CN104201667A - Optimal distributed coordination control method for microgrid in new energy power system - Google Patents

Abstract

The invention discloses an optimal distributed coordination control method for a microgrid in a new energy power system, in the technical field of microgrids in new energy power systems. According to the optimal distributed coordination control method disclosed by the invention, the micro-source output active power and reactive power in the microgrid are measured, and average active power P and reactive power Q are obtained through lowpass filtering; droop control is improved according to the disclosed P-f and a formula described in the specification, and a voltage change rate is taken as a measurement index, so as to reasonably and accurately allocate the powers; finally the overall running performance of the microgrid system is considered, and micro-source power reasonable and accurate allocation under different working conditions is realized by virtue of a multi-target dynamic optimal distributed coordination control method combining optimal distributed coordination control for partial output quantity feedback, P-f and a formula described in the specification, so as to meet the high requirements of the microgrid system on the electric energy quality indexes of a voltage and a frequency, thus the dynamic performance of the microgrid system is improved, the overall running performance is better, and engineering application is facilitated.

Description

The optimal decentralized control method for coordinating of microgrid in a kind of New-energy power system

Technical field

The invention belongs to the microgrid field in New-energy power system, relate in particular to the optimal decentralized control method for coordinating of microgrid in a kind of New-energy power system.

Background technology

In recent years; dual-pressure under the pressure of environmental protection and lack of energy; microgrid is connected on user's side with it; have that cost is low, voltage is low, pollute the feature such as little and withstand natural calamities and safing advantage and become the focus of World Focusing; along with the aggravation of haze problem; intelligent grid is listed five area of collaboration implementation plans of Sino-U.S.'s reply climate change in, the intelligent grid national policy of taking advantage of other's power, and microgrid also starts fast development.Microgrid can be used as subsystem access intelligent distribution network, strengthens interactive, reliability and the controllability of power distribution network, and then promotes the comprehensive energy efficiency of electric power system, and schematic diagram as shown in Figure 1.Microgrid dissolves to utilize for distributing new forms of energy and regenerative resource scale generating provides new effective technical way.During piconet island operation, owing to lacking the electric voltage frequency of large electrical network, support, electric voltage frequency is difficult to stablize, and is subject to the impact of microgrid line impedance and micro-power supply capacity, and power is difficult to accurate distribution, and controller architecture is very complicated, and stable control difficulty is higher.How to control each micro-power supply coordinated operation in microgrid, guaranteed output is the realization of a plurality of targets such as distribution and power supply quality accurately, and realizing micro-grid system overall operation best performance is the key of microgrid stable and high effective operation.

At present, in microgrid, micro-power supply mainly adopts decentralized control to carry out independent control according to local relevant information, and the link that do not need to communicate by letter accordingly just can realize the plug and play of micro-power supply.In decentralized control, normal employing is traditional droop control method, gain merit-frequency and idle-voltage droop control, but due to the dependence of micro-power supply to microgrid line impedance, and droop control belongs to the drawbacks such as droop control, experts and scholars improve traditional droop control both at home and abroad, to reaching the effective coordination of micro-power supply, control.In addition, hierarchical control is also one of micro-power supply control method for coordinating, adopt the microgrid of hierarchical control strategy by the master controller as main control unit, to control on the whole each device of micro-power supply, bottom controller can select principal and subordinate to control or reciprocity control for the characteristic of micro-power supply.Yet, all do not consider that coordinated operation between micro-power supply is to reach micro-grid system runnability optimal problem.

Summary of the invention

For the deficiency of micro-power supply control method for coordinating in the existing microgrid of mentioning in above-mentioned background technology, the present invention proposes the optimal decentralized control method for coordinating of microgrid in a kind of New-energy power system, comprise the following steps:

Step 1: the output that records micro-power supply in microgrid is gained merit, reactive power, obtains average active power P and reactive power Q through low-pass filtering;

Step 2: average meritorious, the reactive power that according to step 1, obtain, adopt P-f and improve droop control, with voltage change ratio as measurement index, droop control expression formula is improved;

Step 3: according to the improvement droop control formula in step 2, and record quantity of state and the controlled quentity controlled variable of each micro-power supply in microgrid, and it is dispersed to take into account micro-position of source, i.e. the difference of output impedance and line impedance, tries to achieve micro-power supply status equation;

Step 4: control target according to the micro-power supply status equation in step 3 and 3 of microgrids, that is: voltage, frequency, power division, determine quadratic performance index, and the dynamic property of micro-grid system is improved, and overall operation performance is more excellent; Solve Levine-Athans equation, obtain part output feedback gain matrix K _d, try to achieve part output feedback gain rule U=K _dy, wherein, U=[U ₁u _iu _n] ^t, $Y=\left[\begin{array}{c}\mathrm{\Δ}{f}_i\\ \mathrm{\Δ}{U}_i\end{array}\right],$ U _i=[Δ P _iΔ Q _iΔ U _l] ^t, Δ f _ifor micro-power supply i frequency variation, Δ U _ifor micro-power supply i outlet voltage variety, Δ P _i, Δ Q _ibe respectively average meritorious, the reactive power variable quantity of output that records micro-power supply i in microgrid, Δ U _lfor load side voltage variety, n is micro-power supply sum;

Step 5: U obtains voltage, frequency reference value according to part output feedback amount, after outer loop voltag PI control and interior circular current PI control, sent into inverter and triggered drive circuit, utilize the pulse signal of drive circuit output to trigger control to inverter, thereby complete whole coordination control flow.

Described P-f and improving droop control expression formula is:

$\left\{\begin{array}{c}{f}_i=f_{0i}-m_i(P_i-P_{0i})\\ {\stackrel{\·}{U}}_i={\stackrel{\·}{U}}_{0i}-n_i(Q_i-Q_{0i})\\ U_i=U_{0i}+{\∫\stackrel{\·}{U}}_i\mathrm{dt}\end{array}\right.$

Wherein:

F _0i, U _0ibe respectively frequency and voltage rating;

F _i, U _ibe respectively frequency and the voltage effective value of micro-power supply i outlet;

P _0i, Q _0ibe respectively output average active power and the average reactive power rated value of micro-power supply i;

P _i, Q _ibe respectively output average active power and the average reactive power of micro-power supply i;

output voltage rate of change rated value for micro-power supply i, is taken as 0;

output voltage rate of change for micro-power supply i;

M _i, n _ibe respectively P-f and sagging coefficient.

The described average active power P that obtains micro-power supply through low-pass filtering _iand reactive power Q _icomputing formula be:

$\left\{\begin{array}{c}{P}_i=\frac{{\mathrm{\ω}}_{\mathrm{fi}}}{s+{\mathrm{\ω}}_{\mathrm{fi}}}{p}_i\\ Q_i=\frac{{\mathrm{\ω}}_{\mathrm{fi}}}{s+{\mathrm{\ω}}_{\mathrm{fi}}}{q}_i\end{array}\right.$

After linearisation, can obtain:

$\left\{\begin{array}{c}{\mathrm{\ΔP}}_i=\frac{{\mathrm{\ω}}_{\mathrm{fi}}}{s+{\mathrm{\ω}}_{\mathrm{fi}}}\mathrm{\Δ}{p}_i\\ {\mathrm{\ΔQ}}_i=\frac{{\mathrm{\ω}}_{\mathrm{fi}}}{s+{\mathrm{\ω}}_{\mathrm{fi}}}\mathrm{\Δ}{q}_i\end{array}\right.$

Wherein, w _fiby micro-power supply i the cut-off frequency of company's low pass filter;

S is Laplce's multiplier;

P _i, q _ibe respectively and record that the output of micro-power supply i in microgrid is meritorious, reactive power;

P _i, Q _ibe respectively average meritorious, the reactive power of output that records micro-power supply i in microgrid;

Δ p _i, Δ q _ibe respectively and record that the output of micro-power supply i in microgrid is meritorious, reactive power variable quantity;

Δ P _i, Δ Q _ibe respectively average meritorious, the reactive power variable quantity of output that records micro-power supply i in microgrid.

Described micro-power supply status equation can obtain with average rating formula by improving sagging expression formula:

$\left\{\begin{array}{c}\mathrm{\Δ}{\mathrm{\δ}}_i=2\mathrm{\π\Δ}{f}_i\\ \mathrm{\Δ}{\stackrel{\·}{f}}_i=-2\mathrm{\π}{w}_{\mathrm{fi}}\mathrm{\Δ}{f}_i-m_i{w}_{\mathrm{fi}}\mathrm{\Δ}{P}_i\\ \mathrm{\Δ}{\stackrel{\·}{U}}_i=-w_{\mathrm{fi}}\mathrm{\Δ}{U}_i-n_i{w}_{\mathrm{fi}}\mathrm{\Δ}{Q}_i\\ \mathrm{\Δ}{\stackrel{\·}{i}}_i=\frac{1}{L_i}\mathrm{\Δ}{U}_i+\frac{R_i}{L_i}\mathrm{\Δ}{i}_i-\frac{1}{L_i}\mathrm{\Δ}{U}_L\end{array}\right.$

Wherein:

Δ δ _ifor micro-power supply i outlet voltage phase angle variable quantity;

Δ f _ifor micro-power supply i frequency variation;

for micro-power supply i frequency change rate;

Δ U _ifor micro-power supply i outlet voltage variety;

for micro-power supply i outlet voltage change ratio;

Δ i _ifor micro-power supply i outlet current change quantity;

for micro-power supply i outlet current changing rate;

Δ U _lfor load side voltage variety;

M _i, n _ibe respectively P-f and sagging coefficient;

R _i, L _ibe respectively micro-power supply i outlet line resistance and reactance;

Δ P _i, Δ Q _ibe respectively average meritorious, the reactive power variable quantity of output that records micro-power supply i in microgrid.

Described step 4 is specially:

Step 4.1: in microgrid, micro-position of source disperses, and output impedance and line impedance there are differences, takes into account improvement droop control characteristic row and writes micro-power supply matrix state equation;

$\stackrel{\·}{X}=\mathrm{AX}+\mathrm{BU}$

Wherein, X=[X ₁x _ix _n] ^t, X _i=[Δ f _iΔ U _iΔ i _i] ^t, U=[U ₁u _iu _n] ^t, U _i=[Δ P _iΔ Q _iΔ U _l] ^t,

Δ f _ifor micro-power supply i frequency variation;

Δ U _ifor micro-power supply i outlet voltage variety;

Δ i _ifor micro-power supply i outlet current change quantity;

Δ U _lfor load side voltage variety;

R _i, L _ibe respectively micro-power supply i outlet line resistance and reactance;

W _fiby micro-power supply i the cut-off frequency of company's low pass filter;

Δ P _i, Δ Q _ibe respectively average meritorious, the reactive power variable quantity of output that records micro-power supply i in microgrid;

A _i, B _ibe respectively the coefficient matrix of quantity of state and controlled quentity controlled variable in state equation;

Step 4.2: determine the quadratic performance index that makes micro-grid system overall performance optimum, write this index expression formula by micro-power supply status equation row;

Step 4.3: Program Levine-Athans equation, obtains part output feedback gain matrix K _d, try to achieve part output feedback gain rule U=K _dy, makes quadratic performance index optimum.

Beneficial effect of the present invention has been to propose the optimal decentralized control method for coordinating of micro-power supply in a kind of microgrid, in conjunction with the improvement droop control in the present invention and part output feedback optimal decentralized coordination control, realize the rationally accurately distribution of micro-power, meet the high request of micro-grid system to voltage and frequency power quality index, micro-grid system dynamic property is improved, overall operation performance reaches more excellent, by partial status amount or part output variable, carry out FEEDBACK CONTROL, do not need too much feedback path, be easy to Project Realization, micro-power of having realized under different operating modes rationally accurately distributes, and met the high request of micro-grid system to voltage and frequency power quality index, micro-grid system dynamic property is improved, overall operation performance reaches more excellent.

Accompanying drawing explanation

Fig. 1 is the micro-grid system structure chart containing many micro-power supplys;

Fig. 2 is droop characteristic schematic diagram;

Fig. 3 is that optimal decentralized control method for coordinating solves flow chart;

Fig. 4 is many micro-power supplys micro-grid system controller architecture in parallel block diagram;

Fig. 5 is many micro-power supply parallel running equivalent electric circuits;

Fig. 6 a is the output reactive power analogous diagram of operating mode 1 in example, and Fig. 6 b is the voltage analogous diagram of operating mode 1;

Fig. 7 a is the active power of output analogous diagram of operating mode 1 in example, and Fig. 7 b is the frequency analogous diagram of operating mode 1;

Fig. 8 a is the output reactive power analogous diagram of operating mode 2 in example, and Fig. 8 b is the voltage analogous diagram of operating mode 2;

Fig. 9 a is the meritorious frequency analogous diagram of the output of operating mode 2 in example, and Fig. 9 b is the frequency analogous diagram of operating mode 2;

Figure 10 is the output voltage rate of change analogous diagram of operating mode 2 in example.

Embodiment

Below in conjunction with accompanying drawing, preferred embodiment is elaborated.Should be emphasized that following explanation is only exemplary, rather than in order to limit the scope of the invention and to apply.

For the Harmonic Control of micro-power supply in microgrid, according to the optimal decentralized control method for coordinating of micro-power supply in microgrid proposed by the invention, can reach the object such as power division, electric voltage frequency control between micro-power supply, specifically comprise the steps:

Step 1: record micro-power supply in microgrid and export meritorious, reactive power, obtain average active power P and reactive power Q through low-pass filtering.

Step 2: according to step 1 on average gained merit, reactive power, adopt P-f and improve droop control, with voltage change ratio as measurement index, droop control formula is improved.

Step 3: according to the improvement droop control formula in step 2, and record quantity of state and the controlled quentity controlled variable of each micro-power supply in microgrid, and it is dispersed to take into account micro-position of source, i.e. the difference of output impedance and line impedance, tries to achieve micro-power supply status equation.

Step 4: control target according to the micro-power supply status equation in step 3 and 3 of microgrids, that is: voltage, frequency, power division, determine quadratic performance index, and the dynamic property of micro-grid system is improved, and overall operation performance is more excellent; Solve Levine-Athans equation, obtain part output feedback gain matrix K _d, try to achieve part output feedback gain rule U=K _dy.

Step 5: U obtains voltage, frequency reference value according to part output feedback amount, after outer loop voltag PI control and interior circular current PI control, sent into inverter and triggered drive circuit, utilize the pulse signal of drive circuit output to trigger control to inverter, thereby complete whole coordination control flow.

In view of the defect of existing control method for coordinating in background technology, the optimal decentralized control method for coordinating of micro-power supply in a kind of microgrid that the present invention proposes, its theory diagram is as shown in Figure 4.The present invention mainly comprise average power calculate module, P-f and improve droop control module, optimal decentralized coordinating control module three parts.First, calculate that the output of micro-power supply is meritorious, reactive power, after low-pass filtering, on average gained merit, reactive power, then, will on average gain merit, reactive power input P-f and improve droop control module, and obtain micro-power supply status equation, obtain quantity of state and controlled quentity controlled variable and coefficient matrix thereof, input optimal decentralized coordinating control module calculates the also reference value of output voltage frequency, after outer loop voltag, interior circular current are controlled, send into inverter and trigger drive circuit, utilize the pulse signal of drive circuit output to trigger control to inverter, thereby complete the optimal decentralized coordination control procedure of micro-power supply in microgrid.

Calculate that the output of micro-power supply is meritorious, reactive power, after low-pass filtering, on average gained merit, reactive power, then, will on average gain merit, reactive power input P-f and improve droop control module, can obtain taking into account the micro-power supply status equation that improves droop control characteristic, improvement droop control expression formula is:

$\left\{\begin{array}{c}{f}_i=f_{0i}-m_i(P_i-P_{0i})\\ {\stackrel{\·}{U}}_i={\stackrel{\·}{U}}_{0i}-n_i(Q_i-Q_{0i})\\ U_i=U_{0i}+{\∫\stackrel{\·}{U}}_i\mathrm{dt}\end{array}\right.---\left(1\right)$

Wherein:

F _0i, U _0ibe respectively frequency and voltage rating;

F _i, U _ibe respectively frequency and the voltage effective value of micro-power supply i outlet;

P _0i, Q _0ibe respectively output average active power and the average reactive power rated value of micro-power supply i;

P _i, Q _ibe respectively output average active power and the average reactive power of micro-power supply i;

output voltage rate of change rated value for micro-power supply i, is taken as 0;

output voltage rate of change for micro-power supply i;

M _i, n _ibe respectively P-f and sagging coefficient.

Improvement droop control principle in the present invention as shown in Figure 2, is improved in droop control and is affected principal element or the power angle that active power is distributed, and by regulating droop characteristic can make frequency stabilization at zone of reasonableness, active power is accurately distributed.So the particularity that the present invention distributes mainly for reactive power, analyzes droop characteristic principle, 2 the micro-power supply parallel runnings of take are example.The distance of 2 micro-generators and loads shown in Fig. 2 is different, establishes initial load reactive power when reactive power by during increase, the close together because of the micro-power supply 1 of load distance, therefore its power output is more, causes reactive power unreasonable distribution.By after droop control regulates, micro-output power of power supply is stabilized in respectively b, d point, and its voltage change ratio equates, by formula (1), can be obtained:

n ₁(Q ₀₁-Q ₁)＝n ₂(Q ₀₂-Q ₂)＝…＝n _i(Q _0i-Q _i) (2)

Therefore by selecting suitable sagging coefficient, can obtain:

$\frac{Q_1}{Q_{01}}=\frac{Q_2}{Q_{02}}=...=\frac{Q_i}{Q_{0i}}---\left(3\right)$

By the known reactive power of formula (3), between each micro-power supply, obtained accurate distribution, and be not subject to the impact of equivalent output impedance between micro-power supply, yet all there is certain fluctuation in voltage, frequency and power, its stability cannot guarantee, and do not consider the multi-objective coordinated operation problem of microgrid, cannot realize micro-grid system runnability optimum.The present invention considers from system-level angle, adopts part output feedback optimal decentralized control method for coordinating, and dynamic stability and the overall performance of realizing micro-grid system are optimum.Due in total state amount Feedback Optimal Control, each controlled quentity controlled variable must be fed back all state variables of total system or with dimension output variable, be difficult to accomplish in real system.In many micro-power supply complication systems, total state amount feedback or feedback path that need to be too much with dimension output feedback, implement comparatively difficulty especially, therefore wish to carry out FEEDBACK CONTROL by partial status amount or part output variable.Therefore, in micro-grid system, each micro-power acquisition is coordinated to control by part output feedback optimal decentralized and is only reasonably effective way of reality, and is easy to engineering application.

In microgrid, the optimal decentralized coordinating control module of micro-power supply is the key that realizes institute of the present invention extracting method, and it solves flow chart as shown in Figure 3, takes into account improvement droop control of the present invention row and writes micro-power supply status equation and be:

$\left\{\begin{array}{c}\mathrm{\Δ}{\mathrm{\δ}}_i=2\mathrm{\π\Δ}{f}_i\\ \mathrm{\Δ}{\stackrel{\·}{f}}_i=-2\mathrm{\π}{w}_{\mathrm{fi}}\mathrm{\Δ}{f}_i-m_i{w}_{\mathrm{fi}}\mathrm{\Δ}{P}_i\\ \mathrm{\Δ}{\stackrel{\·}{U}}_i=-w_{\mathrm{fi}}\mathrm{\Δ}{U}_i-n_i{w}_{\mathrm{fi}}\mathrm{\Δ}{Q}_i\\ \mathrm{\Δ}{\stackrel{\·}{i}}_i=\frac{1}{L_i}\mathrm{\Δ}{U}_i+\frac{R_i}{L_i}\mathrm{\Δ}{i}_i-\frac{1}{L_i}\mathrm{\Δ}{U}_L\end{array}\right.---\left(4\right)$

Wherein: w _fiby micro-power supply i the cut-off frequency of company's low pass filter;

Δ δ _ifor micro-power supply i outlet voltage phase angle variable quantity;

Δ f _ifor micro-power supply i frequency variation;

for micro-power supply i frequency change rate;

Δ U _ifor micro-power supply i outlet voltage variety;

for micro-power supply i outlet voltage change ratio;

Δ i _ifor micro-power supply i outlet current change quantity;

for micro-power supply i outlet current changing rate;

Δ U _lfor load side voltage variety;

M _i, n _ibe respectively P-f and sagging coefficient;

R _i, L _ibe respectively micro-power supply i outlet line resistance and reactance.

Δ P _i, Δ Q _ibe respectively average meritorious, the reactive power variable quantity of output that records micro-power supply i in microgrid;

Micro-power supply status equation is written as matrix form:

$\stackrel{\·}{X}=\mathrm{AX}+\mathrm{BU}---\left(5\right)$

X＝[X ₁ … X _i … X _n] ^T (6)

Wherein, X _i=[Δ f _iΔ U _iΔ i _i] ^t

U＝[U ₁ … U _i … U _n] ^T (7)

Wherein, U _i=[Δ P _iΔ Q _iΔ U _l] ^t

Because the multi-objective coordinated control of microgrid comprises the stable of electric voltage frequency, choose voltage and frequency as partial output feedback amount, output equation is:

Y＝CX (10)

Unknown quantity substitution formula (10) can be obtained:

$\left[\begin{array}{c}\mathrm{\Δ}{f}_i\\ \mathrm{\Δ}{U}_i\end{array}\right]=\left[\begin{array}{ccc}1& 0& 0\\ 0& 1& 0\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}{f}_i\\ \mathrm{\Δ}{U}_i\\ \mathrm{\Δ}{i}_i\end{array}\right]---\left(11\right)$

Micro-power supply status equation and the output equation that in sum, can have a dispersing characteristic are:

$\left\{\begin{array}{c}\stackrel{\·}{X}=\mathrm{AX}+\mathrm{BU}\\ Y=\mathrm{CX}\end{array}\right.---\left(12\right)$

Part output feedback optimal decentralized is coordinated control law:

U _i＝K _dY _i (13)

Or

U _i＝K _dCX _i (14)

Wherein, part output feedback gain matrix n is determined by micro-power supply number.

Finally, by U _ifeed back in each micro-power supply dbjective state amount, reach the object that multiple target dynamic optimal decentralized coordinating is controlled.Like this, K _dask for and become the key that method realizes.For this reason, should choose suitable target function, make the K solving _dmeet corresponding index.Consider the damping of quadratic performance index and system, that is have direct relation with the dynamic response characteristic of system.For strengthening the damping of micro-grid system, improve the dynamic response characteristic of system, selecting quadratic performance index is suitable as target function, expression formula is:

$\underset{K_d}{\min }J(\·)={\∫}_0^{\∞}(X{\left(t\right)}^T\mathrm{QX}\left(t\right)+U{\left(t\right)}^T\mathrm{RU}\left(t\right))\mathrm{dt}---\left(15\right)$

Determine after performance index, will ask for part output feedback gain matrix K according to this index _d, by formula (12), (14), micro-power supply status equation can be rewritten as:

$\stackrel{\·}{X}\left(t\right)=(A+\mathrm{BKC})X\left(t\right)---\left(16\right)$

Solve differential equation (16), can obtain:

X(t)＝Φ(t)X ₀ (17)

Wherein, Φ (t)=e ^{(A+BKC) t}, X ₀for initial condition.By formula (14), (17) substitution quadratic performance index (15), can obtain:

$J=Z_0^T\left[{\∫}_0^{\∞}{\mathrm{\Φ}}^T\left(t\right)(Q+C^T{K}^T\mathrm{RKC})\mathrm{\Φ}\left(t\right)\mathrm{dt}\right]X_0---\left(18\right)$

Order $P={\∫}_0^{\∞}{\mathrm{\Φ}}^T\left(t\right)(Q+C^T{K}^T\mathrm{RKC})\mathrm{\Φ}\left(t\right)\mathrm{dt},$ Quadratic performance index can be written as:

$J=X_0^T{\mathrm{PX}}_0---\left(19\right)$

Visible, P is matrix equation

(A+BKC) ^TP+P(A+BKC)+Q+

(20)

C ^TK ^TRKC＝0

Solution.By formula (20) transposition, can obtain P ^talso be the solution of this equation, i.e. P=P ^t, P is symmetrical matrix.

Definition from trace of a matrix: be that quadratic performance index can be written as:

$J=\mathrm{tr}\left({\mathrm{PX}}_0{X}_0^T\right)---\left(21\right)$

Owing to asking for partial output feedback gain matrix K according to quadratic performance index minimum _d, need to eliminate this index to initial condition X ₀dependence, for this reason, by X ₀be made as the countless random vectors that are distributed on its corresponding dimension unit hyperplane, can obtain desired value be:

$E\left(X_0{X}_0^T\right)=\frac{1}{n}I---\left(22\right)$

Wherein, n is the number of system mode vector, and I is unit matrix.

By formula (22) substitution (21), by performance index equalization, can obtain:

$J=\mathrm{tr}\left(P\frac{1}{n}I\right)=\frac{1}{n}\mathrm{trP}---\left(23\right)$

Constant on not impact of quadratic performance index, that is:

J＝trP (24)

Partial output feedback gain matrix K _dask for and can be summed up as under the constraints of formula (20), try to achieve the K that makes formula (24) minimum _d, be

The extreme-value problem of constraints, available method of Lagrange multipliers solves, order:

G(P，K)＝(A+BKC) ^TP+P(A+BKC)+

(25)

Q+C ^TK ^TRKC＝0

Lagrangian is:

$L=\mathrm{trP}+\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\underset{j=1}{\overset{n}{\mathrm{\Σ}}}{v}_{\mathrm{ij}}{g}_{\mathrm{ij}}---\left(26\right)$

In formula, gi _jfor i in G (P, K) is capable, j column element, vi _jlagrange multiplier for corresponding element.By the definition of trace of a matrix, formula (26) can be written as:

L＝trP+tr[V ^TG(P，K)] (27)

Lagrangian is obtained the necessary condition of extreme value and is:

$\left\{\begin{array}{c}\frac{\∂L}{\∂K}=B^T{\mathrm{PVC}}^T+{\mathrm{RKCVC}}^T=0\\ \frac{\∂L}{\∂P}=(A+\mathrm{BKC})V+V{(A+\mathrm{BKC})}^T+I=0\\ \frac{\∂L}{\∂V}={(A+\mathrm{BKC})}^{T}P+P(A+\mathrm{BKC})+Q+C^T{K}^T\mathrm{RKC}=0\end{array}\right.---\left(28\right)$

By Matlab Program equation group (28), can try to achieve part output feedback gain matrix K _d.Try to achieve part output feedback gain rule U=K _dy.According to part output feedback amount, U obtains voltage, frequency reference value, after outer loop voltag PI control and interior circular current PI control, sent into inverter and triggered drive circuit, utilize the pulse signal of drive circuit output to trigger control to inverter, thereby complete whole coordination control flow.

Finally, correctness and feasibility for checking institute of the present invention extracting method, according to the emulation experiment checking of the 2 kinds of different operating modes when Matlab/Simulink platform has carried out 4 micro-power supply parallel runnings of the micro-grid system equivalent electric circuit shown in Fig. 5, the frequency of system is 50Hz, system voltage is 380V, and the meritorious and load or burden without work of micro-grid system is respectively 1.8MW and 0.6Mvar.Micro-power supply connects line equivalent output impedance and is respectively: Z ₁=R ₁+ jX ₁=0.643+j0.1282 (Ω), Z ₂=R ₂+ jX ₂=0.965+j0.1923 (Ω), Z ₃=R ₃+ jX ₃=1.286+j0.2564 (Ω), Z ₄=R ₄+ jX ₄=1.608+j0.3305 (Ω).2 kinds of operating modes all when 0.5t by traditional droop control strategy meritorious-frequency and idle-voltage droop control switch to the optimal decentralized coordination control strategy of micro-power supply in a kind of microgrid that the present invention proposes.

Operating mode 1 is that micro-power supply capacity is different, and output impedance is different, and emulation experiment figure is as shown in Fig. 6-7.Visible, method is switched front and back voltage, frequency and power fluctuation and is all obviously reduced, Fig. 6 a and Fig. 6 b show that the distribution of reactive power has obtained obvious improvement compared with conventional method, voltage levvl is improved, and Fig. 7 a and Fig. 7 b show that active power is accurately distributed according to micro-power supply capacity and frequency keeps constant.

Operating mode 2 for micro-power supply 1 not by output impedance but directly and the extreme case of loading and being connected, and when 1s, sudden load change, is reduced to half of former load, emulation experiment figure is as shown in Fig. 8-10.When Fig. 8 a and Fig. 8 b show to adopt conventional method, not only emergent power distributes serious unbalance and the micro-power supply reactive power of part to there will be negative value to occur circulation phenomenon, the inventive method has effectively suppressed circulation, make reactive power distribute be improved significantly, and voltage stabilization is in higher level.Fig. 9 a and Fig. 9 b show that active power is also accurately distributed by micro-power supply capacity and frequency keeps constant.Figure 10 shows that voltage change ratio finally becomes 0, makes output voltage reach stable state.

The above; be only the present invention's embodiment preferably, but protection scope of the present invention is not limited to this, is anyly familiar with in technical scope that those skilled in the art disclose in the present invention; the conversion that can expect easily or replacement, within all should being encompassed in 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 (5)

1. an optimal decentralized control method for coordinating for microgrid in New-energy power system, is characterized in that, comprises the following steps:

Step 1: the output that records micro-power supply in microgrid is gained merit, reactive power, obtains average active power P and reactive power Q through low-pass filtering;

Step 2: average meritorious, the reactive power that according to step 1, obtain, adopt P-f and improve droop control, with voltage change ratio as measurement index, droop control expression formula is improved;

Step 3: according to the improvement droop control formula in step 2, and record quantity of state and the controlled quentity controlled variable of each micro-power supply in microgrid, and it is dispersed to take into account micro-position of source, i.e. the difference of output impedance and line impedance, tries to achieve micro-power supply status equation;

Step 4: control target according to the micro-power supply status equation in step 3 and 3 of microgrids, that is: voltage, frequency, power division, determine quadratic performance index, and the dynamic property of micro-grid system is improved, and overall operation performance is more excellent; Solve Levine-Athans equation, obtain part output feedback gain matrix K _d, try to achieve part output feedback gain rule U=K _dy, wherein, U=[U ₁u _iu _n] ^t, $Y=\left[\begin{array}{c}\mathrm{\Δ}{f}_i\\ \mathrm{\Δ}{U}_i\end{array}\right],$ U _i=[Δ P _iΔ Q _iΔ U _l] ^t, Δ f _ifor micro-power supply i frequency variation, Δ U _ifor micro-power supply i outlet voltage variety, Δ P _i, Δ Q _ibe respectively average meritorious, the reactive power variable quantity of output that records micro-power supply i in microgrid, Δ U _lfor load side voltage variety, n is micro-power supply sum;

Step 5: U obtains voltage, frequency reference value according to part output feedback amount, after outer loop voltag PI control and interior circular current PI control, sent into inverter and triggered drive circuit, utilize the pulse signal of drive circuit output to trigger control to inverter, thereby complete whole coordination control flow.

2. method according to claim 1, is characterized in that, described P-f and improving droop control expression formula is:

$\left\{\begin{array}{c}{f}_i=f_{0i}-m_i(P_i-P_{0i})\\ {\stackrel{\·}{U}}_i={\stackrel{\·}{U}}_{0i}-n_i(Q_i-Q_{0i})\\ U_i=U_{0i}+{\∫\stackrel{\·}{U}}_i\mathrm{dt}\end{array}\right.$

Wherein:

F _0i, U _0ibe respectively frequency and voltage rating;

F _i, U _ibe respectively frequency and the voltage effective value of micro-power supply i outlet;

P _0i, Q _0ibe respectively output average active power and the average reactive power rated value of micro-power supply i;

P _i, Q _ibe respectively output average active power and the average reactive power of micro-power supply i;

output voltage rate of change rated value for micro-power supply i, is taken as 0;

output voltage rate of change for micro-power supply i;

M _i, n _ibe respectively P-f and sagging coefficient.

3. method according to claim 1, is characterized in that, the described average active power P that obtains micro-power supply through low-pass filtering _iand reactive power Q _icomputing formula be:

$\left\{\begin{array}{c}{P}_i=\frac{{\mathrm{\ω}}_{\mathrm{fi}}}{s+{\mathrm{\ω}}_{\mathrm{fi}}}{p}_i\\ Q_i=\frac{{\mathrm{\ω}}_{\mathrm{fi}}}{s+{\mathrm{\ω}}_{\mathrm{fi}}}{q}_i\end{array}\right.$

After linearisation:

$\left\{\begin{array}{c}\mathrm{\Δ}{P}_i=\frac{{\mathrm{\ω}}_{\mathrm{fi}}}{s+{\mathrm{\ω}}_{\mathrm{fi}}}{\mathrm{\Δp}}_i\\ {\mathrm{\ΔQ}}_i=\frac{{\mathrm{\ω}}_{\mathrm{fi}}}{s+{\mathrm{\ω}}_{\mathrm{fi}}}{\mathrm{\Δq}}_i\end{array}\right.$

Wherein, w _fiby micro-power supply i the cut-off frequency of company's low pass filter;

S is Laplce's multiplier;

P _i, q _ibe respectively and record that the output of micro-power supply i in microgrid is meritorious, reactive power;

P _i, Q _ibe respectively average meritorious, the reactive power of output that records micro-power supply i in microgrid;

Δ p _i, Δ q _ibe respectively and record that the output of micro-power supply i in microgrid is meritorious, reactive power variable quantity;

Δ P _i, Δ Q _ibe respectively average meritorious, the reactive power variable quantity of output that records micro-power supply i in microgrid.

4. method according to claim 1, is characterized in that, described micro-power supply status equation obtains with average rating formula by improving sagging expression formula:

$\left\{\begin{array}{c}\mathrm{\Δ}{\mathrm{\δ}}_i=2\mathrm{\π\Δ}{f}_i\\ \mathrm{\Δ}{\stackrel{\·}{f}}_i=-2\mathrm{\π}{w}_{\mathrm{fi}}\mathrm{\Δ}{f}_i-m_i{w}_{\mathrm{fi}}\mathrm{\Δ}{P}_i\\ \mathrm{\Δ}{\stackrel{\·}{U}}_i=-w_{\mathrm{fi}}\mathrm{\Δ}{U}_i-n_i{w}_{\mathrm{fi}}\mathrm{\Δ}{Q}_i\\ \mathrm{\Δ}{\stackrel{\·}{i}}_i=\frac{1}{L_i}\mathrm{\Δ}{U}_i+\frac{R_i}{L_i}\mathrm{\Δ}{i}_i-\frac{1}{L_i}\mathrm{\Δ}{U}_L\end{array}\right.$

Wherein:

W _fiby micro-power supply i the cut-off frequency of company's low pass filter;

Δ δ _ifor micro-power supply i outlet voltage phase angle variable quantity;

Δ f _ifor micro-power supply i frequency variation;

for micro-power supply i frequency change rate;

Δ U _ifor micro-power supply i outlet voltage variety;

for micro-power supply i outlet voltage change ratio;

Δ i _ifor micro-power supply i outlet current change quantity;

for micro-power supply i outlet current changing rate;

Δ U _lfor load side voltage variety;

M _i, n _ibe respectively P-f and sagging coefficient;

R _i, L _ibe respectively micro-power supply i outlet line resistance and reactance;

Δ P _i, Δ Q _ibe respectively average meritorious, the reactive power variable quantity of output that records micro-power supply i in microgrid.

5. method according to claim 1, is characterized in that, described step 4 is specially:

Step 4.1: in microgrid, micro-position of source disperses, and output impedance and line impedance there are differences, takes into account improvement droop control characteristic row and writes micro-power supply matrix state equation;

$\stackrel{\·}{X}=\mathrm{AX}+\mathrm{BU}$

Wherein, X=[X ₁x _ix _n] ^t, X _i=[Δ f _iΔ U _iΔ i _i] ^t, U=[U ₁u _iu _n] ^t, U _i=[Δ P _iΔ Q _iΔ U _l] ^t,

Δ f _ifor micro-power supply i frequency variation;

Δ U _ifor micro-power supply i outlet voltage variety;

Δ i _ifor micro-power supply i outlet current change quantity;

Δ U _lfor load side voltage variety;

R _i, L _ibe respectively micro-power supply i outlet line resistance and reactance;

W _fiby micro-power supply i the cut-off frequency of company's low pass filter;

Δ P _i, Δ Q _ibe respectively average meritorious, the reactive power variable quantity of output that records micro-power supply i in microgrid;

A _i, B _ibe respectively the coefficient matrix of quantity of state and controlled quentity controlled variable in state equation;

Step 4.2: determine the quadratic performance index that makes micro-grid system overall performance optimum, write this index expression formula by micro-power supply status equation row;

Step 4.3: Program Levine-Athans equation, obtains part output feedback gain matrix K _d, try to achieve part output feedback gain rule U=K _dy, makes quadratic performance index optimum.