CN102623992A - Method for islanding microgrid control and optimization based on rotating coordinate virtual impedance - Google Patents

Abstract

The invention discloses a method for islanding microgrid control and optimization based on rotating coordinate virtual impedance. Aiming to a fact that the actual microgrids have complicated impedance characteristics, the method for islanding microgrid control and optimization based on the rotating coordinate virtual impedance includes utilizing the coordinate rotation orthogonal transformation to design the coordinate rotation virtual impedance, improving the impedance characteristics of the microgrid, compensating errors of power distribution and improving power decoupling performance; establishing a complete small-signal dynamic model of the microgrid, wherein the small-signal dynamic model comprises distributed energy sources, power converters, loads and power grids, and guiding the selection of an optimal value on the basis of the small-signal dynamic analytical method; and simultaneously, providing a theoretical basis for the optimization selection of islanding microgrid control parameters by using the small-signal dynamic analytical method, wherein the islanding microgrid control parameters comprise droop control coefficients of the power distribution, process identifier (PI) parameters of a voltage current feedback controller, feedforward control coefficients and the like. The microgrid after being subjected to optimization design in an islanded operational mode is capable of effectively achieving power decoupling and improving the accuracy of the power distribution, the stability of the system and the dynamic performances.

Description

Based on little power grid control of the isolated island of rotational coordinates virtual impedance and optimization method

Technical field

The invention belongs to little electric power network technique field, be specifically related to little power grid control of a kind of isolated island and optimization method based on the rotational coordinates virtual impedance.

Background technology

Under the dual-pressure of energy demand and environmental protection, the distributing-supplying-energy technology that not only can improve the traditional energy utilance but also can make full use of various regenerative resources has obtained increasing attention and application.Little electrical network is by distributed power source (Distributed Generators; DGs), energy storage device, energy converter, related load and monitoring, protective device compile and form; Can give full play to DG is technology, economy, the environmental benefit that electric power system and user are brought; Further improving flexibility, high efficiency and the spatter property of power system operation, satisfy the requirement of power consumer to the quality of power supply, power supply reliability better, is the important component part that intelligent grid is built.

Under little electrical network isolated island mode of operation, polytype using energy source inverter perhaps hands over the alternating flow device to be parallel on the ac bus of little electrical network.When keeping voltage magnitude and frequency stabilization, realizing the distribution quick and precisely of power, is the key issue that needs solution in little electrical network islet operation control.According to plug and play and the control thought of " equity " and the voltage magnitude and the sagging control of frequency of design concept proposition; Make DG only need detect the information of access point; Meritorious and the reactive power that frequency through adjusting self output voltage and amplitude are controlled output; Need not the communication link, therefore have higher reliability and flexibility, " Automation of Electric Systems "; 2008; 32 (7): " microgrid Comprehensive Control and the analysis " among the 98-103 and " electrotechnics journal ", 2009,24 (2): " in the microgrid distributed power source inverter change feedback control strategy " among the 100-107 all is based on the whole control strategy of the little electrical network of isolated island of this sagging control method design more.But sagging control method needs line impedance to be perception, and its essence is to exchange the rational power distribution for to sacrifice quality of voltage.Line impedance generally is the complex impedance characteristic in the little electrical network of reality, and the output impedance characteristic of inverter also depends on control strategy and the system parameters of being taked, therefore sagging control method and inapplicable.And the distribution of DG and load causes line impedance uneven, had a strong impact on the accuracy of power division.Therefore, to the little electrical network under the islet operation pattern in the practical application, adopt sagging control not only can't effectively realize power decoupled and divide equally, the stable state of simultaneity factor and dynamic property also can be affected.

Around the control strategy problem of the little electrical network of islet operation, numerous improving one's methods based on sagging control have been proposed both at home and abroad.

Application number is 201110047934.7 Chinese patent " based on the inverter parallel method of virtual impedance ", to every inverter, introduces a virtual generator, through virtual reactance X _V=ω L _VBe connected to the access point of inverter, make the impedance between virtual generator and bus be perception, thereby adopt sagging control method to realize the decoupling zero control of active power and reactive power.But virtual reactance X _V=ω L _VMethod for designing need to carry out differential to electric current, amplified high-frequency noise, produced phase shift and delay again after adding low pass filter.

Application number is 201110047934.7 Chinese patent " a kind of virtual impedance that utilizes improves the method that a plurality of inverters in the micro power network do not have line parallel stability ", guarantees that through continuous adjustment virtual inductor value or virtual resistance value sagging coefficient can make a plurality of inverters parallel connection stable operations.But this patent does not provide, virtual impedance (Z _V=R _V+ j ω L _V) closed loop implementation method under rotating coordinate system, do not provide simultaneously, can not be directly push away to such an extent that comprise the whole control strategy of the little electrical network of isolated island of virtual impedance closed loop from system.The virtual impedance value not only relates to the stability of system, influences transient state and steady-state behaviour, the power control of system simultaneously and distributes performance etc., need further be optimized design.

Comprise the key parameter in the little power grid control strategy of isolated island of rotation of coordinate virtual impedance value; Like the PI parameter of the sagging coefficient of rotation of coordinate virtual impedance value, power division, electric current and voltage feedback controller and feedfoward control coefficient etc.; Not only influence the quality of power supply, the power control of little electrical network and distribute performance; Also influence the stability and the dynamic property of micro-grid system, all need be based on more advanced more perfect theory, in the framework of whole little electrical network; Take all factors into consideration the various performances of system, carry out theory analysis and optimal design and instruct.

Summary of the invention

Technical problem to be solved by this invention is: the complicated impedance operator in actual little electrical network proposes little power grid control of a kind of isolated island based on the rotational coordinates virtual impedance and optimization method; Adopt rotation of coordinate orthogonal transform design rotation virtual impedance closed loop, improve the impedance operator of little electrical network, the error that compensation power distributes improves the power decoupled performance; Based on the small-signal dynamic analysing method, instruct the optimized choice and the coupling of key parameter in the little power grid control strategy of isolated island that comprises rotation of coordinate virtual impedance value.

The technical scheme that the present invention taked is:

Little power grid control of a kind of isolated island and optimization method based on the rotational coordinates virtual impedance; This method adopts the rotation of coordinate orthogonal transform to realize rotation of coordinate virtual impedance closed loop; Improve the impedance operator of little electrical network, the error that compensation power distributes improves the power decoupled performance; Wherein, the performing step of rotation of coordinate virtual impedance closed loop is following:

1) with inverter output current i _oWith virtual impedance Z _V=R _V+ j ω L _VQuadrature decomposes under the dq rotating coordinate system respectively, wherein R _VBe virtual resistance, j ω L _VBe virtual reactance, ω is the anglec of rotation frequency of ac bus voltage in little electrical network;

2) under the dq rotating coordinate system, calculate virtual voltage v _v, mathematic(al) representation is:

$\left[\begin{array}{c}{v}_{\mathrm{vd}}\\ v_{\mathrm{dq}}\end{array}\right]=\left[\begin{array}{cc}{R}_V& -\mathrm{\ω}{L}_V\\ \mathrm{\ω}{L}_V& R_V\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{od}}\\ i_{\mathrm{oq}}\end{array}\right]$

In the formula, v _VdAnd v _VqBe respectively virtual voltage v _vD axle under rotating coordinate system and q axle component; i _OdAnd i _OqBe respectively inverter output current i _oD axle under rotating coordinate system and q axle component;

3) adopt the voltage vector orientation method; With the output of the sagging control of virtual voltage compensation power, i.e. the mathematic(al) representation that its d axle and q axle component under rotating coordinate system of the reference of voltage control closed loop output signal

is respectively the sagging control of power after

and compensation is:

ω＝ω _n-mP

$\left[\begin{array}{c}{v}_{\mathrm{od}}^{*}\\ v_{\mathrm{oq}}^{*}\end{array}\right]=\left[\begin{array}{c}{V}_n-\mathrm{nQ}\\ 0\end{array}\right]-\left[\begin{array}{cc}{R}_V& -\mathrm{\ω}{L}_V\\ \mathrm{\ω}{L}_V& R_V\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{od}}\\ i_{\mathrm{oq}}\end{array}\right]$

Wherein, ω is the anglec of rotation frequency of ac bus voltage in little electrical network, ω _n, V _nBe respectively the rated voltage and the specified angular frequency of inverter; P, Q are respectively active power and reactive power; M, n are respectively meritorious and idle sagging coefficient.

Then, set up the little electrical network integral small signal dynamic model that comprises distributed energy, power inverter, load and electric power networks, instruct the optimal value of rotation of coordinate virtual impedance to choose based on the small-signal dynamic analysing method, i.e. virtual resistance R _VOptimal value and virtual reactance j ω L _VOptimal value choose.Simultaneously, adopt small-signal modeling analysis method also to provide fundamental basis, comprise the sagging control coefrficient of power division, the PI parameter and the feedfoward control coefficient of electric current and voltage feedback controller for the little power grid control parameters selection of isolated island.

Small-signal dynamic analysing method among the present invention, small-signal modeling analysis method are prior art, repeat no more at this.

The invention has the beneficial effects as follows that the present invention adopts rotation of coordinate orthogonal transform design rotation virtual impedance, improve the impedance operator of little electrical network, the error that compensation power distributes improves the power decoupled performance; Based on the small-signal dynamic analysing method, instruct the optimized choice and the coupling of key parameter in the little power grid control strategy of isolated island that comprises rotation of coordinate virtual impedance value.Under the islet operation pattern, can effectively realize power decoupled through the little electrical network after the optimal design, improve accuracy, the stability of a system and the dynamic property of power division.Fig. 9-12 is respectively the dynamic response curve of active power and reactive power in the little electrical network that has or not the rotation of coordinate virtual impedance.

Description of drawings

Fig. 1 is the micro-grid system sketch map;

Fig. 2 is the thevenin equivalent circuit figure that DG inserts little electrical network;

Fig. 3 is DG control and interface circuit figure;

Fig. 4 is the variation diagram of reactive power characteristic root with virtual impedance;

Fig. 5 is the variation diagram of active power characteristic root with virtual impedance;

Fig. 6 is the variation diagram of active power characteristic root with meritorious sagging coefficient;

Fig. 7 is the variation diagram of reactive power characteristic root with idle sagging coefficient;

Fig. 8 is the variation diagram of system features root with the electric current and voltage feedback control parameters;

Fig. 9 is an active power dynamic response curve in little electrical network of no rotation of coordinate virtual impedance;

Figure 10 has active power dynamic response curve in little electrical network of rotation of coordinate virtual impedance;

Figure 11 is a reactive power dynamic response curve in little electrical network of no rotation of coordinate virtual impedance;

Figure 12 has reactive power dynamic response curve in little electrical network of rotation of coordinate virtual impedance.

Embodiment

Below in conjunction with accompanying drawing and instance the present invention is further specified.

Fig. 1 is typical little electric network composition sketch map, and wherein comprising wind-driven generator, photovoltaic cell, 3 typical distributed power supplys of fuel cell (DG1-DG3) and 3 loads that the position is different, each section line impedance is z ₁-z ₅Each distributed power source all is assumed to be the DC source after DC source or the rectification among this paper; Through the SVPWM inverter change three-phase alternating current into and by LCL low pass filter filters out high order harmonic component after; Be parallel-connected on the ac bus of little electrical network, and link to each other with main electrical network at points of common connection PCC place through static diverter switch.The thevenin equivalent circuit of Fig. 2 little electrical network ac bus for distributed power source is connected to.Among the figure, E ∠ φ is the inverter open circuit voltage, and U ∠ 0 is an ac bus voltage, and Z and θ are respectively the amplitude and the phase angle of inverter output impedance.According to equivalent electric circuit, the meritorious of inverter output is respectively with reactive power

$P=\frac{U}{Z}[(E\cos \mathrm{\φ}-U)\cos \mathrm{\θ}+E\sin \mathrm{\φ}\sin \mathrm{\θ}]---\left(1\right)$

$Q=\frac{U}{Z}[(E\cos \mathrm{\φ}-U)\sin \mathrm{\θ}-E\cos \mathrm{\φ}\cos \mathrm{\θ}]---\left(2\right)$

Because the phase angle difference φ of inverter output voltage and ac bus voltage is very little, therefore, formula (1) and (2) can be reduced to

$P=\frac{U}{Z}[(E-U)\cos \mathrm{\θ}+\mathrm{E\φ}\sin \mathrm{\θ}]---\left(3\right)$

$Q=\frac{U}{Z}[(E-U)\sin \mathrm{\θ}-\mathrm{E\φ}\cos \mathrm{\θ}]---\left(4\right)$

According to the difference of system impedance, i.e. the difference of the phase angle theta of Z, the meritorious relation with reactive power and impedance operator of output is as shown in table 1

The relation of table 1 power output and system impedance characteristics

The sagging control strategy of tradition it has been generally acknowledged that the approximate perception that is of system impedance, and active power is mainly by voltage phase angle φ decision, and reactive power is mainly by voltage magnitude E decision, and its power adjustments relation does

ω _o＝ω _n-mP (5)

V _o＝V _n-nQ (6)

In the formula, ω _oAnd ω _nBe respectively the output angle frequency and the specified angular frequency of inverter; V _oAnd V _nBe respectively inverter output voltage amplitude and specified amplitude; M and n are respectively the sagging coefficient of active power and reactive power.Increase sagging coefficient and can improve dynamic response performance, strengthened the skew of voltage magnitude and frequency simultaneously.On the other hand, line impedance generally is the complex impedance characteristic in the little electrical network of reality, and the output impedance of inverter also depends on control strategy and the system parameters of being taked, and the distribution of DG and load more causes line impedance uneven.Line impedance difference and inverter output impedance difference all can influence the accuracy of power division in little electrical network.

Therefore, actual little electrical network middle impedance characteristic is complicated, and traditional sagging control strategy is also inapplicable, and has limited little grid power control and distributed performance.

The present invention proposes the little power grid control method of a kind of isolated island based on the rotational coordinates virtual impedance, and is as shown in Figure 3, adopts rotation of coordinate orthogonal transform design rotation virtual impedance closed loop; Improve the impedance operator of little electrical network; The error that compensation power distributes improves the power decoupled performance, and implementation step is following:

1) with inverter output current i _oWith virtual impedance Z _V=R _V+ j ω L _VQuadrature decomposes under the dq rotating coordinate system respectively;

2) under the dq rotating coordinate system, calculate virtual voltage v _v, its mathematic(al) representation is:

$\left[\begin{array}{c}{v}_{\mathrm{vd}}\\ v_{\mathrm{vq}}\end{array}\right]=\left[\begin{array}{cc}{R}_V& -{\mathrm{\ω}}_o{L}_V\\ {\mathrm{\ω}}_o{L}_V& R_V\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{od}}\\ i_{\mathrm{oq}}\end{array}\right]---\left(7\right)$

In the formula, v _VdAnd v _VqBe respectively virtual voltage v _vD axle under rotating coordinate system and q axle component; i _OdAnd i _OqBe respectively inverter output current i _oD axle under rotating coordinate system and q axle component.

3) adopt the voltage vector orientation method; With the output of the sagging control of virtual voltage compensation power, i.e. the mathematic(al) representation of the sagging control of power after the reference of voltage control closed loop output signal

compensation is:

ω＝ω _n-mP (8)

$\left[\begin{array}{c}{v}_{\mathrm{od}}^{*}\\ v_{\mathrm{oq}}^{*}\end{array}\right]=\left[\begin{array}{c}{V}_n-\mathrm{nQ}\\ 0\end{array}\right]-\left[\begin{array}{cc}{R}_V& -{\mathrm{\ω}}_o{L}_V\\ {\mathrm{\ω}}_o{L}_V& R_V\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{od}}\\ i_{\mathrm{oq}}\end{array}\right]---\left(9\right)$

Wherein, ω is the anglec of rotation frequency of ac bus voltage in little electrical network, ω _n, V _nBe respectively the rated voltage and the specified angular frequency of inverter; P, Q are respectively active power and reactive power; M, n are respectively meritorious and idle sagging coefficient.

Virtual resistance can regulating system damping characteristic, distribute harmonic current automatically at high frequency region, reduce the influence that phase error is distributed meritorious active power.Virtual inductor helps realizing power decoupled, suppresses system's circulation, reduces the influence of impedance unbalance.Adopt rotation of coordinate orthogonal transform design rotation virtual impedance effectively to avoid the introducing of electric current high order harmonic component and phase shift and the delay that filter causes.

Comprise the key parameter in the little power grid control strategy of isolated island of rotation of coordinate virtual impedance value; Like the PI parameter of the sagging coefficient of rotation of coordinate virtual impedance value, power division, electric current and voltage feedback controller and feedfoward control coefficient etc.; Not only influence the quality of power supply, the power control of little electrical network and distribute performance; Also influence the stability and the dynamic property of micro-grid system, all need be based on more advanced more perfect theory, in the framework of whole little electrical network; Take all factors into consideration the various performances of system, carry out theory analysis and optimal design and instruct.The present invention is based on the small-signal dynamic analysing method; Foundation comprises little electrical network integral small signal dynamic model of distributed energy, power inverter, load and electric power networks; Variation tendency according to small-signal sensitivity analysis and root locus; Instruct the optimal value of rotation of coordinate virtual impedance to choose, i.e. virtual resistance R _VOptimal value and virtual reactance j ω L _VOptimal value choose.Simultaneously, adopt small-signal modeling analysis method also to provide fundamental basis, comprise PI parameter and the feedfoward control coefficient etc. of sagging control coefrficient, the electric current and voltage feedback controller of power division for the little power grid control parameters selection of isolated island.

Set up the small-signal dynamic model of little electric network composition shown in Figure 1, the DG control system is as shown in Figure 3.

The inverter model of each DG is based upon the definite dq rotational coordinates of its output voltage and fastens anglec of rotation frequencies omega _iConfirm by corresponding droop characteristic.For setting up the dynamic model of whole little electrical network, need be ω to anglec of rotation frequency with the DG model transferring _ComLittle electrical network overall situation reference frame under, then the angle of the overall reference frame of the inverter reference frame of i DG and little electrical network does

δ＝∫(ω _i-ω _com) (10)

Average power P, Q is calculated after low pass filter obtains by instantaneous output voltage and electric current:

$P=\frac{{\mathrm{\ω}}_c}{s+{\mathrm{\ω}}_c}(v_{\mathrm{od}}{i}_{\mathrm{od}}+v_{\mathrm{oq}}{i}_{\mathrm{oq}})---\left(11\right)$

$Q=\frac{{\mathrm{\ω}}_c}{s+{\mathrm{\ω}}_c}(v_{\mathrm{od}}{i}_{\mathrm{od}}+v_{\mathrm{oq}}{i}_{\mathrm{oq}})---\left(12\right)$

In the formula, ω _cCut-off frequency for low pass filter; v _Od, v _Oq, i _Od, i _OqBe respectively the output voltage and the electric current of dq axle.According to preamble, can get by formula (5)-(9), the droop characteristic relation of regulating of band dq rotation of coordinate virtual impedance closed loop does

ω _i＝ω _n-mP (13)

$\left[\begin{array}{c}{v}_{\mathrm{od}}^{*}\\ v_{\mathrm{oq}}^{*}\end{array}\right]=\left[\begin{array}{c}{V}_n-\mathrm{nQ}\\ 0\end{array}\right]-\left[\begin{array}{cc}{R}_V& -{\mathrm{\ω}}_o{L}_V\\ {\mathrm{\ω}}_o{L}_V& R_V\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{od}}\\ i_{\mathrm{oq}}\end{array}\right]---\left(14\right)$

Following formula adopts the directed control of voltage vector, reference voltage vector is positioned the d axle of rotating coordinate system.

For obtaining stable load voltage and good voltage-regulation performance, outer voltage control adopts the pi regulator of band feedforward compensation to produce the reference current vector, and its dynamic characteristic does

$\frac{d{\mathrm{\φ}}_d}{\mathrm{dt}}=v_{\mathrm{od}}^{*}-v_{\mathrm{od}}$

$\frac{d{\mathrm{\φ}}_q}{\mathrm{dt}}=v_{\mathrm{oq}}^{*}-v_{\mathrm{oq}}$

$i_d^{*}=k_{\mathrm{pv}}(v_{\mathrm{od}}^{*}-v_{\mathrm{od}})+k_{\mathrm{iv}}{\mathrm{\φ}}_d-{\mathrm{\ω}}_{n}C{v}_{\mathrm{oq}}+H{i}_{\mathrm{od}}---\left(15\right)$

$i_q^{*}=k_{\mathrm{pv}}(v_{\mathrm{oq}}^{*}-v_{\mathrm{oq}})+k_{\mathrm{iv}}{\mathrm{\φ}}_q-{\mathrm{\ω}}_{n}C{v}_{\mathrm{od}}+H{i}_{\mathrm{oq}}---\left(16\right)$

In the formula, k _Pv, k _IvBe respectively the ratio and the integral coefficient of voltage PI controller; H is a feedforward gain.

For obtaining good system dynamic characteristic and Current Regulation performance, current inner loop control adopts the pi regulator of band feedforward compensation to produce reference voltage vector, and its dynamic characteristic does

In the formula, k _Pi, k _IiBe respectively the ratio and the integral coefficient of current PI controller; F is a feedforward gain.The electric current and voltage dynamic characteristic of inverter interface circuit can be expressed as:

$\frac{{\mathrm{di}}_d}{\mathrm{dt}}=-\frac{R_f}{L_f}{i}_d+{\mathrm{\ω}}_i{i}_q+\frac{v_d-v_o}{L_f}---\left(19\right)$

$\frac{{\mathrm{di}}_q}{\mathrm{dt}}=-\frac{R_f}{L_f}{i}_q+{\mathrm{\ω}}_i{i}_d+\frac{v_q-v_o}{L_f}---\left(20\right)$

$\frac{{\mathrm{dv}}_{\mathrm{od}}}{\mathrm{dt}}={\mathrm{\ω}}_i{v}_{\mathrm{oq}}+\frac{i_d-i_o}{C}---\left(21\right)$

$\frac{{\mathrm{dv}}_{\mathrm{oq}}}{\mathrm{dt}}=-{\mathrm{\ω}}_i{v}_{\mathrm{od}}+\frac{i_q-i_o}{C}---\left(22\right)$

$\frac{{\mathrm{di}}_{\mathrm{od}}}{\mathrm{dt}}=-\frac{R_c}{L_c}{i}_{\mathrm{od}}+{\mathrm{\ω}}_i{i}_{\mathrm{oq}}+\frac{v_o-v_d}{L_c}---\left(23\right)$

$\frac{{\mathrm{di}}_{\mathrm{oq}}}{\mathrm{dt}}=-\frac{R_c}{L_c}{i}_{\mathrm{oq}}-{\mathrm{\ω}}_i{i}_{\mathrm{od}}+\frac{v_o-v_q}{L_c}---\left(24\right)$

In the formula, v _d, v _q, i _d, i _qBe respectively the voltage and current of inverter dq axle; v _Sd, v _SqBe respectively the ac bus voltage of dq axle; L _f, C, L _cConstitute the LCL filter, R _f, R _cBe equivalent resistance.

The dynamic characteristic of DG in little electrical network has been described in formula (10)-(24), and it can be got in the place's linearisation of steady operation point:

$\mathrm{\Δ}{\stackrel{\·}{x}}_{\mathrm{DG}}=A_{\mathrm{DG}}\mathrm{\Δ}{x}_{\mathrm{DG}}+B_{\mathrm{DG}}\mathrm{\Δ}{v}_{\mathrm{sdq}}---\left(25\right)$

Wherein,

A _DG, B _DGBe respectively state matrix and input matrix, see appendix; Δ v _Sdq=[Δ v _SdΔ v _Sq] ^TNeed to prove that all following variablees that are designated as dq are similar column vector in the literary composition.

The small-signal dynamic model of whole little electrical network comprises: the small-signal dynamic sub-model of DG and network and load small-signal dynamic sub-model.Be similar to the interface circuit model of inverter, obtain after the circuit equivalent differential equation linearisation of network and load small-signal model by network and load.Through coordinate transform the small-signal model of each DG and network and load small-signal model are transformed under the overall reference frame, obtain the small-signal state-space model of whole little electrical network:

$\mathrm{\Δ}\stackrel{\·}{x}=\mathrm{A\Δx}+\mathrm{B\Δu}---\left(26\right)$

Wherein, Δ x is the little electric network state vector that comprises DG, circuit and load condition variable.

When Fig. 4 changes for virtual impedance, the variation of characteristic value root locus under corresponding little electrical network low frequency mode.λ wherein _Q12Be a pair of conjugate pole responsive relatively with the reactive power state variable of DG1 and DG2, λ _Q13Be a pair of conjugate pole responsive relatively with the reactive power state variable of DG1 and DG3, there was overshoot in system and had vibration this moment, and the amplitude of vibration is relevant with the angle of conjugation pole and zero.Simultaneously, conjugate pole is relevant with the system responses speed from the distance of the imaginary axis.Therefore, along with the linearity increase of virtual impedance value, the oscillation amplitude of system is more and more littler, and dynamic response is more and more faster.Fig. 5 is the amplification of figure, wherein λ in the frame of broken lines among Fig. 4 _P12Be a pair of conjugate pole responsive relatively with the active power state variable of DG1 and DG2, λ _P13Be a pair of conjugate pole responsive relatively with the active power power rating variable of DG1 and DG3.When virtual impedance was zero, there was a unstable limit in imaginary axis right side.This shows for the complicated little electrical network of impedance operator, no virtual impedance closed loop, and when only adopting traditional sagging control method, system's instability.When the linear increase of virtual impedance value, unstable limit moves to negative half-plane along real axis, and the stability of a system improves.Simultaneously, conjugate pole λ _P12And λ _P13Move to real axis and to become at a distance of nearer negative real root, active power control becomes the overdamp state by underdamping state, and steady-state error is zero and non-overshoot.If the virtual impedance value continue to increase, limit will along real axis each other away from, system can produce steady-state error.Therefore, the present invention is an example with Fig. 1 system, takes all factors into consideration the stability and the dynamic property of system power control, and getting virtual impedance value optimal value is R _V=-0.055 Ω, L _V=1.1mH.

When Fig. 6 and 7 is respectively the sagging index variation of the sagging coefficient of active power and reactive power, the root locus trend of system.When sagging coefficient increased, the dynamic property of system improved, but the stability margin of system can descend.Therefore, the present invention is an example with Fig. 1 system, takes all factors into consideration the stability of system power control and the power division performance of dynamic property and system, and the optimal value of taking off the coefficient that hangs down is m=0.0002, n=0.001.

When Fig. 8 is the PI parameter variation of electric current and voltage feedback controller, the root locus trend of system.Therefore, the present invention is an example with Fig. 1 system, takes all factors into consideration the stability and the dynamic property of system power control, the PI parameter k of power taking piezoelectricity stream feedback controller _Pv=0.05, k _Iv=500, k _Pi=15, k _Ii=15000.

Fig. 9 and 10 is for introducing rotation of coordinate virtual impedance front and back, the dynamic changing curve of system's active power.

Figure 11 and 12 is for introducing rotation of coordinate virtual impedance front and back, the dynamic changing curve of system's reactive power.

Claims (1)

1. little power grid control of the isolated island based on the rotational coordinates virtual impedance and optimization method; It is characterized in that this method adopts the rotation of coordinate orthogonal transform to realize rotation of coordinate virtual impedance closed loop, improves the impedance operator of little electrical network; The error that compensation power distributes; Improve the power decoupled performance, wherein, the performing step of rotation of coordinate virtual impedance closed loop is following:

1) with inverter output current i _oWith virtual impedance Z _V=R _V+ j ω L _VQuadrature decomposes under the dq rotating coordinate system respectively, wherein R _VBe virtual resistance, j ω L _VBe virtual reactance, ω is the anglec of rotation frequency of ac bus voltage in little electrical network;

2) under the dq rotating coordinate system, calculate virtual voltage v _v, mathematic(al) representation is:

$\left[\begin{array}{c}{v}_{\mathrm{vd}}\\ v_{\mathrm{vq}}\end{array}\right]=\left[\begin{array}{cc}{R}_V& -\mathrm{\ω}{L}_V\\ \mathrm{\ω}{L}_V& R_V\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{od}}\\ i_{\mathrm{oq}}\end{array}\right]$

In the formula, v _VdAnd v _VqBe respectively virtual voltage v _vD axle under rotating coordinate system and q axle component; i _OdAnd i _OqBe respectively inverter output current i _oD axle under rotating coordinate system and q axle component;

3) adopt the voltage vector orientation method; With the output of the sagging control of virtual voltage compensation power, i.e. the mathematic(al) representation that its d axle and q axle component under rotating coordinate system of the reference of voltage control closed loop output signal

is respectively the sagging control of power after

and

compensation is:

ω＝ω _n-mP

$\left[\begin{array}{c}{v}_{\mathrm{od}}^{*}\\ v_{\mathrm{oq}}^{*}\end{array}\right]=\left[\begin{array}{c}{V}_{n-\mathrm{nQ}}\\ 0\end{array}\right]-\left[\begin{array}{cc}{R}_V& -\mathrm{\ω}{L}_V\\ \mathrm{\ω}{L}_V& R_V\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{od}}\\ i_{\mathrm{oq}}\end{array}\right]$

Wherein, ω is the anglec of rotation frequency of ac bus voltage in little electrical network, ω _n, V _nBe respectively the rated voltage and the specified angular frequency of inverter; P, Q are respectively active power and reactive power; M, n are respectively the meritorious sagging coefficient that distributes with reactive power;

And then foundation comprises little electrical network integral small signal dynamic model of distributed energy, power inverter, load and electric power networks; Based on small-signal dynamic analysing method guiding step 1) optimal value of said rotation of coordinate virtual impedance closed loop chooses, i.e. virtual resistance R _VOptimal value and virtual reactance j ω L _VOptimal value choose; Simultaneously; Employing small-signal dynamic analysing method is also for the little power grid control parameters selection of isolated island provides the basis, and the little power grid control parameter of said isolated island comprises gains merit and the sagging control coefrficient of reactive power distribution, the PI parameter and the feedfoward control coefficient of electric current and voltage feedback controller.

Images