CN109728597B - Low-voltage ride through characteristic fitting method and system for photovoltaic inverter - Google Patents

Low-voltage ride through characteristic fitting method and system for photovoltaic inverter Download PDF

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CN109728597B
CN109728597B CN201711041029.4A CN201711041029A CN109728597B CN 109728597 B CN109728597 B CN 109728597B CN 201711041029 A CN201711041029 A CN 201711041029A CN 109728597 B CN109728597 B CN 109728597B
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low
steady
voltage
voltage fault
state
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CN109728597A (en
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葛路明
曲立楠
朱凌志
陈宁
吴福保
丁杰
张磊
韩华玲
施涛
王湘艳
于若英
钱敏慧
赵大伟
刘艳章
赵亮
姜达军
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
Electric Power Research Institute of State Grid Xinjiang Electric Power Co Ltd
State Grid Xinjiang Electric Power Co Ltd
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
Electric Power Research Institute of State Grid Xinjiang Electric Power Co Ltd
State Grid Xinjiang Electric Power Co Ltd
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    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Abstract

The invention provides a photovoltaic inverter low-voltage ride through characteristic fitting method and system, which comprises the steps of obtaining electrical quantity according to a set low-voltage fault ride through test, and checking the consistency of the electrical quantity obtained by the same test and different tests; selecting key electrical quantity according to the consistency of the electrical quantity to perform low voltage ride through feature fitting; the electrical quantity includes: voltage steady-state values before and during a low-voltage fault steady-state interval, active current steady-state values and reactive current steady-state values before and during a low-voltage fault steady-state interval, and a current recovery rate during a low-voltage fault recovery period. The technical scheme provided by the invention is simple to operate, easy to realize, good in universality, capable of accurately fitting the low-voltage ride through external characteristics of the inverter and convenient to popularize.

Description

Photovoltaic inverter low voltage ride through characteristic fitting method and system
Technical Field
The invention belongs to the field of power systems, and particularly relates to a low-voltage ride through characteristic fitting method and system for a photovoltaic inverter.
Background
The photovoltaic power generation scale is rapidly developed, and with the fact that the capacity of a photovoltaic power station in a power grid is larger and larger, the mastering of the low-voltage ride through characteristic of an inverter is of great significance for analyzing the influence of the photovoltaic power station on the power grid.
The photovoltaic inverter can realize active and reactive independent control, has high dynamic response speed and is a core system of a photovoltaic power generation system. The inverter is a typical power electronic system, and unlike a traditional generator, the grid-connection characteristic of the inverter is mainly determined not by the physical structure of the inverter itself but by the controller and parameters thereof. Analyzing the inverter low voltage ride through characteristics is a typical "gray box" problem. In actual engineering, each brand of inverter generally adopts similar circuit topology and control structure, but specific control strategies and parameters are different and are not disclosed externally. If a mechanism analysis method is adopted, control strategies and parameters are lacked, and a testing method is only adopted, and necessary theoretical analysis is lacked. Under the conditions of different strategies and limited known conditions, a low-voltage ride-through characteristic fitting method which is good in universality and convenient to popularize is needed to be researched.
Disclosure of Invention
The invention provides a method and a system for fitting a low voltage ride through characteristic of a photovoltaic inverter, which meet the requirement of fitting the low voltage ride through characteristic of the photovoltaic inverter by calculating the transient response key electrical quantity of the inverter during the low voltage ride through period.
The invention provides a photovoltaic inverter low-voltage ride through characteristic fitting method, which comprises the following steps:
obtaining electrical quantity according to a set low-voltage fault ride-through test, and verifying the consistency of the electrical quantity obtained by different tests of the same test;
selecting key electrical quantity according to the consistency of the electrical quantity to perform low voltage ride through feature fitting;
the electrical quantity includes: voltage steady-state values before and during a low-voltage fault steady-state interval, active and reactive current steady-state values before and during a low-voltage fault steady-state interval, and a current recovery rate during a low-voltage fault recovery period.
Selecting the key electrical quantity according to the consistency of the electrical quantities comprises:
and selecting the electric quantity of the test with the voltage steady state value deviation absolute value less than 0.05pu, the active current and reactive current steady state value deviation absolute value less than 0.1pu and the current recovery rate deviation absolute value less than 0.2pu/s during the low voltage fault recovery period as the key electric quantity.
The low voltage ride through feature fitting comprises: feature fitting during low voltage fault and feature fitting during low voltage recovery.
The feature fitting during low voltage fault comprises:
performing curve fitting on the reactive current steady-state value and the voltage of the low-voltage fault steady-state interval;
and performing curve fitting on the active current steady-state value and the voltage of the low-voltage fault steady-state interval.
And performing curve fitting on the reactive current steady-state value and the voltage of the low-voltage fault steady-state interval according to the following formula:
I q ＝min(K q_LV (U LV -U term )+K Iq0_flag I q0 +I q0_LV ,I qmax_LV )
in the formula I q A steady-state value of reactive current, K, for a steady-state interval of low voltage faults q_LV Is a reactive current support coefficient, U LV To enter the voltage threshold of the low voltage fault, U term Is an AC side terminal voltage, K Iq0_flag For superimposing the index coefficients for the reactive current, I q0 Is a steady-state value of reactive current before low-voltage fault, I q0_LV Initial value of reactive current for low voltage fault, I qmax_LV The maximum reactive current in the steady-state interval of the low-voltage fault.
The steady state value I of reactive current before low voltage fault q0 The calculation formula of (a) is as follows:
Figure BDA0001449392270000021
in the formula i q0 Reactive current value, K, representing steady-state interval before low voltage fault iq0Start Data number, K, indicating the start of the steady-state interval before a low-voltage fault iq0End And a data number indicating the end time of the steady-state section before the low-voltage fault.
The reactive current steady state value I of the low-voltage fault steady state interval q The calculation formula of (c) is as follows:
Figure BDA0001449392270000022
in the formula i q Active current value, K, representing steady-state interval of low voltage fault iqStart Indicating the start of the steady-state interval of a low-voltage faultData sequence number, K iqEnd And a data sequence number indicating the end time of the low-voltage fault steady-state section.
And fitting the active current steady state value and the voltage of the low-voltage fault steady state interval by a curve according to the following formula:
Figure BDA0001449392270000023
in the formula I p Active current steady state value, P, for low voltage fault steady state interval 0 For active power before entering low voltage fault, U term Is an AC side terminal voltage, I max_FRT Maximum current in steady-state interval for low voltage fault, I q Reactive current in steady-state interval for low voltage fault, I p0 Is the steady state value of active current before low voltage fault, K p1_FRT And K p2_ FRT are all Is the active current coefficient, I p0_FRT Active current initial value for low voltage fault, I p_ And flag is an active current amplitude limiting flag bit in a low-voltage fault steady-state interval.
The active current steady state value I before the low voltage fault p0 The calculation formula of (a) is as follows:
Figure BDA0001449392270000031
in the formula i p0 Active current value, K, representing steady state interval before low voltage fault ip0Start Data number, K, indicating the start of the steady-state interval before a low-voltage fault ip0End And a data number indicating the end time of the steady-state section before the low-voltage fault.
The active current steady state value I of the low-voltage fault steady state interval p The calculation formula of (c) is as follows:
Figure BDA0001449392270000032
in the formula i p The active current value of the steady-state interval of the low-voltage fault is shown,K ipStart data number, K, indicating the start of the steady-state interval of a low voltage fault ipEnd And a data sequence number indicating the end time of the low-voltage fault steady-state section.
The feature fitting during low voltage recovery comprises: the average value of the current recovery rate during the voltage ride through recovery is calculated.
The calculation formula of the current recovery rate during the recovery of the low voltage fault is as follows:
Figure BDA0001449392270000033
in the formula, dI p_LV For the rate of current recovery during recovery from low voltage faults, I p_LV2 Active current at the end of low-voltage fault recovery, I p_LV1 Active current at the beginning of low-voltage fault recovery, t p_LV2 For the end of the recovery from the low voltage fault, t p_LV1 The low voltage fault recovery start time.
Setting an initial operation condition of the inverter before setting the low voltage ride through test;
the operation working conditions comprise high power, medium power and low power;
the high-power working condition refers to that the output power of the inverter is 70% -100% of the rated power;
the medium power working condition refers to that the output power of the inverter is 40% -60% of the rated power;
the low-power working condition means that the output power of the inverter is 10% -30% of the rated power.
The set low voltage ride through test comprises the following steps:
respectively dropping the AC side voltage of the inverter into a preset interval of rated voltage;
the preset interval of the rated voltage comprises the following steps: 0 to 20 percent, 20 to 30 percent, 50 to 60 percent and 70 to 90 percent.
The invention provides a fitting system for low voltage ride through characteristics of a photovoltaic inverter, which comprises:
a consistency module: obtaining electrical quantity according to a set low-voltage fault ride-through test, and verifying the consistency of the electrical quantity obtained by different tests of the same test;
a fitting module: selecting key electrical quantity according to the consistency of the electrical quantity to perform low voltage ride through feature fitting;
the electrical quantity includes: voltage steady-state values before and during a low-voltage fault steady-state interval, active current steady-state values and reactive current steady-state values before and during a low-voltage fault steady-state interval, and a current recovery rate during a low-voltage fault recovery period.
The fitting module includes: a low voltage fault period signature fitting submodule and a low voltage recovery period signature fitting submodule.
The low-voltage fault period feature fitting submodule comprises: the device comprises a first fitting unit for performing curve fitting on the reactive current steady-state value and the voltage in the low-voltage fault steady-state interval, and a second fitting unit for performing curve fitting on the active current steady-state value and the voltage in the low-voltage fault steady-state interval.
The first fitting unit performs curve fitting on the reactive current steady-state value and the voltage of the low-voltage fault steady-state interval according to the following formula:
I q ＝min(K q_LV (U LV -U term )+K Iq0_flag I q0 +I q0_LV ,I qmax_LV )
in the formula I q A steady-state value of reactive current, K, for a steady-state interval of low voltage faults q_LV Is a reactive current support coefficient, U LV To enter the voltage threshold of the low voltage fault, U term Is an AC side terminal voltage, K Iq0_flag For superimposing the index coefficients for the reactive current, I q0 Is a steady-state value of reactive current before low-voltage fault, I q0_LV Initial value of reactive current for low voltage fault, I qmax_LV The maximum reactive current in the steady-state interval of the low-voltage fault.
The second fitting unit performs curve fitting on the active current steady-state value and the voltage of the low-voltage fault steady-state interval according to the following formula:
Figure BDA0001449392270000041
in the formula I p Active current steady state value, P, for low voltage fault steady state interval 0 For entering active power before low voltage fault, U term Is an AC side terminal voltage, I max_FRT Maximum current in steady-state interval for low voltage fault, I q Reactive current in steady-state interval for low voltage fault, I p0 Is the steady state value of active current before low voltage fault, K p1_FRT And K p2_ FRT are all Is the active current coefficient, I p0_FRT Active current initial value for low voltage fault, I p_ And flag is an active current amplitude limiting flag bit of a low-voltage fault steady-state interval.
Compared with the closest prior art, the technical scheme provided by the invention has the following beneficial effects:
according to the technical scheme provided by the invention, the key electrical quantity of the inverter in the low-voltage ride through period is calculated, the low-voltage ride through characteristics of inverters of different brands and models are fitted by using a formula, the method has the advantages of simplicity in operation, easiness in implementation and good universality, the low-voltage ride through external characteristics of the inverter can be accurately fitted, and the method is an engineering practical method convenient to popularize.
Drawings
FIG. 1 is a flow chart of a fitting method for low voltage ride through characteristics of a photovoltaic inverter according to the present invention;
FIG. 2 is a schematic diagram of a low-penetration test system of an inverter according to an embodiment of the invention;
FIG. 3 is a basic flow chart of the fitting of the low voltage ride through characteristics of the inverter in an embodiment of the present invention;
FIG. 4 is a comparison graph of simulated values and actual measured values under a high-power condition in the embodiment of the invention;
FIG. 5 is a comparison graph of simulated values and actual measured values under a low-power condition in an embodiment of the present invention;
Detailed Description
The invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, the invention provides a fitting method for low voltage ride through characteristics of a photovoltaic inverter, which includes:
the invention provides a fitting method for low voltage ride through characteristics of a photovoltaic inverter, which comprises the following steps:
obtaining the electrical quantity according to a set low-voltage fault ride-through test, and verifying the consistency of the electrical quantity obtained by different times of tests in the same test;
selecting key electrical quantity according to the consistency of the electrical quantity to perform low voltage ride through feature fitting;
the electrical quantity includes: the voltage steady-state values before the low-voltage fault and in the low-voltage fault steady-state interval, the active current steady-state values and the reactive current steady-state values before the low-voltage fault and in the low-voltage fault steady-state interval, and the current recovery rate during the low-voltage fault recovery.
Selecting the key electrical quantity according to the consistency of the electrical quantities comprises:
and selecting the tested electrical quantity with the voltage steady state value deviation absolute value less than 0.05pu, the active current and reactive current steady state value deviation absolute value less than 0.1pu and the current recovery rate deviation absolute value less than 0.2pu/s during the low-voltage fault recovery period as the key electrical quantity.
The low voltage ride through feature fitting comprises: feature fitting during low voltage fault and feature fitting during low voltage recovery.
The feature fitting during low voltage fault includes:
performing curve fitting on the reactive current steady-state value and the voltage of the low-voltage fault steady-state interval;
and performing curve fitting on the active current steady-state value and the voltage of the low-voltage fault steady-state interval.
And performing curve fitting on the reactive current steady-state value and the voltage of the low-voltage fault steady-state interval according to the following formula:
I q ＝min(K q_LV (U LV -U term )+K Iq0_flag I q0 +I q0_LV ,I qmax_LV )
in the formula I q Is lowReactive current steady state value, K, of voltage fault steady state interval q_LV Is a reactive current support coefficient, U LV To enter the voltage threshold of the low voltage fault, U term Is an AC side terminal voltage, K Iq0_flag For superimposing index coefficients for reactive current, I q0 Is a steady-state value of reactive current before low-voltage fault, I q0_LV Initial value of reactive current for low voltage fault, I qmax_LV The maximum reactive current in the steady-state interval of the low-voltage fault.
The steady state value I of reactive current before low voltage fault q0 The calculation formula of (c) is as follows:
Figure BDA0001449392270000061
in the formula i q0 Reactive current value, K, representing steady-state interval before low voltage fault iq0Start Data number, K, indicating the start of the steady-state interval before a low-voltage fault iq0End And a data number indicating the end time of the steady-state section before the low-voltage failure.
The steady state value I of the reactive current in the low-voltage fault steady state interval q The calculation formula of (c) is as follows:
Figure BDA0001449392270000062
in the formula i q Active current value, K, representing steady state interval of low voltage fault iqStart Data number, K, indicating the start of the steady-state interval of a low voltage fault iqEnd And a data sequence number indicating the end time of the low-voltage fault steady-state section.
And performing curve fitting on the active current steady-state value and the voltage of the low-voltage fault steady-state interval according to the following formula:
Figure BDA0001449392270000063
in the formula I p Active power for low voltage fault steady state intervalSteady state value of flow, P 0 For entering active power before low voltage fault, U term Is an AC side terminal voltage, I max_FRT Maximum current in steady-state region for low voltage fault, I q Reactive current in steady-state interval for low voltage fault, I p0 Is the steady state value of active current before low voltage fault, K p1_FRT And K p2_ FRT are all Is the active current coefficient, I p0_FRT Active current initial value for low voltage fault, I p_ And flag is an active current amplitude limiting flag bit in a low-voltage fault steady-state interval.
The active current steady state value I before the low voltage fault p0 The calculation formula of (c) is as follows:
Figure BDA0001449392270000071
in the formula i p0 Active current value, K, representing steady state interval before low voltage fault ip0Start Data number, K, indicating the start of the steady-state interval before a low-voltage fault ip0End And a data number indicating the end time of the steady-state section before the low-voltage failure.
Active current steady state value I of low voltage fault steady state interval p The calculation formula of (a) is as follows:
Figure BDA0001449392270000072
in the formula i p Active current value, K, representing steady state interval of low voltage fault ipStart Data sequence number, K, indicating the start of the steady-state interval for a low voltage fault ipEnd And a data sequence number indicating the end time of the low-voltage fault steady-state section.
The feature fitting during low voltage recovery comprises: the average value of the current recovery rate during the voltage ride through recovery is calculated.
The calculation formula of the current recovery rate during the recovery of the low voltage fault is as follows:
Figure BDA0001449392270000073
in the formula, dI p_LV For the rate of current recovery during recovery from low voltage faults, I p_LV2 Active current at the end of low-voltage fault recovery, I p_LV1 Active current at the beginning of low voltage fault recovery, t p_LV2 For the end of the recovery from the low voltage fault, t p_LV1 The low voltage fault recovery start time.
Setting an initial operation condition of the inverter before setting the low voltage ride through test;
the operation working conditions comprise high power, medium power and low power;
the high-power working condition refers to that the output power of the inverter is 70% -100% of the rated power;
the medium power working condition refers to that the output power of the inverter is 40% -60% of the rated power;
the low-power working condition means that the output power of the inverter is 10% -30% of the rated power.
The set low voltage ride through test comprises:
respectively dropping the AC side voltage of the inverter into a preset interval of rated voltage;
the preset interval of the rated voltage comprises the following steps: 0 to 20 percent, 20 to 30 percent, 50 to 60 percent and 70 to 90 percent.
The closer the electrical quantities obtained by different tests of the same test are, the better the consistency of the electrical quantities of the test is.
The invention provides a fitting system for low voltage ride through characteristics of a photovoltaic inverter, which comprises the following components:
a consistency module: obtaining electrical quantity according to a set low-voltage fault ride-through test, and verifying the consistency of the electrical quantity obtained by different tests of the same test;
a fitting module: selecting key electrical quantity according to the consistency of the electrical quantity to perform low voltage ride through feature fitting;
the electrical quantity includes: voltage steady-state values before and during a low-voltage fault steady-state interval, active current steady-state values and reactive current steady-state values before and during a low-voltage fault steady-state interval, and a current recovery rate during a low-voltage fault recovery period.
The fitting module comprises: a low voltage fault period feature fitting submodule and a low voltage recovery period feature fitting submodule.
The low voltage fault period feature fitting submodule includes: the device comprises a first fitting unit for performing curve fitting on the reactive current steady-state value and the voltage in the low-voltage fault steady-state interval, and a second fitting unit for performing curve fitting on the active current steady-state value and the voltage in the low-voltage fault steady-state interval.
The first fitting unit performs curve fitting on the reactive current steady-state value and the voltage of the low-voltage fault steady-state interval according to the following formula:
I q ＝min(K q_LV (U LV -U term )+K Iq0_flag I q0 +I q0_LV ,I qmax_LV )
in the formula I q A steady-state value of reactive current, K, for a steady-state interval of low voltage faults q_LV Is a reactive current support coefficient, U LV To enter the voltage threshold of the low voltage fault, U term Is an AC side terminal voltage, K Iq0_flag For superimposing index coefficients for reactive current, I q0 Is a steady-state value of reactive current before low-voltage fault, I q0_LV Initial value of reactive current for low voltage fault, I qmax_LV The maximum reactive current in the steady-state interval of the low-voltage fault.
The second fitting unit performs curve fitting on the active current steady-state value and the voltage of the low-voltage fault steady-state interval according to the following formula:
Figure BDA0001449392270000091
in the formula I p Active current steady state value, P, for low voltage fault steady state interval 0 For active power before entering low voltage fault, U term Is an AC side terminal voltage, I max_FRT Maximum current in steady-state interval for low voltage fault, I q Reactive current in steady-state interval for low voltage fault, I p0 Is the steady state value of active current before low voltage fault, K p1_FRT And K p2_ FRT are all Is the active current coefficient, I p0_FRT Active current initial value for low voltage fault, I p_ And flag is an active current amplitude limiting flag bit in a low-voltage fault steady-state interval.
The feature fitting sub-module during low voltage recovery for performing feature fitting during low voltage recovery includes: the average of the current recovery rates during the voltage ride through recovery is calculated. The consistency module comprises a test submodule for setting a low voltage ride through test;
the test submodule setting low voltage ride through test comprises:
enabling the AC side voltage of the inverter to fall within a preset interval of rated voltage respectively;
the preset interval of the rated voltage comprises the following steps: 0 to 20 percent, 20 to 30 percent, 50 to 60 percent and 70 to 90 percent.
The photovoltaic inverter low-voltage ride through characteristic fitting system further comprises a setting module used for setting the initial operation working condition of the inverter before setting the low-voltage ride through test;
the operation working conditions comprise high power, medium power and low power;
the high-power working condition refers to that the output power of the inverter is 70% -100% of the rated power;
the medium power working condition refers to that the output power of the inverter is 40% -60% of the rated power;
the low-power working condition means that the output power of the inverter is 10% -30% of the rated power.
Examples
Before fitting the low-voltage ride-through characteristic of the photovoltaic inverter, the inverter low-voltage ride-through test system shown in fig. 2 is set up, and the system mainly comprises a photovoltaic group string (square matrix)/analog direct current source, an inverter and a power grid disturbance generation system.
As shown in fig. 3, a basic procedure for fitting the low voltage ride through characteristics of the inverter is as follows:
step one, setting an initial operation working condition of the inverter by adjusting the maximum output of the controllable direct-current power supply, and respectively enabling the inverter to operate under three working conditions of high power, medium power and low power, wherein the high-power working condition refers to that the output power of the inverter is 70% -100% of the rated power, the medium-power working condition refers to that the output power of the inverter is 40% -60% of the rated power, and the low-power working condition refers to that the output power of the inverter is 10% -30% of the rated power.
Step two, setting a low-voltage fault ride-through test to enable the AC side voltage of the inverter to respectively fall to the ranges of 0-20%, 20-30%, 50-60% and 70-90% of the rated voltage, and repeating the same test at least twice;
calculating active current and reactive current steady-state values before a low-voltage fault and during a fault steady-state period, calculating a current recovery rate during a fault recovery period, and checking the consistency of test data of different times in the same group of tests;
step four, distinguishing working conditions, considering overcurrent protection as a boundary condition, and performing feature fitting during low-voltage fault period, wherein the feature fitting comprises the following steps: and performing curve fitting on the relation between the active/reactive current steady-state value and the voltage of the low-voltage fault steady-state interval.
The fitting formula of the reactive current is
I q ＝min(K q_LV (U LV -U term )+K Iq0_flag I q0 +I q0_LV ,I qmax_LV ) (1)
In the formula I q For reactive current during low voltage ride through, K q_LV Is a reactive current support coefficient, U LV To enter the voltage threshold for low voltage ride through control, U term Is an AC side terminal voltage, K Iq0_flag For superimposing index coefficients for reactive current, I q0 To enter reactive current before low voltage ride through control, I q0_LV Initial value of reactive current for low voltage ride through, I qmax_LV Is the maximum reactive current during low voltage ride through control.
The fitting formula of the active current is
Figure BDA0001449392270000101
In the formula I p Active current during low voltage ride through, P 0 For active power before entering low voltage ride through control, U term Is an AC side terminal voltage, I max_FRT To enter maximum current during low voltage ride through control, I q For reactive current during low voltage ride through, K p1_FRT Is an active current coefficient of 1,K p2_FRT Is an active current coefficient of 2, I P0 To enter the active current before the low voltage ride through control, I p0_FRT Initial value of active current for low voltage ride through, I p_ And flag is an active current amplitude limiting flag bit during low voltage ride through.
The calculation formula of the steady state value of the active current before the low-voltage fault is
Figure BDA0001449392270000102
In the formula i p0 Active current value, K, representing steady state interval before low voltage fault ip0Start Data number, K, indicating the start time of the steady-state interval before failure ip0End A data number indicating the end time of the steady-state section before the failure.
The reactive current steady state value before low voltage fault is calculated by the formula
Figure BDA0001449392270000111
In the formula i q0 Reactive current value, K, representing steady-state interval before low voltage fault iq0Start Data sequence number, K, indicating the start time of the steady-state interval before failure iq0End A data number indicating the end time of the steady-state section before the failure.
The active current steady state value calculation formula of the low voltage fault steady state interval is
Figure BDA0001449392270000112
In the formula i p Active current value, K, representing steady state interval of low voltage fault ipStart Data sequence number, K, indicating the start time of a faulted steady-state interval ipEnd And a data number indicating the end time of the failure steady-state section.
The reactive current steady-state value calculation formula of the low-voltage fault steady-state interval is
Figure BDA0001449392270000113
In the formula i q Active current value, K, representing steady state interval of low voltage fault iqStart Data sequence number, K, indicating the start time of a faulted steady-state interval iqEnd And a data sequence number indicating the end time of the failure steady-state section.
The current recovery rate during the recovery of the low voltage fault is calculated by
Figure BDA0001449392270000114
In the formula I p_LV2 Active current at the end of fault recovery, I p_LV1 Active current at the start of fault recovery, t p_LV2 To the end time of the fault recovery, t p_LV1 The failure recovery start time.
Feature fitting during low voltage fault recovery includes: the current recovery rate was calculated and averaged over multiple tests.
In order to verify the correctness of the fitting method, the low-voltage ride through characteristic of a photovoltaic inverter of a certain model is fitted. Calculating reactive current and active current steady-state values during the low-voltage fault steady-state period according to the first, second and third steps of low-voltage ride-through test, and performing curve fitting on the relationship between the active/reactive current and the voltage during the fault steady-state period according to a formula (1) and a formula (2) to obtain K in the formula (1) q_LV Take 2,U LV Taking 0.9,K Iq0_flag Take 0,I q0 Take 0,I q0_LV Take 0,I qmax_LV Taking 1.08; i in the formula (2) p_ The flag is 2,K p1_FRT Take 0,K p2_FRT Take 0,I p0_FRT Taking 0.16,I max_FRT Taking 1.1;
the fitting formula for obtaining the low voltage ride through characteristic of the inverter is as follows:
I q ＝min(2×(0.9-U term ),1.08)
I p ＝0.16。
the average value of the current recovery rate during the recovery of the low voltage fault was measured to be 1.25pu/s.
And substituting the inverter fitting formula and the current recovery rate parameter into the electromechanical transient simulation model to perform electromechanical transient simulation, wherein the simulation curve and the measured curve have good consistency, as shown in fig. 4 and 5. By comparing simulation data with actual test data, the fact that the low-voltage ride through characteristic fitting method provided by the invention can well fit the reality of the inverter no matter under a high-power working condition or a low-power working condition can be found, and the correctness and the effectiveness of the fitting method are verified.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and so forth) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may 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, create a system for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including an instruction system which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the scope of protection thereof, and although the present application is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: numerous variations, modifications, and equivalents will occur to those skilled in the art upon reading the present application and are within the scope of the claims appended hereto.

Claims (7)

1. A fitting method for low voltage ride through characteristics of a photovoltaic inverter is characterized by comprising the following steps:
obtaining the electrical quantity according to a set low-voltage fault ride-through test, and verifying the consistency of the electrical quantity obtained by different times of tests in the same test;
selecting key electrical quantity according to the consistency of the electrical quantity to perform low voltage ride through characteristic fitting;
the electrical quantity includes: voltage steady-state values before a low-voltage fault and in a low-voltage fault steady-state interval, active current steady-state values and reactive current steady-state values before the low-voltage fault and in the low-voltage fault steady-state interval, and a current recovery rate during low-voltage fault recovery;
the fitting of the low voltage ride through characteristics comprises: feature fitting during low voltage fault and feature fitting during low voltage recovery;
the feature fitting during low voltage fault comprises:
carrying out curve fitting on the reactive current steady-state value and the voltage of the low-voltage fault steady-state interval;
performing curve fitting on the active current steady-state value and the voltage of the low-voltage fault steady-state interval;
and performing curve fitting on the reactive current steady-state value and the voltage of the low-voltage fault steady-state interval according to the following formula:
I q ＝min(K q_LV (U LV -U term )+K Iq0_flag I q0 +I q0_LV ,I qmax_LV )
in the formula I q Steady state value of reactive current, K, for steady state interval of low voltage fault q_LV Is a reactive current support coefficient, U LV To enter the voltage threshold of the low voltage fault, U term Is an AC side terminal voltage, K Iq0_flag For superimposing index coefficients for reactive current, I q0 Is a steady-state value of reactive current before low-voltage fault, I q0_LV Initial value of reactive current for low voltage fault, I qmax_LV The maximum reactive current in the steady-state interval of the low-voltage fault;
the steady state value I of reactive current before low voltage fault q0 The calculation formula of (a) is as follows:
Figure FDA0003709597540000011
in the formula i q0 Reactive current value, K, representing steady-state interval before low voltage fault iq0Start Represents lowData sequence number, K, at the start of the steady-state interval before a voltage fault iq0End A data number indicating an end time of the steady-state section before the low-voltage fault;
the steady state value I of the reactive current in the low-voltage fault steady state interval q The calculation formula of (a) is as follows:
Figure FDA0003709597540000012
in the formula i q Active current value, K, representing steady-state interval of low voltage fault iqStart Data number, K, indicating the start of the steady-state interval of a low voltage fault iqEnd A data sequence number indicating an end time of a low-voltage fault steady-state section;
and fitting the active current steady state value and the voltage of the low-voltage fault steady state interval by a curve according to the following formula:
Figure FDA0003709597540000021
in the formula I p Active current steady state value, P, for low voltage fault steady state interval 0 For active power before entering low voltage fault, U term Is an AC side terminal voltage, I max_FRT Maximum current in steady-state interval for low voltage fault, I q Reactive current in steady-state interval for low voltage fault, I p0 Is the steady state value of active current before low voltage fault, K p1_FRT And K p2_ FRT are all Is the active current coefficient, I p0_FRT Active current initial value for low voltage fault, I p_ flag is an active current amplitude limiting flag bit of a low-voltage fault steady-state interval;
the active current steady state value I before the low voltage fault p0 The calculation formula of (a) is as follows:
Figure FDA0003709597540000022
in the formula i p0 Active current value, K, representing steady state interval before low voltage fault ip0Start Data number, K, indicating the start of the steady-state interval before a low-voltage fault ip0End A data number indicating an end time of the steady-state section before the low-voltage fault;
active current steady state value I of low voltage fault steady state interval p The calculation formula of (c) is as follows:
Figure FDA0003709597540000023
in the formula i p Active current value, K, representing steady-state interval of low voltage fault ipStart Data number, K, indicating the start of the steady-state interval of a low voltage fault ipEnd And a data number indicating the end time of the low-voltage fault steady-state section.
2. The fitting method for low voltage ride through characteristics of a photovoltaic inverter according to claim 1, wherein the selecting the key electrical quantity according to the consistency of the electrical quantities comprises:
and selecting the electric quantity of the test with the voltage steady state value deviation absolute value less than 0.05pu, the active current and reactive current steady state value deviation absolute value less than 0.1pu and the current recovery rate deviation absolute value less than 0.2pu/s during the low voltage fault recovery period as the key electric quantity.
3. The photovoltaic inverter low voltage ride through characteristic fitting method of claim 1, wherein the low voltage recovery period characteristic fitting comprises: the average value of the current recovery rate during the voltage ride through recovery is calculated.
4. The fitting method for low voltage ride through characteristics of a photovoltaic inverter according to any one of claims 1 or 3, wherein the calculation formula of the current recovery rate during the low voltage fault recovery is as follows:
Figure FDA0003709597540000031
in the formula, dI p_LV For the rate of current recovery during recovery from low voltage faults, I p_LV2 Active current at the end of low-voltage fault recovery, I p_LV1 Active current at the beginning of low-voltage fault recovery, t p_LV2 For the end of recovery of low voltage fault, t p_LV1 The low voltage fault recovery start time.
5. The fitting method for the low voltage ride through characteristics of the photovoltaic inverter according to claim 1, wherein the step of setting the initial operation condition of the inverter is further included before the step of setting the low voltage ride through test;
the operation working conditions comprise high power, medium power and low power;
the high-power working condition refers to that the output power of the inverter is 70% -100% of the rated power;
the medium power working condition refers to that the output power of the inverter is 40% -60% of the rated power;
the low-power working condition means that the output power of the inverter is 10% -30% of the rated power.
6. The fitting method for low voltage ride through characteristics of a pv inverter of claim 5, wherein the setting the low voltage ride through test comprises:
enabling the AC side voltage of the inverter to fall within a preset interval of rated voltage respectively;
the preset interval of the rated voltage comprises the following steps: 0 to 20 percent, 20 to 30 percent, 50 to 60 percent and 70 to 90 percent.
7. A fitting system for low voltage ride through characteristics of a photovoltaic inverter, comprising:
a consistency module: obtaining electrical quantity according to a set low-voltage fault ride-through test, and verifying the consistency of the electrical quantity obtained by different tests of the same test;
a fitting module: selecting key electrical quantity according to the consistency of the electrical quantity to perform low voltage ride through feature fitting;
the electrical quantity includes: voltage steady-state values before a low-voltage fault and in a low-voltage fault steady-state interval, active current steady-state values and reactive current steady-state values before the low-voltage fault and in the low-voltage fault steady-state interval, and a current recovery rate during a low-voltage fault recovery period;
the fitting module includes: a low voltage fault period characteristic fitting submodule and a low voltage recovery period characteristic fitting submodule;
the low-voltage fault period feature fitting submodule comprises: the device comprises a first fitting unit for performing curve fitting on a reactive current steady-state value and voltage in a low-voltage fault steady-state interval and a second fitting unit for performing curve fitting on an active current steady-state value and voltage in the low-voltage fault steady-state interval;
the first fitting unit performs curve fitting on the reactive current steady-state value and the voltage of the low-voltage fault steady-state interval according to the following formula:
I q ＝min(K q_LV (U LV -U term )+K Iq0_flag I q0 +I q0_LV ,I qmax_LV )
in the formula I q Steady state value of reactive current, K, for steady state interval of low voltage fault q_LV Is a reactive current support coefficient, U LV To enter the voltage threshold of the low voltage fault, U term Is an AC side terminal voltage, K Iq0_flag For superimposing the index coefficients for the reactive current, I q0 Steady state value of reactive current before low voltage fault, I q0_LV Initial value of reactive current for low voltage fault, I qmax_LV The maximum reactive current in the steady-state interval of the low-voltage fault;
the second fitting unit performs curve fitting on the active current steady-state value and the voltage of the low-voltage fault steady-state interval according to the following formula:
Figure FDA0003709597540000041
in the formula I p Active current steady state value, P, for low voltage fault steady state interval 0 For active power before entering low voltage fault, U term Is an AC side terminal voltage, I max_FRT Maximum current in steady-state interval for low voltage fault, I q Reactive current in steady-state interval for low-voltage faults, I p0 Is the steady state value of active current before low voltage fault, K p1_FRT And K p2_ FRT are all Is the active current coefficient, I p0_FRT Active current initial value for low voltage fault, I p_ And flag is an active current amplitude limiting flag bit of a low-voltage fault steady-state interval.
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