CN105449707A - Distributed photovoltaic power generation access method - Google Patents

Abstract

The invention provides a distributed photovoltaic power generation access method, which comprises the following steps: (1) determining health condition characteristic quantities of a power distribution network; (2) establishing a fuzzy membership function for evaluating power quality index health condition characteristic quantities of the power distribution network; (3) determining the power quality health condition of the power distribution network; and (4) accessing distributed photovoltaic power generation, wherein the health condition characteristic quantities of the power distribution network comprise total current harmonic distortion rate, voltage fluctuation, voltage deviation and frequency deviation. According to the distributed photovoltaic power generation access method, the condition that power quality indexes of a common connection point meet the standard requirements after the distributed photovoltaic power generation is accessed into the power distribution network can be relatively well ensured.

Description

A kind of distributed photovoltaic power generation cut-in method

Technical field

The present invention relates to distributed photovoltaic power generation interconnection technology, be specifically related to a kind of distributed photovoltaic power generation cut-in method based on distribution network electric energy quality health status.

Background technology

Along with relaxing of Power policy, become inexorable trend based on the regenerative resource of photovoltaic generation, wind power generation access power distribution network.Influencing each other between renewable energy power generation and power distribution network attracts attention undoubtedly.

Renewable energy power generation is fluctuation power supply, can cause a series of power quality problems such as voltage out-of-limit, frequency departure, harmonic pollution after access power distribution network at points of common connection place.

Rapidly, local power distribution network capital construction falls behind China's central and west regions distributed photovoltaic power generation development, and radius of electricity supply is long, and load factor is high.After generation of electricity by new energy access, more easily quality of power supply overrun issues occurs, initiating failure time serious, causes tremendous economic to lose.

Current, distributed photovoltaic power generation cut-in method spininess carries out control research to single power quality index, or adopts the mode of power distribution network optimum combination to provide the optimum cut-in method of new forms of energy.Above-mentioned cut-in method is all be in a good state of health at hypothesis power distribution network, and distributed photovoltaic power carries out emulating or experimental verification under can accessing the prerequisite of any distribution branch road.In order to reduce failure risk to greatest extent, when planning distributed photovoltaic power access power distribution network, first should do comprehensive assessment and analysis to distribution network electric energy quality health status, and then providing rational cut-in method.

Summary of the invention

The invention provides a kind of distributed photovoltaic power generation cut-in method, be intended to the distribution network electric energy quality overrun issues solved because distributed photovoltaic power generation access power distribution network causes,

Described method comprises the steps:

Step 1. determines power distribution network health status characteristic quantity;

Step 2. establishes the fuzzy membership functions evaluating distribution network electric energy quality index health status characteristic quantity;

Step 3. determines distribution network electric energy quality health status;

Step 4. accesses distributed photovoltaic power generation.

Further, described in step 1, power distribution network health status characteristic quantity comprises: total current percent harmonic distortion, voltage fluctuation, voltage deviation and frequency departure.

Further, described step 2 is according to distributed photovoltaic power generation access capacity determination total current percent harmonic distortion fuzzy membership functions, voltage deviation fuzzy membership functions, voltage fluctuation fuzzy membership functions and frequency departure fuzzy membership functions

Further, described step 3 determines that the step of distribution network electric energy quality health status is as follows:

Step 3-1: the priority level of setting power distribution network health status characteristic quantity;

Step 3-2: carry out distribution network electric energy quality health Evaluation;

Step 3-3: power distribution network health status is classified.

Further, described step 3-1, is set to higher priority by total current percent harmonic distortion, voltage fluctuation and voltage deviation; Frequency departure is set to lower priority.

Further, described step 3-3 comprises: total current percent harmonic distortion, voltage fluctuation and voltage deviation health status all in shape, and when frequency departure health status is in good or general state, distribution network electric energy quality is in a good state of health;

One of them health status of total current percent harmonic distortion, voltage fluctuation, voltage deviation and frequency departure is in poor state, and distribution network electric energy quality health status is poor;

Otherwise distribution network electric energy quality health status is general.

Further, the method that described step 4 accesses distributed photovoltaic power generation comprises:

Under the access capacity of agreement, distribution network electric energy quality is in a good state of health, and allows distributed photovoltaic power generation directly to access;

Health status is poor, must, for nonconformance, allow distributed photovoltaic power generation to access after taking corresponding measures to rectify and reform;

Health status is general, and points of common connection is away from the user of high power supply quality demand, allows distributed photovoltaic power generation directly to access;

Health status is general, and points of common connection is comparatively near apart from high power supply quality demand user, allows distributed photovoltaic power generation to access after taking measures to rectify and reform.

With immediate prior art ratio, technical scheme provided by the invention has following excellent effect:

The present invention proposes a kind of distributed photovoltaic power generation cut-in method based on distribution network electric energy quality health status, before selection photovoltaic generation access point, first determine distribution network electric energy quality health status, provide distributed photovoltaic power generation cut-in method on this basis, after can ensureing distributed photovoltaic access power distribution network better, points of common connection place power quality index meets standard-required.

Accompanying drawing explanation

Fig. 1 is total current percent harmonic distortion fuzzy membership functions;

Fig. 2 is the electricity distribution network model containing distributed photovoltaic power generation;

Fig. 3 is voltage deviation fuzzy membership functions;

Fig. 4 is voltage fluctuation fuzzy membership functions;

Fig. 5 is frequency departure fuzzy membership functions;

Fig. 6 is a kind of distributed photovoltaic power generation cut-in method flow chart based on distribution network electric energy quality health status of the present invention.

Specific embodiment

The concrete implementation step of distribution network electric energy quality health evaluating is as follows:

Select total current percent harmonic distortion, voltage fluctuation and voltage deviation are higher priority; Frequency departure is lower priority, carries out distribution network electric energy quality health Evaluation and is divided into good, general, poor three classes.Total current percent harmonic distortion, voltage fluctuation and voltage deviation health status all in shape, and when frequency departure health status is in good or general state, distribution network electric energy quality is in a good state of health.When one of them health status of above-mentioned four key feature amounts is in poor state, distribution network electric energy quality health status is poor.During all the other situations, distribution network electric energy quality health status is general.

Distributed photovoltaic power generation cut-in method as shown in Figure 6 is specifically implemented as follows:

Under the access capacity of agreement, distribution network electric energy quality is in a good state of health, and allows distributed photovoltaic power generation directly to access; When health status is poor, must, for nonconformance, after taking corresponding measures to rectify and reform, distributed photovoltaic power generation be allowed to access.When health status is general, during the user of points of common connection away from high power supply quality demand, distributed photovoltaic power generation is allowed directly to access.When points of common connection is nearer apart from high power supply quality demand user, after taking measures to rectify and reform, distributed photovoltaic power generation is allowed to access.

When total current percent harmonic distortion general or poor time, can adopt and increase harmonic elimination apparatus or adopt the mode of access via telephone line transformer station, to ensure that user puts harmonic wave and meets its requirement.

When voltage deviation general or poor time, can adopt change distributed photovoltaic power generation on-position, change model and the length of original transmission line, configuration reactive-load compensation equipment, with ensure user's point voltage stablize.

When voltage fluctuation general or poor time, increase energy storage device can be adopted, improve power distribution network capacity of short circuit, access to reduce distributed photovoltaic power generation the voltage fluctuation caused.

When frequency departure is poor, should by once, secondary frequency adjusting method or by dispatching automation, access distributed photovoltaic power generation after frequency departure being adjusted to good condition.

The establishment reason of total current percent harmonic distortion fuzzy membership functions as shown in Figure 1:

Ideally, photovoltaic generating system can be similar to regards current source as, exports fundamental current.The fundamental current of electrical network conveying adds that fundamental current that inverter exports equals to flow through the fundamental current of power load.When load is constant, provide part fundamental current after photovoltaic generating system access power distribution network, power distribution network fundamental current reduces, and electric current high order harmonic component is constant, and points of common connection sampling point place total current percent harmonic distortion becomes large.When access capacity increases, power distribution network total current percent harmonic distortion is more easily above standard limit value.Grid-connected front total current percent harmonic distortion is:

$THDI=\frac{\sqrt{\underset{h=2}{\overset{\mathrm{\∞}}{\Σ}}{\left(I_h\right)}^2}}{I_1}\×100\%---\left(1\right)$

In formula:

I ₁---fundamental current;

I _h---higher harmonic current.

Grid-connected rear total current percent harmonic distortion THDIa is:

${\mathrm{THDI}}_a=\frac{\sqrt{\underset{h=2}{\overset{\mathrm{\∞}}{\Σ}}{\left(I_h\right)}^2}}{I_1-I_{PV}}\×100\%---\left(2\right)$

In formula:

I _pV---the fundamental current that photovoltaic generating system injects.

From formula (1) and formula (2):

${\mathrm{THDI}}_a=\frac{I_1}{I_1-I_{PV}}THDI---\left(3\right)$

Obviously, the total current percent harmonic distortion after photovoltaic generating system access increases with the increase of injecting fundamental current.Distributed photovoltaic power generation access power distribution network, points of common connection place should require higher power supply user away to percent harmonic distortion.Specify in IEEEStd519-1992 that total current percent harmonic distortion answers≤5%.Suppose in real system, when the fundamental current of distributed photovoltaic power generation system input accounts for 30% of total fundamental current, according to formula 3, when electrical network total current percent harmonic distortion is about 3.5%, after distributed photovoltaic power generation access electrical network, this index more easily exceeds standard.Accordingly, the health status of power distribution network total current percent harmonic distortion being divided into good, general, poor three classes, is poor situation when total current percent harmonic distortion is more than 3.5%, is good condition time within 2%.It is general status between 2.5% to 3.5%.

Voltage deviation fuzzy membership functions as shown in Figure 3 establishes reason:

China's town and country power distribution network adopts single supply radial structure mostly, and in power distribution network, feed line length is shorter, ignores line mutual-inductance and adopt invariable power static load in analytic process.Containing distributed photovoltaic power generation power distribution network simplified analysis model as shown in Figure 2.Distribution network system is equivalent to infinitely great power system, and distribution network voltage is approximately rated voltage U _n.Line equivalent impedance between points of common connection and power distribution network is R ₀+ jX ₀, P and Q is respectively meritorious, the reactive power that distribution bus transmits to load direction.Power distribution network load impedance is R _l+ jX _l, apparent power is P _l+ jQ _l.U _pCCfor the voltage at points of common connection place.Assuming that reactive power is all provided by electrical network needed for local load, distributed photovoltaic power generation works in unity power factor pattern, only provides active-power P to system _pV.The voltage U at the points of common connection place before distributed photovoltaic power generation access _{before PCC}for:

The voltage U at points of common connection place after distributed photovoltaic power generation access _{before PCC}for:

Then the voltage difference △ V at points of common connection place, grid-connected front and back is

It can thus be appreciated that, after photovoltaic generation access, there is castering action to points of common connection place voltage.Lifting amplitude and the line impedance between power distribution network and points of common connection, photovoltaic generation power output, line voltage grade and distributed photovoltaic power generation on-position in close relations.On-position is the closer to line end, and load is less, and it is higher that voltage promotes amplitude.When distributed photovoltaic power generation system output power accounts for 30% of total load, after access, distribution network voltage about promotes 1.3 times.Specify in China's supply power voltage standard, 20kV and following three phase supply voltage deviation be nominal voltage ± 7%.Specify accordingly, distribution network voltage deviation is divided into good, general, poor three classes.Voltage deviation is general state-7% to-3.5%, is poor situation between 3.5% to 7%, is good condition between ± 2%.

Voltage fluctuation fuzzy membership functions as shown in Figure 4 establishes reason:

Power distribution network containing distributed power source is in fact multi-power supply system, as shown in Figure 2.Use principle of stacking and Thevenin's theorem, distributed photovoltaic power generation power output changes the voltage fluctuation d caused at points of common connection place and is:

$d=\frac{\mathrm{\Δ}I\×Z_S}{U_N}\×100\%---\left(7\right)$

In formula:

The curent change that the change of △ I---distributed photovoltaic power generation power output causes;

Zs---power distribution network equiva lent impedance.

Under supposing that distributed photovoltaic power generation all works in unity power factor pattern, then formula (7) can be write as:

$d=\frac{{\mathrm{\ΔP}}_{PV}}{U_{PCC}}\×\frac{U_N}{S_d}\×cos\left(\mathrm{\φ}\right)\×100\%---\left(8\right)$

In formula:

△ P _pV---the transformation of distributed photovoltaic active power of output;

U _pCC---the voltage at points of common connection place;

U _n---rated voltage;

S _d---the power distribution network capacity of short circuit at points of common connection place;

φ---electric network impedance angle.

Have when voltage and the rated voltage approximately equal at points of common connection place:

$d\≈\frac{{\mathrm{\ΔP}}_{PV}}{S_d}\×cos\left(\mathrm{\φ}\right)\×100\%---\left(9\right)$

Due to the restriction of power electronic device conveyance capacity, distributed photovoltaic power generation is very little to the contribution of system short circuit capacity.Under desirable distributed power source works in unity power factor pattern, grid-connected front and back can not have an impact to system impedance.Therefore, from formula (9), voltage fluctuation is main relevant with the change of photovoltaic power generation system output power.

A large amount of actual observation results shows: photovoltaic generation power amplitude of variation is generally no more than the half of its peak power output; Distributed photovoltaic power generation system output power accounts for 30% of total load, and the peak to peak caused after distributed photovoltaic connects is 1.15 times of former undulate quantity.≤ 3%U is answered in the fluctuation of 10kV distribution network voltage _n(U _nfor standard voltage value).Accordingly, distribution network voltage fluctuation is divided into good, general, poor three classes.Being poor situation when voltage fluctuation is more than 2%, is good condition time within 1%.

Frequency departure fuzzy membership functions as shown in Figure 5 establishes reason:

When electric power system normally runs, frequency departure limit value is ± 0.2Hz.At this, in conjunction with photovoltaic plant field operator experience, power distribution network frequency departure is divided into good, general, poor three classes.Frequency departure is poor situation more than 0.1Hz, is good condition within 0.05Hz.At this, only getting frequency departure is positive situation, and frequency departure is that negative value is similar.

Finally should be noted that: the restriction of above embodiment only for illustration of technical scheme of the present invention but not to its protection range; although with reference to above-described embodiment to present application has been detailed description; those of ordinary skill in the field are to be understood that: those skilled in the art still can carry out all changes, amendment or equivalent replacement to the embodiment of application after reading the application; but these change, revise or be equal to replacement, all applying within the claims awaited the reply.

Claims (7)

1. a distributed photovoltaic power generation cut-in method, is characterized in that, described method comprises the steps:

Step 1. determines power distribution network health status characteristic quantity;

Step 2. establishes the fuzzy membership functions evaluating distribution network electric energy quality index health status characteristic quantity;

Step 3. determines distribution network electric energy quality health status;

Step 4. accesses distributed photovoltaic power generation.

2. the method for claim 1, is characterized in that, described in step 1, power distribution network health status characteristic quantity comprises: total current percent harmonic distortion, voltage fluctuation, voltage deviation and frequency departure.

3. the method for claim 1, it is characterized in that, described step 2 is according to distributed photovoltaic power generation access capacity determination total current percent harmonic distortion fuzzy membership functions, voltage deviation fuzzy membership functions, voltage fluctuation fuzzy membership functions and frequency departure fuzzy membership functions.

4. the method for claim 1, is characterized in that, described step 3 determines that the step of distribution network electric energy quality health status is as follows:

Step 3-1: the priority level of setting power distribution network health status characteristic quantity;

Step 3-2: carry out distribution network electric energy quality health Evaluation;

Step 3-3: power distribution network health status characteristic quantity is classified.

5. method as claimed in claim 4, is characterized in that, described step 3-1, and the rank of total current percent harmonic distortion, voltage fluctuation and voltage deviation is set to higher priority; The rank of frequency departure is set to lower priority.

6. method as claimed in claim 4, it is characterized in that, described step 3-3 comprises:

Rank by following standard rating distribution network electric energy quality health status:

1) good:

Total current percent harmonic distortion, voltage fluctuation and voltage deviation health status all in shape, and when frequency departure health status is in good or general state, distribution network electric energy quality is in a good state of health;

2) poor:

One of them health status of total current percent harmonic distortion, voltage fluctuation, voltage deviation and frequency departure is in poor state, and distribution network electric energy quality health status is poor;

3) general:

Removing is good and poor, and the distribution network electric energy quality health status under other situation is generally.

7. the method for claim 1, is characterized in that, the method that described step 4 accesses distributed photovoltaic power generation comprises:

1) directly access:

Under the access capacity of agreement, distribution network electric energy quality is in a good state of health, and allows distributed photovoltaic power generation directly to access;

Health status is general, and points of common connection is away from the user of high power supply quality demand, allows distributed photovoltaic power generation directly to access;

2) access after taking measures to rectify and reform:

Health status is poor, must, for nonconformance, allow distributed photovoltaic power generation to access after taking corresponding measures to rectify and reform;

Health status is general, and points of common connection is comparatively near apart from high power supply quality demand user, allows distributed photovoltaic power generation to access after taking measures to rectify and reform.