CN103941118B - Island detection method for photovoltaic power generation grid-connected inverter group system - Google Patents

Abstract

A kind of island detection method for photovoltaic power generation grid-connected inverter group system.When inverter group system generation isolated island, and during grid-connected point voltage frequency reduction, tradition sliding formwork frequency drift method electric current is modified with voltage phase difference, add error compensation angle, thus offset the impact that sliding formwork frequency drift method check frequency and response speed are caused by line impedance, improve reliability of islanding detection.If grid-connected point voltage frequency raises, then using tradition sliding formwork frequency drift method expression formula, isolated island detection effectiveness will not be had undesirable effect by now system line impedance.

Description

Island detection method for photovoltaic power generation grid-connected inverter group system

Technical field

The present invention relates to a kind of detection method being applicable to combining inverter group system.

Background technology

Isolated island refers in grid-connected photovoltaic system, and owing to fault or maintenance cause grid cut-off, and photovoltaic generating system does not stop Only to local load supplying, form the phenomenon of a power supply isolated island.Occurring of isolated island can steady to the safety of maintainer and electrical network Determining operation and cause huge hidden danger, the isolated island detection technique therefore studying microgrid has important practical significance.In recent years, photovoltaic is sent out Electricity system gradually develops to high density, multi-access point direction, the effectiveness of tradition island detection method, especially proactive By new challenge, it is adaptable to the isolated island detection technique of photovoltaic combining inverter group system becomes the focus of current research.

Sliding formwork frequency drift method (SMS) is a kind of active local island detection method with positive feedback effect, sliding formwork frequency The ultimate principle of drift method is inverter control output electric current and grid-connected point voltage same frequency, but one constant phase of leading voltage Position:

${\mathrm{\θ}}_{\mathrm{SMS}}={\mathrm{\θ}}_m\sin (\frac{\mathrm{\π}}{2}\·\frac{f_{\mathrm{PCC}}-f_0}{f_m-f_0})$

Wherein, θ_mOffset for maximum phase, f_PCCFor grid-connected inverters point voltage frequency, f₀For electrical network rated frequency 50Hz, f_m For producing maximum phase skew θ_mTime frequency.When photovoltaic inverter grid-connected runs, θ_SMS=0, do not have between electric current and voltage There are phase contrast, system grid connection dot frequency also will not change；Isolated island once occurs, and inverter group system frequency is no longer by electricity Net is clamped down on, and due to the positive feedback effect of sliding formwork frequency method, grid-connected dot frequency eventually beyond setting threshold value, can detect isolated island The generation of phenomenon.

The inverter group system distribution of multi-access point more disperses, and the line impedance between each inverter and also site can not be neglected Slightly, now, between exit potential and grid-connected point voltage that inverter collects, there is phase contrast, cause inverter to float in mould frequency The current phase deviation theory value of output under shifting method effect, the current and phase difference caused when line impedance and θ_SMSTime in opposite direction, The positive feedback effect that can cause mould frequency drift method (SMS) reduces, and affects the effectiveness of isolated island detection.Wherein affect the most serious Situation be between the grid-connected point voltage of inverter group system and electric current phase contrast equal to load phase angle, isolated island internal power is complete Coupling, as a example by purely resistive load situation, when being to there is line impedance in the case of two inverter parallels as shown in Figure 2 System structure, when load is for purely resistive, grid-connected point voltage when line impedance causes sliding formwork frequency drift method to lose efficacy and current wave Shape is as shown in Figure 3.

Fig. 4 show tradition sliding formwork frequency drift method check frequency in the inverter group system that line impedance can not be ignored Analyze, during for occurring that system frequency f declines after isolated island, θ_SMS< 0, current phase should lag behind grid-connected point voltage, this Time line impedance can cause θ_SMSBeing offset, check frequency strengthens；If θ after isolated island generation_SMS> 0, the phase that line impedance causes Position error and θ_SMSEquidirectional, then check frequency reduces, and line impedance will not reduce the effectiveness of isolated island detection.In general, Owing to system line impedance can cause the check frequency of tradition SMS method to offset, and after isolated island occurs, frequency rises or falls Being random, therefore for a certain particular system, it is impossible to judge that tradition SMS method is whether effective, reduce isolated island detection can By property.

Summary of the invention

When it is an object of the invention to overcome existing sliding formwork frequency drift method to be applied in inverter group system, line impedance causes orphan The shortcoming that island detection method effectiveness reduces, proposes a kind of new method being applicable to the detection of combining inverter group system isolated island.This Invention can effectively reduce the isolated island check frequency in the case of system line impedance can not be ignored, and improves response speed.

The present invention is to solve that its technical problem be the technical scheme is that a kind of Novel island detection method of proposition, the method Improve phase angle θ in tradition mould frequency drift method_SMSThe method of expression formula, to reduce isolated island check frequency.When inverter collection Group's system generation isolated island, and when grid-connected point voltage frequency reduces, tradition sliding formwork frequency drift method electric current is carried out with voltage phase difference Revise, add error compensation angle, thus offset inversion drift method check frequency and impact that response speed causes, improve isolated island inspection The reliability surveyed.Phase angle θ in the present invention_SMSExpression formula be:

${\mathrm{\&theta;}}_{\mathrm{SMS}}=\left\{\begin{array}{cc}{\mathrm{\&theta;}}_m\sin (\frac{\mathrm{\&pi;}}{2}\&CenterDot;\frac{f_{\mathrm{PCC}}-f_0}{f_m-f_0})& (f_{\mathrm{PCC}}>f_0)\\ {\mathrm{\&theta;}}_m\sin (\frac{\mathrm{\&pi;}}{2}\&CenterDot;\frac{f_{\mathrm{PCC}}-f_0}{f_m-f_0})-{\mathrm{\&theta;}}_0& (f_{\mathrm{PCC}}<f_0)\end{array}\right.$

In above formula: θ_mOffset for maximum phase, f_PCCFor grid-connected inverters point voltage frequency, f₀For electrical network rated frequency 50Hz, f_mFor producing maximum phase skew θ_mTime frequency.Frequency rising condition f after isolated island is occurred_PCC＞ f₀, phase angle θ_SMS's Expression formula is identical with tradition mould frequency drift method.When photovoltaic inverter grid-connected runs, phase angle θ_SMS=0, electric current and voltage it Between there is no phase contrast；Once occur island phenomenon, grid-connected point voltage frequency to be no longer influenced by electrical network and clamp down on, if now and site frequency Rate creates little increase, then a θ_SMS＞ 0, current phase will be ahead of voltage, cause electric current to arrive next zero crossing Time shortens, and system current/voltage under island state meets relation:The most grid-connected point voltageOnly by inversion The electric current of device group system outputDetermining with local load impedance Z, the most grid-connected point voltage arrives the time of next zero crossing Also will shorten, frequency raises, now phase angle θ_SMSOwing to positive feedback effect continues to increase, until grid-connected dot frequency will be beyond setting Fixed threshold value, can detect island phenomenon；In like manner, when isolated island occurs moment grid-connected dot frequency to occur declining, phase angle θ_SMS＜ 0, also by by the effect of positive feedback so that frequency constantly declines, can detect the generation of island phenomenon.

If frequency declines f after island phenomenon occurs_PCC＜ f₀, then at phase angle θ_SMSOn the basis of deducted a constant angle θ₀, and θ₀> 0, this angle is that error phase compensates angle, and its effect is that the inverter current phase place that counteracting line impedance causes is advanced, Ensure that electric current lags behind the angle of voltage and reaches theoretical value.Error phase compensates angle θ₀Value by the inverter quantity in system and The distribution distance of each inverter determines, in order to ensure system power quality, error phase compensates angle θ₀It is not to be exceeded maximum phase Skew θ_m, take:

θ₀=K θ_m

Wherein K=K_nK_l, K_nRatio shared by distribution distance inverter farther out in expression system, its expression formula is:

$K_n=\frac{m}{n}$

The inverter platform that during wherein n and m represents total inverter number and inverter cluster respectively, distance is public and site is distant Number, it is known that now K_n∈(0,1)；K_lRepresent inverter cluster overall distribution situation, when each inverter distribution is relatively decentralized, distance Public and site is distant, desirable bigger K_lValue, and for being distributed close combining inverter group system, K_lValue Can be less, its span is K_l∈(0.1,1)。

The control strategy that error phase compensates angle is as follows: start timing when system detects after grid-connected dot frequency changes, due to GB/T15945 regulation isolated island protection should action in 0.2s after island phenomenon occurs, therefore set when amplitude of variation reaches 0.5Hz, persistent period reach 0.1s, and isolated island protection not operating in the case of θ₀Produce, effectively prevent system frequency disturbance Cause the situation of current phase acute variation.

The invention has the beneficial effects as follows, inverter group system line impedance can be suppressed active alone island detection method effectiveness Impact, reduce sliding formwork frequency drift method isolated island check frequency under there is line impedance cases, improve response speed.

Accompanying drawing explanation

The workflow diagram of SMS method after Fig. 1 improvement；

Inverter cluster topology during line impedance is there is in the case of Fig. 2 purely resistive load；

In the case of Fig. 3 purely resistive load, line impedance causes isolated island power grid-connected point voltage and current waveform when mating completely；

Fig. 4 tradition SMS method isolated island check frequency in the case of line impedance can not be ignored；

Before and after Fig. 5 improves, SMS method isolated island check frequency in the case of inverter cluster line impedance be can not ignore compares.

Detailed description of the invention

The present invention is further illustrated below in conjunction with the drawings and specific embodiments.

Present invention improves over phase angle θ in tradition mould frequency drift method_SMSExpression formula, for:

${\mathrm{\&theta;}}_{\mathrm{SMS}}=\left\{\begin{array}{cc}{\mathrm{\&theta;}}_m\sin (\frac{\mathrm{\&pi;}}{2}\&CenterDot;\frac{f_{\mathrm{PCC}}-f_0}{f_m-f_0})& (f_{\mathrm{PCC}}>f_0)\\ {\mathrm{\&theta;}}_m\sin (\frac{\mathrm{\&pi;}}{2}\&CenterDot;\frac{f_{\mathrm{PCC}}-f_0}{f_m-f_0})-{\mathrm{\&theta;}}_0& (f_{\mathrm{PCC}}<f_0)\end{array}\right.$

Wherein θ_mOffset for maximum phase, f_PCCFor grid-connected inverters point voltage frequency, f₀For electrical network rated frequency 50Hz, f_mFor Produce maximum phase skew θ_mTime frequency.Visible, phase angle θ under frequency rising condition after isolated island generation_SMSExpression formula and tradition Mould frequency drift method is identical；If frequency declines, then at former phase angle θ after isolated island occurs_SMSOn the basis of deduct a constant angle Degree θ₀, and θ₀> 0, this angle is that error phase compensates angle, and its effect is that the inverter current phase place that counteracting line impedance causes surpasses Before, it is ensured that electric current lags behind the angle of voltage and reaches theoretical value.

θ₀Value need to be according to the structures shape of photovoltaic DC-to-AC converter cluster, it is considered to factor include the inverter quantity in system, with And the distribution distance of each inverter, in order to ensure system power quality, θ₀It is not to be exceeded θ_m, take:

θ₀=K θ_m

Wherein K=K_nK_l, K_nRatio shared by distribution distance inverter farther out in expression system, its expression formula is:

$K_n=\frac{m}{n}$

Wherein n represents total inverter number, and m represents the inverter number of units that in inverter cluster, distance is public and site is distant, Understand now K_n∈(0,1)；K_lRepresent inverter cluster overall distribution situation, when each inverter distribution is relatively decentralized, apart from public And site is distant, desirable bigger K_lValue, and for being distributed close system, K_lValue can be less, its value model Enclose for K_l∈(0.1,1)。

Abbreviation θ_SMSExpression formula is as follows:

${\mathrm{\&theta;}}_{\mathrm{SMS}}=\left\{\begin{array}{cc}{\mathrm{\&theta;}}_m\sin (\frac{\mathrm{\&pi;}}{2}\&CenterDot;\frac{f_{\mathrm{PCC}}-f_0}{f_m-f_0})& (f_{\mathrm{PCC}}>f_0)\\ {\mathrm{\&theta;}}_m[\sin (\frac{\mathrm{\&pi;}}{2}\&CenterDot;\frac{f_{\mathrm{PCC}}-f_0}{f_m-f_0})-K]& (f_{\mathrm{PCC}}<f_0)\end{array}\right.$

Fig. 5 show the present invention and the isolated island check frequency comparative result of traditional mould frequency drift method.As it is shown in figure 5, inverse In the case of change device group system exists line impedance, check frequency more traditional mould frequency drift method low frequency part of the present invention is Reduce, i.e. affected reduction by line impedance, and HFS is not owing to being affected by line impedance, also will not be impacted after improvement.

In order to ensure that the present invention does not interferes with the quality of power supply of electrical network in the case of inverter group system is incorporated into the power networks, use as follows Control strategy: start timing after grid-connected dot frequency changes when detecting, when change duration long enough, and side-play amount After sufficiently large, error phase compensates angle θ₀Produce, for example, it can be set to reach when grid-connected dot frequency declines the situation persistent period 0.1s, and isolated island protection not operating in the case of, produce θ₀, effectively prevent system frequency disturbance and cause current phase acutely to become Situation about changing.

Fig. 1 show the workflow diagram of the inventive method.As it is shown in figure 1, the inverter being furnished with the inventive method was running Cheng Zhong, persistently to grid-connected point voltage frequency f_PCCSampling and analyze, the most grid-connected dot frequency changes, and inverter judges Grid-connected point voltage frequency f_PCCRise or decline, if f_PCC＞ f₀, inverter will according to tradition sliding formwork frequency drift method action, I.e. control output electric current and grid-connected point voltage phase place

If grid-connected dot frequency f_PCC＜ f₀, then the DSP of inverter starts timing, and inverter continues to detect grid-connected dot frequency simultaneously, Work as f_PCC＜ f₀Persistent period reaches 0.1s, and express possibility generation isolated island, and grid-connected dot frequency declines, now, according to the present invention Method controls output electric current and grid-connected point voltage phase contrast

If f_PCC＜ f₀Persistent period fails to reach 0.1s, then it is assumed that be that system disturbance causes grid-connected dot frequency to change, Bu Huijia Applying aspect error compensation angle θ₀.Inverter finally exports electric current i=I_mcos(2πf₀t+θ_SMS)。

Claims (3)

1. for the island detection method of photovoltaic power generation grid-connected inverter group system, it is characterized in that: when inverter cluster system There is isolated island in system, and when grid-connected point voltage frequency reduces, to phase contrast between electric current and voltage in tradition sliding formwork frequency drift method θ_SMSAdd error compensation angle θ₀:

${\mathrm{\&theta;}}_{SMS}={\mathrm{\&theta;}}_{m}sin(\frac{\mathrm{\&pi;}}{2}\&CenterDot;\frac{f_{PCC}-f_0}{f_m-f_0})-{\mathrm{\&theta;}}_0;$

If grid-connected point voltage frequency raises after isolated island generation, then the phase difference θ between electric current and voltage_SMSExpression formula and biography System sliding formwork frequency drift method is identical:

${\mathrm{\&theta;}}_{SMS}={\mathrm{\&theta;}}_{m}sin(\frac{\mathrm{\&pi;}}{2}\&CenterDot;\frac{f_{PCC}-f_0}{f_m-f_0}),$

Wherein: θ_mOffset for maximum phase, f_PCCFor grid-connected inverters point voltage frequency, f₀For electrical network rated frequency, f_mFor producing Raw maximum phase skew θ_mTime frequency.

Island detection method for photovoltaic power generation grid-connected inverter group system the most according to claim 1, its feature It is: described error compensation angle θ₀Use following control strategy: start timing when detecting after grid-connected dot frequency changes, when Amplitude of variation reaches 0.5Hz, the persistent period reaches 0.1s, and isolated island protection not operating in the case of error compensation angle θ₀Produce.

The most according to claim 1 for photovoltaic power generation grid-connected inverter group system island detection method, it is characterized in that: Described error compensation angle θ₀Value according to the structures shape of photovoltaic DC-to-AC converter cluster, it is considered to factor include combining inverter collection Inverter quantity in group's system, and the distribution distance of each inverter, take error compensation angle θ₀=K θ_m, wherein K=K_nK_l； K_nRatio shared by distribution distance inverter farther out in expression system, its expression formula isWherein n represents total inversion Device number, m represents that distance in inverter group system is public and site inverter number of units farther out, therefore K_n∈(0,1)；K_lRepresent Inverter cluster overall distribution situation, is distributed the most scattered situation for each inverter, apart from public and site is distant, Take bigger K_lValue；For being distributed close combining inverter group system, K_lValue is less, and its span is K_l∈(0.1,1)。