Method and system for controlling grid-connected capacitor voltage of grid-forming inverter under asymmetric fault

Abstract

The invention belongs to the field of power supply control, and provides a control method and system for grid-connected capacitor voltage of a grid-forming inverter under an asymmetric fault, and the method comprises the steps: determining the actual output voltage, actual output current and standard current positive and negative sequence components of the grid-forming inverter under the asymmetric fault; calculating a negative sequence reference voltage; taking the negative-sequence reference voltage as a fluctuation negative-sequence component, taking a reference voltage during normal operation of the power supply system as a direct-current component, and adding the direct-current component and the fluctuation negative-sequence component to obtain an outer-ring reference voltage; inputting the outer ring reference voltage and the actual output voltage into a voltage outer ring controller to obtain an inner ring reference current; inputting the inner ring reference current and the actual output current into a current inner ring controller to obtain an initial modulation signal; and according to the initial modulation signal, controlling a switching device of the network-constructing inverter so as to control the grid-connected capacitor voltage of the network-constructing inverter. According to the scheme provided by the invention, the control reliability and stability of the grid-connected capacitor voltage are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply control, and in particular to a method and system for controlling the voltage of a grid-connected capacitor of a grid-connected inverter under an asymmetric fault. Background Art

[0002] As the global demand for clean energy continues to grow, the proportion of renewable energy generation in the power system continues to rise. Renewable energy such as solar energy and wind energy are connected to the power grid through grid-building inverters. As the key interface device connecting renewable energy and the power grid, the control reliability of grid-building inverters plays a vital role in the stable operation of the power system.

[0003] In the actual operation of the power system, short-circuit faults are common and have great hazards. Among them, most short-circuit faults are asymmetric types, such as single-phase grounding, two-phase short circuit and other typical working conditions. When these asymmetric faults occur, the grid voltage will have significant positive and negative sequence components. This voltage asymmetry will cause a series of complex problems, such as system power oscillation, resulting in unstable power transmission of the power system, and even system decoupling in severe cases; at the same time, it will also cause equipment overload, shorten equipment service life, increase equipment maintenance costs, and even cause equipment damage, which will bring great challenges to the safe and reliable operation of the power system.

[0004] In the related technology, the capacitor voltage control architecture of the grid inverter of the voltage-current dual closed-loop grid-connected converter is usually adopted, but this control architecture does not fully consider the asymmetric operation situation, so that the grid inverter under this architecture lacks the ability to operate stably when facing asymmetric faults, and cannot effectively deal with the impact of the positive and negative sequence components of the grid voltage, and it is difficult to meet the growing stable operation requirements of the power system. Therefore, the traditional capacitor voltage control architecture of the grid inverter has technical problems of insufficient control reliability and stability under asymmetric faults. Summary of the invention

[0005] The present invention provides a method and system for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault, so as to solve the defects of the conventional grid-connected inverter capacitor voltage control architecture in that the control reliability and stability are insufficient under an asymmetric fault.

[0006] In one aspect, the present invention provides a method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault, comprising: Under an asymmetric fault, determine the actual output voltage, actual output current, and standard current positive and negative sequence components of the actual output current in the rotating coordinate system of the grid inverter; The negative sequence reference voltage is calculated based on the set virtual negative sequence reactance and the positive and negative sequence components of the standard current; Taking the negative-sequence reference voltage as the fluctuating negative-sequence component, taking the reference voltage during normal operation of the power supply system as the DC component, and adding the DC component to the fluctuating negative-sequence component to obtain an outer loop reference voltage; Inputting the outer loop reference voltage and the actual output voltage into a voltage outer loop controller to obtain an inner loop reference current output by the voltage outer loop controller; Inputting the inner loop reference current and the actual output current into a current inner loop controller to obtain an initial modulation signal output by the current inner loop controller; The switch device of the grid-connected inverter is controlled according to the initial modulation signal to control the grid-connected capacitor voltage of the grid-connected inverter.

[0007] According to the control method of the grid-connected capacitor voltage of the grid-connected inverter under an asymmetric fault provided by the present invention, the standard current positive and negative sequence components of the actual output current of the grid-connected inverter in the rotating coordinate system are determined, including: Obtain the actual output current of the grid-connected inverter; Input the actual output current into a biquad generalized integrator to obtain initial positive and negative sequence components of the actual output current in a stationary coordinate system; The initial current positive and negative sequence components are subjected to coordinate transformation to obtain standard current positive and negative sequence components of the actual output current in a rotating coordinate system.

[0008] According to the control method of the grid-connected capacitor voltage of the grid-connected inverter under asymmetric fault provided by the present invention, the negative sequence reference voltage is calculated according to the set virtual negative sequence reactance and the positive and negative sequence components of the standard current, including: A first matrix is ​​established according to the set virtual negative-sequence reactance; Establishing a second matrix according to the d-axis current negative sequence component and the q-axis current negative sequence component in the standard current positive and negative sequence components; The first matrix is ​​multiplied by the second matrix to obtain a negative-sequence reference voltage.

[0009] According to the method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault provided by the present invention, the switching device of the grid-connected inverter is controlled according to the initial modulation signal, including: Inputting the initial modulation signal into a modulation wave generation module to obtain a three-phase modulation signal output by the modulation wave generation module; According to the set carrier signal, the three-phase modulated signal is converted into a three-phase alternating current signal; The switching devices of the grid-connecting inverter are controlled by the three-phase AC signal.

[0010] According to the method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault provided by the present invention, the method further includes: In the virtual synchronization phase, the measured active power value and active power reference value of the grid-connected inverter are obtained; Determining a theoretical phase difference between an actual output voltage of the grid-connecting inverter and a grid voltage according to the active power measured value and the active power reference value; Based on the theoretical phase difference, the phase of the actual output voltage is adjusted.

[0011] According to the method for controlling the grid-connected capacitor voltage of the grid-connected inverter under an asymmetric fault provided by the present invention, the theoretical phase difference of the output voltage of the grid-connected inverter relative to the grid voltage is determined according to the active power measured value and the active power reference value, including: Subtracting the active power measured value from the active power reference value to obtain a power deviation; Inputting the power deviation into a virtual inertia controller to obtain a power change trend value output by the virtual inertia controller; Inputting the power change trend value into a virtual damping controller to obtain a theoretical power value output by the virtual damping controller; The theoretical power value is input into an integral controller to obtain a theoretical phase difference output by the integral controller.

[0012] According to the method for controlling the grid-connected capacitor voltage of the grid-connected inverter under asymmetric fault provided by the present invention, after adjusting the phase of the actual output voltage based on the theoretical phase difference, the method further includes: Determine the actual phase difference between the actual output voltage of the grid inverter and the actual grid voltage; Subtract the actual phase difference from the theoretical phase difference to obtain a phase difference deviation; Based on the phase difference deviation, the active power reference value is corrected.

[0013] According to the method for controlling the grid-connected capacitor voltage of the grid-connected inverter under asymmetric fault provided by the present invention, after correcting the active power reference value based on the phase difference deviation, the method further includes: sending the corrected active power reference value to the user terminal; After receiving the correction intervention instruction fed back by the user terminal, the active power reference value is secondarily corrected according to the correction intervention data in the correction intervention instruction.

[0014] According to the method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault provided by the present invention, both the voltage outer loop controller and the current inner loop controller adopt PIR controllers.

[0015] On the other hand, the present invention also provides a control system for the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault, comprising: An acquisition module is used to determine the actual output voltage, actual output current and standard current positive and negative sequence components of the actual output current in a rotating coordinate system of the grid-connected inverter under an asymmetric fault; A first calculation module, used for calculating a negative-sequence reference voltage according to a set virtual negative-sequence reactance and the positive and negative-sequence components of the standard current; A second calculation module is used to take the negative-sequence reference voltage as a fluctuating negative-sequence component, take the reference voltage during normal operation of the power supply system as a DC component, and add the DC component to the fluctuating negative-sequence component to obtain an outer loop reference voltage; An outer loop regulation module, used for inputting the outer loop reference voltage and the actual output voltage into a voltage outer loop controller to obtain an inner loop reference current output by the voltage outer loop controller; An inner loop regulation module, used for inputting the inner loop reference current and the actual output current into a current inner loop controller to obtain an initial modulation signal output by the current inner loop controller; The control module is used to control the switch device of the grid-connected inverter according to the initial modulation signal to control the grid-connected capacitor voltage of the grid-connected inverter.

[0016] The present invention provides a control method and system for the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault. Under the asymmetric fault, the actual output voltage, the actual output current and the standard current positive and negative sequence components of the actual output current in a rotating coordinate system of the grid-connected inverter are determined; a negative sequence reference voltage is calculated according to a set virtual negative sequence reactance and the standard current positive and negative sequence components; the negative sequence reference voltage is used as a fluctuating negative sequence component, and the reference voltage during normal operation of the power supply system is used as a DC component, and the DC component is added to the fluctuating negative sequence component to obtain an outer loop reference voltage; the outer loop reference voltage and the actual output voltage are input into a voltage outer loop controller to obtain an inner loop reference current; the inner loop reference current and the actual output current are input into a current inner loop controller to obtain an initial modulation signal; and the switch device of the grid-connected inverter is controlled according to the initial modulation signal to control the grid-connected capacitor voltage of the grid-connected inverter. Since a negative-sequence component feedback link is introduced in the control of the grid-connected capacitor voltage, the negative-sequence reference voltage is continuously corrected by the positive and negative sequence components of the standard current, thereby introducing a negative-sequence component when an asymmetric fault occurs, thereby achieving accurate control of the positive and negative sequence components of the grid-connected capacitor voltage, thereby improving the control reliability and stability of the grid-connected capacitor voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is a flow chart of a method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of the relationship between the negative sequence voltage of the virtual negative sequence voltage source at the fault point and the capacitor voltage negative sequence vector when there is no voltage negative sequence component; Figure 3 It is a schematic diagram of the relationship between the negative sequence voltage of the virtual negative sequence voltage source at the fault point and the capacitor voltage negative sequence vector in the case of a voltage negative sequence component; Figure 4 It is a schematic diagram of the control principle of the grid-connected capacitor voltage of the grid-connected inverter; Figure 5 It is a schematic diagram of the change curve of the d-axis voltage; Figure 6 It is a schematic diagram of the change curve of the q-axis voltage; Figure 7 It is a schematic diagram of the variation curve of the d-axis current; Figure 8 It is a schematic diagram of the variation curve of the q-axis current; Fig. 9 is a schematic diagram of the change curve of the negative sequence voltage amplitude under different virtual negative sequence reactances; Fig.10 is a schematic diagram of the change curve of the negative sequence current amplitude under different virtual negative sequence reactances; Fig.11 It is a structural schematic diagram of a control system for a grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Combine the following Figures 1 to 11 The detailed scheme of the method and system for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault provided by an embodiment of the present invention is described.

[0021] Figure 1 It is a flow chart of a method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault provided by an embodiment of the present invention.

[0022] like Figure 1 As shown, the method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault provided by the embodiment of the present invention mainly includes the following steps: Step 110: Under an asymmetric fault, determine the actual output voltage, the actual output current, and the standard current positive and negative sequence components of the actual output current in the rotating coordinate system of the grid-connected inverter.

[0023] In practical applications, when an asymmetric fault occurs in the power grid, a negative sequence voltage will be generated at the fault point. The grid-connected scenario under an asymmetric fault can be equivalent to a virtual negative sequence voltage source somewhere in the line. If the resistance of the line is ignored, it is assumed that the equivalent negative sequence reactance between the capacitor negative sequence voltage and the negative sequence voltage of the virtual negative sequence voltage source is The grid-connected capacitor voltage does not have a negative-sequence component. At this time, the output current of the grid-connected inverter may have a large negative-sequence current component, and the traditional grid-connected inverter control link cannot regulate the negative-sequence current. At this time, the negative-sequence voltage of the virtual negative-sequence voltage source at the fault point The relationship between the capacitor voltage negative sequence vector can be seen in Figure 2 As shown, Represents the change in the negative-sequence voltage of the virtual negative-sequence voltage source at the fault point.

[0024] Under the same asymmetric fault condition, assuming that the virtual negative sequence voltage source does not change, if the control strategy is improved, the positive and negative sequence components of the grid-connected capacitor voltage can be controlled separately, such as Figure 3 As shown, when the grid-connected capacitor voltage has a certain negative sequence voltage When the negative sequence current It can also be reduced to a certain extent. By controlling the amplitude and vector direction of the negative sequence voltage, the negative sequence current can be further flexibly suppressed. Therefore, realizing the separate control of the positive and negative sequence components of the grid-connected capacitor voltage can be used as one of the important means of grid-connecting the grid inverter under asymmetric faults.

[0025] Step 120: Calculate and obtain a negative-sequence reference voltage according to the set virtual negative-sequence reactance and the positive and negative-sequence components of the standard current.

[0026] In this embodiment, the virtual negative-sequence reactance can be set to flexibly set the capacitor negative-sequence voltage, thereby enabling flexible control of the negative-sequence current.

[0027] Step 130: taking the negative-sequence reference voltage as the fluctuating negative-sequence component, taking the reference voltage during normal operation of the power supply system as the DC component, and adding the DC component to the fluctuating negative-sequence component to obtain an outer loop reference voltage.

[0028] In this embodiment, the outer loop reference voltage further introduces a fluctuating negative sequence component on the basis of the DC component, which can provide a more effective data basis for the voltage outer loop control.

[0029] Step 140: inputting the outer loop reference voltage and the actual output voltage into the voltage outer loop controller to obtain the inner loop reference current output by the voltage outer loop controller.

[0030] In this embodiment, in the voltage outer loop control link, since a fluctuating negative sequence component is introduced into the outer loop reference voltage, the voltage outer loop control accuracy is improved.

[0031] Step 150: input the inner loop reference current and the actual output current into the current inner loop controller to obtain an initial modulation signal output by the current inner loop controller.

[0032] The current inner loop control link can further regulate the output current of the grid-connected inverter according to the inner loop reference current output by the voltage outer loop control.

[0033] Step 160: Control the switch device of the grid-connected inverter according to the initial modulation signal to control the grid-connected capacitor voltage of the grid-connected inverter.

[0034] The solution provided in this embodiment can provide effective data basis for voltage outer loop control by introducing fluctuating negative sequence components, thereby improving the control accuracy of current inner loop, thereby achieving effective control of the grid-connected capacitor voltage of the grid-connected inverter.

[0035] In one embodiment, determining the standard current positive and negative sequence components of the actual output current of the grid-connected inverter in the rotating coordinate system specifically includes: First, the actual output current of the grid-connected inverter is obtained.

[0036] Then, the actual output current Input the Dual Second Order General Integrator (DSOGI) to obtain the initial current positive and negative sequence components of the actual output current in the stationary coordinate system .

[0037] like Figure 4 As shown, in the positive and negative sequence decomposition link, the actual output voltage go through - dq Transformation can be obtained in the rotating coordinate system .

[0038] Finally, the initial current positive and negative sequence components are transformed to obtain the standard current positive and negative sequence components of the actual output current in the rotating coordinate system.

[0039] In this embodiment, the initial current positive and negative sequence components conduct - dq Transform to obtain the standard current positive and negative sequence components in the rotating coordinate system 、 .

[0040] In one embodiment, the negative sequence reference voltage is calculated based on the set virtual negative sequence reactance and the positive and negative sequence components of the standard current, specifically including: Firstly, a first matrix is ​​established according to the set virtual negative-sequence reactance.

[0041] Then, a second matrix is ​​established according to the d-axis current negative sequence component and the q-axis current negative sequence component in the standard current positive and negative sequence components.

[0042] Finally, the first matrix is ​​multiplied by the second matrix to obtain a negative-sequence reference voltage.

[0043] It can be understood that the capacitor negative sequence voltage can be calculated through the virtual negative sequence reactance and negative sequence current. The calculation formula is as follows: (1) The relationship between the capacitor negative sequence voltage and the negative sequence voltage of the virtual negative sequence voltage source is: (2) If the negative sequence current flowing through the grid-connected capacitor is ignored, and the negative sequence current output by the grid-connected inverter is the same as the negative sequence current flowing through the virtual negative sequence voltage source through the line, the above two equations can be obtained: (3) After adopting the improved control strategy, the negative sequence current output by the grid-connected inverter can be expressed as follows: (4) in, represents the capacitor negative sequence voltage, represents the negative sequence current, represents the virtual negative sequence reactance, represents the negative sequence voltage of the virtual negative sequence voltage source, represents the negative sequence current flowing through the line through the virtual negative sequence voltage source, It represents the equivalent negative-sequence reactance between the grid-connected capacitor and the virtual negative-sequence power supply.

[0044] Due to the equivalent negative-sequence reactance between the grid-connected capacitor and the virtual negative-sequence voltage source It will not change with the change of control strategy, so the negative-sequence reference voltage can be flexibly set by setting the virtual negative-sequence reactance, thereby realizing flexible control of the negative-sequence current output by the grid-connected inverter.

[0045] In the voltage reference value generation link, the negative sequence reference voltage is expressed in matrix form, as follows: (5) in, Represents the d-axis negative-sequence voltage in the negative-sequence reference voltage, Represents the q-axis negative-sequence voltage in the negative-sequence reference voltage, represents the virtual negative sequence reactance, Indicates the negative sequence component of the d-axis current in the positive and negative sequence components of the standard current. Represents the negative sequence component of the q-axis current in the positive and negative sequence components of the standard current.

[0046] In this embodiment, the negative-sequence reference voltage is used as the fluctuating negative-sequence component, and the reference voltage during normal operation of the power supply system is used as the DC component. The DC component and the fluctuating negative-sequence component are added to obtain the outer loop reference voltage. The matrix form of the outer loop reference voltage can be expressed as follows: (6) in, represents the q-axis voltage component in the outer loop reference voltage, represents the d-axis voltage component in the outer loop reference voltage, represents the q-axis voltage positive sequence component in the DC component, Represents the d-axis voltage positive sequence component in the DC component.

[0047] In this embodiment, both the voltage outer loop controller and the current inner loop controller adopt PIR (Proportional Integral Resonant) controller.

[0048] Specifically, the transfer function of the PIR controller is: (7) in, is the proportional coefficient of the outer loop PIR controller, is the integration coefficient, is the resonance coefficient, is the cut-off frequency, is the resonant angular frequency.

[0049] In the voltage and current dual closed-loop control link, for the voltage outer loop controller, the outer loop reference voltage can be The actual output voltage ud 、u q The voltage outer loop controller can effectively track the DC component and AC component (i.e., the fluctuating negative sequence component) by adjusting the deviation, and finally output the inner loop reference current i gdref , i gqref .

[0050] For the current inner loop controller, the inner loop reference current can be i gdref , i gqref The actual output current i d 、i q The deviation is controlled to output the initial modulation signal u gd , u gq .

[0051] In one embodiment, controlling the switch device of the grid-connected inverter according to the initial modulation signal specifically includes: First, the initial modulation signal is input into the modulation wave generation module to obtain a three-phase modulation signal output by the modulation wave generation module.

[0052] Then, the three-phase modulated signal is converted into a three-phase AC signal according to the set carrier signal.

[0053] Finally, the switching devices of the grid-connected inverter are controlled by three-phase AC signals.

[0054] In the modulation wave generation stage, the initial modulation signal can be u gd , u gq Multiply by the modulation factor K mod , and obtain the three-phase modulated signal e gd 、e gq , and then through dq-abc Transformation can get three-phase AC signal , which is used to control the switching devices of the grid-connected inverter, thereby realizing the control of the grid-connected capacitor voltage of the grid-connected inverter. The entire control process can be found in Figure 4 .

[0055] In one embodiment, the method for controlling the grid-connected capacitor voltage of the grid-connected inverter under the asymmetric fault may further include: First, in the virtual synchronization phase, the measured active power value of the grid inverter is obtained.P and active power reference P ref .

[0056] Then, based on the measured value of active power P and active power reference P ref , determine the theoretical phase difference between the actual output voltage of the grid inverter and the grid voltage .

[0057] See also Figure 4 , when the measured value of active power is known P and active power reference P ref Based on the virtual moment of inertia of the synchronous generator J , Rated angular frequency , damping coefficient D And the actual angular frequency , we can get the theoretical phase difference .

[0058] Finally, based on the theoretical phase difference , adjust the phase of the actual output voltage.

[0059] In this embodiment, the introduction of the above control process in the virtual synchronization link can coordinate the synchronization relationship between the grid-forming inverter and the power grid, so as to help improve the stability and control performance of the system under asymmetric faults.

[0060] also, Figure 4 The main circuit part on the right side also shows the resistance of the connection line between the grid inverter and the grid. R g and inductance L g , grid-connected capacitor C, grid-side equivalent inductance L sys and resistor R sys , grid voltage phasor , Output current phasor of grid inverter and into the grid Grid The current phasor .

[0061] In some embodiments, determining the theoretical phase difference of the output voltage of the grid inverter relative to the grid voltage according to the measured active power value and the active power reference value specifically includes: First, the actual active power value is subtracted from the active power reference value to obtain the power deviation.

[0062] Then, the power deviation is input into the virtual inertia controller to obtain the power change trend value output by the virtual inertia controller.

[0063] The virtual inertia controller can simulate the inertia characteristics of the synchronous generator, which is usually implemented by a first-order inertia link. Its transfer function is as follows: (8) in, T is the inertia time constant, is the input parameter.

[0064] Afterwards, the power change trend value is input into the virtual damping controller to obtain the theoretical power value output by the virtual damping controller.

[0065] In this embodiment, the virtual damping controller is implemented by a proportional-differential controller. In this process, the damping force is added to the power change trend value to obtain a theoretical power value after inertia and damping processing.

[0066] Finally, the theoretical power value is input into the integral controller to obtain the theoretical phase difference output by the integral controller.

[0067] In this embodiment, the theoretical power value is input into the integral controller, and the theoretical phase difference can be obtained through integral operation.

[0068] In one embodiment, after adjusting the phase of the actual output voltage based on the theoretical phase difference, the method may further include: First, the actual phase difference between the actual output voltage of the grid inverter and the actual grid voltage is determined.

[0069] In practical applications, the actual phase difference between the actual output voltage of the grid inverter and the actual grid voltage can be detected through the phase-locked loop technology.

[0070] Then, the actual phase difference is subtracted from the theoretical phase difference to obtain the phase difference deviation.

[0071] It can be understood that the phase deviation can represent the error of the actual phase difference relative to the theoretical phase difference.

[0072] Finally, based on the phase difference deviation, the active power reference value is corrected.

[0073] In a specific implementation, based on the phase difference deviation, the active power reference value is corrected, specifically including: If the phase difference deviation is within the first numerical range, the active power correction amount is determined according to the first linear function.

[0074] If the phase difference deviation is within the second numerical range, the active power correction amount is determined according to the second linear function.

[0075] If the phase deviation is within the third numerical range, the power correction is determined according to the third linear function.

[0076] Finally, the active power reference value is corrected according to the active power correction amount.

[0077] Among them, the lower limit values ​​and upper limit values ​​corresponding to the first numerical interval, the second numerical interval and the third numerical interval respectively increase successively, and the slopes corresponding to the first linear function, the second linear function and the third linear function respectively increase successively.

[0078] It should be noted that the phase deviation mentioned in this embodiment refers to the absolute value of the phase deviation, wherein the first numerical interval may be [5, 10), the second numerical interval may be [10, 15), and the third numerical interval may be [15, 20).

[0079] It is understandable that, considering that when it is detected that the actual output voltage of the grid inverter has a large deviation from the actual phase difference and theoretical phase difference relative to the grid voltage, in order to make the grid inverter and the grid operate better synchronously, the active power reference value originally input by the user may not meet the demand. At this time, the active power reference value can be automatically corrected according to the phase deviation, thereby optimizing power transmission and improving the stability and efficiency of the system.

[0080] In practical applications, the phase deviation between the historical phase difference of the historical output voltage of the grid inverter in the actual system relative to the grid voltage and the theoretical phase difference can be obtained, and the active power correction amount in the above situation can be obtained to obtain multiple two-dimensional arrays. After preprocessing the multiple two-dimensional arrays, the theoretical function curve between the phase deviation and the active power correction amount is obtained through data fitting.

[0081] Subsequently, the curve segments corresponding to the phase deviation in the first numerical interval, the second numerical interval and the third numerical interval are intercepted on the theoretical function curve, and the corresponding linear functions are obtained by approximate fitting according to each curve segment. Subsequently, the linear function obtained by approximate fitting can be further fine-tuned to ensure that the slopes corresponding to the first linear function, the second linear function and the third linear function are different and increase successively.

[0082] In one embodiment, after the active power reference value is corrected based on the phase difference deviation, the method may further include: On the one hand, the corrected active power reference value is sent to the user terminal.

[0083] On the other hand, after receiving the correction intervention instruction fed back by the user terminal, the active power reference value is corrected for the second time according to the correction intervention data in the correction intervention instruction.

[0084] It should be noted that after the active power reference value is automatically corrected, the user can be informed of the corrected active power reference value through a human-computer interaction interface, etc., and the user is allowed to intervene in the correction strategy to ensure that the automatic correction operation meets actual application requirements.

[0085] It can be understood that this embodiment uses a corresponding linear function to determine the active power correction amount according to the numerical range of the phase deviation. The larger the phase deviation, the larger the slope of the corresponding linear function, that is, the larger the active power correction amount. Therefore, a correction plan can be provided specifically according to the phase deviation situation, and the correction efficiency is higher.

[0086] In this embodiment, in the process of correcting the active power reference value according to the active power correction amount, the active power reference value and the active power correction amount may be added to obtain the corrected active power.

[0087] In practical applications, a simulation model can be built in the DIgSILENT PowerFactory software. The simulation setting parameters are shown in Table 1.

[0088] Table 1 Simulation setting parameters

[0089] set up Figure 4 The fault occurs at the position shown, where the single-phase amplitude drops to 0.5 pu. In the simulation, it is set that the single-phase amplitude of phase A drops in the power grid at 0.1 s, and the power grid returns to normal at 0.6 s, and the amplitude of phase A rises back to 1 p.u., X eq- =0.1, the d-axis voltage and q-axis voltage of the output voltage of the grid inverter and the d-axis current and q-axis current of the output current of the grid inverter are respectively Figure 5 , Figure 6 , Figure 7 , Figure 8 As shown, it can be seen that the control method of the grid-connected capacitor voltage of the grid-connected inverter under asymmetric fault provided by this embodiment can timely track the positive and negative sequence synthetic reference values, thereby realizing the separate control of the positive and negative sequence components of the grid-connected capacitor voltage.

[0090] Fig. 9 and Fig.10 The following examples are shown in different X eq- The changes in the negative sequence voltage amplitude and negative sequence current amplitude are given by Fig. 9 and Fig.10 It can be seen that X eq- The larger the value of is, the larger the negative sequence voltage amplitude is, and the smaller the negative sequence current amplitude is suppressed.

[0091] In summary, the control method for the grid-connected capacitor voltage of the network-forming inverter under asymmetric faults proposed in this embodiment can achieve flexible control of the positive and negative sequence components of the output voltage, and further achieve flexible control of the positive and negative sequence components of the output current, improving the control reliability and stability of the grid-connected capacitor voltage of the network-forming inverter under asymmetric faults.

[0092] Based on the same general inventive concept, the present invention also protects a control system for the grid-connected capacitor voltage of the network-forming inverter under asymmetric faults. The control system for the grid-connected capacitor voltage of the network-forming inverter under asymmetric faults provided by the present invention will be described below. The control system for the grid-connected capacitor voltage of the network-forming inverter under asymmetric faults described below can be mutually corresponding and referenced with the control method for the grid-connected capacitor voltage of the network-forming inverter under asymmetric faults described above.

[0093] As Fig.11 shown, the control system for the grid-connected capacitor voltage of the network-forming inverter under asymmetric faults provided by the embodiment of the present invention specifically includes: An acquisition module 210, configured to determine the actual output voltage, actual output current of the network-forming inverter, and the standard current positive and negative sequence components of the actual output current in the rotating coordinate system under asymmetric faults.

[0094] A first calculation module 220, configured to calculate a negative sequence reference voltage according to the set virtual negative sequence reactance and the standard current positive and negative sequence components.

[0095] A second calculation module 230, configured to use the negative sequence reference voltage as the fluctuating negative sequence component, and use the reference voltage during normal operation of the power supply system as the DC component, and add the DC component and the fluctuating negative sequence component to obtain an outer loop reference voltage.

[0096] An outer loop adjustment module 240, configured to input the outer loop reference voltage and the actual output voltage into a voltage outer loop controller to obtain an inner loop reference current output by the voltage outer loop controller.

[0097] An inner loop adjustment module 250, configured to input the inner loop reference current and the actual output current into a current inner loop controller to obtain an initial modulation signal output by the current inner loop controller.

[0098] A control module 260, configured to control the switching devices of the network-forming inverter according to the initial modulation signal to control the grid-connected capacitor voltage of the network-forming inverter.

[0099] Regarding the system in the above embodiment, the specific manners in which each module performs operations have been described in detail in the embodiments related to the method, and will not be elaborated in detail here.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault, characterized in that: include: Under an asymmetric fault, determine the actual output voltage, actual output current, and standard current positive and negative sequence components of the actual output current in the rotating coordinate system of the grid inverter; The negative sequence reference voltage is calculated based on the set virtual negative sequence reactance and the positive and negative sequence components of the standard current; Taking the negative-sequence reference voltage as the fluctuating negative-sequence component, taking the reference voltage during normal operation of the power supply system as the DC component, and adding the DC component to the fluctuating negative-sequence component to obtain an outer loop reference voltage; Inputting the outer loop reference voltage and the actual output voltage into a voltage outer loop controller to obtain an inner loop reference current output by the voltage outer loop controller; Inputting the inner loop reference current and the actual output current into a current inner loop controller to obtain an initial modulation signal output by the current inner loop controller; Controlling the switch device of the grid-connected inverter according to the initial modulation signal to control the grid-connected capacitor voltage of the grid-connected inverter; The method further comprises: Determine the actual phase difference between the actual output voltage of the grid inverter and the actual grid voltage; Subtract the actual phase difference from the theoretical phase difference to obtain the phase difference deviation; If the phase difference deviation is within the first numerical interval, the active power correction amount is determined according to the first linear function; if the phase difference deviation is within the second numerical interval, the active power correction amount is determined according to the second linear function; if the phase difference deviation is within the third numerical interval, the active power correction amount is determined according to the third linear function; the active power reference value is corrected according to the active power correction amount; Among them, the lower limit values ​​and upper limit values ​​corresponding to the first numerical interval, the second numerical interval and the third numerical interval respectively increase successively, and the slopes corresponding to the first linear function, the second linear function and the third linear function respectively increase successively.

2. The method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault according to claim 1, characterized in that: Determine the standard current positive and negative sequence components of the actual output current of the grid-connected inverter in the rotating coordinate system, including: Get the actual output current of the grid-connected inverter; Input the actual output current into a biquad generalized integrator to obtain initial positive and negative sequence components of the actual output current in a stationary coordinate system; The initial current positive and negative sequence components are subjected to coordinate transformation to obtain standard current positive and negative sequence components of the actual output current in a rotating coordinate system.

3. The method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault according to claim 1, characterized in that: According to the set virtual negative sequence reactance and the positive and negative sequence components of the standard current, the negative sequence reference voltage is calculated, including: A first matrix is ​​established according to the set virtual negative-sequence reactance; Establishing a second matrix according to the d-axis current negative sequence component and the q-axis current negative sequence component in the standard current positive and negative sequence components; The first matrix is ​​multiplied by the second matrix to obtain a negative-sequence reference voltage.

4. The method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault according to claim 1, characterized in that: Controlling the switching device of the grid-connected inverter according to the initial modulation signal includes: Inputting the initial modulation signal into a modulation wave generation module to obtain a three-phase modulation signal output by the modulation wave generation module; According to the set carrier signal, the three-phase modulated signal is converted into a three-phase alternating current signal; The switching devices of the grid-connecting inverter are controlled by the three-phase AC signal.

5. The method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault according to claim 1, characterized in that: The method further comprises: In the virtual synchronization phase, the measured active power value and active power reference value of the grid-connected inverter are obtained; Determining a theoretical phase difference between an actual output voltage of the grid-connecting inverter and a grid voltage according to the active power measured value and the active power reference value; Based on the theoretical phase difference, the phase of the actual output voltage is adjusted.

6. The method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault according to claim 5, characterized in that: Determining a theoretical phase difference between the output voltage of the grid inverter and the grid voltage according to the active power measured value and the active power reference value includes: Subtracting the active power measured value from the active power reference value to obtain a power deviation; Inputting the power deviation into a virtual inertia controller to obtain a power change trend value output by the virtual inertia controller; Inputting the power change trend value into a virtual damping controller to obtain a theoretical power value output by the virtual damping controller; The theoretical power value is input into an integral controller to obtain a theoretical phase difference output by the integral controller.

7. The method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault according to claim 1, characterized in that: After the active power reference value is corrected based on the phase difference deviation, the method further includes: sending the corrected active power reference value to the user terminal; After receiving the correction intervention instruction fed back by the user terminal, the active power reference value is secondarily corrected according to the correction intervention data in the correction intervention instruction.

8. The method for controlling the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault according to claim 1, characterized in that: The voltage outer loop controller and the current inner loop controller both adopt PIR controllers.

9. A control system for the grid-connected capacitor voltage of a grid-connected inverter under an asymmetric fault, characterized in that: include: An acquisition module is used to determine the actual output voltage, actual output current and standard current positive and negative sequence components of the actual output current in a rotating coordinate system of the grid-connected inverter under an asymmetric fault; A first calculation module, used for calculating a negative-sequence reference voltage according to a set virtual negative-sequence reactance and the positive and negative-sequence components of the standard current; A second calculation module is used to take the negative-sequence reference voltage as a fluctuating negative-sequence component, take the reference voltage during normal operation of the power supply system as a DC component, and add the DC component to the fluctuating negative-sequence component to obtain an outer loop reference voltage; An outer loop regulation module, used for inputting the outer loop reference voltage and the actual output voltage into a voltage outer loop controller to obtain an inner loop reference current output by the voltage outer loop controller; An inner loop regulation module, used for inputting the inner loop reference current and the actual output current into a current inner loop controller to obtain an initial modulation signal output by the current inner loop controller; A control module, used to control the switch device of the grid-connected inverter according to the initial modulation signal to control the grid-connected capacitor voltage of the grid-connected inverter; It is also used to determine the actual phase difference between the actual output voltage of the grid inverter and the actual grid voltage; Subtract the actual phase difference from the theoretical phase difference to obtain the phase difference deviation; If the phase difference deviation is within the first numerical interval, determining the active power correction amount according to the first linear function; If the phase difference deviation is within the second numerical range, determining the active power correction amount according to the second linear function; If the phase deviation is within the third numerical interval, the active power correction amount is determined according to the third linear function; the active power reference value is corrected according to the active power correction amount; wherein, the lower limit value and the upper limit value corresponding to the first numerical interval, the second numerical interval and the third numerical interval respectively increase successively, and the slopes corresponding to the first linear function, the second linear function and the third linear function respectively increase successively.

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