CN105811421A - Improved droop control based microgrid auxiliary master-slave control method - Google Patents

Abstract

The invention relates to an improved droop control based microgrid auxiliary master-slave control method. The method is used for maintaining stability of the voltage and power of the microgrid. The microgrid comprises multiple DGs connected with alternating current buses respectively; each DG comprises a master-control DG, an auxiliary DG and a slave-control DG; the master-control DG and the slave-control DG are used as a master-control unit and a slave-control unit in the master-slave control method respectively; the inverter in the auxiliary DG adopts voltage and current dual-loop control; a load current io is multiplied by a dynamic virtual impedance Zvir, and the obtained product is used as an instruction voltage to be added in a feedback signal to a voltage loop, so that the output impedance of the inverter is sensitive. Compared with the prior art, the inverter of the auxiliary DG adopts the dynamic virtual impedance, so that matching between the output impedance of the inverter and the circuit impedance can be ensured, voltage drop can be effectively relieved, and the power quality is ensured; and in addition, the improved droop control is adopted, and an integral link is introduced in the reactive power control link, so that steady state voltage without static errors is realized, and the steady state performance of the system is improved.

Description

A kind of micro-capacitance sensor based on modified model droop control assists master-slave control method

Technical field

The present invention relates to a kind of micro-grid coordination control method, especially relate to a kind of micro-capacitance sensor based on modified model droop control and assist master-slave control method.

Background technology

Day by day highlighting along with the fast development of national economy, the energy and environmental problem, the micro-capacitance sensor technology based on regenerative resource is arisen at the historic moment, and the proposition of micro-capacitance sensor concept is favorably improved utilization rate and the motility of distributed power source (DG).The coordination how controlling the internal multiple distributed power sources of micro-capacitance sensor controls and takes over seamlessly between grid-connected/island mode to be a problem demanding prompt solution.

Micro-capacitance sensor control model is broadly divided into equity control, hierarchical control, master & slave control.Equity control strategy then thinks that micro-capacitance sensor internal electric source is equal, it is possible to achieve " plug and play ", need not change control method grid-connected to micro-capacitance sensor in island mode transient process, but control mode is single, and some undulatory property micro battery can not economical operation；Muti-layer control tactics can in real time with all of micro battery and load communication, and constantly revise current operating point reference value, the control communication unit on upper strata but it places one's entire reliance upon；Being in the micro-capacitance sensor of master control architecture needs the micro-capacitance sensor of a larger capacity (such as energy accumulation current converter), works in V/F control under island mode, provides voltage and frequency support for micro-grid system, and is switched to PQ control under grid-connect mode.Visible system is very big for the dependency of main control unit when islet operation, and the motility of main control unit and stability are directly connected to stablizing of whole system.But, owing to can integrate existing commercial combining inverter in host-guest architecture easily, therefore each demonstration project of present stage is still based on host-guest architecture.

Droop control (droop) the technological borrowing thought of synchronous generator Parallel Control, it may be achieved the equity of multiple stage inverter is in parallel, it is possible to meritorious, the reactive power of distribution DG automatically, but the droop control of classics has limitation for power distribution.Owing to the uncertainty of the line impedance of micro-capacitance sensor, the output impedance etc. of inverter makes inverter can not realize the coupling of output, droop characteristic needs the perception according to circuit, resistive and capacitive is different, power control loop additionally as droop control system outer ring structure also has important function for stability contorting such as system frequencies, but power controls to belong to droop control in itself, load change bigger when isolated island can cause the deviation of frequency etc., it is necessary to ensures droop characteristic and regulates rapidity.

Summary of the invention

Defect that the purpose of the present invention is contemplated to overcome above-mentioned prior art to exist and provide the micro-capacitance sensor based on modified model droop control of a kind of feasibility and good stability, strong robustness to assist master-slave control method.

The purpose of the present invention can be achieved through the following technical solutions:

A kind of micro-capacitance sensor based on modified model droop control assists master-slave control method, for maintaining voltage and the power stability of micro-capacitance sensor, described micro-capacitance sensor comprises multiple DG being connected respectively with ac bus, it is characterized in that, described DG includes master control DG, auxiliary DG and from controlling DG, described master control DG and running respectively as the main control unit master & slave control method with from control unit from control DG, the inverter in described auxiliary DG adopts voltage x current double-loop control, and by load current i_oIt is multiplied by dynamic virtual impedance Z_virJoin the command voltage of Voltage loop as feedback signal, make inverter output impedance in perception.

Inverter transmission function in described auxiliary DG is:

$u_o=\frac{K_{ip}{K}_{PWM}(K_{up}s+K_{ui})(u_{nref}-Z_{vir}{i}_o)}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}-\frac{({\mathrm{Ls}}^3+K_{ip}{K}_{PWM}s)}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}{i}_o$

In formula, u_nrefFor Voltage loop command voltage, u_oFor Voltage loop output voltage, K_PWMRepresent PWM equivalence link, K_ipFor electric current loop proportionality coefficient, K_upFor the Voltage loop PI proportionality coefficient controlled, K_uiFor the Voltage loop PI integral coefficient controlled, L is inverter filtering inductance, and C is inverter filtering electric capacity, and s is Laplace operator.

Described dynamic virtual impedance Z_virCalculating formula is:

Z_vir(s)=[Δ u/i_o-Z_o(s)-Z_L]/G(s)

In formula, Δ u is the difference between micro-grid load side sampled voltage amplitude and outer voltage command voltage amplitude, i_oFor load current, Z_LFor line impedance between DG and bus, Z_OS () represents the equivalent output impedance of inverter, G (s) representative voltage proportional gain transmission function, Z_OS (), G (s) expression formula are respectively as follows:

$Z_O\left(s\right)=\frac{({\mathrm{Ls}}^3+K_{ip}{K}_{PWM}s)}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}$

$G\left(s\right)=\frac{K_{ip}{K}_{PWM}(K_{up}s+K_{ui})}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}.$

Described auxiliary DG adopts the droop improved to control, and the Reactive Power Control link in droop control is introduced integral element, and active-power P (s), reactive power Q (s) expression formula are respectively as follows:

$\left\{\begin{array}{c}P\left(s\right)=\left({\mathrm{\ω}}^{*}\right(s)-{\mathrm{\ω}}_o(s\left)\right)\frac{1}{s}\frac{u_o^2}{X_n}/(1+\frac{1}{s}\frac{m_n{u}_o^2}{X_n})\\ Q\left(s\right)=\left(u^{*}\right(s)-u_o(s\left)\right)\frac{K}{s}\frac{u_o}{X_n}/(1+\frac{K}{s}\frac{n_n{u}_o}{X_n})\end{array}\right.$

In formula, ω^*S () is reference frequency, ω_oS () is points of common connection bus frequency, u^*S () is for setting reference voltage, u_oFor Voltage loop output voltage, m_n、n_nRespectively droop control coefficient, K is the gain introducing integral element.

Described auxiliary DG arranges multiple.

Described master control DG runs on VF control model under island mode, runs on PQ control model under grid-connect mode.

Described runs on PQ control model from control DG.

Compared with prior art, the invention have the advantages that

(1) the droop control process to traditional droop control that micro battery adopts broken by the inverter in auxiliary DG, controls to adopt dynamic virtual impedance to voltage x current ring, it is achieved output decoupling, it is ensured that inverter output impedance matches with line impedance.

(2) by arrange dynamic virtual impedance with micro-grid load side voltage magnitude variation and change, adaptive adjustment system, make inverter output impedance in perception, be effectively improved voltage landing, it is ensured that the quality of power supply.

(3) auxiliary DG adopts the droop improved to control, and the Reactive Power Control link in droop control is introduced integral element, it is achieved steady state voltage floating, improves systematic steady state performance.

(4) master control DG runs on VF control model under island mode, the reference of voltage and frequency is improved for micro-capacitance sensor, PQ control model is run under grid-connect mode, PQ control model is worked in from control DG, control to be applied in master & slave control by the droop of improvement simultaneously, serve as the auxiliary unit of master control micro battery, make full use of the motility of droop control and have poor property so that master-slave control mode stability strengthens.

Accompanying drawing explanation

Fig. 1 is that the present invention assists the inverter in DG to introduce the Double Loop Control System structure chart of virtual impedance；

Fig. 2 (a) assists the system construction drawing before the inverter introducing virtual impedance in DG for the present invention；

Fig. 2 (b) assists the equivalent system structure chart after the inverter introducing virtual impedance in DG for the present invention；

Fig. 3 is that the present invention assists DG power transmission schematic diagram；

Fig. 4 is tradition DG power controller block diagram；

Fig. 5 is the power controller block diagram that the present invention assists DG；

Fig. 6 is the power control loop that the present invention assists DG；

Fig. 7 (a) adopts classical droop to control the voltage waveform of output for inverter；

Fig. 7 (b) assists the DG voltage waveform exported for the present invention；

Fig. 8 (a) adopts classical droop to control the current waveform of output for inverter；

Fig. 8 (b) assists the DG current waveform exported for the present invention；

Fig. 9 (a) adopts classical droop to control the power waveform of output for inverter；

Fig. 9 (b) assists the DG power waveform exported for the present invention；

Figure 10 (a) adopts classical droop to control the frequency waveform of output for inverter；

Figure 10 (b) assists the DG frequency waveform exported for the present invention；

Figure 11 is that the present invention is with master control DG, from controlling DG and the micro-capacitance sensor artificial circuit of auxiliary DG；

Figure 12 (a) is micro-capacitance sensor busbar voltage wave simulation result figure of the present invention；

Figure 12 (b) is micro-grid load side bus current waveform simulation result figure of the present invention；

Figure 12 (c) is micro-grid load side power waveform simulation result figure of the present invention；

Figure 12 (d) is micro-grid load side bus frequency waveform simulation result figure of the present invention.

Detailed description of the invention

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.The present embodiment is carried out premised on technical solution of the present invention, gives detailed embodiment and concrete operating process, but protection scope of the present invention is not limited to following embodiment.

Embodiment

Novel droop of the present invention controls: first, on ring contravarianter voltage circular current ring control principle basis, is effectively realized power decoupled by adding dynamic antivibration impedance link, for power control loop service；Secondly, power control loop joint improves mainly by by difference on the frequency f-fn and voltage difference U-U₀As feedback signal, except to increase a PI controlling unit on feedback line, also need to be modified the sagging coefficient of feedback line processing, thus constituting a kind of novel droop control method, additionally in view of reactive power expression formula does not have integral term, during stable state there is static difference and robustness is poor in voltage, it is necessary to adds integral element on idle control circuit.

Said method is called novel droop control, is applied in master & slave control micro-grid system as auxiliary unit.Consider the feature that traditional master & slave control controls with equity, by two kinds coordinate controls combine realize band auxiliary principal and subordinate coordinate control, the method adopts multiple control units, wherein, main control unit is the reference that the micro-capacitance sensor of islet operation improves voltage and frequency, under island mode, work in V/F control, voltage and frequency support are provided for micro-grid system, and under grid-connect mode, are switched to PQ control；As the novel droop control method that the auxiliary employing present invention of main control unit proposes, auxiliary unit can have multiple, carries out load output distribution between them, is responsible for voltage and the frequency stable of micro-capacitance sensor, it is achieved in system, the fast power of load change compensates；All the other can adopt PQ control from control unit, thus realizing peak power generating.

Below voltage x current ring of the present invention is controlled and the improvement of power ring control is analyzed successively:

Controlling to improve to voltage x current ring: in the system of actual inverter parallel, there is coupling between P and Q of inverter output, the droop characteristic for P-f, Q-u is affected, and is especially difficult to direct application in the middle of low pressure micro-capacitance sensor.Require over introducing virtual impedance control strategy, its essence is and be multiplied by virtual impedance value by gathering the current signal come, be incorporated in voltage regulator, contribute to increasing system stability and reducing circulation impact.

Based on virtual impedance control loop inverter control principle as it is shown in figure 1, mainly include output voltage current regulator, power droop control ring and virtual impedance control loop, wherein G_u(s)、G_i(s)、Z_vir(s)、K_PWMRepresent outer voltage control respectively, electric current controls internal ring, virtual impedance feedback element, PWM equivalence link, u_nref、u^* _nref、u_oRespectively outer voltage command voltage, introduce the command voltage of virtual impedance, load voltage, i_L、i_oRespectively inductive current, load current, L, C represent filter inductance, filter capacitor respectively.In order to make system have good stability and dynamic responding speed, there is G_u(s)=K_up+K_ui/s、G_i(s)=K_ip, wherein K_up、K_uiFor the proportionality coefficient of Voltage loop PI control, integral coefficient, K_ipFor electric current loop proportionality coefficient.

According to Fig. 1, when voltage control loop is respectively with u_nref、u_oDuring as input, output, after adding virtual impedance, the closed loop transfer function of inverter can be written as:

$u_o=\frac{K_{ip}{K}_{PWM}(K_{up}s+K_{ui})(u_{nref}-Z_{vir}{i}_o)}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}-\frac{({\mathrm{Ls}}^3+K_{ip}{K}_{PWM}s)}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}{i}_o---\left(1\right)$

Can be simplified to

u_o=G (s) (u_nref-Z_viri_o)-Z_o(s)i_o=G (s) u_nref-[G(s)Z_vir+Z_o(s)]i_o(2)

In formula: G (s) representative voltage proportional gain transmission function, Z_OS () represents the equivalent output impedance of inverter closed loop system.It is then:

$G\left(s\right)=\frac{K_{ip}{K}_{PWM}(K_{up}s+K_{ui})}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}---\left(3\right)$

$Z_O\left(s\right)=\frac{({\mathrm{Ls}}^3+K_{ip}{K}_{PWM}s)}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}---\left(4\right)$

So, after introducing virtual impedance controlling unit, the equivalent output impedance that inverter is new is:

$Z_o^{*}\left(s\right)=[G\left(s\right)Z_{\mathrm{vir}}+Z_o\left(s\right)]---\left(5\right)$

Can be seen that, introduce virtual impedance feedback element and just can control the output impedance characteristic of system, make system not changing on external hardware basis by regulable control device parameter, the coupling condition of inverter power can be changed neatly, so that corresponding droop characteristic improves.

As shown in Fig. 2 (a), it does not have when adding virtual impedance, the line impedance Z between DG and bus_L=R+jX is in resistive in low-voltage circuit, and as shown in Fig. 2 (b), the circuit that can realize between micro battery and bus after introducing virtual impedance presents perception, if power adopts droop control can realize the uneoupled control of power undoubtedly in controlling.

As can be seen from Figure 2 system total voltage landing expression formula is:

$\mathrm{\Δ}u=\[Z_o^{*}\left(s\right)+Z_L\]i_o=\[G\left(s\right)Z_{vir}+Z_o\left(s\right)+Z_L\]i_o---\left(6\right)$

In order to ensure the quality of power supply, reduce system voltage landing and circulation, if dynamic virtual impedance is:

Z_vir(s)=[Δ u/i_o-Z_o(s)-Z_L]]/G(s)(7)

In formula: Δ u is system difference between the voltage magnitude and inverter command voltage of micro-grid load side sampled point, i₀For load current, Z_LFor line impedance.Along with being continually changing of system mode, fixing virtual impedance improvement result cannot meet needs, and dynamic virtual impedance can the voltage of real-time monitoring system, electric current, corresponding dynamic virtual impedance is calculated by formula (7), automatic regulating system adaptively, effectively improve voltage landing, it is ensured that the quality of power supply.

It is directed to power ring to control to be analyzed as follows: in classical sagging theory of algorithm, oneself can realize stable state current-sharing effect good between shunt chopper.But inverter tradition droop control substantially belongs to droop control, it is contemplated that when load change or electromotor switching, it is necessary to better transient response ability, power control loop joint is improved by the present invention.

For system shown in Figure 3, line impedance Z_L=R+jX, from the power S=P+jQ that A point injects, then:

$\left\{\begin{array}{c}P=\frac{E_1\[R(E_1-E_2\cos \mathrm{\δ})\]+E_{2}X\sin \mathrm{\δ}}{R^2+X^2}\\ Q=\frac{E_1\[X(E_1-E_2\cos \mathrm{\δ})\]-E_{2}R\sin \mathrm{\δ}}{R^2+X^2}\end{array}\right.---\left(8\right)$

Under normal circumstances, angular difference δ is only small for merit, cos δ ≈ 1, if X is > > R, can omit resistance, it is possible to be converted into when analysis:

$\{\begin{array}{c}P=\frac{E_1{E}_2}{X}\sin \mathrm{\δ}\\ Q=\frac{E_1(E_1-E_2)}{X}\end{array}---\left(9\right)$

From formula (9), in perception system, P is linear with merit angular difference δ, Q and voltage difference, often f substitutes merit angle in actual applications, therefore can realize the reasonable distribution of distributed power source P, Q in parallel is controlled by adjustment f and voltage, it is hereby achieved that droop control characteristic curve is:

$\left\{\begin{array}{c}f=f^{*}+m_n{P}_n\\ u=u^{*}-n_n{Q}_n\end{array}\right.---\left(10\right)$

In formula: m_n、n_nRespectively sagging coefficient, f^*、u^*Respectively reference frequency and reference voltage.The traditional power control block figure obtained according to formula (10) as indicated at 4, P in figure_set、Q_setThe respectively setting value of power, s is Laplace operator.

Expression formula according to Fig. 4 active power and reactive power that can obtain the output of micro-source is:

$\left\{\begin{array}{c}P\left(s\right)=\left({\mathrm{\ω}}^{*}\right(s)-{\mathrm{\ω}}_o(s\left)\right)\frac{1}{s}\frac{u_o^2}{X_n}/(1+\frac{1}{s}\frac{m_n{u}_o^2}{X_n})\\ Q\left(s\right)=\left(u^{*}\right(s)-u_o(s\left)\right)\frac{u_o}{X_n}/(1+\frac{n_n{u}_o}{X_n})\end{array}\right.---\left(11\right)$

From formula (11) it can be seen that because of the existence of integral term, stable state moment active power and Equivalent conjunction impedance X_nUnrelated, when multiple stage micro battery parallel running, it is possible to achieve the accurate distribution of active power；And not integral term in reactive power formula, the output of stable state moment reactive power is subject to outreaching the impact of equiva lent impedance, according to pertinent literature be appreciated that only passing ratio link stable state time voltage there is static difference, and robustness is poor.According to above-mentioned analysis, in order to realize steady state voltage floating, it is necessary to Reactive Power Control link is constructed integral element, improving systematic steady state performance, new expression formula such as formula (12), its structure chart is as shown in Figure 5.

$\left\{\begin{array}{c}P\left(s\right)=\left({\mathrm{\ω}}^{*}\right(s)-{\mathrm{\ω}}_o(s\left)\right)\frac{1}{s}\frac{u_o^2}{X_n}/(1+\frac{1}{s}\frac{m_n{u}_o^2}{X_n})\\ Q\left(s\right)=\left(u^{*}\right(s)-u_o(s\left)\right)\frac{K}{s}\frac{u_o}{X_n}/(1+\frac{K}{s}\frac{n_n{u}_o}{X_n})\end{array}\right.---\left(12\right)$

Additionally, during classical droop controls, droop characteristic is a straight line tilted, when load variations or electromotor switching time, the changed power of micro battery output is very big, it is not applied for environment complicated and changeable, conventional method is all be simply introduced into a feedback variable to improve this situation, but owing to the numerical value of sagging coefficient is only small, improves result inconspicuous.The present invention is controlled by increase feedback element, addition PI, is revised a kind of novel droop control methods of technological maheup such as the sagging coefficient of feedback on the basis of Fig. 5, realize the compensation of system frequency and voltage, the stability of improvement system, adaptability, corresponding structure is as shown in Figure 6.Concrete expression formula is:

$\{\begin{array}{c}f=f^{*}+m_n{P}_n+m^{*}(K_p+\frac{K_i}{s})(f-f^{*})\\ u=u^{*}-n_n{Q}_n-n^{*}(K_p+\frac{K_i}{s})(u-u^{*})\end{array}---\left(13\right)$

In formula: m^*、n^*For revised sagging coefficient, generally big than m, n；K_p、K_iFor the proportionality coefficient of PI control, integral coefficient；.From formula it can be seen that its essence above formula is using frequency difference, the voltage difference feedback signal that controls as power of sagging coefficient link by PI control loop, correction, wherein m^*、n^*For increasing the compensating action of feedback.

Finally, the present invention also propose a kind of with auxiliary master-slave control strategy control method for coordinating analyze as follows:

The control strategy of micro-capacitance sensor aspect can be divided mainly into equity control, master & slave control, hierarchical control control.Equity controls the feature with " plug and play ", each micro battery has only to respective access-in point information and participates in the regulation and control of voltage and frequency, and power supply is all without changing control method in micro-capacitance sensor isolated island/grid-connected switching, but during islet operation, the micro-capacitance sensor being in equity control belongs to and has poor control and sensitivity not high；The micro-capacitance sensor of master & slave control can keep the maintenance set-point of voltage and frequency when isolated island, but this control model is bigger for the degree of dependence of main control unit, once main control unit breaks down, the micro-capacitance sensor of islet operation loses the support of voltage, frequency, and microgrid can not run；So-called hierarchical control pattern; it is generally provided with central controller for sending control signal; the load to micro battery, power prediction can be realized; according to system each status information, operational plan is adjusted; and relevant defencive function can be improved for system; but it is required for communication line between the micro battery of hierarchical control and central controller, the operation of communication failure meeting influential system.

Master & slave control micro-capacitance sensor exists main control unit and from control unit, wherein main control unit is the reference that the micro-capacitance sensor of islet operation improves voltage and frequency, this kind of inverter is generally adopted single V/F and controls, also or single droop or multiple droop control, in time adopting single V/F to control or droop controls, capacity and the motility of main control unit are directly connected to system stability, and multiple droop controls as principal and subordinate's part, system belongs to droop control, main control unit can not be assisted again from control cell operation to regulate voltage and frequency in PQ control model.In view of the droop characteristic of droop control can distribute by flexible power, the present invention proposes to make full use of the droop characteristic of droop control inverter, on the basis of tradition master & slave control, using the droop control Auxiliary Control Element as main control unit, the suitability of adjustable height system.

In order to verify effectiveness of the invention, carry out analogue simulation also by MATLAB/Simulink software platform, mainly verify modified model droop control and assist two aspects of master & slave control based on modified model droop control:

First the present invention has built the modified model droop control of present invention proposition to verify the effectiveness of proposed control strategy based on MATLAB/Simulink software platform.Simulation parameter as illustrated in chart 1, f_sFor carrier frequency.Load adopts firm power P=10kW, Q=5kVar.In table, R_fFor filter resistance, P_setSetting value for active power.

Fig. 7 (a), 7 (b) are the voltage waveform comparison diagram of inverter output before and after improving, before improvement, the voltage wave amplitude of inverter output is about 311V, after improving, voltage magnitude becomes about 340V, the droop control indicating improvement contributes to reducing voltage landing, provides guarantee for improving load supply voltage quality.

Table 1

Fig. 8 (a) to Figure 10 (b) is followed successively by and improves the electric current of front and back inverter output, power, frequency, can be seen that when system just brings into operation from image, the speed that droop control after improvement tends towards stability is faster, system can enter steady-state operation quickly, it is bad that meritorious and idle before improvement divides equally effect, stability is not good, it can be seen that, the droop control of improvement effect when voltage, electric current, power, frequency regulate is more excellent.

Secondly, utilizing MATLAB/Simulink software to build the micro-capacitance sensor structure simulation model shown in Figure 11, what thus the simulating, verifying present invention proposed assists principal and subordinate's control method for coordinating based on the modified model droop micro-capacitance sensor band controlled.In Figure 11, micro-capacitance sensor includes two micro battery of DG1, DG2, DG3, wherein: master control micro battery (also referred to as main control unit) DG1 adopts V/F to control when islet operation, adopt PQ to control when being incorporated into the power networks, then having been used up PQ control from control micro battery (also referred to as from controlling unit) DG2, DG2 then adopts improvement droop control as the auxiliary unit of main control unit DG1.

Simulation parameter is chosen as follows: V/F controls U in module_ref=300V, f=50Hz, Voltage loop K_p=10, K_i=2000, electric current loop K_p=0.5；PQ controls P in module_ref=10kW, Q_ref=0kVar, electric current loop ring K_p=0.5, K_iIn=20 transmission lines of electricity, micro battery low-voltage circuit parameter R₁=R₂=R₃=0.0642 Ω/km, X₁=X₂=X₃=0.00083 Ω/km, load adopts firm power load: P₁=P₃=10kW, P₂=20kW, Q₁=Q₃=5kVar, Q₂=10kVar.Common load, PQ control, modified model droop, power distribution network parameter with above-mentioned tradition principal and subordinate consistent.

In order to verify feasibility and the stability of the proposed master-slave control strategy with auxiliary, taking simulation time 2s, wherein micro-capacitance sensor islet operation during 0～1s, micro-grid connection during 1s, 1～2s is the time of being incorporated into the power networks.Simulation operations is as shown in table 2, and simulation curve is such as shown in Figure 12 (a)～(d).

1) 0～1s micro-capacitance sensor islet operation, wherein 0～0.5s is that band auxiliary master & slave control runs, it is that classical master & slave control state is run during 0.5～1s, the comparison of two line segments can be passed through, when can analyze isolated island, the difference of two control models: Figure 12 (a) shows that band auxiliary master & slave control voltage has just started as 320V, it is upgraded to 340V during excision common load 3, and classical master & slave control properly functioning time voltage be 250V, it is increased to 280V, it can be seen that modified model droop helps compensate for voltage landing during excision common load 3；Figure 12 (b) is simulated current oscillogram, closer at about 100A, being conducive to system in the stability of grid-connected/island mode switching time band is assisted master & slave control current waveform and be grid-connected；Figure 12 (c) is the power patterns at load 2 side place, and contrastingly the waveform with auxiliary master & slave control is more steady, and with waveform time grid-connected closer to, in grid-connected/island mode, the realization for power distribution is easier to；Figure 12 (d) is frequency waveform, hence it is evident that it can be seen that band auxiliary master & slave control is closer to rated frequency 50Hz, and when excising common load 3, the waveform of classical principal and subordinate has very big fluctuation, is unfavorable for devices in system life-span and stability.By comparing it can be seen that in islet operation pattern, no matter be current-voltage waveform or power-frequency waveform, hence it is evident that find out that the master & slave control with auxiliary is more stable.

2) micro-grid connection is run, similar with islet operation operating process, experienced by band auxiliary master & slave control (1～1.5s) and classical master & slave control (1.5～2s) two processes respectively, the two process is also carried out the switching of common load 3, can be seen that from the waveform of Figure 12 (a)～(d), under whole grid-connect mode, voltage maintains about 320V, frequency changes not quite near 50Hz, electric current and power also remain unchanged substantially, visible two kinds of master & slave control can both operate in the middle of grid-connect mode well, band auxiliary principal and subordinate's micro-capacitance sensor at this time has been considered as equity microgrid (droop is main) and has been incorporated into the power networks, and the addition of droop makes in system grid connection/pattern switching more stable.

Table 2

First the present embodiment derives inverter closed-loop structure, power equation according to the grid-connected equivalent circuit of voltage source inverter, obtain inverter closed loop transfer function, power decoupled control method, then start with from the topological structure of droop control, the inverter ultimate principle analyzing classical droop control is saved from voltage x current double-loop control and power control loop, finally propose novel droop control inverter control method: by adopting dynamic virtual impedance to realize power decoupled, control to improve to power simultaneously, improve the stability and adaptability of system.It addition, it is excessive for main control unit dependency to present invention is directed at master & slave control, it is proposed to using the auxiliary micro battery as main control unit of the droop control inverter after one or more improvement, make full use of the poor characteristic that has of droop control, improve the stability of master & slave control.Simulation results show control method of the present invention is applied to effectiveness and the feasibility that many principals and subordinates mix in coordinated control system.

Claims (7)

1. the micro-capacitance sensor based on modified model droop control assists master-slave control method, for maintaining voltage and the power stability of micro-capacitance sensor, described micro-capacitance sensor comprises multiple DG being connected respectively with ac bus, it is characterized in that, described DG includes master control DG, auxiliary DG and from controlling DG, described master control DG and running respectively as the main control unit master & slave control method with from control unit from control DG, the inverter in described auxiliary DG adopts voltage x current double-loop control, and by load current i_oIt is multiplied by dynamic virtual impedance Z_virJoin the command voltage of Voltage loop as feedback signal, make inverter output impedance in perception.

2. a kind of micro-capacitance sensor based on modified model droop control according to claim 1 assists master-slave control method, it is characterised in that the inverter transmission function in described auxiliary DG is:

$u_o=\frac{K_{ip}{K}_{PWM}(K_{up}s+K_{ui})(u_{nref}-Z_{vir}{u}_o)}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}-\frac{({\mathrm{Ls}}^3+K_{ip}{K}_{PWM}s)}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}{i}_o$

In formula, u_nrefFor Voltage loop command voltage, u_oFor Voltage loop output voltage, K_PWMRepresent PWM equivalence link, K_ipFor electric current loop proportionality coefficient, K_upFor the Voltage loop PI proportionality coefficient controlled, K_uiFor the Voltage loop PI integral coefficient controlled, L is inverter filtering inductance, and C is inverter filtering electric capacity, and s is Laplace operator.

3. a kind of micro-capacitance sensor based on modified model droop control according to claim 2 assists master-slave control method, it is characterised in that described dynamic virtual impedance Z_virCalculating formula is:

Z_vir(s)=[Δ u/i_o-Z_o(s)-Z_L]/G(s)

In formula, Δ u is the difference between micro-grid load side sampled voltage amplitude and outer voltage command voltage amplitude, i_oFor load current, Z_LFor line impedance between DG and bus, Z_OS () represents the equivalent output impedance of inverter, G (s) representative voltage proportional gain transmission function, Z_OS (), G (s) expression formula are respectively as follows:

$Z_O\left(s\right)=\frac{({\mathrm{Ls}}^3+K_{ip}{K}_{PWM}s)}{{\mathrm{LCs}}^2+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}$

$G\left(s\right)=\frac{K_{ip}{K}_{PWM}(K_{up}s+K_{ui})}{{\mathrm{LCs}}^3+K_{ip}{K}_{PWM}{\mathrm{Cs}}^2+(1+K_{PWM}{K}_{up})s+K_{ip}{K}_{PWM}{K}_{up}}.$

4. a kind of micro-capacitance sensor based on modified model droop control according to claim 1 assists master-slave control method, it is characterized in that, described auxiliary DG adopts the droop improved to control, Reactive Power Control link in droop control is introduced integral element, and active-power P (s), reactive power Q (s) expression formula are respectively as follows:

$\left\{\begin{array}{c}P\left(s\right)=\left({\mathrm{\ω}}^{*}\right(s)-{\mathrm{\ω}}_o\left(s\right))\frac{1}{s}\frac{u_o^2}{X_n}/(1+\frac{1}{s}\frac{m_n{u}_o^2}{X_n})\\ Q\left(s\right)=\left(u^{*}\right(s)-u_o\left(s\right))\frac{K}{s}\frac{u_o}{X_n}/(1+\frac{K}{s}\frac{n_n{u}_o}{X_n})\end{array}\right.$

In formula, ω^*S () is reference frequency, ω_oS () is points of common connection bus frequency, u^*S () is for setting reference voltage, u_oFor Voltage loop output voltage, m_n、n_nRespectively droop control coefficient, K is the gain introducing integral element.

5. a kind of micro-capacitance sensor based on modified model droop control according to claim 1 assists master-slave control method, it is characterised in that described auxiliary DG arranges multiple.

6. a kind of micro-capacitance sensor based on modified model droop control according to claim 1 assists master-slave control method, it is characterised in that described master control DG runs on VF control model under island mode, runs on PQ control model under grid-connect mode.

7. a kind of micro-capacitance sensor based on modified model droop control according to claim 1 assists master-slave control method, it is characterised in that described runs on PQ control model from control DG.