Method and device for designing voltage control parameters of grid-connected point of ac weak power grid and medium

Abstract

The application discloses a grid-connected point voltage control parameter design method and device for an alternating current weak power grid and a medium, and the method comprises the following steps: 1. According to the transfer function of the system, the control parameter of the alternating current voltage loop is obtained by using the zero-pole elimination method; 2. The capacitor voltage of the sampling filter LCL is sampled, and the voltage is taken as the input signal of the alternating current voltage loop in the grid-connected converter controller, the input signal generates an output signal through the alternating current voltage loop control, and the pulse generation signal is obtained after the output signal is processed. According to the system operating voltage, the current and the related control loop parameters, the related regulation coefficients can be designed, so that the problem of grid-connected point voltage drop caused by impedance increase in the weak power grid can be eliminated, the grid-connected inverter can operate in the weak power grid with maximum grid impedance, and the operation stability of the grid-connected inverter can be significantly improved.

Description

Technical Field

[0001] This invention relates to a method, device, and medium for designing grid connection point voltage control parameters for AC weak grids, belonging to the field of voltage control for grid-connected inverters. Background Technology

[0002] With the booming development of distributed grid-connected power generation from new energy sources, grid-connected inverters, as a key component, have received widespread attention and play an important role in applications such as new energy power generation, DC transmission, and energy storage systems. The increasing number of inverters connected to the grid is causing the grid to exhibit increasingly pronounced weak grid characteristics. The increased grid impedance in a weak grid leads to a decrease in the control performance of grid-connected inverters, resulting in poorer power quality and even instability. In three-phase grid-connected inverters, as the short-circuit specific capacity (SCR) at the grid connection point continues to decrease, the voltage drop across the line impedance between the grid connection point and the AC grid will also continue to increase, causing a significant shift in the operating point of the inverter system and subsequently leading to system stability issues.

[0003] Several academic papers have analyzed and proposed solutions to the voltage drop phenomenon caused by the high impedance of a weak power grid, such as:

[0004] 1. The article titled "Control of Grid-Tied Inverter with L Filter in Weak Grid Considering Grid Impedance and Harmonics", Hao Tu; Bei Xu, et al, IECON 2018-44th Annual Conference of the IEEE Industrial Electronics Society, designed an inverter current controller considering grid impedance and grid harmonics, but the problem of voltage drop at the grid connection point remains unresolved.

[0005] 2. The article entitled "Improved Design of PLL Controller for LCL-Type Grid-Connected Converter in Weak Grid", D. Zhu, S. Zhou, X. Zou, Y. Kang, IEEE Transactions on Power Electronics, vol. 35, pp. 4715-4727. ("Improved Design of PLL Controller for LCL-Type Grid-Connected Converter in Weak Grid", 2020 IEEE Power Electronics Journal, Vol. 35, pp. 4715-4727) reduces the negative damping region of inverter output admittance in weak grids through parameter design of the phase-locked loop, but the design of control parameters for the AC voltage loop is still not solved.

[0006] In summary, the existing technologies have the following problems: the grid impedance increases under weak grid conditions, the voltage drop caused by the line impedance between the grid connection point and the weak grid increases, and the grid connection point voltage decreases. Existing literature has not yet proposed a complete solution to the specific calculation of AC voltage loop control parameters and to eliminate the inverter system stability problem caused by changes in grid connection point voltage. Summary of the Invention

[0007] To overcome the limitations of the above-mentioned technical solutions and solve the voltage drop problem caused by the large grid impedance under weak grid conditions, this invention proposes a design method, equipment, and medium for grid connection point voltage control parameters of AC weak grids. The aim is to enable grid-connected inverters to operate under weak grid conditions with extremely large grid impedance while effectively offsetting the impact of grid connection point voltage deviation, thereby significantly improving the operational stability of grid-connected inverters.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] The present invention discloses a method for designing grid-connected voltage control parameters for an AC low-voltage power grid, characterized in that it is applied to a three-phase LCL-type grid-connected inverter and includes: a main circuit and a controller. The main circuit consists of an AC low-voltage power grid, an LCL filter, and an inverter system connected in sequence. The controller includes: a phase-locked loop (PLL), an AC voltage control loop (AVC), an AC current control loop (ACC), and a pulse generator (PWM). The control parameter design method includes the following steps:

[0010] The inductor L1 and current i in the filter LCL that are connected to the inverter system are sampled. L1 And the capacitance C and voltage u of the filter LCL C ;

[0011] The voltage u of capacitor C of filter LCL in three-phase stationary coordinate system. CAfter performing the Park transformation, the d-axis and q-axis voltage variables in the synchronously rotating coordinate system are obtained. The q-axis voltage variable After processing by the phase-locked loop (PLL), the phase angle θ of the grid-side capacitor voltage is obtained;

[0012] Based on the phase angle θ of the grid-side capacitor voltage, the current i in the three-phase stationary coordinate system is... L1 After performing the Park transformation, the d-axis and q-axis current variables in the rotating coordinate system are obtained.

[0013] According to the bandwidth ω of the AC voltage control loop AVC AVC The bandwidth ω of the AC current control loop ACC ACC The impedance L of the AC weak current grid g The open-loop transfer function of the AC voltage control loop (AVC) and the closed-loop transfer function of the AC current control loop (ACC) are processed by the pole elimination method to obtain the PI control parameters of the AC voltage control loop (AVC). and

[0014] The q-axis voltage variable of capacitor C Input the AC voltage into the AVC control loop and according to the PI control parameters. and right After processing, the q-axis input reference signal of the AC current control loop ACC is obtained.

[0015] d-axis and q-axis voltage variables and d-axis and q-axis current variables as well as d-axis input reference signal After being processed in the AC current control loop ACC, the d-axis and q-axis control signals of the inverter system are obtained.

[0016] Based on the phase angle θ of the grid-side capacitor voltage, the control signal for the inverter is... After performing the inverse Park transform, the control signal in the stationary coordinate system is obtained.

[0017] The pulse generator PWM controls the signal. After pulse width modulation, switching signals for the power devices in the inverter system are generated, which are then used by the drive circuit to control the power devices to turn on and off.

[0018] The characteristic of the grid connection point voltage control parameter design method of the AC weak grid described in this invention is that the phase angle θ of the grid-side capacitor voltage is obtained using equation (1):

[0019]

[0020] In equation (1), This is the open-loop transfer function of the phase-locked loop (PLL). This refers to the proportional adjustment coefficient of the phase-locked loop (PLL). ω is the integral adjustment coefficient of the phase-locked loop (PLL). g Let ω be the rated angular frequency of the AC weak grid voltage, and s be the Laplace operator.

[0021] Furthermore, the open-loop transfer functions of the AC voltage control loop AVC and the AC current control loop ACC are obtained using equation (2).

[0022]

[0023] Combining bandwidth design with pole elimination method, the PI control parameters of AC voltage control loop AVC are calculated using equation (3). and

[0024]

[0025] Furthermore, based on the q-axis voltage variable of the capacitor The input signal of the AC current control loop ACC is obtained using equation (4).

[0026]

[0027] In equation (4), u ref It is the set value of the grid connection point voltage, G AVC This represents the open-loop transfer function of the AC voltage loop (AVC).

[0028] Furthermore, the d-axis and q-axis control signals of the inverter system are obtained using equation (5).

[0029]

[0030] In equation (5), G ACC Let represent the open-loop transfer function of the AC voltage loop ACC, and we have:

[0031]

[0032] The present invention provides a grid-connected voltage control parameter design device for an AC weak current grid, characterized in that the three-phase LCL type grid-connected inverter includes: a main circuit and a controller. The main circuit is composed of an AC weak current grid, an LCL filter, and an inverter system connected in sequence. The controller includes: a phase-locked loop (PLL), an AC voltage control loop (AVC), an AC current control loop (ACC), and a pulse generator (PWM). The control parameter design device includes:

[0033] The sampling module is used to sample the inductor L1 and current i in the filter LCL that are connected to the inverter system. L1 And the capacitance C and voltage u of the filter LCL C ;

[0034] The phase angle processing module is used to convert the voltage u of capacitor C of the filter LCL in a three-phase stationary coordinate system. C After performing the Park transformation, the d-axis and q-axis voltage variables in the synchronously rotating coordinate system are obtained. The q-axis voltage variable After processing by the phase-locked loop (PLL), the phase angle θ of the grid-side capacitor voltage is obtained;

[0035] The current processing module is used to process the current i in the three-phase stationary coordinate system based on the phase angle θ of the grid-side capacitor voltage. L1 After performing the Park transformation, the d-axis and q-axis current variables in the rotating coordinate system are obtained.

[0036] The parameter processing module is used to determine the bandwidth ω of the AC voltage control loop AVC. AVC The bandwidth ω of the AC current control loop ACC ACC The impedance L of the AC weak current grid g The open-loop transfer function of the AC voltage control loop (AVC) and the closed-loop transfer function of the AC current control loop (ACC) are processed by the pole elimination method to obtain the PI control parameters of the AC voltage control loop (AVC). and

[0037] The control module is used to control the q-axis voltage variable of capacitor C. Input the AC voltage into the AVC control loop and according to the PI control parameters. and right After processing, the q-axis input reference signal of the AC current control loop ACC is obtained. This will change the voltage variables along the d and q axes. and d-axis and q-axis current variables as well as d-axis input reference signal After being processed in the AC current control loop ACC, the d-axis and q-axis control signals of the inverter system are obtained.

[0038] Then, based on the phase angle θ of the grid-side capacitor voltage, the control signal for the inverter is adjusted. After performing the inverse Park transform, the control signal in the stationary coordinate system is obtained. The PWM signal is transmitted to the pulse generator.

[0039] The pulse generator PWM controls the signal. After pulse width modulation, switching signals for the power devices in the inverter system are generated, which are then used by the drive circuit to control the power devices to turn on and off.

[0040] The characteristic of the grid connection point voltage control parameter design method of the present invention for a weak AC power grid is that the phase angle processing module obtains the phase angle θ of the grid-side capacitor voltage using equation (1):

[0041]

[0042] In equation (1), This is the open-loop transfer function of the phase-locked loop (PLL). This refers to the proportional adjustment coefficient of the phase-locked loop (PLL). ω is the integral adjustment coefficient of the phase-locked loop (PLL). g Let ω be the rated angular frequency of the AC weak grid voltage, and s be the Laplace operator.

[0043] The parameter processing module uses equation (2) to obtain the open-loop transfer functions of the AC voltage control loop AVC and the AC current control loop ACC.

[0044]

[0045] Combining bandwidth design with pole elimination method, the PI control parameters of AC voltage control loop AVC are calculated using equation (3). and

[0046]

[0047] Furthermore, based on the q-axis voltage variable of the capacitor The input signal of the AC current control loop ACC is obtained using equation (4).

[0048]

[0049] In equation (4), u ref It is the set value of the grid connection point voltage, GAVC This represents the open-loop transfer function of the AC voltage loop (AVC).

[0050] The control module uses equation (5) to obtain the d-axis and q-axis control signals of the inverter system.

[0051]

[0052] In equation (5), G ACC Let represent the open-loop transfer function of the AC voltage loop ACC, and we have:

[0053]

[0054] The present invention discloses a computer-readable storage medium, wherein a computer program is stored on the computer-readable storage medium, and the computer program is executed by a processor to perform the steps of the grid connection point voltage control parameter design and control method.

[0055] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0056] 1. This invention achieves the elimination of the voltage drop at the grid connection point caused by the maximum grid impedance under weak grid conditions by designing the control parameters of the AC voltage control loop, effectively improving the power transmission level of the grid-connected inverter and enabling the grid-connected inverter to maintain stable operation.

[0057] 2. This invention only requires the design of relevant control coefficients based on the system operating voltage, current and related parameters, which significantly improves the power transmission problem caused by voltage deviation in grid-connected inverters under weak grid conditions. The implementation method is simple and effective.

[0058] 3. This invention employs AC voltage control (AVC), which can effectively improve the voltage quality at the grid connection point, correct the system operating point, and improve the power transmission level of the inverter system. At the same time, this control method naturally introduces the voltage support characteristics of grid-connected inverters, achieving perfect integration with the existing new power systems dominated by grid-connected inverters. This enables the grid-connected inverter to operate under weak grid conditions with extremely high grid impedance, significantly improving the operational stability of the grid-connected inverter. Attached Figure Description

[0059] Figure 1 This is a diagram of the main circuit topology of the three-phase LCL grid-connected inverter according to the present invention.

[0060] Figure 2 This is a block diagram of the controller structure of a three-phase LCL grid-connected inverter according to an embodiment of the present invention;

[0061] Figure 3The voltage waveforms at the inverter's grid connection point are shown before and after applying the control strategy of this invention when the grid short-circuit ratio is 2 (SCR = 2, weak grid).

[0062] Figure 4 The output current waveforms of the inverter before and after applying the control strategy of this invention are shown under a grid short-circuit ratio of 2 (SCR = 2, weak grid). Detailed Implementation

[0063] In this embodiment, a method for designing grid connection point voltage control parameters suitable for AC weak grids is presented to address the problem of grid connection point voltage drop caused by grid impedance in existing weak grid technologies. This is achieved by adding an AC voltage loop to provide voltage support at the grid connection point and designing control parameters for the AC transformer loop to stabilize the system. This invention can maintain stable system operation while suppressing the grid connection point voltage drop caused by grid impedance in weak grids. The technical solution of this invention will be described in detail below with reference to the accompanying drawings.

[0064] The topology used in this embodiment is as follows: Figure 1 As shown. This topology includes a three-phase full-bridge inverter, inverter arm inductor L1, filter capacitor C, grid-side inductor L2, and grid impedance L. g In this embodiment, L1 = 2mH, C = 6μF, L2 = 1mH, L g =15.5mH.

[0065] Figure 2 This is a schematic diagram of the control structure of a three-phase LCL grid-connected inverter. Figure 2 As can be seen, the method of the present invention consists of the following steps:

[0066] The inductor L1 and current i in the sampling filter LCL are connected to the inverter system L1 And the capacitance C and voltage u of the filter LCL C ;

[0067] The voltage u of capacitor C of filter LCL in three-phase stationary coordinate system. C After performing the Park transformation, the d-axis and q-axis voltage variables in the synchronously rotating coordinate system are obtained. q-axis voltage variable After processing by the phase-locked loop (PLL), the phase angle θ of the grid-side capacitor voltage is obtained.

[0068] The formula for calculating the phase angle θ of the grid-side capacitor voltage is shown in equation (1):

[0069]

[0070] In equation (1), This is the open-loop transfer function of the phase-locked loop (PLL). This refers to the proportional adjustment coefficient of the phase-locked loop (PLL). ω is the integral adjustment coefficient of the phase-locked loop (PLL). g Let be the rated angular frequency of the AC weak grid voltage, and s be the Laplace operator. In this embodiment, ω g = 100πrad / s.

[0071] Based on the phase angle θ of the grid-side capacitor voltage, the current i in the three-phase stationary coordinate system is... L1 After performing the Park transformation, the d-axis and q-axis current variables in the rotating coordinate system are obtained.

[0072] Based on the bandwidth ω of the AC voltage control loop AVC AVC The bandwidth ω of the AC current control loop ACC ACC The impedance L of the AC weak current grid g The open-loop transfer function of the AC voltage control loop (AVC) and the closed-loop transfer function of the AC current control loop (ACC) are processed by the pole elimination method to obtain the PI control parameters of the AC voltage control loop (AVC). and

[0073] The open-loop transfer function of the system, including the open-loop transfer function G of the AC voltage loop, is derived using equation (2). AVC The closed-loop transfer function G of the AC current loop ACC :

[0074]

[0075] In equation (2), G AVC G ACC As shown in equations (3) and (4) respectively:

[0076]

[0077]

[0078] Substituting equations (3) and (4) into equation (2), we obtain the open-loop transfer function (5) of the system:

[0079]

[0080] Combining bandwidth design with pole elimination method, the control parameters of AVC are calculated using equation (6). and

[0081]

[0082] A switching frequency with an inner current loop bandwidth of 1 / 10 is selected. Under this condition, Therefore, we can approximate it as follows: Based on the above analysis and calculations, under the influence of the AC voltage loop, the open-loop and closed-loop transfer functions of the system are as shown in equation (7):

[0083]

[0084] In this example, the design

[0085] The q-axis voltage variable of capacitor C Input AC voltage into the control loop AVC, and according to the PI control parameters and right After processing, the input reference signal of the AC current control loop ACC is obtained using equation (8).

[0086]

[0087] In equation (8), u ref It is the set value of the grid connection point voltage, G AVC This represents the open-loop transfer function of the AC voltage loop (AVC).

[0088] d-axis and q-axis voltage variables and d-axis and q-axis current variables as well as d-axis input reference signal After processing in the AC current control loop (ACC), the d-axis and q-axis control signals of the inverter system are obtained.

[0089] The control signal of the inverter is obtained using equation (9).

[0090]

[0091] In equation (9), G ACC As shown in equations (10) and (11):

[0092]

[0093] In this example, the design

[0094] Based on the phase angle θ of the grid-side capacitor voltage, the control signal for the inverter is... After performing the inverse Park transform, the control signal in the stationary coordinate system is obtained.

[0095] PWM pulse generator controls the signal After pulse width modulation, switching signals for the power devices in the inverter system are generated, which are then used by the drive circuit to control the power devices to turn on and off.

[0096] In this embodiment, a grid-connected voltage control parameter design device for an AC weak current grid is applied to a three-phase LCL type grid-connected inverter, including: a main circuit and a controller. The main circuit consists of an AC weak current grid, an LCL filter, and an inverter system connected in sequence. The controller includes: a phase-locked loop (PLL), an AC voltage control loop (AVC), an AC current control loop (ACC), and a pulse generator (PWM). The control parameter design device includes:

[0097] The sampling module is used to sample the inductor L1 and current i in the LCL filter that are connected to the inverter system. L1 And the capacitance C and voltage u of the filter LCL C ;

[0098] The phase angle processing module is used to convert the voltage u of capacitor C of the filter LCL in a three-phase stationary coordinate system. C After performing the Park transformation, the d-axis and q-axis voltage variables in the synchronously rotating coordinate system are obtained. q-axis voltage variable After processing by the phase-locked loop (PLL), the phase angle θ of the grid-side capacitor voltage is obtained using equation (1).

[0099]

[0100] In equation (1), This is the open-loop transfer function of the phase-locked loop (PLL). This refers to the proportional adjustment coefficient of the phase-locked loop (PLL). ω is the integral adjustment coefficient of the phase-locked loop (PLL). g Let ω be the rated angular frequency of the AC weak grid voltage, and s be the Laplace operator.

[0101] The current processing module is used to process the current i in the three-phase stationary coordinate system according to the phase angle θ of the grid-side capacitor voltage using equation (1). L1 After performing the Park transformation, the d-axis and q-axis current variables in the rotating coordinate system are obtained.

[0102] The parameter processing module is used to determine the bandwidth ω of the AC voltage control loop AVC. AVC The bandwidth ω of the AC current control loop ACC ACC The impedance L of the AC weak current grid gThe open-loop transfer function of the AC voltage control loop AVC and the closed-loop transfer function of the AC current control loop ACC are processed by eliminating poles, and the open-loop transfer functions of the AC voltage control loop AVC and the AC current control loop ACC are obtained using equation (2). Combining bandwidth design with pole elimination method, the PI control parameters of AC voltage control loop AVC are obtained using equation (3). and

[0103]

[0104]

[0105] The control module is used to control the q-axis voltage variable of capacitor C. Input AC voltage into the control loop AVC, and according to the PI control parameters and right After processing, the q-axis input reference signal of the AC current control loop ACC is obtained using equation (4). This will change the voltage variables along the d and q axes. and d-axis and q-axis current variables as well as d-axis input reference signal After processing in the AC current control loop (ACC), the d-axis and q-axis control signals of the inverter system are obtained.

[0106]

[0107] In equation (4), u ref It is the set value of the grid connection point voltage, G AVC This represents the open-loop transfer function of the AC voltage loop (AVC).

[0108] Then, based on the phase angle θ of the grid-side capacitor voltage, the control signal of the inverter is determined using equation (5). After performing the inverse Park transform, the control signal in the stationary coordinate system is obtained. The PWM signal is transmitted to the pulse generator.

[0109]

[0110] In equation (5), G ACC Let represent the open-loop transfer function of the AC voltage loop ACC, and we have:

[0111]

[0112] PWM pulse generator controls the signal After pulse width modulation, switching signals for the power devices in the inverter system are generated, which are then used by the drive circuit to control the power devices to turn on and off.

[0113] In this embodiment, a computer-readable storage medium stores a computer program, which is executed by a processor to perform the steps of the above method.

[0114] Figure 3 The output waveforms of the inverter's grid connection point voltage are shown before and after applying the control strategy of this invention under a grid short-circuit ratio of 2 (SCR = 2, weak grid). Figure 3 It can be clearly observed that after adopting this invention, the grid connection point voltage of the inverter under weak power grid can reach the set value. When this invention is withdrawn, the grid connection point voltage of the grid-connected inverter drops significantly.

[0115] Figure 4 The output current waveforms of the inverter before and after applying the control strategy of this invention are shown under a grid short-circuit ratio of 2 (SCR = 2, weak grid). Figure 4 It can be clearly observed that after adopting this invention, the grid-connected inverter system under weak power grid conditions can be stable, but when this invention is withdrawn, the grid-connected inverter system becomes unstable.

[0116] In summary, the control method for improving grid impedance adaptability based on AC voltage loop under weak grid conditions proposed in this invention can effectively improve the voltage drop problem at the grid connection point of the inverter system under weak grid conditions and improve the stability of the grid-connected inverter.

Claims

1. A method for designing grid connection point voltage control parameters for an AC weak current grid, characterized in that, This is applied in a three-phase LCL type grid-connected inverter and includes: a main circuit and a controller. The main circuit consists of an AC low-voltage grid, an LCL filter, and an inverter system connected in sequence. The controller includes: a phase-locked loop (PLL), an AC voltage control loop (AVC), an AC current control loop (ACC), and a pulse generator (PWM). The control parameter design method includes the following steps: The inductor L1 and current i in the filter LCL that are connected to the inverter system are sampled. L1 And the capacitance C and voltage u of the filter LCL C ; The voltage u of capacitor C of filter LCL in three-phase stationary coordinate system. C After performing the Park transformation, the d-axis and q-axis voltage variables in the synchronously rotating coordinate system are obtained. The q-axis voltage variable After processing by the phase-locked loop (PLL), the phase angle θ of the grid-side capacitor voltage is obtained; Based on the phase angle θ of the grid-side capacitor voltage, the current i in the three-phase stationary coordinate system is... L1 After performing the Park transformation, the d-axis and q-axis current variables in the rotating coordinate system are obtained. According to the bandwidth ω of the AC voltage control loop AVC AVC The bandwidth ω of the AC current control loop ACC ACC The impedance L of the AC weak current grid g The open-loop transfer function of the AC voltage control loop (AVC) and the closed-loop transfer function of the AC current control loop (ACC) are processed by the pole elimination method to obtain the PI control parameters of the AC voltage control loop (AVC). and The q-axis voltage variable of capacitor C Input the AC voltage into the AVC control loop and according to the PI control parameters. and right After processing, the q-axis input reference signal of the AC current control loop ACC is obtained. d-axis and q-axis voltage variables and d-axis and q-axis current variables as well as d-axis input reference signal After being processed in the AC current control loop ACC, the d-axis and q-axis control signals of the inverter system are obtained. Based on the phase angle θ of the grid-side capacitor voltage, the control signal for the inverter is... After performing the inverse Park transform, the control signal in the stationary coordinate system is obtained. The pulse generator PWM controls the signal. After pulse width modulation, switching signals for the power devices in the inverter system are generated, which are then used by the drive circuit to control the power devices to turn on and off.

2. The method for designing grid connection point voltage control parameters for an AC weak current grid according to claim 1, characterized in that, The phase angle θ of the grid-side capacitor voltage is obtained using equation (1): In equation (1), This is the open-loop transfer function of the phase-locked loop (PLL). This refers to the proportional adjustment coefficient of the phase-locked loop (PLL). ω is the integral adjustment coefficient of the phase-locked loop (PLL). g Let ω be the rated angular frequency of the AC weak grid voltage, and s be the Laplace operator.

3. The method for designing grid connection point voltage control parameters for an AC weak current grid according to claim 2, characterized in that, The open-loop transfer functions of the AC voltage control loop AVC and the AC current control loop ACC are obtained using equation (2). Combining bandwidth design with pole elimination method, the PI control parameters of AC voltage control loop AVC are calculated using equation (3). and 4. The method for designing grid connection point voltage control parameters for an AC weak current grid according to claim 3, characterized in that, Based on the q-axis voltage variable of the capacitor The input signal of the AC current control loop ACC is obtained using equation (4). In equation (4), u ref It is the set value of the grid connection point voltage, G AVC This represents the open-loop transfer function of the AC voltage loop (AVC).

5. According to the design method of grid connection point voltage control parameters for an AC weak grid as described in claim 4, the d-axis and q-axis control signals of the inverter system are obtained using equation (5). In equation (5), G ACC Let represent the open-loop transfer function of the AC voltage loop ACC, and we have:

6. A device for designing grid connection point voltage control parameters for an AC weak current grid, characterized in that, The three-phase LCL grid-connected inverter includes a main circuit and a controller. The main circuit consists of an AC low-voltage grid, an LCL filter, and an inverter system connected in sequence. The controller includes a phase-locked loop (PLL), an AC voltage control loop (AVC), an AC current control loop (ACC), and a pulse generator (PWM). The control parameter design device includes: The sampling module is used to sample the inductor L1 and current i in the filter LCL that are connected to the inverter system. L1 And the capacitance C and voltage u of the filter LCL C ; The phase angle processing module is used to convert the voltage u of capacitor C of the filter LCL in a three-phase stationary coordinate system. C After performing the Park transformation, the d-axis and q-axis voltage variables in the synchronously rotating coordinate system are obtained. The q-axis voltage variable After processing by the phase-locked loop (PLL), the phase angle θ of the grid-side capacitor voltage is obtained; The current processing module is used to process the current i in the three-phase stationary coordinate system based on the phase angle θ of the grid-side capacitor voltage. L1 After performing the Park transformation, the d-axis and q-axis current variables in the rotating coordinate system are obtained. The parameter processing module is used to determine the bandwidth ω of the AC voltage control loop AVC. AVC The bandwidth ω of the AC current control loop ACC ACC The impedance L of the AC weak current grid g The open-loop transfer function of the AC voltage control loop (AVC) and the closed-loop transfer function of the AC current control loop (ACC) are processed by the pole elimination method to obtain the PI control parameters of the AC voltage control loop (AVC). and The control module is used to control the q-axis voltage variable of capacitor C. Input the AC voltage into the AVC control loop and according to the PI control parameters. and right After processing, the q-axis input reference signal of the AC current control loop ACC is obtained. This will change the voltage variables along the d and q axes. and d-axis and q-axis current variables as well as d-axis input reference signal After being processed in the AC current control loop ACC, the d-axis and q-axis control signals of the inverter system are obtained. Then, based on the phase angle θ of the grid-side capacitor voltage, the control signal for the inverter is adjusted. After performing the inverse Park transform, the control signal in the stationary coordinate system is obtained. The PWM signal is transmitted to the pulse generator. The pulse generator PWM controls the signal. After pulse width modulation, switching signals for the power devices in the inverter system are generated, which are then used by the drive circuit to control the power devices to turn on and off.

7. The device for designing grid connection point voltage control parameters for an AC weak current grid according to claim 6, characterized in that, The phase angle processing module obtains the phase angle θ of the grid-side capacitor voltage using equation (1): In equation (1), This is the open-loop transfer function of the phase-locked loop (PLL). This refers to the proportional adjustment coefficient of the phase-locked loop (PLL). ω is the integral adjustment coefficient of the phase-locked loop (PLL). g Let ω be the rated angular frequency of the AC weak grid voltage, and s be the Laplace operator.

8. The device for designing grid connection point voltage control parameters for an AC weak current grid according to claim 6, characterized in that, The parameter processing module uses equation (2) to obtain the open-loop transfer functions of the AC voltage control loop AVC and the AC current control loop ACC. Combining bandwidth design with pole elimination method, the PI control parameters of AC voltage control loop AVC are calculated using equation (3). and 9. The device for designing grid connection point voltage control parameters for an AC weak current grid according to claim 6, characterized in that, Based on the q-axis voltage variable of the capacitor The input signal of the AC current control loop ACC is obtained using equation (4). In equation (4), u ref It is the set value of the grid connection point voltage, G AVC This represents the open-loop transfer function of the AC voltage loop (AVC).

10. A grid connection point voltage control parameter design device for an AC weak grid according to claim 6, wherein the control module obtains the d-axis and q-axis control signals of the inverter system using equation (5). In equation (5), G ACC Let represent the open-loop transfer function of the AC voltage loop ACC, and we have:

11. A computer-readable storage medium storing a computer program thereon, characterized in that, When the computer program is run by the processor, it executes the steps of the grid connection point voltage control parameter design and control method according to any one of claims 1-5.

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