10 The figures show the dynamic response characteristics of the variable speed pumped storage unit under three control strategies. Figure 10 (a) shows the electromagnetic torque waveforms of the variable speed pumped storage unit under three control strategies. Figure 10 (b) shows the rotor speed waveforms of the variable speed pumped storage unit under three control strategies. Figure 10 (c) shows the guide vane opening waveforms of the variable speed pumped storage unit under three control strategies. Figure 10 (d) shows the frequency response waveforms of the variable speed pumped storage unit under three control strategies.

[0057] Figure 11 The dynamic response characteristics of variable speed pumped storage units under three control strategies after a 5% increase in load are shown in the figure. Figure 11 (a) Electromagnetic torque waveform of variable speed pumped storage unit under three control strategies after the load is increased by 5%. Figure 11 (b) Rotor speed waveforms of variable speed pumped storage units under three control strategies after a 5% increase in load; Figure 11 (c) Waveform of guide vane opening of variable speed pumped storage unit under three control strategies after the load is increased by 5%; Figure 11 (d) is the frequency response waveform of the variable speed pumped storage unit under the three control strategies after the load increases by 5%. Detailed Implementation

[0058] To make the objectives and technical solutions of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.

[0059] In one embodiment, see Figure 1This application provides a two-stage frequency regulation device 2 for a variable speed pumped storage unit 1, which is used to control the variable speed pumped storage unit 1. The variable speed pumped storage unit 1 may include a hydraulic machine 11, a gearbox 12, a motor 13, and a converter module 14. The hydraulic machine 11 converts water flow into mechanical energy and outputs it to the gearbox 12, or converts mechanical energy into high-pressure water flow. The gearbox 12 transmits the mechanical energy output by the hydraulic machine 11 to the motor 13. The motor 13 converts mechanical energy into electrical energy and outputs it to the converter module 14. The converter module 14 adjusts the electrical energy of the motor 13 to adapt to the power grid 15. The four modules are connected in sequence to realize bidirectional energy flow. The two-stage frequency regulation device 2 of the variable-speed pumped storage unit may include a frequency observation module 21, a staged frequency regulation control module 22, a rotor-side converter control module 23, a guide vane control module 24, and a speed protection module 25. The frequency observation module 21 collects the frequency signal of the power grid 15 and outputs the system frequency change rate. The staged frequency regulation control module 22 determines the switching time of the frequency regulation stage based on the system frequency change rate and outputs electrical frequency regulation commands and hydraulic frequency regulation commands. The rotor-side converter control module 23 adjusts the power of the variable-speed pumped storage unit 1 according to the electrical frequency regulation commands. The guide vane control module 24 receives the hydraulic frequency regulation commands and outputs guide vane opening control signals to adjust the water flow power. The speed protection module 25 performs speed protection on the rotor-side converter control module 23 and the guide vane control module 24 respectively based on the system frequency change rate.

[0060] As an example, the variable speed pumped storage unit 1 can be a single variable speed booster turbine generator unit or a power station that includes multiple variable speed booster turbine generator units.

[0061] As an example, the hydraulic machinery 11 includes an upper reservoir 111, a dam 112, a water conveyance pipeline 113, a first valve 114, a water turbine 115, and a second valve 116. The upper reservoir 111 and the dam 112 maintain a water level difference and store water. The water conveyance pipeline 113 serves as a water transport channel. The first valve 114 and the second valve 116 regulate the water flow rate. The water turbine 115 performs bidirectional conversion between water flow and mechanical energy.

[0062] Specifically, in power generation mode, the high-level water in the upper reservoir 111 is transported through the water pipeline 113 by the stable head maintained by the dam 112. The first valve 114 and the second valve 116 regulate the flow rate and drive the turbine 115 to rotate and output mechanical energy. In pumping mode, the turbine 115 rotates in reverse, pressurizes the low-level water and transports it through the first valve 114, the water pipeline 113 and the dam 112 to the upper reservoir 111 to store gravitational potential energy, thereby realizing the bidirectional flow of water and energy.

[0063] As an example, turbine 115 can be a reversible pump-turbine.

[0064] As an example, gearbox 12 is used to connect turbine 115 and motor 13, adjust speed matching, and efficiently transmit mechanical torque.

[0065] As an example, motor 13 can be a variable speed motor, which includes a stator-side winding 131 and a rotor-side winding 132. The stator-side winding 131 is directly connected to the power grid 15, and the rotor-side winding 132 is connected to the converter module 14. Through the doubly fed structure of motor 13 and the electromagnetic coupling between the stator-side winding 131 and the rotor-side winding 132, bidirectional and efficient conversion of mechanical energy and electrical energy can be achieved, and the speed can be flexibly adjusted to adapt to the operating requirements of both power generation and water pumping.

[0066] As an example, converter module 14 includes converter 141 and capacitor. Cr ,inductance L c Transformer 142, transformer 143, capacitor C r With inductance L c The first transformer 142 receives electrical energy from the rotor winding 132 of the motor 13, and outputs stable electrical energy after filtering and voltage regulation. The converter 141 receives the stable electrical energy, regulates it, and outputs regulated electrical energy. The first transformer 142 receives electrical energy from the stator winding 131 of the motor 13, and outputs electrical energy that matches the grid voltage after voltage transformation. The second transformer 143 receives the regulated electrical energy output from the converter 141, and outputs electrical energy that matches the grid voltage after voltage transformation.

[0067] As an example, the converter module 14 can realize bidirectional power conversion, power filtering and voltage regulation, and voltage level matching between the motor and the power grid, ensuring stable energy flow between the motor and the power grid, completing the power conversion between the motor 13 and the power grid 15, and achieving voltage matching and grid connection through two transformers.

[0068] As an example, capacitor C r With inductance L c This forms a filter and voltage regulator circuit.

[0069] As an example, converter 141 can be a back-to-back converter, including a rotor-side converter RSC, a grid-side converter GSC, and capacitors. C It can complete the bidirectional power flow of pumping and power generation without the need for additional switching devices. The rotor-side converter RSC can independently adjust the speed and electromagnetic torque of motor 13, while the grid-side converter GSC can stabilize the DC bus voltage and flexibly adjust the grid-connected reactive power, significantly improving the response speed and control accuracy of variable speed pumped storage units in participating in grid frequency and voltage regulation.

[0070] As an example, the first transformer 142 can be the main transformer, and the second transformer 143 can be the excitation transformer. The first transformer 142 is responsible for the power transmission between the stator winding 131 and the power grid 15, and is responsible for voltage level matching and electrical isolation; the second transformer 143 provides a stable excitation power supply for the converter 141, and outputs a voltage that matches the parameters of the rotor winding 132. The two are functionally independent, which can effectively avoid the interference of grid fluctuations on the rotor excitation circuit, and also prevent the harmonics of the excitation system from affecting the grid in the reverse direction, thereby improving the overall system's anti-interference capability.

[0071] As an example, the frequency observation module 21 is used to acquire the frequency signal of the power grid 15 and calculate the system frequency change rate.

[0072] As an example, the phased frequency modulation control module 22 determines the switching time of the frequency modulation stage based on the system frequency change rate. When a system frequency disturbance occurs, it performs the first stage of frequency modulation control, and performs the second stage of frequency modulation control after the phase switching condition based on the system frequency change rate is met, so as to achieve coordinated control of frequency support and speed recovery.

[0073] As an example, the rotor-side converter control module 23 is used to generate electromagnetic torque reference values ​​or active power reference values ​​in the first stage frequency regulation control and the second stage frequency regulation control, respectively, and control the rotor-side converter to track the electromagnetic torque reference values ​​or active power reference values.

[0074] As an example, the rotor-side converter control module 23 may include a rotor-side converter control unit 231, a grid-side converter control unit 232, a flux vector control unit 233, and a sinusoidal pulse width modulation unit 234. The flux vector control unit 233 receives electrical frequency modulation commands and generates flux and torque control parameters, which are then transmitted to the rotor-side converter control unit 231 and the grid-side converter control unit 232, respectively. The rotor-side converter control unit 231 generates a rotor-side converter modulation reference signal based on the flux and torque control parameters. The grid-side converter control unit 232 generates a grid-side converter modulation reference signal based on the flux and torque control parameters. The sinusoidal pulse width modulation unit 234 modulates the received rotor-side converter modulation reference signal and the grid-side converter modulation reference signal to generate an output drive pulse signal, thereby completing the bidirectional power regulation and power quality optimization of the converter 141 and ensuring stable signal and energy flow.

[0075] As an example, the guide vane control module 24 is used to adjust the guide vane opening during frequency regulation to coordinate the turbine input power and electromagnetic power requirements.

[0076] As an example, the guide vane control module 24 includes a speed sensor 241, a guide vane opening proportional-integral-derivative (PID) controller 242, and a speed optimizer 243. The speed sensor 241 collects the speed signals between the variable-speed pumped storage units 1 and outputs them to the guide vane opening PID controller 242. The speed optimizer 243 receives the hydraulic frequency regulation command and generates an optimized speed reference signal. The guide vane opening PID controller 242 generates a guide vane opening control signal based on the speed signal and the optimized speed reference signal, and outputs it to the variable-speed pumped storage unit 1 to achieve precise control of the guide vane opening.

[0077] As an example, the speed protection module 25 is used to monitor the rotor speed of the variable speed pumped storage unit 1 throughout the frequency regulation process, and to limit or correct the control quantity when the rotor speed is close to or lower than the preset speed lower limit.

[0078] As an example, the speed protection module 25 includes a speed lower limit calculation unit 251, a pullback threshold generation unit 252, and a control correction unit 253. The speed lower limit calculation unit 251 determines the speed lower limit based on the operating constraints of the variable speed pumped storage unit and the system frequency change rate. The pullback threshold generation unit 252 receives the speed lower limit and obtains the speed pullback threshold based on the system frequency change rate. The control correction unit 253 corrects the current frequency regulation control quantity based on the real-time rotor speed and the speed pullback threshold to obtain the corrected frequency regulation control quantity, thereby realizing the monitoring and protection of the rotor speed of the variable speed pumped storage unit throughout the frequency regulation process.

[0079] As an example, the speed lower limit calculation unit 251 is used to determine the speed lower limit based on the operating constraints of the variable speed pumped storage unit and the system frequency change rate; the pullback threshold generation unit 252 is used to adaptively determine the pullback threshold based on the system frequency change rate; and the control correction unit 253 is used to back down or correct the electromagnetic torque reference value, active power reference value, and / or guide vane opening given when the rotor speed of the variable speed pumped storage unit reaches the speed lower limit or meets the pullback threshold condition.

[0080] As an example, the lower limit of the rotational speed varies between preset boundaries with the rate of change of the system frequency, so as to establish a monotonic correspondence between the severity of the disturbance and the degree of kinetic energy release of the variable speed pumped storage unit.

[0081] In the aforementioned two-stage frequency regulation device of the variable speed pumped storage unit, the staged frequency regulation control module enables precise control in stages. Combined with the doubly fed structure of the variable speed motor, the back converter, and the adaptation design of the dual transformer, it can efficiently complete the bidirectional conversion of electromechanical energy and optimize electrical energy, thereby improving the frequency regulation response speed and control accuracy of the variable speed pumped storage unit. Through the speed optimization and proportional-integral-derivative regulation of the guide vane control module, the input power of the turbine and the electromagnetic power requirements are coordinated, ensuring stable water flow and energy circulation. Through the speed protection module, the rotor speed is monitored in real time and the control quantity is dynamically corrected, thus avoiding the risk of speed instability. The device proposed in this application can fully utilize the rapid power regulation capability of the variable speed pumped storage unit in the early stage of system frequency disturbance, and at the same time achieve safe and stable recovery of the variable speed pumped storage unit speed in the later stage of frequency regulation. It can coordinate and improve the frequency regulation performance of the power system and the operational safety of the variable speed pumped storage unit without relying on additional energy storage devices, adapt to the dual operation of unit power generation and pumping, enhance the frequency and voltage regulation capability of the power grid, improve power quality and system operational reliability, and achieve a coordinated unity of frequency support and speed recovery.

[0082] In another embodiment, please refer to Figure 2 This application provides a two-stage frequency regulation method for a variable speed pumped storage unit, which is applied to the two-stage frequency regulation device of the variable speed pumped storage unit in the above embodiment. The two-stage frequency regulation method of the variable speed pumped storage unit may include the following steps: steps S1 to S4.

[0083] Step S1: Collect the motor's status parameters and divide the primary frequency regulation process of the variable speed pumped storage unit into the first stage frequency regulation control and the second stage frequency regulation control. When the power system frequency deviates and triggers the primary frequency regulation response of the variable speed pumped storage unit, the first stage frequency regulation control is performed.

[0084] Step S2: In the first stage of frequency regulation control, the electromagnetic torque is adjusted under operating constraints through the coordinated control of the rotor-side converter and guide vanes to release rotor kinetic energy.

[0085] Step S3: Monitor the system frequency change rate in real time, calculate the lower limit of the rotational speed based on the relationship between the system frequency change rate and the pull-back threshold, determine the switching conditions based on the system frequency change characteristics, and switch from the first stage frequency modulation control to the second stage frequency modulation control when the switching conditions are met.

[0086] Step S4: In the second stage of frequency regulation control, maintain the frequency support of the variable speed pumped storage unit for the power system, adjust the rotor speed of the variable speed pumped storage unit until the rotor speed is restored to the rated speed or stable operating range, the system frequency tends to stabilize, and the entire frequency regulation process is completed.

[0087] In the two-stage frequency regulation method of the variable speed pumped storage unit of this application, by dividing the primary frequency regulation process into a first-stage frequency control and a second-stage frequency control, the two traditionally contradictory goals of maximizing frequency support for releasing rotor kinetic energy and ensuring the long-term safe and stable operation of the variable speed pumped storage unit can be decoupled and orderly achieved in the time dimension. In the first stage, through the coordinated control of the rotor-side converter and guide vanes, the active power output of the variable speed pumped storage unit can be rapidly increased, releasing rotor kinetic energy to suppress the rapid drop in system frequency. By dynamically calculating the lower limit of speed through the system frequency change rate and using this as a condition for adaptive stage switching, the control strategy can intelligently sense the severity of disturbances, prioritize equipment protection during minor disturbances, and maximize the utilization of the short-term overload capacity of the variable speed pumped storage unit during severe disturbances, thereby accurately grasping the balance point between frequency support strength and the safety risks of the variable speed pumped storage unit.

[0088] In step S1, please refer to Figure 2 In step S1, the state parameters of the motor are collected, and the primary frequency regulation process of the variable speed pumped storage unit is divided into the first stage frequency regulation control and the second stage frequency regulation control. When the power system frequency deviates and triggers the primary frequency regulation response of the variable speed pumped storage unit, the first stage frequency regulation control is performed.

[0089] Specifically, the motor's state parameters are collected through a measurement process. These state parameters may include stator voltage, stator current, rotor voltage, rotor current, and rotor speed. The real-time frequency is determined based on these state parameters. The expression is ,in, The rate of change of phase angle, , , where are the instantaneous values ​​of the stator voltage in the αβ coordinate system, and t is the sampling time.

[0090] Further, the real-time frequency is calculated. Deviation from rated frequency According to the deviation Determine the system frequency change rate The expression is: .

[0091] Furthermore, regarding the system frequency change rate High-pass filtering is performed on the real-time frequency, and low-pass filtering is performed on the frequency to remove low-frequency steady-state components and high-frequency noise.

[0092] As an example, the measurement process It can be represented as:

[0093]

[0094] in, , This represents the coefficients used in constructing the measurement process. This represents the Laplace operator.

[0095] As an example, state parameters can be collected using devices such as voltage sensors and speed sensors.

[0096] Furthermore, the primary frequency regulation process of the variable speed pumped storage unit is divided into a first-stage frequency regulation control and a second-stage frequency regulation control, when the system frequency change rate... When the frequency exceeds the preset primary frequency regulation dead zone threshold, the primary frequency regulation of the variable speed pumped storage unit is triggered, and the first stage of frequency regulation control is entered.

[0097] As an example, the preset primary frequency regulation dead zone threshold refers to the frequency deviation non-operation range set to stabilize the operation of the variable-speed pumped storage unit and avoid responding to minor frequency fluctuations. Its specific value is set according to the dispatching regulations of the power grid, the control performance of the variable-speed pumped storage unit itself, and the power system's assessment requirements for primary frequency regulation. Typically, an appropriate value can be selected based on national standards, industry practices, or the latest standards, depending on the actual application scenario. In this invention, the dead zone threshold for triggering primary frequency regulation can be configured according to the actual engineering situation.

[0098] As an example, the first stage of frequency modulation control is the rapid power support stage, and the second stage of frequency modulation control is the rapid recovery coordination stage.

[0099] In step S2, please refer to Figure 2 In step S2, during the first stage of frequency regulation control, the electromagnetic torque is adjusted under operating constraints through the coordinated control of the rotor-side converter and the guide vanes to release the rotor kinetic energy.

[0100] For example, please refer to Figure 3 Step S2 may include the following steps: Step S21 to Step S23.

[0101] Step S21: Construct the electromagnetic equations for the variable speed pumped storage unit.

[0102] Step S22: Determine the power boundary based on the electromagnetic equation of the variable speed pumped storage unit. Under the premise of satisfying the power boundary, set the power command value when the frequency of the variable speed pumped storage unit is disturbed to the maximum value of the stator power.

[0103] Step S23: Under the premise of satisfying the dynamic constraints of the hydraulic system and the limit of the guide vane opening change rate, drive the guide vane opening to the maximum allowable value.

[0104] As an example, in the first-stage frequency regulation control, the control objective is to prioritize and rapidly increase the active power output of the variable-speed pumped storage unit during the initial stage of frequency disturbance, maximizing the release of rotor kinetic energy, and suppressing the rapid drop in system frequency by adjusting the electromagnetic power output of the variable-speed pumped storage unit. The first-stage frequency regulation control is achieved through the coordinated control of the rotor-side converter and guide vanes, and strictly adheres to the various operating constraints of the variable-speed pumped storage unit and converter.

[0105] Specifically, when a sudden power imbalance occurs, the grid frequency begins to drop, during which rapid power injection from inertial or quasi-inertial units is crucial. Therefore, it is essential to ensure that variable-speed pumped-storage units achieve maximum feasible electromagnetic power output during the initial frequency dip. The rapid release of rotor kinetic energy gives variable-speed pumped-storage units a superior power response compared to synchronous generators.

[0106] To fully unleash the frequency regulation potential of variable-speed pumped-storage units, it is necessary to first quantify the permissible active power range of the units. Since the rotor-side converter control module operates on the active power path of the rotor-side converter (RSC), the corresponding power limits are calculated using the motor equations and enforced in the control loop. This ensures that the required power support is provided without violating the operating constraints of the generator and converter. Safe operation can be ensured as long as the stator voltage, stator current, rotor current, and rotor voltage remain within the permissible range.

[0107] In step S21, in the rotor-side converter, the d-axis of the stator flux can be selected as the reference vector. Ignoring the changes in stator voltage, stator flux, and stator resistance during frequency regulation, the electromagnetic equations of the variable-speed pumped storage unit can be expressed as follows:

[0108]

[0109]

[0110] in, , These represent the q-axis and d-axis components of the rotor current, respectively. , Indicates the active power coefficient. Indicates the reactive power coefficient. Indicates the mutual inductance between the stator and rotor. Indicates electronic-side inductance; Indicates stator flux linkage; Indicates the stator active power; Indicates the stator reactive power; Indicates the rotor-side inductance; Indicates the rotor speed; , representing the leakage inductance coefficient; , These represent the d-axis and q-axis components of the rotor voltage, respectively.

[0111] As an example, the active power factor reactive power coefficient Leakage inductance coefficient It can be treated as a constant during frequency modulation.

[0112] Furthermore, in step S22, the power boundary is determined based on the electromagnetic equations of the variable-speed pumped storage unit, and the stator current during the frequency regulation process is... Rotor current Rotor voltage The power limitation can be written as:

[0113]

[0114]

[0115]

[0116] in, Indicates the maximum allowable value of stator current; Indicates the maximum allowable rotor current; , These represent the q-axis and d-axis components of the rotor current, respectively. , Indicates the active power coefficient. Indicates the reactive power coefficient. Indicates the grid voltage after orientation. Indicates the mutual inductance between the stator and rotor. Indicates electronic-side inductance; Indicates stator flux linkage; Indicates the stator active power; Indicates the stator reactive power; Indicates the maximum allowable rotor voltage; , These represent the d-axis and q-axis components of the rotor voltage, respectively. Indicates the rotor-side inductance; Indicates the rotor speed; , representing the leakage inductance coefficient.

[0117] As an example, the maximum allowable stator current Maximum allowable rotor current Maximum allowable rotor voltage The maximum allowable value of the stator current can be set based on experiments conducted by variable-speed pumped storage unit manufacturers. The maximum allowable rotor current is 1.0 pu. The maximum allowable rotor voltage is 0.8 pu. It is 1.0 pu.

[0118] Furthermore, under the premise of satisfying the above power boundary, when the frequency of the variable speed pumped storage unit is disturbed, the power command value is set to the maximum stator power value to replace the traditional PI output, and the expression is:

[0119]

[0120] in, This represents the target / reference value of stator power at time t. This indicates the maximum stator power.

[0121] As an example, since the electromagnetic power output is directly controlled by the rotor-side converter, the related internal current and power control loops operate on the electromagnetic transient time scale. The electromagnetic torque regulation of the variable-speed pumped storage unit is achieved by adjusting the dq-axis component of the rotor current through the rotor-side converter. Therefore, the actual stator power at time t... P e (t) It can track the saturation baseline value within hundreds of milliseconds and maintain a level close to the maximum value during the initial stage of a disturbance.

[0122] Furthermore, in step S23, the guide vane opening is incrementally adjusted to increase the turbine input power while meeting the dynamic constraints of the hydraulic system and the limit of the guide vane opening change rate, so as to cooperate with the electromagnetic power support in the first stage.

[0123] As an example, the guide vane opening can be determined based on the full characteristic curve of the variable speed pumped storage unit. For instance, when the active power output of the variable speed pumped storage unit is 0.8 pu, the guide vane opening is given as 0.54 pu.

[0124] As an example, the limit of the guide vane opening change rate can be determined by the pump turbine model and can be set to 0.05 pu / s.

[0125] As an example, the dynamic constraint of the hydraulic system refers to the maximum rate of change of the guide vane opening, which is jointly determined by the limits of the hydraulic servo system's oil pressure, flow rate, mechanical strength, and water hammer pressure.

[0126] Furthermore, the guide vane opening is driven to its maximum value to accelerate the mechanical power response and maximize the mechanical power ramp-up rate while satisfying the dynamic constraints of the hydraulic system. The guide vane opening at time t... The expression is:

[0127]

[0128] in, This indicates the maximum guide vane opening.

[0129] As an example, the maximum guide vane opening It can be determined by the model of the water pump and turbine, and can be set to 0.05 pu / s.

[0130] As an example, in the first stage control of this application, driving the guide vane opening to the maximum allowable value means using the maximum rate of change of the guide vane opening as the command slope or speed saturation limit, so that the actual opening of the guide vane responds at the fastest speed allowed by the system, thereby maximizing the initial climbing rate of mechanical power while ensuring equipment safety.

[0131] As an example, during the entire process of rotor kinetic energy release, speed lower limit constraint control is implemented to prevent the rotor speed from dropping excessively into an unsafe range, thus ensuring the safe operation of the variable speed pumped storage unit.

[0132] In step S3, please refer to Figure 2 In step S3, the system frequency change rate is monitored in real time. Based on the relationship between the system frequency change rate and the pull-back threshold, the lower limit of the rotational speed is calculated. The switching conditions are determined based on the system frequency change characteristics. When the switching conditions are met, the system switches from the first stage frequency modulation control to the second stage frequency modulation control.

[0133] For example, please refer to Figure 4 Step S3 may include the following steps: Step S31 to Step S32.

[0134] Step S31: Determine the maximum and minimum lower speed limits based on the operating mode of the variable speed pumped storage unit and the rotor-side power limit to obtain the pull-back threshold.

[0135] Step S32: Monitor the system frequency change rate in real time. When the rotor speed reaches the lower speed limit or the system frequency change rate meets the switching adaptive threshold, switch from the first stage frequency regulation control to the second stage frequency regulation control.

[0136] As an example, in step S31, the release of kinetic energy from the rotor of the variable-speed pumped storage unit is controlled by a lower speed limit constraint to prevent the rotor speed from dropping to an unsafe operating range. To protect the variable-speed pumped storage unit, the minimum permissible rotor speed is limited by frequency regulation control in the first stage to prevent overcurrent in the grid-side converter. Throughout the first stage, the rotor speed of the variable-speed pumped storage unit is monitored in real time. Based on constraints such as the converter's short-time / continuous capacity and the unit's safe operating range, the minimum permissible speed point of the variable-speed pumped storage unit is calculated, and the lower speed limit is determined accordingly. ω low The lower limit of the rotational speed ωlow Used to limit the allowable range of rotor kinetic energy release during frequency regulation control, speed lower limit constraint control is executed throughout the entire rotor kinetic energy release process. When the rotor speed drops to near the speed lower limit, the power boost command of the rotor-side converter is dynamically limited or rolled back to prevent the rotor speed from dropping excessively into an unsafe range and to ensure the safe operation of the variable speed pumped storage unit.

[0137] As an example, the lower limit of the rotational speed ω low It can be adaptively determined based on the severity of real-time power grid disturbances.

[0138] Specifically, for a variable-speed pumped-storage unit operating in turbine mode, the total effective power output of the variable-speed pumped-storage unit is... Then the rotor active power It can be represented as:

[0139]

[0140] in, Indicates the rotor speed. Indicates synchronous speed. This represents the total effective power.

[0141] Furthermore, set This is the rated power of the continuous rotor-side converter. To address rotor-side power limitations, the rotor-side converter must meet the following constraints during the speed support phase:

[0142]

[0143] in, P Indicates total active power. ω s To achieve synchronous speed, ω r This represents the rotor speed.

[0144] Furthermore, when the rotor speed ω r Less than synchronous speed ω s ,Right now ω r < ω s At that time, the rotor speed can be obtained. ,in, Indicates the lower limit of the rotational speed. For total effective power, For rotor-side power limitation.

[0145] Furthermore, when rotor-side power is limited Equal to the rated power of the continuous rotor-side converter ,Right now At that time, the maximum lower limit of the rotational speed can be obtained. for:

[0146]

[0147] in, Indicates synchronous speed. This represents the total effective power.

[0148] Furthermore, when rotor-side power is limited Equal to 1.2 times the rated power of the continuous rotor-side converter ,Right now At that time, the minimum lower limit of the rotational speed can be obtained. for:

[0149]

[0150] in, Indicates synchronous speed. This represents the total effective power.

[0151] As an example, when rotor-side power is limited At that time, the 20% short-term overcurrent allowed by the strain gauge can form a short-term constraint condition.

[0152] Furthermore, the range of the pullback threshold can be obtained as follows: This indicates the feasible design range of the dwell speed that triggers the transition from the first stage to the second stage.

[0153] As an example, to incorporate the severity of the disturbance into the selection, a high-pass filter is applied to the coefficient frequency change rate, and the lower limit of the rotational speed is set. ω low Parameterized as a function of the magnitude of the rate of change of the frequency of the filtered coefficients The expression is:

[0154]

[0155] in, This indicates saturation to [0,1]. , Two thresholds representing the rate of change of system frequency. This represents the amplitude of the system's rate of change of frequency.

[0156] As an example, two thresholds for the system frequency change rate. , Specific values ​​can be determined through simulation and experimental calibration based on the operating constraints of variable speed pumped storage units, converter performance parameters, and system frequency regulation requirements.

[0157] As an example, the system frequency change rate Dependency pull-back threshold The pullback threshold is obtained by linear interpolation between the two converter capacity boundaries. Amplitude of the rate of change of system frequency The pullback threshold varies linearly within its range. The expression is:

[0158]

[0159] in, This indicates the maximum lower limit of the rotational speed. Indicates the total effective power. This indicates the minimum lower limit of the rotational speed. This represents the amplitude of the system's rate of change of frequency.

[0160] As an example, when a variable-speed pumped-storage unit is in the frequency support phase, a pullback threshold can be determined based on the magnitude and / or sign of the system frequency change rate. This threshold is used to trigger the retraction control of the electromagnetic power support strength of the variable-speed pumped-storage unit and / or to trigger the switch from the frequency support phase to the speed recovery phase. Specifically, when the system frequency change rate is larger, the pullback threshold is set to trigger the pullback action earlier or the pullback amplitude is larger, so as to reduce the risk of the speed continuing to decline. When the system frequency change rate decreases, the pullback threshold is adjusted accordingly to reduce the suppression of the continuous frequency regulation capability of the variable-speed pumped-storage unit.

[0161] Furthermore, in step S32, when the rotor speed reaches the lower speed limit or the system frequency change rate satisfies either the switching adaptive threshold, the frequency control is switched from the first stage to the second stage.

[0162] Specifically, when When setting the lower speed limit At this point, the variable-speed pumped storage unit exits the first stage of control earlier, keeping the rotor-side converter within its continuous rated operating range. When setting the lower speed limit This allows for the lowest permissible speed point while allowing for a short-term overload of 20%. Otherwise, the lower speed limit... Within the pullback threshold range The linear variation between them establishes a simple monotonic mapping relationship between the severity of the disturbance and the degree of rotor kinetic energy utilization.

[0163] In step S4, please refer to Figure 2In step S4, during the second stage of frequency regulation control, the variable speed pumped storage unit maintains frequency support for the power system, and the rotor speed of the variable speed pumped storage unit is adjusted until the rotor speed returns to the rated speed or stable operating range, the system frequency tends to stabilize, and the entire frequency regulation process is completed.

[0164] For example, please refer to Figure 5 Step S4 may include the following steps: Step S41 to Step S45.

[0165] Step S41: Determine the speed recovery target of the variable speed pumped storage unit in the second stage frequency regulation control based on the dynamic adaptation logic.

[0166] Step S42: Based on the deviation between the actual rotor speed and the speed recovery target, generate the electromagnetic torque reference value or active power reference value for the second stage frequency modulation control.

[0167] Step S43: Adjust the rotor current through the rotor-side converter to drive the rotor speed to gradually converge toward the speed recovery target.

[0168] Step S44: Switch the guide vane control mode to power tracking mode, input the frequency deviation into the power PI controller to obtain an additional power command, and superimpose the additional power command onto the reference power setting value to obtain the total power reference value of the guide vane.

[0169] Step S45: Based on the total power reference value of the guide vanes and the speed recovery target, coordinate and adjust the guide vane opening to match the turbine input power with the electromagnetic power demand. Continuously monitor the rotor speed and system frequency until the rotor speed recovers to the rated speed or its stable operating range, and the system frequency tends to stabilize. Terminate the second stage of frequency regulation control and complete the entire frequency regulation process.

[0170] As an example, in the second stage of frequency regulation control, the variable speed pumped storage unit continuously provides the necessary frequency support while taking rotor speed recovery as the main control objective, so that the rotor speed of the variable speed pumped storage unit can be smoothly restored to the rated speed or the target range near the rated speed.

[0171] Specifically, in step S41, the speed recovery target is determined based on the system frequency regulation requirements and equipment safety boundaries, combined with dynamic adaptation logic. The speed recovery target This includes the target rotational speed or the target rotational speed change trajectory. The target rotational speed describes the updated maximum power point rotational speed and is the final steady-state target value for speed recovery.

[0172] Further, in step S42, the deviation between the actual rotor speed of the variable speed pumped storage unit and the speed recovery target is calculated, and the electromagnetic torque reference value or active power reference value for the second stage frequency regulation control is generated based on the deviation.

[0173] Furthermore, in step S43, the rotor current is adjusted by the rotor-side converter to gradually restore the rotor speed of the variable-speed pumped storage unit to the target speed. Convergence, while maintaining the primary frequency regulation output support of the variable speed pumped storage unit for the system.

[0174] As an example, to enhance the controllability of the rotor speed recovery process and achieve precise electromagnetic power... P e The retraction curve reflects a constant angular acceleration control strategy implemented in the rotor speed controller. Specifically, this is achieved by setting a constant acceleration reference value. α ref The rotor speed is driven according to a preset speed restoration law. ω r Towards the updated maximum power point speed ω MPPT The transition yields a path from the current rotor speed to the target speed recovery. The reference trajectory for a smooth transition is expressed as:

[0175]

[0176] in, express Rotor speed at any given time This represents a constant acceleration reference value. This indicates the start time of the second phase.

[0177] As an example, constant acceleration reference value It can be set to 0.03 pu / s.

[0178] During this period, electromagnetic power P e Power from turbomachinery P m Determined in conjunction with the rotor's kinetic energy release rate. Constant acceleration reference value. α ref Essentially, it fixes the power extracted from kinetic energy:

[0179]

[0180] in, Represents the moment of inertia. This indicates the rotor speed.

[0181] As an example, the core principle of the second-stage frequency regulation control is to transform the speed recovery process from a passive hydraulic mechanical process to an active and dispatchable power dispatch process. This ensures that the variable speed pumped storage unit can continuously deliver active power to the grid at a preset rate throughout the entire speed recovery period.

[0182] Furthermore, in step S44, the guide vane opening is adjusted in a coordinated manner according to the speed recovery target and the output demand of the variable speed pumped storage unit, so as to match the turbine input power with the electromagnetic power demand, thereby reducing the electromechanical stress fluctuation during the speed recovery process and avoiding sudden changes in the output of the variable speed pumped storage unit.

[0183] Specifically, to coordinate with rotor-side control and maintain responsiveness to system frequency, the guide vane control target is switched to power point tracking mode, and the real-time frequency is... Deviation from rated frequency The input power PI controller has the system frequency deviation as its input. Receive additional power command The additional power command is used for main frequency regulation. Superimposed on the reference power setting The reference value of the total power of the guide vane is obtained above. .

[0184] As an example, additional power command The expression is:

[0185]

[0186] in, , These represent the proportional and integral coefficients of the power PI controller, respectively. t represents frequency deviation, and t represents time.

[0187] As an example, the total power reference value of the guide vane The expression is:

[0188]

[0189] in, Indicates the reference power setting value. This indicates an additional power command.

[0190] As an example, frequency deviation is the difference between the real-time frequency and the rated frequency. In control systems, the per-unit value (pu) is often used.

[0191] As an example, to ensure a smooth transition between speed control mode and power control mode, the PI controller incorporates anti-saturation and tracking functions. When the loop is inactive, its internal state tracks the control signal of the active loop, thereby maintaining the continuity of the controller output during switching and preventing the hydraulic actuator from experiencing sudden transients.

[0192] Further, in step S45, based on the total power reference value of the guide vanes... and speed recovery target The guide vane opening is coordinated and adjusted to match the turbine input power with the electromagnetic power demand, thereby reducing electromechanical stress fluctuations and avoiding sudden changes in the process.

[0193] Furthermore, the rotor speed and system frequency are continuously monitored until the rotor speed recovers to the rated speed or its stable operating range, and the system frequency tends to stabilize. Then, the second stage of frequency regulation control is terminated, and the entire frequency regulation process is completed.

[0194] As an example, the rated speed of a variable speed pumped storage unit can be obtained by looking up the full characteristic curve in a table. That is, the rated speed can be obtained from the current power of the variable speed pumped storage unit, which is set to 0.93 pu at low power.

[0195] Figure 6 The figure shows the frequency deviation and system frequency change rate waveforms of the strategy proposed in this application, where CoI represents the inertial center frequency. It can be seen that the locally established central system frequency change rate is basically consistent with the actual central system frequency change rate throughout the entire observation period, proving that the strategy proposed in this application reconstructs the inertial center frequency through a piecewise linear approximation of the inflection point of the local frequency curve, exhibiting strong robustness.

[0196] Figure 7 The waveforms of torque and rotor speed under the traditional strategy are shown. Figure 8 The diagram shows the torque and rotor speed waveforms under the strategy proposed in this application. Represents mechanical torque. This represents the electromagnetic torque. It can be seen that the entire frequency process under the traditional strategy can be divided into three stages: the rotor kinetic energy release stage, the acceleration to the new maximum power point tracking (MPPT) stage, and the steady-state allowable stage. The maximum power point tracking speed of the traditional strategy... Minimum rotor speed The proposed strategy divides the entire frequency process into two stages: the rotor kinetic energy release stage and the acceleration to the new maximum power point tracking stage. The maximum power point tracking speed of the proposed strategy is... Minimum rotor speed Therefore, compared with traditional strategies, the strategy proposed in this application makes full use of the fast response capability of the rotor-side converter in the initial stage to provide maximum power support, while in the speed recovery stage, the longer acceleration process enables the variable speed pumped storage unit to maintain good power contribution.

[0197] In one example, a detailed MATLAB / Simulink model was built to evaluate the proposed frequency response strategy. This model is based on an improved IEEE 39-bus system, integrating a wind farm and a variable-speed pumped storage unit. Key system and controller parameters are summarized in Table 1. H n This represents the inertia time constant of a variable-speed pumped storage unit. μl, μf These represent the load friction coefficient and the no-load friction coefficient of a variable speed pumped storage unit, respectively. T w Represents the water hammer time constant. T y This represents the time constant of the electro-hydraulic servo mechanism. e qy 、e qω 、e qh These are coefficients representing the sensitivity of a reversible pump-turbine flow rate to changes in guide vane opening, rotational speed, and head, respectively. e Ty 、e Tω 、e Th These represent the linearization coefficients of the sensitivity of the mechanical torque of a reversible pump-turbine to changes in guide vane opening, rotational speed, and head, respectively. k fp 、k fd These represent the proportional gain coefficient and integral gain coefficient of the frequency modulation controller, respectively. k ωp 、k ωi These represent the proportional gain coefficient and integral gain coefficient of the speed pullback controller, respectively.

[0198] Table 1 Typical parameters of variable speed pumped storage units

[0199]

[0200] Figure 9The improved IEEE 39-node topology is shown, where bold black lines represent buses, G represents generator nodes, and RES represents renewable energy. A 300 MW Variable Speed ​​Pump Storage Plant (VSPSP) is connected to bus 25 with an initial operating frequency of 0.8 pu. Renewable energy is connected to bus 26. The effectiveness of the proposed control strategy in power systems with a high proportion of renewable energy has been verified. By simulating scenarios such as generator tripping and load disturbances, and comparing with traditional methods, the superiority of the proposed method in terms of frequency support and unit safety is demonstrated.

[0201] In one specific embodiment, to verify the effectiveness of the proposed strategy, for a typical severe frequency drop caused by machine switching, the conventional control strategy (CCS) and the decoupled control strategy (DCS) were used as benchmarks to evaluate the effectiveness of the two-stage strategy proposed in this application. Figure 10 The figures show the dynamic response characteristics of the variable speed pumped storage unit under three control strategies. Figure 10 (a), (b), (c), and (d) respectively demonstrate the electromagnetic torque of the variable speed pumped storage unit under three control strategies. Rotor speed Guide vane opening Y and frequency response waveform diagram. (Example) Figure 10 As shown in (a), compared to the decoupling strategy and the conventional strategy, the proposed strategy provides the maximum power support in the initial stage of frequency regulation. Figure 10 (b) shows that the minimum rotor speeds during the frequency response process are 0.917 pu and 0.914 pu for the decoupling strategy and the traditional strategy, respectively, while the proposed strategy reduces it to 0.91 pu, indicating that the proposed strategy releases the maximum kinetic energy when the power grid encounters severe disturbances; the rotor speed recovery stage further verifies the effectiveness of the speed recovery scheme in the proposed strategy. Figure 10 As shown in (c), the proposed strategy achieves the fastest guide vane opening response. Furthermore, since rotor speed recovery is primarily achieved by the rotor-side converter, the maximum guide vane opening Y of the proposed strategy is [not specified]. max The maximum guide vane opening is 0.78 pu, while the maximum guide vane opening of the traditional strategy is 0.90 pu. The maximum guide vane opening under the proposed strategy is smaller than that under the traditional strategy, which indicates that the proposed strategy can effectively reduce the driving stress of the guide vane and the blade load under strong disturbance conditions. Figure 10 The frequency response curve in (d) illustrates the frequency support capability of the proposed strategy, while the maximum absolute frequency deviation of the traditional strategy is shown. The maximum absolute frequency deviation of the decoupling strategy is 1.209 Hz. The maximum absolute frequency deviation of the proposed strategy is 1.034 Hz. The proposed strategy achieves a frequency reduction of 0.809 Hz, which is 33.1% and 21.8% compared to the traditional strategy and the decoupling strategy, respectively.

[0202] In yet another specific embodiment, the adaptive behavior of the proposed strategy under a 5% increase in load was also investigated. Figure 11 The dynamic response characteristics of variable speed pumped storage units under three control strategies after a 5% increase in load are shown in the figure. Figure 11 (a), (b), (c), and (d) respectively demonstrate the electromagnetic torque of the variable speed pumped storage unit under three control strategies after a 5% increase in load. Rotor speed Guide vane opening Y and frequency response waveform diagram. (Example) Figure 11 As shown in (a), when the rotor reluctance coefficient is small, the proposed strategy can adaptively adjust the switching time between the two stages. According to Figure 11 (b) It can be seen that the minimum rotor speed achieved by the proposed strategy is 0.920 pu, which is very close to the 0.922 pu under the traditional strategy. This verifies that under small system disturbances, the variable speed pumped storage unit can effectively protect the converter and rotor through the proposed strategy. Figure 11 (c) It can be seen that for small disturbances, the guide vane of the proposed strategy also exhibits the maximum response speed. The guide vane opening of the proposed strategy is 0.654 pu, while the guide vane opening of the traditional strategy is 0.623 pu. Compared with the traditional strategy, the peak guide vane opening generated by the proposed strategy is slightly higher. The increase in guide vane opening of the proposed strategy stems from the need to coordinate and meet the maximum electromagnetic power output requirements in the first stage. Therefore, the turbine must provide corresponding mechanical power support in the initial stage. Figure 11 (d) It can be seen that the maximum frequency deviation of the proposed strategy is 0.414 Hz, the maximum frequency deviation of the decoupling strategy is 0.533 Hz, the proposed strategy reduces the frequency deviation by 22.3% compared with the decoupling strategy, and the maximum frequency deviation of the traditional strategy is 0.621 Hz, the proposed strategy reduces the frequency deviation by 33.4% compared with the traditional strategy, which proves that the proposed strategy can improve the frequency regulation performance.

[0203] It is understood that the specific software environments Matlab and Simulink mentioned above are merely exemplary means of implementing this technical solution and are not intended to limit the present invention. Those skilled in the art can choose other suitable simulation tools to achieve the same technical purpose based on the teachings of this disclosure.

[0204] The two-stage frequency regulation method for variable-speed pumped storage units in this application divides the primary frequency regulation process into a first stage focusing on rapid power support and a second stage focusing on coordinated speed recovery. This decouples and orderly achieves the two traditionally contradictory goals of maximizing frequency support by releasing rotor kinetic energy and ensuring the long-term safe and stable operation of the unit in the time dimension. Combined with the coordinated control of the rotor-side converter and guide vanes, it can rapidly release rotor kinetic energy and output active power close to the upper limit in the early stage of system frequency disturbance, effectively suppressing rapid frequency drop. Compared with traditional methods, it significantly reduces the maximum frequency deviation and meets the requirements of high-proportion renewable energy access. The system requires rapid frequency regulation. By adaptively determining the stage switching time based on the system frequency change rate, and in conjunction with speed lower limit constraint control, it can avoid unit instability or converter protection actions caused by excessive rotor speed drop. Under severe disturbances, the converter is allowed to overload briefly to release more kinetic energy, while under minor disturbances, it switches to the speed recovery stage early, achieving a precise match between the severity of the disturbance and the release of kinetic energy. Through the synergy of second-stage constant angular acceleration control and guide vane power tracking mode, it can continuously provide frequency support while allowing the rotor speed to smoothly recover to the rated range, reducing electromechanical stress fluctuations and lowering guide vane drive stress and blade load. This method can fully utilize the rapid power regulation capability of variable-speed pumped storage units in the early stages of system frequency disturbances, and achieve safe and stable speed recovery of variable-speed pumped storage units in the later stages of frequency regulation. Thus, without relying on additional energy storage devices, it coordinates and improves the frequency regulation performance of the power system and the operational safety of variable-speed pumped storage units, significantly improving the minimum frequency point and stable speed of high-proportion new energy power systems, while ensuring the operational safety and regulatory sustainability of the pumped storage units themselves.

[0205] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some of the steps in the accompanying drawings may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0206] In yet another embodiment, the present invention also provides a computer device for controlling a variable-speed pumped-storage unit, comprising: one or more processors; a storage device for storing one or more programs; and when the one or more programs are executed by the one or more processors, causing the one or more processors to implement the two-stage frequency regulation method for the variable-speed pumped-storage unit described in the above embodiments.

[0207] In yet another embodiment, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements all the steps of the two-stage frequency regulation method for the variable-speed pumped storage unit described in the above embodiments.

[0208] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0209] Although this application has been disclosed above with reference to embodiments, it is not intended to limit this application. Anyone skilled in the art can make some modifications and refinements without departing from the spirit and scope of this application.

Claims

1. A two-stage frequency regulation method for a variable-speed pumped storage unit, characterized in that, Includes the following steps: The motor's state parameters are collected, and the primary frequency regulation process of the variable speed pumped storage unit is divided into the first stage frequency regulation control and the second stage frequency regulation control. When the power system frequency deviates and triggers the primary frequency regulation response of the variable speed pumped storage unit, the first stage frequency regulation control is performed. In the first stage of frequency regulation control, the electromagnetic torque is adjusted and the rotor kinetic energy is released under operating constraints through the coordinated control of the rotor-side converter and guide vanes. The system monitors the system frequency change rate in real time, calculates the lower speed limit based on the relationship between the system frequency change rate and the pull-back threshold, determines the switching conditions based on the system frequency change characteristics, and switches from the first stage frequency regulation control to the second stage frequency regulation control when the switching conditions are met. This includes: determining the maximum and minimum lower speed limits based on the operating mode of the variable speed pumped storage unit and the rotor-side power limit to obtain the pull-back threshold; monitoring the system frequency change rate in real time, and switching from the first stage frequency regulation control to the second stage frequency regulation control when either the rotor speed reaches the lower speed limit or the system frequency change rate meets the switching adaptive threshold; and when the rotor-side power limit... Equal to the rated power of the continuous rotor-side converter ,Right now At that time, the maximum lower limit of the rotational speed is obtained. for: When rotor-side power is limited Equal to 1.2 times the rated power of the continuous rotor-side converter ,Right now At that time, the minimum lower limit of the rotational speed is obtained. for: Pull back threshold The expression is: ,in, Indicates synchronous speed. Indicates the total effective power. This represents the magnitude of the system's rate of change. In the second stage of frequency regulation control, the variable speed pumped storage unit maintains frequency support for the power system, and the rotor speed of the variable speed pumped storage unit is adjusted until the rotor speed returns to the rated speed or stable operating range, the system frequency tends to stabilize, and the entire frequency regulation process is completed.

2. The two-stage frequency regulation method for variable-speed pumped storage units according to claim 1, characterized in that, In the first stage of frequency regulation control, the electromagnetic torque is adjusted under operating constraints through the coordinated control of the rotor-side converter and guide vanes to release rotor kinetic energy, including: Construct the electromagnetic equations for a variable-speed pumped storage unit; The power boundary is determined based on the electromagnetic equation of the variable speed pumped storage unit. Under the premise of satisfying the power boundary, the power command value when the frequency of the variable speed pumped storage unit is disturbed is set as the maximum value of the stator power. Under the premise of meeting the dynamic constraints of the hydraulic system and the limit of the guide vane opening change rate, the guide vane opening is driven to the maximum allowable value.

3. The two-stage frequency regulation method for variable-speed pumped storage units according to claim 2, characterized in that, The power boundary expression is: in, Indicates the maximum allowable value of stator current; Indicates the maximum allowable rotor current; , These represent the q-axis and d-axis components of the rotor current, respectively. , Indicates the active power coefficient. Indicates the reactive power coefficient. Indicates the grid voltage after orientation. Indicates the mutual inductance between the stator and rotor. Indicates electronic-side inductance; Indicates stator flux linkage; Indicates the stator active power; Indicates the stator reactive power; Indicates the maximum allowable rotor voltage; , These represent the d-axis and q-axis components of the rotor voltage, respectively. Indicates the rotor-side inductance; Indicates the rotor speed; , representing the leakage inductance coefficient.

4. The two-stage frequency regulation method for a variable-speed pumped storage unit according to claim 1, characterized in that, In the second stage of frequency regulation control, the variable-speed pumped storage unit maintains frequency support for the power system. The rotor speed of the variable-speed pumped storage unit is adjusted until the rotor speed returns to the rated speed or stable operating range, and the system frequency tends to stabilize, completing the entire primary frequency regulation process, including: The target speed recovery of the variable speed pumped storage unit in the second stage frequency regulation control is determined based on dynamic adaptation logic. Based on the deviation between the actual rotor speed and the speed recovery target, an electromagnetic torque reference value or an active power reference value for the second-stage frequency modulation control is generated. By adjusting the rotor current through the rotor-side converter, the rotor speed is driven to gradually converge toward the speed recovery target. Switch the guide vane control mode to power tracking mode, input the frequency deviation into the power PI controller to obtain an additional power command, and superimpose the additional power command on the reference power set value to obtain the total power reference value of the guide vane. Based on the reference value of the total power of the guide vanes and the speed recovery target, the guide vane opening is coordinated and adjusted to match the turbine input power with the electromagnetic power demand. The rotor speed and system frequency are continuously monitored until the rotor speed recovers to the rated speed or its stable operating range, and the system frequency tends to stabilize. The second stage of frequency regulation control is then terminated, and the entire frequency regulation process is completed.

5. A two-stage frequency regulation device for a variable-speed pumped storage unit, characterized in that, A two-stage frequency regulation method for implementing a variable-speed pumped-storage unit as described in any one of claims 1 to 4, for controlling the variable-speed pumped-storage unit, wherein the variable-speed pumped-storage unit includes hydraulic machinery, a gearbox, a motor, and a converter module; the hydraulic machinery converts water flow into mechanical energy and outputs it to the gearbox or converts mechanical energy into high-pressure water flow; the gearbox transmits the mechanical energy output by the hydraulic machinery to the motor; the motor converts mechanical energy into electrical energy and outputs it to the converter module; the converter module adjusts the electrical energy of the motor to adapt to the power grid; The two-stage frequency regulation device of the variable-speed pumped storage unit includes a frequency observation module, a staged frequency regulation control module, a rotor-side converter control module, a guide vane control module, and a speed protection module. The frequency observation module collects the frequency signal of the power grid and outputs the system frequency change rate. The staged frequency regulation control module determines the switching time of the frequency regulation stage based on the system frequency change rate and outputs electrical frequency regulation commands and hydraulic frequency regulation commands. The rotor-side converter control module adjusts the power of the variable-speed pumped storage unit according to the electrical frequency regulation commands. The guide vane control module receives the hydraulic frequency regulation commands and outputs guide vane opening control signals to adjust the water flow power. The speed protection module protects the speed of the rotor-side converter control module and the guide vane control module respectively based on the system frequency change rate.

6. The two-stage frequency regulation device for a variable-speed pumped storage unit according to claim 5, characterized in that, The speed protection module includes a speed lower limit calculation unit, a pullback threshold generation unit, and a control correction unit. The speed lower limit calculation unit determines the speed lower limit based on the operating constraints of the variable speed pumped storage unit and the system frequency change rate. The pullback threshold generation unit receives the speed lower limit and obtains the speed pullback threshold based on the system frequency change rate. The control correction unit corrects the current frequency control quantity based on the real-time rotor speed and the speed pullback threshold to obtain the corrected frequency control quantity.

7. A computer device, characterized in that, It includes one or more processors; a storage device for storing one or more programs; and when the one or more programs are executed by the one or more processors, the one or more processors implement the two-stage frequency regulation method for a variable-speed pumped storage unit as described in any one of claims 1 to 4.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the two-stage frequency regulation method for the variable speed pumped storage unit as described in any one of claims 1 to 4.

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