Frequency support control method for following net type direct drive fan

Abstract

The invention discloses a frequency support control method for a following net type direct drive fan. The method comprises the following steps: calculating a d-axis voltage reference value corresponding to a grid-side converter, a q-axis voltage reference value corresponding to the grid-side converter, a d-axis voltage reference value corresponding to a machine-side converter, a q-axis voltage reference value corresponding to a computer-side converter, a machine-side phase and a pitch angle according to operation data; and based on the common coupling point AC voltage q-axis feedback value, the reference frequency and the machine side power deviation feedback value, a network side control phase corresponding to the network side converter is calculated, and when phase control is carried out on the network side, the network side phase can be controlled based on the change of the machine side power deviation. On the basis that the power reference changing along with the frequency is introduced from the grid side to the machine side, the phase reference of the power deviation change from the machine side to the grid side is added, so that the grid side and the machine side of the power grid system can mutually perform feedback control based on the response of the other side, and the stability and the safety of the grid-connected system of the direct-driven wind generating set are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power regulation and control, and in particular to a frequency support control method for a grid-following direct-drive fan. Background Art

[0002] The development of wind power effectively alleviates the pressure of energy transformation and contributes to the goal of "carbon peak and carbon neutrality". On the one hand, with the scale of wind farm installations and the decline in the proportion of synchronous machines in traditional power systems, the power system has gradually shown low inertia and weak grid characteristics, and the risk of grid instability has increased. On the other hand, traditional direct-drive wind turbines use grid-side fixed DC voltage and machine-side maximum power tracking control. They do not have frequency support capabilities and are at risk of instability in low short-circuit ratio grids. Therefore, some scholars have gradually proposed to detect grid frequency changes through a grid-side phase-locked loop, and then synchronously change the power reference on the machine side through differential and proportional links, so as to achieve changes in wind turbine output power and support grid frequency.

[0003] The existing grid-following control method is prone to system instability due to the unilateral introduction of a power reference that changes with frequency from the grid side to the generator side, resulting in low safety of the direct-drive wind turbine grid-connected system.

[0004] Therefore, there is an urgent need for a frequency support control strategy for grid-connected direct-drive wind turbines to solve the problem of low safety of the grid-connected system of direct-drive wind turbines. Summary of the invention

[0005] The embodiment of the present invention provides a frequency support control method for a grid-connected direct-drive wind turbine to solve the problem of low safety of a grid-connected system of a direct-drive wind turbine generator set.

[0006] In order to solve the above problem, an embodiment of the present invention provides a frequency support control method for a grid-following direct-drive wind turbine, comprising:

[0007] Obtaining operation data corresponding to the grid-connected system of the direct-drive wind turbine generator set; wherein the operation data includes: AC voltage at the common coupling point, frequency change, reference frequency and machine-side feedback power change value;

[0008] According to the operating data, calculate the d-axis voltage reference value u corresponding to the grid-side converter dref , the q-axis voltage reference value u corresponding to the grid-side converter qref , the d-axis voltage reference value u corresponding to the machine-side converter drefm , the q-axis voltage reference value u corresponding to the computer-side converter qrefm 、Machine side phase θ m and pitch angle β;

[0009] Based on the q-axis feedback value of the AC voltage at the common coupling point, the reference frequency and the power deviation feedback value at the generator side, the grid-side control phase θ corresponding to the grid-side converter is calculated. s ; Wherein, the power deviation feedback value on the receiver side is used to change the generated grid-side control phase based on the power deviation feedback value on the machine side;

[0010] According to the d-axis voltage reference value u corresponding to the grid-side converter dref , q-axis voltage reference value u qref , grid side control phase θ s , the voltage reference value u corresponding to the machine-side converter drefm , q-axis voltage reference value u qrefm 、Machine side phase θ m , and the pitch angle β, to control the grid-connected system of the direct-drive wind turbine to achieve frequency support for the direct-drive wind turbine.

[0011] The grid-side control phase θ corresponding to the grid-side converter is calculated based on the common coupling point AC voltage, reference frequency and machine-side power deviation feedback value. s ,include:

[0012] Substitute the q-axis feedback value of the common coupling point AC voltage, the reference frequency and the machine-side power deviation feedback value into the grid-side phase calculation formula to calculate the grid-side control phase θ corresponding to the grid-side converter. s ; Among them, the grid-side phase calculation formula meets the following conditions:

[0013]

[0014] In the formula, u q is the q-axis feedback value of the AC voltage at the common coupling point, ω ref is the reference frequency, ΔP m is the power deviation feedback value on the generator side, k ωph is the high-pass gain, k ωp is the steady-state gain, T ωp is the filtering time constant, k ppll With k ipll They are proportional integral PI of the phase-locked loop pll The proportional coefficient and integral coefficient of , s is the Laplace operator.

[0015] As an improvement of the above solution, the power support control of the machine-side converter based on the frequency differential and deviation control strategy includes:

[0016] Based on the q-axis feedback value of the common coupling point AC voltage, the power support control of the generator-side converter is performed in combination with the frequency differential and deviation control strategy; wherein the frequency differential and deviation control strategy satisfies the following conditions:

[0017]

[0018] Where P ref is the reference power, H wt With D ω are the simulated inertia time constant and droop frequency modulation coefficient respectively; T ω is the filter time constant.

[0019] As an improvement of the above scheme, the operating data also includes: a DC voltage feedback value, a DC voltage reference value, a grid-side inductor current d-axis feedback value, a grid-side inductor current q-axis feedback value, a common coupling point AC voltage d-axis feedback value, an AC voltage amplitude reference value, a voltage amplitude feedback value, a reactive power feedback value, a reactive power reference value, a grid-side inductor current d-axis feedback value, a grid-side inductor current q-axis feedback value, a common coupling point AC voltage q-axis feedback value, a machine-side inductor current d-axis feedback value, a machine-side inductor current q-axis feedback value, an active power feedback value, a synchronous machine output electrical angular velocity, a maximum allowable speed value, and a maximum allowable speed deviation value.

[0020] As an improvement of the above solution, the d-axis voltage reference value u corresponding to the grid-side converter is calculated according to the operating data. dref , the q-axis voltage reference value u corresponding to the grid-side converter qref , the d-axis voltage reference value u corresponding to the machine-side converter drefm , the q-axis voltage reference value u corresponding to the computer-side converter qrefm 、Machine side phase θ m and pitch angle β, including:

[0021] According to the DC voltage feedback value, the reference value of the DC bus voltage, the grid-side inductor current d-axis feedback value, the grid-side inductor current q-axis feedback value, and the common coupling point AC voltage d-axis feedback value, the d-axis voltage reference value u corresponding to the grid-side converter is calculated. dref ;

[0022] According to the AC voltage amplitude reference value, voltage amplitude feedback value, reactive power feedback value, reactive power reference value, grid-side inductor current d-axis feedback value, grid-side inductor current q-axis feedback value, and common coupling point AC voltage q-axis feedback value, calculate the q-axis voltage reference value u corresponding to the grid-side converter qref ;

[0023] According to the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current, the d-axis voltage reference value u corresponding to the computer-side converter drefm ;

[0024] According to the active power feedback value, the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current, the q-axis voltage reference value u corresponding to the computer-side converter is qrefm ;

[0025] According to the synchronous machine output electrical angular velocity, determine the machine side phase θ m ;

[0026] The pitch angle β is determined based on the synchronous machine output electrical angular velocity, the maximum allowable speed value and the maximum allowable speed deviation.

[0027] As an improvement of the above scheme, the d-axis voltage reference value u corresponding to the grid-side converter is calculated according to the DC voltage feedback value, the DC voltage reference value, the grid-side inductor current d-axis feedback value, the grid-side inductor current q-axis feedback value, and the common coupling point AC voltage d-axis feedback value. dref ,include:

[0028] Substitute the DC voltage feedback value, DC voltage reference value, grid-side inductor current d-axis feedback value, grid-side inductor current q-axis feedback value, and common coupling point AC voltage d-axis feedback value into the grid-side d-axis voltage calculation formula to obtain the d-axis voltage reference value u corresponding to the grid-side converter. dref ; The grid-side d-axis voltage calculation formula satisfies the following conditions:

[0029]

[0030] In the formula, u dc is the DC voltage feedback value, u dcref is the DC voltage reference value, T dc is the filtering time constant of the DC voltage, i cd is the d-axis feedback value of the grid-side inductor current, i cq is the q-axis feedback value of the grid-side inductor current, u d is the d-axis feedback value of the AC voltage at the common coupling point, k pdc With k idc The DC voltage PI is dc The proportionality coefficient and integration coefficient, k pi With k ii They are the current inner loop PI i The proportionality coefficient and integration coefficient, k f With k d are the feedforward coefficient and the cross decoupling coefficient respectively, and s is the Laplace operator.

[0031] As an improvement of the above scheme, the q-axis voltage reference value u corresponding to the grid-side converter is calculated according to the AC voltage amplitude reference value, the voltage amplitude feedback value, the reactive power feedback value, the reactive power reference value, the grid-side inductor current d-axis feedback value, the grid-side inductor current q-axis feedback value, and the common coupling point AC voltage q-axis feedback value. qref ,include:

[0032] Substitute the AC voltage amplitude reference value, voltage amplitude feedback value, reactive power feedback value, reactive power reference value, grid-side inductor current d-axis feedback value, grid-side inductor current q-axis feedback value, and common coupling point AC voltage q-axis feedback value into the grid-side q-axis voltage reference value calculation formula to obtain the q-axis voltage reference value u corresponding to the grid-side converter. qref ; Wherein, the grid-side q-axis voltage reference value calculation formula satisfies the following conditions:

[0033]

[0034] In the formula, k pq With k iq Reactive power control PI q The proportional and integral coefficients, Q ref with U ref are reactive power reference value and AC voltage amplitude reference value, Q out with U mag are reactive power feedback value and AC voltage amplitude feedback value respectively, k q is the voltage reactive power droop coefficient, k pi With k ii They are the current inner loop PI i The proportionality coefficient and integration coefficient, k f With k d are the feedforward coefficient and the cross-decoupling coefficient, i cq is the q-axis feedback value of the grid-side inductor current, i cd is the d-axis feedback value of the grid-side inductor current, u q The q-axis feedback value of the AC voltage at the common coupling point, s is the Laplace operator.

[0035] As an improvement of the above scheme, according to the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current, the d-axis voltage reference value u corresponding to the computer-side converter is calculated. drefm ,include:

[0036] Substitute the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current into the calculation formula of the machine-side d-axis voltage reference value to obtain the d-axis voltage reference value u corresponding to the machine-side converter. drefm ; Wherein, the calculation formula of the machine side d-axis voltage reference value meets the following conditions:

[0037]

[0038] In the formula, k pi With k ii They are the current inner loop PI i The proportional coefficient and integral coefficient, i md is the d-axis feedback value of the machine-side inductor current, i mqis the q-axis feedback value of the machine-side inductor current, k dm is the cross-decoupling coefficient, and s is the Laplace operator.

[0039] As an improvement of the above scheme, the q-axis voltage reference value u corresponding to the computer-side converter is calculated based on the active power feedback value, the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current. qrefm ,include:

[0040] Substitute the active power feedback value, the d-axis feedback value of the machine-side inductor current, and the q-axis feedback value of the machine-side inductor current into the calculation formula of the machine-side q-axis voltage reference value to obtain the q-axis voltage reference value u corresponding to the machine-side converter. qrefm ; Among them, the calculation formula of the machine-side q-axis voltage reference value meets the following conditions:

[0041]

[0042] In the formula, k pp With k ip PI is the proportional integral of the active power controller p The proportional coefficient and integral coefficient, P ref is the active power reference value, P out is the active power feedback value, k pi With k ii They are the current inner loop PI i The proportional coefficient and integral coefficient, i md is the d-axis feedback value of the machine-side inductor current, i mq is the q-axis feedback value of the machine-side inductor current, ω 0 With ψ r are the rated speed of the fan and the rotor flux, k dm is the cross-decoupling coefficient, and s is the Laplace operator.

[0043] As an improvement of the above solution, the pitch angle β is determined according to the output electrical angular velocity of the synchronous machine, the maximum allowable value of the rotational speed and the maximum allowable deviation of the rotational speed, including:

[0044] Substitute the synchronous machine output electrical angular velocity, the maximum allowable speed value and the maximum allowable speed deviation into the pitch angle calculation formula to obtain the pitch angle β; wherein the pitch angle calculation formula satisfies the following conditions:

[0045]

[0046] In the formula, k ppitch With k ipitch are the proportional and integral coefficients of pitch control, ω sm is the output electrical angular velocity of the synchronous machine, ω max With Δω maxare the maximum allowable speed value and the maximum allowable speed deviation respectively, and s is the Laplace operator.

[0047] As can be seen from the above, the present invention has the following beneficial effects:

[0048] The present invention provides a frequency support control method for a grid-following direct-drive wind turbine. The method calculates the d-axis voltage reference value corresponding to the grid-side converter, the q-axis voltage reference value corresponding to the grid-side converter, the d-axis voltage reference value corresponding to the machine-side converter, the q-axis voltage reference value corresponding to the computer-side converter, the machine-side phase and the pitch angle of the operation data. At the same time, based on the q-axis feedback value of the AC voltage at the common coupling point, the reference frequency and the machine-side power deviation feedback value, the grid-side control phase corresponding to the grid-side converter is calculated. When the grid-side phase is controlled, the machine-side power deviation feedback value is introduced, and the grid-side phase is controlled based on the change of the machine-side power deviation. On the basis of introducing a power reference that changes with frequency from the grid-side to the machine-side, a phase reference of the power deviation change from the machine-side to the grid-side is added, so that the grid-side and the machine-side of the power grid system can feedback control each other based on the response of the other side, so that the control of the grid-connected system of the direct-drive wind turbine generator set is more stable, thereby improving the safety of the grid-connected system of the direct-drive wind turbine generator set. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a flow chart of a frequency support control method for a grid-following direct-drive wind turbine provided by an embodiment of the present invention;

[0050] Figure 2 It is a structural schematic diagram of a frequency support control device for a grid-following direct-drive fan provided by an embodiment of the present invention;

[0051] Figure 3 It is a schematic diagram of the structure of a terminal device provided by an embodiment of the present invention.

[0052] Figure 4 It is a schematic diagram of the electrical topology structure of a direct-drive wind turbine generator grid-connected system provided by an embodiment of the present invention;

[0053] Figure 5 It is a schematic diagram of the dominant pole of the inertia time constant H_wt supporting the control from 0.1s to 3s frequency under the traditional control strategy provided by one embodiment of the present invention;

[0054] Figure 6 It is a schematic diagram of a phase-locked loop bandwidth f_pll supporting a control dominant pole from 1 Hz to 50 Hz frequency under a conventional control strategy provided by an embodiment of the present invention;

[0055] Figure 7 An SCR provided by an embodiment of the present invention = 2H wt= Schematic diagram of the simulation waveform of the traditional frequency support control under the change of the phase-locked loop bandwidth under 2s;

[0056] Figure 8 It is a schematic diagram of a frequency support control strategy for a grid-following direct-drive wind turbine provided by an embodiment of the present invention;

[0057] Fig. 9 It is the inertia time constant H under the frequency support control strategy of the grid-type direct-drive fan provided by one embodiment of the present invention. wt Schematic diagram of the dominant pole of the frequency support control from 0.1s to 4s;

[0058] Fig.10 The phase-locked loop bandwidth f is provided in an embodiment of the present invention under the frequency support control strategy of the grid-type direct-drive wind turbine. pll Schematic diagram of the dominant pole of the control support from 1Hz to 50Hz frequency;

[0059] Fig.11 It is a schematic diagram of the system power response of the frequency support control strategy of the grid-type direct-drive wind turbine provided by an embodiment of the present invention under a frequency step of 50.2 Hz;

[0060] Fig.12 It is a schematic diagram of the power response of the frequency support control strategy of the grid-following direct-drive wind turbine provided by an embodiment of the present invention under a phase jump of 30°;

[0061] Fig.13 It is a schematic diagram of the power response of the frequency support control strategy of a grid-following direct-drive wind turbine provided by an embodiment of the present invention when the frequency ramp increases from 0.5 Hz / s to 51 Hz. DETAILED DESCRIPTION

[0062] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] Embodiment 1

[0064] See also Figure 1 , Figure 1 FIG. 1 is a flow chart of a frequency support control method for a grid-type direct-drive fan provided by an embodiment of the present invention. Figure 1 As shown, this embodiment includes step 101 to step 10X, and each step is specifically as follows:

[0065] Step 101: Acquire operation data corresponding to the grid-connected system of the direct-drive wind turbine generator set; wherein the operation data includes: common coupling point AC voltage, frequency change, reference frequency and machine-side feedback power change value.

[0066] In this embodiment, the operating data also includes: a DC voltage feedback value, a DC voltage reference value, a grid-side inductor current d-axis feedback value, a grid-side inductor current q-axis feedback value, a common coupling point AC voltage d-axis feedback value, an AC voltage amplitude reference value, a voltage amplitude feedback value, a reactive power feedback value, a reactive power reference value, a grid-side inductor current d-axis feedback value, a grid-side inductor current q-axis feedback value, a common coupling point AC voltage q-axis feedback value, a machine-side inductor current d-axis feedback value, a machine-side inductor current q-axis feedback value, an active power feedback value, a synchronous machine output electrical angular velocity, a maximum allowable speed value, and a maximum allowable speed deviation value.

[0067] In a specific embodiment, the electrical topology diagram of the direct-drive wind turbine generator grid-connected system is as follows: Figure 4 As shown, the machine-side converter is connected to the permanent magnet synchronous generator through an LC filter, and the machine-side inductance and capacitance are L m With C m , R Lm With R Cm The grid-side converter is connected to the common coupling point through the LC filter, and the grid-side inductance and capacitance are L f With C f , R Lf With R Cf are the equivalent series resistance of the machine-side LC filter. dc With R cp are the DC side capacitance and energy dissipation resistance respectively. g With R g They are the grid inductance and resistance respectively, among which the parasitic series resistance of the filter inductor and capacitor is not specially drawn in the figure but has been marked.

[0068] In order to better illustrate the direct-drive wind turbine grid-connected system, Tables 1 and 2 are provided to illustrate the operating data and the parameters involved:

[0069] Table 1 Parameters of direct-drive wind turbine and machine-side converter

[0070]

[0071] Table 2 Grid-side converter parameters

[0072]

[0073] Step 102: Calculate the d-axis voltage reference value u corresponding to the grid-side converter according to the operating data dref, the q-axis voltage reference value u corresponding to the grid-side converter qref , the d-axis voltage reference value u corresponding to the machine-side converter drefm , the q-axis voltage reference value u corresponding to the computer-side converter qrefm 、Machine side phase θ m and pitch angle β.

[0074] In this embodiment, the d-axis voltage reference value u corresponding to the grid-side converter is calculated according to the operating data. dref , the q-axis voltage reference value u corresponding to the grid-side converter qref , the d-axis voltage reference value u corresponding to the machine-side converter drefm , the q-axis voltage reference value u corresponding to the computer-side converter qrefm 、Machine side phase θ m and pitch angle β, including:

[0075] According to the DC voltage feedback value, the reference value of the DC bus voltage, the grid-side inductor current d-axis feedback value, the grid-side inductor current q-axis feedback value, and the common coupling point AC voltage d-axis feedback value, the d-axis voltage reference value u corresponding to the grid-side converter is calculated. dref ;

[0076] According to the AC voltage amplitude reference value, voltage amplitude feedback value, reactive power feedback value, reactive power reference value, grid-side inductor current d-axis feedback value, grid-side inductor current q-axis feedback value, and common coupling point AC voltage q-axis feedback value, calculate the q-axis voltage reference value u corresponding to the grid-side converter qref ;

[0077] According to the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current, the d-axis voltage reference value u corresponding to the computer-side converter drefm ;

[0078] According to the active power feedback value, the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current, the q-axis voltage reference value u corresponding to the computer-side converter is qrefm ;

[0079] According to the synchronous machine output electrical angular velocity, determine the machine side phase θ m ;

[0080] The pitch angle β is determined based on the synchronous machine output electrical angular velocity, the maximum allowable speed value and the maximum allowable speed deviation.

[0081] As an improvement of the above scheme, the d-axis voltage reference value u corresponding to the grid-side converter is calculated according to the DC voltage feedback value, the DC voltage reference value, the grid-side inductor current d-axis feedback value, the grid-side inductor current q-axis feedback value, and the common coupling point AC voltage d-axis feedback value. dref ,include:

[0082] Substitute the DC voltage feedback value, DC voltage reference value, grid-side inductor current d-axis feedback value, grid-side inductor current q-axis feedback value, and common coupling point AC voltage d-axis feedback value into the grid-side d-axis voltage calculation formula to obtain the d-axis voltage reference value u corresponding to the grid-side converter. dref ; The grid-side d-axis voltage calculation formula satisfies the following conditions:

[0083]

[0084] In the formula, u dc is the DC voltage feedback value, u dcref is the DC voltage reference value, T dc is the filtering time constant of the DC voltage, i cd is the d-axis feedback value of the grid-side inductor current, i cq is the q-axis feedback value of the grid-side inductor current, u d is the d-axis feedback value of the AC voltage at the common coupling point, k pdc With k idc The DC voltage PI is dc The proportionality coefficient and integration coefficient, k pi With k ii They are the current inner loop PI i The proportionality coefficient and integration coefficient, k f With k d are the feedforward coefficient and the cross decoupling coefficient respectively, and s is the Laplace operator.

[0085] As an improvement of the above scheme, the q-axis voltage reference value u corresponding to the grid-side converter is calculated according to the AC voltage amplitude reference value, the voltage amplitude feedback value, the reactive power feedback value, the reactive power reference value, the grid-side inductor current d-axis feedback value, the grid-side inductor current q-axis feedback value, and the common coupling point AC voltage q-axis feedback value. qref ,include:

[0086] Substitute the AC voltage amplitude reference value, voltage amplitude feedback value, reactive power feedback value, reactive power reference value, grid-side inductor current d-axis feedback value, grid-side inductor current q-axis feedback value, and common coupling point AC voltage q-axis feedback value into the grid-side q-axis voltage reference value calculation formula to obtain the q-axis voltage reference value u corresponding to the grid-side converter. qref ; Wherein, the grid-side q-axis voltage reference value calculation formula satisfies the following conditions:

[0087]

[0088] In the formula, k pq With k iq Reactive power control PI qThe proportional and integral coefficients, Q ref with U ref are reactive power reference value and AC voltage amplitude reference value, Q out with U mag are reactive power feedback value and AC voltage amplitude feedback value respectively, k q is the voltage reactive power droop coefficient, k pi With k ii They are the current inner loop PI i The proportionality coefficient and integration coefficient, k f With k d are the feedforward coefficient and the cross-decoupling coefficient, i cq is the q-axis feedback value of the grid-side inductor current, i cd is the d-axis feedback value of the grid-side inductor current, u q The q-axis feedback value of the AC voltage at the common coupling point, s is the Laplace operator.

[0089] In a specific embodiment, the direct-drive fan control usually adopts a constant DC voltage control on the grid side, i dref 、i qref is the d-axis reference value and q-axis reference value of the AC current to realize the outer loop control; u dref 、u qref The d-axis electrical reference value and the q-axis reference value of the output voltage are used to realize the current loop.

[0090] As an improvement of the above scheme, according to the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current, the d-axis voltage reference value u corresponding to the computer-side converter is calculated. drefm ,include:

[0091] Substitute the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current into the calculation formula of the machine-side d-axis voltage reference value to obtain the d-axis voltage reference value u corresponding to the machine-side converter. drefm ; Wherein, the calculation formula of the machine side d-axis voltage reference value meets the following conditions:

[0092]

[0093] In the formula, k pi With k ii They are the current inner loop PI i The proportional coefficient and integral coefficient, i md is the d-axis feedback value of the machine-side inductor current, i mq is the q-axis feedback value of the machine-side inductor current, k dm is the cross-decoupling coefficient, and s is the Laplace operator.

[0094] As an improvement of the above scheme, the q-axis voltage reference value u corresponding to the computer-side converter is calculated based on the active power feedback value, the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current. qrefm ,include:

[0095] Substitute the active power feedback value, the d-axis feedback value of the machine-side inductor current, and the q-axis feedback value of the machine-side inductor current into the calculation formula of the machine-side q-axis voltage reference value to obtain the q-axis voltage reference value u corresponding to the machine-side converter. qrefm ; Among them, the calculation formula of the machine-side q-axis voltage reference value meets the following conditions:

[0096]

[0097] In the formula, k pp With k ip PI is the proportional integral of the active power controller p The proportional coefficient and integral coefficient, P ref is the active power reference value, P out is the active power feedback value, k pi With k ii They are the current inner loop PI i The proportional coefficient and integral coefficient, i md is the d-axis feedback value of the machine-side inductor current, i mq is the q-axis feedback value of the machine-side inductor current, ω 0 With ψ r are the rated speed of the fan and the rotor flux, k dm is the cross-decoupling coefficient, and s is the Laplace operator.

[0098] On the machine side, d-axis current control is adopted. At this time, the coordinate transformation phase directly adopts the synchronous machine output electrical angular velocity n p ω sm The resulting phase where n p is the pole pair number, ω sm With θ sm are the mechanical angular velocity and mechanical angular displacement respectively.

[0099] As an improvement of the above solution, the pitch angle β is determined according to the output electrical angular velocity of the synchronous machine, the maximum allowable value of the rotational speed and the maximum allowable deviation of the rotational speed, including:

[0100] Substitute the synchronous machine output electrical angular velocity, the maximum allowable speed value and the maximum allowable speed deviation into the pitch angle calculation formula to obtain the pitch angle β; wherein the pitch angle calculation formula satisfies the following conditions:

[0101]

[0102] In the formula, kppitch With k ipitch are the proportional and integral coefficients of pitch control, ω sm is the output electrical angular velocity of the synchronous machine, ω max With Δω max are the maximum allowable speed value and the maximum allowable speed deviation respectively, and s is the Laplace operator.

[0103] Step 103: Calculate the grid-side control phase θ corresponding to the grid-side converter based on the q-axis feedback value of the common coupling point AC voltage, the reference frequency and the machine-side power deviation feedback value s ; Among them, the power deviation feedback value on the receiver side is used to make the generated network side control phase change based on the power deviation feedback value on the machine side.

[0104] In this embodiment, the grid-side control phase θ corresponding to the grid-side converter is calculated based on the common coupling point AC voltage, reference frequency and machine-side power deviation feedback value. s ,include:

[0105] Substitute the q-axis feedback value of the common coupling point AC voltage, the reference frequency and the machine-side power deviation feedback value into the grid-side phase calculation formula to calculate the grid-side control phase θ corresponding to the grid-side converter. s ; Among them, the grid-side phase calculation formula meets the following conditions:

[0106]

[0107] In the formula, u q is the q-axis feedback value of the AC voltage at the common coupling point, ω ref is the reference frequency, ΔP m is the power deviation feedback value on the generator side, k ωph is the high-pass gain, k ωp is the steady-state gain, T ωp is the filtering time constant, k ppll With k ipll They are proportional integral PI of the phase-locked loop pll The proportional coefficient and integral coefficient of , s is the Laplace operator.

[0108] Step 104: According to the d-axis voltage reference value u corresponding to the grid-side converter dref , q-axis voltage reference value u qref , grid side control phase θ s , the voltage reference value u corresponding to the machine-side converter drefm , q-axis voltage reference value u qrefm 、Machine side phase θ m, and the pitch angle β, to control the grid-connected system of the direct-drive wind turbine generator set to achieve frequency support for the direct-drive wind turbine; wherein, the power support control of the machine-side converter is performed based on the frequency differential and deviation control strategy.

[0109] In this embodiment, the power support control of the machine-side converter based on the frequency differential and deviation control strategy includes:

[0110] Based on the q-axis feedback value of the common coupling point AC voltage, the power support control of the generator-side converter is performed in combination with the frequency differential and deviation control strategy; wherein the frequency differential and deviation control strategy satisfies the following conditions:

[0111]

[0112] Where P ref is the reference power, H wt With D ω are the simulated inertia time constant and droop frequency modulation coefficient respectively; T ω is the filter time constant.

[0113] In a specific embodiment, the conventional control strategy is adopted, the short circuit ratio SCR=2, the phase-locked loop bandwidth f pll =10Hz, inertia time constant H wt =2s, the filtering time constant is T ω = 0.1s, further analysis of the critical stability boundaries of inertia time constant, phase-locked loop bandwidth, power grid strength and filter time constant under the parameters in Table 1 and Table 2 is shown in Table 3 (traditional active support control), and the control strategy parameters are selected as shown in Table 4. Figure 5 Under the traditional control strategy, the inertia time constant H wt From 0.1s to 3s frequency support control dominant pole, Figure 6 Under the traditional control strategy, the phase-locked loop bandwidth f pll The frequency range from 1Hz to 50Hz supports the control of the dominant pole.

[0114] Table 3 Stability boundary of traditional active support control

[0115]

[0116] Table 4 Selection of control strategy parameters

[0117]

[0118] From the above analysis, we can know that the filter time constant cannot be too small, that is, T_ω>0.11s can maintain SCR=2, f_pll=10Hz, H_wt=2s and maintain stability under the parameters shown in Table 1 and Table 2. Similarly, the inertia time constant needs to be less than 2.7s, that is, H_wt<2.7s, and the phase-locked loop bandwidth needs to be less than 15Hz, that is, f_pll<15Hz. That is, under weak power grids, the frequency support differential gain that can be simulated cannot be too large. The electromagnetic transient simulation model was carried out through Matlab / Simulink, and the phase-locked loop bandwidth change was simulated. Figure 7 SCR=2H wt =2s, the simulation waveform of the traditional frequency support control under the change of the phase-locked loop bandwidth shows that the simulation waveform becomes unstable after the phase-locked loop bandwidth increases by 15Hz, which shows the disadvantage of traditional control that the system becomes unstable when the phase-locked loop bandwidth increases under weak power grid.

[0119] The improved control strategy of this embodiment introduces the idea of ​​deviation feedback control from the machine side to the grid side to address the system stability problem under weak power grids. Based on this idea, the relevant control framework is further refined, and the frequency support control strategy of the grid-following direct-drive wind turbine involved in the present invention is proposed as an improved control strategy. The effect of stable simulation of large inertia under weak power grids is achieved. The proposed control strategy is simple, effective, and easy to modify. It has a good prospect for the existing stock of grid-following direct-drive wind turbines, such as Figure 8 shown.

[0120] According to the above analysis, the critical stability boundary of the system becomes the parameters shown in Table 3 (improved active support control). It can be found that the system stability is greatly improved, the allowed inertia time constant and phase-locked loop bandwidth are effectively increased, and the allowed minimum filter time constant is reduced to 0.03s. Fig. 9 is the inertia time constant H under the improved control strategy wt From 0.1s to 4s frequency support control dominant pole, Fig.10 Under the improved control strategy, the phase-locked loop bandwidth f pll From 1Hz to 50Hz frequency support control dominant pole, it can be seen that the system stability has been greatly improved compared with traditional control.

[0121] In order to verify the above analysis, an electromagnetic transient simulation model was carried out through Matlab / Simulink, and the difference between the traditional control and the proposed control strategy under frequency step was compared. wt = 2s, at SCR = 2, f pll =10Hz, the stability of the traditional control system can be guaranteed (such as Fig.11 As shown on the left), when the inertia time constant H wt = 3s, at SCR = 2, fpll =10Hz, the stability of the traditional control system cannot be guaranteed, and the power diverges, which shows the effectiveness of the proposed control strategy (such as Fig.11 shown on the right).

[0122] In order to further verify the effectiveness of the proposed control strategy, Fig.12 The power response of the proposed control strategy under a 30° phase jump shows the response of the proposed control strategy under a grid phase jump. The proposed control can operate stably under large / small inertia. The larger the inertia, the greater the power drop, and thus the greater the change in synchronous machine speed. Similarly, Fig.13 The power response of the proposed control strategy when the frequency ramp increases from 0.5Hz / s to 51Hz is shown, showing the response waveform under the change of grid frequency. The system remains stable under large and small inertia. The above analysis and simulation verification verify the effectiveness of the proposed control.

[0123] See also Figure 2 , Figure 2 It is a structural schematic diagram of a frequency support control device for a grid-following direct-drive wind turbine provided by an embodiment of the present invention, comprising: a data acquisition module 201, a data calculation module 202, a phase calculation module 203 and a control module 204;

[0124] The data acquisition module is used to acquire the operation data corresponding to the grid-connected system of the direct-drive wind turbine generator set; wherein the operation data includes: the AC voltage at the common coupling point, the frequency change, the reference frequency and the machine-side feedback power change value;

[0125] The data calculation module is used to calculate the d-axis voltage reference value u corresponding to the grid-side converter according to the operating data. dref , the q-axis voltage reference value u corresponding to the grid-side converter qref , the d-axis voltage reference value u corresponding to the machine-side converter drefm , the q-axis voltage reference value u corresponding to the computer-side converter qrefm 、Machine side phase θ m and pitch angle β;

[0126] The phase calculation module is used to calculate the grid-side control phase θ corresponding to the grid-side converter based on the q-axis feedback value of the common coupling point AC voltage, the reference frequency and the machine-side power deviation feedback value. s ; Wherein, the power deviation feedback value on the receiver side is used to change the generated grid-side control phase based on the power deviation feedback value on the machine side;

[0127] The control module is used to control the d-axis voltage reference value u corresponding to the grid-side converter. dref , q-axis voltage reference value u qref , grid side control phase θ s, the voltage reference value u corresponding to the machine-side converter drefm , q-axis voltage reference value u qrefm 、Machine side phase θ m , and the pitch angle β, to control the grid-connected system of the direct-drive wind turbine generator set to achieve frequency support for the direct-drive wind turbine; wherein, the power support control of the machine-side converter is performed based on the frequency differential and deviation control strategy.

[0128] It can be understood that the above-mentioned system item embodiments correspond to the method item embodiments of the present invention, which can implement the grid-following direct-drive wind turbine frequency support control method provided by any of the above-mentioned method item embodiments of the present invention.

[0129] This embodiment calculates the d-axis voltage reference value corresponding to the grid-side converter, the q-axis voltage reference value corresponding to the grid-side converter, the d-axis voltage reference value corresponding to the machine-side converter, the q-axis voltage reference value corresponding to the computer-side converter, the machine-side phase and the pitch angle of the operation data. At the same time, based on the q-axis feedback value of the common coupling point AC voltage, the reference frequency and the machine-side power deviation feedback value, the grid-side control phase corresponding to the grid-side converter is calculated. When the grid side performs phase control, the machine-side power deviation feedback value can be introduced, and the grid-side phase can be controlled based on the change of the machine-side power deviation. On the basis of introducing a power reference that changes with the frequency from the grid side to the machine side, a phase reference of the power deviation change from the machine side to the grid side is added, so that the grid side and the machine side of the power grid system can feedback control each other based on the response of the other side, so that the control of the direct-drive wind turbine generator set grid-connected system is more stable, thereby improving the safety of the direct-drive wind turbine generator set grid-connected system.

[0130] Embodiment 2

[0131] See also Figure 3 , Figure 3 It is a schematic diagram of the structure of a terminal device provided in one embodiment of the present invention.

[0132] A terminal device of this embodiment includes: a processor 301, a memory 302, and a computer program stored in the memory 302 and executable on the processor 301. When the processor 301 executes the computer program, the steps of the above-mentioned frequency support control method for a grid-following direct-drive wind turbine in the embodiment are implemented, for example: Figure 1 Alternatively, when the processor executes the computer program, the functions of each module in the above-mentioned system embodiments are realized, for example: Figure 2 The grid-type direct-drive fan frequency shown supports all modules of the control system.

[0133] In addition, an embodiment of the present invention also provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute the grid-following direct-drive wind turbine frequency support control method as described in any of the above embodiments.

[0134] Those skilled in the art will understand that the schematic diagram is merely an example of a terminal device and does not constitute a limitation on the terminal device. The terminal device may include more or fewer components than shown in the diagram, or a combination of certain components, or different components. For example, the terminal device may also include input and output devices, network access devices, buses, etc.

[0135] The processor 301 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc. The processor 301 is the control center of the terminal device, and uses various interfaces and lines to connect various parts of the entire terminal device.

[0136] The memory 302 can be used to store the computer program and / or module. The processor 301 implements various functions of the terminal device by running or executing the computer program and / or module stored in the memory and calling the data stored in the memory 302. The memory 302 can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, an application required for at least one function (such as a sound playback function, an image playback function, etc.), etc.; the data storage area can store data created according to the use of the mobile phone (such as audio data, a phone book, etc.), etc. In addition, the memory can include a high-speed random access memory, and can also include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other volatile solid-state storage devices.

[0137] Wherein, if the module / unit integrated in the terminal device is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Wherein, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form, etc. The computer-readable medium may include: any entity or system capable of carrying the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium, etc.

[0138] It should be noted that the system embodiment described above is merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. In addition, in the drawings of the system embodiment provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, which may be specifically implemented as one or more communication buses or signal lines. A person of ordinary skill in the art may understand and implement it without paying any creative effort.

[0139] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A frequency support control method for a grid-following direct-drive fan, characterized in that: include: Obtaining operation data corresponding to the grid-connected system of the direct-drive wind turbine generator set; wherein the operation data includes: AC voltage at the common coupling point, frequency change, reference frequency and machine-side feedback power change value; According to the operating data, calculate the d-axis voltage reference value u corresponding to the grid-side converter dref , the q-axis voltage reference value u corresponding to the grid-side converter qref , the d-axis voltage reference value u corresponding to the machine-side converter drefm , the q-axis voltage reference value u corresponding to the computer-side converter qrefm 、Machine side phase θ m and pitch angle β; Based on the q-axis feedback value of the AC voltage at the common coupling point, the reference frequency and the power deviation feedback value at the generator side, the grid-side control phase θ corresponding to the grid-side converter is calculated. s ; Wherein, the power deviation feedback value on the receiver side is used to change the generated grid-side control phase based on the power deviation feedback value on the machine side; According to the d-axis voltage reference value u corresponding to the grid-side converter dref , q-axis voltage reference value u qref , grid side control phase θ s , the voltage reference value u corresponding to the machine-side converter drefm , q-axis voltage reference value u qrefm 、Machine side phase θ m , and the pitch angle β, to control the grid-connected system of the direct-drive wind turbine generator set to achieve stable frequency support for the direct-drive wind turbine; among them, the power support control of the machine-side converter is carried out based on the frequency differential and deviation control strategy.

2. The frequency support control method of a grid-following direct-drive fan according to claim 1 is characterized in that: The grid-side control phase θ corresponding to the grid-side converter is calculated based on the common coupling point AC voltage, reference frequency and machine-side power deviation feedback value. s ,include: Substitute the q-axis feedback value of the common coupling point AC voltage, the reference frequency and the machine-side power deviation feedback value into the grid-side phase calculation formula to calculate the grid-side control phase θ corresponding to the grid-side converter. s ; Among them, the grid-side phase calculation formula meets the following conditions: In the formula, u q is the q-axis feedback value of the AC voltage at the common coupling point, ω ref is the reference frequency, ΔP m is the power deviation feedback value on the generator side, k ωph is the high-pass gain, k ωp is the steady-state gain, T ωp is the filtering time constant, k ppll With k ipll They are proportional integral PI of the phase-locked loop pll The proportional coefficient and integral coefficient of , s is the Laplace operator.

3. The frequency support control method of a grid-following direct-drive fan according to claim 2 is characterized in that: The power support control of the machine-side converter based on the frequency differential and deviation control strategy includes: Based on the q-axis feedback value of the common coupling point AC voltage, the power support control of the generator-side converter is performed in combination with the frequency differential and deviation control strategy; wherein the frequency differential and deviation control strategy satisfies the following conditions: Where P ref is the reference power, H wt With D ω are the simulated inertia time constant and droop frequency modulation coefficient respectively; T ω is the filter time constant.

4. The frequency support control method of a grid-following direct-drive fan according to claim 1, characterized in that: The operating data also includes: a DC voltage feedback value, a DC voltage reference value, a grid-side inductor current d-axis feedback value, a grid-side inductor current q-axis feedback value, a common coupling point AC voltage d-axis feedback value, an AC voltage amplitude reference value, a voltage amplitude feedback value, a reactive power feedback value, a reactive power reference value, a grid-side inductor current d-axis feedback value, a grid-side inductor current q-axis feedback value, a common coupling point AC voltage q-axis feedback value, a machine-side inductor current d-axis feedback value, a machine-side inductor current q-axis feedback value, an active power feedback value, a synchronous machine output electrical angular velocity, a maximum allowable speed value, and a maximum allowable speed deviation value.

5. The frequency support control method of a grid-following direct-drive fan according to claim 1, characterized in that: The d-axis voltage reference value u corresponding to the grid-side converter is calculated according to the operating data. dref , the q-axis voltage reference value u corresponding to the grid-side converter qref , the d-axis voltage reference value u corresponding to the machine-side converter drefm , the q-axis voltage reference value u corresponding to the computer-side converter qrefm 、Machine side phase θ m and pitch angle β, including: According to the DC voltage feedback value, the reference value of the DC bus voltage, the grid-side inductor current d-axis feedback value, the grid-side inductor current q-axis feedback value, and the common coupling point AC voltage d-axis feedback value, the d-axis voltage reference value u corresponding to the grid-side converter is calculated. dref ; According to the AC voltage amplitude reference value, voltage amplitude feedback value, reactive power feedback value, reactive power reference value, grid-side inductor current d-axis feedback value, grid-side inductor current q-axis feedback value, and common coupling point AC voltage q-axis feedback value, calculate the q-axis voltage reference value u corresponding to the grid-side converter qref ; According to the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current, the d-axis voltage reference value u corresponding to the computer-side converter drefm ; According to the active power feedback value, the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current, the q-axis voltage reference value u corresponding to the computer-side converter is qrefm ; According to the synchronous machine output electrical angular velocity, determine the machine side phase θ m ; The pitch angle β is determined based on the synchronous machine output electrical angular velocity, the maximum allowable speed value and the maximum allowable speed deviation.

6. The frequency support control method for a grid-following direct-drive fan according to claim 5 is characterized in that: The d-axis voltage reference value u corresponding to the grid-side converter is calculated according to the DC voltage feedback value, the DC voltage reference value, the grid-side inductor current d-axis feedback value, the grid-side inductor current q-axis feedback value, and the common coupling point AC voltage d-axis feedback value. dref ,include: Substitute the DC voltage feedback value, DC voltage reference value, grid-side inductor current d-axis feedback value, grid-side inductor current q-axis feedback value, and common coupling point AC voltage d-axis feedback value into the grid-side d-axis voltage calculation formula to obtain the d-axis voltage reference value u corresponding to the grid-side converter. dref ; The grid-side d-axis voltage calculation formula satisfies the following conditions: In the formula, u dc is the DC voltage feedback value, u dcref is the DC voltage reference value, T dc is the filtering time constant of the DC voltage, i cd is the d-axis feedback value of the grid-side inductor current, i cq is the q-axis feedback value of the grid-side inductor current, u d is the d-axis feedback value of the AC voltage at the common coupling point, k pdc With k idc The DC voltage PI is dc The proportionality coefficient and integration coefficient, k pi With k ii They are the current inner loop PI i The proportionality coefficient and integration coefficient, k f With k d are the feedforward coefficient and the cross decoupling coefficient respectively, and s is the Laplace operator.

7. The frequency support control method of a grid-following direct-drive fan according to claim 5, characterized in that: The q-axis voltage reference value u corresponding to the grid-side converter is calculated according to the AC voltage amplitude reference value, the voltage amplitude feedback value, the reactive power feedback value, the reactive power reference value, the grid-side inductor current d-axis feedback value, the grid-side inductor current q-axis feedback value, and the common coupling point AC voltage q-axis feedback value. qref ,include: Substitute the AC voltage amplitude reference value, voltage amplitude feedback value, reactive power feedback value, reactive power reference value, grid-side inductor current d-axis feedback value, grid-side inductor current q-axis feedback value, and common coupling point AC voltage q-axis feedback value into the grid-side q-axis voltage reference value calculation formula to obtain the q-axis voltage reference value u corresponding to the grid-side converter. qref ; Wherein, the grid-side q-axis voltage reference value calculation formula satisfies the following conditions: In the formula, k pq With k iq Reactive power control PI q The proportional and integral coefficients, Q ref with U ref are reactive power reference value and AC voltage amplitude reference value, Q out with U mag are reactive power feedback value and AC voltage amplitude feedback value respectively, k q is the voltage reactive power droop coefficient, k pi With k ii They are the current inner loop PI i The proportionality coefficient and integration coefficient, k f With k d are the feedforward coefficient and the cross-decoupling coefficient, i cq is the q-axis feedback value of the grid-side inductor current, i cd is the d-axis feedback value of the grid-side inductor current, u q The q-axis feedback value of the AC voltage at the common coupling point, s is the Laplace operator.

8. The frequency support control method for a grid-following direct-drive fan according to claim 5, characterized in that: According to the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current, the d-axis voltage reference value u corresponding to the computer-side converter drefm ,include: Substitute the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current into the calculation formula of the machine-side d-axis voltage reference value to obtain the d-axis voltage reference value u corresponding to the machine-side converter. drefm ; Wherein, the calculation formula of the machine side d-axis voltage reference value meets the following conditions: In the formula, k pi With k ii They are the current inner loop PI i The proportional coefficient and integral coefficient, i md is the d-axis feedback value of the machine-side inductor current, i mq is the q-axis feedback value of the machine-side inductor current, k dm is the cross-decoupling coefficient, and s is the Laplace operator.

9. The frequency support control method of a grid-following direct-drive fan according to claim 5, characterized in that: According to the active power feedback value, the d-axis feedback value of the machine-side inductor current and the q-axis feedback value of the machine-side inductor current, the q-axis voltage reference value u corresponding to the computer-side converter is calculated. qrefm ,include: Substitute the active power feedback value, the d-axis feedback value of the machine-side inductor current, and the q-axis feedback value of the machine-side inductor current into the calculation formula of the machine-side q-axis voltage reference value to obtain the q-axis voltage reference value u corresponding to the machine-side converter. qrefm ; Among them, the calculation formula of the machine-side q-axis voltage reference value meets the following conditions: In the formula, k pp With k ip PI is the proportional integral of the active power controller p The proportional coefficient and integral coefficient, P ref is the active power reference value, P out is the active power feedback value, k pi With k ii They are the current inner loop PI i The proportional coefficient and integral coefficient, i md is the d-axis feedback value of the machine-side inductor current, i mq is the q-axis feedback value of the inductor current on the machine side, ω0 and ψ r are the rated speed of the fan and the rotor flux, k dm is the cross-decoupling coefficient, and s is the Laplace operator.

10. The frequency support control method of a grid-following direct-drive fan according to claim 5, characterized in that: Determining the pitch angle β according to the synchronous machine output electrical angular velocity, the maximum allowable speed value and the maximum allowable speed deviation value includes: Substitute the synchronous machine output electrical angular velocity, the maximum allowable speed value and the maximum allowable speed deviation into the pitch angle calculation formula to obtain the pitch angle β; wherein the pitch angle calculation formula satisfies the following conditions: In the formula, k ppitch With k ipitch are the proportional and integral coefficients of pitch control, ω sm is the output electrical angular velocity of the synchronous machine, ω max With Δω max are the maximum allowable speed value and the maximum allowable speed deviation respectively, and s is the Laplace operator.

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