CN102611099A - Method for reducing loss of micro power grid - Google Patents

Abstract

The invention discloses a method for reducing the loss of a micro power grid by establishing a reactive power optimization model of the micro power grid and calculating the reactive power compensation of a capacitor bank in the micro power grid by adopting the optimization algorithm when the current network has the lowest active loss. The reactive power compensation is calculated by adopting the optimization algorithm comprises the following steps: (1) generating an initialization group; (2) calculating the network loss of individuals in the group, searching the individuals with the lowest active loss, saving as the optimal values, and recording the position; subjecting all the individual positions to iteration update according to a update formula, searching the individuals with lowest active loss, saving as the new optimal values and (3) comparing the new optimal values with the original optimal values, returning the individuals of the new optimal values to the last-time iteration position if some optimal values are updated, and outputting the final optimization result after finishing the iterative computation. Compared with the prior art, the method has the advantages of reducing the loss of the micro power grid and improving the overall utilization rate of the electric energy. The selected optimization algorithm is not liable to lead to the local optimization; the equation parameters used for iterative computation are few and convenient to adjust and are more stable.

Description

A kind of little electrical network reduces the method that net decreases

Technical field

The present invention relates to a kind of little electrical network power-economizing method, particularly a kind of little electrical network reduces the method that net decreases.

Background technology

Along with development and national economy, electricity needs increases rapidly, and power department is built large-scale centralized power supply and superhigh pressure long distance power transmission nets such as thermoelectricity, water power and nuclear power energetically.But along with the continuous expansion of scale of power, ultra-large power system operation cost is high, and difficulty is big, is difficult to adapt to increasingly high safety of user and reliability requirement, and diversified power demands.In recent years, large area blackout several times taking place in succession in the world wide, has fully exposed the fragility of electrical network.

Little electrical network (micro-grid) is meant by distributed power source, energy storage device, energy conversion device, relevant load and monitoring, protective device and compiles the small-sized electric system of being transported to that forms; It is an autonomous system that can realize oneself's control, protection and management; Both can be incorporated into the power networks with big electrical network, also can independent operating.The distributed power generation of little electrical network have pollution less, many-sided advantage such as reliability is high, efficiency of energy utilization is high, the infield is flexible, efficiently solve many potential problems of large-scale centralized electrical network.

Compare with the big electrical network of tradition, the characteristic of little electrical network mainly contains 2 differences: 1. the output characteristic of power supply is complicated.Common little power supply comprises photovoltaic cell, fuel cell, wind-driven generator, small-sized gas turbine etc. at present; The regenerative resource that wherein with the photovoltaic cell is representative receives effect of natural conditions big; Power output is unstable, and considers the maximum power of trying one's best output from environmental protection and energy-conservation angle.2. the loss of transmission line obviously increases.For high voltage overhead line; Line reactance is much larger than resistance, and the transmission line resistance of the little electrical network of low pressure is much larger than reactance, because transmission line characteristics is different; There is very big difference in the NATURAL DISTRIBUTION of power; Compare with high voltage power transmisson system, the transmission line loss of the little electrical network of low pressure is relatively large, when carrying out the system power configuration optimization, must take in.

Little electrical network is connected to low-voltage network usually, and near load, little reactive power optimization is to reduce the important measures that net decreases.Through the idle work optimization scheduling, the reactive power flow that can optimize little electrical network distributes, and reduces the active loss and the voltage loss of little electrical network, thereby improves performance driving economy, improves the quality of power supply, and the electricity consumption device security is moved reliably.

Chinese patent " a kind of independent micro-grid system " (patent No. CN 201010572995.0) has proposed a kind of system that is used to address the above problem; And following technical scheme disclosed: " each zone comprises power quality controlling unit, the 3rd renewable energy power generation power supply and the 3rd combining inverter, and described power quality controlling unit is connected to electric power transmission network through corresponding interconnection switch ".But the power quality controlling unit described in the above-mentioned patent has just generally comprised reactive power compensator, harmonic treating apparatus etc., does not propose the control strategy and the method for these devices, does not also consider to reduce in little operation of power networks the needs that net decreases.

Chinese patent " little power system reactive power compensation method and system " (patent No. CN 201110258294.4) has proposed a kind of system that is used to address the above problem, and discloses following technical scheme: " netting idle control strategy carries out idle output to said reactive power compensator or said reactive power compensator and distributed power source adjusting according to the orphan of the little electrical network of setting of adjusting target exploitation ".But the orphan described in the above-mentioned patent nets idle control strategy is just taking traditional nine district figure control strategies to carry out on the basis of reactive power compensation control; Increase the busbar voltage restrictive condition; Main starting point is to improve the voltage stability of little electrical network, does not consider to reduce in little operation of power networks the needs that net decreases.

Summary of the invention

Goal of the invention: the present invention is directed to prior art, propose a kind of little electrical network and reduce the method that net decreases, improve performance driving economy, improve the quality of power supply, the electricity consumption device security is moved reliably.

Technical scheme: to achieve these goals, the present invention relates to a kind of little electrical network and reduce the method that net decreases, comprise the steps:

(1) set up little reactive power optimization Mathematical Modeling, Mathematical Modeling does

Wherein, P _LossBe the network active loss of little electrical network, min P _LossExpression makes the network active loss minimum; V _iAnd V _jBe respectively the voltage magnitude of node i and j; θ _IjPhase difference of voltage for node i and j; G _IjIt is the element that is designated as ij in the admittance matrix down; Q _CiIt is the capacity of capacitor bank of the reactive power compensation point in little electrical network;

(2) adopt optimized Algorithm to find the solution problem, step is following:

1) generates initialization colony;

2) calculate each individual corresponding net damage value in the colony, seek net and decrease minimum individuality, save as optimal value, write down this position; The position that all are individual is carried out iteration according to new formula more and is upgraded; Calculate each individual corresponding net damage value, seek net and decrease minimum individuality, save as new optimal value;

3) new optimal value and original optimal value are compared; If new optimal value is better than original optimal value; Then upgrade original optimal value and position thereof; And position that should the individuality place when being reduced to last iteration to the individuality of new optimal value position, if new optimal value is not superior to original optimal value, then directly gets into next iteration and calculate; When iterations reaches the upper limit, or all individualities are when all no longer changing, output final optimization pass result, and described Optimization result is capacitor group reactive power compensation size in the active loss of network little electrical network hour.

Described little reactive power optimization Mathematical Modeling is set up following formula:

$\begin{array}{cc}{Q}_{\mathrm{Ci}}^{\min }\left\}{Q}_{\mathrm{ci}}\right\}{Q}_{\mathrm{Ci}}^{\max }& Q_{\mathrm{ci}}P{Q}_C\end{array}$

$X_i^{\min }\left\}{X}_i\right\}{X}_i^{\max }$ (2)

Wherein,

With Be respectively the upper and lower bound of the capacity of capacitor bank of i reactive power compensation point in little electrical network, according to actual disposition situation value; Q _CIt is the capacitor group reactive power vector in little electrical network; X _iBe other required state variables that satisfy bound in little electrical network, comprise branch power restriction, each node voltage bound restriction;

With Be respectively the upper and lower bound of this state variable, according to the actual conditions value;

Be to solve required satisfied power flow equation in the optimizing process.

The more new formula that uses in the iterative process is following:

Wherein:

JP [1, D], and kP [1, C ^Max], and i, j, k P Z; D is the number of control variables, according to the capacitor reactive compensation configuration decision of little electrical network; N is an initiation parameter, and the number range of N is the integer between the 10-50;

Represent the j dimension component of i individuality after the k time iteration; η is a random number, and η P (0,1); V representes renewal speed;

The j dimension component of representing historical optimum node; V _BeginIt is initial renewal speed; C is the current iteration number of times, C ^MaxBe maximum iteration time, C ^MaxValue be 50 or 100;

Be final updated speed.

V _Begin＜V _End, and

Beneficial effect: the present invention has the following advantages compared with prior art:

(1) in little electrical network under the metastable situation of distributed power source energy output; Through the capacitor group reactive power compensation size in little electrical network is regulated control, reach systems stabilisation voltage, improve the purpose of the power supply quality of power supply; Reduce little grid net loss, improve the overall utilization ratio of electric energy;

(2) during the solving-optimizing problem; After each iteration, seek net and decrease minimum individuality; And when historical optimal value is upgraded; Position that should the individuality place when individuality of optimal value position is reduced to last iteration avoids individual more excellent the separating that possibly exist of in the change procedure of position, omitting, and solved the problem that other optimized Algorithm is absorbed in local optimum easily;

(3) during the solving-optimizing problem, the equation parameter that uses during interative computation is few, and convenient the adjusting when guaranteeing precision, reduced operand, and stronger stability is arranged.

Description of drawings

Fig. 1 is the basic structure sketch map of little electrical network according to the invention;

Fig. 2 is the algorithm flow chart of solving-optimizing problem of the present invention;

Fig. 3 is the control block diagram of optimal control of the present invention.

Embodiment

Shown in Figure 1 is the basic structure sketch map of little electrical network according to the invention.1 is system power supply among the figure, the 2nd, and little electrical network and power distribution network connection bus, the 3rd, little electrical network is connected transformer with power distribution network; The 4th, little electrical network bus; 5, the 7,9,10,11,13,14,15,18,19, the 20th, load, the 6,16, the 21st, reactive-load compensation capacitor, the 8,12, the 17th, distributed power source.Little electrical network links to each other with system power supply 1 with transformer 3 through bus 2; Be connected with load 5 and reactive-load compensation capacitor 21 on little electrical network bus 4; Be connected with two feeder lines on the bus 4; Be connected to corresponding distributed power source and load respectively, wherein reactive-load compensation capacitor 6 is connected to respectively on two feeder lines with reactive-load compensation capacitor 16.Special, the inverter that distributed power source 8,12,17 inserts electrical network does not draw separately, is included in the power supply, and the kind of distributed power source comprises photovoltaic cell, fuel cell, wind-driven generator, small-sized gas turbine etc., does not do concrete restriction.

Shown in Figure 2 is the algorithm flow chart of solving-optimizing problem of the present invention.

Practical implementation process of the present invention is following:

1, sets up little reactive power optimization Mathematical Modeling

The capacitor group reactive power compensation size of choosing in little electrical network is a control variables, is optimization aim with network active loss minimum, and it is following to set up little reactive power optimization model:

Following formula is set up:

$\begin{array}{cc}{Q}_{\mathrm{Ci}}^{\min }\left\}{Q}_{\mathrm{ci}}\right\}{Q}_{\mathrm{Ci}}^{\max }& Q_{\mathrm{ci}}P{Q}_C\end{array}$

$X_i^{\min }\left\}{X}_i\right\}{X}_i^{\max }$ (2)

Wherein, P _LossBe the network active loss of little electrical network, min P _LossExpression makes the network active loss minimum; V _iAnd V _jBe respectively the voltage magnitude of node i and j; θ _IjPhase difference of voltage for node i and j; G _IjIt is the element that is designated as ij in the admittance matrix down; Q _CiIt is the capacity of capacitor bank of i reactive power compensation point in little electrical network;

With

Be respectively the upper and lower bound of the capacity of capacitor bank of i reactive power compensation point in little electrical network, according to actual disposition situation value; Q _CIt is the capacitor group reactive power vector in little electrical network; X _iBe other required state variables that satisfy bound in little electrical network, comprise branch power restriction, each node voltage bound restriction etc.;

With

Be respectively the upper and lower bound of this state variable, according to the actual conditions value;

Be to solve required satisfied power flow equation in the optimizing process.

2, adopt optimized Algorithm to find the solution problem

Various because the load in little electrical network is complicated, find the solution the idle work optimization problem and need adopt a kind of optimized Algorithm stable, that global optimizing ability is stronger.The reactive power compensation size of choosing the capacitor group is control variables, adopts optimized Algorithm, through interative computation, finds the solution the minimum capacitance reactive compensation size of little grid net loss of sening as an envoy to, and concrete steps are following:

(1) generate initialization colony, colony's number is by the number decision of control variables;

Suppose total D control variables, initialized colony is divided into two parts:

A. each control variables bound constitute first kind colony, always have 2 ^DIndividual;

When b. each control variables was in maximum or minimum value separately, other control variables all were taken at the interior random value of bound scope separately, total 2D such situation, and every kind of situation generates the N individuals, so the always total 2*D*N of this type individuality is individual.

The individual summation of above two parts forms initialization colony, and totally 2 ^D+ 2*D*N.

(2) calculate each individual corresponding net damage value in the colony, seek net and decrease minimum individuality, save as optimal value, write down this position; The position that all are individual is carried out iteration according to new formula more and is upgraded; Calculate each individual corresponding net damage value; Seek net and decrease minimum individuality, save as new optimal value, compare with original optimal value; If new optimal value is better than original optimal value; Then upgrade original optimal value and position thereof, and position that should the individuality place when being reduced to last iteration to the individuality of new optimal value position, this measure is more excellent the separating in order to prevent possibly omit in the change procedure; If new optimal value is not superior to original optimal value, then directly gets into next iteration and calculate; When iterations reaches the upper limit, or all individualities are when all no longer changing, output final optimization pass result.The more new formula that uses in the iterative process is following:

Wherein: JP [1, D], and kP [1, C ^Max], and i, j, k P Z; D is the number of control variables, according to the capacitor reactive compensation configuration decision of little electrical network; N is an initiation parameter, generally gets the integer between the 10-50; Represent the j dimension component of i individuality after the k time iteration; η is a random number, and η P (0,1); V representes renewal speed;

The j dimension component of representing historical optimum node; V _BeginIt is initial renewal speed; C is the current iteration number of times,

C ^MaxBe maximum iteration time, generally get 50 or 100;

Be final updated speed.When parameter is provided with, initial velocity V _BeginLess, and V _EndNeed be bigger,

The above; Be merely the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, any technical staff who is familiar with the present technique field is in the technical scope that the present invention discloses; The variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (4)

1. a little electrical network reduces the method that net decreases, and it is characterized in that: comprise the steps:

(1) set up little reactive power optimization Mathematical Modeling, Mathematical Modeling does

$\begin{array}{cc}\min & P_{\mathrm{loss}}=-\frac{1}{2}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\underset{j=1}{\overset{n}{\mathrm{\Σ}}}(V_i^2-2V_i{V}_j\cos {\mathrm{\θ}}_{\mathrm{ij}}+V_j^2)\·G_{\mathrm{ij}}\end{array},---\left(1\right)$

P wherein _LossBe the network active loss of little electrical network, min P _LossExpression makes the network active loss minimum; V _iAnd V _jBe respectively the voltage magnitude of node i and j; θ _IjPhase difference of voltage for node i and j; G _IjIt is the element that is designated as ij in the admittance matrix down;

(2) adopt optimized Algorithm to find the solution problem, its step is following:

1) generates initialization colony;

2) calculate each individual corresponding net damage value in the colony, seek net and decrease minimum individuality, save as optimal value, write down this position; The position that all are individual is carried out iteration according to new formula more and is upgraded; Calculate each individual corresponding net damage value, seek net and decrease minimum individuality, save as new optimal value;

3) new optimal value and original optimal value are compared; If new optimal value is better than original optimal value; Then upgrade original optimal value and position thereof; And position that should the individuality place when being reduced to last iteration to the individuality of new optimal value position, if new optimal value is not superior to original optimal value, then directly gets into next iteration and calculate; When iterations reaches the upper limit, or all individualities are when all no longer changing, output final optimization pass result, and described Optimization result is capacitor group reactive power compensation size in the active loss of network little electrical network hour.

2. a kind of little electrical network according to claim 1 reduces the method that net decreases, and it is characterized in that: described little reactive power optimization Mathematical Modeling is set up following formula:

$\begin{array}{cc}{Q}_{\mathrm{Ci}}^{\min }\≤Q_{\mathrm{Ci}}\≤Q_{\mathrm{Ci}}^{\max }& Q_{\mathrm{Ci}}\∈Q_C\end{array}$

$X_i^{\min }\≤X_i\≤X_i^{\max }---\left(2\right)$

$f(Q_C,T_K)=0$

Q wherein _CiIt is the capacity of capacitor bank of i reactive power compensation point in little electrical network;

With

Be respectively the upper and lower bound of the capacity of capacitor bank of i reactive power compensation point in little electrical network, according to actual disposition situation value; Q _CIt is the capacitor group reactive power vector in little electrical network; X _iBe other required state variables that satisfy bound in little electrical network, comprise branch power restriction, each node voltage bound restriction;

With

Be respectively the upper and lower bound of this state variable, according to the actual conditions value; F (Q _C, T _K)=the 0th solves required satisfied power flow equation in the optimizing process.

3. a kind of little electrical network according to claim 1 reduces the method that net decreases, and it is characterized in that: the more new formula that uses in the iterative process is following:

$x_{\mathrm{ij}}^k=x_{\mathrm{ij}}^{k-1}+\mathrm{\η}*V*(x_j^{\mathrm{Hbest}}-x_{\mathrm{ij}}^{k-1})---\left(3\right)$

$V=V_{\mathrm{begin}}+V_{\mathrm{end}}*(C-1)/C^{\max }$

Wherein: i ∈ [1,2 ^D+ 2*N*D], j ∈ [1, D], k ∈ [1, C ^Max], and i, j, k ∈ Z; D is the number of control variables, according to the capacitor reactive compensation configuration decision of little electrical network; N is an initiation parameter, and the number range of N is the integer between the 10-50;

Represent the j dimension component of i individuality after the k time iteration; η is a random number, and η ∈ (0,1); V representes renewal speed; The j dimension component of representing historical optimum node; V _BeginIt is initial renewal speed; C is the current iteration number of times, and C ∈ [1, C ^Max]; C ^MaxBe maximum iteration time, C ^MaxValue be 50 or 100; V _Begin+ V _EndBe final updated speed.

4. a kind of little electrical network according to claim 1 reduces the method that net decreases, and it is characterized in that: V _Begin＜V _End, and 0＜V _Begin+ V _End≤1.

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