An Adaptive Grid-Following and Grid-Forming Hybrid Control Method and System for Grid-Connected Converters

Abstract

The present invention relates to the technical field of grid-connected converters, and specifically discloses an adaptive grid-following and grid-forming hybrid control method and system for a grid-connected converter. The method includes: in the grid-following control part, calculating the d-axis and q-axis grid-following modulation signals and the grid-following phase angle; in the grid-forming control part, calculating the d-axis and q-axis grid-forming modulation signals and the grid-forming phase angle; generating the phase angle of the hybrid control by weighting the grid-following phase angle and the grid-forming phase angle; weighting the d-axis and q-axis grid-following modulation signals and the d-axis and q-axis grid-forming modulation signals to obtain the modulation signal of the hybrid control; the phase angle of the hybrid control and the modulation signal of the hybrid control are subjected to coordinate transformation and PWM modulation to obtain the switching control signal of the grid-connected converter for the hybrid control. The weight of the modulation signal in the present invention can be dynamically adjusted with the change of the real-time grid impedance, so that the converter can preferentially track the power command to achieve the maximum output under strong grid conditions, and actively enhance the voltage / frequency support ability under weak grid conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-connected converters, and in particular to an adaptive grid-following and grid-forming hybrid control method and system for grid-connected converters. Background Art

[0002] The statements in this part only provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] Grid-connected converters play a key role in new energy power generation and are widely used in systems such as micro-energy, distributed generation, energy storage, AC-DC microgrids, etc. Due to the intermittency, randomness, and output volatility of new energy power generation, the grid strength often fluctuates significantly. Traditional grid-following control or grid-forming control has poor stability in weak grids and strong grids respectively and is difficult to adapt to the working conditions of variable grid strength; traditional grid-following / grid-forming switching control faces problems such as capacity allocation calculation in multi-inverter systems and has significant engineering difficulties in complex systems. Therefore, studying the control scheme of grid-connected converters when the grid impedance fluctuates greatly under high penetration conditions is of great significance for the reliable operation of new energy power generation grid-connected systems.

[0004] Traditional hybrid control strategies synchronize according to the phase angle generated by droop control (classical grid-forming control GFM), fuse PQ control (classical grid-following control GFL) and droop control, and use fixed weight coefficients. Although the system stability can be maintained, it is difficult to achieve the optimal economic benefit; at the same time, under the premise of synchronizing based on droop control, the traditional method is restricted by stability constraints and it is difficult to improve the adjustment freedom and control performance by changing the weight coefficients. This method weights the modulation signals output by PQ control and droop control, improving the stability of the converter under a wide range of short circuit ratios (SCR).

[0005] However, the existing hybrid control methods adopt a fixed weight coefficient hybrid strategy and cannot adjust the control weights in real time when the grid strength changes dynamically, resulting in too high a proportion of grid-forming control in strong grid conditions, which limits the power output capacity, and too large a weight of grid-following control in weak grid conditions, which weakens the support strength for the grid. This rigid control mode is restricted by the constraint of droop control synchronization, resulting in limited adjustment freedom and it is difficult to balance system stability and economy when the grid strength fluctuates widely, easily triggering a series of problems such as a decline in power generation efficiency and limited new energy consumption. Summary of the Invention

[0006] To solve the above problems, the present invention proposes a grid-connected converter adaptive following-network and grid-forming hybrid control method and system, which dynamically adjusts the following-network / grid-forming weight coefficients by real-time sensing of the grid impedance changes, enabling the converter to preferentially track the power command to achieve the maximum output under strong grid conditions, actively enhance the voltage or frequency support ability under weak grid conditions, construct a flexible control architecture matching the grid strength fluctuations, realize the coordinated optimization of the stability and energy conversion efficiency of the new energy grid-connected system, and provide an effective and reliable converter control solution for high-penetration new energy power generation.

[0007] In some embodiments, the following technical solutions are adopted:

[0008] A grid-connected converter adaptive following-network and grid-forming hybrid control method, comprising:

[0009] In the following-network control part, calculate the d-axis and q-axis following-network modulation signals and the following-network phase angle;

[0010] In the grid-forming control part, calculate the d-axis and q-axis grid-forming modulation signals and the grid-forming phase angle;

[0011] Weight the following-network phase angle and the grid-forming phase angle through angle weighting to generate the phase angle of the hybrid control; weight the d-axis and q-axis following-network modulation signals and the d-axis and q-axis grid-forming modulation signals to obtain the modulation signal of the hybrid control; the phase angle of the hybrid control and the modulation signal of the hybrid control are subjected to coordinate transformation and PWM modulation to obtain the switching control signal of the grid-connected converter of the hybrid control.

[0012] Among them, calculate the short-circuit ratio based on the grid impedance, combine the frequency-domain model of the converter output impedance, and solve the maximum critical stability threshold corresponding to different short-circuit ratios respectively under the Nyquist stability criterion based on the frequency-domain characteristics. The maximum critical stability threshold is used as the weight coefficient of the following-network modulation signal corresponding to the short-circuit ratio.

[0013] As a further solution, weighting the following-network phase angle and the grid-forming phase angle through angle weighting to generate the phase angle of the hybrid control specifically includes:

[0014] Convert the following-network phase angle and the grid-forming phase angle into unit vectors respectively, perform a linear combination on the obtained unit vectors to obtain a composite vector, and based on the projections of the composite vector on the x-axis and y-axis and , obtain the hybrid phase angle :

[0015] .

[0016] As a further solution, the composite vector is specifically:

[0017] ;

[0018] Among them, , are unit vectors obtained by converting the grid-following phase angle and the grid-forming phase angle respectively, is the weight coefficient of the grid-following modulation signal, is the weight coefficient of the grid-forming modulation signal.

[0019] As a further solution, the short-circuit ratio is calculated based on the grid impedance, specifically:

[0020] ;

[0021] Among them, is the rated capacity of the converter system connected to the grid, is the short-circuit capacity of the grid, is the rated effective value of the grid voltage, is the modulus value of the grid impedance.

[0022] As a further solution, under the Nyquist stability criterion based on the frequency-domain characteristics, the maximum critical stability thresholds of the weight coefficients of the grid-following modulation signals corresponding to different short-circuit ratios are solved respectively, specifically:

[0023] Adopt the Nyquist stability criterion analysis method based on the frequency-domain characteristics, and sequentially draw the zero-pole distribution diagram of the closed-loop transfer function when the short-circuit ratio is , analyze the pole distribution of the closed-loop transfer function corresponding to the grid-following control right coefficient increasing from 0 to 1, so as to determine the corresponding maximum critical stability threshold ; is the frequency-domain model of the converter output impedance, is the grid impedance.

[0024] As a further solution, the maximum critical stability threshold is used as the weight coefficient of the grid-following modulation signal under the corresponding short-circuit ratio, specifically:

[0025] If , then ;

[0026] Among them, is the short-circuit ratio, is the weight coefficient of the grid-following modulation signal, is the maximum critical stability threshold corresponding to the short-circuit ratio of i.

[0027] As a further solution, in the grid-following control part, the grid-following modulation signals and the grid-following phase angles of the d-axis and q-axis are calculated, specifically:

[0028] Based on the active power reference value, reactive power reference value, and output voltage amplitude, calculate the grid-connected output current reference values on the d-axis and q-axis;

[0029] Subtract the grid-connected output current reference values from the instantaneous current measurement values on the d-axis and q-axis respectively, and then through PI regulation, obtain the grid-connected modulation signals;

[0030] Three-phase output voltage Through abc-dq coordinate transformation, obtain the grid-connected instantaneous output voltage values on the d-axis and q-axis. The grid-connected instantaneous output voltage value on the q-axis passes through a PI controller and an integrator to obtain the grid-connected phase angle.

[0031] As a further solution, in the grid-forming control part, calculate the grid-forming modulation signals and grid-forming phase angle on the d-axis and q-axis. Specifically:

[0032] Calculate the grid-forming output voltage reference value and grid-forming angular frequency on the d-axis through droop control; based on the grid-forming output voltage reference value on the d-axis, calculate the grid-forming output current reference values on the d-axis and q-axis. The grid-forming output current reference values on the d-axis and q-axis are respectively subtracted from the instantaneous output current values of the converters on the d-axis and q-axis, and the differences pass through PI regulators to obtain the grid-forming modulation signals on the d-axis and q-axis;

[0033] Integrate the grid-forming angular frequency to obtain the grid-forming phase angle.

[0034] In some other embodiments, the following technical solutions are adopted:

[0035] A grid-connected converter adaptive grid-following-grid-forming hybrid control system, comprising:

[0036] A grid-following control module, used to calculate the grid-following modulation signals and grid-following phase angle on the d-axis and q-axis in the grid-following control part;

[0037] A grid-forming control module, used to calculate the grid-forming modulation signals and grid-forming phase angle on the d-axis and q-axis in the grid-forming control part;

[0038] A hybrid control module, used to generate the phase angle of hybrid control by angle weighting the grid-following phase angle and grid-forming phase angle; weight the grid-following modulation signals on the d-axis and q-axis and the grid-forming modulation signals on the d-axis and q-axis to obtain the modulation signals of hybrid control; the phase angle of hybrid control and the modulation signals of hybrid control pass through coordinate transformation and PWM modulation to obtain the switching control signals of the grid-connected converter for hybrid control;

[0039] Among them, calculate the short-circuit ratio based on the grid impedance, combine the frequency-domain model of the converter output impedance, and under the Nyquist stability criterion based on frequency-domain characteristics, respectively solve the maximum critical stability thresholds corresponding to different short-circuit ratios. The maximum critical stability thresholds are used as the weight coefficients of the grid-following modulation signals corresponding to the short-circuit ratios.

[0040] In some other embodiments, the following technical solutions are adopted:

[0041] A terminal device includes a processor and a memory. The processor is used to implement instructions; the memory is used to store multiple instructions, and the instructions are adapted to be loaded and executed by the processor to perform the above grid-connected converter adaptive grid-following and grid-forming hybrid control method.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] (1) The present invention determines the weights of the grid-following modulation signal and the grid-forming modulation signal according to the value of the short-circuit ratio, and the value of the short-circuit ratio is calculated based on the real-time grid impedance. Therefore, the weights of the modulation signals can be dynamically adjusted with the change of the real-time grid impedance, enabling the converter to preferentially track the power command to achieve the maximum output under strong grid conditions, and actively enhancing the voltage / frequency support ability under weak grid conditions, constructing a flexible control architecture that matches the fluctuation of the grid strength, and realizing the collaborative optimization of the stability and energy conversion efficiency of the new energy grid-connected system, providing an effective and reliable converter control solution for high-penetration new energy power generation.

[0044] (2) The traditional method uses fixed weight coefficients, resulting in insufficient control freedom. Even when using variable hybrid weight coefficients, the improvement of the control effect is relatively limited. The present invention performs angle weighting on the grid-following phase angle and the grid-forming phase angle, breaking through the above limitations of the traditional method. It not only retains the strong voltage / frequency support of the grid-forming mode in a weak grid but also exhibits good power output characteristics under a strong grid, thus realizing the collaborative optimization of stability and power output under wide-range fluctuations of the grid strength.

[0045] Other features and advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of this aspect. Description of the Drawings

[0046] Figure 1 It is a schematic diagram of the structure of the converter grid-connected system;

[0047] Figure 2 It is a schematic diagram of the adaptive grid-following and grid-forming hybrid control architecture of the grid-connected converter in the embodiment of the present invention;

[0048] Figure 3 It is a schematic diagram of the hybrid angle weighting in the embodiment of the present invention. Detailed Embodiments

[0049] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0050] It should be noted that the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0051] Embodiment 1

[0052] The structure of the converter grid-connected system is as Figure 1 shown, and it includes a DC source, a three-phase bridge PWM inverter, a filter inductor and a filter capacitor to form an LC filter, a grid-side inductor and an AC grid.

[0053] The traditional hybrid method synchronizes based on the phase angle generated by droop control and obtains modulation signals in the grid-following control part and the grid-forming control part respectively, and then weights the modulation signals obtained by the grid-following and grid-forming controls; however, the weight coefficients of the two are usually fixed and cannot be adjusted in real time when the grid strength changes dynamically, resulting in too high a proportion of grid-forming control in strong grid conditions and restricting the power output ability, and too large a weight of grid-following control in weak grid conditions and weakening the support strength for the grid.

[0054] Based on this, in one or more embodiments, an adaptive grid-following-grid-forming hybrid control method for grid-connected converters is disclosed, which combines Figure 2 and specifically includes the following process:

[0055] S101: In the grid-following control part, calculate the d-axis and q-axis grid-following modulation signals and the grid-following phase angle.

[0056] Specifically, in the grid-following control part, given the active and reactive power reference values , and the output voltage amplitude , calculate according to the instantaneous power: , to obtain the d-axis and q-axis grid-following output current reference values and , and then subtract them from the instantaneous current measurement values and respectively, and after PI regulation, obtain the grid-following modulation signals and ; where ; , They respectively represent the instantaneous output voltage values of the converter on the d-axis and q-axis.

[0057] The phase-locked loop adopts a typical synchronous rotating coordinate structure, and the three-phase output voltage is transformed through the abc-dq coordinate transformation to obtain the instantaneous output voltage values following the grid on the d-axis and q-axis and , and the q-axis component passes through a PI controller and an integrator to obtain the phase angle following the grid .

[0058] S102: In the grid-forming control part, calculate the grid-forming modulation signals and the grid-forming phase angle on the d-axis and q-axis.

[0059] Specifically, in the grid-forming control part, the calculation formula for droop control is:

[0060] ;

[0061] Among them, , , , respectively represent the reference value of the grid-forming output voltage on the d-axis, the reactive power droop coefficient, the actual reactive power output of the converter, and the reference value of the given voltage, , , , respectively represent the grid-forming angular frequency, the active power droop coefficient, the actual active power output of the converter, and the reference value of the angular frequency.

[0062] , The calculation formulas of

[0063] are as follows:

[0064] , are respectively the grid-forming voltage deviation value and the grid-forming angular frequency deviation value, and ;

[0065] Integrating can obtain the grid-forming phase angle .

[0066] and 0 are respectively subtracted from the instantaneous output voltage values of the converter on the d-axis and q-axis , , and the difference passes through a PI regulator to obtain the reference values of the grid-forming output currents on the d-axis and q-axis and ; , are respectively compared with the instantaneous output current values of the converter on the d-axis and q-axis , Take the difference. After passing the difference through a PI regulator, the grid-forming modulation signals for the d-axis and q-axis can be obtained. and .

[0067] S103: Weight the grid-following phase angle and the grid-forming phase angle to generate a phase angle for hybrid control; weight the grid-following modulation signals for the d-axis and q-axis and the grid-forming modulation signals for the d-axis and q-axis to obtain a modulation signal for hybrid control; the phase angle for hybrid control and the modulation signal for hybrid control are subjected to coordinate transformation and PWM modulation to obtain the switching control signal for the grid-connected converter in hybrid control.

[0068] The traditional method uses fixed weight coefficients, resulting in insufficient control freedom. If one attempts to use variable hybrid weight coefficients within the framework of the traditional method (generating phase angle synchronization by droop control), the improvement in control effect is also limited. For example, in a strong power grid, the ideal situation is that the grid-following weight coefficient is 1 and the grid-forming weight coefficient is 0, which can improve the new energy consumption rate of the converter; however, restricted by stability constraints, the grid-following weight coefficient cannot be taken as 1 under the premise of droop synchronization.

[0069] In this embodiment, the hybrid control with adjustable weight coefficients based on hybrid phase angle synchronization breaks through the above limitations of the traditional method. It not only retains the strong voltage / frequency support of the grid-forming mode in a weak power grid (grid-forming weight coefficient = 1, grid-following weight coefficient = 0, equivalent to grid-forming control), but also exhibits good power output characteristics in a strong power grid (grid-following weight coefficient = 1, grid-forming weight coefficient = 0, equivalent to grid-following control), thus achieving the coordinated optimization of stability and power output under the condition of wide-range fluctuations in grid strength.

[0070] Specifically, the hybrid angle weighting structure is as Figure 3 shown. By angle weighting, a phase angle for hybrid control is generated. First, use the vector space projection method to , be transformed into unit vectors:

[0071] ;

[0072] ;

[0073] , are the unit vectors obtained by transforming the grid-following phase angle and the grid-forming phase angle respectively. Perform a linear combination of the vectors , to obtain the composite vector , The projections of on the x and y axes are respectively , and the hybrid phase angle 。

[0074] is the weight coefficient of the grid-following modulation signal is the weight coefficient of the grid-forming modulation signal. The determination process of the value of k is described in detail later.

[0075] In this embodiment, the modulation signals obtained by grid-following and grid-forming control are weighted to obtain a modulation signal for hybrid control:

[0076] ;

[0077] wherein, is the weight coefficient of the grid-following modulation signal is the weight coefficient of the grid-forming modulation signal. The modulation signal for hybrid control , and the phase angle After dq / abc coordinate transformation, it is input into PWM modulation to obtain a switching control signal for hybrid control.

[0078] In this embodiment, the determination method of the weight coefficient of the grid-following modulation signal is specifically as follows:

[0079] Based on the grid impedance, calculate the short-circuit ratio. Combining with the frequency-domain model of the converter output impedance, under the Nyquist stability criterion based on frequency-domain characteristics, solve the maximum critical stability threshold corresponding to different short-circuit ratios respectively, and use the maximum critical stability threshold as the weight coefficient of the grid-following modulation signal corresponding to the short-circuit ratio.

[0080] As a specific implementation scheme, considering that the grid impedance is usually inductive, the formula of the grid impedance is , represents the grid inductance, and the relationship between the grid impedance modulus and the grid inductance is , is the angular frequency reference value.

[0081] Calculate the SCR by detecting the grid impedance , wherein, is the rated capacity of the converter system connected to the grid, is the short-circuit capacity of the grid, is the rated effective value of the grid voltage, is the grid impedance modulus.

[0082] Construct a frequency-domain model of the converter output impedance under grid-following-grid-forming hybrid control Specifically:

[0083]

[0084] Among them, represents a complex variable, represents the imaginary unit; and represent the weight coefficients of the grid-following modulation signal and the grid-forming modulation signal respectively; is the filter inductor, is the DC source voltage, is the PWM coefficient; and are the reference values of the grid-following output current in the d-axis and q-axis respectively, and are the active droop coefficient and the reactive droop coefficient of the grid-forming respectively; is the reference value of the angular frequency, is the reference value of the voltage, is the fundamental voltage, is the phase angle of the fundamental current; represents the transfer function of the grid-following control current loop, and represent the transfer functions of the grid-forming control current loop and the voltage loop respectively, represents the transfer function of the phase-locked loop.

[0085] Adopt the Nyquist stability criterion analysis method based on frequency-domain characteristics, and draw the zero-pole distribution diagrams of the closed-loop transfer function when in sequence, analyze the pole distribution of the closed-loop transfer function corresponding to the weight coefficient of the grid-following modulation signal increasing from 0 to 1, so as to determine the corresponding maximum critical stability threshold .

[0086] Determine the weights of the grid-following modulation signal and the grid-forming modulation signal according to the value of the short-circuit ratio:

[0087] ;

[0088] For example: when SCR = 1, i = 1, at this time, then .

[0089] Thus, on the premise of ensuring that the interaction process between the power electronic device and the power grid does not induce oscillation instability, the advantage of the grid-following control for flexible regulation of new energy is maintained to the greatest extent.

[0090] In this embodiment, by dynamically adjusting the grid-following and grid-forming weight coefficients in real-time according to the changes in the grid impedance, the converter can preferentially track the power command to achieve the maximum output under strong grid conditions, and actively enhance the voltage / frequency support ability under weak grid conditions, constructing a flexible control architecture that matches the fluctuations in the grid strength, realizing the collaborative optimization of the stability and energy conversion efficiency of the new energy grid-connected system, and providing an effective and reliable converter control solution for high-penetration new energy power generation.

[0091] Embodiment 2

[0092] In one or more embodiments, a grid-connected converter adaptive grid-following and grid-forming hybrid control system is disclosed, which specifically includes:

[0093] A grid-following control module, which is used to calculate the d-axis and q-axis grid-following modulation signals and the grid-following phase angle in the grid-following control part;

[0094] A grid-forming control module, which is used to calculate the d-axis and q-axis grid-forming modulation signals and the grid-forming phase angle in the grid-forming control part;

[0095] A hybrid control module, which is used to generate the phase angle of hybrid control by weighting the grid-following phase angle and the grid-forming phase angle; weight the d-axis and q-axis grid-following modulation signals and the d-axis and q-axis grid-forming modulation signals to obtain the modulation signal of hybrid control; the phase angle of hybrid control and the modulation signal of hybrid control are subjected to coordinate transformation and PWM modulation to obtain the switching control signal of the grid-connected converter for hybrid control;

[0096] Among them, the short-circuit ratio is calculated based on the grid impedance, combined with the frequency-domain model of the converter output impedance, and under the Nyquist stability criterion based on the frequency-domain characteristics, the maximum critical stability thresholds corresponding to different short-circuit ratios are respectively solved, and the maximum critical stability threshold is used as the weight coefficient of the grid-following modulation signal under the corresponding short-circuit ratio.

[0097] It should be noted that the specific implementation manners of the above-mentioned modules are exactly the same as those in Embodiment 1 and will not be elaborated here.

[0098] Embodiment 3

[0099] In one or more embodiments, a terminal device is disclosed, which includes a processor and a memory. The processor is used to implement instructions; the memory is used to store multiple instructions, and the instructions are suitable for being loaded and executed by the processor to perform the grid-connected converter adaptive grid-following and grid-forming hybrid control method described in Embodiment 1.

[0100] It should be understood that in this embodiment, the processor may be a central processing unit (CPU), and the processor may also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0101] The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A part of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the device type.

[0102] In the implementation process, the steps of the above method may be completed by the integrated logic circuit in the hardware of the processor or the instructions in the form of software.

[0103] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that based on the technical solutions of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. An adaptive grid-following and grid-forming hybrid control method for a grid-connected converter, characterized in that It includes: In the grid-following control part, calculate the d-axis and q-axis grid-following modulation signals and the grid-following phase angle; In the grid-forming control part, calculate the d-axis and q-axis grid-forming modulation signals and the grid-forming phase angle; Angle-weight the grid-following phase angle and the grid-forming phase angle to generate the phase angle for hybrid control; weight the d-axis and q-axis grid-following modulation signals and the d-axis and q-axis grid-forming modulation signals to obtain the modulation signal for hybrid control; the phase angle for hybrid control and the modulation signal for hybrid control undergo coordinate transformation and PWM modulation to obtain the switching control signal for the grid-connected inverter for hybrid control; Among them, calculate the short-circuit ratio based on the grid impedance, combine the frequency-domain model of the converter output impedance, and solve the maximum critical stability threshold corresponding to different short-circuit ratios respectively under the Nyquist stability criterion based on frequency-domain characteristics, and the maximum critical stability threshold is used as the weight coefficient of the grid-following modulation signal corresponding to the short-circuit ratio.

2. The adaptive grid-following and grid-forming hybrid control method for a grid-connected converter according to claim 1, wherein Angle-weight the grid-following phase angle and the grid-forming phase angle to generate the phase angle for hybrid control, specifically: Convert the network-connected phase angle and the network-forming phase angle into unit vectors respectively, perform a linear combination of the obtained unit vectors to obtain a composite vector, and based on the projections of the composite vector on the x and y axes and , obtain the hybrid phase angle : 。 3. The adaptive grid-following and grid-forming hybrid control method for a grid-connected converter according to claim 2, characterized in that, The synthesized vector is specifically: ； Among them, and are unit vectors obtained by transforming the network-following phase angle and network-forming phase angle respectively, is the weight coefficient of the network-following modulation signal, is the weight coefficient of the network-forming modulation signal.

4. The adaptive grid-following and grid-forming hybrid control method for a grid-connected converter according to claim 1, wherein, Calculate the short-circuit ratio based on the grid impedance, specifically: ； Among them, is the rated capacity of the converter system connected to the power grid, is the short-circuit capacity of the power grid, is the rated effective value of the power grid voltage, is the modulus of the power grid impedance.

5. The adaptive grid-following and grid-forming hybrid control method for a grid-connected converter according to claim 1, wherein Under the Nyquist stability criterion based on frequency-domain characteristics, solve the maximum critical stability threshold of the weight coefficient of the grid-following modulation signal corresponding to different short-circuit ratios respectively, specifically: Adopt the Nyquist stability criterion analysis method based on frequency-domain characteristics, and successively plot the short-circuit ratio when the closed-loop transfer function zero-pole distribution diagram, analyze the grid connection control right coefficient increase from 0 to 1 corresponding to the closed-loop transfer function pole distribution, so as to determine the corresponding maximum critical stability threshold ; is the frequency-domain model of the converter output impedance, is the grid impedance.

6. The adaptive grid-following and grid-forming hybrid control method for a grid-connected converter according to claim 1 or 5, characterized in that The maximum critical stability threshold is used as the weight coefficient of the grid-following modulation signal corresponding to the short-circuit ratio, specifically: If , then ; Among them, is the short-circuit ratio, is the weight coefficient of the grid-connected modulation signal, is the maximum critical stability threshold corresponding to the short-circuit ratio of i.

7. The adaptive grid-following and grid-forming hybrid control method for a grid-connected converter according to claim 1, wherein In the grid-following control part, calculate the d-axis and q-axis grid-following modulation signals and the grid-following phase angle, specifically: Based on the active power reference value, reactive power reference value, and output voltage amplitude, calculate the d-axis and q-axis grid-following output current reference values; Subtract the grid-following output current reference values from the d-axis and q-axis instantaneous current measurement values respectively, and then through PI regulation, obtain the grid-following modulation signals; Three-phase output voltage The instantaneous output voltage values of the d-axis and q-axis are obtained through abc-dq coordinate transformation, and the instantaneous output voltage value of the q-axis passes through a PI controller and an integrator to obtain the phase angle following the grid.

8. The adaptive grid-following and grid-forming hybrid control method for a grid-connected converter according to claim 1, characterized in that, In the grid-forming control part, calculate the d-axis and q-axis grid-forming modulation signals and the grid-forming phase angle, specifically: Calculate the grid-forming output voltage reference value and grid-forming angular frequency of the d-axis through droop control; based on the grid-forming output voltage reference value of the d-axis, calculate the d-axis and q-axis grid-forming output current reference values, and subtract the d-axis and q-axis grid-forming output current reference values from the d-axis and q-axis converter instantaneous output current values respectively, and the difference passes through a PI regulator to obtain the d-axis and q-axis grid-forming modulation signals; Integrate the grid-forming angular frequency to obtain the grid-forming phase angle.

9. An adaptive grid-following and grid-forming hybrid control system for a grid-connected converter, characterized in that, It includes: A grid-following control module for calculating the d-axis and q-axis grid-following modulation signals and the grid-following phase angle in the grid-following control part; A grid-forming control module for calculating the d-axis and q-axis grid-forming modulation signals and the grid-forming phase angle in the grid-forming control part; A hybrid control module for angle-weighting the grid-following phase angle and the grid-forming phase angle to generate the phase angle for hybrid control; weighting the d-axis and q-axis grid-following modulation signals and the d-axis and q-axis grid-forming modulation signals to obtain the modulation signal for hybrid control; the phase angle for hybrid control and the modulation signal for hybrid control undergo coordinate transformation and PWM modulation to obtain the switching control signal for the grid-connected inverter for hybrid control; Among them, the short-circuit ratio is calculated based on the grid impedance, combined with the frequency-domain model of the converter output impedance. Under the Nyquist stability criterion based on frequency-domain characteristics, the maximum critical stability thresholds corresponding to different short-circuit ratios are respectively solved, and the maximum critical stability threshold is used as the weight coefficient of the grid-following modulation signal at the corresponding short-circuit ratio.

10. A terminal device, comprising a processor and a memory, the processor being configured to implement instructions; the memory being configured to store a plurality of instructions, characterized in that, The instructions are adapted to be loaded and executed by a processor for the grid-connected converter adaptive grid-following and grid-forming hybrid control method according to any one of claims 1-8.

Images