Three-phase inverter impedance modeling method and system under condition of unbalanced power grid load

Abstract

The invention discloses a three-phase inverter impedance modeling method under the condition of unbalanced power grid load. The method comprises the following steps: determining the total structure of a three-phase grid-connected inverter and the structure of a current controller; obtaining current and voltage of a grid-connected point according to the total structure and the structure of a current controller; under the condition that a phase-locked loop is ignored, positive and negative sequence current components are decoupled; obtaining a transfer function after positive and negative sequence current decoupling, and establishing an inverter impedance model under the condition of ignoring a phase-locked loop according to the expression; under the condition of considering the phase-locked loop, the positive and negative sequence current components are decoupled to obtain an inverter small signal model when the phase-locked loop is considered, an output signal is obtained according to the model, and inverter output impedance and inverter coupling admittance when the phase-locked loop is considered are deduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of distributed renewable energy grid-connected power generation, and relates to a three-phase inverter impedance modeling method and system under the condition of unbalanced grid load. Background Art

[0002] As an important means of utilizing new energy, the capacity proportion of distributed power generation systems in the power grid is continuously increasing; the grid-connected inverter is the key interface connecting distributed generator sets and the power grid. The grid-connected inverter can convert the electricity generated by new energy from direct current to alternating current and transmit it to the power grid. Therefore, the impact of grid-connected inverters on the power quality and stability of power systems is increasingly becoming a hot topic of current research.

[0003] It is a common and effective research method to judge the stability of the grid-connected system by studying the small signal impedance model of the inverter. A large number of studies on inverter impedance modeling assume that the power grid is three-phase balanced. Under this assumption, even if it is an AC time-varying system, the inverter model can be converted to the dq coordinate system through Park transformation, and small signal linearization can be performed at a certain time-invariant steady-state DC operating point. However, in reality, due to reasons such as asymmetric three-phase loads, asymmetric cable arrangement, and asymmetric faults, most three-phase power grids are unbalanced, and negative sequence voltage or negative sequence current will appear, which brings certain challenges to the linear impedance modeling of the inverter.

[0004] In the grid-connected system, the current controller will also affect the impedance model of the inverter. Previous studies have selected a dual synchronous reference frame (DSRF) current controller, which creates two dq coordinate systems, one rotating in the positive sequence direction and the other rotating in the negative sequence direction, and controls the grid voltage and current through the two coordinate systems. In addition, in the case of unbalanced load, a phase-locked loop (PLL) is required to simultaneously track the phase angles of the positive and negative sequence voltages. Currently, there are a variety of phase-locked loops that can track the phase angle of the positive sequence voltage, but there are not many phase-locked loops (PLLs) that can quickly and accurately track the phase angle of the negative sequence voltage. The decoupled dual synchronous reference frame phase-locked loop (DDSRF-PLL) is one of them.

[0005] Although previous studies have applied the decoupled dual synchronous reference frame phase-locked loop (DDSRF-PLL) to small signal impedance modeling in inverter systems, they either ignored the role of the phase-locked loop (PLL) or oversimplified the design of the decoupled dual synchronous reference frame phase-locked loop (DDSRF-PLL) and failed to fully consider the impact of unbalanced factors. These relatively rough modeling methods may not accurately reflect the impedance model of the inverter system in practical applications, causing certain deviations in the stability analysis of the system. Therefore, in the process of impedance modeling, more rigorous research is needed on each part and link to ensure the accuracy and reliability of the stability analysis results. Summary of the invention

[0006] Technical problem: At present, the modeling research of three-phase grid-connected inverter based on dual synchronous reference frame (DSRF) current controller has not fully considered the impact of load imbalance on impedance model, and has not been rigorously processed and analyzed when applying decoupled dual synchronous reference frame phase-locked loop (DDSRF-PLL), which may lead to inaccurate impedance model and affect the stability analysis of grid-connected system. To solve this problem, this paper proposes a three-phase grid-connected inverter impedance modeling method under load imbalance power grid, which can improve the accuracy of inverter grid-connected system stability judgment.

[0007] The present invention provides a three-phase grid-connected inverter impedance modeling method considering load unbalanced power grid:

[0008] Determine the overall structure of the three-phase grid-connected inverter and the structure of the current controller; obtain the grid-connected point current and voltage according to the overall structure and the structure of the current controller;

[0009] Under the condition of ignoring the phase-locked loop, the positive and negative sequence current components are decoupled; the transfer function after the positive and negative sequence currents are decoupled is obtained, and the inverter impedance model under the condition of ignoring the phase-locked loop is established according to the expression;

[0010] When the phase-locked loop is considered, the positive and negative sequence current components are decoupled to obtain the inverter small signal model when the phase-locked loop is considered. The output signal is obtained based on the model, and the inverter output impedance and inverter coupling admittance when the phase-locked loop is considered are derived.

[0011] Furthermore, the inverter is a resistor R L The three-phase grid-connected inverter with an inductor L filter adopts a dual synchronous reference coordinate system current controller and a decoupled dual synchronous reference coordinate system phase-locked loop with a positive and negative sequence component decoupling structure; in order to obtain the frequency domain harmonic linearization model of the inverter, the time domain expressions of the grid-connected point voltage and current of the unbalanced load are considered:

[0012]

[0013] Among them, V p 、V n It represents the amplitude of the positive and negative sequence components of the grid connection point voltage taking into account the unbalanced grid connection point voltage, I p ,I n It represents the amplitude of the positive and negative sequence components of the grid-connected point current taking into account the unbalanced current. is the initial phase angle of each time domain component.

[0014] Ignoring the influence of the phase-locked loop, it is assumed that the positive and negative sequence output phase angle of the phase-locked loop In the case of unbalanced power grid, there is a positive-negative sequence coupling relationship between the electrical components. In order to better study the impact of positive- and negative-sequence components on the impedance model and inverter stability, independent control of positive- and negative-sequence currents is achieved, the positive- and negative-sequence currents are decoupled, and the transfer function expression after the positive- and negative-sequence currents are obtained.

[0015] According to the positive and negative sequence component decoupling structure, in the positive sequence coordinate system, we get:

[0016]

[0017] Where F(s) is the cutoff frequency ω f The low-pass filter is expressed as F(s) = ω f / (s+ω f ); is the current containing positive and negative sequence components under the positive dq axis, is the current that contains only the positive sequence component under the positive dq axis; definition is the transfer function between two current quantities.

[0018] Contains real and imaginary parts, defined as The specific expression is:

[0019]

[0020] Similar to the positive sequence coordinate system, in the negative sequence coordinate system, we have

[0021] In order to simplify the analysis process and provide a reference for building an impedance model when considering the phase-locked loop, the inverter small signal model corresponding to ignoring the phase-locked loop is established. According to the superposition principle, the expression of the output signal grid-connected current of the model under the αβ axis is obtained:

[0022]

[0023] in, is the current reference quantity under the positive sequence αβ axis, is the closed-loop transfer function of the positive sequence current, is the current reference quantity under the negative sequence αβ axis, is the closed-loop transfer function of the negative sequence current;

[0024] is the grid-connected voltage under the αβ axis. The grid-connected voltage is divided into two parts as input signals. One part is generated inside the grid-connected system, and the transfer function Related, inverter output admittance The other part is generated by the feedforward compensation signal, and the transfer function Related, parallel to Additional admittance

[0025] The expressions of the four transfer functions are:

[0026]

[0027]

[0028] When the phase-locked loop is ignored, the inverter output impedance formula is:

[0029]

[0030] Phase-locked loop positive and negative sequence output phase angle θ PLL+ =θ 1+ +Δθ 1+ ,θ PLL- =θ 1- +Δθ 1- The ideal positive and negative sequence dq axes are respectively θ 1+ and θ 1- Rotation, non-ideal positive and negative sequence dq axis according to θ PLL+ and θ PLL- Rotation; using the small angle approximation, the signals in the two coordinate systems are related by the following expression:

[0031]

[0032] in, is the voltage quantity under the non-ideal positive sequence dq axis, is the voltage under the ideal positive sequence dq axis, is the voltage under the non-ideal negative sequence dq axis, is the voltage under the ideal negative sequence dq axis;

[0033] The decoupled dual synchronous reference frame phase-locked loop contains six rotation transformations, which are represented by letters A, B, C, D, E and F. For transformation A, we have:

[0034]

[0035] For transformation B, in steady state, the input of transformation B is About V n , the output is approximately Therefore, the output of transformation B is approximately expressed as:

[0036]

[0037] For transformation C, its output is approximately expressed as:

[0038]

[0039] Transformations D, E, and F are similar to transformations A, B, and C; according to the six transformations in the decoupled dual synchronous reference frame phase-locked loop, the decoupling structure of the phase-locked loop itself is obtained, and then Δθ is obtained. 1+ and Δθ 1- The expression is:

[0040]

[0041]

[0042] in, is the positive sequence dq axis transfer function corresponding to transformation A~F, is the negative sequence dq axis transfer function corresponding to transformation A~F.

[0043] The above expressions are established to describe the behavior of the phase-locked loop under dynamic conditions, including phase tracking error and frequency coupling. These dynamic characteristics will directly affect the output current and voltage of the inverter, and further affect the impedance characteristics of the inverter.

[0044] Considering the transformation in the phase-locked loop, according to the positive and negative sequence component decoupling structure, in the positive sequence coordinate system, we can obtain:

[0045]

[0046] The negative sequence filter current expression is similar to the positive sequence;

[0047] Considering the small interference phase angle of the phase-locked loop, the corresponding inverter small signal model can be obtained. According to the superposition principle, the expression of the output signal grid-connected current of the model under the αβ axis is obtained:

[0048]

[0049] Among them, Δθ 1+ The additional voltage caused By transferring the function Output current, phase-locked loop positive sequence shunt admittance By Δθ 1- The additional voltage caused By transferring the function Output current, phase-locked loop negative sequence shunt admittance Conjugate and frequency-shifted voltage and Through the transfer function and Output current, and They are all negative values ​​of the inverter coupling admittance;

[0050] For the sake of brevity, this is not given here. and The expression of only gives the total impedance expression of the inverter:

[0051]

[0052] The inverter coupling impedance expression is:

[0053]

[0054] Among them, the expressions of A(s) and B(s) are:

[0055]

[0056] Through the above steps, the modeling is finally completed.

[0057] A three-phase inverter impedance modeling system under unbalanced load conditions of a power grid, characterized by comprising:

[0058] A time domain expression module is used to determine the overall structure of the three-phase grid-connected inverter and the structure of the current controller; and obtain the grid-connected point current and voltage according to the overall structure and the structure of the current controller;

[0059] A decoupling module is used to decouple the positive and negative sequence current components while ignoring the phase-locked loop; obtain the transfer function after the positive and negative sequence currents are decoupled, and establish an inverter impedance model while ignoring the phase-locked loop;

[0060] The inverter output impedance module is used to decouple the positive and negative sequence current components when considering the phase-locked loop, obtain the inverter small signal model when considering the phase-locked loop, obtain the output signal based on the model, and derive the inverter output impedance and inverter coupling admittance when considering the phase-locked loop.

[0061] The time domain expression module includes:

[0062] The inverter is with resistor R LThe three-phase grid-connected inverter with an inductor L filter adopts a current controller of a dual synchronous reference coordinate system with a positive and negative sequence component decoupling structure and a decoupled dual synchronous reference coordinate system phase-locked loop; the time domain expressions of the grid-connected point voltage and current considering the unbalanced load are:

[0063]

[0064] Among them, V p 、V n It represents the amplitude of the positive and negative sequence components of the grid connection point voltage taking into account the unbalanced grid connection point voltage, I p ,I n It represents the amplitude of the positive and negative sequence components of the grid-connected point current taking into account the unbalanced current. is the initial phase angle of each time domain component.

[0065] The decoupling module comprises:

[0066] Ignoring the influence of the phase-locked loop, it is assumed that the positive and negative sequence output phase angle of the phase-locked loop According to the positive and negative sequence component decoupling structure, in the positive sequence coordinate system, we get:

[0067]

[0068] Where F(s) is the cutoff frequency ω f The low-pass filter is expressed as F(s) = ω f / (s+ω f ); is the current containing positive and negative sequence components under the positive dq axis, is the current that contains only the positive sequence component under the positive dq axis; definition is the transfer function between two current quantities.

[0069] Contains real and imaginary parts, defined as The specific expression is:

[0070]

[0071] Similar to the positive sequence coordinate system, in the negative sequence coordinate system, we have

[0072] Ignoring the phase-locked loop, the corresponding inverter small signal model is obtained. According to the superposition principle, the expression of the model's output signal grid-connected current under the αβ axis is obtained:

[0073]

[0074] in, is the current reference quantity under the positive sequence αβ axis, is the closed-loop transfer function of the positive sequence current, is the current reference quantity under the negative sequence αβ axis, is the closed-loop transfer function of the negative sequence current;

[0075] is the grid-connected voltage under the αβ axis. The grid-connected voltage is divided into two parts as input signals. One part is generated inside the grid-connected system, and the transfer function Related, inverter output admittance The other part is generated by the feedforward compensation signal, and the transfer function Related, parallel to Additional admittance

[0076] The expressions of the four transfer functions are:

[0077]

[0078] When the phase-locked loop is ignored, the inverter output impedance formula is:

[0079]

[0080] The inverter output impedance module comprises:

[0081] Phase-locked loop positive and negative sequence output phase angle θ PLL+ =θ 1+ +Δθ 1+ ,θ PLL- =θ 1- +Δθ 1- The ideal positive and negative sequence dq axes are respectively θ 1+ and θ 1- Rotation, non-ideal positive and negative sequence dq axis according to θ PLL+ and θ PLL- Rotation; using the small angle approximation, the signals in the two coordinate systems are related by the following expression:

[0082]

[0083] in, is the voltage quantity under the non-ideal positive sequence dq axis, is the voltage under the ideal positive sequence dq axis, is the voltage under the non-ideal negative sequence dq axis, is the voltage under the ideal negative sequence dq axis;

[0084] The decoupled dual synchronous reference frame phase-locked loop contains six rotation transformations, which are represented by letters A, B, C, D, E and F respectively; for transformation A, there are:

[0085]

[0086] For transformation B, in steady state, the input of transformation B is About V n , the output is approximately Therefore, the output of transformation B is approximately expressed as:

[0087]

[0088] For transformation C, its output is approximately expressed as:

[0089]

[0090] Transformations D, E, and F are similar to transformations A, B, and C; according to the six transformations in the decoupled dual synchronous reference frame phase-locked loop, the decoupling structure of the phase-locked loop itself is obtained, and then Δθ is obtained. 1+ and Δθ 1- The expression is:

[0091]

[0092] in, is the positive sequence dq axis transfer function corresponding to transformation A~F, is the negative sequence dq axis transfer function corresponding to transformation A~F.

[0093] The inverter output impedance module comprises:

[0094] Considering the transformation in the phase-locked loop, according to the positive and negative sequence component decoupling structure, in the positive sequence coordinate system, we can obtain:

[0095]

[0096] The negative sequence filter current expression is similar to the positive sequence;

[0097] Considering the small interference phase angle of the phase-locked loop, the corresponding inverter small signal model can be obtained. According to the superposition principle, the expression of the output signal grid-connected current of the model under the αβ axis is obtained:

[0098]

[0099] Among them, Δθ 1+ The additional voltage caused By transferring the function Output current, phase-locked loop positive sequence shunt admittance By Δθ 1- The additional voltage caused By transferring the function Output current, phase-locked loop negative sequence shunt admittance Conjugate and frequency-shifted voltage and Through the transfer function and Output current, and They are all negative values ​​of the inverter coupling admittance;

[0100] The total impedance expression of the inverter is:

[0101]

[0102] The inverter coupling impedance expression is:

[0103]

[0104] Among them, the expressions of A(s) and B(s) are:

[0105]

[0106] Through the above steps, the modeling is finally completed.

[0107] The present invention also provides an electronic device, comprising one or more processors for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors execute the aforementioned multi-converter grid-connected frequency domain stability analysis method based on the system admittance matrix dynamic model.

[0108] The present invention also provides a storage medium storing a computer program, wherein the computer program is configured to execute the aforementioned multi-converter grid-connected frequency domain stability analysis method based on the system admittance matrix dynamic model when running.

[0109] Beneficial effect: The model constructed by the present invention is based on a dual synchronous reference frame (DSRF) current controller, applies a decoupled dual synchronous reference frame phase-locked loop (DDSRF-PLL), and fully considers the load imbalance factor. It can accurately establish the output impedance model of the three-phase grid-connected inverter and improve the accuracy of the grid-connected system stability judgment. BRIEF DESCRIPTION OF THE DRAWINGS

[0110] Figure 1 It is the structural diagram of the three-phase grid-connected inverter.

[0111] Figure 2 It is a block diagram of a current controller based on a dual synchronous reference frame (DSRF).

[0112] Figure 3 It is the structure diagram of the positive and negative sequence component decoupling network.

[0113] Figure 4 It is a control block diagram of a decoupled dual synchronous reference frame phase-locked loop (DDSRF-PLL).

[0114] Figure 5 It is the small signal model of the inverter when the phase-locked loop is ignored.

[0115] Figure 6 It is a decoupling structure diagram of the phase-locked loop (PLL) itself.

[0116] Figure 7 It is the small signal model of the inverter considering the small interference phase angle of the phase-locked loop (PLL).

[0117] Figure 8 Yes V n =5%, I p =I n Verification diagram of inverter output admittance and coupling admittance when =5A.

[0118] Fig. 9 Yes V n =40%, I p =I n Verification diagram of inverter output admittance and coupling admittance when =5A.

[0119] Fig.10 Yes V n =5%, I p =I n Verification diagram of inverter output admittance and coupling admittance when =10A.

[0120] Fig.11 Yes V n =5%, I p =5A, I n Verification diagram of inverter output admittance and coupling admittance when =0A. DETAILED DESCRIPTION

[0121] The following is combined with Figure 1-11 The present invention is further described.

[0122] The present invention proposes a three-phase grid-connected inverter impedance modeling method considering load unbalanced power grid:

[0123] Determine the overall structure of the three-phase grid-connected inverter and the structure of the current controller, and construct the time domain expressions of the grid-connected point voltage and grid-connected point current considering the unbalanced load;

[0124] When the phase-locked loop is ignored, the positive and negative sequence current components are decoupled, and the expression of the inverter output impedance is derived based on the inverter small signal model when the phase-locked loop is ignored.

[0125] According to the structure of the phase-locked loop, the transfer function of each transformation in the phase-locked loop and the expression of the small interference phase angle are derived;

[0126] When the phase-locked loop is considered, the positive and negative sequence current components are decoupled, and the expressions of the inverter output impedance and the inverter coupling admittance are derived based on the inverter small signal model when the phase-locked loop is considered.

[0127] Furthermore, the method specifically includes the following steps:

[0128] Determine the overall structure of the three-phase grid-connected inverter and the structure of the current controller, and construct the time domain expressions of the grid-connected point voltage and grid-connected point current considering the unbalanced load;

[0129] Figure 1 With resistance R L The structure diagram of the three-phase grid-connected inverter with an inductor L filter adopts a dual synchronous reference frame (DSRF) current controller and a decoupled dual synchronous reference frame phase-locked loop (DDSRF-PLL) including a positive and negative sequence component decoupling structure. The block diagram of the DSRF current controller and the positive and negative sequence component decoupling network structure are shown in Figure 1. Figure 2 and 3 As shown, the control block diagram of DDSRF-PLL is as follows Figure 4 As shown. The time domain expressions of unbalanced grid voltage and current are:

[0130]

[0131] Among them, V p 、V n It represents the amplitude of the positive and negative sequence components of the grid connection point voltage taking into account the unbalanced grid connection point voltage, I p ,I n It represents the amplitude of the positive and negative sequence components of the grid-connected point current taking into account the unbalanced current. is the initial phase angle of each time domain component.

[0132] When the phase-locked loop is ignored, the positive and negative sequence current components are decoupled, and the expression of the inverter output impedance is derived based on the inverter small signal model when the phase-locked loop is ignored.

[0133] Ignoring the influence of the phase-locked loop, it is assumed that the positive and negative sequence output phase angle of the phase-locked loop According to Figure 3 The positive and negative sequence component decoupling structure shown in the figure can be obtained in the positive sequence coordinate system:

[0134]

[0135] Properly process the above formula and combine it with Figure 3 ,available:

[0136]

[0137] Where F(s) is the cutoff frequency ω f The low-pass filter is expressed as F(s) = ω f / (s+ω f ); is the current containing positive and negative sequence components under the positive dq axis, is the current that contains only the positive sequence component under the positive dq axis; definition is the transfer function between two current quantities.

[0138] Contains real and imaginary parts, defined as The specific expression is:

[0139]

[0140] Similar to the positive sequence coordinate system, in the negative sequence coordinate system, we have

[0141] Ignoring the phase-locked loop, the corresponding inverter small signal model can be obtained, such as Figure 5 As shown, where Y L (s) = 1 / (Ls + R L ). According to the superposition principle, the expression of the model's output signal grid-connected current under the αβ axis is obtained:

[0142]

[0143] in, is the current reference quantity under the positive sequence αβ axis, is the closed-loop transfer function of the positive sequence current, is the current reference quantity under the negative sequence αβ axis, is the closed-loop transfer function of the negative sequence current; is the grid-connected voltage under the αβ axis, which is divided into two parts as input signals, one part is generated inside the grid-connected system, and the transfer function Related, inverter output admittance The other part is generated by the feedforward compensation signal, and the transfer function Related, parallel to Additional admittance The expressions of the four transfer functions are:

[0144]

[0145] When the phase-locked loop is ignored, the inverter output impedance formula is:

[0146]

[0147] According to the structure of the phase-locked loop, the transfer function of each transformation in the phase-locked loop and the expression of the small interference phase angle are derived;

[0148] Phase-locked loop positive and negative sequence output phase angle θ PLL+ =θ 1+ +Δθ 1+ ,θ PLL- =θ 1- +Δθ 1- The ideal positive and negative sequence dq axes are respectively θ 1+ and θ 1- Rotation, non-ideal positive and negative sequence dq axis according to θ PLL+ and θ PLL- Rotation. Using the small angle approximation, the signals in the two coordinate systems are related by the following expression:

[0149]

[0150] in, is the voltage quantity under the non-ideal positive sequence dq axis, is the voltage under the ideal positive sequence dq axis, is the voltage under the non-ideal negative sequence dq axis, It is the voltage under the ideal negative sequence dq axis.

[0151] like Figure 3 As shown, DDSRF-PLL contains six kinds of rotation transformations, which are represented by letters A, B, C, D, E and F. For transformation A, we have:

[0152]

[0153] For transformation B, in steady state, the input of transformation B is About V n , the output is approximately Therefore, the output of transformation B can be approximately expressed as:

[0154]

[0155] For transformation C, its output can be approximately expressed as:

[0156]

[0157] Transformations D, E, and F are similar to transformations A, B, and C. Based on the six transformations in DDSRF-PLL, we can get Figure 6 The decoupling structure of the phase-locked loop itself is shown, and then Δθ is obtained 1+ and Δθ 1-The expression is:

[0158]

[0159] in, is the positive sequence dq axis transfer function corresponding to transformation A~F, and there is is the negative sequence dq axis transfer function corresponding to transformation A~F, and there is

[0160] When the phase-locked loop is considered, the positive and negative sequence current components are decoupled, and the expressions of the inverter output impedance and the inverter coupling admittance are derived based on the inverter small signal model when the phase-locked loop is considered.

[0161] Considering the transformation in the phase-locked loop, according to the positive and negative sequence component decoupling structure, in the positive sequence coordinate system, we can obtain:

[0162]

[0163] Negative sequence filter current The expression is similar to the positive sequence.

[0164] Considering the small interference phase angle of the phase-locked loop, the corresponding inverter small signal model can be obtained, such as Figure 7 shown.

[0165] According to the superposition principle, the expression of the model's output signal grid-connected current under the αβ axis is obtained:

[0166]

[0167] Among them, Δθ 1+ The additional voltage caused By transferring the function Output current, phase-locked loop positive sequence shunt admittance By Δθ 1- The additional voltage caused By transferring the function Output current, phase-locked loop negative sequence shunt admittance Conjugate and frequency-shifted voltage and Through the transfer function and Output current, and Both are negative values ​​of the inverter coupling admittance.

[0168] For the sake of brevity, this is not given here. and The expression of only gives the total impedance expression of the inverter:

[0169]

[0170] The inverter coupling impedance expression is:

[0171]

[0172] Among them, the expressions of A(s) and B(s) are:

[0173]

[0174] Select V n =5%, I p =I n =5A; V n =40%, I p =I n =5A; V n =5%, I p =I n =10A; V n =5%, I p =5A, I n =0A, four positive and negative sequence grid-connected point voltage and current levels, and simulations are performed under different balance conditions to verify the accuracy of the inverter impedance model proposed in the present invention. Figure 8 V n =5%, I p =I n =Verification diagram of inverter output admittance and coupling admittance when 5A, Fig. 9 V n =40%, I p =I n =Verification diagram of inverter output admittance and coupling admittance when 5A, Fig.10 V n =5%, I p =I n =Verification diagram of inverter output admittance and coupling admittance when 10A, Fig.11 V n =5%, I p =5A, I n = 0A when the inverter output admittance and coupling admittance verification diagram. The results show that the inverter impedance model proposed in the present invention is accurate under different unbalance levels and can effectively improve the accuracy of grid-connected inverter system stability analysis.

[0175] The present invention also relates to an electronic device, comprising one or more processors for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors execute the aforementioned multi-converter grid-connected frequency domain stability analysis method based on the system admittance matrix dynamic model.

[0176] The present invention also relates to a storage medium storing a computer program, wherein the computer program is configured to execute the aforementioned multi-converter grid-connected frequency domain stability analysis method based on the system admittance matrix dynamic model when running.

[0177] Although the present invention has been described above with preferred embodiments, it is not intended to limit the present invention. A person skilled in the art of the present invention may make various modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the definition of the claims.

Claims

1. A three-phase inverter impedance modeling method under unbalanced grid load conditions, characterized in that: The steps include: Determine the overall structure of the three-phase grid-connected inverter and the structure of the current controller; obtain the grid-connected point current and voltage according to the overall structure and the structure of the current controller; Ignoring the phase-locked loop, the positive and negative sequence current components are decoupled; The transfer function after positive and negative sequence current decoupling is obtained, and the inverter impedance model is established when the phase-locked loop is ignored. When the phase-locked loop is considered, the positive and negative sequence current components are decoupled to obtain the inverter small signal model when the phase-locked loop is considered. The output signal is obtained according to the model, and the inverter output impedance and inverter coupling admittance when the phase-locked loop is considered are derived.

2. The three-phase inverter impedance modeling method under the condition of unbalanced power grid load according to claim 1, characterized in that: The inverter is with resistor R L The three-phase grid-connected inverter with an inductor L filter adopts a current controller of a dual synchronous reference coordinate system with a positive and negative sequence component decoupling structure and a decoupled dual synchronous reference coordinate system phase-locked loop; the time domain expressions of the grid-connected point voltage and current considering the unbalanced load are: Among them, V p 、V n It represents the amplitude of the positive and negative sequence components of the grid connection point voltage taking into account the unbalanced grid connection point voltage, I p ,I n It represents the amplitude of the positive and negative sequence components of the grid-connected point current taking into account the unbalanced current. is the initial phase angle of each time domain component.

3. The three-phase inverter impedance modeling method under the condition of unbalanced power grid load according to claim 1, characterized in that: Ignoring the influence of the phase-locked loop, it is assumed that the positive and negative sequence output phase angle of the phase-locked loop According to the positive and negative sequence component decoupling structure, in the positive sequence coordinate system, we get: Where F(s) is the cutoff frequency ω f The low-pass filter is expressed as F(s) = ω f / (s+ω f ); is the current containing positive and negative sequence components under the positive dq axis, is the current that contains only the positive sequence component under the positive dq axis; definition is the transfer function between two current quantities; Contains real and imaginary parts, defined as The specific expression is: Similar to the positive sequence coordinate system, in the negative sequence coordinate system, we have Ignoring the phase-locked loop, the corresponding inverter small signal model is obtained. According to the superposition principle, the expression of the model's output signal grid-connected current under the αβ axis is obtained: in, is the current reference quantity under the positive sequence αβ axis, is the closed-loop transfer function of the positive sequence current, is the current reference quantity under the negative sequence αβ axis, is the closed-loop transfer function of the negative sequence current; is the grid-connected voltage under the αβ axis. The grid-connected voltage is divided into two parts as input signals. One part is generated inside the grid-connected system, and the transfer function Related, inverter output admittance The other part is generated by the feedforward compensation signal, and the transfer function Related, parallel to Additional admittance The expressions of the four transfer functions are: When the phase-locked loop is ignored, the inverter output impedance formula is:

4. The three-phase inverter impedance modeling method under the condition of unbalanced power grid load according to claim 1, characterized in that: Phase-locked loop positive and negative sequence output phase angle θ PLL+ =θ 1+ +Δθ 1+ ,θ PLL- =θ 1- +Δθ 1- The ideal positive and negative sequence dq axes are respectively θ 1+ and θ 1- Rotation, non-ideal positive and negative sequence dq axis according to θ PLL+ and θ PLL- Rotation; using the small angle approximation, the signals in the two coordinate systems are related by the following expression: in, is the voltage quantity under the non-ideal positive sequence dq axis, is the voltage under the ideal positive sequence dq axis, is the voltage under the non-ideal negative sequence dq axis, is the voltage under the ideal negative sequence dq axis; The decoupled dual synchronous reference frame phase-locked loop contains six rotation transformations, which are represented by letters A, B, C, D, E and F respectively; for transformation A, there are: For transformation B, in steady state, the input of transformation B is About V n , the output is approximately Therefore, the output of transformation B is approximately expressed as: For transformation C, its output is approximately expressed as: Transformations D, E, and F are similar to transformations A, B, and C; according to the six transformations in the decoupled dual synchronous reference frame phase-locked loop, the decoupling structure of the phase-locked loop itself is obtained, and then Δθ is obtained. 1+ and Δθ 1- The expression is: in, is the positive sequence dq axis transfer function corresponding to transformation A~F, is the negative sequence dq axis transfer function corresponding to transformation A~F.

5. The three-phase inverter impedance modeling method under the condition of unbalanced power grid load according to claim 1, characterized in that: Considering the transformation in the phase-locked loop, according to the positive and negative sequence component decoupling structure, in the positive sequence coordinate system, we can obtain: The negative sequence filter current expression is similar to the positive sequence; Considering the small interference phase angle of the phase-locked loop, the corresponding inverter small signal model can be obtained. According to the superposition principle, the expression of the output signal grid-connected current of the model under the αβ axis is obtained: Among them, Δθ 1+ The additional voltage caused By transferring the function Output current, phase-locked loop positive sequence shunt admittance By Δθ 1- The additional voltage caused By transferring the function Output current, phase-locked loop negative sequence shunt admittance Conjugate and frequency-shifted voltage and Through the transfer function and Output current, and Both are negative values ​​of the inverter coupling admittance; The total impedance expression of the inverter is: The inverter coupling impedance expression is: Among them, the expressions of A(s) and B(s) are: Through the above steps, the modeling is finally completed.

6. A three-phase inverter impedance modeling system under unbalanced grid load conditions, characterized in that: include: A time domain expression module is used to determine the overall structure of the three-phase grid-connected inverter and the structure of the current controller; According to the overall structure and the structure of the current controller, the grid-connected point current and voltage are obtained; A decoupling module, used for decoupling positive and negative sequence current components while ignoring the phase-locked loop; The transfer function after positive and negative sequence current decoupling is obtained, and the inverter impedance model is established when the phase-locked loop is ignored. The inverter output impedance module is used to decouple the positive and negative sequence current components when considering the phase-locked loop, obtain the inverter small signal model when considering the phase-locked loop, obtain the output signal based on the model, and derive the inverter output impedance and inverter coupling admittance when considering the phase-locked loop.

7. The three-phase inverter impedance modeling system under the condition of unbalanced power grid load according to claim 6, characterized in that: The time domain expression module includes: The inverter is with resistor R L The three-phase grid-connected inverter with an inductor L filter adopts a current controller of a dual synchronous reference coordinate system with a positive and negative sequence component decoupling structure and a decoupled dual synchronous reference coordinate system phase-locked loop; the time domain expressions of the grid-connected point voltage and current considering the unbalanced load are: Among them, V p 、V n It represents the amplitude of the positive and negative sequence components of the grid connection point voltage taking into account the unbalanced grid connection point voltage, I p ,I n It represents the amplitude of the positive and negative sequence components of the grid-connected point current taking into account the unbalanced current. is the initial phase angle of each time domain component.

8. The three-phase inverter impedance modeling system under the condition of unbalanced power grid load according to claim 6, characterized in that: The decoupling module comprises: Ignoring the influence of the phase-locked loop, it is assumed that the positive and negative sequence output phase angle of the phase-locked loop According to the positive and negative sequence component decoupling structure, in the positive sequence coordinate system, we get: Where F(s) is the cutoff frequency ω f The low-pass filter is expressed as F(s) = ω f / (s+ω f ); is the current containing positive and negative sequence components under the positive dq axis, is the current that contains only the positive sequence component under the positive dq axis; definition is the transfer function between two current quantities; Contains real and imaginary parts, defined as The specific expression is: Similar to the positive sequence coordinate system, in the negative sequence coordinate system, we have Ignoring the phase-locked loop, the corresponding inverter small signal model is obtained. According to the superposition principle, the expression of the model's output signal grid-connected current under the αβ axis is obtained: in, is the current reference quantity under the positive sequence αβ axis, is the closed-loop transfer function of the positive sequence current, is the current reference quantity under the negative sequence αβ axis, is the closed-loop transfer function of the negative sequence current; is the grid-connected voltage under the αβ axis. The grid-connected voltage is divided into two parts as input signals. One part is generated inside the grid-connected system, and the transfer function Related, inverter output admittance The other part is generated by the feedforward compensation signal, and the transfer function Related, parallel to Additional admittance The expressions of the four transfer functions are: When the phase-locked loop is ignored, the inverter output impedance formula is:

9. The three-phase inverter impedance modeling system under the condition of unbalanced power grid load according to claim 6, characterized in that: The inverter output impedance module comprises: Phase-locked loop positive and negative sequence output phase angle θ PLL+ =θ 1+ +Δθ 1+ ,θ PLL- =θ 1- +Δθ 1- The ideal positive and negative sequence dq axes are respectively θ 1+ and θ 1- Rotation, non-ideal positive and negative sequence dq axis according to θ PLL+ and θ PLL- Rotation; using the small angle approximation, the signals in the two coordinate systems are related by the following expression: in, is the voltage quantity under the non-ideal positive sequence dq axis, is the voltage under the ideal positive sequence dq axis, is the voltage under the non-ideal negative sequence dq axis, is the voltage under the ideal negative sequence dq axis; The decoupled dual synchronous reference frame phase-locked loop contains six rotation transformations, which are represented by letters A, B, C, D, E and F respectively; for transformation A, there are: For transformation B, in steady state, the input of transformation B is About V n , the output is approximately Therefore, the output of transformation B is approximately expressed as: For transformation C, its output is approximately expressed as: Transformations D, E, and F are similar to transformations A, B, and C; according to the six transformations in the decoupled dual synchronous reference frame phase-locked loop, the decoupling structure of the phase-locked loop itself is obtained, and then Δθ is obtained. 1+ and Δθ 1- The expression is: in, is the positive sequence dq axis transfer function corresponding to transformation A~F, is the negative sequence dq axis transfer function corresponding to transformation A~F.

10. The three-phase inverter impedance modeling system under the condition of unbalanced power grid load according to claim 6, characterized in that: The inverter output impedance module comprises: Considering the transformation in the phase-locked loop, according to the positive and negative sequence component decoupling structure, in the positive sequence coordinate system, we can obtain: The negative sequence filter current expression is similar to the positive sequence; Considering the small interference phase angle of the phase-locked loop, the corresponding inverter small signal model can be obtained. According to the superposition principle, the expression of the output signal grid-connected current of the model under the αβ axis is obtained: Among them, Δθ 1+ The additional voltage caused By transferring the function Output current, phase-locked loop positive sequence shunt admittance By Δθ 1- The additional voltage caused By transferring the function Output current, phase-locked loop negative sequence shunt admittance Conjugate and frequency-shifted voltage and Through the transfer function and Output current, and Both are negative values ​​of the inverter coupling admittance; The total impedance expression of the inverter is: The inverter coupling impedance expression is: Among them, the expressions of A(s) and B(s) are: Through the above steps, the modeling is finally completed.

11. An electronic device, characterized in that: It comprises one or more processors for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors execute the three-phase inverter impedance modeling method under the condition of unbalanced grid load as described in any one of claims 1 to 5.

12. A storage medium storing a computer program, wherein: in, The computer program is configured to execute the three-phase inverter impedance modeling method under unbalanced grid load conditions as described in any one of claims 1 to 5 when running.

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