Photovoltaic grid-connected system oscillation control method and system based on wide-area branch response

Abstract

This invention discloses a method and system for oscillation control in a photovoltaic grid-connected system based on wide-area branch response. Based on the voltage amplitude and phase difference at the two endpoints of each branch in the system, a simplified branch transient transmission capacity index is calculated. The branch corresponding to the smallest simplified branch transient transmission capacity index is identified as a critical branch. The photovoltaic unit closest to the critical branch is identified, and the number of times the photovoltaic unit triggers low-voltage ride-through control is obtained. When the number of times the photovoltaic unit triggers low-voltage ride-through control reaches a preset control number, the low-voltage ride-through control parameters of the photovoltaic unit are optimized to suppress system oscillations. Based on the simplified branch transient transmission capacity index, this invention proposes a critical branch identification method characterizing the power angle stability of a photovoltaic grid-connected system, as well as an emergency control strategy to suppress oscillations and reduce the threat of instability. The effectiveness of the emergency control is verified through simulation for an actual power grid.

Description

Technical Field

[0001] This invention relates to the field of power system safety and stability analysis technology, and more specifically, to a method and system for oscillation control of photovoltaic grid-connected systems based on wide-area branch response. Background Technology

[0002] Driven by the dual carbon goals of peak carbon emissions and carbon neutrality, the grid-connected capacity of new energy sources such as wind power and photovoltaics will continue to grow, and the development of power electronics in the power system will become increasingly prominent. Unlike conventional synchronous generators that generate electricity based on the principle of electromagnetic induction, new energy sources connected to the grid using power electronic converters exhibit significantly different active and reactive power responses after disturbances. The stability of the system power angle after new energy grid connection is an important focus of the power engineering community and academia. To ensure the grid-connected safety of photovoltaic power generation equipment and its reactive power support to the grid under large disturbances, photovoltaics possess low voltage ride-through (LVRT) control functions. However, existing research on the oscillation problem of photovoltaic grid-connected systems has not considered the impact of LVRT triggered by photovoltaic units on oscillation.

[0003] Therefore, based on easily measurable wide-area branch response information, studying the impact of photovoltaic unit LVRT triggered by bus voltage fluctuations on system oscillation damping under oscillating conditions, assessing the risk of power angle oscillation in photovoltaic grid-connected systems, and taking timely emergency control measures to suppress oscillations and restore stable system operation has important theoretical significance and urgent practical needs. Summary of the Invention

[0004] The present invention provides a method and system for controlling the oscillation of a photovoltaic grid-connected system based on wide-area branch response, in order to solve the problem of how to control the oscillation of a photovoltaic grid-connected system based on wide-area branch response.

[0005] To address the aforementioned problems, this invention provides an oscillation control method for a photovoltaic grid-connected system based on wide-area branch response, the method comprising:

[0006] Based on the voltage amplitude and voltage phase difference at the two ends of each branch in the system, the simplified branch transient transmission capacity index of each branch is calculated.

[0007] The branch corresponding to the smallest simplified branch transient transmission capacity index is identified as the critical branch;

[0008] Identify the photovoltaic unit closest to the critical branch and obtain the number of times the photovoltaic unit triggers low-voltage ride-through control;

[0009] When the number of times the photovoltaic unit triggers low voltage ride-through control reaches the preset control number, the low voltage ride-through control parameters of the photovoltaic unit are optimized to suppress system oscillation.

[0010] Preferably, it further includes:

[0011] When system oscillations are not suppressed, the photovoltaic unit is disconnected.

[0012] Preferably, it further includes:

[0013] When the number of times the photovoltaic unit triggers low voltage ride-through control does not reach the preset number of control times, it is determined whether the simplified branch transient transmission capacity index of the key branch is less than the preset threshold value.

[0014] When the simplified branch transient transmission capacity index of the key branch is less than a preset threshold value, the vertical voltage of the key branch is determined based on the defined position coefficient to determine whether it is located on the key branch.

[0015] When it is determined that the vertical foot voltage of the critical branch is located on the critical branch, the photovoltaic unit is disconnected.

[0016] Preferably, the calculation of the simplified branch transient transmission capacity index for each branch based on the voltage amplitude and voltage phase difference at both ends of each branch in the system includes:

[0017]

[0018] in, m , n This indicates the positions of two measurement points taken along a line. , indicating a branch i The voltage phase difference between the two nodes; , Branch roads i of m , n End node voltage amplitude, branch road i superior m Voltage phase of the terminal node, branch road i superior n Voltage phase at the terminal node, sBTTC i branch road i The simplified branch transient transmission capacity index.

[0019] Preferably, when the number of times the photovoltaic unit triggers low-voltage ride-through control reaches a preset number, the low-voltage ride-through control parameters of the photovoltaic unit are optimized, including:

[0020] Reduce the trigger start-up voltage of the photovoltaic unit, or change the active power recovery rate of the photovoltaic unit.

[0021] Preferably, the vertical voltage of the critical branch is:

[0022]

[0023] in, As a key branch k The vertical foot voltage, , , They are The absolute values ​​of the real and imaginary parts, yes The absolute value of the real part, branch road k of m End node voltage amplitude, branch road k of n Terminal node voltage amplitude;

[0024] Define position coefficient When the position coefficient If the condition is greater than 1 and less than 2, then the critical branch is determined. k The vertical voltage is located on the critical branch:

[0025]

[0026] in, , , They are respectively and voltage phasor amplitude difference, and voltage phasor amplitude difference, and Voltage phasor amplitude difference:

[0027]

[0028]

[0029] in, , yes phase angle, yes The phase angle.

[0030] Preferably, the position coefficient When the value is less than or equal to 1 or greater than or equal to 2, determine the critical branch. kThe vertical voltage is located outside the critical branch.

[0031] Based on another aspect of the present invention, the present invention provides an oscillation control system for a photovoltaic grid-connected system based on wide-area branch response, the system comprising:

[0032] The initial unit is used to calculate the simplified branch transient transmission capacity index of each branch based on the voltage amplitude and voltage phase difference at the two ends of each branch in the system.

[0033] The determination unit is used to identify the branch corresponding to the calculated minimum simplified branch transient transmission capacity index as the critical branch;

[0034] The acquisition unit is used to identify the photovoltaic unit closest to the critical branch and acquire the number of times the photovoltaic unit triggers low voltage ride-through control;

[0035] The result unit is used to optimize the low voltage ride-through control parameters of the photovoltaic unit and suppress system oscillations when the number of times the photovoltaic unit triggers low voltage ride-through control reaches a preset number of control times.

[0036] Preferably, the result unit is further configured to:

[0037] When system oscillations are not suppressed, the photovoltaic unit is disconnected.

[0038] Preferably, the result unit is further configured to:

[0039] When the number of times the photovoltaic unit triggers low voltage ride-through control does not reach the preset number of control times, it is determined whether the simplified branch transient transmission capacity index of the key branch is less than the preset threshold value.

[0040] When the simplified branch transient transmission capacity index of the key branch is less than a preset threshold value, the vertical voltage of the key branch is determined based on the defined position coefficient to determine whether it is located on the key branch.

[0041] When it is determined that the vertical foot voltage of the critical branch is located on the critical branch, the photovoltaic unit is disconnected.

[0042] Preferably, the initial unit is used to calculate the simplified branch transient transmission capacity index of each branch based on the voltage amplitude and voltage phase difference at both ends of each branch in the system, and is also used to:

[0043]

[0044] in, m , n This indicates the positions of two measurement points taken along a line. , indicating a branchi The voltage phase difference between the two nodes; , Branch roads i of m , n End node voltage amplitude, branch road i superior m Voltage phase of the terminal node, branch road i superior n Voltage phase at the terminal node, sBTTC i branch road i The simplified branch transient transmission capacity index.

[0045] Preferably, the result unit is used to optimize the low-voltage ride-through control parameters of the photovoltaic unit when the number of times the photovoltaic unit triggers low-voltage ride-through control reaches a preset number of control attempts, and is also used to:

[0046] Reduce the trigger start-up voltage of the photovoltaic unit, or change the active power recovery rate of the photovoltaic unit.

[0047] Preferably, the vertical voltage of the critical branch is:

[0048]

[0049] in, As a key branch k The vertical foot voltage, , , They are The absolute values ​​of the real and imaginary parts, yes The absolute value of the real part, branch road k of m End node voltage amplitude, branch road k of n Terminal node voltage amplitude;

[0050] Define position coefficient When the position coefficient If the condition is greater than 1 and less than 2, then the critical branch is determined. k The vertical voltage is located on the critical branch:

[0051]

[0052] in, , , They are respectively and voltage phasor amplitude difference, and voltage phasor amplitude difference, and Voltage phasor amplitude difference:

[0053]

[0054]

[0055] in, , yes phase angle, yes The phase angle.

[0056] Preferably, the position coefficient When the value is less than or equal to 1 or greater than or equal to 2, determine the critical branch. k The vertical voltage is located outside the critical branch.

[0057] This invention provides a method and system for oscillation control of a photovoltaic grid-connected system based on wide-area branch response. The method includes: calculating a simplified branch transient transmission capacity index for each branch based on the voltage amplitude and phase difference at both ends of the branch; identifying the branch corresponding to the smallest calculated simplified branch transient transmission capacity index as the critical branch; identifying the photovoltaic unit closest to the critical branch and obtaining the number of times the photovoltaic unit triggers low-voltage ride-through control; and optimizing the low-voltage ride-through control parameters of the photovoltaic unit when the number of times the photovoltaic unit triggers low-voltage ride-through control reaches a preset control number to suppress system oscillations. This invention provides an oscillation control method for a photovoltaic grid-connected system based on wide-area branch response, which has advantages such as fast control and accurate search, helping to reduce the risk of power angle oscillations in photovoltaic grid-connected systems. The information collected by this invention is easy to measure, and the calculation formulas and control strategies are simple. This method has high engineering feasibility and has been verified through simulation in examples that conform to the complex scale and conditions of actual power grids. Attached Figure Description

[0058] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0059] Figure 1 This is a flowchart of a photovoltaic grid-connected system oscillation control method based on wide-area branch response according to a preferred embodiment of the present invention;

[0060] Figure 2 This is a schematic diagram of a typical system for photovoltaic grid-connected power angle stability analysis according to a preferred embodiment of the present invention;

[0061] Figure 3 This is a flowchart of an emergency control strategy for oscillations in a photovoltaic grid-connected system based on a critical branch, according to a preferred embodiment of the present invention.

[0062] Figure 4 This is a schematic diagram of a test system according to a preferred embodiment of the present invention;

[0063] Figure 5 This is a schematic diagram of the transient response of the Hotan power transmission system after a short-circuit fault impact according to a preferred embodiment of the present invention.

[0064] Figure 6 This is a schematic diagram illustrating the effect of optimizing LVRT parameters to suppress oscillations according to a preferred embodiment of the present invention;

[0065] Figure 7 This is a schematic diagram illustrating the effect of photovoltaic oscillation suppression after multiple consecutive LVRTs according to a preferred embodiment of the present invention; and

[0066] Figure 8 This is a structural diagram of an oscillation control system for a photovoltaic grid-connected system based on a preferred embodiment of the present invention. Detailed Implementation

[0067] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0068] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0069] Figure 1This is a flowchart of a photovoltaic grid-connected system oscillation control method based on wide-area branch response according to a preferred embodiment of the present invention. The present invention proposes a dynamic assessment and emergency control method for oscillations in photovoltaic grid-connected systems based on wide-area branch response. Regarding the construction of instability criteria, the present invention utilizes a simplified branch transient transmission capacity index to determine each branch in the system experiencing power angle oscillations, screening out key branches to be disconnected. Its calculation formula is simple and involves few calculation steps, thus saving determination time and making rapid disconnection more likely. Regarding the selection of control methods, the present invention proposes that when the low-voltage ride-through of photovoltaic units has reached a specified number of times, priority should be given to suppressing oscillations by optimizing the LVRT control parameters of the photovoltaic units. If the optimized parameters cannot suppress the oscillations, measures should be taken to disconnect the oscillation-related photovoltaic units. When the low-voltage ride-through of photovoltaic units has not reached the specified number of times, but the system power angle stability has severely deteriorated, multi-level oscillation suppression measures are directly implemented by disconnecting the oscillation-related photovoltaic units. The purpose of this multi-level suppression measure is to minimize control costs; that is, if oscillations can be suppressed through optimization of the LVRT parameters of the photovoltaic units, disconnection of photovoltaic units should be avoided as much as possible.

[0070] This invention belongs to the field of power system safety and stability analysis, and relates to a method for dynamically assessing the oscillation risk of a photovoltaic grid-connected system and implementing emergency control when the power angle oscillation of the photovoltaic grid-connected system causes fluctuations in the bus voltage at the photovoltaic grid connection point.

[0071] like Figure 1 As shown, this invention provides an oscillation control method for a photovoltaic grid-connected system based on wide-area branch response, the method comprising:

[0072] Step 101: Based on the voltage amplitude and voltage phase difference at the two ends of each branch in the system, calculate the simplified branch transient transmission capacity index for each branch.

[0073] Preferably, based on the voltage amplitude and voltage phase difference at both ends of each branch in the system, a simplified branch transient transmission capacity index is calculated for each branch, including:

[0074]

[0075] in, m , n This indicates the positions of two measurement points taken along a line. , indicating a branch i The voltage phase difference between the two nodes; , Branch roads i of m , n End node voltage amplitude, branch road i superiorm Voltage phase of the terminal node, branch road i superior n Voltage phase at the terminal node, sBTTC i branch road i The simplified branch transient transmission capacity index.

[0076] In step 101-1 of this invention: setting relevant parameters ε Lth , N th .

[0077] ε Lth A threshold value set by an individual, representing the lower limit of the sBTTC index;

[0078] N th The number of times is set manually, specifically referring to the number of times the photovoltaic unit triggers LVRT.

[0079] In step 101-2 of this invention: each branch in the measurement system i ( i =1,2,3,..., N, N The voltage magnitude at both ends of the system (representing the total number of branches in the system). , and voltage phase difference The simplified branch transient transmission capacity (sBTTC) index of each branch is calculated according to equation (1), and the key branches are sorted and located according to equation (2).

[0080] (1)

[0081] In equation (1), , indicating a branch i The voltage phase difference between the two nodes. , , , exist Figure 2 All have been marked, subscript m , n This indicates the locations of two measurement points along a line, typically at both ends of the line. It is a side road i The voltage amplitude at node m, It is a side road i The voltage amplitude at node n, It is a side road iThe voltage phase at node m, It is a side road i The voltage phase at node n.

[0082] Step 102: Identify the branch corresponding to the calculated minimum simplified branch transient transmission capacity index as the critical branch;

[0083] (2)

[0084] This invention sorts the sBTTC indices of each branch according to equation (2). The branch with the smallest sBTTC index value is defined as the critical branch, and its branch number is denoted as... k .

[0085] Step 103: Identify the photovoltaic unit closest to the critical branch and obtain the number of times the photovoltaic unit triggers low voltage ride-through control;

[0086] Step 104: When the number of times the photovoltaic (PV) unit triggers low-voltage ride-through control reaches the preset control count, the low-voltage ride-through control parameters of the PV unit are optimized to suppress system oscillations. Preferably, when the number of times the PV unit triggers low-voltage ride-through control reaches the preset control count, the low-voltage ride-through control parameters of the PV unit are optimized, including:

[0087] Reduce the triggering voltage of the photovoltaic unit, or change the active power recovery rate of the photovoltaic unit.

[0088] Preferably, it further includes:

[0089] When system oscillations are not suppressed, the photovoltaic units should be disconnected.

[0090] In step 104-1 of this invention: the photovoltaic unit closest to the faulty line is identified, and the number of times the photovoltaic unit triggers LVRT is determined, and it is determined whether the number of times the photovoltaic unit triggers LVRT has reached the required threshold. N th Second-rate.

[0091] If satisfied, proceed to step 104-2;

[0092] In step 104-2 of this invention, the LVRT control parameters of the photovoltaic unit are dynamically optimized.

[0093] The main control parameters of the LVRT of a photovoltaic unit include the trigger start-up voltage. U pL Parameters such as active power recovery rate (Amperes per second) are also considered. The purpose of optimizing these parameters is to reduce the number of times the photovoltaic unit triggers LVRT (Low Voltage Recovery Time). Therefore, optimization measures mainly include reducing the trigger start-up voltage. U pL1. Change the active power recovery rate (increase or decrease it, simply by staggering the photovoltaic active power recovery sequence from the system oscillation cycle).

[0094] If the photovoltaic unit implements dynamic parameter optimization, the system oscillation is suppressed, then... And return to step 101;

[0095] If the system oscillation is not suppressed after the photovoltaic unit implements dynamic optimization parameters, the photovoltaic unit should be disconnected.

[0096] If the conditions are not met, proceed to step 105.

[0097] Preferably, it further includes:

[0098] Step 105: When the number of times the photovoltaic unit triggers low voltage ride-through control does not reach the preset number of control times, determine whether the simplified branch transient transmission capacity index of the key branch is less than the preset threshold value.

[0099] Step 106: When the simplified branch transient transmission capacity index of the critical branch is less than the preset threshold value, determine whether the vertical voltage of the critical branch is located on the critical branch based on the defined location coefficient.

[0100] When it is determined that the vertical foot voltage of the critical branch is located on the critical branch, the photovoltaic unit is disconnected.

[0101] Preferably, the vertical voltage of the critical branch:

[0102]

[0103] in, As a key branch k The vertical foot voltage, , , They are The absolute values ​​of the real and imaginary parts, yes The absolute value of the real part, branch road k of m End node voltage amplitude, branch road k of n Terminal node voltage amplitude;

[0104] Define position coefficient When the position coefficient Determine the critical branch when it satisfies a condition greater than 1 and less than 2. k The vertical voltage is located on the critical branch:

[0105]

[0106] in, , , They are respectively and voltage phasor amplitude difference, and voltage phasor amplitude difference, and Voltage phasor amplitude difference:

[0107]

[0108]

[0109] in, , yes phase angle, yes The phase angle.

[0110] Preferably, position coefficient Determine the critical branch when the value is less than or equal to 1 or greater than or equal to 2. k The vertical voltage is located outside the critical branch.

[0111] This invention determines critical branches k Does it satisfy equation (3)?

[0112] The key branch with the minimum sBTTC index has characteristic electrical quantities that characterize the trend of unit power angle stability. The sBTTC value of the key branch decreases as power angle stability decreases, and when it is lower than a set threshold value... ε Lth This indicates that the stability of the power angle has deteriorated significantly, as shown in equation (3).

[0113] (3)

[0114] If equation (3) is satisfied, proceed to step six;

[0115] If not satisfied, then make Then return to step 101.

[0116] Step 106: Determine whether the critical branch k satisfies equation (5).

[0117] Define critical branches k vertical foot voltage The calculation formula is as follows:

[0118] (4)

[0119] in, , that is, , They are The absolute values ​​of the real and imaginary parts, yes The absolute value of the real part.

[0120] To determine the voltage at the foot of the vertical Is it located on a side road? k Above, define the position coefficient. As shown in equation (5). If If it is located on a side road, then it must have and ,Right now Greater than 1 and less than 2; if If it is located outside the side road, then it must have or ,correspond Less than or equal to 1 or greater than or equal to 2.

[0121] (5)

[0122] in, , , They are respectively and voltage phasor amplitude difference, and voltage phasor amplitude difference, and The voltage phasor amplitude difference, , , Calculate according to equations (6) and (7):

[0123] (6)

[0124] (7)

[0125] in, , yes phase angle, yes The phase angle.

[0126] If equation (5) is satisfied, the photovoltaic unit is disconnected.

[0127] If not satisfied, then make Then return to step 101.

[0128] The method provided by this invention has advantages such as fast control and accurate search, which helps to reduce the risk of power angle oscillation in photovoltaic grid-connected systems. Because the collected information is easy to measure and the calculation formulas and control strategies are simple, this method has high engineering feasibility and has been verified through simulation in examples that conform to the complex scale and conditions of actual power grids.

[0129] This invention, based on a simplified branch transient transmission capacity index, proposes a method for identifying key branches that can quantitatively characterize the power angle stability of a photovoltaic grid-connected system, an assessment criterion for assessing the threat of power angle instability caused by oscillations, and an emergency control strategy to suppress oscillations and reduce the threat of instability. The effectiveness of the assessment criterion and emergency control measures is verified through simulation on a real power grid. Two auxiliary criteria—that the simplified branch transient transmission capacity of the key branch is less than a set threshold and that the vertical voltage position coefficient of the key branch conforms to a specified range—improve the accuracy of system stability assessment and the timing accuracy of emergency control measures.

[0130] The following are examples illustrating embodiments of the present invention:

[0131] Build such in simulation software Figure 4 The test system shown simulates the structural characteristics of an actual power grid. Therefore, simulation can be used to verify the beneficial effects of this technical solution in a real power grid. ε Lth , ε Hth and N th They were set to 0.6, 0.8, and 10 respectively.

[0132] If a three-phase permanent short-circuit fault occurs on one circuit of the 220kV AC transmission line from Moyu to Yecheng within 1 second, the transient response curve of the system after the fault is as follows: Figure 5 As shown, after the fault, the voltage at the photovoltaic grid-connected nodes such as Xinhua at the Moyu power station fluctuated periodically, triggering the activation of the photovoltaic LVRT. The step change in photovoltaic output power caused the power of the Yecheng-Moyu line, the power angle of units such as Bobona, and the main grid to oscillate at nearly the same amplitude, making the system unable to operate stably. It is necessary to suppress the oscillation by adjusting and optimizing the photovoltaic LVRT parameters or by implementing system-level emergency control.

[0133] Optimize the LVRT parameters of the photovoltaic unit and set the photovoltaic LVRT trigger start-up voltage. U pL Figure 6 shows a comparison of the system's transient response after adjusting the PU from 0.9 PU to 0.8 PU. It can be seen that reducing the PU... U pLThe photovoltaic system only triggers the LVRT during faults and does not trigger it again during subsequent voltage fluctuations. The approximately constant photovoltaic output power does not worsen the system damping, and the oscillations decay rapidly.

[0134] Without control parameter optimization, the oscillation continues, and the photovoltaic system continuously triggers LVRT. As shown in Figure 6(b), after the 8th consecutive LVRT corresponding to the Nth time, considering the 0.2s communication and control delay, according to... Figure 3 The strategy shown implements system-level emergency control to cut off the photovoltaic power at 15.3s, eliminating the adverse effects of photovoltaic power fluctuations on oscillations. The transient response of the system after control is shown in Figure 7, and the oscillations can be suppressed.

[0135] In summary, based on the network disturbance response information of the photovoltaic grid-connected system, the sBTTC index of the key branch is used to characterize the deterioration of the power angle stability level. Combined with the number of consecutive LVRTs of the photovoltaic system, the optimization and adjustment of LVRT parameters or emergency photovoltaic control can effectively reduce the risk of low-frequency continuous oscillation or power angle instability caused by LVRT.

[0136] Figure 8 This is a structural diagram of an oscillation control system for a photovoltaic grid-connected system based on a preferred embodiment of the present invention.

[0137] like Figure 8 As shown, this invention provides an oscillation control system for a photovoltaic grid-connected system based on wide-area branch response. The system includes:

[0138] The initial unit 801 is used to calculate the simplified branch transient transmission capacity index of each branch based on the voltage amplitude and voltage phase difference at the two ends of each branch in the system.

[0139] The optimization method, initial unit 801, is used to calculate the simplified branch transient transmission capacity index of each branch based on the voltage amplitude and voltage phase difference at both ends of each branch in the system, and is also used for:

[0140]

[0141] in, m , n This indicates the positions of two measurement points taken along a line. , indicating a branch i The voltage phase difference between the two nodes; , Branch roads i of m , n End node voltage amplitude, branch road i superior mVoltage phase of the terminal node, branch road i superior n Voltage phase at the terminal node, sBTTC i branch road i The simplified branch transient transmission capacity index.

[0142] The determination unit 802 is used to determine the branch corresponding to the calculated minimum simplified branch transient transmission capacity index as the critical branch;

[0143] The acquisition unit 803 is used to identify the photovoltaic unit closest to the critical branch and acquire the number of times the photovoltaic unit triggers low voltage ride-through control;

[0144] The result unit 804 is used to optimize the low voltage ride-through control parameters of the photovoltaic unit and suppress system oscillations when the number of times the photovoltaic unit triggers low voltage ride-through control reaches the preset number of control times.

[0145] Preferably, the result unit 804 is further configured to:

[0146] When system oscillations are not suppressed, the photovoltaic units should be disconnected.

[0147] Preferably, the result unit 804 is further configured to:

[0148] When the number of times the photovoltaic unit triggers low voltage ride-through control does not reach the preset number of control times, it is determined whether the simplified branch transient transmission capacity index of the key branch is less than the preset threshold value.

[0149] When the simplified branch transient transmission capacity index of the critical branch is less than the preset threshold value, the vertical foot voltage of the critical branch is determined based on the defined location coefficient to determine whether it is located on the critical branch.

[0150] When it is determined that the vertical foot voltage of the critical branch is located on the critical branch, the photovoltaic unit is disconnected.

[0151] Preferably, the result unit 804 is used to optimize the low-voltage ride-through control parameters of the photovoltaic unit when the number of times the low-voltage ride-through control is triggered by the photovoltaic unit reaches a preset number of control attempts, and is also used to:

[0152] Reduce the triggering voltage of the photovoltaic unit, or change the active power recovery rate of the photovoltaic unit.

[0153] Preferably, the vertical voltage of the critical branch:

[0154]

[0155] in, As a key branch k The vertical foot voltage, , , They are The absolute values ​​of the real and imaginary parts, yes The absolute value of the real part, branch road k of m End node voltage amplitude, branch road k of n Terminal node voltage amplitude;

[0156] Define position coefficient When the position coefficient Determine the critical branch when it satisfies a condition greater than 1 and less than 2. k The vertical voltage is located on the critical branch:

[0157]

[0158] in, , , They are respectively and voltage phasor amplitude difference, and voltage phasor amplitude difference, and Voltage phasor amplitude difference:

[0159]

[0160]

[0161] in, , yes phase angle, yes The phase angle.

[0162] Preferably, position coefficient Determine the critical branch when the value is less than or equal to 1 or greater than or equal to 2. k The vertical voltage is located outside the critical branch.

[0163] The preferred embodiment of the present invention provides an oscillation control system for a photovoltaic grid-connected system based on wide-area branch response, which corresponds to the preferred embodiment of the present invention providing an oscillation control method for a photovoltaic grid-connected system based on wide-area branch response. These will not be described in detail here.

[0164] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0165] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0166] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0167] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0168] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0169] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0170] The invention has been described with reference to a few embodiments. However, as will be known to those skilled in the art, and as defined in the appended claims, other embodiments besides those disclosed above fall equivalently within the scope of the invention.

[0171] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to “a / the / the [device, component, etc.]” ​​are openly interpreted as at least one instance of said device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed unless explicitly stated otherwise.

Claims

1. A method for oscillation control of a photovoltaic grid-connected system based on wide-area branch response, the method comprising: Based on the voltage amplitude and voltage phase difference at the two ends of each branch in the system, the simplified branch transient transmission capacity index of each branch is calculated. The branch corresponding to the smallest simplified branch transient transmission capacity index is identified as the critical branch; Identify the photovoltaic unit closest to the critical branch and obtain the number of times the photovoltaic unit triggers low-voltage ride-through control; When the number of times the photovoltaic unit triggers low voltage ride-through control reaches the preset control number, the low voltage ride-through control parameters of the photovoltaic unit are optimized to suppress system oscillation.

2. The method according to claim 1, further comprising: When system oscillations are not suppressed, the photovoltaic unit is disconnected.

3. The method according to claim 1, further comprising: When the number of times the photovoltaic unit triggers low voltage ride-through control does not reach the preset number of control times, it is determined whether the simplified branch transient transmission capacity index of the key branch is less than the preset threshold value. When the simplified branch transient transmission capacity index of the key branch is less than a preset threshold value, the vertical voltage of the key branch is determined based on the defined position coefficient to determine whether it is located on the key branch. When it is determined that the vertical foot voltage of the critical branch is located on the critical branch, the photovoltaic unit is disconnected.

4. The method according to claim 1, wherein calculating the simplified branch transient transmission capacity index of each branch based on the voltage amplitude and voltage phase difference at both ends of each branch in the system includes: in, m , n This indicates the positions of two measurement points taken along a line. , indicating a branch i The voltage phase difference between the two nodes; , Branch roads i of m , n End node voltage amplitude, branch road i superior m Voltage phase of the terminal node, branch road i superior n Voltage phase at the terminal node, sBTTC i branch road i The simplified branch transient transmission capacity index.

5. The method according to claim 1, wherein when the number of times the photovoltaic unit triggers low-voltage ride-through control reaches a preset number of control events, the low-voltage ride-through control parameters of the photovoltaic unit are optimized, including: Reduce the trigger start-up voltage of the photovoltaic unit, or change the active power recovery rate of the photovoltaic unit.

6. The method according to claim 3, wherein the vertical voltage of the critical branch is: in, As a key branch k The vertical foot voltage, , , They are The absolute values ​​of the real and imaginary parts, yes The absolute value of the real part, branch road k of m End node voltage amplitude, branch road k of n Terminal node voltage amplitude; Define position coefficient When the position coefficient If the condition is greater than 1 and less than 2, then the critical branch is determined. k The vertical foot voltage is located on the critical branch: in, , , They are respectively and voltage phasor amplitude difference, and voltage phasor amplitude difference, and Voltage phasor amplitude difference: in, , yes phase angle, yes The phase angle.

7. The method according to claim 6, wherein the position coefficient When the value is less than or equal to 1 or greater than or equal to 2, determine the critical branch. k The vertical voltage is located outside the critical branch.

8. An oscillation control system for a photovoltaic grid-connected system based on wide-area branch response, the system comprising: The initial unit is used to calculate the simplified branch transient transmission capacity index of each branch based on the voltage amplitude and voltage phase difference at the two ends of each branch in the system. The determination unit is used to identify the branch corresponding to the calculated minimum simplified branch transient transmission capacity index as the critical branch; The acquisition unit is used to identify the photovoltaic unit closest to the critical branch and acquire the number of times the photovoltaic unit triggers low voltage ride-through control; The result unit is used to optimize the low voltage ride-through control parameters of the photovoltaic unit and suppress system oscillations when the number of times the photovoltaic unit triggers low voltage ride-through control reaches a preset number of control times.

9. The system according to claim 8, wherein the result unit is further configured to: When system oscillations are not suppressed, the photovoltaic unit is disconnected.

10. The system according to claim 8, wherein the result unit is further configured to: When the number of times the photovoltaic unit triggers low voltage ride-through control does not reach the preset number of control times, it is determined whether the simplified branch transient transmission capacity index of the key branch is less than the preset threshold value. When the simplified branch transient transmission capacity index of the key branch is less than a preset threshold value, the vertical voltage of the key branch is determined based on the defined position coefficient to determine whether it is located on the key branch. When it is determined that the vertical foot voltage of the critical branch is located on the critical branch, the photovoltaic unit is disconnected.

11. The system according to claim 8, wherein the initial unit is configured to calculate a simplified branch transient transmission capacity index for each branch based on the voltage amplitude and voltage phase difference at both ends of each branch in the system, and is further configured to: in, m , n This indicates the positions of two measurement points taken along a line. , indicating a branch i The voltage phase difference between the two nodes; , Branch roads i of m , n End node voltage amplitude, branch road i superior m Voltage phase of the terminal node, branch road i superior n Voltage phase at the terminal node, sBTTC i branch road i The simplified branch transient transmission capacity index.

12. The system according to claim 8, wherein the result unit is configured to optimize the low-voltage ride-through control parameters of the photovoltaic unit when the number of times the photovoltaic unit triggers low-voltage ride-through control reaches a preset number of control events, and is further configured to: Reduce the trigger start-up voltage of the photovoltaic unit, or change the active power recovery rate of the photovoltaic unit.

13. The system according to claim 10, wherein the vertical voltage of the critical branch is: in, As a key branch k The vertical foot voltage, , , They are The absolute values ​​of the real and imaginary parts, yes The absolute value of the real part, branch road k of m End node voltage amplitude, branch road k of n Terminal node voltage amplitude; Define position coefficient When the position coefficient If the condition is greater than 1 and less than 2, then the critical branch is determined. k The vertical foot voltage is located on the critical branch: in, , , They are respectively and voltage phasor amplitude difference, and voltage phasor amplitude difference, and Voltage phasor amplitude difference: in, , yes phase angle, yes The phase angle.

14. The system according to claim 13, wherein the position coefficient When the value is less than or equal to 1 or greater than or equal to 2, determine the critical branch. k The vertical voltage is located outside the critical branch.

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