New energy GCI nonlinear modeling method considering multi-loop frequency coupling effect

Abstract

The invention relates to a new energy GCI nonlinear modeling method considering a multi-loop frequency coupling effect, and the method comprises the following steps: firstly, respectively building a frequency coupling model, a phase-locked loop model, a voltage outer loop model, a current inner loop model and an admittance model of a GCI; secondly, decoupling improvement is carried out on a traditional synchronous reference coordinate system PLL, and an improved phase-locked loop nonlinear mathematical model is established; and finally, performing time domain simulation on the nonlinear mathematical model of the GCI by utilizing MATLAB / Simulink simulation software, adding small disturbance, and comparing with a response curve of a detailed circuit model, thereby verifying the accuracy of the established nonlinear mathematical model, and verifying the correctness of the improved PLL strategy by comparing the dynamic performance of the traditional PLL and the dynamic performance of the improved PLL. Through simulation analysis, the accuracy of the new energy GCI nonlinear model established by the method and the correctness of the improved PLL strategy are verified.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic power electronics technology, and in particular to a new energy GCI nonlinear modeling method considering multi-loop frequency coupling effect. Background Art

[0002] The rapid development of the new energy industry has prompted the extensive integration of renewable energy power generation units with the power grid, which not only brings severe tests to the safety and stability of the grid-connected inverter (GCI), but also triggers new technical challenges. When a high proportion of new energy is connected to the grid, the impact of its power fluctuation on the stability of the grid becomes increasingly significant, and the nonlinear interaction between power electronic control and the grid system becomes increasingly severe, which in turn gives rise to complex oscillation interaction patterns under the background of high proportion of new energy access. This quantitative change caused by large-scale grid-connected power generation equipment clusters has triggered a qualitative change in the stability of the grid, seriously restricting the cross-regional power transmission capacity of the grid and posing a challenge to the grid-connected and renewable energy absorption capacity.

[0003] Given that GCI is the key power electronic interface for renewable energy access to the grid, accurately establishing its model is a prerequisite for analyzing system stability, and the primary task is to construct a nonlinear mathematical model of the system. Currently, state space modeling and transfer function modeling are two modeling strategies widely adopted in academia and engineering practice. The latter has been widely used in the study of the interactive stability between renewable energy grid-connected systems and power grids because of its intuitiveness in describing the external characteristics of each subsystem and its advantages in model scalability. In the existing GCI impedance model, when a sinusoidal voltage disturbance of a specific frequency and phase sequence occurs at the grid connection point, the disturbance only excites a sinusoidal current response of the same frequency and phase sequence. The interconnected system of GCI and the power grid can be decomposed into two independent subsystems, positive sequence and negative sequence. When both subsystems meet the Nyquist stability criterion, the entire interconnected system can operate stably. However, if the phase-locked loop control bandwidth of the GCI is wide, the DC bus capacitance is small, or the bandwidth of the DC bus voltage controller is large, it may cause a current response of a different frequency in addition to the same frequency current response under a voltage disturbance of a specific frequency. This phenomenon is called the frequency coupling effect. At this time, the traditional impedance model will not be able to fully describe the stability of the system. Therefore, it is of great significance to establish a nonlinear mathematical model of the GCI that considers the frequency coupling characteristics for analyzing the stability of the system. At the same time, a large number of studies have shown that the phase-locked loop based on the traditional synchronous reference coordinate system is the main cause of subsynchronous and supersynchronous oscillations in the grid-connected inverter. A larger PLL (Phase-Locked Loop) bandwidth will increase the negative real part of the GCI output impedance, thereby destroying the stability of the weak power grid. There is also a certain coupling effect between the traditional PLL and the actual power grid impedance, which makes them mutually affect and restrict each other. Therefore, improving the traditional PLL so that it has good dynamic response performance has certain engineering practical significance for improving the stability of the power system.

[0004] Based on the above background, a GCI nonlinear mathematical model considering the frequency coupling effect is established by using the transfer function modeling method and the traditional PLL is improved, which has important practical significance for in-depth research and ensuring the stable operation of high-proportion renewable energy power systems. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art, to accurately establish a nonlinear model of new energy GCI, and to improve the dynamic response performance of frequency tracking of traditional PLL. A new energy GCI nonlinear modeling method considering multi-loop frequency coupling effect is proposed.

[0006] The technical solution adopted by the present invention is: a new energy GCI nonlinear modeling method considering multi-loop frequency coupling effect, comprising the following steps:

[0007] Step 1: Establish the frequency coupling model, phase-locked loop model, voltage outer loop model, current inner loop model and admittance model of GCI respectively;

[0008] Step 2: Decouple and improve the phase-locked loop, and establish the improved nonlinear mathematical model of the phase-locked loop;

[0009] Step 3: Use MATLAB / Simulink simulation software to perform time domain simulation on the GCI nonlinear mathematical model, introduce disturbance, and verify the nonlinear mathematical model of GCI.

[0010] Specifically, the step 1 is to respectively establish the frequency coupling model, phase-locked loop model, voltage outer loop model, current inner loop model and admittance model of the GCI. It includes the following steps:

[0011] Step 1.1, the construction process of the frequency coupling model of GCI is as follows:

[0012] When the frequency is f p1 When the positive sequence disturbance voltage is injected into the GCI system, it will generate a positive sequence response current of the corresponding frequency. According to the frequency coupling effect, a frequency of f p2 =f p1 -2f1 negative sequence response current (f1 is the fundamental frequency), and then a frequency of f appears at the common coupling point (PCC) p2 Taking phase a as an example, after the positive sequence disturbance voltage is injected, its voltage u a and current i a The time domain expression of is:

[0013]

[0014] Where t is the time, U1 is the base frequency voltage; I1 and are the amplitude and phase of the fundamental frequency current respectively; U p1 and are the amplitude and phase of the positive sequence disturbance voltage respectively; U p2 and are the amplitude and phase of the negative sequence disturbance voltage respectively; I p1 and are the amplitude and phase of the positive sequence current response; I p2 and are the amplitude and phase of the negative sequence response current response, respectively.

[0015] Voltage u a and current i a The frequency domain expression of is:

[0016]

[0017]

[0018] In the above formula, f is the frequency, U1 = U1 / 2; j is the imaginary unit; Note: Both sides of the equation here represent complex numbers. The ones on the left of the letters (U, I) are bold, which means they are complex vectors, and the ones on the right are not bold, which means they are constant scalars.

[0019] Similarly, the voltage and current of phases b and c can be expressed in the above form.

[0020] Step 1.2, establish the phase-locked loop model of GCI. The specific process is as follows:

[0021] Since the grid voltage contains a frequency of f p1 and f p2 The disturbance component of the phase-locked loop output angle θ PLL Will be affected by the disturbance component, making θ PLL and the phase-locked loop input angle θ PCC There is a phase angle deviation Δθ between PLL , there is Δθ PLL =θ PLL -θ PCC , the frequency corresponding to the angular disturbance is f p1 -f1, the relationship between the disturbance component and the grid-connected point voltage disturbance satisfies:

[0022]

[0023] In the formula, s2=±j2π(f p1 -f1); Tp1 is the forward channel transfer function of the phase-locked loop; Tp2 is the open-loop transfer function of the phase-locked loop; G PLL (s) is the phase-locked loop transfer function, G PLL (s)=(K pp +K pi / s) / s, where s is a complex variable, K pp and K pi They are the proportional coefficient and integral coefficient of the phase-locked loop PI regulator respectively.

[0024] Three-phase current i at the grid connection point a 、i b and i c It is necessary to transform to the dq coordinate system through coordinate transformation. Since the coordinate transformation matrix contains sine and cosine operations, it is necessary to transform i a 、i b and i c The linearization process is performed as follows:

[0025]

[0026] Where T represents the linear transformation matrix.

[0027] The d-axis current I obtained by coordinate transformation d and q-axis current I q The frequency domain expression of is:

[0028]

[0029]

[0030] I d (f) I q (f) is the d-axis and q-axis current when the frequency is f;

[0031] Step 1.3, establish the nonlinear model of the voltage outer loop of GCI. When the switching loss of the GCI switch device is ignored, the power on the DC side is equal to the power on the AC side, that is:

[0032] (i dc -sC dc u dc ) dc =(u a +sL f i a )i a +(u b +sL f i b )i b +(u c +sL f i c )i c

[0033] In the formula, u dc 、i dc are the DC side voltage and current respectively; C dc is the DC side capacitance; u a 、u b 、u c are three-phase voltages respectively; i a 、i b 、i c They are three-phase currents; L f For the filter inductor.

[0034] The DC side voltage in the above formula can be obtained by the following formula:

[0035]

[0036] In the formula, u dc_ref is the reference value of the DC side voltage; the superscript * indicates the conjugate of the variable.

[0037] Then the reference value i of the d-axis current is obtained by the following formula: d_ref (s2):

[0038] i d_ref (s2) = u dc (s2)G u (s2)

[0039] In the formula, G u (s2) is the transfer function of the voltage loop PI regulator, and the calculation formula is:

[0040]

[0041] In the formula, K p_u is the proportionality coefficient; K i_u is the integration coefficient.

[0042] Step 1.4: Establish the nonlinear model of the inner current loop of GCI. The input of the current loop is the d and q axis current i q 、i q and its reference value i q_ref 、i q_ref , the output is the dq axis modulation signal m d 、m q , the disturbance component expressions of the d-axis and q-axis modulation signals are:

[0043]

[0044] In the formula, i q_ref 、i q_ref are the reference values ​​of the filter inductor current on the d and q axes respectively; K d represents the decoupling coefficient; and They are the d-axis and q-axis current loop PI regulator transfer functions, which can be uniformly expressed as:

[0045]

[0046] In the formula, G i (s) is the transfer function of the current loop PI regulator; K p_i is the proportionality coefficient; K i_i is the integration coefficient.

[0047] By using the inverse Park transform, m d and m q After transformation to the abc coordinate system, the modulation signal m of phase a in the abc coordinate system can be obtained. a The frequency domain expression of is:

[0048]

[0049] In the formula, Represents the convolution operation. Among them, the base frequency component m1 in the modulated signal is:

[0050]

[0051] In the formula, K pwm is the modulation coefficient; s1=j2πf1.

[0052] Similarly, the modulation signal m of phase b and c in the abc coordinate system b 、m c It can also be obtained through the above process.

[0053] Step 1.5: Establish the admittance model of GCI. According to the current loop, the three-phase modulation signal m in the abc coordinate system is obtained. a 、m b 、m c After that, the GCI main circuit equation can be expressed as:

[0054]

[0055] K pwm is the modulation coefficient. Combined with the nonlinear mathematical model of the current inner loop, the output admittance model of the inverter can be obtained as follows:

[0056]

[0057] Where Y 11 , Y 22 is the self-admittance, Y 12 , Y 21 is the coupling admittance, and the specific calculation formula is:

[0058]

[0059]

[0060]

[0061]

[0062] In the formula, the calculation formulas of each element are as follows:

[0063]

[0064]

[0065]

[0066]

[0067]

[0068] In the formula, m d0 and m q0 are the real and imaginary parts of m1.

[0069] Specifically, in step 2, the phase-locked loop is decoupled and improved, and an improved nonlinear mathematical model of the phase-locked loop is established. Since there is also a coupling effect between the PLL and the grid impedance, when the bandwidth of the PLL is too high, the stability of the grid may be destroyed. In order to avoid the above problems, a decoupling strategy is introduced to improve the traditional PLL. The improvement process is as follows:

[0070] First, the PLL input voltage u dq Decoupling is performed, and the decoupling formula is as follows:

[0071]

[0072] In the formula, u dq_D is the PCC voltage after decoupling; Y gdq (s) is the grid admittance in the dq coordinate system; ω is the angular frequency; w bc is the resonant bandwidth of the bandpass filter.

[0073] The decoupled voltage in the above equation is passed through a conventional synchronous reference coordinate system phase-locked loop to output the decoupled phase-locked angle θ PLL_D and d-axis PCC voltage u d_D Through the above formula, the PLL can be decoupled from the grid impedance. At the same time, in order to ensure that the GIC output voltage is synchronized with the PCC voltage, the PLL output angle and PCC voltage need to be corrected. The correction formula is:

[0074]

[0075]

[0076] In the formula, θ PLL_C 、u d_C are the corrected phase-locked loop output angle and d-axis voltage respectively; Re() represents the real part operation; Im() represents the imaginary part operation; Y g is the grid admittance; Z g is the grid impedance; ||·||2 is the second norm.

[0077] Specifically, in step 3, the nonlinear mathematical model of GCI is simulated in the time domain using MATLAB / Simulink simulation software, and a disturbance is introduced to verify the nonlinear mathematical model of GCI. The detailed circuit model and the nonlinear mathematical model (including the voltage loop, the current loop and the PLL model) are simulated in the time domain using MATLAB / Simulink simulation software respectively, and a small disturbance is introduced. The accuracy of the nonlinear mathematical model is verified by comparing the waveforms of active power, reactive power, PCC voltage and line q-axis current. At the same time, the effectiveness of the proposed improved method is verified by comparing the dynamic response characteristics of the traditional PLL and the improved PLL.

[0078] Compared with the prior art, the present invention has the following beneficial effects:

[0079] 1. The present invention adopts the transfer function modeling method to carry out nonlinear mathematical modeling of the new energy GIC. The modeling objects include the frequency coupling model, phase-locked loop model, voltage outer loop model, current inner loop model and admittance model of the GCI. It can lay a detailed mathematical model theoretical foundation for the stability analysis of high-proportion new energy power systems, and also has a certain guiding role in the parameter design of the inverter.

[0080] 2. The input voltage u of the improved PLL proposed by the present invention to the traditional PLL dq Decoupling processing is performed, and then the output angle and decoupling voltage of the PLL are corrected to ensure the synchronization of the GIC and PCC voltages. The proposed improved PLL can effectively improve the dynamic performance of the traditional PLL, thereby laying a theoretical foundation for improving the stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Attached Figure 1 The main circuit topology and control principle diagram of the photovoltaic power generation system in the present invention;

[0082] Attached Figure 2 The schematic diagrams of the structures of the conventional synchronous reference coordinate system PLL (a) and the improved PLL (b) in the present invention;

[0083] Attached Figure 3 The output response curve of the GCI nonlinear mathematical model and the detailed circuit model in the embodiment of the present invention;

[0084] Attached Figure 4 The figure is a comparison of the frequency tracking curves of the traditional PLL and the improved PLL in the embodiment of the present invention. DETAILED DESCRIPTION

[0085] The effectiveness of the proposed method will be verified by using an embodiment below, and the technical solution in the embodiment of the present invention will be clearly and completely described in conjunction with the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0086] Attached Figure 1 The main circuit topology and control principle block diagram of the photovoltaic power generation system. In the figure, the voltage at the common coupling point is recorded as u a 、u b 、u c ;i a 、i b and i c is the filter inductor current; i dc is the DC side current; i d 、i q is the current in the dq coordinate system, i d_ref 、i q_ref is the reference value; i ga 、i gb 、i gc is the three-phase current on the grid side; u ga 、u gb 、u gc is the three-phase voltage on the grid side; C dc is the DC bus capacitance; u dc is the DC bus capacitor voltage, u dc_ref is the reference value; θ PLL is the output angle after the phase-locked loop; m is the modulation signal; K d is the decoupling coefficient; L f , C f and R f They are filter inductor, filter capacitor and damping resistor respectively; R g , L g is the resistance and inductance on the grid side; G u (s), G i (s) is the transfer function of the voltage loop and current loop PI regulator; Q1~Q6 are switch devices, S1~S6 are trigger signals; θ PLL is the phase-locked loop output angle.

[0087] Attached Figure 2 The schematic diagram of the traditional PLL and improved PLL structure is shown in Figure 2. d 、u q is the voltage in the dq coordinate system; PI is the PI regulator.

[0088] Specifically, the main parameter settings of the system are as follows:

[0089] L f , Cf and R f They are 0.15mH, 500μF, 0.02Ω respectively; C dc 0.01mF; i q_ref is 0; u dc_ref is 311.12V; voltage loop PI regulator K p_u is 5.21, K i_u is 10; current loop PI regulator K p_i is 3.08, K i_i is 8; decoupling parameter K d 7.25×10 -5 ; Modulation coefficient K pwm is 0.5; the phase-locked loop proportional coefficient K pp is 1, the integral coefficient K pi is 100; the sampling frequency is 4.5kHz; ω bc It is 120rad / s.

[0090] The present invention provides a new energy GCI nonlinear modeling method considering multi-loop frequency coupling effect, comprising the following steps:

[0091] Step 1: Establish the frequency coupling model, phase-locked loop model, voltage outer loop model, current inner loop model and admittance model of GCI respectively;

[0092] Step 2: Decouple and improve the phase-locked loop, and establish the improved nonlinear mathematical model of the phase-locked loop;

[0093] Step 3: Use MATLAB / Simulink simulation software to perform time domain simulation on the GCI nonlinear mathematical model, introduce disturbance, and verify the nonlinear mathematical model of GCI.

[0094] According to step 1, in order to verify that the established new energy GCI nonlinear mathematical model can accurately simulate the actual simulation circuit model, the GCI nonlinear mathematical model is simulated in the time domain using MATLAB / Simulink simulation software, a small disturbance is introduced into the system, and the accuracy of the nonlinear mathematical model is verified by comparing the four response waveform curves of active power, reactive power, PCC voltage, and line q-axis current. The results are as shown in the attached figure. Figure 3The simulation results of the two models are compared. It can be seen intuitively from the figure that the nonlinear mathematical model fits the detailed simulation circuit model well under various response curves. The specific changes include: the grid voltage amplitude increases by 3% at t = 0.5 seconds, the active power increases from 5kW to 5.2kW at t = 1 second, the reactive power decreases from 2.5kVar to 2.3kVar at t = 1.5 seconds, and the grid voltage frequency decreases by 0.1Hz at t = 2 seconds. The nonlinear mathematical model can fit the change trend of the detailed simulation circuit model very well, and the accuracy of the established nonlinear mathematical model of GCI for new energy units is demonstrated through comparison.

[0095] Then, in order to verify the effectiveness of the proposed improved PLL, the frequency tracking curves of the traditional PLL and the improved PLL are obtained by simulation. Figure 4 As shown in the figure, it can be seen that the transient response of the traditional PLL has large overshoot and undershoot phenomena, while the improved PLL avoids this situation. The frequency fluctuation amplitude of the improved PLL is smaller and the adjustment time is shorter. It can quickly maintain the stability of the system frequency, effectively improving the dynamic performance of the traditional PLL, thereby improving the stability of the system and verifying the correctness of the proposed improved PLL.

[0096] In summary, the comparison of the two experiments illustrates the accuracy of the new energy GCI nonlinear model established by the present invention and the correctness of the improved PLL.

[0097] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that fall within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A nonlinear modeling method for new energy GCI considering multi-loop frequency coupling effect, characterized in that: The following steps are involved: S1: Establish the frequency coupling model, phase-locked loop model, voltage outer loop nonlinear model, current inner loop nonlinear model and admittance model of GCI respectively; S2: Decouple and improve the phase-locked loop, and establish the improved nonlinear mathematical model of the phase-locked loop; S3: Use MATLAB / Simulink software to perform time domain simulation on the nonlinear mathematical model of GCI, introduce disturbance, and verify the nonlinear mathematical model of GCI.

2. A nonlinear modeling method for new energy GCI considering multi-loop frequency coupling effect according to claim 1, characterized in that: Step S1 The process of establishing the frequency coupling model of GCI is as follows: When the frequency is f p1 When the positive sequence disturbance voltage is injected into the GCI, it will generate a positive sequence response current of the corresponding frequency. According to the frequency coupling effect, a frequency of f p2 =f p1 -2f1 negative sequence response current, f1 is the fundamental frequency, and then the frequency f appears at the common coupling point p2 The negative sequence disturbance voltage, taking phase a as an example, after the positive sequence disturbance voltage is injected, its voltage u a and current i a The time domain expression of is: Where t is the time, U1 is the base frequency voltage; I1 and are the amplitude and phase of the fundamental frequency current respectively; U p1 and are the amplitude and phase of the positive sequence disturbance voltage respectively; U p2 and are the amplitude and phase of the negative sequence disturbance voltage respectively; I p1 and are the amplitude and phase of the positive sequence response current response; I p2 and are the amplitude and phase of the negative sequence response current response, respectively; Voltage u a and current i a The frequency domain expression of is: In the above formula, f is the frequency, U1 = U1 / 2; j is the imaginary unit; Similarly, the voltage and current of phases b and c are also expressed in the above manner.

3. A new energy GCI nonlinear modeling method considering multi-loop frequency coupling effect according to claim 2, characterized in that: The specific process of step S1 establishing the phase-locked loop model of GCI is as follows: Since the grid voltage contains a frequency of f p1 and f p2 The disturbance component of the phase-locked loop output angle θ PLL Will be affected by the disturbance component, making θ PLL and the phase-locked loop input angle θ PCC There is a phase angle deviation Δθ between PLL , there is Δθ PLL =θ PLL -θ PCC , the angular perturbation Δθ PLL The corresponding frequency is f p1 -f1, the relationship between the disturbance component and the grid-connected point voltage disturbance satisfies: In the formula, s2=±j2π(f p1 -f1); T p1 is the forward channel transfer function of the phase-locked loop; T p2 is the open-loop transfer function of the phase-locked loop; G PLL (s) is the phase-locked loop transfer function, G PLL (s)=(K pp +K pi / s) / s, where s is a complex variable, K pp and K pi They are the proportional coefficient and integral coefficient of the phase-locked loop PI regulator respectively. Three-phase current i at the grid connection point a 、i b and i c Through coordinate transformation to dq coordinate system, since the coordinate transformation matrix contains sine and cosine operations, it is necessary to a 、i b and i c The linearization process is performed as follows: Where T represents the linear transformation matrix. The frequency domain expressions of the d-axis and q-axis currents obtained by coordinate transformation are: In the formula, I d (f) I q (f) is the d-axis and q-axis current when the frequency is f.

4. The nonlinear modeling method of new energy GCI considering multi-loop frequency coupling effect according to claim 2 is characterized in that: Step S1 establishes the nonlinear model of the voltage outer loop of the GCI as follows: when the switching loss of the GCI switching device is ignored, the power on the DC side is equal to the power on the AC side, that is, (and dc -sC dc in dc )in dc =(in a +sL f and a )and a +(in b +sL f and b )and b +(in c +sL f and c )and c In the formula, u dc 、i dc are the DC side voltage and current respectively; C dc is the DC side capacitance; u a 、u b 、u c are three-phase voltages respectively; i a 、i b 、i c They are three-phase currents; L f is the filter inductor; In the above formula, the DC side voltage is obtained by the following formula: In the formula, u dc_ref is the reference value of DC side voltage; The superscript * indicates the conjugate of the variable. Then the reference value i of the d-axis current is obtained by the following formula: d_ref (s2): i d_ref (s2)=u dc (s2)G u (s2) In the formula, G u (s2) is the transfer function of the voltage loop PI regulator, and the calculation formula is: In the formula, K p_u is the proportionality coefficient; K i_u is the integration coefficient.

5. The nonlinear modeling method of new energy GCI considering multi-loop frequency coupling effect according to claim 1 is characterized in that: Step S1: Establish the nonlinear model process of the inner current loop of GCI: The input of the current loop is the d and q axis current i q 、i q and its reference value i q_ref 、i q_ref , the output is the dq axis modulation signal m d 、m q , the disturbance component expressions of the d-axis and q-axis modulation signals are: In the formula, K d represents the decoupling coefficient (); and They are the transfer functions of the d-axis and q-axis current loop PI regulators respectively; By using the inverse Park transform, m d and m q After transformation to the abc coordinate system, the modulation signal m of phase a in the abc coordinate system is obtained. a The frequency domain expression of is: In the formula, Represents the convolution operation; Similarly, the modulation signal m of the b and c phases of the abc coordinate system b 、m c It is also obtained through the above process.

6. The nonlinear modeling method of new energy GCI considering multi-loop frequency coupling effect according to claim 1 is characterized in that: Step S1 is the process of establishing the GCI admittance model: according to the current loop, the three-phase modulation signal m in the abc coordinate system is obtained. a 、m b 、m c After that, the GCI main circuit equation is expressed as: K pwm is the modulation coefficient. Combined with the nonlinear model of the current inner loop, the output admittance model of the inverter is obtained as follows: Where Y 11 , Y 22 is the self-admittance, Y 12 , Y 21 is the coupling admittance.

7. The nonlinear modeling method of new energy GCI considering multi-loop frequency coupling effect according to claim 1 is characterized in that: The specific process of step S2: Introducing the decoupling strategy, the improvement process is as follows: First, the PLL input voltage u dq Decoupling is performed, and the decoupling formula is as follows: In the formula, u dq_D is the PCC voltage after decoupling; Y gdq is the grid admittance in the dq coordinate system; ω is the angular frequency; w bc is the resonant bandwidth of the bandpass filter. The decoupled voltage in the above equation is passed through a conventional synchronous reference coordinate system phase-locked loop to output the decoupled phase-locked angle θ PLL_D and d-axis PCC voltage u d_D , through the above formula, the PLL is decoupled from the grid impedance, and the PLL output angle and PCC voltage are corrected at the same time. The corrected PLL output angle and d-axis PCC voltage are: In the formula, θ PLL_C 、u d_C are the corrected phase-locked loop output angle and d-axis voltage respectively; Re() represents the real part operation; Im() represents the imaginary part operation; Y g is the grid admittance; Z g is the grid impedance; ||·||2 is the second norm.

8. The nonlinear modeling method of new energy GCI considering multi-loop frequency coupling effect according to claim 1 is characterized in that: The step S3 specifically comprises: using MATLAB / Simulink simulation software to perform time domain simulation on the detailed circuit model and nonlinear mathematical model of GCI, introducing small disturbances, and verifying the accuracy of the nonlinear mathematical model through active power, reactive power, PCC voltage, and line q-axis current waveform comparison experiments. At the same time, the effectiveness of the proposed improved method is verified by comparing the dynamic response characteristics of the traditional PLL and the improved PLL.

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