Methods, devices, equipment and media for improving the stability of grid-connected inverters

Abstract

This application relates to the field of inverter technology, and discloses a method for improving the stability of a grid-connected inverter: establishing a small-signal model of DC bus voltage, a small-signal model of internal potential, a small-signal model of phase angle, a small-signal model of reactive power, and a small-signal model of active power; obtaining a first expression based on the small-signal models of internal potential and reactive power; obtaining a second expression based on the small-signal models of phase angle and active power; obtaining a third expression based on the small-signal models of internal potential, phase angle, and the first expression; obtaining a grid-connected inverter impedance model based on the small-signal models of DC bus voltage, internal potential, phase angle, the first expression, the second expression, and the third expression; and determining the stability of the grid-connected inverter based on the hysteresis matrix obtained from the grid-connected inverter impedance model and the grid impedance model. This method aims to increase the disturbance rejection capability of the grid-connected inverter and its adaptability to grid impedance.

Description

Technical Field

[0001] This application relates to the field of inverter technology, and specifically to a method, apparatus, equipment and medium for improving the stability of a grid-connected inverter. Background Technology

[0002] Grid-connected inverters, serving as the power interaction interface between new energy sources and the power grid, are key equipment and core technologies for promoting high-quality power generation, efficient power transmission, and high-quality power consumption. With the continuous increase in distributed photovoltaic (PV) grid connection capacity, grid-connected inverters need to respond to changes in grid voltage and frequency. Specifically, they must autonomously output corresponding active and reactive power based on changes in the voltage and frequency at the grid connection point to maintain voltage and frequency stability in the new power system.

[0003] In existing technologies, the control of grid-connected inverters with voltage and frequency support mainly focuses on the rotor motion equations and stator excitation equations of a simulated synchronous machine, i.e., virtual synchronous mechanism network control. However, some parameter values ​​fluctuate during the operation of the grid-connected inverter, resulting in low stability. Summary of the Invention

[0004] The purpose of this application is to provide a method, apparatus, device, and medium for improving the stability of a grid-connected inverter, in order to solve the technical defect in the prior art that does not take into account the fact that some parameter values ​​will change during the operation of the grid-connected inverter, resulting in inaccurate judgment of the stability of the grid-connected inverter.

[0005] To achieve the above objectives, the first aspect of this application provides a method for improving the stability of a grid-connected inverter. The grid-connected inverter includes a control circuit and a main circuit. The control circuit includes a reactive voltage loop, a virtual impedance loop, an inner current loop, an active frequency loop, a DC bus voltage loop, a multiplier, and a coordinate transformer. The reactive voltage loop, virtual impedance loop, inner current loop, and coordinate transformer are connected sequentially. The DC bus voltage loop and active frequency loop are connected through a multiplier, and after Laplace transformation, they are connected to the coordinate transformer. The coordinate transformer is connected to the equivalent delay loop of the main circuit. The main circuit is connected to the power grid. The inner current loop includes a phase angle compensator for compensating the phase angle of the active power amplitude. The method includes:

[0006] Based on the grid-connected inverter, a small-signal model of the DC bus voltage in the dq coordinate system of the main circuit is established.

[0007] Based on the reactive voltage loop and the active frequency loop, we establish the internal potential small-signal model in the dq coordinate system of the main circuit, the phase angle small-signal model in the dq coordinate system of the active frequency loop, the reactive power small-signal model, and the active power small-signal model.

[0008] Based on the small-signal model of internal potential and the small-signal model of reactive power, the first expression is obtained. The first expression is used to characterize the relationship between the small-signal model of internal potential and the output current and output voltage in the dq coordinate system of the main circuit.

[0009] Based on the phase angle small-signal model and the active power small-signal model, a second expression is obtained. The second expression is used to characterize the relationship between the phase angle small-signal model and the output current and output voltage in the dq coordinate system of the main circuit.

[0010] Based on the internal potential small-signal model, the phase angle small-signal model and the first expression, the third expression is obtained. The third expression is used to characterize the relationship between the phase angle small-signal model and the output current, output voltage and duty cycle in the dq coordinate system of the main circuit.

[0011] Based on the small-signal model of DC bus voltage, the small-signal model of internal potential, the small-signal model of phase angle, the first expression, the second expression, and the third expression, the impedance model of the grid-connected inverter is obtained.

[0012] Based on the impedance model of the grid-connected inverter and the impedance model of the power grid, the hysteresis matrix is ​​obtained;

[0013] The stability of the grid-connected inverter is determined when the Nyquist curves of the eigenvalues ​​of the hysteresis matrix do not encircle the setpoint.

[0014] In this embodiment of the application, the small-signal model of the DC bus voltage includes:

[0015]

[0016] In the formula, C dc The DC-side capacitor of the grid-connected inverter is represented by s, which represents the complex frequency variable, and D is the DC-side capacitor. d0 D represents the steady-state value of the d-axis duty cycle signal in the dq coordinate system of the main circuit of the grid-connected inverter. q0 This represents the steady-state value of the q-axis duty cycle signal in the dq coordinate system of the main circuit of the grid-connected inverter. This represents the disturbance signal of the output current reference value of the grid-connected inverter along the d-axis in the dq coordinate system of the main circuit of the grid-connected inverter. I represents the disturbance signal of the output current reference value of the grid-connected inverter on the q-axis in the dq coordinate system of the main circuit of the grid-connected inverter. d0 I represents the steady-state d-axis component of the grid connection point current in the dq coordinate system of the main circuit of the grid-connected inverter. q0 This represents the steady-state q-axis value of the grid connection point current in the dq coordinate system of the main circuit of the grid-connected inverter. This represents the disturbance signal along the d-axis of the duty cycle signal in the dq coordinate system of the main circuit of the grid-connected inverter, indicating the steady-state value of the duty cycle signal. This represents the q-axis disturbance signal of the duty cycle signal in the dq coordinate system of the main circuit of the grid-connected inverter, representing the steady-state value of the duty cycle signal.

[0017] In this embodiment of the application, the small-signal model of internal potential and the small-signal model of phase angle include:

[0018]

[0019] In the formula, ΔE m Let Δθ represent the small-signal model of internal potential, Δθ represent the small-signal model of phase angle, K represent the reactive power loop inertia coefficient, and D represent the small-signal model of phase angle. q This represents the damping coefficient of the reactive voltage loop. ΔQ represents the d-axis disturbance signal of the actual output voltage of the grid-connected inverter in the active frequency loop dq coordinate system. o G represents the actual reactive power value of the grid-connected inverter. pδ (s) represents the transfer function model of the compensation function for the active power amplitude and phase angle, ΔP o H represents the actual active power of the grid-connected inverter, H represents the inertia coefficient of the active frequency loop, and ω represents the actual active power of the grid-connected inverter. n D represents the rated angular frequency of the power grid. p k represents the damping coefficient of the active frequency loop. pu k represents the proportional gain of the PI controller in the DC bus voltage loop. iu The integral coefficients of the PI controller representing the DC bus voltage loop are given, where the transfer function model of the compensation function for the active power amplitude phase angle includes:

[0020]

[0021] In the formula, T1 represents the first correction coefficient, T2 represents the second correction coefficient, T3 represents the third correction coefficient, and T4 represents the fourth correction coefficient.

[0022] In this embodiment of the application, the first expression includes:

[0023]

[0024] In the formula, U represents the q-axis disturbance signal of the actual output voltage of the grid-connected inverter in the dq coordinate system of the active frequency loop. q0 U represents the steady-state q-axis component of the common grid connection point voltage of the power grid in the active frequency loop dq coordinate system. d0 This represents the steady-state d-axis component of the voltage at the common grid connection point of the power grid in the active frequency loop dq coordinate system. This represents the d-axis disturbance signal of the actual output current of the grid-connected inverter in the dq coordinate system of the active frequency loop. This represents the q-axis disturbance signal of the actual output current of the grid-connected inverter in the dq coordinate system of the active frequency loop.

[0025] In this embodiment of the application, the second expression includes:

[0026]

[0027] In the formula, This represents the steady-state d-axis component of the output voltage of the grid-connected inverter in the dq coordinate system of the main circuit of the grid-connected inverter. This represents the steady-state q-axis component of the output voltage of the grid-connected inverter in the dq coordinate system of the main circuit of the grid-connected inverter.

[0028] In this embodiment of the application, the third expression includes:

[0029] The third expression includes:

[0030]

[0031] In the formula, This represents the disturbance signal of the output voltage reference value of the grid-connected inverter along the d-axis in the dq coordinate system of the main circuit of the grid-connected inverter. This represents the disturbance signal of the output voltage reference value of the grid-connected inverter on the q-axis in the dq coordinate system of the main circuit of the grid-connected inverter.

[0032] In this embodiment of the application, the impedance model of the grid-connected inverter includes:

[0033]

[0034] In the formula, I2 represents the steady-state value of the output current of the grid-connected inverter, and Z... f K represents the filter impedance. PWM G represents the pulse width modulation gain. de (s) represents the transfer function of the equivalent delay loop, G ic (s) represents the transfer function of the PI controller in the inner current loop, G Lv (s) represents the equivalent transfer function of the virtual impedance loop, D d D represents the steady-state value of the modulated signal along the d-axis in the dq coordinate system of the active frequency loop. q This represents the steady-state value of the q-axis modulated signal in the dq coordinate system of the active frequency loop.

[0035] A second aspect of this application provides a stability improvement device for a grid-connected inverter. The grid-connected inverter includes a control circuit and a main circuit. The control circuit includes a reactive voltage loop, a virtual impedance loop, an inner current loop, an active frequency loop, a DC bus voltage loop, a multiplier, and a coordinate transformer. The reactive voltage loop, virtual impedance loop, inner current loop, and coordinate transformer are connected sequentially. The DC bus voltage loop and active frequency loop are connected through a multiplier, and after Laplace transformation, they are connected to the coordinate transformer. The coordinate transformer is connected to the equivalent delay loop of the main circuit. The main circuit is connected to the power grid. The inner current loop includes a phase angle compensator for compensating the phase angle of the active power amplitude. The device includes:

[0036] The first module is used to establish a small-signal model of the DC bus voltage in the dq coordinate system of the main circuit based on the grid-connected inverter.

[0037] The second module is used to establish the internal potential small-signal model, the phase angle small-signal model, the reactive power small-signal model, and the active power small-signal model in the dq coordinate system of the main circuit based on the reactive voltage loop and the active frequency loop.

[0038] The first module is used to obtain a first expression based on the internal potential small-signal model and the reactive power small-signal model. The first expression is used to characterize the relationship between the internal potential small-signal model and the output current and output voltage in the dq coordinate system of the main circuit.

[0039] The second module is used to obtain a second expression based on the phase angle small-signal model and the active power small-signal model. The second expression is used to characterize the relationship between the phase angle small-signal model and the output current and output voltage in the dq coordinate system of the main circuit.

[0040] The third module is used to obtain the third expression based on the internal potential small-signal model, the phase angle small-signal model and the first expression. The third expression is used to characterize the relationship between the phase angle small-signal model and the output current, output voltage and duty cycle in the dq coordinate system of the main circuit.

[0041] The fourth module is used to obtain the impedance model of the grid-connected inverter based on the small-signal model of DC bus voltage, the small-signal model of internal potential, the small-signal model of phase angle, the first expression, the second expression, and the third expression.

[0042] The fifth module is used to obtain the hysteresis matrix based on the impedance model of the grid-connected inverter and the impedance model of the power grid.

[0043] The determination module is used to determine the stability of the grid-connected inverter when the Nyquist curves of the eigenvalues ​​of the hysteresis matrix do not encircle the setpoint.

[0044] A third aspect of this application provides a stability improvement device for a grid-connected inverter, comprising:

[0045] The memory is configured to store instructions; and

[0046] The processor is configured to retrieve instructions from memory and, when executing the instructions, to implement the stability improvement method for the grid-connected inverter described in the first aspect above.

[0047] A fourth aspect of this application provides a machine-readable storage medium storing instructions for causing a machine to execute the stability improvement method for a grid-connected inverter described in the first aspect.

[0048] The above technical solution, based on the small-signal model of DC bus voltage, the small-signal model of internal potential, the small-signal model of phase angle, and the first, second, and third expressions, derives the impedance model of the grid-connected inverter. Based on the impedance model of the grid-connected inverter and the impedance model of the power grid, a hysteresis matrix is ​​obtained. The stability of the grid-connected inverter is determined by whether the Nyquist curves of the eigenvalues ​​of the hysteresis matrix do not encircle the setpoint. By setting a phase angle compensator in the inner current loop to compensate for the active power amplitude phase angle, the disturbance rejection capability of the grid-connected inverter and its adaptability to the power grid impedance are increased, and the stability of the grid-connected inverter can be accurately determined.

[0049] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description

[0050] The accompanying drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the following detailed description to explain the embodiments of this application, but do not constitute a limitation on the embodiments of this application. In the drawings:

[0051] Figure 1 A schematic diagram of the control circuit structure of a grid-connected inverter according to an embodiment of this application is shown.

[0052] Figure 2 A schematic diagram illustrating the topology of a grid-connected system according to an embodiment of this application is shown.

[0053] Figure 3 The schematic diagram illustrates a process flow of a method for improving the stability of a grid-connected inverter according to an embodiment of this application;

[0054] Figure 4 A schematic diagram of the small-signal control block diagram of the control circuit of a grid-connected inverter according to an embodiment of this application is shown.

[0055] Figure 5The illustration schematically shows the Nyquist plot of the grid impedance of 11mH without the addition of a phase angle compensator and a DC bus voltage loop according to an embodiment of this application.

[0056] Figure 6 The illustration shows the Nyquist plot of the grid impedance of 12mH without the addition of a phase angle compensator and a DC bus voltage loop according to an embodiment of this application.

[0057] Figure 7 The diagram schematically illustrates the three-phase current waveforms of a grid-connected inverter with a grid impedance of 11mH without the addition of a phase angle compensator and a DC bus voltage loop, according to an embodiment of this application.

[0058] Figure 8 The diagram schematically illustrates the three-phase current waveforms of a grid-connected inverter with a grid impedance of 12mH without the addition of a phase angle compensator and a DC bus voltage loop, according to an embodiment of this application.

[0059] Figure 9 The illustration schematically shows the Nyquist plot of the grid impedance of 17mH when a phase angle compensator and a DC bus voltage loop are added according to an embodiment of this application.

[0060] Figure 10 The illustration shows a Nyquist plot of the grid impedance of 19mH when a phase angle compensator and a DC bus voltage loop are added according to an embodiment of this application.

[0061] Figure 11 The diagram schematically illustrates the three-phase current waveforms of a grid-connected inverter with a grid impedance of 17mH when a phase angle compensator and a DC bus voltage loop are added according to an embodiment of this application.

[0062] Figure 12 The diagram schematically illustrates the three-phase current waveforms of a grid-connected inverter with a grid impedance of 19mH when a phase angle compensator and a DC bus voltage loop are added according to an embodiment of this application. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for illustration and explanation of the embodiments of this application and are not intended to limit the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0064] It should be noted that the acquisition, transmission, storage, use, and processing of data in the technical solution of this application all comply with the relevant provisions of national laws and regulations. In the embodiments of this application, certain existing industry solutions such as software, components, and models may be mentioned. These should be considered exemplary, intended only to illustrate the feasibility of implementing the technical solution of this application, and do not imply that the applicant has already used or necessarily used such solutions.

[0065] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0066] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0067] This application provides a method for improving the stability of a grid-connected inverter, which includes a control circuit and a main circuit. Figure 1 A schematic diagram of the control circuit structure of a grid-connected inverter according to an embodiment of this application is shown, such as... Figure 1 As shown, the control circuit includes a reactive voltage loop, a virtual impedance loop, an inner current loop, an active frequency loop, a DC bus voltage loop, a multiplier, and a coordinate transformer. The reactive voltage loop, virtual impedance loop, inner current loop, and coordinate transformer are connected in sequence. The DC bus voltage loop and active frequency loop are connected through a multiplier, and after Laplace transformation, they are connected to the coordinate transformer. The coordinate transformer is connected to the equivalent delay loop of the main circuit. The main circuit is connected to the power grid. The inner current loop is equipped with a phase angle compensator for compensating the phase angle of the active power amplitude.

[0068] Figure 2 A schematic diagram illustrating the topology of a grid-connected system according to an embodiment of this application is shown. Figure 2 As shown, the topology of the grid-connected system includes a photovoltaic (PV) panel 200, a voltage converter 210, a grid-connected inverter main circuit 220, and a power grid 230 connected in sequence.

[0069] The voltage converter 210 includes a first capacitor C f1 Inductor L f1 Transistor, diode, and second capacitor C dc First capacitor C f1 The high-voltage and low-voltage terminals are connected to the two ends of the photovoltaic panel 200, and the first capacitor C f1 The high voltage terminal and inductor L f1 The diode is connected to its anode, and the diode's cathode is connected to the second capacitor C. dc The high-voltage terminal of the diode is connected, and the positive terminal of the diode is also connected to the collector of the transistor. The first capacitor C f1 The low-voltage terminal is connected to the emitter of the transistor, and the emitter of the transistor is also connected to the second capacitor C. dc The low-voltage end connection.

[0070] The grid-connected inverter main circuit 220 includes an equivalent delay loop, a three-phase circuit, and three sets of MOSFETs connected in parallel. Each set of MOSFETs includes a first MOSFET and a second MOSFET connected in series. The first MOSFET is located at the upper end of the main circuit, and the second MOSFET is located at the lower end of the main circuit. The three sets of MOSFETs are connected to the three-phase circuit respectively. Each phase of the three-phase circuit includes a second inductor L connected in series. f and the first resistor R f The second inductance L of each phase of a three-phase circuit f These should be connected to the source (S) terminal of the first MOSFET and the drain (D) terminal of the second MOSFET, respectively. The drain terminal of the first MOSFET is connected to the capacitor C. dc The high-voltage terminal of the first MOSFET is connected, and the source (S) terminal of the second MOSFET is connected to the capacitor C. dc The low-voltage side is connected. The equivalent delay loop SPWM2 is connected to the control circuit of the grid-connected inverter.

[0071] The power grid 230 includes multiple power grid inductors, multiple power grid resistors, and multiple power grid voltage sources corresponding to the three-phase circuit. Each phase of the three-phase circuit includes a power grid inductor, a power grid resistor, and a power grid voltage source connected in series, and the power grid voltage source is grounded.

[0072] Figure 3 This illustration schematically shows a flowchart of a method for improving the stability of a grid-connected inverter according to an embodiment of this application, such as... Figure 3 As shown, the method may include the following steps.

[0073] Step 110: Based on the grid-connected inverter, establish a small-signal model of the DC bus voltage in the dq coordinate system of the main circuit;

[0074] In step 110, the DC side voltage u of the grid-connected inverter is taken into account. dcTo mitigate the impact of voltage fluctuations, a small-signal model of the DC bus voltage in the dq coordinate system of the main circuit is established. The dq coordinate system is based on the angle of the grid common connection point (PCC). The small-signal model of the DC bus voltage describes its dynamic behavior under minute disturbances. The stability of the DC bus voltage is crucial for the normal operation of the grid-connected inverter. To analyze the stability of the DC bus voltage, a small-signal model of the DC bus voltage needs to be established to capture the dynamic response of the grid-connected inverter under minute disturbances.

[0075] The small-signal model of DC bus voltage includes:

[0076]

[0077] In the formula, C dc The DC-side capacitor of the grid-connected inverter is represented by s, which represents the complex frequency variable, and D is the DC-side capacitor. d0 D represents the steady-state value of the d-axis duty cycle signal in the dq coordinate system of the main circuit of the grid-connected inverter. q0 This represents the steady-state value of the q-axis duty cycle signal in the dq coordinate system of the main circuit of the grid-connected inverter. This represents the disturbance signal of the output current reference value of the grid-connected inverter along the d-axis in the dq coordinate system of the main circuit of the grid-connected inverter. I represents the disturbance signal of the output current reference value of the grid-connected inverter on the q-axis in the dq coordinate system of the main circuit of the grid-connected inverter. d0 I represents the steady-state d-axis component of the grid connection point current in the dq coordinate system of the main circuit of the grid-connected inverter. q0 This represents the steady-state q-axis value of the grid connection point current in the dq coordinate system of the main circuit of the grid-connected inverter. This represents the disturbance signal along the d-axis of the duty cycle signal in the dq coordinate system of the main circuit of the grid-connected inverter, indicating the steady-state value of the duty cycle signal. This represents the q-axis disturbance signal of the duty cycle signal in the dq coordinate system of the main circuit of the grid-connected inverter, representing the steady-state value of the duty cycle signal.

[0078] Step 120: Based on the reactive voltage loop and the active frequency loop, establish the internal potential small-signal model in the dq coordinate system of the main circuit, the phase angle small-signal model in the dq coordinate system of the active frequency loop, the reactive power small-signal model, and the active power small-signal model.

[0079] In step 120, the internal potential small-signal model linearizes the internal potential by describing its change under small perturbations, thus depicting the dynamic behavior of the internal potential under small-signal perturbations. The phase angle describes the relative frequency shift of the signal; the phase angle small-signal model allows for more accurate analysis of the phase relationship and frequency response in the control circuit.

[0080] The reactive power small-signal model includes:

[0081]

[0082] In the formula, This represents the d-axis disturbance signal of the actual output voltage of the grid-connected inverter in the dq coordinate system of the active frequency loop. U represents the q-axis disturbance signal of the actual output voltage of the grid-connected inverter in the dq coordinate system of the active frequency loop. q0 U represents the steady-state q-axis component of the common grid connection point voltage of the power grid in the active frequency loop dq coordinate system. d0 This represents the steady-state d-axis component of the voltage at the common grid connection point of the power grid in the active frequency loop dq coordinate system. This represents the d-axis disturbance signal of the actual output current of the grid-connected inverter in the dq coordinate system of the active frequency loop. This represents the q-axis disturbance signal of the actual output current of the grid-connected inverter in the dq coordinate system of the active frequency loop.

[0083] The active power small-signal model includes:

[0084]

[0085] The small-signal models of internal potential and phase angle include:

[0086]

[0087] In the formula, ΔE m Let Δθ represent the small-signal model of internal potential, Δθ represent the small-signal model of phase angle, K represent the reactive power loop inertia coefficient, and D represent the small-signal model of phase angle. q This represents the damping coefficient of the reactive voltage loop. ΔQ represents the d-axis disturbance signal of the actual output voltage of the grid-connected inverter in the active frequency loop dq coordinate system. o G represents the actual reactive power value of the grid-connected inverter. pδ (s) represents the transfer function model of the compensation function for the active power amplitude and phase angle, ΔP o H represents the actual active power of the grid-connected inverter, H represents the inertia coefficient of the active frequency loop, and ω represents the actual active power of the grid-connected inverter. n D represents the rated angular frequency of the power grid. p k represents the damping coefficient of the active frequency loop. pu k represents the proportional gain of the PI controller in the DC bus voltage loop. iu The integral coefficients of the PI controller representing the DC bus voltage loop are given, where the transfer function model of the compensation function for the active power amplitude phase angle includes:

[0088]

[0089] In the formula, T1 represents the first correction coefficient, T2 represents the second correction coefficient, T3 represents the third correction coefficient, and T4 represents the fourth correction coefficient.

[0090] Step 130: Based on the small-signal model of internal potential and the small-signal model of reactive power, the first expression is obtained. The first expression is used to characterize the relationship between the small-signal model of internal potential and the output current and output voltage in the dq coordinate system of the main circuit.

[0091] In step 130, by combining the small-signal model of internal potential and the small-signal model of reactive power, the relationship between the small-signal model of internal potential and the output current and output voltage in the dq coordinate system of the main circuit can be obtained. The first expression includes:

[0092]

[0093] Step 140: Based on the phase angle small-signal model and the active power small-signal model, the second expression is obtained. The second expression is used to characterize the relationship between the phase angle small-signal model and the output current and output voltage in the dq coordinate system of the main circuit.

[0094] In step 140, by combining the phase angle small-signal model and the active power small-signal model, the relationship between the phase angle small-signal model and the output current and output voltage in the dq coordinate system of the main circuit can be obtained. The second expression includes:

[0095]

[0096] In the formula, This represents the steady-state d-axis component of the output voltage of the grid-connected inverter in the dq coordinate system of the main circuit of the grid-connected inverter. This represents the steady-state q-axis component of the output voltage of the grid-connected inverter in the dq coordinate system of the main circuit of the grid-connected inverter.

[0097] Step 150: Based on the internal potential small-signal model, the phase angle small-signal model, and the first expression, the third expression is obtained. The third expression is used to characterize the relationship between the phase angle small-signal model and the output current, output voltage, and duty cycle in the dq coordinate system of the main circuit.

[0098] By combining the small-signal model of internal potential, the small-signal model of phase angle, and the first expression, the relationship between the small-signal model of phase angle and the output current, output voltage, and duty cycle in the dq coordinate system of the main circuit can be obtained. The third expression includes:

[0099]

[0100] In the formula, This represents the disturbance signal of the output voltage reference value of the grid-connected inverter along the d-axis in the dq coordinate system of the main circuit of the grid-connected inverter. This represents the disturbance signal of the output voltage reference value of the grid-connected inverter on the q-axis in the dq coordinate system of the main circuit of the grid-connected inverter.

[0101] Step 160: Based on the small-signal model of DC bus voltage, the small-signal model of internal potential, the small-signal model of phase angle, the first expression, the second expression, and the third expression, obtain the impedance model of the grid-connected inverter;

[0102] In step 160, the main circuit dq coordinate system and the active frequency loop dq coordinate system need to be transformed. The transformation formula includes:

[0103]

[0104] In the formula, This represents the d-axis component of the inverter's state variables in the active frequency loop dq coordinate system. δ0 represents the q-axis component of the inverter's state variables in the active frequency loop dq coordinate system, and δ0 represents the steady-state phase angle difference between the inverter's state variables in the main circuit dq coordinate system and the active frequency loop dq coordinate system. This represents the d-axis component of the inverter's state variables in the dq coordinate system of the main circuit. This represents the q-axis component of the inverter's state variables in the dq coordinate system of the main circuit. This represents the steady-state value of the inverter's state variables along the d-axis in the dq coordinate system of the main circuit. This represents the steady-state value of the inverter's state variables along the q-axis in the dq coordinate system of the main circuit.

[0105] Figure 4 The diagram schematically illustrates a small-signal control block diagram of the control circuit of a grid-connected inverter according to an embodiment of this application. Combining the small-signal model of the DC bus voltage, the small-signal model of the internal potential, the small-signal model of the phase angle, the first expression, the second expression, and the third expression obtained in the preceding steps, the small-signal control block diagram of the grid-connected inverter control circuit is drawn, as follows: Figure 4 As shown, the small-signal control block diagram of the grid-connected inverter's control circuit is used to obtain the impedance model of the grid-connected inverter. The impedance model of the grid-connected inverter plays an important role in analyzing the stability of the interaction between the grid-connected inverter and the power grid.

[0106] The impedance model of the grid-connected inverter includes:

[0107]

[0108] In the formula, I2 represents the steady-state value of the output current of the grid-connected inverter, and Z... f K represents the filter impedance. PWM G represents the pulse width modulation gain. de (s) represents the transfer function of the equivalent delay loop, G ic(s) represents the transfer function of the PI controller in the inner current loop, G Lv (s) represents the equivalent transfer function of the virtual impedance loop, D d D represents the steady-state value of the modulated signal along the d-axis in the dq coordinate system of the active frequency loop. q This represents the steady-state value of the q-axis modulated signal in the dq coordinate system of the active frequency loop.

[0109] Step 170: Based on the impedance model of the grid-connected inverter and the impedance model of the power grid, obtain the hysteresis matrix;

[0110] In step 170, combining the impedance model of the grid-connected inverter and the impedance model of the power grid, the resulting hysteresis matrix formula includes:

[0111] L(s) = Y FM (s)Z gdq (s)

[0112] In the formula, L(s) represents the return matrix, Y FM (s) represents the impedance model of the grid-connected inverter, Z gdq (s) represents the impedance model of the power grid.

[0113] Step 180: Determine the stability of the grid-connected inverter if the Nyquist curves of the eigenvalues ​​of the hysteresis matrix do not encircle the setpoint.

[0114] In step 180, to verify the stability of the grid-connected inverter in this embodiment, a stability test of the inverter's impedance model is required. Based on the parameter values ​​in Table 1, a model is constructed in the modeling and simulation software as shown below. Figure 1 A schematic diagram of the control circuit structure of a grid-connected inverter according to an embodiment of this application is shown. Figure 2 A schematic diagram of the topology of a grid-connected system according to an embodiment of this application is shown.

[0115] Table 1

[0116]

[0117] The eigenvalues ​​are calculated based on the cyclic matrix, which includes a first eigenvalue and a second eigenvalue.

[0118] The following analysis, using two cases—without and with phase angle compensators added to the inner current loop—further verifies that the stability improvement method for grid-connected inverters in this application increases the inverter's anti-interference capability and adaptability to grid impedance.

[0119] First, regarding the case where no phase angle compensator is added to the inner current loop. Figure 5The illustration schematically shows the Nyquist plot of the grid impedance of 11mH without the addition of a phase angle compensator and a DC bus voltage loop according to an embodiment of this application. Figure 5 As shown, λ1(s) represents the first eigenvalue of the cyclic matrix, and λ2(s) represents the second eigenvalue of the cyclic matrix. Neither the first nor the second eigenvalue encloses the setpoint (-1, j0). In other words, without the addition of a phase angle compensator and a DC bus voltage loop, the grid-connected inverter maintains stable operation when the grid impedance is 11mH.

[0120] Figure 6 The illustration schematically shows the Nyquist plot of a grid impedance of 12mH without the addition of a phase angle compensator and a DC bus voltage loop, according to an embodiment of this application. Figure 6 As shown, the first eigenvalue does not enclose the setpoint (-1, j0), while the second eigenvalue does. In other words, without adding a phase angle compensator and a DC bus voltage loop, the grid-connected inverter will remain unstable when the grid impedance is 12mH.

[0121] To further verify the aforementioned theoretical analysis, the accuracy was verified by observing the three-phase current waveforms of the grid-connected inverter.

[0122] Figure 7 The diagram schematically illustrates the three-phase current waveforms of a grid-connected inverter with a grid impedance of 11mH, without the addition of a phase angle compensator and a DC bus voltage loop, according to an embodiment of this application. Figure 7 As shown, i 2a i 2b and i 2c This indicates the three-phase current of the grid-connected inverter. Without adding a phase angle compensator and a DC bus voltage loop, the three-phase current of the grid-connected inverter is stable when the grid impedance is 11mH. In other words, without adding a phase angle compensator and a DC bus voltage loop, the grid-connected inverter maintains stable operation when the grid impedance is 11mH.

[0123] Figure 8 The diagram schematically illustrates the three-phase current waveforms of a grid-connected inverter with a grid impedance of 12mH, without the addition of a phase angle compensator and a DC bus voltage loop, according to an embodiment of this application. Figure 8 As shown, when the grid impedance is 12mH without the addition of a phase angle compensator and a DC bus voltage loop, the three-phase current of the grid-connected inverter is distorted. In other words, without the addition of a phase angle compensator and a DC bus voltage loop, the grid-connected inverter loses stability when the grid impedance is 12mH. The grid-connected inverter without the addition of a phase angle compensator and a DC bus voltage loop can only adapt to a grid impedance of up to 11mH.

[0124] Second, regarding the case where a phase angle compensator is added to the inner current loop. Figure 9The illustration schematically shows the Nyquist plot of the grid impedance of 17mH when a phase angle compensator and a DC bus voltage loop are added according to an embodiment of this application. Figure 9 As shown, λ1(s) represents the first eigenvalue of the eigenvalue matrix, and λ2(s) represents the second eigenvalue of the eigenvalue matrix. Neither the first nor the second eigenvalue encloses the setpoint (-1, j0). In other words, when the grid-connected inverter is equipped with a phase angle compensator and a DC bus voltage loop, and the grid impedance is 17mH, the grid-connected inverter maintains stable operation.

[0125] Figure 10 The illustration schematically shows the Nyquist plot of the grid impedance of 19mH when a phase angle compensator and a DC bus voltage loop are added according to an embodiment of this application. Figure 10 As shown, the first eigenvalue does not enclose the setpoint (-1, j0), while the second eigenvalue does. This means that when a phase angle compensator and a DC bus voltage loop are added, the grid-connected inverter loses stability when the grid impedance is 19mH.

[0126] To further verify the aforementioned theoretical analysis, the accuracy was verified by observing the three-phase current waveforms of the grid-connected inverter.

[0127] Figure 11 The diagram schematically illustrates the three-phase current waveforms of a grid-connected inverter with a grid impedance of 17mH when a phase angle compensator and a DC bus voltage loop are added according to an embodiment of this application. Figure 11 As shown, i 2a i 2b and i 2c This indicates the three-phase current of the grid-connected inverter. With the addition of a phase angle compensator and a DC bus voltage loop, the three-phase current of the grid-connected inverter remains stable when the grid impedance is 17mH. In other words, with the addition of a phase angle compensator and a DC bus voltage loop, the grid-connected inverter maintains stable operation when the grid impedance is 17mH.

[0128] Figure 12 The diagram schematically illustrates the three-phase current waveforms of a grid-connected inverter with a grid impedance of 19mH when a phase angle compensator and a DC bus voltage loop are added according to an embodiment of this application. Figure 12 As shown, when a phase angle compensator and a DC bus voltage loop are added, and the grid impedance is 19mH, the three-phase current of the grid-connected inverter becomes distorted. In other words, when the grid impedance is 19mH, the grid-connected inverter with added phase angle compensators and a DC bus voltage loop loses stability.

[0129] The stability improvement method for grid-connected inverters in this application embodiment considers the impact of DC-side voltage fluctuations in the grid-connected inverter. It adds a DC bus voltage loop and a phase angle compensator for compensating the active power amplitude phase angle in the inner current loop. This enhances the anti-interference capability of the photovoltaic grid-connected inverter, significantly increases the adaptability of the grid-connected inverter to grid impedance, and solves the technical problem of difficulty in improving the stability of grid-connected inverters. The grid-connected inverter in this application embodiment can adapt to a grid impedance of 17mH, improving the safe and stable operation capability of the grid-connected inverter.

[0130] Corresponding to the stability improvement method for grid-connected inverters provided in this application embodiment, this application embodiment also provides a stability improvement device for grid-connected inverters. The grid-connected inverter includes a control circuit and a main circuit. The control circuit includes a reactive voltage loop, a virtual impedance loop, an inner current loop, an active frequency loop, a DC bus voltage loop, a multiplier, and a coordinate transformer. The reactive voltage loop, virtual impedance loop, inner current loop, and coordinate transformer are connected sequentially. The DC bus voltage loop and active frequency loop are connected through a multiplier, and after Laplace transformation, they are connected to the coordinate transformer. The coordinate transformer is connected to the equivalent delay loop of the main circuit. The main circuit is connected to the power grid. The inner current loop is provided with a phase angle compensator for compensating the phase angle of the active power amplitude. The device includes:

[0131] The first module is used to establish a small-signal model of the DC bus voltage in the dq coordinate system of the main circuit based on the grid-connected inverter.

[0132] The second module is used to establish the internal potential small-signal model, the phase angle small-signal model, the reactive power small-signal model, and the active power small-signal model in the dq coordinate system of the main circuit based on the reactive voltage loop and the active frequency loop.

[0133] The first module is used to obtain a first expression based on the internal potential small-signal model and the reactive power small-signal model. The first expression is used to characterize the relationship between the internal potential small-signal model and the output current and output voltage in the dq coordinate system of the main circuit.

[0134] The second module is used to obtain a second expression based on the phase angle small-signal model and the active power small-signal model. The second expression is used to characterize the relationship between the phase angle small-signal model and the output current and output voltage in the dq coordinate system of the main circuit.

[0135] The third module is used to obtain the third expression based on the internal potential small-signal model, the phase angle small-signal model and the first expression. The third expression is used to characterize the relationship between the phase angle small-signal model and the output current, output voltage and duty cycle in the dq coordinate system of the main circuit.

[0136] The fourth module is used to obtain the impedance model of the grid-connected inverter based on the small-signal model of DC bus voltage, the small-signal model of internal potential, the small-signal model of phase angle, the first expression, the second expression, and the third expression.

[0137] The fifth module is used to obtain the hysteresis matrix based on the impedance model of the grid-connected inverter and the impedance model of the power grid.

[0138] The determination module is used to determine the stability of the grid-connected inverter when the Nyquist curves of the eigenvalues ​​of the hysteresis matrix do not encircle the setpoint.

[0139] It is understood that the stability improvement device for grid-connected inverters provided in this application embodiment can realize each process of the defect structure improvement method of copper calcium titanate ceramic in the above embodiment, and can achieve the same technical effect. To avoid repetition, it will not be described again here.

[0140] This application embodiment also provides a stability improvement device for a grid-connected inverter, including:

[0141] The memory is configured to store instructions; and

[0142] The processor is configured to retrieve instructions from memory and, when executing those instructions, implement the aforementioned method for improving the stability of grid-connected inverters. It achieves the same technical effect, and to avoid repetition, will not be elaborated upon here.

[0143] This application also provides a machine-readable storage medium storing instructions that cause a machine to execute the aforementioned method for improving the stability of a grid-connected inverter. This method achieves the same technical effect and will not be repeated here to avoid repetition.

[0144] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0145] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0146] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0147] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0148] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0149] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0150] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0151] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0152] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for improving the stability of a grid-connected inverter, characterized in that, The grid-connected inverter includes a control circuit and a main circuit. The control circuit includes a reactive voltage loop, a virtual impedance loop, an inner current loop, an active frequency loop, a DC bus voltage loop, a multiplier, and a coordinate transformer. The reactive voltage loop, the virtual impedance loop, the inner current loop, and the coordinate transformer are connected sequentially. The DC bus voltage loop and the active frequency loop are connected via a multiplier, and after Laplace transformation, they are connected to the coordinate transformer. The coordinate transformer is connected to the equivalent delay loop of the main circuit. The main circuit is connected to the power grid. The inner current loop includes a phase angle compensator for compensating the phase angle of the active power amplitude. The method includes: Based on the grid-connected inverter, a small-signal model of the DC bus voltage in the dq coordinate system of the main circuit is established. Based on the reactive voltage loop and the active frequency loop, establish the internal potential small-signal model in the dq coordinate system of the main circuit, the phase angle small-signal model in the dq coordinate system of the active frequency loop, the reactive power small-signal model, and the active power small-signal model. Based on the internal potential small-signal model and the reactive power small-signal model, a first expression is obtained. The first expression is used to characterize the relationship between the internal potential small-signal model and the output current and output voltage in the dq coordinate system of the main circuit. Based on the phase angle small-signal model and the active power small-signal model, a second expression is obtained. The second expression is used to characterize the relationship between the phase angle small-signal model and the output current and output voltage in the dq coordinate system of the main circuit. Based on the internal potential small-signal model, the phase angle small-signal model and the first expression, a third expression is obtained. The third expression is used to characterize the relationship between the phase angle small-signal model and the output current, output voltage and duty cycle in the dq coordinate system of the main circuit. Based on the DC bus voltage small-signal model, the internal potential small-signal model, the phase angle small-signal model, the first expression, the second expression, and the third expression, the impedance model of the grid-connected inverter is obtained. Based on the impedance model of the grid-connected inverter and the impedance model of the power grid, the hysteresis matrix is ​​obtained; The grid-connected inverter is determined to be stable if the Nyquist curves of the eigenvalues ​​of the hysteresis matrix do not encircle the setpoint.

2. The method according to claim 1, characterized in that, The small-signal model of the DC bus voltage includes: In the formula, C dc s represents the DC-side capacitor of the grid-connected inverter, s represents the complex frequency variable, and D represents the DC-side capacitor of the grid-connected inverter. d0 D represents the steady-state value of the d-axis duty cycle signal in the dq coordinate system of the main circuit of the grid-connected inverter. q0 This represents the steady-state value of the q-axis duty cycle signal in the dq coordinate system of the main circuit of the grid-connected inverter. This represents the disturbance signal of the output current reference value of the grid-connected inverter along the d-axis in the dq coordinate system of the main circuit of the grid-connected inverter. I represents the disturbance signal of the output current reference value of the grid-connected inverter on the q-axis in the dq coordinate system of the main circuit of the grid-connected inverter. d0 I represents the steady-state d-axis component of the common grid connection point current of the power grid in the dq coordinate system of the main circuit of the grid-connected inverter. q0 This represents the steady-state q-axis value of the common grid connection point current of the power grid in the dq coordinate system of the main circuit of the grid-connected inverter. The steady-state value of the duty cycle signal represents the disturbance signal along the d-axis in the dq coordinate system of the main circuit of the grid-connected inverter. The steady-state value of the duty cycle signal represents the q-axis disturbance signal in the dq coordinate system of the main circuit of the grid-connected inverter.

3. The method according to claim 2, characterized in that, The internal potential small-signal model and the phase angle small-signal model include: In the formula, ΔE m Let Δθ represent the small-signal model of the internal potential, Δθ represent the small-signal model of the phase angle, K represent the reactive power loop inertia coefficient, and D represent the small-signal model of the phase angle. q This represents the damping coefficient of the reactive voltage loop. The actual output voltage value of the grid-connected inverter is represented by the d-axis disturbance signal ΔQ in the active frequency loop dq coordinate system. o G represents the actual reactive power value of the grid-connected inverter. pδ (s) represents the transfer function model of the compensation function for the active power amplitude phase angle, ΔP o H represents the actual active power of the grid-connected inverter, H represents the inertia coefficient of the active frequency loop, and ω represents the actual active power of the grid-connected inverter. n D represents the rated angular frequency of the power grid. p k represents the damping coefficient of the active frequency loop. pu k represents the proportional gain of the PI controller in the DC bus voltage loop. iu The integral coefficients of the PI controller for the DC bus voltage loop are represented, wherein the transfer function model of the compensation function for the active power amplitude phase angle includes: In the formula, T1 represents the first correction coefficient, T2 represents the second correction coefficient, T3 represents the third correction coefficient, and T4 represents the fourth correction coefficient.

4. The method according to claim 3, characterized in that, The first expression includes: In the formula, U represents the q-axis disturbance signal of the actual output voltage of the grid-connected inverter in the dq coordinate system of the active frequency loop. q0 U represents the steady-state component of the common grid connection point voltage of the power grid in the active frequency loop dq coordinate system along the q-axis. d0 This represents the steady-state d-axis component of the common grid connection point voltage of the power grid in the active frequency loop dq coordinate system. This represents the d-axis disturbance signal of the actual output current of the grid-connected inverter in the dq coordinate system of the active frequency loop. This represents the q-axis disturbance signal of the actual output current of the grid-connected inverter in the dq coordinate system of the active frequency loop.

5. The method according to claim 4, characterized in that, The second expression includes: In the formula, This represents the steady-state d-axis component of the output voltage of the grid-connected inverter in the dq coordinate system of the main circuit of the grid-connected inverter. The output voltage of the grid-connected inverter represents the steady-state component of the q-axis in the dq coordinate system of the main circuit of the grid-connected inverter.

6. The method according to claim 5, characterized in that, The third expression includes: In the formula, This represents the disturbance signal of the output voltage reference value of the grid-connected inverter on the d-axis in the dq coordinate system of the main circuit of the grid-connected inverter. This represents the disturbance signal of the output voltage reference value of the grid-connected inverter on the q-axis in the dq coordinate system of the main circuit of the grid-connected inverter.

7. The method according to claim 1, characterized in that, The impedance model of the grid-connected inverter includes: In the formula, I2 represents the steady-state value of the output current of the grid-connected inverter, and Z f K represents the filter impedance. PWM G represents the pulse width modulation gain. de (s) represents the transfer function of the equivalent delay loop, G ic (s) represents the transfer function of the PI controller in the inner current loop, G Lv (s) represents the equivalent transfer function of the virtual impedance loop, D d D represents the steady-state value of the d-axis modulation signal in the dq coordinate system of the active frequency loop. q This represents the steady-state value of the q-axis modulation signal in the dq coordinate system of the active frequency loop.

8. A stability improvement device for a grid-connected inverter, characterized in that, The grid-connected inverter includes a control circuit and a main circuit. The control circuit includes a reactive voltage loop, a virtual impedance loop, an inner current loop, an active frequency loop, a DC bus voltage loop, a multiplier, and a coordinate transformer. The reactive voltage loop, the virtual impedance loop, the inner current loop, and the coordinate transformer are connected sequentially. The DC bus voltage loop and the active frequency loop are connected via a multiplier, and after Laplace transformation, they are connected to the coordinate transformer. The coordinate transformer is connected to the equivalent delay loop of the main circuit. The main circuit is connected to the power grid. The inner current loop includes a phase angle compensator for compensating the phase angle of the active power amplitude. The device includes: The first module is used to establish a small-signal model of the DC bus voltage in the dq coordinate system of the main circuit based on the grid-connected inverter. The second establishment module is used to establish, based on the reactive voltage loop and the active frequency loop, the internal potential small-signal model in the dq coordinate system of the main circuit, the phase angle small-signal model in the dq coordinate system of the active frequency loop, the reactive power small-signal model and the active power small-signal model. The first obtaining module is used to obtain a first expression based on the internal potential small-signal model and the reactive power small-signal model. The first expression is used to characterize the relationship between the internal potential small-signal model and the output current and output voltage in the dq coordinate system of the main circuit. The second obtaining module is used to obtain a second expression based on the phase angle small-signal model and the active power small-signal model. The second expression is used to characterize the relationship between the phase angle small-signal model and the output current and output voltage in the dq coordinate system of the main circuit. The third module is used to obtain a third expression based on the internal potential small-signal model, the phase angle small-signal model and the first expression. The third expression is used to characterize the relationship between the phase angle small-signal model and the output current, output voltage and duty cycle in the dq coordinate system of the main circuit. The fourth module is used to obtain the impedance model of the grid-connected inverter based on the small-signal model of the DC bus voltage, the small-signal model of the internal potential, the small-signal model of the phase angle, the first expression, the second expression, and the third expression. The fifth module is used to obtain the hysteresis matrix based on the impedance model of the grid-connected inverter and the impedance model of the power grid; The determination module is used to determine the stability of the grid-connected inverter when the Nyquist curves of the eigenvalues ​​of the hysteresis matrix do not encircle the setpoint.

9. A stability improvement device for a grid-connected inverter, characterized in that, include: The memory is configured to store instructions; as well as A processor is configured to retrieve the instructions from the memory and, when executing the instructions, to implement the stability improvement method for a grid-connected inverter according to any one of claims 1 to 7.

10. A machine-readable storage medium, characterized in that, The machine-readable storage medium stores instructions for causing the machine to perform the stability improvement method for a grid-connected inverter according to any one of claims 1 to 7.

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