Grid construction type cooperative control method for improving power anti-interference capability of grid-following type inverter

Abstract

The invention discloses a control method for cooperatively improving the power anti-interference capability of a grid-following type inverter system by a grid-forming type inverter, and relates to the technical field of grid-connected inverter control, and a system researched by the method comprises a direct current source, a three-phase inverter bridge and a three-phase filter. The method disclosed by the invention is simple, and the anti-interference capability of the other grid-following type inverters can be improved only by selecting part of inverters from the n grid-following type inverters which are connected in parallel to be changed into the grid-constructing type inverters, and redundant hardware does not need to be added. The phase-locked loop bandwidth of the grid-following inverter does not need to be reduced, the original grid-following control strategy can stably operate in a weak power grid or even an extremely weak power grid without any improvement, and the rapidity of the grid-following inverter is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of grid-connected inverter control, and in particular relates to a collaborative control method for improving the power anti-interference capability of a grid-connected inverter. Background Art

[0002] Inverter control methods primarily include grid-following and grid-forming. Grid-following control is widely used due to its fast response and ability to operate at the maximum power point of renewable energy sources. As renewable energy penetration continues to increase, the power grid is gradually shifting from being dominated by synchronous generators to being dominated by inverters, resulting in weak or even extremely weak grid characteristics.

[0003] To maintain the stability of grid-controlled inverters, it's necessary to reduce the phase-locked loop (PLL) bandwidth or adjust its structure. However, adjusting the PLL bandwidth or structure significantly reduces the grid-controlled inverter's power immunity. Its output power is susceptible to power fluctuations from other grid-controlled inverters connected to the same PCC point, causing overshoot and ultimately shutting down. Therefore, improving the grid-controlled inverter's power immunity is crucial.

[0004] At present, there are related papers and patents on the control method of grid-following inverters in weak power grids, such as:

[0005] 1. "Study on the Effect of Phase-Locked Loop on the Stability of LCL-Type Grid-Connected Inverters under Weak Grid Conditions and Phase-Locked Loop Parameter Design," Proceedings of the Chinese Society of Electrical Engineering, Vol. 34, No. 30, 2014, pp. 5259-5268. This article reduces the bandwidth of the grid-connected inverter's phase-locked loop based on the phase margin, improving the inverter's stability under weak grid conditions. However, this method requires a significant reduction in the phase-locked loop's bandwidth under extremely weak grid conditions, which not only reduces the inverter's speed but also its power immunity.

[0006] 2. The Chinese invention patent publication number CN109950926A discloses a stable control method for grid-connected inverters based on q-axis voltage integral feedforward in weak grid conditions. The method proposes a method for shaping the q-axis impedance of the grid-connected inverter to improve its stability in weak grid conditions. However, the method can only guarantee the stability of the grid-connected inverter in weak grid conditions, and it is difficult to guarantee its stability and anti-interference capability in extremely weak grid conditions.

[0007] 3. “Robust Vector Control of a Very Weak-Grid-Connected Voltage-Source Converter Considering the Phase-Locked Loop Dynamics,” M. Davari and Y. A.I. Mohamed, IEEE Transactions on Power Electronics, 2017: 977–994 (published online in IEEE Transactions on Power Electronics, 2017), proposes a robust vector control method to eliminate the effects of the phase-locked loop on the stability of grid-connected inverters. However, this method is complex and requires restructuring existing inverter control methods.

[0008] Based on the above literature, the existing technology has the following deficiencies:

[0009] 1. Improving the control strategy of the grid-following inverter itself is too complicated and requires large-scale shutdown to modify the control algorithm. It is difficult to modify existing equipment that has been connected to the grid.

[0010] 2. Although the method of reducing the bandwidth of the phase-locked loop can improve the stability of the grid-following inverter to a certain extent, it will also have a significant negative impact on its speed and anti-interference performance. Therefore, it is necessary to study methods to improve the stability and power anti-interference capabilities of the grid-following inverter without reducing the bandwidth of the phase-locked loop. Summary of the Invention

[0011] The technical problem to be solved by the present invention addresses the shortcomings of the existing technology. The present invention can improve the power interference rejection capability of grid-connected inverters without requiring large-scale modifications to existing equipment. Specifically, the present invention only requires replacing some of the original grid-connected inverters at a PCC site with grid-connected inverters to improve the power interference rejection capability of the remaining grid-connected inverters at that PCC site, without incurring additional hardware costs.

[0012] The present invention provides a collaborative control method for improving the power anti-interference capability of a grid-type inverter. The collaborative control method is used in a system with n inverters connected in parallel, where n is a positive number and n>1; wherein each inverter includes a DC source, a three-phase inverter bridge, and a three-phase filter connected in series in sequence; the three-phase filter includes a filter inductor, a filter capacitor, and a passive damping resistor;

[0013] The steps of the collaborative control method are as follows:

[0014] Step 1: Set n inverters to operate in grid-following mode, and record the grid connection point as the PCC point;

[0015] Step 2: Change the k inverters in the system from the grid-following mode to the grid-forming mode, where k = 0, 1, 2, ..., n-1. The selection of k depends on the requirements for the anti-interference capability of the grid-following inverter. The higher the requirement, the larger k is.

[0016] Step 3: End this control process and realize the coordinated control of the grid-forming inverter to improve the power anti-interference capability of the grid-following inverter.

[0017] Preferably, the control steps in the network-following mode are as follows:

[0018] Step 1.1, sample the output grid-connected current i ga ,i gb ,i gc , sampling PCC point voltage u pcca ,u pccb ,u pccc ;

[0019] Step 1.2: The PCC point voltage u obtained by sampling in step 1.1 is pcca ,u pccb ,u pccc The dq-axis component u of the PCC voltage is obtained by transforming the three-phase stationary coordinate system to the two-phase rotating coordinate system. pccd ,u pccq ; Set the PCC point voltage u pcca ,u pccb ,u pccc The voltage phase angle θ at the PCC point is obtained by phase-locking the phase-locked loop (PLL). The calculation formula for the voltage phase angle θ at the PCC point is:

[0020]

[0021] Where ω0 is the rated angular frequency of the PCC point voltage, K p_PLL K is the proportional adjustment coefficient of the phase-locked loop PI regulator, i_PLL is the integral adjustment coefficient of the phase-locked loop PI regulator, and s is the Laplace operator;

[0022] Step 1.3: Based on the PCC point voltage phase angle θ obtained in step 1.2, the output grid-connected current i sampled in step 1.1 is converted to ga ,i gb ,i gc Converted into the output grid-connected current dq component i in the two-phase rotating coordinate system gd ,i gq ;

[0023] Step 1.4, set the dq axis output grid-connected current command signal i gdref ,i gqref, and according to step 1.3, the output grid-connected current dq component i is obtained gd ,i gq , the dq axis control signal u is obtained through the grid current closed-loop control equation d ,u q ; The grid current closed-loop control equation is:

[0024]

[0025] Among them, K p is the proportional control coefficient of the PI regulator in the grid current closed-loop control equation, K i is the integral control coefficient of the PI regulator in the closed-loop control equation of the grid current;

[0026] Step 1.5: According to the PCC point voltage phase angle θ obtained in step 1.2, the dq axis control signal u obtained in step 1.4 is converted to d ,u q After the transformation from the two-phase rotating coordinate system to the three-phase stationary coordinate system, it is converted into the control signal component u in the three-phase stationary coordinate system a ,u b ,u c ;

[0027] Step 1.6: The control signal component u in the three-phase stationary coordinate system obtained in step 1.5 is a ,u b ,u c , respectively, with the PCC point voltage u obtained in step 1.1 pcca ,u pccb ,u pccc Add together to get the three-phase grid-connected inverter bridge arm voltage control signal, which are u a +u pcca ,u b +u pccb ,u c +u pccc , and then generate the switching signal of the grid-connected inverter power device through SPWM modulation, and control the opening and closing of the power devices of the three-phase inverter bridge through the drive circuit.

[0028] Preferably, the control steps of the networking mode are as follows:

[0029] Step 2.1, sample the output grid-connected current i ga ,i gb ,i gc , sampling PCC point voltage u pcca ,u pccb ,u pccc ;

[0030] Step 2.2: The output grid-connected current i obtained by sampling in step 2.1 is ga ,i gb ,i gc , the output grid-connected current αβ axis component i is obtained by transforming the three-phase stationary coordinate system to the two-phase stationary coordinate system gα ,i gβ ; The PCC point voltage u sampled in step 2.1 pcca ,u pccb ,u pccc The αβ-axis component u of the PCC point voltage is obtained by transforming the three-phase stationary coordinate system to the two-phase stationary coordinate system. pccα ,u pccβ ;

[0031] Step 2.3, according to the output grid-connected current αβ axis component i obtained in step 2.2 gα ,i gβ , and the PCC point voltage αβ axis component u pccα ,u pccβ , first use the average active power calculation equation to get the average active power Then the average reactive power is obtained through the average reactive power calculation equation The calculation equations are:

[0032]

[0033] Where, τ is the time constant of the first-order low-pass filter, and s is the Laplace operator;

[0034] Step 2.4, the average active power obtained according to step 2.3 The output angular frequency ω of the grid-connected inverter is obtained by the active power-frequency droop control equation. And calculate the grid-connected inverter output phase angle θ0, θ0 = ω / s, where P n Give the active power command to the grid-connected inverter, ω n D is the rated angular frequency corresponding to the given active power command Pn, p is the active power droop coefficient;

[0035] Step 2.5: According to the PCC point voltage u sampled in step 2.1 pcca ,u pccb ,u pccc The grid-connected inverter output phase angle θ0 obtained in step 2.4 is transformed from the three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the PCC point voltage dq axis component u pccd ,u pccq ;

[0036] Step 2.6: According to the output grid-connected current i sampled in step 2.1 ga,i gb ,i gc The grid-connected inverter output phase angle θ0 obtained in step 2.4 is transformed from the three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the output grid-connected current dq component i gd ,i gq ;

[0037] Step 2.7, according to the average reactive power output of the grid-connected inverter obtained in step 2.3 The dq component reference value u of the PCC point voltage of the grid-connected inverter is obtained by the reactive power-amplitude droop control equation pccdref ,u pccqref , the reactive power-amplitude droop control equation is:

[0038]

[0039] u pccqref =0

[0040] Among them, U n The grid-connected inverter gives the reactive power instruction Q n The corresponding rated output voltage, D q is the reactive power droop coefficient;

[0041] Step 2.8, according to the PCC point voltage dq axis component u obtained in step 2.5 pccd ,u pccq and the PCC point voltage dq component reference value u obtained in step 2.7 pccdref ,u pccqref , the dq axis output grid-connected current command signal i is obtained through the voltage loop control equation garef ,i gqref ; The voltage loop control equation is:

[0042]

[0043] Among them, K p1 is the proportional control coefficient of the PI regulator in the voltage loop control equation, K i1 is the integral control coefficient of the PI regulator in the voltage loop control equation;

[0044] Step 2.9: According to the dq axis output grid-connected current command signal i obtained in step 2.8 gdref ,i gqref , and according to step 2.6, the output grid-connected current dq component i is obtained gd ,i gq , the dq axis control signal u is obtained through the current loop control equation d ,u q , the current loop control equation is:

[0045]

[0046] Among them, K p2 is the proportional control coefficient of the PI regulator in the current loop control equation, K i2 is the integral control coefficient of the PI regulator in the current loop control equation;

[0047] Step 2.10: convert the dq axis control signal u obtained in step 2.9 into d ,u q , which is transformed from the two-phase rotating coordinate system to the three-phase stationary coordinate system into the control signal component u in the three-phase stationary coordinate system a ,u b ,u c ;

[0048] Step 2.11: Substitute the component u obtained in step 2.10 for the three-phase stationary coordinate system a ,u b ,u c and the PCC point voltage u obtained in step 2.1 pcca ,u pccb ,u pccc Add together to get the three-phase grid-connected inverter bridge arm voltage control signal u a +u pcca ,u b +u pccb ,u c +u pccc , and then generate the switching signal of the grid-connected inverter power device through SPWM modulation, and control the opening and closing of the three-phase inverter bridge power device through the drive circuit.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] 1. The present invention is simple to implement. It only requires selecting some of the n parallel grid-following inverters and converting them into grid-forming inverters. This improves the anti-interference capability of the remaining grid-following inverters at the same PCC point without adding any extra hardware.

[0051] 2. The present invention does not need to reduce the phase-locked loop bandwidth of the grid-following inverter. The original grid-following control strategy can operate stably in a weak or even extremely weak grid without any improvement, thereby improving the speed of the grid-following inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a topological diagram of the system described in the present invention.

[0053] Figure 2 This is the power simulation waveform of the full-grid system under extremely weak power grid before and after power disturbance.

[0054] Figure 3 The power simulation waveforms of the remaining grid-type inverters before and after they are subjected to power disturbance after some grid-type inverters are replaced with grid-type inverters in an extremely weak power grid. DETAILED DESCRIPTION

[0055] This embodiment will be described in detail below with reference to the accompanying drawings.

[0056] Figure 1 This is a topological diagram of the system involved in the present invention. Figure 1 As can be seen, the system is a system with n inverters connected in parallel, where n is a positive number and n>1. Each inverter includes a DC source, a three-phase inverter bridge, and a three-phase filter connected in series. The three-phase filter includes a filter inductor, a filter capacitor, and a passive damping resistor.

[0057] Depend on Figure 1 It can be seen that in this embodiment, a DC capacitor is connected in parallel between the DC source and the three-phase inverter bridge. Figure 1 Up, V dc is the DC side voltage, L f is the inductance of the filter inductor, C f is the capacitance of the filter capacitor, R f is the resistance of the passive damping resistor, L g is the inductance of the circuit, C dc is the capacitance of the DC capacitor, e gabc It is a three-phase power grid.

[0058] In this embodiment, n=3, that is, three inverters are included, which are respectively denoted as inverter 1, inverter 2 and inverter 3.

[0059] The parameters of each inverter in this embodiment are: V dc =770V, L f =0.9mH, C f =11.6uF, passive damping resistor R f =2.18Ω, L g =15.4mH. The rated output line voltage of the inverter is 380V / 50Hz, and the rated power of a single inverter is 20kW.

[0060] The present invention provides a collaborative control method for improving the power anti-interference capability of a grid-type inverter, and the steps are as follows:

[0061] Step 1: Set n inverters to operate in grid-following mode, and record the grid connection point as the PCC point;

[0062] Step 2: Change the k inverters in the system from the grid-following mode to the grid-forming mode, where k = 0, 1, 2, ..., n-1. The selection of k depends on the requirements for the anti-interference capability of the grid-following inverter. The higher the requirement, the larger k is.

[0063] Step 3: End this control process and realize the coordinated control of the grid-forming inverter to improve the power anti-interference capability of the grid-following inverter.

[0064] In this embodiment, k is set to 1. Specifically, the inverter 3 is changed from the grid-following operation mode to the grid-forming operation mode.

[0065] In this embodiment, the control steps in the network-following mode are as follows:

[0066] Step 1.1, sample the output grid-connected current i ga ,i gb ,i gc , sampling PCC point voltage u pcca ,u pccb ,u pccc .

[0067] In a specific implementation, the current sensor sampling proportional coefficient is 10, and the voltage sensor sampling proportional coefficient is 120.

[0068] Step 1.2: The PCC point voltage u obtained by sampling in step 1.1 is pcca ,u pccb ,u pccc The dq-axis component u of the PCC voltage is obtained by transforming the three-phase stationary coordinate system to the two-phase rotating coordinate system. pccd ,u pccq ; Set the PCC point voltage u pcca ,u pccb ,u pccc The voltage phase angle θ at the PCC point is obtained by phase-locking the phase-locked loop (PLL). The calculation formula for the voltage phase angle θ at the PCC point is:

[0069]

[0070] Where ω0 is the rated angular frequency of the PCC point voltage, K p_PLL K is the proportional adjustment coefficient of the phase-locked loop PI regulator, i_PLL is the integral adjustment coefficient of the phase-locked loop PI regulator, and s is the Laplace operator.

[0071] In the specific implementation, ω0=314rad / s, K p_PLL =0.28, K i_PLL =12.

[0072] PCC point voltage u pcca ,upccb ,u pccc The transformation equation from the three-phase stationary coordinate system to the two-phase rotating coordinate system is:

[0073]

[0074] Step 1.3: Based on the PCC point voltage phase angle θ obtained in step 1.2, the output grid-connected current i sampled in step 1.1 is converted to ga ,i gb ,i gc Converted into the output grid-connected current dq component i in the two-phase rotating coordinate system gd ,i gq .

[0075] Output grid-connected current i ga ,i gb ,i gc The transformation equation from the three-phase stationary coordinate system to the two-phase rotating coordinate system is:

[0076]

[0077] Step 1.4, set the dq axis output grid-connected current command signal i gdref ,i gqref , and according to step 1.3, the output grid-connected current dq component i is obtained gd ,i gq , the dq axis control signal u is obtained through the grid current closed-loop control equation d ,u q ; The grid current closed-loop control equation is:

[0078]

[0079] Among them, K p is the proportional control coefficient of the PI regulator in the grid current closed-loop control equation, K i is the integral control coefficient of the PI regulator in the closed-loop control equation of the grid current.

[0080] In the specific implementation, K p =4,K i =10.

[0081] Step 1.5: According to the PCC point voltage phase angle θ obtained in step 1.2, the dq axis control signal u obtained in step 1.4 is converted to d ,u q After the transformation from the two-phase rotating coordinate system to the three-phase stationary coordinate system, it is converted into the control signal component u in the three-phase stationary coordinate system a ,u b ,u c .

[0082] dq axis control signal u d ,u q The transformation equation from the two-phase rotating coordinate system to the three-phase stationary coordinate system is:

[0083] u a =u d cosθ-u q sinθ

[0084]

[0085] Step 1.6: The control signal component u in the three-phase stationary coordinate system obtained in step 1.5 is a ,u b ,u c , respectively, with the PCC point voltage u obtained in step 1.1 pcca ,u pccb ,u pccc Add together to get the three-phase grid-connected inverter bridge arm voltage control signal, which are u a +u pcca ,u b +u pccb ,u c +u pccc , and then generate the switching signal of the grid-connected inverter power device through SPWM modulation, and control the opening and closing of the power devices of the three-phase inverter bridge through the drive circuit.

[0086] In this embodiment, the control steps of the networking mode are as follows:

[0087] Step 2.1, sample the output grid-connected current i ga ,i gb ,i gc , sampling PCC point voltage u pcca ,u pccb ,u pccc .

[0088] Step 2.2: The output grid-connected current i obtained by sampling in step 2.1 is ga ,i gb ,i gc , the output grid-connected current αβ axis component i is obtained by transforming the three-phase stationary coordinate system to the two-phase stationary coordinate system gα ,i gβ ; The PCC point voltage u sampled in step 2.1 pcca ,u pccb ,u pccc The αβ-axis component u of the PCC point voltage is obtained by transforming the three-phase stationary coordinate system to the two-phase stationary coordinate system. pecα ,u pccβ .

[0089] Output grid-connected current iga ,i gb ,i gc The transformation equation from the three-phase stationary coordinate system to the two-phase stationary coordinate system is:

[0090]

[0091] PCC point voltage u pcca ,u pccb ,u pccc The transformation equation from the three-phase stationary coordinate system to the two-phase stationary coordinate system is:

[0092]

[0093] Step 2.3, according to the output grid-connected current αβ axis component i obtained in step 2.2 gα ,i gβ , and the PCC point voltage αβ axis component u pccα ,u pccβ , first use the average active power calculation equation to get the average active power Then the average reactive power is obtained through the average reactive power calculation equation The calculation equations are:

[0094]

[0095] Where τ is the time constant of the first-order low-pass filter and s is the Laplace operator.

[0096] In a specific implementation, T=0.00318s.

[0097] Step 2.4, the average active power obtained according to step 2.3 The output angular frequency ω of the grid-connected inverter is obtained by the active power-frequency droop control equation. And calculate the grid-connected inverter output phase angle θ0, θ0 = ω / s, where P n Give the active power command to the grid-connected inverter, ω n D is the rated angular frequency corresponding to the given active power command Pn, p is the active power droop coefficient.

[0098] In the specific implementation, n =314rad / s, P n =20kW, D p =0.0001.

[0099] Step 2.5: According to the PCC point voltage u sampled in step 2.1 pcca ,u pccb ,u pcccThe grid-connected inverter output phase angle θ0 obtained in step 2.4 is transformed from the three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the PCC point voltage dq axis component u pccd ,u pccq .

[0100] PCC point voltage u pcca ,u pccb ,u pccc The transformation equation from the three-phase stationary coordinate system to the two-phase rotating coordinate system is:

[0101]

[0102] Step 2.6: Sample the output grid-connected current i according to step 2.1. ga ,i gb ,i gc The grid-connected inverter output phase angle θ0 obtained in step 2.4 is transformed from the three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the output grid-connected current dq component i gd ,i gq .

[0103] Output grid-connected current i ga ,i gb ,i gc The transformation equation from the three-phase stationary coordinate system to the two-phase rotating coordinate system is:

[0104]

[0105] Step 2.7, according to the average reactive power output of the grid-connected inverter obtained in step 2.3 The dq component reference value u of the PCC point voltage of the grid-connected inverter is obtained by the reactive power-amplitude droop control equation pccdref ,u pccqref , the reactive power-amplitude droop control equation is:

[0106]

[0107] u pccqref =0

[0108] Among them, U n The grid-connected inverter gives the reactive power instruction Q n The corresponding rated output voltage, D q is the reactive power droop coefficient.

[0109] In the specific implementation, U n =220V, Q n =0,D q =0.0001.

[0110] Step 2.8, according to the PCC point voltage dq axis component u obtained in step 2.5 pccd ,u pccq and the PCC point voltage dq component reference value u obtained in step 2.7 pccdref ,u pccqref , the dq axis output grid-connected current command signal i is obtained through the voltage loop control equation gdref ,i gqref ; The voltage loop control equation is:

[0111]

[0112] Among them, K p1 is the proportional control coefficient of the PI regulator in the voltage loop control equation, K i1 is the integral control coefficient of the PI regulator in the voltage loop control equation.

[0113] In the specific implementation, K p1 =0.05, K i1 =120.

[0114] Step 2.9: According to the dq axis output grid-connected current command signal i obtained in step 2.8 gdref ,i gqref , and according to step 2.6, the output grid-connected current dq component i is obtained gd ,i gq , the dq axis control signal u is obtained through the current loop control equation d ,u q , the current loop control equation is:

[0115]

[0116] Among them, K p2 is the proportional control coefficient of the PI regulator in the current loop control equation, K i2 is the integral control coefficient of the PI regulator in the current loop control equation.

[0117] In the specific example, K p2 =4,K i2 =10.

[0118] Step 2.10: convert the dq axis control signal u obtained in step 2.9 into d ,u q , which is transformed from the two-phase rotating coordinate system to the three-phase stationary coordinate system into the control signal component u in the three-phase stationary coordinate system a ,u b ,u c .

[0119] dq axis control signal u d ,uq The transformation equation from the two-phase rotating coordinate system to the three-phase stationary coordinate system is:

[0120] u a =u d cosθ0-u q sinθ0

[0121]

[0122] Step 2.11: Substitute the component u obtained in step 2.10 for the three-phase stationary coordinate system a ,u b ,u c and the PCC point voltage u obtained in step 2.1 pcca ,u pccb ,u pccc Add together to get the three-phase grid-connected inverter bridge arm voltage control signal u a +u pcca ,u b +u pccb ,u c +u pccc , and then generate the switching signal of the grid-connected inverter power device through SPWM modulation, and control the opening and closing of the three-phase inverter bridge power device through the drive circuit.

[0123] In order to verify the effect of the present invention, MATLAB / simulink simulation was performed on the present invention.

[0124] Figure 2 In the case of three grid-type inverters connected in parallel, inverter 1 and inverter 3 maintain a rated output power of 20kW, and the output power instruction of inverter 2 steps from 10kW to 20kW, the power response process of inverter 1.

[0125] Figure 3 is Figure 2 Based on the topology, when inverter 3 is replaced with a grid-type inverter, inverter 1 and inverter 3 maintain the rated output power of 20kW, and the output power instruction of inverter 2 steps from 10kW to 20kW, the power response process of inverter 1 is shown in the figure. Figure 2 , at this time, the power disturbance of inverter 1 is reduced, and the recovery time after the power disturbance is also shortened.

[0126] Figure 2 、 Figure 3 The comparison well proves the effectiveness of the method proposed in this invention.

Claims

1. A collaborative control method for improving the power anti-interference capability of grid-connected inverters, wherein the collaborative control method is used for a system with n inverters connected in parallel, where n is a positive number and n>1; Each inverter includes a DC source, a three-phase inverter bridge and a three-phase filter connected in series; the three-phase filter includes a filter inductor, a filter capacitor and a passive damping resistor; It is characterized in that the steps of the collaborative control method are as follows: Step 1: Set n inverters to operate in grid-following mode, and record the grid connection point as the PCC point; Step 2: Change k inverters in the system from grid-following mode to grid-forming mode, where k = 0, 1, 2, ..., n-1. The selection of k depends on the requirements for the anti-interference capability of the grid-following inverter. The higher the requirement, the larger k is. Step 3: End this control process and realize the coordinated control of the grid-forming inverter to improve the power anti-interference capability of the grid-following inverter.

2. A collaborative control method for improving the power anti-interference capability of a grid-connected inverter according to claim 1, characterized in that: The control steps in the following network mode are as follows: Step 1.1, sample the output grid-connected current i ga ,i gb ,i gc , sampling PCC point voltage u pcca ,u pccb ,u pccc ; Step 1.2: The PCC point voltage u obtained by sampling in step 1.1 is pcca ,u pccb ,u pccc The dq-axis component u of the PCC voltage is obtained by transforming the three-phase stationary coordinate system to the two-phase rotating coordinate system. pccd ,u pccq ; Set the PCC point voltage u pcca ,u pccb ,u pccc The voltage phase angle θ at the PCC point is obtained by phase-locking the phase-locked loop (PLL). The calculation formula for the voltage phase angle θ at the PCC point is: Where ω0 is the rated angular frequency of the PCC point voltage, K p_PLL K is the proportional adjustment coefficient of the phase-locked loop PI regulator, i_PLL is the integral adjustment coefficient of the phase-locked loop PI regulator, and s is the Laplace operator; Step 1.3: Based on the PCC point voltage phase angle θ obtained in step 1.2, the output grid-connected current i sampled in step 1.1 is converted to ga ,i gb ,i gc Converted into the output grid-connected current dq component i in the two-phase rotating coordinate system gd ,i gq ; Step 1.4, set the dq axis output grid-connected current command signal i gdref ,i gqref , and according to step 1.3, the output grid-connected current dq component i is obtained gd ,i gq , the dq axis control signal u is obtained through the grid current closed-loop control equation d ,u q ; The grid current closed-loop control equation is: Among them, K p is the proportional control coefficient of the PI regulator in the grid current closed-loop control equation, K i is the integral control coefficient of the PI regulator in the closed-loop control equation of the grid current; Step 1.5: According to the PCC point voltage phase angle θ obtained in step 1.2, the dq axis control signal u obtained in step 1.4 is converted to d ,u q After the transformation from the two-phase rotating coordinate system to the three-phase stationary coordinate system, it is converted into the control signal component u in the three-phase stationary coordinate system a ,u b ,u c ; Step 1.6: The control signal component u in the three-phase stationary coordinate system obtained in step 1.5 is a ,u b ,u c , respectively, with the PCC point voltage u obtained in step 1.1 pcca ,u pccb ,u pccc Add together to get the three-phase grid-connected inverter bridge arm voltage control signal, which are u a +u pcca ,u b +u pccb ,u c +u pccc , and then generate the switching signal of the grid-connected inverter power device through SPWM modulation, and control the opening and closing of the power devices of the three-phase inverter bridge through the drive circuit.

3. The collaborative control method for improving the power anti-interference capability of grid-connected inverters according to claim 1, characterized in that: The control steps of the networking mode are as follows: Step 2.1, sample the output grid-connected current i ga ,i gb ,i gc , sampling PCC point voltage u pcca ,u pccb ,u pccc ; Step 2.2: The output grid-connected current i obtained by sampling in step 2.1 is ga ,i gb ,i gc , the output grid-connected current αβ axis component i is obtained by transforming the three-phase stationary coordinate system to the two-phase stationary coordinate system gα ,i gβ ; The PCC point voltage u sampled in step 2.1 pcca ,u pccb ,u pccc The αβ-axis component u of the PCC point voltage is obtained by transforming the three-phase stationary coordinate system to the two-phase stationary coordinate system. pccα ,u pccβ ; Step 2.3, according to the output grid-connected current αβ axis component i obtained in step 2.2 gα ,i gβ , and the PCC point voltage αβ axis component u pccα ,u pccβ , first use the average active power calculation equation to get the average active power Then the average reactive power is obtained through the average reactive power calculation equation The calculation equations are: Where, τ is the time constant of the first-order low-pass filter, and s is the Laplace operator; Step 2.4, the average active power obtained according to step 2.3 The output angular frequency ω of the grid-connected inverter is obtained by the active power-frequency droop control equation. And calculate the grid-connected inverter output phase angle θ0, θ0 = ω / s, where P n Give the active power command to the grid-connected inverter, ω n is the given active power instruction P n The rated angular frequency corresponding to p is the active power droop coefficient; Step 2.5: According to the PCC point voltage u sampled in step 2.1 pcca ,u pccb ,u pccc The grid-connected inverter output phase angle θ0 obtained in step 2.4 is transformed from the three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the PCC point voltage dq axis component u pccd ,u pccq ; Step 2.6: Sample the output grid-connected current i according to step 2.

1. ga ,i gb ,i gc The grid-connected inverter output phase angle θ0 obtained in step 2.4 is transformed from the three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the output grid-connected current dq component i gd ,i gq ; Step 2.7, according to the average reactive power output of the grid-connected inverter obtained in step 2.3 The dq component reference value u of the PCC point voltage of the grid-connected inverter is obtained by the reactive power-amplitude droop control equation pccdref ,u pccqref , the reactive power-amplitude droop control equation is: u pccqref ＝0 Among them, U n The grid-connected inverter gives the reactive power instruction Q n The corresponding rated output voltage, D q is the reactive power droop coefficient; Step 2.8, according to the PCC point voltage dq axis component u obtained in step 2.5 pccd ,u pccq and the PCC point voltage dq component reference value u obtained in step 2.7 pccdref ,u pccqref , the dq axis output grid-connected current command signal i is obtained through the voltage loop control equation gdref ,i gqref ; The voltage loop control equation is: Among them, K p1 is the proportional control coefficient of the PI regulator in the voltage loop control equation, K i1 is the integral control coefficient of the PI regulator in the voltage loop control equation; Step 2.9: According to the dq axis output grid-connected current command signal i obtained in step 2.8 gdref ,i gqref , and according to step 2.6, the output grid-connected current dq component i is obtained gd ,i gq , the dq axis control signal u is obtained through the current loop control equation d ,u q , the current loop control equation is: Among them, K p2 K is the proportional control coefficient of the PI regulator in the current loop control equation, i2 is the integral control coefficient of the PI regulator in the current loop control equation; Step 2.10: convert the dq axis control signal u obtained in step 2.9 into d ,u q , which is transformed from the two-phase rotating coordinate system to the three-phase stationary coordinate system into the control signal component u in the three-phase stationary coordinate system a ,u b ,u c ; Step 2.11: Substitute the component u obtained in step 2.10 for the three-phase stationary coordinate system a ,u b ,u c and the PCC point voltage u obtained in step 2.1 pcca ,u pccb ,u pccc Add together to get the three-phase grid-connected inverter bridge arm voltage control signal u a +u pcca ,u b +u pccb ,u c +u pccc , and then generate the switching signal of the grid-connected inverter power device through SPWM modulation, and control the opening and closing of the three-phase inverter bridge power device through the drive circuit.

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