CN105119301A - Micro-grid reactive power sharing control method based on equivalent feed line theory - Google Patents

Abstract

The invention discloses a micro-grid reactive power sharing control method based on an equivalent feed line theory, and the method can accurately achieve the reactive power equalization in a micro-grid. The inconsistency of a local load in the micro-grid and the mismatching of feed line parameters are main factors which cause the imbalance of inverter output reactive power. The method enables a network mismatching factor, which causes a reactive power equalization error, to be parameterized through the concept of an equivalent feed line at first, and calculates an equivalent feed line parameter in real time through employing feed line current sensing. The method sets virtual impedance secondly according to the obtained parameters, and effectively eliminates the reactive power equalization error through the compensation of the mismatching factor in a connection circuit. Compared with a conventional virtual impedance method, the method gives consideration to the factor of a local load, can make parameter adjustment for the change of the load, and achieves the accurate power equalization.

Description

A kind of micro-capacitance sensor based on equivalent feeder line theory is idle divides equally control method

[technical field]

The invention belongs to microgrid power and distribute field, particularly the control method of reactive power equilibrium assignment in a kind of micro-capacitance sensor.

[background technology]

The attention rate of the world today to new forms of energy improves day by day, such as photovoltaic generation, wind power generation, miniature gas turbine, and the form of the green energy resources such as fuel cell power supply (distributedgeneration, DG) all in a distributed manner enters bulk power grid.Along with the increase of distributed power source permeability, bring new problem to bulk power grid, as grid stability, the control etc. of DG unit.

For solving this kind of problem, microgrid concept is arisen at the historic moment.The DG unit controls of dispersion, by coordinating the working method of DG unit, is become unified entirety by it, and is connected with bulk power grid by points of common connection (pointofcommoncoupling, PCC).Under microgrid can be operated in grid-connected and isolated island two kinds of patterns: time grid-connected, it is as controllable source; During isolated island, it provides electric power to support for net internal loading.Under island mode, the load power in the necessary equilibrium assignment net of each DG unit.Droop control method is one of important means realizing power equalization.Although droop control can effectively realize meritorious balanced, there is idle equalization problem in it all the time.This is because not mating of feeder line pressure drop in microgrid causes; In addition, when DG unit is connected with local load, idle equalization problem can increase the weight of further.Improving one's methods as droop control, virtual impedance can solve preferably idlely divides equally problem.

Found by literature search, solve idle problem of dividing equally for virtual impedance, have researcher to propose kinds of schemes.Be eliminate an idle balancing error by setting not mating between virtual impedance compensation feeder line, but local loading condition is not taken into account.One is estimated feeder line pressure drop by default virtual impedance, to revise droop control coefficient, but the pressure drop of centre estimation not real-time process, it is ageing poor.Therefore, utilize virtual impedance to solve the idle droop control strategy divided equally at present and all there is limitation.

[summary of the invention]

The object of the present invention is to provide that a kind of micro-capacitance sensor based on equivalent feeder line theory is idle divides equally control method, solving feeder line parameter very well under without communication form does not mate the problem inconsistent with local load, and have well control ageing; Idle limitation of dividing equally problem is solved to overcome current virtual impedance.

To achieve these goals, the present invention adopts following technical scheme:

Micro-capacitance sensor based on equivalent feeder line theory is idle divides equally a control method, comprises the following steps:

Step 1, when after DG cellular installation each in micro-grid system, measures the corresponding feed line impedance value R of each DG unit _fiwith X _fi;

Step 2, calculates DG unit active-power P by each DG unit output voltage and output current _i, DG unit reactive power Q _i, the active-power P of common load consumption is calculated by output voltage and feeder current _fi, common load consume reactive power Q _fi;

Step 3, by the unknown parameter U in rating formula ₀utilize known quantity to substitute, formula is as follows:

$\left\{\begin{array}{c}{U}_i{U}_0{\mathrm{sin\δ}}_i=-P_{fi}\frac{B_{fi}}{G_{fi}^2+B_{fi}^2}-Q_{fi}\frac{G_{fi}}{G_{fi}^2+B_{fi}^2}=A_i\\ U_i\left(U_i-U_0{\mathrm{cos\δ}}_i\right)=P_{fi}\frac{G_{fi}}{G_{fi}^2+B_{fi}^2}-Q_{fi}\frac{B_{fi}}{G_{fi}^2+B_{fi}^2}=B_i\end{array}\right.$

According to the transformational relation of impedance and admittance, above formula is reduced to:

$\left\{\begin{array}{c}{A}_i=P_{fi}{X}_{fi}-Q_{fi}{R}_{fi}\\ B_i=P_{fi}{R}_{fi}+Q_{fi}{X}_{fi}\end{array}\right.$

Obtain two by known quantity P _fi, Q _fi, R _fi, X _fithe parameter A represented _i, B _i;

Step 4, the parameter G that equivalent feeder line model uses _efi, B _efi, R _efi, X _eficalculated by above-mentioned several known parameters, formula is as follows:

$\left\{\begin{array}{c}{G}_{efi}=\frac{P_i{B}_i-Q_i{A}_i}{A_i^2+B_i^2}\\ B_{efi}=\frac{-P_i{A}_i-Q_i{B}_i}{A_i^2+B_i^2}\end{array}\right.$

All the other two parameter R _efi, X _efidrawn by the transformational relation of impedance and admittance;

Step 5, utilizes the parameter G calculated _efi, B _efi, R _efi, X _efi, by equivalent feeder resistances R _efiwith equivalent feeder line reactance X _efiobtain equivalent feed line impedance Z _ef, setting virtual impedance value Z _v=Z _ref-Z _ef, realize real-time reactive power and divide equally control; Wherein, Z _reffor feeder line reference value, set according to requirement of engineering.

Further, the active power calculating formula of common load consumption is: the reactive power of common load consumption calculates formula and is: $Q_{fi}=U_i{U}_0{B}_{fi}{\mathrm{cos\δ}}_i-U_i^2{B}_{fi}-U_i{U}_0{G}_{fi}{\mathrm{sin\δ}}_i.$

Further, $P_i=U_i^2{G}_{efi}-U_i{U}_0{G}_{efi}{\mathrm{cos\δ}}_i-U_i{U}_0{B}_{efi}{\mathrm{sin\δ}}_i;Q_i=U_i{U}_0{B}_{efi}{\mathrm{cos\δ}}_i-U_i^2{B}_{efi}-U_i{U}_0{G}_{efi}{\mathrm{sin\δ}}_i;$ Wherein, G _efiand B _efifor the equivalent feeder line admittance of DG unit i.

Relative to prior art, the present invention has following beneficial effect: not mating of the inconsistent and feeder line parameter of local load in micro-capacitance sensor, is to cause inverter to export idle unbalanced principal element; First the present invention does not mate factor parametrization by equivalent feeder line concept by causing the network of idle balancing error, and utilizes feeder current sensing to calculate equivalent feeder line parameter in real time; Secondly according to parameters obtained setting virtual impedance, not mating factor by compensating in connection line, can effectively eliminate idle balancing error.Compared to conventional virtual impedance methodologies, the present invention not only considers local load-factor, and can make parameter adjustment in real time for the change of load, realizes exact power equilibrium.

[accompanying drawing explanation]

Fig. 1 is microgrid structural representation.

Fig. 2 is microgrid model schematic.

Fig. 3 is the equivalent moving model schematic diagram of single DG unit.

Fig. 4 is for implementing equivalent feeder line instrumentation plan.

Fig. 5 is the local control strategy schematic diagram of DG unit.

Fig. 6 is the power equalization performance schematic diagram of each inverter under conventional virtual impedance methodologies.Wherein, Fig. 6 (a) is active power output schematic diagram; Fig. 6 (b) is reactive power output schematic diagram.

Fig. 7 is the micro-capacitance sensor equivalent model simulation result schematic diagram based on equivalent feeder line theory.Wherein, Fig. 7 (a) is active power output schematic diagram; Fig. 7 (b) is reactive power output schematic diagram.

Fig. 8 is the power equalization performance schematic diagram of each inverter under self adaptation virtual impedance method.Wherein, Fig. 8 (a) is active power output; Fig. 8 (b) is reactive power output.

[embodiment]

The present invention is divided into following components:

1. obtained the parameter not match condition of external circuit corresponding to each DG unit by modeling, and introduce that equivalent feeder line is theoretical to unitize each not match parameter, in order to set corresponding virtual impedance.

2. calculate the controling parameters used based on equivalent feeder line theoretical demand.

3. utilize above-mentioned controling parameters to realize the idle of self adaptation virtual impedance adjustment and divide equally control method.

Unbalanced two principal elements of micro-capacitance sensor are affected: feeder line parameter is not mated with local load inconsistent for solving, each DG unit of micro-capacitance sensor is as shown in Figure 1 set up equivalent feeder line model by the present invention, eliminate local load in form, be simplified the moving model of DG unit, see Fig. 2.Based on this model, propose idlely to divide equally control method, specific as follows:

(1) microgrid equivalence moving model

When micro-capacitance sensor enters island mode, each DG unit is coordinated mutually, the load power in equilibrium assignment net.The active power that the DG unit that capacity is larger exports is larger.And at idle output facet, feeder line pressure drop not to be mated etc. and is made each DG unit can not realize by reactive requirement in appearance distribution network.

For each DG unit, power output comprises two parts: local load consuming power with transmit through feeder line the power consumed by common load.It is as follows that the active power that common load consumes calculates formula: it is as follows that reactive power calculates formula: wherein G _fiand B _fifor conductance component and the susceptance component of feeder line, U _ifor the output voltage amplitude of DG unit, U ₀represent public exchange busbar voltage amplitude, δ _iit is the phase angle difference of two voltages.Divide because power comprises two compositions, the operation difference between DG unit can not be analyzed intuitively.In order to realize power integration, it is theoretical that the present invention proposes equivalent feeder line, local load consuming power and common load consumed power is integrated together, and obtains in form consistent with common load consumed power result, and it is as follows that active power calculates formula: it is as follows that reactive power calculates formula: wherein G _efiand B _efifor conductance component and the susceptance component of the equivalent feeder line of DG unit i.When micro-grid system is known, equivalent feeder line parameter can be now uniquely determined.

(2) equivalent feeder line calculation of parameter

In the microgrid of droop control application, idle unbalanced problem has outside connecting circuit parameter not mate to cause.When traditional virtual impedance method solves idle unbalanced problem, direct coupling does not comprise the feeder line parameter of local load information.Virtual impedance, from the angle of equivalent moving model, is mated equivalent feeder line by the present invention, solves idle equalization problem.The wherein set point Z of virtual impedance _vparametric compensation standard value Z _refwith equivalent feeder line virtual impedance Z _efdifference.

P can be calculated by DG unit output voltage and output current _i, Q _i, can P be obtained by output voltage and feeder current _fi, Q _fi.Under normal circumstances, the voltage magnitude U of micro-capacitance sensor PCC point ₀the unknown, therefore the present invention utilizes feeder line power information P _fiwith Q _fiindirect calculation equivalence feeder line parameter.After each DG cellular installation, the resistance value R of feeder line corresponding to it _fiwith reactance value X _fifixing and can survey, therefore by calculating, the unknown message in formula can be passed through P _fi, Q _fi, R _fi, X _firepresent.In conjunction with the known parameters P of micro-grid system _i, Q _i, the equivalent feeder line parameter G of micro-capacitance sensor can be obtained _efi, B _efi, R _efi, X _efi, and then the set point of virtual impedance can be obtained.

(3) self adaptation is idle divides equally control method

The parameter of equivalence feeder line model is all obtain from the local measurement of DG unit, and the measurement between parameter is independent of each other, and therefore equivalent feeder line calculates when DG unit runs, and can carry out in real time.

Feeder current referring to Fig. 5, DG unit runtime system changes, and can affect P _i, Q _ietc. parameter.Such system can obtain equivalent feeder line parameter G in real time _efi, B _efi, R _efi, X _efideng change, affect set point and the virtual voltage of virtual impedance, thus realize the idle Balance route of self adaptation.

During stable state, each DG unit calculates equivalent feed line impedance in real time according to feeder current information, and respective settings virtual impedance is to compensate not mating of external physical connecting circuit.When the load, no matter be local load or common load, new not match information can feed back in the calculating of equivalent feeder line immediately, thus causes the adaptive change of virtual impedance.In this way, idle equilibrium remains accurate.

Refer to shown in Fig. 5, a kind of micro-capacitance sensor based on equivalent feeder line theory of the present invention is idle divides equally control method, by measuring the power situation of micro-grid system in real time, utilizes equivalent feeder line model, calculate the virtual impedance value under different situations, the reactive power realizing micro-capacitance sensor is divided equally.Specifically comprise the following steps:

Step 1, when after DG cellular installation each in micro-grid system, measures the corresponding feed line impedance value R of each DG unit _fiwith X _fi; R _fifor resistance, X _fifor reactance;

Step 2, see Fig. 4, calculates DG unit active-power P by DG unit output voltage and output current _i, DG unit reactive power Q _i, calculate by the output voltage of DG unit and feeder current the active-power P that common load consumes _fi, common load consume reactive power Q _fi.Equivalence feeder line calculates when DG unit runs, and can carry out simultaneously.

Step 3, utilize known quantity to substitute the unknown parameter U0 in rating formula, formula is as follows:

$\left\{\begin{array}{c}{U}_i{U}_0{\mathrm{sin\δ}}_i=-P_{fi}\frac{B_{fi}}{G_{fi}^2+B_{fi}^2}-Q\frac{G_{fi}}{G_{fi}^2+B_{fi}^2}=A_i\\ U_i\left(U_i-U_0{\mathrm{cos\δ}}_i\right)=P_{fi}\frac{G_{fi}}{G_{fi}^2+B_{fi}^2}-Q_{if}\frac{B_{fi}}{G_{fi}^2+B_{fi}^2}=B_i\end{array}\right.$

Wherein G _efi, B _efi, R _efi, X _efirepresent admittance and the impedance parameter of equivalent feeder line model.According to the transformational relation of impedance and admittance, above formula can be reduced to:

$\left\{\begin{array}{c}{A}_i=P_{fi}{X}_{fi}-Q_{fi}{R}_{fi}\\ B_i=P_{fi}{R}_{fi}+Q_{fi}{X}_{fi}\end{array}\right.$

Now can obtain two by known quantity common load active-power P _fi, common load reactive power Q _fi, R _fi, X _fithe parameter A represented _i, B _i.

Step 4, the parameter G that equivalent feeder line model uses _efi, B _efi, R _efi, X _efican be calculated by above-mentioned several known parameters, formula is as follows:

$\left\{\begin{array}{c}{G}_{efi}=\frac{P_i{B}_i-Q_i{A}_i}{A_i^2+B_i^2}\\ B_{efi}=\frac{-P_i{A}_i-Q_i{B}_i}{A_i^2+B_i^2}\end{array}\right.$

All the other two parameter R _efi, X _efidrawn by the transformational relation of impedance and admittance.

Step 5, utilizes the parameter G calculated _efi, B _efi, R _efi, X _efi, by equivalent feeder resistances R _efiwith equivalent feeder line reactance X _efiobtain equivalent feed line impedance Z _ef, setting virtual impedance value Z _v=Z _ref-Z _ef, realize real-time reactive power and divide equally control; Wherein, Z _reffor feeder line reference value, set according to requirement of engineering.

The micro-capacitance sensor based on equivalent feeder line theory that the present invention proposes idlely divides equally control method, considers feeder line parameter and does not mate the situation such as inconsistent with local load, the distribution condition of reactive power in adjustment micro-capacitance sensor that can be real-time.Simulation result as shown in Figure 8, in the 2s moment, introduce self adaptation virtual impedance simultaneously and control by three inverters.Compensate the not matching degree between equivalent feeder line by virtual impedance, the not matching degree of outside connecting circuit obtains equivalent compensation.From simulation result, this strategy well eliminates idle balancing error, realizes idle equilibrium accurately.In the 6s moment, net internal burden changes.Can find out, the equivalent feeder line based on feeder current sensing calculates can rapid feedback network not matching degree, adjusts virtual impedance rapidly, recovers idle balanced accuracy within the extremely short time.

Claims (3)

1. divide equally a control method based on the micro-capacitance sensor of equivalent feeder line theory is idle, it is characterized in that, comprise the following steps:

Step 1, when after DG cellular installation each in micro-grid system, measures the corresponding feed line impedance value R of each DG unit _fiwith X _fi;

Step 2, calculates DG unit active-power P by each DG unit output voltage and output current _i, DG unit reactive power Q _i, the active-power P of common load consumption is calculated by output voltage and feeder current _fi, common load consume reactive power Q _fi;

Step 3, by the unknown parameter U in rating formula ₀utilize known quantity to substitute, formula is as follows:

According to the transformational relation of impedance and admittance, above formula is reduced to:

$\left\{\begin{array}{c}{A}_i=P_{fi}{X}_{fi}-Q_{fi}{R}_{fi}\\ B_i=P_{fi}{R}_{fi}+Q_{fi}{X}_{fi}\end{array}\right.$

Obtain two by known quantity P _fi, Q _fi, R _fi, X _fithe parameter A represented _i, B _i;

Step 4, the parameter G that equivalent feeder line model uses _efi, B _efi, R _efi, X _eficalculated by above-mentioned several known parameters, formula is as follows:

All the other two parameter R _efi, X _efidrawn by the transformational relation of impedance and admittance;

Step 5, utilizes the parameter G calculated _efi, B _efi, R _efi, X _efi, by equivalent feeder resistances R _efiwith equivalent feeder line reactance X _efiobtain equivalent feed line impedance Z _ef, setting virtual impedance value Z _v=Z _ref-Z _ef, realize real-time reactive power and divide equally control; Wherein, Z _reffor feeder line reference value.

2. a kind of micro-capacitance sensor based on equivalent feeder line theory according to claim 1 is idle divides equally control method, it is characterized in that,

The active power of common load consumption calculates formula and is:

The reactive power of common load consumption calculates formula and is:

3. a kind of micro-capacitance sensor based on equivalent feeder line theory according to claim 1 is idle divides equally control method, it is characterized in that,

$P_i=U_i^2{G}_{efi}-U_i{U}_0{G}_{efi}{\mathrm{cos\δ}}_i-U_i{U}_0{B}_{efi}{\mathrm{sin\δ}}_i;$

$Q_i=U_i{U}_0{B}_{efi}{\mathrm{cos\δ}}_i-U_i^2{B}_{efi}-U_i{U}_0{G}_{efi}{\mathrm{sin\δ}}_i;$

Wherein, G _efiand B _efifor the equivalent feeder line admittance of DG unit i.