Oscillation source analysis method for wind farm through flexible external transmission system

Abstract

The present application relates to a kind of wind farm through flexible sending system oscillation source analysis method, belong to wind power generation system technical field, solve the problem that existing technology cannot accurately determine the oscillation source when wind farm through flexible sending system is disturbed.The method includes the following steps: collecting the voltage and current of the flexible converter port, the port of each direct-drive wind turbine;Using Fourier transform to extract the sub-synchronous component of the voltage and current, obtain the initial value of the sub-synchronous component corresponding to the voltage and current;The initial value of the sub-synchronous component is substituted into the system energy calculation model constructed in advance, to obtain the coupling energy of each direct-drive wind turbine;According to the coupling energy of each direct-drive wind turbine, obtain the oscillation source of the wind farm through flexible sending system.Accurately determine the oscillation source when wind farm through flexible sending system is disturbed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wind power generation system, and particularly relates to a wind farm through flexible direct transmission system oscillation source analysis method. BACKGROUND

[0002] With the application of large-scale wind farm through flexible direct transmission system, the dynamic characteristics of the power system have changed greatly, which poses a potential threat to the stable operation of the wind farm through flexible direct transmission system.

[0003] The interaction among direct-drive wind turbines, flexible converters and transmission lines can induce sub / super-synchronous oscillation of the wind farm through flexible direct transmission system, which is easy to cause large-scale wind turbine off-grid and wind farm through flexible direct transmission system shutdown.

[0004] How to determine the oscillation source of sub / super-synchronous oscillation in the wind farm through flexible direct transmission system has become a technical problem to be solved at present. SUMMARY

[0005] In view of the above analysis, the embodiments of the present application aim to provide a wind farm through flexible direct transmission system oscillation source analysis method to solve the problem that the existing technology cannot accurately determine the oscillation source when the wind farm through flexible direct transmission system is disturbed.

[0006] The embodiments of the present application provide a wind farm through flexible direct transmission system oscillation source analysis method, which comprises the following steps:

[0007] Collecting the voltage and current of the flexible converter port and each direct-drive wind turbine port;

[0008] Extracting the sub / super-synchronous components of the voltage and current by using Fourier transform to obtain the initial values of the sub / super-synchronous components corresponding to the voltage and current; substituting the initial values of the sub / super-synchronous components into a pre-constructed system energy calculation model to obtain the coupling energy of each direct-drive wind turbine;

[0009] According to the coupling energy of each direct-drive wind turbine, the oscillation source of the wind farm through flexible direct transmission system is obtained.

[0010] Based on the further improvement of the above method, the oscillation source of the wind farm through flexible direct transmission system is obtained according to the coupling energy of each direct-drive wind turbine, which comprises:

[0011] If the coupling energy between a certain direct-drive wind turbine and any other direct-drive wind turbine is less than zero, the direct-drive wind turbine is the oscillation source.

[0012] Based on the further improvement of the above method, the system energy calculation model is constructed by the following steps:

[0013] The dynamic equation of the inner loop control of the HVDC converter, the dynamic equation of the outer loop control of the HVDC converter, the HVDC converter port voltage equation, the direct-drive wind turbine port voltage equation, the dynamic component equation of the direct-drive wind turbine port current reference value, the dynamic control equation of the direct-drive wind turbine phase-locked loop, and the constraint equation of the HVDC converter and the direct-drive wind turbine are constructed under the disturbed condition of the HVDC transmission system of the wind farm.

[0014] The dynamic equation of the inner loop control of the HVDC converter, the dynamic equation of the outer loop control of the HVDC converter, the HVDC converter port voltage equation, the direct-drive wind turbine port voltage equation, the dynamic component equation of the direct-drive wind turbine port current reference value, the dynamic control equation of the direct-drive wind turbine phase-locked loop, and the constraint equation of the HVDC converter and the direct-drive wind turbine are brought into the system energy calculation equation to obtain the total system energy.

[0015] The total system energy is decomposed into the direct-drive wind turbine induction energy, the direct-drive wind turbine coupling energy, the HVDC converter induction energy, and the HVDC converter coupling energy.

[0016] The direct-drive wind turbine coupling energy is taken as the output of the system energy calculation model.

[0017] Based on the further improvement of the above method, the dynamic equation of the inner loop control of the HVDC converter is:

[0018]

[0019] wherein k p1 , k i1 are the proportional coefficient and the integral coefficient of the HVDC converter respectively; R r , L r are the filter resistance and the filter inductance of the HVDC converter respectively; are the dynamic component of the d-axis reference value of the HVDC converter current caused by the nth oscillation and the dynamic component of the q-axis reference value of the HVDC converter current caused by the nth oscillation respectively; are the d-axis component of the nth oscillation current of the HVDC converter and the q-axis component of the nth oscillation current of the HVDC converter respectively; are the d-axis component of the (n-1)th oscillation voltage of the HVDC converter and the q-axis component of the (n-1)th oscillation voltage of the HVDC converter respectively;

[0020] The dynamic equation of the outer loop control of the HVDC converter is:

[0021]

[0022] wherein, are the dynamic component of the d-axis reference value of the HVDC converter voltage caused by the nth oscillation and the dynamic component of the q-axis reference value of the HVDC converter voltage caused by the nth oscillation respectively, and in the steady state process, both are 0;

[0023] The straight converter port voltage equation is:

[0024]

[0025] Let

[0026]

[0027]

[0028] Wherein, k p2 , k i2 are the proportional coefficient and integral coefficient of the direct drive wind turbine respectively; s is the Laplace operator; are the voltage d-axis state quantity corresponding to the inner ring integral link of the straight converter and the voltage q-axis state quantity corresponding to the inner ring integral link of the straight converter respectively.

[0029] Based on the further improvement of the above method, the straight converter port voltage equation is:

[0030]

[0031] Let

[0032]

[0033]

[0034] Wherein, are the mth direct drive wind turbine n+1th oscillation voltage d-axis component and the mth direct drive wind turbine n+1th oscillation voltage q-axis component respectively; is the phase-locked loop phase angle initial value of the mth direct drive wind turbine; are the mth direct drive wind turbine current d reference value dynamic component and the mth direct drive wind turbine current q reference value dynamic component respectively caused by the nth oscillation; are the mth direct drive wind turbine port current d-axis steady-state value and the mth direct drive wind turbine port current q-axis steady-state value respectively; are the mth direct drive wind turbine port voltage d-axis steady-state value and the mth direct drive wind turbine port voltage q-axis steady-state value respectively; ω0 is the rated angular velocity of the wind farm through the HVDC transmission system; L fm is the filter inductance of the mth direct drive wind turbine; is the mth direct drive wind turbine nth oscillation phase-locked loop dynamic angle; are the mth direct drive wind turbine nth oscillation current d-axis component and the mth direct drive wind turbine nth oscillation current q-axis component respectively; are the voltage d-axis state quantity corresponding to the inner ring integral link of the mth direct drive wind turbine and the voltage q-axis state quantity corresponding to the inner ring integral link of the mth direct drive wind turbine respectively.

[0035] The dynamic component equation of the direct-drive wind turbine port current reference value is:

[0036]

[0037]

[0038] Wherein, C fm is the DC capacitor of the direct-drive wind turbine; is the voltage steady-state value of the direct-drive wind turbine; is the d reference value dynamic component of the direct-drive wind turbine voltage caused by the nth oscillation; is the output power change amount generated by the nth oscillation of the mth direct-drive wind turbine;

[0039] The phase-locked loop dynamic control equation of the direct-drive wind turbine is:

[0040]

[0041] Wherein, k p_pllm , k i_pllm are the control parameters and integral parameters of the phase-locked loop of the mth direct-drive wind turbine, respectively;

[0042] The constraint equation of the HVDC converter and the direct-drive wind turbine is:

[0043]

[0044] Wherein, L k , R k are the filter inductance and filter resistance of the first transmission line, respectively, and the first transmission line is the transmission line between the HVDC converter and the point of common coupling; L xm , R xm are the filter inductance and filter resistance of the second transmission line connected to the mth direct-drive wind turbine, respectively, and the second transmission line is the transmission line between the direct-drive wind turbine and the point of common coupling.

[0045] Based on the further improvement of the above method, the system energy calculation equation is:

[0046]

[0047] Wherein, N represents the total number of oscillations; M represents the total number of direct-drive wind turbines;

[0048] The total energy of the system is:

[0049]

[0050] Wherein, are the d-axis components of the nth oscillation current of the mth and hth direct-drive wind turbines, respectively. The mth direct-drive wind turbine nth oscillation current q-axis component.

[0051] Based on the further improvement of the above method, the direct-drive wind turbine induction energy is:

[0052]

[0053]

[0054]

[0055] Wherein, The mth direct-drive wind turbine induction energy; The mth direct-drive wind turbine first part induction energy and the mth direct-drive wind turbine second part induction energy.

[0056] Based on the further improvement of the above method, the direct-drive wind turbine coupling energy is:

[0057]

[0058] Wherein, The mth and hth direct-drive wind turbine coupling energy.

[0059] Based on the further improvement of the above method, the HVDC inverter induction energy is:

[0060]

[0061] Based on the further improvement of the above method, the HVDC inverter coupling energy is:

[0062]

[0063] Compared with the prior art, the present application collects the voltage and current of the HVDC inverter port and each direct-drive wind turbine port; adopts Fourier transform to extract the sub-synchronous component of the voltage and current, obtains the sub-synchronous component initial value corresponding to the voltage and current; substitutes the sub-synchronous component initial value into the pre-constructed system energy calculation model to obtain the coupling energy of each direct-drive wind turbine; and obtains the oscillation source of the wind farm through the HVDC external sending system according to the coupling energy of each direct-drive wind turbine, so as to accurately determine the oscillation source when the wind farm through the HVDC external sending system is disturbed.

[0064] In the present application, the above technical solutions can also be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification or be understood by implementing the present application. The purposes and other advantages of the present application can be realized and obtained from the contents specifically pointed out in the specification and the drawings. Attached Figure Description

[0065] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0066] Figure 1 A flowchart illustrating the analysis method for oscillation sources in a wind farm's flexible DC transmission system;

[0067] Figure 2 This is a schematic diagram of the structure of a wind farm's power transmission system via flexible direct current.

[0068] Figure 3 This is a graph showing the change in the coupling energy curve of the direct-drive fan in the scenario of Example 1;

[0069] Figure 4 This is a graph showing the change in the coupling energy curve of the direct-drive fan in the scenario of Example 2.

[0070] Figure label:

[0071] 1-Flexible DC converter; 2-First transmission line; 3-Second transmission line;

[0072] 4-Direct drive fan; 5-Common connection point. Detailed Implementation

[0073] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0074] A specific embodiment of the present invention discloses a method for analyzing oscillation sources in a wind farm-to-power transmission system via flexible DC transmission, such as... Figure 1 As shown, the method includes the following steps:

[0075] Step S100: Collect the voltage and current at the ports of the flexible DC converter and each direct-drive wind turbine;

[0076] Step S200: Use Fourier transform to extract the sub-supersynchronous components of the voltage and current to obtain the initial values ​​of the sub-supersynchronous components corresponding to the voltage and current; substitute the initial values ​​of the sub-supersynchronous components into the pre-constructed system energy calculation model to obtain the coupling energy of each direct-drive wind turbine.

[0077] Step S300: Based on the coupling energy of each of the direct-drive wind turbines, obtain the oscillation source of the wind farm via the flexible direct-drive transmission system.

[0078] Specifically, such as Figure 2As shown, the wind farm's flexible DC transmission system includes a flexible DC converter 1 and multiple PMSGs (Permanent Magnet Synchronous Generators, direct-drive wind turbines). The flexible DC converter 1 is connected to a common connection point 5 via a first transmission line 2, and the multiple direct-drive wind turbines 4 are connected to the common connection point 5 via their respective second transmission lines 3.

[0079] like Figure 1 As shown, in step S100, the wind farm oscillation source analysis method provided in this embodiment of the invention collects the voltage and current at the port of the flexible DC converter and the port of each direct-drive wind turbine.

[0080] Understandably, a wind farm-to-flexible-DC transmission system typically contains only one flexible-DC converter, so voltage and current acquisition devices can be used to collect the voltage and current at the converter's ports. However, a wind farm-to-flexible-DC transmission system may contain multiple direct-drive wind turbines, such as M turbines, thus requiring voltage and current acquisition devices to collect the current and voltage at the ports of all M turbines. Furthermore, these voltage and current acquisition devices can be either voltage data acquisition units or current data acquisition units.

[0081] In step S200, the oscillation source analysis method of the wind farm through flexible direct transmission system provided in this embodiment of the invention extracts the sub-supersynchronous components of the voltage and current by using Fourier transform to obtain the initial value of the sub-supersynchronous components corresponding to the voltage and current; and substitutes the initial value of the sub-supersynchronous components into the pre-constructed system energy calculation model to obtain the coupling energy of each direct-drive wind turbine.

[0082] Understandably, after acquiring the voltage and current at the ports of the flexible DC converter and each direct-drive wind turbine, the sub-supersynchronous components of the voltage and current can be extracted using Fourier transform to obtain initial values ​​of the sub-supersynchronous components corresponding to the voltage and current. These initial values ​​are then substituted into a pre-built system energy calculation model, through which the coupling energy of each direct-drive wind turbine can be obtained.

[0083] It is understood that the wind farm transmission system via flexible DC power transmission provided by this invention includes M direct-drive wind turbines, where m represents the m-th direct-drive wind turbine, and the collected voltage and current at the flexible DC converter port can be expressed as u. r i r The voltage and current collected at the port of the m-th direct-drive fan can be expressed as u. fm i fm The initial values ​​of the sub-supersynchronous components corresponding to the voltage and current of the flexible DC converter, extracted by Fourier transform, can be expressed as follows: The d-axis and q-axis components are respectively The initial value of the sub-super synchronous component corresponding to the voltage and current of the mth direct-drive wind turbine extracted by Fourier transform can be expressed as The d-axis and q-axis components are respectively

[0084] The initial value of the sub-super synchronous component corresponding to the voltage and current is brought into the system energy calculation model, that is, the initial value of the sub-super synchronous component is brought into the following equations constructed by the system energy model: dynamic equation of inner loop control of the HVDC converter, dynamic equation of outer loop control of the HVDC converter, port voltage equation of the HVDC converter, port voltage equation of the direct-drive wind turbine, dynamic component equation of the direct-drive wind turbine port current reference value, dynamic control equation of the direct-drive wind turbine phase-locked loop, and constraint equation of the HVDC converter and the direct-drive wind turbine.

[0085] It is worth noting that the coupling energy of the direct-drive wind turbine is the coupling energy between one direct-drive wind turbine and other direct-drive wind turbines. For example, in the wind farm HVDC transmission system provided by the present application, M direct-drive wind turbines are included, and the number of coupling energies of the direct-drive wind turbines obtained is: Wherein, the number of coupling energies of one direct-drive wind turbine and other wind turbines is M-1.

[0086] In step S300, the wind farm HVDC transmission system oscillation source analysis method provided by the present application obtains the oscillation source of the wind farm HVDC transmission system according to the coupling energy of each direct-drive wind turbine.

[0087] It can be understood that after obtaining the coupling energy of the direct-drive wind turbine in the number of M, the oscillation source of the wind farm HVDC transmission system is obtained by analyzing the coupling energy of the direct-drive wind turbine.

[0088] Compared with the prior art, the wind farm HVDC transmission system oscillation source analysis method provided by the present application collects the voltage and current of the HVDC converter port and the port of each direct-drive wind turbine, extracts the sub-super synchronous component of the voltage and current by Fourier transform, obtains the initial value of the sub-super synchronous component corresponding to the voltage and current, substitutes the initial value of the sub-super synchronous component into the pre-constructed system energy calculation model, obtains the coupling energy of each direct-drive wind turbine, and obtains the oscillation source of the wind farm HVDC transmission system according to the coupling energy of each direct-drive wind turbine, thereby accurately determining the oscillation source when the wind farm HVDC transmission system is disturbed.

[0089] Optionally, in the wind farm HVDC transmission system oscillation source analysis method provided by the present application, the oscillation source of the wind farm HVDC transmission system is obtained according to the coupling energy of each direct-drive wind turbine, which includes:

[0090] ​If the coupling energy between the certain direct-drive wind turbine and any other direct-drive wind turbine is less than zero, the direct-drive wind turbine is an oscillation source.

[0091] Specifically, after obtaining the coupling energy of the M number of direct-drive wind turbines, whether each direct-drive wind turbine is an oscillation source is determined by analyzing the M-1 coupling energies between each direct-drive wind turbine and other direct-drive wind turbines. For example, if the coupling energy between one direct-drive wind turbine and any other direct-drive wind turbine is less than zero, it can be determined that the direct-drive wind turbine is an oscillation source.

[0092] Compared with the prior art, the wind farm through the HVDC transmission system oscillation source analysis method provided by the embodiment of the application realizes accurate determination of the oscillation source when the wind farm through the HVDC transmission system is disturbed according to the coupling energy between the direct-drive wind turbine and other direct-drive wind turbines.

[0093] Optionally, in the wind farm through the HVDC transmission system oscillation source analysis method provided by the embodiment of the application, the system energy calculation model is constructed by the following steps:

[0094] The dynamic equation of the inner loop control of the HVDC converter, the dynamic equation of the outer loop control of the HVDC converter, the port voltage equation of the HVDC converter, the port voltage equation of the direct-drive wind turbine, the dynamic component equation of the port current reference value of the direct-drive wind turbine, the dynamic control equation of the phase-locked loop of the direct-drive wind turbine, and the constraint equation of the HVDC converter and the direct-drive wind turbine are constructed.

[0095] The dynamic equation of the inner loop control of the HVDC converter, the dynamic equation of the outer loop control of the HVDC converter, the port voltage equation of the HVDC converter, the port voltage equation of the direct-drive wind turbine, the dynamic component equation of the port current reference value of the direct-drive wind turbine, the dynamic control equation of the phase-locked loop of the direct-drive wind turbine, and the constraint equation of the HVDC converter and the direct-drive wind turbine are brought into the system energy calculation equation to obtain the total system energy.

[0096] The total system energy is decomposed into the direct-drive wind turbine induction energy, the direct-drive wind turbine coupling energy, the HVDC converter induction energy, and the HVDC converter coupling energy.

[0097] The direct-drive wind turbine coupling energy is taken as the output of the system energy calculation model.

[0098] Specifically, the dynamic equation of the inner loop control of the HVDC converter, the dynamic equation of the outer loop control of the HVDC converter, the port voltage equation of the HVDC converter, the port voltage equation of the direct-drive wind turbine, the dynamic component equation of the port current reference value of the direct-drive wind turbine, the dynamic control equation of the phase-locked loop of the direct-drive wind turbine, and the constraint equation of the HVDC converter and the direct-drive wind turbine are constructed in any order, which can be executed simultaneously or sequentially. ​

[0099] The inner ring control dynamic equation of the HVDC converter, the outer ring control dynamic equation of the HVDC converter, the HVDC converter port voltage equation, the direct-driven wind turbine port voltage equation, the direct-driven wind turbine port current reference value dynamic component equation, the direct-driven wind turbine phase-locked loop dynamic control equation and the constraint equation of the HVDC converter and the direct-driven wind turbine are brought into the system energy calculation equation to obtain the total system energy; the total system energy is decomposed into direct-driven wind turbine induction energy, direct-driven wind turbine coupling energy, HVDC converter induction energy and HVDC converter coupling energy; the direct-driven wind turbine coupling energy is taken as the output of the system energy calculation model.

[0100] Specifically, as shown in Figure 2 , the wind farm through the HVDC transmission system generates an oscillation in one of the M direct-driven wind turbines, generating a sub-synchronous component of a current, and the remaining direct-driven wind turbines correspondingly induce a first oscillation current and input it to the HVDC converter, generating a first oscillation current of the HVDC converter, and then the wind farm through the HVDC transmission system induces a first oscillation current of the remaining direct-driven wind turbines and the disturbance of the first oscillation current of the HVDC converter, and again induces an oscillation current of the M direct-driven wind turbines and the HVDC converter. By analogy, the system continuously generates new disturbance components, leading to the continuous induction of new oscillation currents in the wind farm through the HVDC transmission system.

[0101] In the wind farm through the HVDC transmission system, the inner ring control dynamic equation of the HVDC converter is constructed as:

[0102]

[0103] wherein k p1 , k i1 are the proportional coefficient and the integral coefficient of the HVDC converter respectively; R r , L r are the filter resistance and the filter inductance of the HVDC converter respectively; are the dynamic component of the d-axis reference value of the HVDC converter current induced by the nth oscillation and the dynamic component of the q-axis reference value of the HVDC converter current induced by the nth oscillation respectively; are the d-axis component of the nth oscillation current of the HVDC converter and the q-axis component of the nth oscillation current of the HVDC converter respectively, when n=0, indicating the component of the initial value of the sub-synchronous component of the current of the HVDC converter on the d-axis and the q-axis; are the d-axis component of the (n-1)th oscillation voltage of the HVDC converter and the q-axis component of the (n-1)th oscillation voltage of the HVDC converter respectively, when n=1, indicating the component of the initial value of the sub-synchronous component of the voltage of the HVDC converter on the d-axis and the q-axis.

[0104] In the wind farm through the HVDC transmission system, the outer ring control dynamic equation of the HVDC converter is constructed as:

[0105]

[0106] wherein, respectively, the dynamic component of the d-axis reference value of the HVDC converter voltage caused by the nth oscillation, the dynamic component of the q-axis reference value of the HVDC converter voltage caused by the nth oscillation, in the steady state process, both are 0.

[0107] In the wind farm sending system through the HVDC, the HVDC port voltage equation is constructed as:

[0108]

[0109] Let

[0110]

[0111]

[0112] wherein, k p2 , k i2 are respectively the proportional coefficient and the integral coefficient of the direct-drive wind turbine; s is the Laplace operator; respectively, the d-axis state variable corresponding to the inner loop integral link of the HVDC, and the q-axis state variable corresponding to the inner loop integral link of the HVDC.

[0113] In the wind farm sending system through the HVDC, the direct-drive wind turbine port voltage equation is constructed as:

[0114]

[0115] Let

[0116]

[0117]

[0118] wherein, respectively, the d-axis component of the nth oscillation voltage of the mth direct-drive wind turbine, the q-axis component of the nth oscillation voltage of the mth direct-drive wind turbine, when n=0, the component of the initial value of the corresponding super-synchronous component of the voltage of the mth direct-drive wind turbine in the d-axis and q-axis; is the initial value of the phase-locked loop phase angle of the mth direct-drive wind turbine; respectively, the dynamic component of the d-axis reference value of the current of the mth direct-drive wind turbine caused by the nth oscillation, the dynamic component of the q-axis reference value of the current of the mth direct-drive wind turbine caused by the nth oscillation; respectively, the d-axis steady-state value of the port current of the mth direct-drive wind turbine, and the q-axis steady-state value of the port current of the mth direct-drive wind turbine; respectively are the steady-state value of the port voltage d-axis of the mth direct-drive wind turbine, the steady-state value of the port voltage q-axis of the mth direct-drive wind turbine; ω0 is the rated angular velocity of the wind farm through the flexible external sending system; L fm is the filter inductance of the mth direct-drive wind turbine; is the dynamic angle of the mth direct-drive wind turbine for the nth oscillation phase-locked loop; respectively are the d-axis component of the mth direct-drive wind turbine for the nth oscillation current, the q-axis component of the mth direct-drive wind turbine for the nth oscillation current, when n = 0, the component of the initial value of the corresponding sub-synchronous component of the current of the mth direct-drive wind turbine in the d-axis and q-axis; respectively are the voltage d-axis state variable corresponding to the inner loop integral element of the mth direct-drive wind turbine, the voltage q-axis state variable corresponding to the inner loop integral element of the mth direct-drive wind turbine.

[0119] In the wind farm through the flexible external sending system, the dynamic component equation of the direct-drive wind turbine port current reference value is constructed as:

[0120]

[0121]

[0122] wherein, C fm is the DC capacitor of the direct-drive wind turbine; is the voltage steady-state value of the direct-drive wind turbine; is the dynamic component of the voltage d reference value of the direct-drive wind turbine caused by the nth oscillation; is the output power variation of the mth direct-drive wind turbine caused by the nth oscillation.

[0123] In the wind farm through the flexible external sending system, the dynamic control equation of the direct-drive wind turbine phase-locked loop is constructed as:

[0124]

[0125] wherein, k p_pllm , k i_pllm respectively are the control parameters and integral parameters of the phase-locked loop of the mth direct-drive wind turbine.

[0126] In the wind farm through the flexible external sending system, the constraint equation of the flexible converter and the direct-drive wind turbine is constructed as:

[0127]

[0128] wherein, L k , R k respectively are the filter inductance and filter resistance of the first transmission line, the first transmission line is the transmission line between the flexible converter and the point of common coupling; L xm , R xmThe second transmission line filter inductance and the second transmission line filter resistance are respectively connected with the mth direct drive wind turbine.

[0129] It should be noted that in the steps of constructing the inner loop control dynamic equation of the HVDC converter, constructing the outer loop control dynamic equation of the HVDC converter, constructing the port voltage equation of the HVDC converter, constructing the port voltage equation of the direct drive wind turbine, constructing the dynamic component equation of the direct drive wind turbine port current reference value, constructing the phase-locked loop dynamic control equation of the direct drive wind turbine, and constructing the constraint equation of the HVDC converter and the direct drive wind turbine, all steps are not in order, and can be constructed at the same time or sequentially.

[0130] Specifically, the constructed inner loop control dynamic equation of the HVDC converter, the outer loop control dynamic equation of the HVDC converter, the port voltage equation of the HVDC converter, the port voltage equation of the direct drive wind turbine, the dynamic component equation of the direct drive wind turbine port current reference value, the phase-locked loop dynamic control equation of the direct drive wind turbine, and the constraint equation of the HVDC converter and the direct drive wind turbine are substituted into the system energy calculation equation to obtain the total system energy.

[0131] The system energy calculation equation is:

[0132]

[0133] Wherein, N represents the total number of oscillations; M represents the total number of direct drive wind turbines.

[0134] The total system energy is:

[0135]

[0136] Wherein, The mth and hth direct drive wind turbine n-time oscillation current d-axis component is respectively: The mth and hth direct drive wind turbine n-time oscillation current q-axis component is respectively.

[0137] Specifically, the total system energy is decomposed into direct drive wind turbine induction energy, direct drive wind turbine coupling energy, HVDC converter induction energy, and HVDC converter coupling energy.

[0138] The direct drive wind turbine induction energy is:

[0139]

[0140]

[0141]

[0142] Wherein, The mth direct drive wind turbine induction energy is: The first part of the induction energy of the mth direct-drive wind turbine, the second part of the induction energy of the mth direct-drive wind turbine.

[0143] It can be understood that the function part of the induction energy of the direct-drive wind turbine is composed of the integral form of the state variable product, which can be expressed as:

[0144]

[0145] Where ω is the oscillation frequency of the system in the d, q axis coordinate system. A1 and A2 are the oscillation amplitudes of the state variables Δx1 and Δx2, and is the oscillation phase angle of the state variables Δx1 and Δx2, and α is the damping coefficient.

[0146] Therefore, By simplifying, we get:

[0147]

[0148] Where, are the oscillation amplitudes of and , α is the damping coefficient, and ω is the oscillation frequency of the wind farm through the flexible transmission system.

[0149] It is worth noting that in the case of oscillation of the wind farm through the flexible transmission system, the control parameters satisfy: It can be seen that: is greater than zero.

[0150] At the same time, it can be understood that the transfer function has a phase frequency characteristic curve of about 0 degrees and can be obtained which is also greater than zero.

[0151] That is, the induction energy generated in the direct-drive wind turbine is also not conducive to system stability, and dynamic energy is emitted externally.

[0152] The coupling energy of the direct-drive wind turbine is:

[0153]

[0154] Where, is the coupling energy between the mth and hth direct-drive wind turbines.

[0155] It can be understood that, similar to the simplification principle of the induction energy of the direct-drive wind turbine, the coupling energy of the direct-drive wind turbine is: simplifying, we get:

[0156]

[0157] Where, are the oscillation amplitudes of the oscillation amplitude of the n-th wind turbine, the oscillation phase angle of the n-th wind turbine; the oscillation amplitude of the n-th wind turbine, the oscillation phase angle of the n-th wind turbine.

[0158] It can be understood that, under the same oscillation frequency, the non-initial oscillation direct-driven wind turbine satisfies:

[0159] The control parameters satisfy: Substituting the above formula, the coupling energy between the non-initial disturbance oscillation direct-driven wind turbine and the other direct-driven wind turbines is greater than zero, that is, it is not conducive to system stability, and dynamic energy is emitted to the outside.

[0160] Under the same oscillation frequency, the initial oscillation direct-driven wind turbine satisfies:

[0161] It can be obtained that the coupling energy between the oscillation source direct-driven wind turbine and the other direct-driven wind turbines is less than zero, that is, it is conducive to system stability, and absorbs the dynamic energy of the system, while the coupling energy between the non-oscillation source direct-driven wind turbines is positive, which is not conducive to system stability, and releases the dynamic energy of the system.

[0162] Therefore, the initial oscillation source can be judged by that is, the oscillation source of the wind farm through the flexible HVDC transmission system is judged by

[0163] The inductive energy of the flexible HVDC converter is:

[0164]

[0165] It can be understood that, by simplifying , we can obtain:

[0166]

[0167] wherein, the oscillation amplitude of the n-th wind turbine, the oscillation phase angle of the n-th wind turbine; the oscillation amplitude of the n-th wind turbine, the oscillation phase angle of the n-th wind turbine. At the same time, the flexible HVDC converter satisfies:

[0168]

[0169] ​​​​​​​​

[0170] And, The phase-frequency curve of the phase angle difference is always 0°, so less than zero.

[0171] The coupling energy of the HVDC converter is:

[0172]

[0173] Taking as input and as output, the state space model of the HVDC transmission system can be obtained. If the phase angle difference is in the range of [-90°, 90°], the coupling energy of the HVDC converter is greater than zero, that is, the coupling energy of the HVDC converter is not conducive to system stability, and dynamic energy is emitted.

[0174] If the phase angle difference is in the range of [-270°, -90°], the coupling energy of the HVDC converter is less than zero, that is, the coupling energy of the HVDC converter is conducive to system stability and absorbs dynamic energy.

[0175] Therefore, in the oscillation process of the wind farm through the HVDC transmission system, the induction energy of the direct-drive wind turbine and the coupling energy of the HVDC converter are always greater than zero, and the induction energy of the HVDC converter is always less than zero. For the coupling energy of the direct-drive wind turbine, the coupling energy of the oscillation source direct-drive wind turbine and the remaining direct-drive wind turbines is less than zero, and the coupling energy of the non-oscillation direct-drive wind turbine and the remaining direct-drive wind turbines is greater than zero. It has obvious characteristics of changing based on whether the direct-drive wind turbine is an oscillation source, which can be used as a basis for locating the oscillation source direct-drive wind turbine.

[0176] The following two specific embodiments are used to illustrate the wind farm through the HVDC transmission system oscillation source analysis method provided by the present application.

[0177] Embodiment one:

[0178] In this embodiment, the wind farm through the HVDC transmission system includes four PMSGs, namely PMSG1, PMSG2, PMSG3 and PMSG4, and the line parameters of the four PMSGs are set to 0.75mH, 0.5mH, 0.25mH and 0.125mH.

[0179] A self-oscillation simulation scenario is set, and a disturbance is set in the current loop of PMSG1 to trigger self-oscillation of the direct-drive wind farm.

[0180] The currents and voltages at the ports of the HVDC converter, PMSG1, PMSG2, PMSG3 and PMSG4 are collected, and the corresponding sub-synchronous components are extracted. The sub-synchronous components are input into the system energy calculation model to obtain the coupling energy of each direct-drive wind turbine, such as Figure 3As shown, the coupling energy of PMSG1 and PMSG2, the coupling energy of PMSG1 and PMSG3 and the coupling energy of PMSG1 and PMSG4 are all negative values, while the coupling energy of PMSG2 and PMSG3, the coupling energy of PMSG2 and PMSG4 and the coupling energy of PMSG3 and PMSG4 are all positive values.

[0181] According to the coupling energy of the direct-drive wind turbine, it can be determined that PMSG1 is the oscillation source.

[0182] Embodiment two:

[0183] In this embodiment, the wind farm is sent out by a flexible HVDC system, which includes four PMSGs, PMSG1, PMSG2, PMSG3 and PMSG4. The line parameters of the four PMSGs are set to 0.85mH, and the output of PMSG1, PMSG2, PMSG3 and PMSG4 is adjusted to 2.5MW, 2MW, 1.5MW and 1MW respectively.

[0184] A self-oscillation simulation scenario is set, and a disturbance is set in the current loop of PMSG1 to trigger the self-oscillation of the direct-drive wind farm.

[0185] The currents and voltages at the ports of the flexible HVDC converter, PMSG1, PMSG2, PMSG3 and PMSG4 are collected, and the corresponding sub-synchronous components are extracted. The sub-synchronous components are input into the system energy calculation model to obtain the coupling energy of each direct-drive wind turbine, as shown in the following table. Figure 4 As shown, the coupling energy of PMSG1 and PMSG2, the coupling energy of PMSG1 and PMSG3 and the coupling energy of PMSG1 and PMSG4 are all negative values, while the coupling energy of PMSG2 and PMSG3, the coupling energy of PMSG2 and PMSG4 and the coupling energy of PMSG3 and PMSG4 are all positive values.

[0186] Those skilled in the art can understand that all or part of the processes of the above-mentioned embodiments can be completed by a computer program instructing relevant hardware. The program can be stored in a computer readable storage medium, such as a magnetic disk, an optical disk, a read-only memory or a random access memory.

[0187] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed by the present application can be easily thought by those skilled in the art, which should be covered within the protection scope of the present application.

Claims

1. A method for analyzing oscillation sources in a wind farm-to-electricity transmission system via flexible DC transmission, characterized in that, The method includes the following steps: Collect the voltage and current at the ports of the flexible DC converter and each port of the direct-drive fan; The sub-supersynchronous components of the voltage and current are extracted using Fourier transform to obtain the initial values ​​of the sub-supersynchronous components corresponding to the voltage and current; the initial values ​​of the sub-supersynchronous components are substituted into the pre-constructed system energy calculation model to obtain the coupling energy of each direct-drive wind turbine. Based on the coupling energy of each of the direct-drive wind turbines, the oscillation source of the wind farm via the flexible direct-drive transmission system is obtained; The method of obtaining the oscillation source of the wind farm via the flexible DC transmission system based on the coupling energy of each of the direct-drive wind turbines includes: If the coupling energy between a certain direct-drive fan and any other direct-drive fan is less than zero, then the direct-drive fan is an oscillation source. The system energy calculation model is constructed through the following steps: The following dynamic equations are constructed for the flexible DC-DC converter inner loop control, flexible DC-DC converter outer loop control, flexible DC-DC converter port voltage, direct-drive wind turbine port voltage, direct-drive wind turbine port current reference value dynamic component equation, direct-drive wind turbine phase-locked loop dynamic control equation, and constraint equations for the flexible DC-DC converter and direct-drive wind turbine under disturbance conditions: The system energy calculation equations are obtained by substituting the following equations into the system energy calculation equations: the inner loop control dynamic equation of the flexible DC converter, the outer loop control dynamic equation of the flexible DC converter, the port voltage equation of the flexible DC converter, the port voltage equation of the direct-drive wind turbine, the dynamic component equation of the port current reference value of the direct-drive wind turbine, the phase-locked loop dynamic control equation of the direct-drive wind turbine, and the constraint equations of the flexible DC converter and the direct-drive wind turbine. The total energy of the system is decomposed into the direct-drive fan induced energy, the direct-drive fan coupled energy, the flexible-DC converter induced energy, and the flexible-DC converter coupled energy. The coupled energy of the direct-drive wind turbine is used as the output of the system energy calculation model.

2. The method for analyzing oscillation sources in a wind farm via a flexible DC transmission system according to claim 1, characterized in that, The dynamic equation for the inner loop control of the flexible DC converter is: Where, k p1 k i1 These are the proportional gain and integral gain of the flexible DC converter, respectively; R r L r These are the filter resistor and filter inductor of the flexible DC converter, respectively. These are the dynamic components of the d-axis reference value of the flexible DC converter current caused by the nth oscillation and the dynamic components of the q-axis reference value of the flexible DC converter current caused by the nth oscillation, respectively. These are the d-axis component and q-axis component of the nth oscillation current of the flexible DC converter, respectively. These are the d-axis component and q-axis component of the (n-1)th oscillation voltage of the flexible DC converter, respectively. The dynamic equation for the outer loop control of the flexible DC converter is: in, These are the dynamic components of the d-axis reference value of the flexible DC converter voltage caused by the nth oscillation and the dynamic components of the q-axis reference value of the flexible DC converter voltage caused by the nth oscillation, respectively. Both are 0 during the steady state process. The port voltage equation of the flexible DC converter is as follows: make Where, k p2 k i2 are the proportional coefficient and integral coefficient of the direct-drive fan, respectively; s is the Laplace operator; These are the voltage d-axis state variables corresponding to the inner loop integral element of the flexible DC converter, and the voltage q-axis state variables corresponding to the inner loop integral element of the flexible DC converter, respectively.

3. The method for analyzing oscillation sources in a wind farm via a flexible DC transmission system according to claim 2, characterized in that, The equation for the port voltage of the direct-drive fan is: make in, These are the d-axis component of the (n+1)th oscillation voltage of the m-th direct-drive fan and the q-axis component of the (n+1)th oscillation voltage of the m-th direct-drive fan, respectively. Let be the initial value of the phase angle of the phase-locked loop for the m-th direct-drive fan; These are the dynamic components of the reference value d of the m-th direct-drive fan caused by the n-th oscillation and the dynamic components of the reference value q of the m-th direct-drive fan caused by the n-th oscillation, respectively. These are the d-axis steady-state value of the port current of the m-th direct-drive fan and the q-axis steady-state value of the port current of the m-th direct-drive fan, respectively. These are the d-axis steady-state values ​​of the port voltage of the m-th direct-drive wind turbine and the q-axis steady-state value of the port voltage of the m-th direct-drive wind turbine, respectively; ω0 is the rated angular velocity of the wind farm via the flexible direct-drive transmission system; L fm Let be the filter inductance for the m-th direct-drive fan; The dynamic angle of the phase-locked loop during the nth oscillation of the m-th direct-drive fan; These are the d-axis component of the nth oscillation current of the m-th direct-drive fan and the q-axis component of the nth oscillation current of the m-th direct-drive fan, respectively. These are the voltage d-axis state variables corresponding to the inner loop integral element of the m-th direct-drive fan and the voltage q-axis state variables corresponding to the inner loop integral element of the m-th direct-drive fan, respectively. The dynamic component equation for the reference value of the direct-drive fan port current is: Among them, C fm For direct-drive fans, the DC capacitor is used. This represents the steady-state voltage value of the direct-drive fan. The reference value dynamic component of the direct-drive fan voltage d caused by the nth oscillation; Let be the change in output power generated by the nth oscillation of the m-th direct-drive fan; The dynamic control equation for the phase-locked loop of the direct-drive fan is as follows: Where, k p_pllm k i_pllm These are the control parameters and integral parameters of the phase-locked loop for the m-th direct-drive fan, respectively. The constraint equations for the flexible DC converter and the direct-drive wind turbine are as follows: Among them, L k R k These are the filter inductor and filter resistor of the first transmission line, which is the transmission line between the flexible DC converter and the common connection point; L xm R xm These are the filter inductor and filter resistor for the second transmission line connecting the m-th direct-drive fan, respectively. The second transmission line is the transmission line between the direct-drive fan and the common connection point.

4. The method for analyzing oscillation sources in a wind farm-to-flexible DC transmission system according to claim 3, characterized in that, The system energy calculation equation is as follows: Where N represents the total number of oscillations; M represents the total number of direct-drive fans; The total energy of the system is: in, These are the d-axis components of the nth oscillation current of the mth and hth direct-drive fans, respectively. These are the q-axis components of the nth oscillation current of the m-th and h-th direct-drive fans, respectively.

5. The method for analyzing oscillation sources in a wind farm via a flexible DC transmission system according to claim 4, characterized in that, The induced energy of the direct-drive fan is: in, The induced energy of the m-th direct-drive fan; These represent the first and second portions of the induced energy of the m-th direct-drive fan, respectively.

6. The method for analyzing oscillation sources in a wind farm-to-flexible DC transmission system according to claim 4, characterized in that, The coupling energy of the direct-drive fan is: in, Let m be the coupling energy between the m-th and h-th direct-drive fans.

7. The method for analyzing oscillation sources in a wind farm-to-flexible DC transmission system according to claim 4, characterized in that, The induced energy of the flexible DC converter is:

8. The method for analyzing oscillation sources in a wind farm via a flexible DC transmission system according to claim 4, characterized in that, The coupling energy of the flexible DC converter is:

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