CN101976851B - Method for improving wireless internet stability of multiple inverters in microgrid by utilizing virtual impedance - Google Patents

Abstract

The invention discloses a method for improving the wireless internet stability of a plurality of inverters in a microgrid by utilizing virtual impedance. The method comprises the following steps of: (1) calculating a droop control coefficient according to the requirement of the microgrid on power quality; (2) estimating a grid line parameter and calculating the stable range of the droop coefficient; (3) substituting the droop coefficient calculated in the step (1) into the range calculated in the step (2) for verifying; if the droop coefficient is not in the stable range, performing a step (4); if the droop coefficient can stabilize completely, performing a step (5); (4) according to a result calculated in the step (3), properly changing virtual inductance or resistance and repeating the step (2) and the step (3) in turn; and (5) realizing the droop control of the virtual impedance. In the method, feedback control is performed on an output voltage by utilizing output current of each micro power supply per se in the microgrid, so as to fulfill the aim of improving the stability of an overall microgrid system and save line conductors.

Description

A kind of method of utilizing virtual impedance to improve the wireless interconnected stability of a plurality of inverters in the micro power network

Technical field:

Present technique relates to the stability that improves a plurality of inverter wireless networkings of micro power network, the method that belongs to the power division in a plurality of little sources in the optimization and improvement micro power network and improve the whole microgrid stability of a system.

Background technology:

The sharing control technology of microgrid mainly is divided into principal and subordinate's control and two kinds of equity controls at present.Principal and subordinate control can increase cost on the one hand greatly owing to need order wire, and it is bigger to make that on the other hand the operation of microgrid receives the influence of environment, and in the abominable occasion of some environment, possibly can't install and use at all.In reciprocity control technology, the widest technology of using is sagging control, but traditional sagging control technology is relatively stricter to the impedance requirement of circuit, needs the impedance of the induction reactance of circuit much larger than circuit, causes system relatively stricter to the requirement of sagging coefficient.Present technology is primarily aimed at the top research of choosing of sagging control coefrficient, and thinks that line impedance can not change, and causes the stability of a system to receive very big restriction.

Because the fast development of generations of electricity by new energy such as solar energy, wind energy technology; And the distributed power generation technology intermittence that is difficult to solve generation of electricity by new energy causes the unstable factor of electrical network; And have the microgrid system of self load and energy storage owing to can accept the scheduling of electrical network; Realize unity power factor, so can improve the stability of generation of electricity by new energy greatly.A plurality of inverters are arranged in the microgrid system, and these inverters are the collaborative work technical difficult problem that is present microgrid how.The scheme that solves at present has two kinds, and a kind of is to connect through order wire between the inverter, and its cost is higher, and communication is comparatively difficult under some geographical conditions, is difficult to generally be suitable for; A kind of in addition is to adopt sagging control technology to carry out the no line parallel between the inverter.When but present technology does not have line parallel at the processing inverter; Often only rely on choosing or relying on the improvement of sagging control mode to reach the purpose that the stability of a system is provided of sagging coefficient; Its process is loaded down with trivial details, and because line parameter circuit value limits, might cause the instability of system.

Summary of the invention:

The present invention utilizes the output current of inner each the little power supply self of microgrid that output voltage is carried out FEEDBACK CONTROL, reaches the purpose that improves the whole microgrid stability of a system, and can save line conductor.

The objective of the invention is to overcome the shortcoming of above-mentioned prior art, a kind of method of utilizing virtual impedance to improve the wireless interconnected stability of a plurality of inverters in the micro power network is provided, according to following steps:

(1) according to the requirement of microgrid, calculates sagging control coefrficient to the quality of power supply;

(2) estimate the power network line parameter, calculate the stability range of sagging coefficient according to the condition of system stability;

(3) bring the sagging coefficient that calculates in the step (1) into calculate in the step (2) scope and test,, then carry out step (4) if not in stability range; If can stablize fully, then carry out step (5).

(4), change virtual inductor or resistance, repeating step (2) (3) according to step (3) result calculated.

(5) realization adds the sagging control of virtual impedance.

The sagging control coefrficient of said calculating adopts following formula:

$k_p=\frac{{\mathrm{\Δ\ω}}_{\max }}{P_N}$

(4)；

$k_q=\frac{\mathrm{\Δ}{U}_{\max }}{Q_N}$

K wherein _p, k _qBe respectively meritorious and idle sagging coefficient, Δ ω _MaxFrequency variation in the time of for inverter rated power, general value is in the frequency variation of microgrid permission, P _NBe inverter rated power, Δ U _MaxThe variable quantity of inverter output voltage amplitude in the time of for rated power.

The stability range of the sagging coefficient of said system is confirmed according to following formula:

$k_p<\frac{2R({\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">R</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2{\mathrm{\&omega;}}^2)({\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2{\mathrm{\&tau;}}^2{\mathrm{\&omega;}}^2+{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2+2\mathrm{LR\&tau;}+{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">R</figure-callout>}}^2{\mathrm{\&tau;}}^2)}{3\mathrm{\&omega;}{U}^2{L}^2{(L+2\mathrm{R\&tau;})}^2}---\left(5\right);$

$k_q<\frac{2R({\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2{\mathrm{\&tau;}}^2{\mathrm{\&omega;}}^2+{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2+2\mathrm{LR\&tau;}+{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">R</figure-callout>}}^2{\mathrm{\&tau;}}^2)}{3{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2\mathrm{U\&tau;\&omega;}}---\left(6\right);$

Wherein: R represents the circuit all-in resistance, and L represents the circuit total inductance, and on behalf of circuit phase voltage effective value, τ, U represent the firstorder filter time constant, and ω is the electrical network angular frequency, k _p, k _qBe respectively meritorious and idle sagging coefficient.

Method of the present invention adopts the virtual impedance technology, can be so that the stability of the interconnected microgrid of no signal system is greatly improved.The rated power of supposing inverter is P _N=1kW, phase voltage effective value are U=220V, and the time constant filter value is τ=0.1s; Line resistance is R=0.1 Ω, and line inductance is L=1mH, and the inner peak frequency that allows of microgrid is changed to 0.2Hz; Mains frequency is 50Hz, and can obtain maximum meritorious sagging coefficient by (9) is k _p=1.2 * 10 ^-3Rad/ (sW) is if but the sagging coefficient that adopts traditional sagging control coefrficient choosing method (8) to obtain is k _p=1.3 * 10 ^-3Rad/ (sW) can cause the instability of system.At this moment, if through the virtual impedance technology, virtual inductor is set to L=9mH, adds the 1mH inductance of original circuit, can make the total inductance of circuit reach 10mH, so the upper limit of meritorious sagging coefficient has become k according to (9) _p=0.0477, so very big degree has improved the stability of system.

Description of drawings:

Fig. 1 is connected to the microgrid system for single inverter of the present invention.

Fig. 2 is a sagging control block diagram of the present invention.

Fig. 3 is an active power dynamic allocation procedure of the present invention.

Fig. 4 is the sagging control block diagram of active power closed loop of the present invention.

Fig. 5 is the sagging control block diagram of reactive power closed loop of the present invention.

Fig. 6 is the topological diagram that single inverter of the present invention connects microgrid.

Fig. 7 is the three-phase inverter control block diagram of employing virtual inductor control of the present invention.

Fig. 8 is the three-phase inverter control block diagram of employing virtual resistance control of the present invention.

Fig. 9 is a method flow diagram of the present invention.

Embodiment:

Below in conjunction with accompanying drawing the present invention is done and to describe in further detail:

Referring to Fig. 1-9, the method that tradition improves sagging control stability is to realize the distribution of power through choosing suitable sagging control coefrficient.Present technique utilizes the negative feedback of inverter output current to come the output voltage of dynamic adjustments inverter, makes the stability of the interconnected microgrid of no signal line system be greatly improved.Consider three-phase system as shown in Figure 1; Wherein the phase voltage effective value of 2 of A, B is respectively U and E; Impedance that circuit is total and induction reactance are respectively R and X; It is δ that the phase place that A is ordered is ahead of the phase angle that B orders, and when the induction reactance in the circuit was far longer than impedance, active power P and reactive power Q that the little source in the microgrid sends out can be expressed as respectively:

$P=3\frac{\mathrm{EU}}{X}\sin \left(\mathrm{\&delta;}\right)$

(7)

$Q=3\frac{U^2-\mathrm{UE}\cos \left(\mathrm{\&delta;}\right)}{X}$

When the leading angle δ in little source was very little, active power P that can obtain transmitting and angle δ were directly proportional from (7), and reactive power Q is directly proportional with the amplitude U in little source.The integration of considering frequency is exactly an angle; So can the FREQUENCY CONTROL f of inverter be become with active power P be inversely proportional to; The amplitude U of inverter is controlled to reactive power Q is inversely proportional to, so just can form the closed loop of active power and reactive power, realize that meritorious idle equilibrium distributes.Sagging control block diagram is as shown in Figure 2.

Dynamic assignment with Fig. 3 active power is an example, explains how sagging control realizes the process of power-sharing:

The meritorious sagging coefficient of inverter A and inverter B operation is respectively k _P1And k _P2, both steady operation points are respectively at A ₀And B ₀, promptly must operate at same frequency two inverter stable states the time.Suppose that because certain situation the inverter power output fluctuation or two inverters takes place from dynamic entering stable state, again because total bearing power is constant, the A if inverter A fluctuates ₁Point output is meritorious to be P ₁+ Δ P, the inverter B B that can fluctuate so ₁Point output is meritorious to be P ₂-Δ P.This time, the frequency of inverter A was lower than ω ₀, and the frequency of inverter B is higher than ω ₀So, cause the phase angle of inverter B to begin slowly the phase angle of inverter A forward, so inverter B sends active power to inverter A, cause inverter A to A ₀Point moves, and inverter B is to B ₀Point moves, and final two inverters all reach stable state.So can draw, different sagging control coefrficients will constitute very big influence to the stability of whole microgrid system.Decision that but the frequency that the value of sagging coefficient is generally allowed at rated power by inverter descends and amplitude descends, that is:

$k_p=\frac{{\mathrm{\&Delta;\&omega;}}_{\max }}{P_N}$

(8)

$k_q=\frac{\mathrm{\&Delta;}{U}_{\max }}{Q_N}$

K wherein _p, k _qBe respectively meritorious and idle sagging coefficient, Δ ω _MaxFrequency variation in the time of for inverter rated power, general value is in the frequency variation of microgrid permission, P _NBe inverter rated power, Δ U _MaxThe variable quantity of inverter output voltage amplitude in the time of for rated power, also necessary value is in the scope that microgrid allows.So traditional sagging control method improves the stability of system often with the research emphasis that is chosen for to sagging coefficient.The present invention improves the stability of microgrid system through introducing the negative feedback of electric current to voltage from the another one angle.Adopt the dynamic vector method to be not difficult to draw, the transfer function block diagram 4 of sagging control inverter, shown in Figure 5, wherein R represents the circuit all-in resistance; L represents the circuit total inductance; On behalf of circuit phase voltage effective value, τ, U represent the firstorder filter time constant, and ω is the electrical network angular frequency, k _p, k _qBe respectively meritorious and idle sagging coefficient.To adopting Routh Criterion to analyze to the meritorious closed loop of system and the stability of idle closed loop, the sagging coefficient scope that can get system stability is respectively:

$k_p<\frac{2R({\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">R</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2{\mathrm{\&omega;}}^2)({\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2{\mathrm{\&tau;}}^2{\mathrm{\&omega;}}^2+{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2+2\mathrm{LR\&tau;}+{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">R</figure-callout>}}^2{\mathrm{\&tau;}}^2)}{3\mathrm{\&omega;}{U}^2{L}^2{(L+2\mathrm{R\&tau;})}^2}---\left(9\right)$

$k_q<\frac{2R({\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2{\mathrm{\&tau;}}^2{\mathrm{\&omega;}}^2+{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2+2\mathrm{LR\&tau;}+{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">R</figure-callout>}}^2{\mathrm{\&tau;}}^2)}{3{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000029740540000013.png"\; state="\{\{state\}\}">L</figure-callout>}}^2\mathrm{U\&tau;\&omega;}}---\left(10\right)$

Can draw from (9) (10) two formulas, when parameters such as the impedance of circuit and inverter output voltage are under the situation about confirming, make system stability, then sagging coefficient has a peaked scope.The another one aspect, owing to receive hardware condition restriction (like the resolution of processor etc.), sagging coefficient can not be obtained too little.So cause the interconnected microgrid system of no signal line in some cases, get into relatively difficulty of stable state.Can draw from top two formulas, increase the stability that inverter output impedance and induction reactance can increase system greatly.The present invention is added in above the voltage through introducing inverter output current feedback, realizes the purpose of virtual increase line impedance.The topological structure of inverter is as shown in Figure 6, can adopt two kinds of control methods of virtual inductor and virtual resistance.

Adopt the control block diagram of virtual inductor as shown in Figure 7, adopt the control block diagram of virtual resistance as shown in Figure 8.

If adopt the virtual inductor technology, the d shaft voltage adds the pressure drop of q axle load electric current on virtual inductor with reference to needs so, and the q shaft voltage deducts the pressure drop of d axle load electric current on virtual inductor with reference to needs.If virtual resistance technology commonly used, the d shaft voltage adds the pressure drop of d axle load electric current on virtual resistance with reference to needs so, and the q shaft voltage deducts the pressure drop of q axle load electric current on virtual resistance with reference to needs.When adopting the virtual inductor technology; An inductance that size is L has been equivalent to connect in the line; And when adopting the virtual resistance technology, the resistance that size is R that has been equivalent to connect in the line, thus make the stable of system be greatly improved.

Above content is to combine concrete preferred implementation to further explain that the present invention did; Can not assert that embodiment of the present invention only limits to this; Those of ordinary skill for technical field under the present invention; Under the prerequisite that does not break away from the present invention's design, can also make some simple deduction or replace, all should be regarded as belonging to the present invention and confirm scope of patent protection by claims of being submitted to.

Claims (2)

1. a method of utilizing virtual impedance to improve the wireless interconnected stability of a plurality of inverters in the micro power network is characterized in that, according to following steps:

(1) according to the requirement of microgrid, calculates sagging coefficient to the quality of power supply;

(2) estimate the power network line parameter, calculate the stability range of sagging coefficient according to the condition of system stability;

(3) bring the sagging coefficient that calculates in the step (1) into calculate in the step (2) scope and test,, then carry out step (4) if not in the stability range of sagging coefficient; If can stablize fully, then carry out step (5);

(4), change virtual inductor or resistance, repeating step (2) and step (3) successively according to step (3) result calculated;

(5) realization adds the sagging control of virtual impedance, improves the whole microgrid stability of a system;

The sagging coefficient scope of said system stability is confirmed according to following formula:

$k_p<\frac{2R(R^2+L^2{\mathrm{\&omega;}}^2)(L^2{\mathrm{\&tau;}}^2{\mathrm{\&omega;}}^2+L^2+2\mathrm{LR\&tau;}+R^2{\mathrm{\&tau;}}^2)}{3\mathrm{\&omega;}{U}^2{L}^2{(L+2\mathrm{R\&tau;})}^2}---\left(1\right);$

$k_q<\frac{2R(L^2{\mathrm{\&tau;}}^2{\mathrm{\&omega;}}^2+L^2+2\mathrm{LR\&tau;}+R^2{\mathrm{\&tau;}}^2)}{3L^2\mathrm{U\&tau;\&omega;}}---\left(2\right);$

Wherein: R represents line resistance and virtual resistance sum, and L represents line inductance and virtual inductor sum, and on behalf of circuit phase voltage effective value, τ, U represent the firstorder filter time constant, and ω is the electrical network angular frequency, k _p, k _qBe respectively meritorious and idle sagging coefficient.

2. a kind of according to claim 1 method of utilizing virtual impedance to improve the wireless interconnected stability of a plurality of inverters in the micro power network is characterized in that the sagging coefficients by using following formula of said calculating:

$k_p=\frac{\mathrm{\&Delta;}{\mathrm{\&omega;}}_{\max }}{P_N}$ (3)；

$k_q=\frac{\mathrm{\&Delta;}{U}_{\max }}{Q_N}$

K wherein _p, k _qBe respectively meritorious and idle sagging coefficient, Δ ω _MaxFrequency variation in the time of for inverter rated power, value are in the frequency variation of microgrid permission, P _NBe inverter rated power, Δ U _MaxThe variable quantity of inverter output voltage amplitude in the time of for rated power.

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