Virtual inertia control method and device for multiple wind turbines connected in parallel based on energy storage

Abstract

The invention discloses an energy storage-based virtual inertia control method and device for multiple wind turbines connected in parallel, and the method comprises the steps: controlling the capacity proportion between a first virtual inertia and a second virtual inertia, and carrying out the corresponding distribution of the active power of a first wind turbine system and a second wind turbine system according to the capacity proportion; establishing a reactive power error function between the first wind turbine system and the second wind turbine system; constructing virtual impedance for decoupling active power and reactive power of the wind turbine system; and when the system is subjected to disturbance oscillation, droop coefficients of the first wind turbine system and the second wind turbine system are adjusted in real time, and reactive power distribution is carried out on the multi-wind-turbine parallel system. According to the technical scheme, the virtual inertia, the virtual damping and the droop coefficient of the single-wind-motor energy storage system in the whole system are controlled and adjusted, the system oscillation problem caused by low inertia and under-damping is solved, and the voltage and frequency stability of the whole system is guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology of wind power systems, and in particular to a virtual inertia control method and device for parallel connection of multiple wind turbines based on energy storage. Background Art

[0002] The penetration rate of renewable energy such as wind power and photovoltaics has increased significantly, and power electronic equipment has been widely used. Therefore, the power system has shifted from a traditional power system dominated by synchronous generators to a new energy power system with a high proportion of power electronic equipment. However, this has brought about problems of low inertia and underdamping, and the stability of power system voltage and frequency has become increasingly prominent.

[0003] In existing engineering practices, due to the real-time differences in operating conditions or assembly scales of single wind turbine energy storage systems within a wind farm group formed by multiple wind turbines in parallel, the power capacity carried by a single wind turbine energy storage system after being connected to the grid is not always equal. When a disturbance occurs and oscillation occurs, the overall system has low inertia and underdamping problems, making it difficult and slow to overcome or recover from the oscillation. Summary of the invention

[0004] Purpose of the invention: The present invention provides a virtual inertia control method and device for multiple wind turbines in parallel based on energy storage, aiming to overcome the technical problem of difficult and slow recovery from oscillation due to low inertia and underdamping problems in the prior art in multiple wind turbine parallel systems.

[0005] Technical solution: The present invention provides a virtual inertia control method for multiple wind turbines in parallel based on energy storage, including: controlling the capacity ratio between the first virtual inertia and the second virtual inertia, and the active power of the first wind turbine system and the second wind turbine system is correspondingly distributed according to the capacity ratio; the first virtual inertia and the second virtual inertia are parameters in the first wind turbine system and the second wind turbine system respectively: through the operation model of the wind turbine system, and introducing the droop coefficient therein, a reactive power error function between the first wind turbine system and the second wind turbine system is established, and the corresponding reactive power error value is calculated; and according to the line impedance of the wind turbine system, a virtual impedance for decoupling the active power and reactive power of the wind turbine system is constructed; when the multiple wind turbine parallel system is disturbed and oscillates, the virtual output voltage and the reconstructed output voltage of the wind turbine system are obtained through the operation model and the virtual impedance, the droop coefficients of the first wind turbine system and the second wind turbine system are respectively adjusted in real time, and the reactive power of the multiple wind turbine parallel system is distributed based on the droop system.

[0006] Specifically, the capacity ratio between the first virtual inertia and the second virtual inertia is controlled to be consistent with the capacity ratio between the first virtual damping and the second virtual damping, the active power of the first wind turbine system and the second wind turbine system is allocated according to the capacity ratio, and the first virtual damping and the second virtual damping are parameters in the first wind turbine system and the second wind turbine system, respectively.

[0007] Specifically, the operation model of the wind turbine system includes the following active power output model and reactive power output model:

[0008] P = [(EUcosα-U 2 )R+EUXsinα] / (R 2 +X 2 ),

[0009] Q=[(EUcosα-U 2 )X-EUXsinα] / (R 2 +X 2 ),

[0010] Among them, P represents active power output, Q represents reactive power output, E represents output voltage amplitude, U represents AC bus voltage amplitude, α represents the phase angle of transmission impedance, X represents transmission impedance, and R represents transmission resistance.

[0011] Specifically, when the transmission impedance is inductive, a voltage reactive function with a reactive droop coefficient introduced is obtained based on the active power output of the wind turbine system.

[0012] Specifically, the active power output based on the wind turbine system, wherein the active power output model is as follows:

[0013] P m =UEsinα / X,

[0014] Among them, P m Indicates the active power output when the transmission impedance is inductive;

[0015] The voltage reactive function is as follows:

[0016] Q m =(UEcosα-U 2 ) / (X+UK Q ),

[0017] Among them, Q m Indicates the reactive power output when the transmission impedance is inductive, K Q Represents the reactive power droop coefficient.

[0018] Specifically, the reactive power error function is as follows:

[0019] ΔQ=QA -Q B =U(Ecosα-U)[(X A -X B )+U(K QA -K QB )] / (X A +UK QA )(X B +UK QB ),

[0020] Wherein, ΔQ represents the reactive power error value between the first wind turbine system and the second wind turbine system, Q A and Q B Respectively represent the reactive power output of the first wind turbine system and the second wind turbine system, X A and X B Respectively represent the transmission impedance of the first wind turbine system and the second wind turbine system, K QA and K QB Respectively represent the reactive power droop coefficients of the first wind turbine system and the second wind turbine system.

[0021] Specifically, the difference between the virtual impedance and the line impedance is controlled to be within a standard threshold range, and the virtual impedance is as follows:

[0022] X m =R m +sω(L0+K L L m ),

[0023] Among them, X m Represents virtual impedance, R m represents the virtual negative resistance, ω represents the operating frequency of the wind turbine system, L0 represents the initial virtual inductance, K L Indicates the impedance adjustment coefficient, L m =|L ref –L A |, L ref Represents the reference inductance, L A Represents the inductance of the first wind turbine system.

[0024] Specifically, the virtual output voltage is as follows:

[0025] U m =X m Q / U,

[0026] Among them, U m represents the virtual output voltage,

[0027] Based on the operation model of the wind turbine system with the droop coefficient introduced, the reconstructed output voltage is as follows:

[0028] UT * =(UEcosα+(X+X m )Q) / U+ΔU n =U * -μQ n ,

[0029] Among them, U T * Represents the reconstructed output voltage, ΔU n It represents the voltage difference between the original voltage of the wind turbine system and the voltage obtained after the introduction of virtual impedance and dynamic droop coefficient, U * Indicates the reference value of the wind turbine output state in no-load state, Q n Represents the reactive power introduced in the dynamic droop coefficient, μ represents the dynamic droop coefficient, μ=K n +ω i K i Q n , where K n Represents the reactive power droop curve adjustment coefficient, ω i Indicates reactive power value signal, i ranges from 1 to 2, K i Indicates reactive power adjustment coefficient.

[0030] Specifically, the output voltage slope deviation between the first wind turbine system and the second wind turbine system is calculated, and the droop coefficients of the first wind turbine system and the second wind turbine system are adjusted according to the magnitude of the output voltage slope deviation;

[0031] Among them, the output voltage slope of the wind turbine system is as follows:

[0032] M=((X A +X A1 )-(X B +X B2 )) / (U 2 +(X A +X A1 )(X B +X B2 )),

[0033] Where M represents the output voltage slope, X A1 and X B2 respectively represent the transmission impedance of the first wind turbine system and the second wind turbine system after the load increases;

[0034] When the output voltage slope M1 of the first wind turbine system is equal to the output voltage slope M2 of the second wind turbine system, the reactive power value signals of the first wind turbine system w1 and the first wind turbine system w2 are: w1=w2=0; when M1 is greater than M2, the reactive power value signals are: w1=-0.1, w2=0.1; when M1 is less than M2, the reactive power value signals are: w1=0.1, w2=-0.1.

[0035] The present invention also provides a virtual inertia control device for multiple wind turbines in parallel based on energy storage, comprising: an active power distribution unit, a reactive power error calculation unit, a virtual impedance construction unit and a reactive power distribution unit, wherein: the active power distribution unit is used to control the capacity ratio between the first virtual inertia and the second virtual inertia, and the active power of the first wind turbine system and the second wind turbine system is correspondingly distributed according to the capacity ratio; the first virtual inertia and the second virtual inertia are parameters in the first wind turbine system and the second wind turbine system respectively; the reactive power error calculation unit is used to pass through the operation model of the wind turbine system and introduce the droop coefficient therein , establish a reactive power error function between the first wind turbine system and the second wind turbine system, and calculate the corresponding reactive power error value; the virtual impedance construction unit is used to calculate and construct a virtual impedance for decoupling the active power and reactive power of the wind turbine system according to the line impedance of the wind turbine system; the reactive power distribution unit is used to obtain the virtual output voltage and reconstruct the output voltage of the wind turbine system through the operation model and the virtual impedance when the multi-wind turbine parallel system is disturbed and oscillates, and adjust the droop coefficients of the first wind turbine system and the second wind turbine system in real time, and perform reactive power distribution for the multi-wind turbine parallel system based on the droop system.

[0036] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: by controlling and adjusting the virtual inertia, virtual damping and droop coefficient of the single wind turbine energy storage system in the overall system, the system oscillation problem caused by low inertia and underdamping is overcome, and the stability of the voltage and frequency of the overall system is ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of the control principle of the virtual inertia control method for multiple wind turbines in parallel based on energy storage provided by the present invention;

[0038] Figure 2 A schematic diagram of the system flow of a virtual inertia control method for multiple wind turbines in parallel based on energy storage provided by the present invention;

[0039] FIG3(a) and FIG3(b) are respectively schematic diagrams of a first reactive power distribution principle and a second reactive power distribution principle of a multi-wind turbine parallel system;

[0040] FIG4(a) and FIG4(b) are respectively a schematic diagram of a first active power distribution principle and a schematic diagram of a second active power distribution principle of a multi-wind turbine parallel system;

[0041] FIG. 5( a ) and FIG. 5( b ) are respectively a first reactive power control simulation schematic diagram and a second reactive power control simulation schematic diagram of a multi-wind turbine parallel system. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0043] See also Figure 1 , which is a schematic diagram of the control principle of the virtual inertia control method of multiple wind turbines in parallel based on energy storage provided by the present invention; refer to Figure 2 , which is a system flow diagram of the virtual inertia control method for multiple wind turbines in parallel based on energy storage provided by the present invention.

[0044] In a specific implementation, in a power system, inertia and damping are characteristics associated with (virtual) synchronous generators.

[0045] Inertia refers to the ability of an object to resist changes in its state of motion. In power systems, inertia is mainly provided by the mechanical part of the synchronous generator, including the mass of the generator rotor, the turbine or hydro turbine connected to the generator shaft, etc. When a disturbance occurs in the power system (such as a sudden load change or a power generation unit tripping), a system with a larger inertia is better able to maintain frequency stability because the larger inertia can absorb or release more energy to buffer such disturbances.

[0046] Damping is the process of reducing the amplitude of oscillations. In power systems, damping is used to describe the ability of the system to respond to disturbances, which can help the system return to a stable state more quickly. Damping can be achieved in many ways, including mechanical damping (through dampers), electrical damping (through excitation system control), and additional damping controllers. Good damping characteristics help prevent the system from sustained oscillations and ensure stable operation of the system.

[0047] With the increase of renewable energy (such as wind and solar energy), renewable resources do not have obvious inertia and damping effects like traditional synchronous generators, so new technologies and methods are needed to simulate or compensate for these characteristics to maintain the stability of the power system. For example, virtual inertia and additional damping controllers are used to enhance the dynamic performance of renewable energy generation systems based on power electronic interfaces.

[0048] In power systems, the droop coefficient is an important parameter used to describe the relationship between power output and grid frequency or voltage. Droop control is a common control strategy that is used to achieve power sharing and frequency or voltage regulation between distributed power sources (such as inverters, energy storage systems, etc.) by imitating the natural droop characteristics of traditional synchronous generators. In a microgrid or grid containing multiple distributed power sources, droop control can ensure that each power source shares the load in proportion to its capacity. By adjusting the droop coefficient of each power source, the active and reactive power distribution between them can be controlled. For frequency regulation, when the grid frequency drops (indicating insufficient active power in the system), the power source with droop characteristics will increase its output power, and vice versa. For voltage regulation, when the grid voltage decreases (indicating insufficient reactive power in the system), the power source with droop characteristics will increase its output reactive power to support the voltage level. Droop control helps maintain the frequency and voltage stability of the system, which is particularly important in island mode, and can help avoid overloading of a single power source, thereby improving the reliability of the entire system.

[0049] In the embodiment of the present invention, the capacity ratio between the first virtual inertia and the second virtual inertia is controlled, and the active power of the first wind turbine system and the second wind turbine system is distributed accordingly according to the capacity ratio.

[0050] In the embodiment of the present invention, the first virtual inertia and the second virtual inertia are parameters in the first wind turbine system and the second wind turbine system respectively. The wind turbine system is provided with a VSG, that is, a virtual synchronous generator. A , the second wind turbine system is VSG B .

[0051] In a specific implementation, the present invention uses a first wind turbine system and a second wind turbine system connected in parallel to illustrate the control of the overall parallel system. In practical applications, multiple wind turbines in parallel may include multiple wind turbine systems, not limited to two.

[0052] In an embodiment of the present invention, the capacity ratio between the first virtual inertia and the second virtual inertia is controlled to be consistent with the capacity ratio between the first virtual damping and the second virtual damping, the active power of the first wind turbine system and the second wind turbine system is allocated according to the capacity ratio, and the first virtual damping and the second virtual damping are parameters in the first wind turbine system and the second wind turbine system, respectively.

[0053] In a specific implementation, the active power and reactive power of the first wind turbine system and the second wind turbine system have the following relationship:

[0054] (P ref_A / Pref_B )=(Q ref_A / Q ref_B )=(S A / S B )=N, formula (1),

[0055] Among them, P ref_A represents the active reference value of the first wind turbine system, Q ref_A Represents the reactive power reference value of the first wind turbine system, P ref_B represents the active reference value of the second wind turbine system, Q ref_B Represents the reactive power reference value of the second wind turbine system, S A represents the complex power of the first wind turbine system, S B represents the complex power of the second wind turbine system, and N represents the capacity ratio.

[0056] When the P of the wind turbine system m (mechanical power) and P e (electromagnetic power) is equal to the output active power and output reactive power of the two wind turbine systems. The output active power and output reactive power of the two wind turbine systems are also distributed according to the above power capacity ratio N:

[0057] P A / P B =Q A / Q B =N, formula (2),

[0058] Among them, P A is the active output of the first wind turbine system, Q A is the reactive power output of the first wind turbine system, P B is the active output value of the second wind turbine system, Q B It is the reactive power output of the second wind turbine system.

[0059] In the specific implementation, for several wind turbine systems connected in parallel to the same power grid and adjacent to each other, their operating states are basically coupled with the connected power grid. In order to ensure the synchronous and stable operation of the power grid and the multi-machine parallel system, the line rated voltage U n The operating angular frequency ω of the wind turbine system must meet the following requirements:

[0060] U nA =U nB ,ω A =ω B , formula (3),

[0061] Among them, U nA and U nB Respectively represent the rated voltages of the first wind turbine system and the second wind turbine system, ω A and ω BRespectively represent the operating angular frequencies of the first wind turbine system and the second wind turbine system.

[0062] The active power droop coefficient and reactive power droop coefficient of the first wind turbine system and the second wind turbine system in the multi-wind turbine parallel system control have the following ratio relationship:

[0063] K PA / K PB =K QB / K QA =N, formula (4),

[0064] Among them, K PA and K PB They represent the active droop coefficients of the first wind turbine system and the second wind turbine system, K QA and K QB Respectively represent the reactive power droop coefficients of the first wind turbine system and the second wind turbine system.

[0065] In the specific implementation, due to K PA =NK PB , and ω n is the grid reference frequency, ω0 is 50HZ, then D A =ND B , (D A and D B Respectively represent the virtual damping of the first wind turbine system and the second wind turbine system) At this time:

[0066] ΔP / Δω=(P ref –P m ) / (ω-ω0)=Jω0s+Dω0, formula (5),

[0067] Among them, P ref represents the active reference value of the wind turbine system, s represents the complex frequency domain variable, J and D represent the virtual inertia and virtual damping of the wind turbine system respectively, ΔP / Δω represents the relationship between the output angular frequency and the virtual power, that is, the rewriting of the mechanical equation of the wind turbine rotor, which is converted into the S domain.

[0068] In the specific implementation, the operating frequency ω of the two wind turbine systems is equal, ω0 is 50Hz and remains unchanged, and the active power P of the two wind turbine systems is ref and P m If they both satisfy the ratio relationship of N times, the following ratio relationship involving virtual inertia J and virtual damping D can be obtained:

[0069] (J A ω0s+D A ω0) / (J B ω0s+D B ω0)=N, formula (6),

[0070] Among them, J A and J B Denote the virtual inertia of the first wind turbine system and the second wind turbine system, respectively, and D A and D B They represent the virtual damping of the first wind turbine system and the second wind turbine system respectively.

[0071] In a specific implementation, the virtual inertia and virtual damping of the first wind turbine system and the second wind turbine system satisfy the following:

[0072] J A / J B =D A / D B =N, formula (7).

[0073] When the parameter settings of the virtual inertia and virtual damping of the two wind turbine systems need to satisfy the relationship of the above formula (7), the active power of the multi-machine parallel control system composed of the wind turbine systems is distributed according to the power capacity ratio N.

[0074] In the embodiment of the present invention, the reactive power error function between the first wind turbine system and the second wind turbine system is established by introducing the droop coefficient into the operation model of the wind turbine system, and the corresponding reactive power error value is calculated.

[0075] In the embodiment of the present invention, the operation model of the wind turbine system includes the following active power output model and reactive power output model:

[0076] P = [(EUcosα-U 2 )R+EUXsinα] / (R 2 +X 2 ),

[0077] Q=[(EUcosα-U 2 )X-EUXsinα] / (R 2 +X 2 ), formula (8),

[0078] Wherein, P represents the active power output of (virtual synchronous generator), Q represents the reactive power output of (virtual synchronous generator), E represents the output voltage amplitude of (virtual synchronous generator), U represents the AC bus voltage amplitude of (virtual synchronous generator), α represents the phase angle of transmission impedance, X (virtual synchronous generator) represents transmission impedance, and R represents the transmission resistance of (virtual synchronous generator).

[0079] In the specific implementation, the output power of the system is affected by the phase angle amplitude difference of the voltage and the change of line impedance. Only when the transmission impedance is purely inductive can the active power and reactive power be decoupled and controlled independently. The active power and reactive power can be adjusted respectively by controlling the phase angle and voltage amplitude. However, in the actual power system, transmission lines of different voltage levels have different line impedance ratios. In the low-voltage distribution network, the impedance ratio is relatively high and resistive, while in the medium-voltage line, the transmission impedance is resistive-inductive.

[0080] In practice, power decoupling refers to a method of controlling active power (P) and reactive power (Q) independently of each other in a power system. In traditional power systems, active power and reactive power are usually coupled together, indicating that controlling one power may affect the other power. In modern power systems, especially those containing a large number of power electronic devices, active power and reactive power can be controlled independently by decoupling them.

[0081] In the embodiment of the present invention, when the transmission impedance is inductive, a voltage reactive function introducing a reactive droop coefficient is obtained based on the active power output of the wind turbine system.

[0082] In the embodiment of the present invention, when the transmission impedance is inductive, the active power output model is as follows:

[0083] P m =UEsinα / X, formula (9),

[0084] Among them, P m Indicates the active power output when the transmission impedance is inductive (single wind turbine system);

[0085] (Virtual synchronous machine) voltage reactive function is as follows:

[0086] Q m =(UEcosα-U 2 ) / (X+UK Q ), formula (10),

[0087] Among them, Q m Indicates the reactive power output when the transmission impedance is inductive (single wind turbine system), K Q Represents the reactive power droop coefficient.

[0088] In the embodiment of the present invention, the reactive power error function is as follows:

[0089] ΔQ=Q A -Q B=U(Ecosα-U)[(X A -X B )+U(K QA -K QB )] / (X A +UK QA )(X B +UK QB ), formula (11),

[0090] Wherein, ΔQ represents the reactive power error value between the first wind turbine system and the second wind turbine system, Q A and Q B Respectively represent the reactive power output of the first wind turbine system and the second wind turbine system, X A and X B Respectively represent the transmission impedance of the first wind turbine system and the second wind turbine system, K QA and K QB Respectively represent the reactive power droop coefficients of the first wind turbine system and the second wind turbine system.

[0091] In the specific implementation, it can be seen from formula (11) that since the transmission impedance exists and the numerator Ecosα-U cannot be zero, the transmission impedance difference X between the two virtual synchronous generators is reduced. A -X B and the droop coefficient difference K QA -K QB , and increasing the transmission impedance and increasing the reactive power droop coefficient can reduce the difference in reactive power. The main reason affecting the reactive power error is X A -X B and K QA -K QB Excessive transmission impedance and reactive power droop coefficient will cause the load voltage U to drop beyond the allowable lower limit, resulting in the inability to evenly distribute reactive power.

[0092] In the embodiment of the present invention, a virtual impedance for decoupling active power and reactive power of the wind turbine system is constructed based on the calculated line impedance of the wind turbine system.

[0093] In a specific implementation, the first-end complex power of the energy storage equivalent circuit of the offshore wind turbine is:

[0094]

[0095] Among them, S 1A Indicates the complex power at the first end, U 1A represents the phase voltage at the first end, δ represents U 1A The phase angle, represents the impedance angle, j represents the imaginary part, I 2A It represents the current after the wind turbine system introduces virtual impedance, I2A * It represents the conjugate of the current after the wind turbine system introduces virtual impedance, which is divided into real and imaginary parts, which is equivalent to adding the original δ angle Get the current of the system.

[0096] In a specific implementation, the terminal complex power of the energy storage equivalent circuit of the offshore wind turbine is:

[0097]

[0098] Among them, S 2A represents the terminal complex power, U 2A Indicates the terminal phase voltage.

[0099] In a specific implementation, the complex power difference of the energy storage equivalent circuit of the offshore wind turbine is:

[0100] ΔS=S 1A -S 2A =3I 2A 2 (R L +jωL L ), formula (14),

[0101] Among them, R L Represents the real part of the measured line impedance, that is, the line resistance, L L It represents the imaginary part of the measured line impedance, that is, the line inductance.

[0102] Solving formula (14), we obtain:

[0103]

[0104] In the specific implementation, the line impedance value can be calculated in real time through formula (14) and formula (15). After the introduction of virtual reactance, the equivalent output impedance of the parallel multi-wind turbine system is approximately equal to the virtual impedance. After the introduction of virtual negative resistance to offset the line resistance, the power decoupling requirement can be met.

[0105] In a specific implementation, the head-end complex power refers to the complex power measured or calculated at the head end of a line or transformer in a power system. In power system analysis, the head end and the tail end usually refer to different locations at both ends of a line or transformer.

[0106] In the embodiment of the present invention, according to the power decoupling requirement, the difference between the virtual impedance and the line impedance is controlled within the standard threshold value (which can be set according to the actual application scenario), and the introduced virtual impedance is

[0107] X m =R m +sω(L0+KL L m ), formula (16),

[0108] Among them, X m Represents virtual impedance, R m Represents virtual negative resistance, R m =-R A (Formula (17)), s represents the complex frequency domain variable, ω represents the operating frequency of the wind turbine system, L0 represents the initial virtual inductance, K L Indicates the impedance adjustment coefficient, L m =|L ref –L A |(Formula (18)), L ref Represents the reference inductance, L A Represents the inductance of the first wind turbine system.

[0109] In an embodiment of the present invention, when a parallel system of multiple wind turbines is disturbed and oscillates, a virtual output voltage and a reconstructed output voltage of the wind turbine system are obtained by operating a model and a virtual impedance, and the droop coefficients of the first wind turbine system and the second wind turbine system are adjusted in real time respectively, and reactive power distribution is performed on the parallel system of multiple wind turbines based on the droop system.

[0110] In the embodiment of the present invention, the virtual output voltage generated by the system is as follows:

[0111] U m =X m Q / U, formula (19),

[0112] Among them, U m Indicates the virtual output voltage, X m is the virtual impedance obtained from formula (18).

[0113] In the specific implementation, the reactive voltage function of the system is obtained by combining formulas (11) and (19), and the output voltage satisfies:

[0114] U T =(UEcosα+(X+X m )Q) / U=U * -K n Q n , formula (20).

[0115] Among them, U T Indicates the output voltage of the wind turbine system, U * Indicates the reference value of the wind turbine system output voltage in no-load state, K n It represents the slope of the reactive voltage equation of the wind turbine system after the introduction of virtual impedance, Q n Represents the reactive power output of the wind turbine system after the introduction of virtual impedance.

[0116] In specific implementation, the addition of virtual reactance actually changes the slope of the reactive voltage function curve, effectively improving the reactive power sharing accuracy.

[0117] In the embodiment of the present invention, the output voltage slope deviation between the first wind turbine system and the second wind turbine system is calculated, and the droop coefficients of the first wind turbine system and the second wind turbine system are adjusted according to the magnitude of the output voltage slope deviation;

[0118] Among them, the output voltage slope of the wind turbine system is as follows:

[0119] M=((X A +X A1 )-(X B +X B2 )) / (U 2 +(X A +X A1 )(X B +X B2 )), formula (21),

[0120] Where M represents the output voltage slope, X A1 and X B2 They represent the transmission impedance of the first wind turbine system and the second wind turbine system after the load increases. When the load increases, the reactive power point moves backward, and it is difficult to ensure the system reactive power sharing only by relying on the virtual impedance method. At this time, the dynamic droop coefficient is introduced, and X A1 and X B2 They respectively represent the transmission impedance of the first wind turbine system and the second wind turbine system after the load increases.

[0121] In formula (21), reduce U 2 , the output voltage curve slope difference ΔM of the first wind turbine system and the second wind turbine system increases, and at the same time, the shift of the reactive power point backward will also cause the reactive power difference to increase. It can be seen that the load switching in the wind turbine system will cause the reactive power difference to increase and the reactive power sharing effect to deteriorate.

[0122] In a specific implementation, based on the operation model of the wind turbine system with the droop coefficient introduced, and the droop coefficient can be dynamically adjusted, the reactive power difference between the first wind turbine system and the second wind turbine system is reduced, and the output voltage is reconstructed as follows:

[0123] U T * =(UEcosα+(X+X m )Q) / U+ΔU n =U * -μQ n , formula (22),

[0124] Among them, U T * represents the reconstructed output voltage, ΔU n It represents the voltage difference between the original voltage of the wind turbine system and the voltage obtained after the introduction of virtual impedance and dynamic droop coefficient, U * Indicates the output state reference value of the wind turbine in no-load state, Q n Represents the reactive power introduced in the dynamic droop coefficient (the reactive power introduced in the reactive droop equation), μ represents the dynamic droop coefficient, μ=K n +ω i K i Q n , where K n Represents the reactive power droop curve adjustment coefficient, ω i Indicates reactive power value signal, i value range is 1 and 2, K i Indicates reactive power adjustment coefficient.

[0125] In an embodiment of the present invention, when the output voltage slope M1 of the first wind turbine system is equal to the output voltage slope M2 of the second wind turbine system (M1=M2), the slope difference is 0, and the multi-wind turbine parallel system can achieve reactive power sharing, and the reactive value signals of the first wind turbine system w1 and the first wind turbine system w2 are: w1=w2=0.

[0126] In the embodiment of the present invention, when M1 is greater than M2 (M1>M2), in order to reduce the voltage slope difference of the multi-wind turbine parallel system, the reactive value signal is: w1=-0.1, w2=0.1.

[0127] In the embodiment of the present invention, when M1 is smaller than M2 (M1<M2), in order to reduce the voltage slope difference of the multi-wind turbine parallel system, the reactive value signal is: w1=0.1, w2=-0.1.

[0128] In the specific implementation, after adding the dynamic droop coefficient, the reactive power difference of the multi-machine parallel control system of offshore wind power energy storage is greatly reduced, the reactive power distribution accuracy is better, and it basically meets the requirements.

[0129] In specific implementation, for direct-drive permanent magnet synchronous power generation systems, due to the real-time differences in operating conditions or assembly scales of each single-machine wind storage system within the multi-wind turbine parallel system, the power capacity that each single-machine wind storage system can carry when connected to the grid is not necessarily always evenly divided.

[0130] The beneficial effect of the present invention is that, compared with the prior art, the control method proposed by the present invention, compared with the traditional offshore wind power energy storage system, realizes virtual inertia control of the wind farm group by controlling multiple wind turbine systems in parallel, calculating the given power according to the total load capacity and the capacity of each inverter, and adjusting the virtual impedance value in real time according to the given reactive power, compensating for the voltage drop difference caused by the line impedance difference, constructing a dynamic droop coefficient according to the difference in the output reactive variable, and adaptively adjusting the output voltage to realize power distribution on demand.

[0131] In the control system proposed by the present invention, the main circuit topology of the virtual synchronous machine is not required, and only the local variable information of each inverter is used, which is convenient for specific implementation.

[0132] Compared with the prior art, the control method of the present invention has better effects, which are manifested in smaller power deviation of the control system, higher accuracy, shorter adjustment time, and effectively avoiding the influence of parameter incoordination on system quality and stability.

[0133] 3(a) and 3(b) are schematic diagrams of a first reactive power distribution principle and a second reactive power distribution principle of a multi-wind turbine parallel system, respectively.

[0134] In Figure 3(a), taking two parallel wind turbine systems as an example, when the line impedance is different, A and B are the output voltage curves of the first wind turbine system and the second wind turbine system, respectively. Line (1) is the reactive voltage droop curve. The reactive voltage droop curves of the first wind turbine system and the second wind turbine system are the same. U * It is the output voltage reference value in no-load state.

[0135] Before adding virtual impedance, in line (1), A intersects at point a, corresponding to the reactive power generated by the first wind turbine system; in line (1), A intersects at point b, corresponding to the reactive power generated by the second wind turbine system. Due to the difference in line impedance, the difference in reactive power generated by the first wind turbine system and the second wind turbine system is Q 1T , the reactive power difference is large, and the reactive power sharing effect is poor. When a positive virtual reactance is added to the first wind turbine system and a negative virtual reactance is added to the second wind turbine system, the adjusted reactive power difference is Q 2T , relative to Q 1T , the reactive power difference is greatly reduced, indicating that virtual impedance can effectively improve the reactive power sharing accuracy.

[0136] In Figure 3(b), although the virtual impedance can ensure the accuracy of reactive power sharing when the load is constant, when the load increases, the reactive power point moves backward, the line current increases, and the load bus voltage decreases. The slope M of the system voltage curve is calculated by formula (21). In formula (21), U decreases, and the difference ΔM in the slope of the output voltage curves of the first wind turbine system and the second wind turbine system increases. The angle between the output voltage curves E and F of the first wind turbine system and the second wind turbine system gradually increases due to the switching of the load, and the difference ΔM in the slopes of the two also gradually increases. It can be seen that the switching of the load will cause the reactive power difference to increase and the reactive power sharing effect to deteriorate.

[0137] After the load is switched, in order to improve the reactive power sharing accuracy of the system, reactive power is introduced into the reactive voltage droop equation, and a dynamic droop coefficient is constructed. The dynamic droop coefficient is used to adjust the slope of the reactive voltage droop curve of the wind turbine system to reduce the reactive power difference between the first wind turbine system and the second wind turbine system. In Figure 3(b), after adding the dynamic droop coefficient, the reactive power difference between the first wind turbine system and the second wind turbine system is calculated by Q 3T Adjust to Q 4T , relative to Q 3T , realizing power allocation on demand.

[0138] 4( a ) and 4 ( b ), which are respectively a schematic diagram of a first active power distribution principle and a schematic diagram of a second active power distribution principle of a multi-wind turbine parallel system.

[0139] When the power capacities of the two wind turbine systems are not equal, if N is 1.5 and the relevant parameters are set, the first wind turbine system will bear 60% and the second wind turbine system will bear 40%; the waveform simulation results of the system output power and system frequency are shown in Figure (a) and Figure (b) respectively.

[0140] 5( a ) and 5 ( b ) are respectively a first reactive power control simulation schematic diagram and a second reactive power control simulation schematic diagram of a multi-wind turbine parallel system.

[0141] Figure 5(a) is the waveform when the control method provided by the present invention is not used, and the reactive power has obvious deviation. Figure 5(b) is the waveform when the control method provided by the present invention is used, and the reactive power is basically evenly distributed, meeting the accuracy requirements.

Claims

1. A virtual inertia control method for multiple wind turbines in parallel based on energy storage, characterized in that: include: The capacity ratio between the first virtual inertia and the second virtual inertia is controlled, and the active power of the first wind turbine system and the second wind turbine system is distributed accordingly according to the capacity ratio; the first virtual inertia and the second virtual inertia are parameters in the first wind turbine system and the second wind turbine system respectively: By using the operation model of the wind turbine system and introducing the droop coefficient therein, a reactive power error function between the first wind turbine system and the second wind turbine system is established, and a corresponding reactive power error value is calculated; Calculate and construct a virtual impedance for decoupling active power and reactive power of the wind turbine system according to the line impedance of the wind turbine system; When the multi-wind turbine parallel system is disturbed and oscillates, the virtual output voltage and reconstructed output voltage of the wind turbine system are obtained by running the model and virtual impedance, and the droop coefficients of the first wind turbine system and the second wind turbine system are adjusted in real time respectively, and reactive power distribution is performed on the multi-wind turbine parallel system based on the droop system.

2. The virtual inertia control method for multiple wind turbines in parallel based on energy storage according to claim 1 is characterized in that: The active power of the first wind turbine system and the second wind turbine system is distributed accordingly according to the capacity ratio, including: The capacity ratio between the first virtual inertia and the second virtual inertia is controlled to be consistent with the capacity ratio between the first virtual damping and the second virtual damping. The active power of the first wind turbine system and the second wind turbine system is distributed according to the capacity ratio. The first virtual damping and the second virtual damping are parameters in the first wind turbine system and the second wind turbine system, respectively.

3. The virtual inertia control method for multiple wind turbines in parallel based on energy storage according to claim 1 is characterized in that: The operation model of the wind turbine system includes the following active power output model and reactive power output model: P=[(EUcosα-U 2 )R+EUXsinα] / (R 2 +X 2 ), Q=[(EUcosα-U 2 )X-EUXsinα] / (R 2 +X 2 ), Among them, P represents active power output, Q represents reactive power output, E represents output voltage amplitude, U represents AC bus voltage amplitude, α represents the phase angle of transmission impedance, X represents transmission impedance, and R represents transmission resistance.

4. The virtual inertia control method for multiple wind turbines in parallel based on energy storage according to claim 3 is characterized in that: The method introduces a droop coefficient and establishes a reactive power error function between the first wind turbine system and the second wind turbine system, including: When the transmission impedance is inductive, the voltage-reactive function with the reactive droop coefficient introduced is obtained based on the active power output of the wind turbine system.

5. The virtual inertia control method for multiple wind turbines in parallel based on energy storage according to claim 4 is characterized in that: The active power output based on the wind turbine system, wherein the active power output model is as follows: P m =UEsinα / X, Among them, P m Indicates the active power output when the transmission impedance is inductive; The voltage reactive function is as follows: Q m =(UEcosα-U 2 ) / (X+UK Q ), Among them, Q m Indicates the reactive power output when the transmission impedance is inductive, K Q Represents the reactive power droop coefficient.

6. The virtual inertia control method for multiple wind turbines in parallel based on energy storage according to claim 5 is characterized in that: The step of establishing a reactive power error function between the first wind turbine system and the second wind turbine system comprises: The reactive power error function is as follows: ΔQ=Q A -Q B =U(Ecosα-U)[(X A -X B )+U(K QA -K QB )] / (X A +UK QA )(X B +UK QB ), Wherein, ΔQ represents the reactive power error value between the first wind turbine system and the second wind turbine system, Q A and Q B Respectively represent the reactive power output of the first wind turbine system and the second wind turbine system, X A and X B Respectively represent the transmission impedance of the first wind turbine system and the second wind turbine system, K QA and K QB Respectively represent the reactive power droop coefficients of the first wind turbine system and the second wind turbine system.

7. The virtual inertia control method for multiple wind turbines in parallel based on energy storage according to claim 6 is characterized in that: The virtual impedance structure is used to decouple the active power and reactive power of the wind turbine system, and includes: The difference between the virtual impedance and the line impedance is controlled to be within a standard threshold range, and the virtual impedance is as follows: X m =R m +sω(L0+K L L m ), Among them, X m Represents virtual impedance, R m represents virtual negative resistance, s represents complex frequency domain variable, ω represents the operating frequency of the wind turbine system, L0 represents the initial virtual inductance, K L Indicates the impedance adjustment coefficient, L m =|L ref –L A |, L ref Represents the reference inductance, L A Represents the inductance of the first wind turbine system.

8. The virtual inertia control method for multiple wind turbines in parallel based on energy storage according to claim 7 is characterized in that: The virtual output voltage and reconstructed output voltage of the wind turbine system are obtained by running the model and the virtual impedance, wherein the virtual output voltage is as follows: U m =X m Q / U, Among them, U m represents the virtual output voltage, Based on the operation model of the wind turbine system with the droop coefficient introduced, the reconstructed output voltage is as follows: The T * =(UEcosα+(X+X m )Q) / U+ΔU n =U * -μQ n , Among them, U T * Represents the reconstructed output voltage, ΔU n It represents the voltage difference between the original voltage of the wind turbine system and the voltage obtained after the introduction of virtual impedance and dynamic droop coefficient, U * Indicates the output state reference value of the wind turbine in no-load state, Q n It represents the reactive power output after the introduction of virtual impedance, μ represents the dynamic droop coefficient, μ=K n +ω i K i Q n , where K n Represents the reactive power droop curve adjustment coefficient, ω i Indicates reactive power value signal, i value range is 1 and 2, K i Indicates reactive power adjustment coefficient.

9. The virtual inertia control method for multiple wind turbines in parallel based on energy storage according to claim 8 is characterized in that: The real-time adjustment of the droop coefficients of the first wind turbine system and the second wind turbine system respectively comprises: Calculating an output voltage slope deviation between the first wind turbine system and the second wind turbine system, and adjusting droop coefficients of the first wind turbine system and the second wind turbine system according to the magnitude of the output voltage slope deviation; Among them, the output voltage slope of the wind turbine system is as follows: M=((X A +X A1 )-(X B +X B2 )) / (U 2 +(X A +X A1 )(X B +X B2 )), Where M represents the output voltage slope, X A1 and X B2 respectively represent the transmission impedance of the first wind turbine system and the second wind turbine system after the load increases; When the output voltage slope M1 of the first wind turbine system is equal to the output voltage slope M2 of the second wind turbine system, the reactive power value signals of the first wind turbine system w1 and the first wind turbine system w2 are: w1=w2=0; when M1 is greater than M2, the reactive power value signals are: w1=-0.1, w2=0.1; when M1 is less than M2, the reactive power value signals are: w1=0.1, w2=-0.

1.

10. A virtual inertia control device for multiple wind turbines in parallel based on energy storage, characterized in that: include: Active power distribution unit, reactive power error calculation unit, virtual impedance construction unit and reactive power distribution unit, wherein: The active power distribution unit is used to control the capacity ratio between the first virtual inertia and the second virtual inertia, and the active power of the first wind turbine system and the second wind turbine system is distributed accordingly according to the capacity ratio; the first virtual inertia and the second virtual inertia are parameters in the first wind turbine system and the second wind turbine system respectively: The reactive power error calculation unit is used to establish a reactive power error function between the first wind turbine system and the second wind turbine system by introducing a droop coefficient into the operation model of the wind turbine system, and calculate the corresponding reactive power error value; The virtual impedance construction unit is used to calculate and construct a virtual impedance for decoupling the active power and reactive power of the wind turbine system according to the line impedance of the wind turbine system; The reactive power distribution unit is used to obtain the virtual output voltage and reconstructed output voltage of the wind turbine system by running the model and the virtual impedance when the multi-wind turbine parallel system is disturbed and oscillates, and to adjust the droop coefficients of the first wind turbine system and the second wind turbine system in real time respectively, and to perform reactive power distribution for the multi-wind turbine parallel system based on the droop system.

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