A power allocation method to accelerate the response of power instructions of grid-connected wind turbines

Abstract

The present invention discloses a power allocation method for accelerating the power command response of grid-connected wind turbines. The method comprises the following steps: 1) establishing a mathematical model of a virtual synchronous machine and calculating the power expression between the virtual synchronous machine and the power grid; 2) constructing a small-signal model of the virtual synchronous machine and a transfer function of active power based on the mathematical model and power expression, and establishing a state-space equation for the virtual synchronous machine; 3) establishing discretized state-space equations for multiple virtual synchronous machines based on the state-space equations for the virtual synchronous machine; 4) obtaining current constraints and active power constraints based on the current loop model and active power capacity of the grid-connected wind turbine; and 5) constructing and solving a power tracking performance optimization problem for the grid-connected wind turbine based on the discretized state-space equations for the multiple virtual synchronous machines, as well as the current constraints and active power constraints. This method has advantages such as good power tracking performance.

Description

Technical Field

[0001] The present invention mainly relates to the field of new energy technology, and in particular to a power distribution method for accelerating the response of power instructions of grid-connected wind turbines. Background Art

[0002] With the large-scale grid connection of new energy, a series of problems have emerged. For example, the intermittent and volatile nature of new energy power generation cannot provide the inertia support required by the power system. The large-scale grid connection of new energy will reduce the stability of the power system and affect the safe operation of the power grid.

[0003] Currently, there are two main control schemes for grid connection: grid-following control and grid-forming control. Traditional grid-following control methods rely on phase-locked loops (PLLs) to maintain synchronization with the grid and are unable to provide inertia. When the power system load increases, the frequency change rate increases, which can trigger cascade disconnection of units and further deteriorate the stable operation of the power system. Grid-forming control methods, on the other hand, provide inertia support by simulating the dynamic characteristics of synchronous generators. For example, virtual synchronous machine control incorporates the synchronous motor's rotor motion equations to impart virtual inertia and virtual damping to the converter.

[0004] Under current technical conditions, grid-connected wind turbines also present a number of challenges. For example, they respond more slowly to power commands than grid-connected wind turbines, which, to some extent, restricts the rapid regulation of the power system. Future research should focus on improving the power response speed of grid-connected wind turbines to more effectively address this slow power response issue. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, the present invention provides a power distribution method for improving the stability of the power grid and accelerating the power instruction response of the grid-connected wind turbine generator set.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0007] A power distribution method for accelerating the response of power instructions of a grid-type wind turbine generator system comprises the following steps:

[0008] 1) Establish a mathematical model of the virtual synchronous machine and calculate the power expression between the virtual synchronous machine and the power grid;

[0009] 2) Based on the mathematical model of the virtual synchronous machine and the power expression between the virtual synchronous machine and the power grid, a small signal model of the virtual synchronous machine and the active power transfer function are constructed, and the state space equation of the virtual synchronous machine is established;

[0010] 3) Based on the state space equation of the virtual synchronous machine, establish the state space equations of multiple virtual synchronous machines and the corresponding discretized state space equations;

[0011] 4) Based on the current loop model and active power capacity of the grid-connected wind turbine, the current constraint and active power constraint conditions are obtained;

[0012] 5) Based on the discretized state space equations of multiple virtual synchronous machines, as well as the current constraints and active power constraints, a power tracking performance optimization problem for grid-connected wind turbines is constructed. By solving this optimization problem, the turbines can achieve better power tracking performance.

[0013] Preferably, in step 1), the mathematical model of the virtual synchronous machine is:

[0014]

[0015]

[0016]

[0017] in J represents the virtual inertia, D p represents virtual damping, Represents the reactive power regulation coefficient, Represents the reactive voltage droop coefficient, represents the phase angle of the virtual synchronous machine; , and represents the angular frequency of the virtual synchronous machine and the grid angular frequency, E Indicates the voltage amplitude of the virtual synchronous machine; , and Indicates the rated voltage and grid voltage amplitude; , ; 、 、 and Indicates active power, active power reference value, reactive power, and reactive power reference value.

[0018] Preferably, in step 1), the power expression between the virtual synchronous machine and the power grid is:

[0019]

[0020] represents the power angle between the virtual synchronous machine and the grid, It represents the reactance of the line connecting the virtual synchronous machine to the grid.

[0021] Preferably, in step 2), the state space equation of the virtual synchronous machine is:

[0022]

[0023] represents the time constant; where and Indicates the increment of the virtual synchronous machine active power and the increment of the active power reference value.

[0024] Preferably, the specific process of step 3) is:

[0025] The state space equations of multiple virtual synchronous machines are:

[0026]

[0027] in , N represents the number of grid-type wind turbines, ; 、 and are the state space equation coefficients;

[0028] The corresponding discretized state space equation is:

[0029]

[0030] in , , , Indicates the controller sampling period; Indicates the state of multiple virtual synchronous machines at time k, and k+1 is the state at the next time; Indicates the state of the state variable at the next moment, Represents the state of the output variable at the kth moment.

[0031] Preferably, in step 4), the current loop model of the grid-type wind turbine generator set is:

[0032]

[0033] in , and represents the coefficient of the PI controller, s represents the complex variable, Indicates the output voltage of the grid-type wind turbine d Axis component, 、 and It represents the real-time measured current value, current reference value and maximum allowable current of the grid-type wind turbine.

[0034] Preferably, in step 4), the current constraint condition is:

[0035]

[0036] Indicates the size relationship between the integral link and the linear expression; represents the reactive power regulation coefficient; and Indicates the active power increment coefficient; and Indicates the reactive power increment coefficient; Indicates the active power increment of the virtual synchronous machine; Indicates the current reference value increment.

[0037] Preferably, in step 4), the active power constraint condition is:

[0038]

[0039]

[0040] in Indicates the total active power dispatch instruction, Indicates the available capacity of grid-type wind turbines; and represents the active power and active power reference value of the i-th virtual synchronous machine; N is the number of wind turbines.

[0041] Preferably, in step 5), the objective function of the power tracking performance optimization problem of the grid-type wind turbine generator set is:

[0042]

[0043]

[0044]

[0045] in, represents the overall optimization goal, and represents the weight coefficient, Indicates the deviation between the active power of a single grid-connected wind turbine and the active power reference value. Indicates the deviation between the active power of multiple grid-connected wind turbines and the total active power command. represents the number of prediction steps, Indicates the reference value of the active power of a single grid-connected wind turbine; Indicates the active power of a single grid-connected wind turbine at the current moment. It represents the increment of active power of a single grid-connected wind turbine at the kth moment.

[0046] Compared with the prior art, the advantages of the present invention are:

[0047] The present invention establishes a mathematical model of the virtual synchronous machine and calculates the power between it and the power grid, constructs a small signal model and transfer function of the virtual synchronous machine, further obtains the state space equation of the virtual synchronous machine, and derives the state space equations and corresponding discretization equations of multiple virtual synchronous machines. At the same time, considering the problem of the remaining available capacity of the saturated grid-type wind turbine set of the PI controller in the current loop, the constraint conditions of the optimization problem are established. Combining the above model and constraint conditions, a power tracking performance optimization problem of the grid-type wind turbine set is formed. By solving this optimization problem, the unit can obtain better power tracking performance, further improving the stability of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 FIG. 4 is a flow chart of a power tracking method according to an embodiment of the present invention.

[0049] Figure 2 Schematic diagram of the small signal model of the virtual synchronous machine in the present invention.

[0050] Figure 3 The figure is a comparison diagram of the power instruction response of a given active power of the present invention and the traditional method.

[0051] Figure 4 Schematic diagram comparing the step power response of the present invention with the traditional method.

[0052] Figure 5 Schematic diagram for comparing active power reference values ​​between the present invention and the traditional method; (a) is a schematic diagram for comparing active power reference values ​​under a given active power instruction; (b) is a schematic diagram for comparing active power reference values ​​under step power. DETAILED DESCRIPTION

[0053] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0054] like Figure 1 As shown, the power distribution method for accelerating the power instruction response of the grid-type wind turbine generator system provided by the embodiment of the present invention includes the following steps:

[0055] 1) Establish a mathematical model of the virtual synchronous machine and calculate the power expression between the virtual synchronous machine and the power grid. The mathematical model of the virtual synchronous machine includes the dynamic characteristics of the virtual synchronous generator.

[0056] 2) Based on the mathematical model of the virtual synchronous machine obtained in step 1) and the power expression between the virtual synchronous machine and the power grid, a small signal model of the virtual synchronous machine and the transfer function of active power are constructed, and the state space equation of the virtual synchronous machine is established;

[0057] 3) Based on the state space equation of the virtual synchronous machine obtained in step 2), establish the state space equations of multiple virtual synchronous machines and the corresponding discretized state space equations;

[0058] 4) Based on the current loop model and active power capacity of the grid-connected wind turbine, the current constraint and active power constraint conditions are obtained; the current loop model is a transfer function related to the active power and current of the grid-connected wind turbine;

[0059] 5) Based on the discretized state-space equations of the multiple virtual synchronous machines obtained in step 3), as well as the current constraints and active power constraints in step 4), a power tracking performance optimization problem for the grid-connected wind turbine is constructed. By solving this optimization problem, the turbine can achieve better power tracking performance.

[0060] In step 1), the mathematical model of the virtual synchronous machine is established as:

[0061] (1)

[0062] (2)

[0063] (3)

[0064] in J represents the virtual inertia, D p represents virtual damping, Represents the reactive power regulation coefficient, Represents the reactive voltage droop coefficient, represents the phase angle of the virtual synchronous machine; , and represents the angular frequency of the virtual synchronous machine and the grid angular frequency, E Indicates the voltage amplitude of the virtual synchronous machine; , and Indicates the rated voltage and grid voltage amplitude; , , 、 、 and Indicates active power, active power reference value, reactive power, and reactive power reference value.

[0065] According to the calculation formula of complex power:

[0066] (4)

[0067] in S represents the complex power between the virtual synchronous machine and the grid, UIndicates the voltage difference between the virtual synchronous machine and the grid connection line. The horizontal component of the complex power is the active power between the virtual synchronous machine and the grid, and the vertical component is the reactive power:

[0068] (5)

[0069] (6)

[0070] in represents the power angle between the virtual synchronous machine and the grid, and represents the resistance and reactance of the line connecting the virtual synchronous machine to the grid, .

[0071] The incremental form of formula (5) and formula (6) is:

[0072] (7)

[0073] (8)

[0074] in and Indicates the active power increment coefficient, , , and represents the voltage amplitude and power angle at the virtual synchronous machine operating point, and Represents the reactive power increment coefficient, , .

[0075] Under actual working conditions, the power angle between the virtual synchronous machine and the grid is generally small in steady state, that is, , , and the reactance in the actual connection line is much greater than the resistance, that is, , formula (5) can be simplified as:

[0076] (9)

[0077] like Figure 2 As shown, in step 2), a small signal model of the virtual synchronous machine is established. Specifically, the increment of the active power reference value is taken as input, and the increment of the active power output by the virtual synchronous machine is taken as output. The transfer function is:

[0078] (10)

[0079] in and Represents the increment of the active power of the virtual synchronous machine and the increment of the active power reference value, and s represents a complex variable. This transfer function is a second-order transfer function, which can be converted into a first-order transfer function by reducing the order:

[0080] (11)

[0081] Based on formula (11), the active power loop of the virtual synchronous machine is:

[0082] (12)

[0083] in represents the time constant, .

[0084] The state space equation of the virtual synchronous machine is:

[0085] (13)

[0086] In step 3), based on equation (13), the state space equations of multiple virtual synchronous machines are:

[0087] (14)

[0088] in , N represents the number of grid-type wind turbines, ; 、 and are the state space equation coefficients;

[0089] ;

[0090] , ;

[0091] Based on formula (14), the corresponding discretization equation is:

[0092] (15)

[0093] in , , , Indicates the controller sampling period; Indicates the state of multiple virtual synchronous machines at time k, and k+1 is the state at the next time; Indicates the state of the state variable at the next moment, Represents the state of the output variable at the kth moment.

[0094] In step 4), the current loop model of the grid-type wind turbine is:

[0095] (16)

[0096] in , and represents the coefficient of the PI controller, Indicates the output voltage of the grid-type wind turbine d Axis component, 、 and It represents the real-time measured current value, current reference value and maximum allowable current of the grid-type wind turbine.

[0097] Considering that the constraints of the optimization problem are generally in linear form, Equation (16) contains an integral link. The size relationship between the area enclosed by the integral link and the linear expression can be equivalent:

[0098] (17)

[0099] in Indicates the size relationship between the integral link and the linear expression.

[0100] The incremental linear form of the current loop model is obtained as follows:

[0101] (18)

[0102] in Indicates the voltage amplitude increment of the grid-type wind turbine generator set, Indicates the current reference value increment.

[0103] The constraints of the optimization problem are linear expressions containing control quantities, based on the incremental form of formula (3):

[0104] (19)

[0105] Substituting equations (7), (8) and (19) into equation (18), we obtain:

[0106] (20)

[0107] At the same time, the active power output by multiple grid-connected wind turbines should meet the active power dispatching instructions and the dispatchable active power of a single grid-connected wind turbine should be less than its available capacity:

[0108] (twenty one)

[0109] (twenty two)

[0110] in Indicates the total active power dispatch instruction, It represents the available capacity of grid-type wind turbines; N is the number of wind turbines.

[0111] In step 5), the objective function of the power tracking performance optimization problem of multiple grid-type wind turbines is:

[0112] (twenty three)

[0113] (twenty four)

[0114] (25)

[0115] in, represents the overall optimization goal, and represents the weight coefficient, Indicates the deviation between the active power of a single grid-connected wind turbine and the active power reference value. Indicates the deviation between the active power of multiple grid-connected wind turbines and the total active power command. represents the number of prediction steps, It represents the reference value of the active power of a single grid-connected wind turbine. Indicates the active power of a single grid-connected wind turbine at the current moment. It represents the increment of active power of a single grid-connected wind turbine at the kth moment.

[0116] By solving the problem of improving the power tracking performance of grid-type wind turbines such as Equations (21) to (25), the power response speed of multiple grid-type wind turbines can be optimized at the same time, thereby better tracking the power instructions.

[0117] The present invention establishes a mathematical model of the virtual synchronous machine and calculates the power between it and the power grid, constructs a small-signal model and transfer function of the virtual synchronous machine, further obtains the state-space equation of the virtual synchronous machine, and derives the state-space equations and corresponding discretization equations of multiple virtual synchronous machines. Simultaneously, the constraint conditions of the optimization problem are established, taking into account the saturated residual available capacity of the PI controller in the current loop of the grid-type wind turbine. Combining the above model and constraint conditions, a power tracking performance optimization problem for the grid-type wind turbine is formed. By solving this optimization problem, the turbine achieves better power tracking performance, further improving grid stability. Compared with the control method with a given active power reference value, the present invention has better tracking performance for active power, while also avoiding overshoot and oscillation.

[0118] In order to verify the effectiveness of the present invention, a virtual synchronous machine is used to replace the grid-type wind turbine. Multiple parallel virtual synchronous machines are connected to the power grid. There is a transmission line between the power grid and the first virtual synchronous machine node, and there are also transmission lines between each virtual synchronous machine node. The operating condition comparison is selected under a given power reference value. After multiple parallel virtual synchronous machines are connected to the power grid, the operating response of one of the grid-type wind turbines is checked.

[0119] The power response of the grid-type wind turbine generator system under a given power command and a step power command after running for a period of time after the given command is as follows: Figure 3 and Figure 4 As shown in the figure, after the total power command is given at the initial moment and under the total step power command at 40 seconds, the grid-type wind turbine generator system has a faster response speed and power tracking performance to the power command under the two working conditions compared with the given total power reference value.

[0120] like Figure 5 As shown, the power reference value in the present invention is temporarily greater than the given power reference value before the unit power reaches the reference value under the above two operating conditions. The larger the reference value, the greater the difference between the power of the grid-type wind turbine and the reference value, and its response speed will also increase, thereby achieving a faster response speed to the power command. When it approaches the reference value, the reference value decreases, ensuring the stable operation of the grid-type wind turbine after responding to the command.

[0121] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A power distribution method for accelerating the response of power instructions of grid-type wind turbines, characterized in that: Including steps: 1) Establish a mathematical model of the virtual synchronous machine and calculate the power expression between the virtual synchronous machine and the power grid; 2) Based on the mathematical model of the virtual synchronous machine and the power expression between the virtual synchronous machine and the power grid, a small signal model of the virtual synchronous machine and the active power transfer function are constructed, and the state space equation of the virtual synchronous machine is established; 3) Based on the state space equation of the virtual synchronous machine, establish the state space equations of multiple virtual synchronous machines and the corresponding discretized state space equations; 4) Based on the current loop model and active power capacity of the grid-connected wind turbine, the current constraint and active power constraint conditions are obtained; 5) Based on the discretized state space equations of multiple virtual synchronous machines, as well as current and active power constraints, a power tracking performance optimization problem for grid-connected wind turbines is constructed. By solving this optimization problem, the turbines can achieve better power tracking performance. In step 4), the current loop model of the grid-type wind turbine is: ； in , and represents the coefficient of the PI controller, s represents the complex variable, Indicates the output voltage of the grid-type wind turbine d Axis component, 、 and Indicates the real-time measured current value, current reference value and maximum allowable current of the grid-type wind turbine generator set; E Indicates the voltage amplitude of the virtual synchronous machine; In step 4), the current constraint is: ； Indicates the size relationship between the integral link and the linear expression; represents the reactive power regulation coefficient; and Indicates the active power increment coefficient; and Indicates the reactive power increment coefficient; Indicates the active power increment of the virtual synchronous machine; Indicates the current reference value increment.

2. The power distribution method for accelerating the power instruction response of a grid-connected wind turbine generator system according to claim 1, characterized in that: In step 1), the mathematical model of the virtual synchronous machine is: in J represents the virtual inertia, D p represents virtual damping, Represents the reactive power regulation coefficient, Represents the reactive voltage droop coefficient, represents the phase angle of the virtual synchronous machine; , and represents the angular frequency of the virtual synchronous machine and the grid angular frequency, E Indicates the voltage amplitude of the virtual synchronous machine; , and Indicates the rated voltage and grid voltage amplitude; , ; 、 、 and Indicates active power, active power reference value, reactive power, and reactive power reference value.

3. The power distribution method for accelerating the response of power instructions of grid-connected wind turbines according to claim 2, characterized in that: In step 1), the power expression between the virtual synchronous machine and the grid is: in represents the power angle between the virtual synchronous machine and the grid, It represents the reactance of the line connecting the virtual synchronous machine to the grid.

4. The power distribution method for accelerating the power instruction response of a grid-connected wind turbine generator system according to claim 1, 2 or 3, characterized in that: In step 2), the state space equation of the virtual synchronous machine is: ； represents the time constant; where and Indicates the increment of the virtual synchronous machine active power and the increment of the active power reference value.

5. The power distribution method for accelerating the power instruction response of a grid-connected wind turbine generator system according to claim 4, characterized in that: The specific process of step 3) is as follows: The state space equations of multiple virtual synchronous machines are: in , N represents the number of grid-type wind turbines, ; 、 and are the state space equation coefficients; The corresponding discretized state space equation is: in , , , Indicates the controller sampling period; Indicates the state of multiple virtual synchronous machines at time k, and k+1 is the state at the next time; Indicates the state of the state variable at the next moment, Represents the state of the output variable at the kth moment.

6. The power distribution method for accelerating the power instruction response of a grid-connected wind turbine generator system according to claim 1, characterized in that: In step 4), the active power constraint is: in Indicates the total active power dispatch instruction, Indicates the available capacity of grid-type wind turbines; and represents the active power and active power reference value of the i-th virtual synchronous machine; N is the number of wind turbines.

7. The power distribution method for accelerating the power instruction response of a grid-connected wind turbine generator system according to claim 6, characterized in that: In step 5), the objective function of the power tracking performance optimization problem of the grid-type wind turbine is: in, represents the overall optimization goal, and represents the weight coefficient, Indicates the deviation between the active power of a single grid-connected wind turbine and the active power reference value. Indicates the deviation between the active power of multiple grid-connected wind turbines and the total active power command. represents the number of prediction steps, Indicates the reference value of the active power of a single grid-connected wind turbine; Indicates the active power of a single grid-connected wind turbine at the current moment. It represents the increment of active power of a single grid-connected wind turbine at the kth moment.

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