A multi-state piecewise linear modeling method for doubly-fed pumped storage system

Abstract

The application discloses a kind of multi-state segmented linearization modeling methods of double-fed pumped storage system belonging to the technical field of hydroelectric energy storage, which is a kind of multi-state segmented linearization control method considering power instruction fluctuation frequency change and considering water pump water turbine segmented linearization;Its modeling method is first introduced into multi-state module, and the multi-state module is divided into power multi-state module and speed multi-state module;From this, a multi-state parameter adjustment strategy is proposed, and the specific method is first to Fourier decomposition of new energy power grid power shortage signal, then the power signal of different frequency is respectively input into the set PI regulator, then the output of each PI regulator is added and connected to the PWM link, that is, set multiple PI parameters, so that the pumped storage unit still has good output characteristics under the power instruction with uncertain frequency and amplitude;It can make the best effect of pumped storage unit on new energy power grid power fluctuation suppression.

Description

Technical Field

[0001] This invention belongs to the field of hydropower energy storage technology, and specifically relates to a multi-state piecewise linearization modeling method for a doubly fed pumped storage system. Background Technology

[0002] With the continuous increase in the grid-connected capacity of new energy power generation, energy storage is beginning to play its role in the integration of new energy power grids. Pumped storage is currently the largest energy storage method worldwide. It not only boasts advantages such as being clean and pollution-free, but also demonstrates its capabilities in peak shaving, frequency and voltage regulation, and spinning reserve. Through human control and regulation of pumped storage power stations, not only can the grid's absorption capacity of new energy power generation be improved, but the overall efficiency of grid power generation can also be enhanced. A typical doubly-fed variable-speed pumped storage unit consists of a pump-turbine that can operate in both pump and turbine modes, an electric generator that can generate electricity and also function as a motor, generator-side and grid-side converters, and corresponding control components. It can improve the power quality of the power system by increasing the unit's power generation efficiency, and also improve the stability of the power system through rapid regulation of active and reactive power. In conclusion, the new energy power grid does indeed require the auxiliary integration of energy storage to achieve higher power system operating efficiency, and doubly-fed variable-speed pumped storage is very suitable as a means to smooth out fluctuations in the new energy power grid. Therefore, it is particularly important to model the doubly fed variable speed pumped storage unit to achieve the best suppression effect on the fluctuations of the new energy power grid.

[0003] Existing domestic and international scholars have researched modeling methods for doubly-fed variable-speed pumped storage units, with many attempting to combine traditional PID control with advanced methods to improve its regulation adaptability and control capabilities. One example is "A Real-Time Accurate Model and Its Predictive Fuzzy PID Controller for Pumped Storage Unit via Error Compensation" published in Energies, Volume 11, Issue 1, 2018. This technique is based on fuzzy PID control while performing rolling prediction, replacing the current control quantity with a weighted value obtained from the future control sequence. Another example is "Design of afuzzy-PID controller for a nonlinear hydraulicturbine governing system by using a novel gravitational search algorithm based on Cauchy mutation and mass weighting" published in Applied Soft Computing, Volume 52, pp. 290-305, 2017. This technique incorporates a fuzzy PID mechanism into the variable-speed pumped storage unit and optimizes the aforementioned fuzzy PID control parameters by improving the gravitational search algorithm. However, none of the above modeling methods are designed for scenarios that suppress power fluctuations in the renewable energy grid, and therefore have certain limitations. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-state piecewise linearization modeling method for a doubly-fed pumped storage system. The method is characterized by being a multi-state piecewise linearization control method that considers the frequency variation of power command fluctuations and the piecewise linearization of the pump and turbine. The modeling steps are as follows:

[0005] Step 1: First, a multi-state module is introduced, which is divided into a power multi-state module and a speed multi-state module. The reason for introducing the power multi-state module is that when the pumped-storage unit is connected to the renewable energy grid, the power deficit command received from the renewable energy grid is a command with uncertain frequency and amplitude. The regulation effect of the PI regulator is closely related to the frequency and other characteristics of the input signal. If the PI parameter of the power closed loop is set to a constant value, the unit's ability to smooth out fluctuations will be greatly reduced. Therefore, a multi-state parameter regulation strategy is proposed, that is, setting multiple sets of PI parameters, so that the pumped-storage unit still has good output characteristics under power commands with uncertain frequency and amplitude.

[0006] Step 2: Secondly, a multi-state speed module needs to be introduced. This is because when the guide vane opening of the unit's pump-turbine is not at its rated opening, the mathematical model of the pump-turbine changes with the guide vane opening. This further leads to the transfer function of the speed closed-loop also changing with the guide vane opening. Therefore, another multi-state module needs to be added to ensure that the speed closed-loop has good output characteristics under different guide vane openings.

[0007] Step 3: Based on the mathematical models and control strategies of each part of the doubly fed variable speed pumped storage system, draw a complete control block diagram of the entire system. Since the mathematical models of the pump turbine are different when it is in power generation mode and when it is in electric mode, it is necessary to establish control block diagrams for different operating conditions.

[0008] Step 4: Set relevant PI parameters and perform simulation analysis of the doubly-fed motor's generator and motoring conditions to verify the effectiveness of the multi-state piecewise linearization control method.

[0009] The specific method of the multi-state parameter adjustment strategy in step 1 is to first perform Fourier decomposition of the power deficit signal of the new energy grid, then pass power signals of different frequencies into each set PI regulator, and then sum the outputs of each PI regulator and connect them to the PWM stage. This will enable the pumped storage unit to achieve the best effect in suppressing power fluctuations in the new energy grid. The number and combination of PI regulators inside the multi-state module are determined by the input signal, and their internal characteristics are different when facing different power reference value changes.

[0010] The beneficial effect of this invention is that it establishes a relevant simulation method to obtain the output characteristics of a doubly-fed variable-speed pumped storage unit when receiving a small power fluctuation command from a new energy grid, thus realizing the effective suppression of new energy power fluctuations by the doubly-fed variable-speed pumped storage unit. Simulation results show that grid fluctuations are also effectively suppressed. Attached Figure Description

[0011] Figure 1 Control strategy diagram for doubly-fed generator units

[0012] Figure 2 The diagram shows the control block diagram for the power generation operation of the doubly fed generator unit after the introduction of the multi-state module;

[0013] Figure 3 The diagram shows the control block diagram for the electric operating conditions of the doubly-fed generator unit after the introduction of the multi-state module.

[0014] Figure 4 This is a diagram of composite power fluctuation signals under the power generation conditions of a doubly-fed induction generator unit.

[0015] Figure 5 This is a diagram showing the power output of a doubly-fed induction generator unit under power generation conditions.

[0016] Figure 6 This is a graph showing the speed fluctuation of a doubly-fed induction generator unit under power generation conditions.

[0017] Figure 7 This is a diagram showing the speed fluctuation of a doubly-fed generator unit under electric operating conditions. Detailed Implementation

[0018] This invention provides a multi-state piecewise linearization modeling method for a doubly-fed pumped storage system. This method is a multi-state piecewise linearization control method that considers the frequency variation of power command fluctuations and the piecewise linearization of the pump and turbine. The modeling method steps are as follows:

[0019] Step 1: First, a multi-state module is introduced, which is divided into a power multi-state module and a speed multi-state module. The reason for introducing the power multi-state module is that when the pumped-storage unit is connected to the renewable energy grid, the power deficit command received from the renewable energy grid is a command with uncertain frequency and amplitude. The regulation effect of the PI regulator is closely related to the frequency and other characteristics of the input signal. If the PI parameter of the power closed loop is set to a fixed value, the unit's ability to smooth fluctuations will be greatly reduced. Therefore, a multi-state parameter regulation strategy is proposed, that is, setting multiple sets of PI parameters so that the pumped-storage unit still has good output characteristics under power commands with uncertain frequency and amplitude. The specific method of the multi-state parameter regulation strategy is to first perform Fourier decomposition of the renewable energy grid power deficit signal, then pass power signals of different frequencies into the set PI regulators respectively, and then sum the outputs of the PI regulators and connect them to the PWM stage. This allows the pumped-storage unit to achieve the best smoothing effect on the power fluctuations of the renewable energy grid. The number and combination of PI regulators inside the multi-state module are determined by the input signal, and their internal characteristics are also different when facing different power reference value changes.

[0020] Step 2: Secondly, a multi-state speed module needs to be introduced. This is because when the guide vane opening of the unit's pump-turbine is not at its rated opening, the mathematical model of the pump-turbine changes with the guide vane opening. This further leads to the transfer function of the speed closed-loop also changing with the guide vane opening. Therefore, another multi-state module needs to be added to ensure that the speed closed-loop has good output characteristics under different guide vane openings.

[0021] Step 3: Based on the mathematical models and control strategies of each part of the doubly fed variable speed pumped storage system, draw a complete control block diagram of the entire system. Since the mathematical models of the pump turbine are different when it is in power generation mode and when it is in electric mode, it is necessary to establish control block diagrams for different operating conditions.

[0022] Step 4: Set relevant PI parameters and perform simulation analysis of the doubly-fed motor's generator and motoring conditions to verify the effectiveness of the multi-state piecewise linearization control method.

[0023] The present invention will be further described below with reference to the accompanying drawings.

[0024] Figure 1 The diagram shows the control strategy for a doubly-fed generator unit. Figure 1 In this system, when the active power command value of the doubly-fed variable-speed pumped storage unit changes, regulators PI1 and PI2 activate, which in turn causes the servo motor to operate, resulting in changes in the guide vane opening and the grid-side converter to operate. Under the combined effect of these two factors, the doubly-fed motor can output the active power required by the grid according to the power command. Of course, the optimal speed signal is also transmitted along the PI1 regulator line. This optimal speed is calculated using the comprehensive characteristic curve of the pump-turbine and the current active power command value. Operating the unit at this speed will result in the best overall system efficiency. Among these, P... m It is mechanical power; P s Q s These are the active and reactive power on the stator side of the doubly-fed induction generator; P r Q r These are the active and reactive power on the rotor side of the doubly-fed induction generator; P c Q c These are the active and reactive power transmitted from the grid to the converter, respectively; P g Q g These represent the active and reactive power transmitted from the variable-speed pumped-storage unit to the power grid, respectively; u sa u sb u sc and i sa i sb i sc These represent the three-phase voltage and current on the stator side of the doubly-fed induction generator; MSC and GSC are the generator-side and grid-side converters, respectively; P ref and Q ref P and Q are reference values ​​for active and reactive power; P and Q are actual feedback values ​​for active and reactive power; n r It is the actual feedback value of the rotational speed; n rref This is a reference value for the rotational speed; i rd and i rq These are the d-axis and q-axis currents on the rotor side of the doubly-fed motor, respectively; i rdref and i rqref These are the reference current values ​​for the d-axis and q-axis on the rotor side of the doubly-fed induction generator, respectively; u dc and u dcref These are the DC-side voltage and the DC-side voltage reference value; i gd and i gqThese are the q-axis and q-axis currents transmitted from the variable-speed pumped-storage unit to the power grid, respectively; i gdref and i gqref These are the d-axis and q-axis current reference values ​​transmitted from the variable-speed pumped storage unit to the power grid, respectively; u gd and u gq These are the d-axis and q-axis voltages transmitted from the variable-speed pumped storage unit to the power grid, respectively.

[0025] Figure 2 The diagram shown is a control block diagram of the doubly-fed generator unit's power generation operation after the introduction of a multi-state module. Figure 2 First, let's look at the power closed loop. The FDM module in the diagram is a Fourier decomposition module, designed to decompose power signals of different frequencies for use by multi-state module I. The multi-state module is a comprehensive device containing multiple PI controllers, each with different parameters corresponding to different frequency input signals. These parameter differences ensure good output performance for power signals of varying frequencies. Next, let's look at the speed closed loop. The SSM module is a state selection module that transmits the current guide vane opening information to multi-state module II. Multi-state module II is also a comprehensive device containing multiple PI controllers, each with different parameters corresponding to the optimal parameters for different guide vane openings. This means that regardless of changes in the pump-turbine module, the speed closed-loop controller maintains a good regulating effect. It's clear that although multi-state modules I and II have some similar internal configurations, they are fundamentally different. Firstly, the number of internal modules differs. The number of modules in Multi-State Module I is related to the unit's operating conditions; that is, the number of modules installed in Multi-State Module I corresponds to the number of typical frequency values ​​of power fluctuations in the renewable energy grid connected to the unit. Multi-State Module II, on the other hand, selects modules based on the guide vane opening, so its number of internal modules corresponds to the number of guide vane opening intervals, meaning it contains 10 modules. Furthermore, since renewable energy grid power fluctuation signals are generally a combination of multiple frequency signals, this means that multiple modules in Multi-State Module I can operate simultaneously. However, because the guide vane opening of any unit at any given moment is fixed, in Multi-State Module II, except during module switching periods, only one module corresponding to the current guide vane opening is active. Wherein, P... ref This is the active power reference value; P s The active power output of the generator unit; w ref This is the reference value for rotational speed; w r Unit speed; FDM is the Fourier transform module; SSM is the status selection module; i rdref ∑ represents the summation of reference values ​​for the d-axis current on the rotor side; i rd K represents the d-axis component of the rotor-side current. PWM K is the proportional coefficient of the PWM stage. PWMThe value of T is related to the PWM stage itself. s Its time constant; U s L represents the stator-side voltage amplitude of the doubly-fed induction generator. m The mutual inductance between the stator and rotor windings in the dq coordinate system; L s w represents the stator-side inductance in the dq coordinate system. s T is the stator speed of the doubly-fed motor; w T is the coefficient of inertia of the water flow in the pump-turbine system; e T is the electromagnetic torque. m y is the mechanical torque; y is the guide vane opening of the pump-turbine; J is the moment of inertia of the doubly-fed induction generator; p n This refers to the number of pole pairs of the doubly-fed induction motor, which is taken as 12 here; P base This is the power reference value.

[0026] Figure 3 The diagram shown is a block diagram of the electric operating condition control of a doubly-fed generator unit after the introduction of a multi-state module. Figure 3 In the process of operating the pump-turbine under electric conditions with guide vane opening greater than 50%, its mathematical model is no longer the same as that under generator conditions. At this time, there is no speed reference value; the guide vane opening is directly determined by the active power reference value, and the mechanical power is directly proportional to the cube of the speed. Therefore, a PI controller is no longer needed in the speed closed-loop, and the multi-state module II is also unnecessary. Thus, in this case, only the parameters in multi-state module I need to be designed. The parameters in the figure and... Figure 2 Consistent.

[0027] Figure 4 The image shows a composite power fluctuation signal diagram under the power generation condition of a doubly-fed induction generator (DFIG). Figure 4 In this case, the assumption is that the unit is operating in a stable state with an output of 85% of the rated power. At this time, a fluctuating signal Pflu is generated, consisting of a 0.01Hz signal with an amplitude of 10MW, a 0.5Hz signal with an amplitude of 5MW, and a 1Hz signal with an amplitude of 1MW. The duration of this fluctuation is 10s.

[0028] Figure 5 The diagram shown is the power output of a doubly-fed induction generator (DFIG) under generating conditions. Figure 5 When the doubly-fed pumped-storage unit receives the input signal within 250 seconds, all three modules in the power multi-state module are operational because the signal contains three frequencies. As the power commands at different frequencies change, each multi-state module in the power closed-loop system sends its respective current command to the stator, causing the unit to output the corresponding active power. It can be seen that at this point, the output power of the doubly-fed pumped-storage unit can almost perfectly smooth out power fluctuations in the renewable energy grid.

[0029] Figure 6 The diagram shown illustrates the speed fluctuation of a doubly-fed induction generator (DFIG) under power generation conditions. Figure 6 As can be seen from the data, the unit reacts immediately upon receiving the signal. Initially, as the unit's output power changes continuously, the speed changes accordingly due to the torque difference. After the unit's output power stabilizes, the speed begins to approach the command value under the action of the speed closed loop. After about 130 seconds, it stabilizes at 330 rpm, effectively smoothing out power fluctuations in the new energy grid.

[0030] Figure 7 The diagram shows the speed fluctuation of a doubly-fed generator unit under electric operating conditions. Figure 7 In the middle, assuming the unit is in Figure 4 Under power fluctuations, once the unit's output power stabilizes, the speed also immediately stabilizes and reaches a new stable speed state.

Claims

1. A multi-state piecewise linearization modeling method for a doubly-fed pumped storage system, characterized in that, This method is a multi-state piecewise linearized control method that considers the frequency variation of power command fluctuations and takes into account the piecewise linearization of the pump and turbine; its modeling steps are as follows: Step 1: First, a multi-state module is introduced, which is divided into a power multi-state module and a speed multi-state module. The reason for introducing the power multi-state module is that when the pumped-storage unit is connected to the renewable energy grid, the power deficit command received from the renewable energy grid is a command with uncertain frequency and amplitude. The regulation effect of the PI regulator is closely related to the frequency characteristics of the input signal. If the PI parameter of the power closed loop is set to a fixed value, the unit's ability to smooth out fluctuations will be greatly reduced. Therefore, a multi-state parameter regulation strategy is proposed, that is, setting multiple sets of PI parameters so that the pumped-storage unit still has good output characteristics under power commands with uncertain frequency and amplitude. The specific method of the multi-state parameter adjustment strategy in step 1 is to first decompose the power deficit signal of the new energy grid into Fourier decomposition, then pass the power signals of different frequencies into each set PI regulator, and then sum the output of each PI regulator and connect it to the PWM link. This will enable the pumped storage unit to have the best effect on suppressing the power fluctuation of the new energy grid. The number and combination of PI regulators inside the multi-state module are determined by the input signal. Their internal characteristics are also different when facing different power reference value changes. Step 2: Secondly, a multi-state speed module needs to be introduced. The reason is that when the guide vane opening of the unit's pump-turbine is not at the rated opening, the mathematical model of the pump-turbine changes with the guide vane opening. This further leads to the transfer function of the speed closed loop also changing with the guide vane opening. Therefore, another multi-state module needs to be added to ensure that the speed closed loop has good output characteristics under different guide vane openings. Step 3: Based on the mathematical models and control strategies of each part of the doubly fed variable speed pumped storage system, draw a complete control block diagram of the entire system. Since the mathematical models of the pump turbine are different when it is in power generation mode and when it is in electric mode, it is necessary to establish control block diagrams for different operating conditions. Step 4: Set relevant PI parameters and perform simulation analysis of the doubly-fed motor's generator and motoring conditions to verify the effectiveness of the multi-state piecewise linearization control method.

2. The multi-state piecewise linearization modeling method for a doubly-fed pumped storage system according to claim 1, characterized in that, In step 2, when the guide vane opening of the pump-turbine is not at its rated opening, the mathematical model of the pump-turbine changes with the guide vane opening. Specifically, when the active power command value of the doubly-fed variable speed pumped storage unit changes, regulators PI1 and PI2 activate, which in turn causes the servo motor to activate, resulting in a change in the guide vane opening and the grid-side converter to activate. Under the combined action of these two factors, the doubly-fed motor can output the active power required by the grid according to the power command. Of course, the optimal speed signal is also being transmitted on the PI1 regulator line. This optimal speed is calculated using the comprehensive characteristic curve of the pump-turbine as a reference and the current active power command value. When the unit operates at this speed, the efficiency of the entire system will be optimal.

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