Autonomous voltage supporting method and device for network-forming converter and medium

Abstract

The invention discloses an autonomous voltage support method and device for a network-constructed converter and a medium, and the method comprises the steps: constructing a converter network-constructed control topological structure, determining a droop control output frequency and a droop control output voltage amplitude according to the topological structure, obtaining the resistance and inductance of a power grid, and the voltage and current of a PCC point, and carrying out the control of the droop control output frequency and the droop control output voltage amplitude. The droop control output frequency and the droop control output voltage amplitude are combined to obtain droop control positive and negative sequence active / reactive reference power, so that an autonomous voltage support strategy is generated to carry out coordinated adjustment of a voltage outer loop / current inner loop, and the real-time impedance measurement is combined with reference power calculation based on autonomous voltage support to obtain the real-time impedance of the droop control output frequency and the droop control output voltage amplitude. According to the invention, accurate voltage support and power adjustment of the grid-forming converter in the weak power grid can be realized, the correctness of the support method is improved, the support capability of the grid-forming converter can be obviously improved, and the power quality and the power supply reliability of the grid-forming converter in the weak power grid with low short circuit ratio and high impedance can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of converters, and in particular to an autonomous voltage support method, device and medium for a grid-type converter. Background Art

[0002] The share of renewable energy generation has increased rapidly in the past decade, and most of them are connected to the grid through power electronic devices. Due to land resource constraints, large renewable energy power plants are usually located in remote areas, such as deserts or mountainous areas with high wind speeds. This geographical feature leads to long transmission distances, which significantly increases the electrical impedance of the transmission line and significantly reduces the short-circuit ratio of the grid. In this case, the weak current characteristics of the grid (low short-circuit ratio and high impedance) pose a severe challenge to the stable operation of the grid-connected converter. In addition, compared with traditional synchronous generators, the power electronic devices in renewable energy systems lack physical rotational inertia, resulting in the new power system showing low inertia and weak damping characteristics. This characteristic weakens the grid's ability to respond to disturbances and the stability of the system, thereby affecting the ability to form a grid and operate reliably. To address this problem, grid-forming control can be added to the converter and certain auxiliary services, such as autonomous voltage support, can be provided to improve the quality of power supply in weak grids and ensure the power supply reliability of point of common coupling (PCC) loads.

[0003] However, the basic principle of the current grid-based control method, which takes droop control as an example, is to influence the voltage and current dual-loop input of the converter by adjusting the reference power. The implementation of autonomous voltage support requires a real-time reference power adjustment strategy, which is directly affected by the impedance characteristics of the grid. In practical applications, the grid impedance may change dynamically or be difficult to obtain accurately, which makes the existing methods perform poorly when facing unknown or changing grid impedance, resulting in limited voltage support effects. In addition, the adjustment accuracy of traditional autonomous voltage support strategies is insufficient, and they fail to fully consider the complexity and nonlinear characteristics in dynamic grid environments. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the existing methods perform poorly when facing unknown or changing grid impedance, which leads to limited voltage support effect, and the adjustment accuracy of traditional autonomous voltage support strategies is insufficient, and the complexity and nonlinear characteristics in the dynamic grid environment are not fully considered. The purpose is to provide an autonomous voltage support method, device and medium for a grid-forming converter. By dynamically estimating the grid impedance and combining the autonomous voltage support reference power algorithm, the limitations brought by unknown grid parameters can be overcome, the reference power can be accurately adjusted, and the autonomous voltage support strategy of the grid-forming converter is optimized. Compared with the problems of inaccuracy and dependence on given grid impedance of traditional methods, by combining real-time impedance measurement with reference power calculation based on autonomous voltage support, accurate voltage support and power adjustment of the grid-forming converter in a weak grid can be achieved, the correctness of the support method can be improved, and at the same time, the support capacity of the grid-forming converter can be significantly improved, so that it can improve the power quality and power supply reliability in a weak grid with low short-circuit ratio and high impedance.

[0005] The present invention is achieved through the following technical solutions:

[0006] A first aspect of the present invention provides an autonomous voltage support method for a grid-connected converter, comprising the following specific steps:

[0007] Constructing the inverter grid control topology structure, and determining the droop control output frequency and the droop control output voltage amplitude according to the topology structure;

[0008] Obtain the grid resistance and grid inductance, the voltage and current of the PCC point, and combine the droop control output frequency and the droop control output voltage amplitude to obtain the droop control positive and negative sequence active / reactive reference power;

[0009] Based on the droop control of positive and negative sequence active / reactive reference power, an autonomous voltage support strategy is generated to coordinate the voltage outer loop / current inner loop.

[0010] Furthermore, the constructed converter network control topology structure includes a converter, a filter inductor Lf1, a filter capacitor Cf, a secondary filter inductor Lf2, a grid impedance Lg, a grid resistor Rg and a weak grid;

[0011] The converter is used to adjust the conversion of DC power to AC power. The converter converts DC power into AC power iL1;

[0012] The AC current iL1 passes through the filter inductor Lf1, the filter capacitor Cf and the secondary filter inductor Lf2 to obtain the filtered output AC current io and AC voltage vo;

[0013] The AC current io and the AC voltage vo are transmitted to the weak grid through the grid impedance Lg and the grid resistance Rg.

[0014] Further, the determining of the droop control output frequency and the droop control output voltage amplitude according to the topology structure specifically includes:

[0015] The droop control output frequency is obtained according to the rated frequency, the active-frequency droop coefficient, the active power output by the converter, the active power reference value, the proportional parameter and the integral parameter of the frequency pre-synchronization PI controller, and the difference between the converter output voltage frequency and the grid voltage;

[0016] The droop control output voltage amplitude is obtained according to the constant voltage amplitude, the reactive-voltage droop coefficient, the reactive power output by the converter, the reactive power reference value, the proportional parameter and the integral parameter of the voltage amplitude pre-synchronization PI controller, and the difference between the converter output voltage amplitude and the grid voltage;

[0017] A droop control strategy is generated according to the droop control output frequency and the droop control output voltage amplitude.

[0018] Furthermore, the calculation step of the droop control output frequency and the droop control output voltage amplitude includes:

[0019]

[0020]

[0021] Where: ω represents the droop control output frequency, V represents the droop control output voltage amplitude, ω ref Indicates rated frequency, V ref Indicates the rated voltage amplitude, k p Indicates the active power-frequency droop coefficient, k q represents the reactive power-voltage droop coefficient, P represents the active power output by the converter, Q represents the reactive power output by the converter, and P ref Indicates the active power reference value, Q ref Represents the reactive power reference value, k p1 represents the frequency presynchronization PI controller proportional parameter, k i1 represents the integral parameter of the frequency presynchronization PI controller, k p2 is the voltage amplitude pre-synchronization PI controller proportional parameter, k i2 is the integral parameter of the voltage amplitude pre-synchronization PI controller.

[0022] Furthermore, the obtaining of the grid resistance and grid inductance specifically includes:

[0023] Fourier analysis is used to extract the corresponding frequency components in voltage and current;

[0024] Determine the frequency-dependent grid impedance based on the extracted voltage frequency component and current frequency component;

[0025] Based on the frequency-dependent grid impedance, the grid resistance and grid inductance are extracted.

[0026] Furthermore, the calculation steps of the grid resistance and grid inductance specifically include:

[0027]

[0028] R g =|Re[Z g (ω)]|=|Re[R g +jX g (ω)]|

[0029]

[0030] Among them, U(ω) represents the disturbance voltage of Fourier transform, I(ω) represents the disturbance current of Fourier transform, U(ω)R g Represents the grid resistance, X g Represents the grid impedance, L g Represents the grid inductance, Z g (ω) represents the impedance of the circuit, ω represents the droop control output frequency, and Im[] represents the impedance Z g The real part of (ω), Re[] represents the impedance Z g The imaginary part of (ω).

[0031] Further, the obtaining of the droop control positive and negative sequence active / reactive reference power specifically includes:

[0032] Calculate the AC current and AC voltage of the filtered output of the PCC point;

[0033] Convert AC current and AC voltage into voltage and current in dq coordinate system and voltage and current in α-β coordinate system;

[0034] According to the voltage and current in the dq coordinate system and the voltage and current in the α-β coordinate system, combined with the grid resistance and grid inductance, the converter current reference value is determined;

[0035] Calculate the active / reactive output of the converter through the converter current reference value;

[0036] According to the converter current reference value and the active / reactive output of the converter, the droop control positive and negative sequence active / reactive reference power is obtained.

[0037] Furthermore, the calculation step of the droop control positive and negative sequence active / reactive reference power specifically includes:

[0038]

[0039]

[0040] Among them, P ref Indicates the positive and negative sequence active power reference of droop control, Q ref Represents the positive and negative sequence reactive power reference power for droop control, ω c represents the characteristic angular frequency of the dynamic response, s represents the complex frequency variable, which is used to describe the dynamic characteristics of the system, V gd represents the voltage component of the d-axis, I loadd represents the load current component of the d-axis, V gq represents the voltage component of the q axis, I loadq represents the load current component of the q axis, V ref Indicates the reference voltage, V g Represents the grid voltage, R g Represents the grid resistance, X g Represents the grid impedance.

[0041] A second aspect of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, an autonomous voltage support method for a grid-connected converter is implemented.

[0042] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements an autonomous voltage support method for a grid-connected converter.

[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0044] By dynamically estimating the grid impedance and combining it with an autonomous voltage support reference power algorithm, the limitations brought by unknown grid parameters can be overcome, the reference power can be accurately adjusted, and the autonomous voltage support strategy of the grid-forming converter can be optimized. Compared with the traditional method, which is inaccurate and relies on a given grid impedance, by combining real-time impedance measurement with reference power calculation based on autonomous voltage support, the precise voltage support and power adjustment of the grid-forming converter in a weak grid can be achieved, the correctness of the support method can be improved, and at the same time, the support capacity of the grid-forming converter can be significantly improved, thereby improving the power quality and power supply reliability in a weak grid with a low short-circuit ratio and high impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0046] Figure 1 This is an autonomous voltage support process in an embodiment of the present invention;

[0047] Figure 2 is a topological structure in an embodiment of the present invention;

[0048] Figure 3 It is the overall control framework in the embodiment of the present invention;

[0049] Figure 4 The effect comparison between the strategy proposed in the embodiment of the present invention and the traditional support strategy when the voltage is temporarily reduced is shown;

[0050] Figure 5 The figure is a comparison of the supporting effects of the estimated grid impedance control and the actual grid impedance control during voltage sag in the embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0052] As a possible implementation, Figure 1 As shown in the figure, in a weak grid with low short-circuit ratio and high impedance, traditional grid-connected converters face severe challenges in stability and anti-interference performance. Grid-connected converters can improve the inertia level and grid-connecting capability of the system, and adding auxiliary services such as autonomous voltage support to grid-connected converters has become a trend. However, the existing autonomous voltage support method of grid-connected converters is highly dependent on grid impedance and has insufficient adjustment accuracy, making it difficult to adapt to dynamic and complex grid environments. In this case, this embodiment provides an autonomous voltage support method for a grid-type converter, and the implementation process mainly includes three parts: converter grid control, real-time impedance measurement control, and reference power calculation of autonomous voltage support, specifically including constructing a converter grid control topology, determining the droop control output frequency and the droop control output voltage amplitude according to the topology; obtaining the grid resistance and grid inductance, the voltage and current of the PCC point, and combining the droop control output frequency and the droop control output voltage amplitude to obtain the droop control positive and negative sequence active / reactive reference power; based on the droop control positive and negative sequence active / reactive reference power, generate an autonomous voltage support strategy to coordinate the voltage outer loop / current inner loop. By measuring the grid impedance in real time and dynamically estimating its change trend, combined with an autonomous reference power adjustment algorithm, the output power of the grid-type converter can be accurately controlled, thereby optimizing the voltage support effect, improving the voltage support accuracy and dynamic adaptability of the grid-type converter, and improving the quality of power supply in weak power grids, which has significant engineering application value.

[0053] The specific implementation process includes:

[0054] 1. Converter network control

[0055] Droop control is a control strategy widely used in distributed power sources and energy storage systems. Its basic idea is to simulate the characteristics of traditional synchronous generators and achieve stable operation and power distribution of distributed power sources by controlling the relationship between voltage and frequency and active power and reactive power. The present invention adopts droop control as the basic control of the converter, and proposes an autonomous voltage support strategy on this basis. In addition, in order to filter out power fluctuations and improve control accuracy, the active and reactive powers are processed by a first-order low-pass filter.

[0056] At the same time, grid-connected pre-synchronization control is added to enable the converter to switch seamlessly between grid-connected and off-grid modes. This control uses the difference between the converter output voltage amplitude and phase and the grid voltage as a feedback signal, which is adjusted by a proportional integral (PI) controller to generate compensation for the converter voltage and frequency. The droop formula after adding grid-connected pre-synchronization can be expressed as:

[0057]

[0058]

[0059] Where: ω represents the droop control output frequency, V represents the droop control output voltage amplitude, ω ref Indicates rated frequency, V ref Indicates the rated voltage amplitude, k p and k q They represent active-frequency and reactive-voltage droop coefficients respectively. P and Q represent the active and reactive power output of the converter respectively. ref and Q ref Respectively represent the active and reactive power reference values, k p1 , k i1 Respectively represent the proportional and integral parameters of the frequency pre-synchronization PI controller, k p2 , k i2 They represent the proportional and integral parameters of the voltage amplitude pre-synchronization PI controller, Δω mg and ΔV mg Respectively represent the difference between the frequency and amplitude of the converter output voltage and the grid voltage, which can be calculated by the following formula:

[0060] ΔV mg =V g -V o (3)

[0061]

[0062] Where: V g and ω g are the grid voltage amplitude and frequency, Vo and ω o are the converter output voltage amplitude and frequency respectively.

[0063] 2. Impedance parameter measurement

[0064] The grid impedance is measured by the inverter itself: the inverter generates a broadband injection on top of the normal output current, measures the response of the grid voltage, and applies Fourier analysis to extract the corresponding frequency components in the voltage and current. The grid impedance is then determined from the ratio between the perturbed voltage and current.

[0065]

[0066] where Z(ω) is the frequency-dependent grid impedance, and U(ω) and I(ω) are the Fourier transformed disturbance voltage and current.

[0067] Maximum-length binary sequence (MLBS) is widely used for online measurements of grid-connected equipment. MLBS is a periodic binary sequence, so the measurements can be averaged over multiple periods, and MLBS provides the lowest possible crest factor. These characteristics allow for relatively low injection amplitudes while still providing adequate signal-to-noise ratio. In continuous measurements, low injection amplitudes are desirable to minimize output current distortion. MLBS is periodic over a sequence length of N = 2n-1 and can be generated using an n-stage shift register and specific feedback. The frequency resolution of MLBS is defined as: f res =f gen / N, where f gen To generate frequency. Therefore, the measurement time is a sequence period T meas =N / f gen .

[0068] In this work, the disturbance sequence is injected from the inverter side and built into the MLBS generation block inside the inverter control system. The sequence is continuously generated and injected above the d-component current reference. In this setup, a 127-bit long MLBS is generated at 4kHz, so the frequency resolution is about 31.5Hz. The disturbed grid current and voltage are measured using the output sensor inside the LCL filter, and the grid impedance is extracted by Fourier analysis. When the grid impedance is approximated as consisting of only resistive and inductive components below 450Hz, the imaginary part represents the grid inductance and the real part represents the grid resistance. Thus, the estimated grid resistance and inductance are:

[0069] R g =|Re[Z g (ω)]|=|Re[R g +jX g(ω)]| (6)

[0070]

[0071] Among them, U(ω) represents the disturbance voltage of Fourier transform, I(ω) represents the disturbance current of Fourier transform, U(ω)R g Represents the grid resistance, X g Represents the grid impedance, L g Represents the grid inductance, Z g (ω) represents the impedance of the circuit, ω represents the droop control output frequency, the frequency (ω / (2π)) is less than 450Hz, and Im[ ] represents the impedance Z g The real part of (ω), Re[ ] represents the impedance Z g The imaginary part of (ω).

[0072] ③ Reference power calculation based on autonomous voltage support

[0073] When a weak power grid has power quality problems such as voltage sag, the traditional droop control strategy lacks the ability to adjust the reference power, resulting in deviations after support. Therefore, based on the measured impedance parameters, the present invention proposes a reference power calculation method based on autonomous voltage support. The module calculates the appropriate power reference value according to the voltage drop degree, and realizes dynamic adjustment of the power reference value.

[0074] The voltage and current at the PCC point can both be expressed using the αβ coordinate system, where the voltage is expressed as shown in equation (4) and the current is expressed as shown in equation (5).

[0075]

[0076]

[0077] Among them, V o is the voltage amplitude of PCC, I gP and I gQ are the amplitudes of active and reactive currents, respectively; is the phase angle of the voltage phasor; ω is the angular frequency.

[0078] Then, V in equations (8) and (9) o ,I gP ,I gQ Converted to dq coordinate system, we can get:

[0079] V od =V o (10)

[0080] V oq =0 (11)

[0081] Igd =I gP (12)

[0082] I gq =I gQ (13)

[0083] Wherein, formula (10) indicates that the component of the converter output voltage in the αβ coordinate system is equal to the output voltage V o , Formula (11) indicates that the grid voltage component on the q-axis is 0, which usually means that the grid voltage is balanced and has no q-axis component. Formula (12) indicates that the grid current component on the α-axis is equal to the active current I gP , Formula (13) indicates that the component of the grid current on the β axis is equal to the reactive current I gQ .

[0084] The relationship between the PCC point voltage and the grid voltage in the αβ coordinate system is:

[0085]

[0086]

[0087] Where: v oα 、v oβ are the αβ components of the converter output voltage, v g_α 、v g_β are the αβ components of the grid voltage, i gα 、i gβ are the α and β components of the grid current, respectively. Formula (14) describes the relationship between the α component of the converter output voltage and the α component of the grid voltage, the α component of the grid current, and the resistance and inductance of the grid. Formula (15) describes the relationship between the β component of the converter output voltage and the β component of the grid voltage, the β component of the grid current, and the resistance and inductance of the grid.

[0088] Substituting (8)-(9) into (11)-(15) yields:

[0089] V o -V g =I gd R g +I gq ωL g (16)

[0090] Equation (16) expresses the difference between the converter output voltage and the grid voltage as a function of the active and reactive components of the grid current and the resistance and inductance of the grid. This equation can be used to design the converter control strategy to achieve voltage support. From Equation (16), it can be seen that if the weak grid is regarded as resistive rather than purely inductive, the impact of the active current component on the grid voltage support cannot be ignored. ref Substituting into the above equation and considering the load current, the converter current reference value ( and ) can be obtained:

[0091]

[0092]

[0093] Among them I loadd and I loadq is the load current in the dq coordinate system.

[0094] The formulas for calculating the active / reactive output (P and Q) of the converter using a low-pass filter are as follows:

[0095]

[0096]

[0097] Where ω c is the cutoff frequency of the low-pass filter.

[0098] Substituting the current reference values ​​in equations (17)-(18) into equations (19)-(20), we can obtain the positive and negative sequence active / reactive reference power (P ref and Q ref ) is shown in the following formula:

[0099]

[0100]

[0101] The required reference power is sent to the droop control loop to provide autonomous voltage support for the grid, where P ref Indicates the positive and negative sequence active power reference of droop control, Q ref Represents the positive and negative sequence reactive power reference power for droop control, ω c represents the characteristic angular frequency of the dynamic response, s represents the complex frequency variable, which is used to describe the dynamic characteristics of the system, V gd represents the voltage component of the d-axis, I loadd represents the load current component of the d-axis, V gq represents the voltage component of the q axis, I loadq represents the load current component of the q axis, Vref Indicates the reference voltage, V g Represents the grid voltage, R g Represents the grid resistance, X g Represents the grid impedance.

[0102] like Figure 2 As shown in the figure, the converter in the topology is the core device, regulating the conversion of DC side power to AC side. The DC side voltage is 750V. The converter converts DC power into AC power, and outputs AC voltage vo after filtering harmonics through filter inductor Lf1, filter capacitor Cf and secondary filter inductor Lf2. iL1 is the output current of the converter. The AC current io output by the converter after filtering is transmitted to the weak grid through grid impedance Lg and Rg, and the voltage level is converted (380V to 35kV) through the isolation transformer. The AC load is connected to the output end of the system, and the load current is iload. vg and ig are the grid voltage and current respectively.

[0103] like Figure 3 As shown, it is the overall control framework proposed in this embodiment. The control process is based on real-time grid impedance measurement and reference power calculation. The autonomous voltage support function is realized through the cooperation of the upper and lower parts. The upper part includes a real-time impedance measurement module, which uses the dynamic changes of voltage and current to calculate the grid impedance Lg and Rg, and uses it as input to participate in the calculation of reference power Pref and Qref. The lower part includes a droop control link and a voltage outer loop / current inner loop control. According to the calculated reference power, the target voltage uref and frequency ω are adjusted through droop control. Finally, the voltage outer loop and the current inner loop realize precise control of the converter, improve the quality of power supply in weak power grids, and ensure the power supply reliability of the load at the common connection point.

[0104] The system simulation model was built based on MATLAB / Simulink, and the autonomous voltage support performance of the proposed strategy was tested under a 25% voltage sag. Figure 4 As shown in the figure, the grid impedance of the traditional support strategy is directly given. Under normal circumstances, the phase voltage amplitude is 311V, the voltage sag occurs at t = 0.2s, and disappears at t = 0.5s. It can be seen from the figure that the PCC voltage is 0.96pu under the traditional support method, and the PCC voltage is 1.0pu under the proposed support strategy, which verifies the support accuracy of the proposed control strategy.

[0105] Comparison of the supporting effects of estimated grid impedance control and actual grid impedance control Figure 5As shown, both use the reference power calculation based on autonomous voltage support proposed in the present invention. Under normal circumstances, the phase voltage amplitude is 311V, the voltage sag occurs at t=0.2s, and disappears at t=0.5s. As can be seen from the figure, the PCC voltage after the estimated grid impedance control support is almost the same as the actual grid impedance control, which verifies the correctness of the grid-type converter autonomous voltage support method based on real-time grid impedance estimation of weak grids.

[0106] As a possible implementation method, this embodiment provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, an autonomous voltage support method for a grid-connected converter is implemented.

[0107] As a possible implementation, this embodiment provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, an autonomous voltage support method for a grid-connected converter is implemented.

[0108] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An autonomous voltage support method for a grid-connected converter, characterized in that: The specific steps include: Constructing the inverter grid control topology structure, and determining the droop control output frequency and the droop control output voltage amplitude according to the topology structure; Obtain the grid resistance and grid inductance, the voltage and current of the PCC point, and combine the droop control output frequency and the droop control output voltage amplitude to obtain the droop control positive and negative sequence active / reactive reference power; Based on the droop control of positive and negative sequence active / reactive reference power, an autonomous voltage support strategy is generated to coordinate the voltage outer loop / current inner loop.

2. The autonomous voltage support method of a grid-connected converter according to claim 1, characterized in that: The inverter network control topology structure constructed includes an inverter, a filter inductor L f1 、Filter capacitor C f , Secondary filter inductor L f2 , grid impedance L g , Grid resistance R g and weak grids; The converter is used to adjust the conversion of DC power to AC power. L1 ; The alternating current i L1 After filtering inductor L f1 、Filter capacitor C f And the secondary filter inductor L f2 , get the AC current i after filtering o and AC voltage v o ; The alternating current i o and AC voltage v o Through the grid impedance L g and grid resistance R g Transmission to weak grid.

3. The autonomous voltage support method of a grid-connected converter according to claim 1, characterized in that: The step of determining the droop control output frequency and the droop control output voltage amplitude according to the topology structure specifically includes: The droop control output frequency is obtained according to the rated frequency, the active-frequency droop coefficient, the active power output by the converter, the active power reference value, the proportional parameter and the integral parameter of the frequency pre-synchronization PI controller, and the difference between the converter output voltage frequency and the grid voltage; The droop control output voltage amplitude is obtained according to the constant voltage amplitude, the reactive-voltage droop coefficient, the reactive power output by the converter, the reactive power reference value, the proportional parameter and the integral parameter of the voltage amplitude pre-synchronization PI controller, and the difference between the converter output voltage amplitude and the grid voltage; A droop control strategy is generated according to the droop control output frequency and the droop control output voltage amplitude.

4. The autonomous voltage support method of a grid-connected converter according to claim 3, characterized in that: The calculation steps of the droop control output frequency and the droop control output voltage amplitude include: Where: ω represents the droop control output frequency, V represents the droop control output voltage amplitude, ω ref Indicates rated frequency, V ref Indicates the rated voltage amplitude, k p Indicates the active power-frequency droop coefficient, k q represents the reactive power-voltage droop coefficient, P represents the active power output by the converter, Q represents the reactive power output by the converter, and P ref Indicates the active power reference value, Q ref Represents the reactive power reference value, k p1 represents the frequency presynchronization PI controller proportional parameter, k i1 represents the integral parameter of the frequency presynchronization PI controller, k p2 is the voltage amplitude pre-synchronization PI controller proportional parameter, k i2 is the integral parameter of the voltage amplitude pre-synchronization PI controller.

5. The autonomous voltage support method of a grid-connected converter according to claim 1, characterized in that: The obtaining of the grid resistance and grid inductance specifically includes: Fourier analysis is used to extract the corresponding frequency components in voltage and current; Determine the frequency-dependent grid impedance based on the extracted voltage frequency component and current frequency component; Based on the frequency-dependent grid impedance, the grid resistance and grid inductance are extracted.

6. The autonomous voltage support method of a grid-connected converter according to claim 5, characterized in that: The calculation steps of the grid resistance and grid inductance specifically include: R g =|Re[Z g (ω)]|=|Re[R g +jX g (ω)]| Among them, U(ω) represents the disturbance voltage of Fourier transform, I(ω) represents the disturbance current of Fourier transform, U(ω)R g Represents the grid resistance, X g Represents the grid impedance, L g Represents the grid inductance, Z g (ω) represents the impedance of the circuit, ω represents the droop control output frequency, and Im[] represents the impedance Z g The real part of (ω), Re[] represents the impedance Z g The imaginary part of (ω).

7. The autonomous voltage support method of a grid-connected converter according to claim 1, characterized in that: The obtaining of the droop control positive and negative sequence active / reactive reference power specifically includes: Calculate the AC current and AC voltage of the filtered output of the PCC point; Convert AC current and AC voltage into voltage and current in dq coordinate system and voltage and current in α-β coordinate system; According to the voltage and current in the dq coordinate system and the voltage and current in the α-β coordinate system, combined with the grid resistance and grid inductance, the converter current reference value is determined; Calculate the active / reactive output of the converter through the converter current reference value; According to the converter current reference value and the active / reactive output of the converter, the droop control positive and negative sequence active / reactive reference power is obtained.

8. The autonomous voltage support method of a grid-connected converter according to claim 7, characterized in that: The calculation steps of the droop control positive and negative sequence active / reactive reference power specifically include: Among them, P ref Indicates the positive and negative sequence active power reference of droop control, Q ref Represents the positive and negative sequence reactive power reference power for droop control, ω c represents the characteristic angular frequency of the dynamic response, s represents the complex frequency variable, which is used to describe the dynamic characteristics of the system, V gd represents the voltage component of the d-axis, I loadd represents the load current component of the d-axis, V gq represents the voltage component of the q axis, I loadq represents the load current component of the q axis, V ref Indicates the reference voltage, V g Represents the grid voltage, R g Represents the grid resistance, X g Represents the grid impedance.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the autonomous voltage support method for the grid-connected converter according to any one of claims 1 to 8 is implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the autonomous voltage support method for a grid-connected converter as claimed in any one of claims 1 to 8 is implemented.

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