Adaptive power control method for variable-speed pumped storage system based on water head fluctuation

Abstract

The invention discloses a self-adaptive power control method for a variable-speed pumped storage system based on water head fluctuation. The self-adaptive power control method is used for performing power control on the variable-speed pumped storage system. Comprising the following steps: constructing a variable-speed pumped storage unit mathematical model; based on the relation of the water head, the flow and the output power of the water turbine, a water head self-adaptive variable speed pumped storage system control strategy is designed, self-adaptive correction is conducted on a power instruction issued by a power grid according to the water head change, and the corrected instruction is made to be within a preset feasible range; the power correction is also used for compensating the influence of the load change, so that the unit is prevented from chasing an infeasible power target under a low water head. The rotating speed is optimized by combining water head and power dual feedback, and it is ensured that the unit operates near a high-efficiency area within the full working condition range.

Description

Technical Field

[0001] This invention relates to the field of frequency regulation technology for variable speed pumped storage, specifically to an adaptive power control method for variable speed pumped storage systems based on head fluctuations. Background Technology

[0002] New energy sources are growing rapidly and have gradually become the main power source. As of 2024, their installed capacity reached 1.889 billion kilowatts, accounting for 56% of the total. New energy sources are intermittent and uncertain, while large-scale energy storage, with its bidirectional source-load characteristics, can smooth out fluctuations in new energy supply and achieve a balance between power grid supply and demand. Pumped storage is an economical and efficient large-scale long-term energy storage technology. Statistics from the International Hydropower Association (IHA) show that there are over 400 pumped storage power plants in operation globally, with an installed capacity of nearly 200 GW, accounting for over 90% of the global long-term energy storage capacity.

[0003] Pumped storage is a key technology for ensuring the stable operation of power grids with a high proportion of renewable energy. Variable-speed pumped storage units, with their flexible adjustment capabilities provided by their AC excitation systems, have become a major development direction. Current technologies generally employ control strategies such as adding power feedforward control to the speed regulator of the pump-turbine to accelerate the adjustment speed of the guide vane valves and shorten the response time of the pump-turbine's output mechanical torque; or using doubly-fed variable-speed pumped storage units to smooth out wind power output fluctuations and thus reduce system frequency deviations. However, when participating in grid frequency regulation, variable-speed units face unresolved issues regarding the inherent conflict between speed control objectives and additional frequency control objectives, as well as the complex dynamic process response problems of the system. Summary of the Invention

[0004] 1. The technical problem to be solved:

[0005] To address the aforementioned technical problems, this invention provides an adaptive power control method for variable speed pumped storage units based on head fluctuations. This method resolves the conflict between the speed control target and the additional frequency control target in variable speed pumped storage frequency regulation, and provides technical support for achieving coordinated optimization between the generator and the grid.

[0006] 2. Technical Solution:

[0007] An adaptive power control method for variable-speed pumped storage systems based on head fluctuations is proposed for power control of such systems. The variable-speed pumped storage system includes a doubly-fed induction motor, a pump-turbine, and an AC excitation system. The pump-turbine is mechanically connected to the rotor of the doubly-fed induction motor via its shaft, enabling the conversion between mechanical and electrical energy. The AC excitation system regulates the unit speed and power by controlling the AC excitation current of the doubly-fed induction motor rotor. During power generation, the system converts the mechanical energy of the water flow into electrical energy to feed power into the grid. The system absorbs electrical energy from the power grid during pumping operation to drive the pumps and turbines to pump water to the upper reservoir. Its key features include: constructing a mathematical model of the variable-speed pumped-storage unit; designing a head-adaptive control strategy for the variable-speed pumped-storage system based on the relationship between head, flow rate, and turbine output power, enabling adaptive correction of power commands issued by the power grid according to head changes, ensuring the corrected commands are within a preset feasible range; power correction also compensates for the impact of load changes, preventing the unit from pursuing infeasible power targets under low head conditions.

[0008] Furthermore, the head adaptive variable speed pumped storage unit model includes the following steps:

[0009] S11: Model the doubly-fed induction motor to obtain its mathematical model, which specifically includes:

[0010] By transforming the mathematical model of the doubly-fed induction generator into a dq coordinate system that rotates synchronously with the synchronous speed through coordinate transformation using the Park transformation, the flux linkage equation is obtained as follows:

[0011] (1);

[0012] The electromagnetic torque equation is as follows:

[0013] (2);

[0014] In the above formula, L s For stator synchronous inductance; L m For the main mutual inductance between the stator and rotor; L r T is the rotor synchronous inductor; e The electromagnetic torque is p; the number of pole pairs is p. These are the d-axis and q-axis components of the stator and rotor flux linkages, respectively. These are the d-axis and q-axis components of the stator and rotor currents, respectively.

[0015] S12: Model the AC excitation system to obtain the mathematical model of the AC excitation system, specifically:

[0016] The AC excitation system mainly consists of a machine-side converter and a grid-side converter. The machine-side converter controls the orientation of the d-axis of the synchronous rotating coordinate system toward the stator flux linkage vector. Direction, as shown in the following formula:

[0017] (3);

[0018] Electromagnetic power P s and torque T e The equation is as follows:

[0019] (4);

[0020] In the above formula, U ds Uqs represents the d-axis component of the stator voltage; Uqs represents the q-axis component of the stator voltage.

[0021] Furthermore, the control strategy for the design head adaptive regulating variable speed pumped storage unit model includes:

[0022] S21: Adaptive head adjustment algorithm; specifically including:

[0023] Based on the relationship between the turbine's output power, head, and flow rate, the following energy conversion equation for the turbine is obtained:

[0024] (5);

[0025] In the above formula, P is the output power of the turbine; H is the head of the water; Q is the flow rate; ρ is the density of water; g is the acceleration due to gravity; and η is the overall efficiency of the unit.

[0026] The flow rate at which the unit outputs its rated power under the design rated head is defined as the rated flow rate, as shown in the following formula:

[0027] (6);

[0028] In the above formula, H rated Indicates the rated head height; P rated Q is the rated power output of the generator unit. rated This refers to the rated flow rate of the water turbine.

[0029] When the current head is far from the rated head, the maximum output capacity of the unit will change; with the turbine guide vane opening limited, the flow rate cannot be increased indefinitely, i.e., the current head H... current Maximum power P max The ratio to the rated power approximately satisfies:

[0030] (7);

[0031] Based on real-time water head values, power commands are adaptively corrected; the feasible power range of the turbine is preset, and the P command issued by the power grid is adjusted accordingly. demand The command is corrected to ensure that the corrected power command always remains within the feasible power range; specifically: if the real-time head height Adjust the current power of the water turbine. To avoid overshooting; if At that time, it is allowed Increase the power of the water turbine;

[0032] S22: Turbine speed optimization algorithm; specifically:

[0033] The unit speed of a water turbine is defined as:

[0034] (8);

[0035] In the above formula: D is the runner diameter; n is the actual rotational speed of the turbine rotor; n 11 Q is the unit rotational speed; 11 n is the unit flow rate; rated This is the rated speed; when the same unit operates at its optimal efficiency point, n 11 It is a constant value, denoted as ;

[0036] Under rated operating conditions, the unit operates at its highest efficiency point, and the unit speed at this point is as follows (9):

[0037] (9);

[0038] To maintain optimal efficiency under variable head conditions, the current unit rotational speed must always be equal to... ,Right now:

[0039] (10);

[0040] In the above formula: The target rotational speed of the turbine rotor;

[0041] Combine (9) and (10) to eliminate D and Later I learned:

[0042] (11);

[0043] Since the above formula (11) only considers the effect of water head on rotational speed and does not involve power change, the design power correction is required. Compensation for the impact of load changes;

[0044] Therefore, the final target rotational speed is:

[0045] (12);

[0046] Adjusting the turbine speed based on the final target speed allows the unit to approach its optimal efficiency point.

[0047] 3. Beneficial effects:

[0048] This invention provides an adaptive power control method for variable-speed pumped-storage units based on head fluctuations, decomposing rapid frequency support and long-term efficiency optimization into independent yet interconnected control links. The power correction in this scheme not only ensures the corrected command is within a preset feasible range but also compensates for the impact of load changes, preventing the unit from chasing infeasible power targets under low head conditions and thus preventing regulation instability. This method combines head and power dual feedback to optimize speed, ensuring the unit operates near its high-efficiency zone across the entire operating range. When grid frequency deviations occur, the adaptive algorithm corrects the power command, and the feedback-optimized operating speed works synergistically. System simulation curves show that, compared to traditional control methods, the unit can still participate in the primary frequency regulation of the power system with high quality even under complex operating conditions with large head fluctuations or even step changes. Attached Figure Description

[0049] Figure 1 To verify the hierarchical coordination control block diagram used in this invention in the example;

[0050] Figure 2 To verify the simulation of the rotational speed waveform during continuous water consumption in the reservoir in the example;

[0051] Figure 3 To verify the active power waveform diagram of the reservoir during continuous water consumption in the example;

[0052] Figure 4 To verify the active power waveform diagram of the reservoir during continuous water storage in the example;

[0053] Figure 5 To verify the active power waveform diagram during a sudden load surge in the power grid in the example;

[0054] Figure 6 To verify the waveform diagram of active power when the power grid suddenly stops generating electricity in the example. Detailed Implementation

[0055] The present invention will now be described in detail with reference to the accompanying drawings.

[0056] As attached Figure 1As shown, an adaptive power control method for a variable-speed pumped storage system based on head fluctuation is used for power control of the system. The variable-speed pumped storage system includes a doubly-fed induction motor, a pump-turbine, and an AC excitation system. The pump-turbine is mechanically connected to the rotor of the doubly-fed induction motor via its shaft, realizing the mutual conversion of mechanical energy and electrical energy. The AC excitation system regulates the unit speed and power by controlling the AC excitation current of the doubly-fed induction motor rotor. Under power generation conditions, the system converts the mechanical energy of the water flow into electrical energy to feed the power. The system is connected to the power grid; under pumping conditions, the system absorbs electrical energy from the power grid to drive the pump turbine to pump water to the upper reservoir; its key features include: constructing a mathematical model of the variable speed pumped storage unit; based on the relationship between head, flow rate and turbine output power, designing a head-adaptive variable speed pumped storage system control strategy to adaptively correct the power command issued by the power grid according to head changes, so that the corrected command is within a preset feasible range; the power correction is also used to compensate for the impact of load changes, avoiding the unit from pursuing infeasible power targets under low head conditions.

[0057] Furthermore, the head adaptive variable speed pumped storage unit model includes the following steps:

[0058] S11: Model the doubly-fed induction motor to obtain its mathematical model, which specifically includes:

[0059] By transforming the mathematical model of the doubly-fed induction generator into a dq coordinate system that rotates synchronously with the synchronous speed through coordinate transformation using the Park transformation, the flux linkage equation is obtained as follows:

[0060] (1)

[0061] The electromagnetic torque equation is as follows:

[0062] (2);

[0063] In the above formula, L s For stator synchronous inductance; L m For the main mutual inductance between the stator and rotor; L r T is the rotor synchronous inductor; e The electromagnetic torque is p; the number of pole pairs is p. These are the d-axis and q-axis components of the stator and rotor flux linkages, respectively. These are the d-axis and q-axis components of the stator and rotor currents, respectively.

[0064] S12: Model the AC excitation system to obtain the mathematical model of the AC excitation system, specifically:

[0065] The AC excitation system mainly consists of a machine-side converter and a grid-side converter. The machine-side converter controls the orientation of the d-axis of the synchronous rotating coordinate system toward the stator flux linkage vector. Direction, as shown in the following formula:

[0066] (3);

[0067] Electromagnetic power P s and torque T e The equation is as follows:

[0068] (4);

[0069] In the above formula, U ds Uqs represents the d-axis component of the stator voltage; Uqs represents the q-axis component of the stator voltage.

[0070] Furthermore, the control strategy for the design head adaptive regulating variable speed pumped storage unit model includes:

[0071] S21: Adaptive head adjustment algorithm; specifically including:

[0072] Based on the relationship between the turbine's output power, head, and flow rate, the following energy conversion equation for the turbine is obtained:

[0073] (5);

[0074] In the above formula, P is the output power of the turbine; H is the head of the water; Q is the flow rate; ρ is the density of water; g is the acceleration due to gravity; and η is the overall efficiency of the unit.

[0075] The flow rate at which the unit outputs its rated power under the design rated head is defined as the rated flow rate, as shown in the following formula:

[0076] (6);

[0077] In the above formula, H rated Indicates the rated head height; P rated Q is the rated power output of the generator unit. rated This refers to the rated flow rate of the water turbine.

[0078] When the current head is far from the rated head, the maximum output capacity of the unit will change; with the turbine guide vane opening limited, the flow rate cannot be increased indefinitely, i.e., the current head H... current Maximum power P max The ratio to the rated power approximately satisfies:

[0079] (7);

[0080] Based on real-time water head values, power commands are adaptively corrected; the feasible power range of the turbine is preset, and the P command issued by the power grid is adjusted accordingly. demand The command is corrected to ensure that the corrected power command always remains within the feasible power range; specifically: if the real-time head height Adjust the current power of the water turbine. To avoid overshooting; if At that time, it is allowed Increase the power of the water turbine;

[0081] S22: Turbine speed optimization algorithm; specifically:

[0082] The unit speed of a water turbine is defined as:

[0083] (8);

[0084] In the above formula: D is the runner diameter; n is the actual rotational speed of the turbine rotor; n 11 Q is the unit rotational speed; 11 n is the unit flow rate; rated This is the rated speed; when the same unit operates at its optimal efficiency point, n 11 It is a constant value, denoted as ;

[0085] Under rated operating conditions, the unit operates at its highest efficiency point, and the unit speed at this point is as follows (9):

[0086] (9);

[0087] To maintain optimal efficiency under variable head conditions, the current unit rotational speed must always be equal to... ,Right now:

[0088] (10);

[0089] In the above formula: The target rotational speed of the turbine rotor;

[0090] Combine (9) and (10) to eliminate D and Later I learned:

[0091] (11);

[0092] Since the above formula (11) only considers the effect of water head on rotational speed and does not involve power change, the design power correction is required. Compensation for the impact of load changes;

[0093] Therefore, the final target rotational speed is:

[0094] (12);

[0095] Adjusting the turbine speed based on the final target speed allows the unit to approach its optimal efficiency point.

[0096] Verification example:

[0097] To verify the effectiveness of the control strategy in this application, a simulation system was built in Matlab / Simulink and analyzed.

[0098] Variable-speed turbine units that excessively prioritize rapid response to grid frequency fluctuations can cause the pump-turbine operating conditions to deviate from their optimal efficiency range. Conversely, if long-term operating efficiency is prioritized, the resulting adjustment lag may prevent them from meeting the grid's frequency support requirements. Based on this solution, the attached... Figure 1 The hierarchical coordination control strategy shown decomposes rapid frequency support and long-term efficiency optimization into independent yet interconnected control links. The hierarchical coordination control block diagram is as follows: Figure 1 As shown.

[0099] The simulated rotational speed waveform of the reservoir during continuous water consumption is shown below. Figure 2 As shown in the figure, n_target represents the target rotational speed of the turbine, and n_actual represents the actual rotational speed. When the water head decreases, the centerline of the target rotational speed continuously rises. Due to the mechanical inertia of the pump and turbine, the actual rotational speed cannot keep up with the high-frequency fluctuations of the target rotational speed, and its overall trend follows the rise of the target rotational speed centerline.

[0100] Figure 3 This is a waveform diagram of active power during continuous water consumption in the reservoir. In the diagram, P_demand represents the power command issued by the grid, and P_actual represents the actual output active power. Throughout the simulation, P_demand is a stable periodic signal, with two peak absolute values ​​of 25MW at t=16s and t=79s. At t=16s, the absolute value of the P_actual peak is 29.20MW; at t=79s, the absolute value of the P_actual peak drops to 26.08MW. Within these 63s, for the same peak power demand, the absolute value of the system's allowed output power decreases by 3.12MW. As the water head decreases, this algorithm successfully lowers the upper limit of the power command, effectively preventing unit overload under low water head conditions. When the water head is high, the amplitude of P_actual is higher than that of P_demand, and the unit outputs more power to support the grid; when the water head decreases, the amplitude of P_actual is lower than that of P_demand, and the unit outputs less power to protect itself.

[0101] Combined with speed waveform Figure 2 and active power waveform Figure 3 It can be seen that the power control loop responds quickly to external frequency regulation requirements, while the speed optimization loop adjusts slowly, thus decoupling the two on the time scale.

[0102] Figure 4 The graph shows the active power waveform during continuous reservoir impoundment. At t=16s, the absolute value of the peak P_actual is 20.78MW; at t=79s, the absolute value of the peak P_actual rises to 25.01MW. Within these 63s, for the same peak power demand, the absolute value of the system's allowable output power increases by 4.23MW. As the water head rises, this method amplifies the upper limit of the power command, providing greater power support to the grid.

[0103] Figure 5 The diagram shows the active power waveform during a sudden load surge in the power grid. When t < 50s, the system is in a step-steady-state period, encouraging generating units to increase power output by 20%. When t = 50s, the system is in a step-response period, experiencing a step drop in head. The algorithm responds to this sudden drop from above-rated head by canceling previous amplification actions and recalculating commands based on the new low head, entering a power-limiting protection mode. When t > 50s, P_actual enters a new steady state to adapt to the low head condition after the step. Throughout the process, the peak value of P_actual decreases from 30.00MW before the step to 19.01MW after the step, an absolute decrease of 10.99MW and a relative decrease of 36.63%.

[0104] Figure 6 The graph shows the active power waveform when the power grid suddenly stops generating electricity. When t < 55s, the system is in a step-steady-state period, and the strategy restricts generator power generation. When t = 55s, the system is in a step-response period, and the head drops sharply. The algorithm responds to the sudden increase in head from below the rated head by releasing the power restriction command and recalculating the command based on the new high head, entering a mode that encourages generators to generate more electricity. When t > 55s, P_actual enters a new steady state to adapt to the high head condition after the step. Throughout the process, the peak value of P_actual increases from 20MW before the step to 29MW after the step, an absolute increase of 9MW and a relative increase of 45%.

[0105] As can be seen from the simulation curves of the above-mentioned different operating conditions, compared with the traditional control method, the unit of this application can still participate in the primary frequency regulation of the power system with high quality under complex operating conditions with large fluctuations or even step changes in head.

[0106] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be defined by the scope of the claims of this application.

Claims

1. A variable speed pumped storage system adaptive power control method based on water head fluctuation, used for power control of a variable speed pumped storage system; the variable speed pumped storage system comprises a doubly-fed induction motor, a pump-turbine, and an alternating current excitation system; the pump-turbine is mechanically connected with the rotor of the doubly-fed induction motor through a rotating shaft to realize mutual conversion between mechanical energy and electrical energy; the alternating current excitation system controls the alternating current excitation current of the rotor of the doubly-fed induction motor to realize speed and power regulation of the unit; in a power generation condition, the system converts mechanical energy of water flow into electrical energy to feed into a power grid; in a water pumping condition, the system absorbs electrical energy from the power grid to drive the pump-turbine to pump water to an upper reservoir; characterized in that: A variable-speed pumped storage unit mathematical model is constructed; a variable-speed pumped storage system control strategy adaptive to water head is designed based on the relationship between water head, flow and the output power of the water turbine, so as to realize adaptive correction of the power instruction issued by the power grid according to the change of water head, so that the corrected instruction is in the preset feasible range; the power correction is also used to compensate the influence of load change, so as to avoid the unit to pursue the unfeasible power target under low water head.

2. The water head fluctuation based variable speed pumped hydro system adaptive power control method of claim 1, wherein: The water head adaptive regulation variable-speed pumped storage unit model comprises the following steps: S11: model the doubly-fed induction motor to obtain a mathematical model of the doubly-fed induction motor, specifically comprising: The mathematical model of the doubly-fed motor is transformed through coordinate transformation, and the three-phase stationary coordinate system model is transformed into the dq coordinate system rotating with the synchronous speed to obtain the flux linkage equation as follows: （1）； The electromagnetic torque equation is as follows: （2）； In the above formula, L s is the stator synchronous inductance; L m is the main mutual inductance between the stator and the rotor; L r is the rotor synchronous inductance; T e is the electromagnetic torque; p is the number of pole pairs; are the d-axis and q-axis components of the stator and rotor fluxes, respectively; are the d-axis and q-axis components of the stator and rotor currents, respectively; S12: model the AC excitation system to obtain a mathematical model of the AC excitation system, specifically comprising: The AC excitation system is mainly composed of a machine-side converter and a grid-side converter. The machine-side converter controls the d-axis of a synchronous rotating coordinate system to be oriented to a stator flux linkage vector direction, as follows: （3）； Electromagnetic power P s and torque T e of the equation as follows: （4）； In the above formula, U ds represents the stator voltage d-axis component; Uqs represents the stator voltage q-axis component.

3. The water head fluctuation based variable speed pumped hydro energy storage system adaptive power control method of claim 2, wherein: The control strategy of the water head adaptive regulation variable-speed pumped storage unit model comprises: S21: water head adaptive regulation algorithm; specifically comprising: Based on the relationship between the output power of the water turbine and the water head and flow, the energy conversion equation of the water turbine is obtained as follows: （5）； In the above formula, P is the output power of the water turbine; H is the height of the water head; Q is the flow; ρ is the density of water; g is the acceleration of gravity; η is the comprehensive efficiency of the unit; The flow of the unit under the rated water head and the rated power is defined as the rated flow, as follows: （6）； In the above formula, H rated represents the rated water head height; P rated is the rated power output of the unit; Q rated is the rated flow of the water turbine; The maximum output capacity of the unit will change when the current water head deviates from the rated water head; under the condition that the guide vane opening of the water turbine is limited, the flow cannot be infinitely increased, i.e., the ratio of the maximum power P max under the current water head H current to the rated power approximately satisfies: （7） Based on the real-time water head value, the power instruction is adaptively corrected; the preset power feasible range of the water turbine is used to correct the P demand instruction issued by the power grid, so that the corrected power instruction is always within the power feasible range; specifically, if the real-time height of the water head is lower than the preset lower limit of the water head, the current power of the water turbine is adjusted to avoid overshoot; if the real-time height of the water head is higher than the preset upper limit of the water head, the power of the water turbine is adjusted to be higher ; if the real-time height of the water head is within the preset range of the water head, the current power of the water turbine is maintained ; if the real-time height of the water head is within the preset range of the water head, the current power of the water turbine is maintained ; if the real-time height of the water head is within the preset range of the water head, the current power of the water turbine is maintained . S22: speed optimization algorithm of the water turbine; specifically comprising: The unit speed of the water turbine is defined as: （8）； In the above formula: D is the runner diameter; n is the actual speed of the turbine rotor; n 11 is the unit speed; Q 11 is the unit flow; n rated is the rated speed; when the same unit is operated at the optimal efficiency point, n 11 is a constant value, denoted as ; Under the rated working condition, the unit operates at the highest efficiency point, and the unit speed at this time is as follows: （9）； To maintain the optimal efficiency under variable head conditions, the current unit speed must always be equal to i.e. （10）； In the above formulae: is the target rotational speed of the hydraulic turbine rotor; Combining (9) and (10), eliminate D and We get: （11）； Since only the influence of water head on rotational speed is considered in the above equation (11), the power variation is not involved, and the design power correction compensate the influence of load variation; The final target speed is obtained as follows: （12）； The speed of the water turbine is adjusted based on the final target speed, so that the unit approaches the optimal efficiency point.

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