CN104836221A - DC micro network secondary adjusting control method based on line loss optimization - Google Patents

Abstract

The invention belongs to the interdisciplinary field of a power distribution network technology and an electric power and electronics technology, and especially relates to a DC micro network secondary adjusting control method based on line loss optimization. First of all, a DC micro network system is constructed, an upper-layer control center, according to sampling information of each converter, calculates the line loss power of the DC micro network system; then a controllable voltage source sagging control intercept common mode and a differential mode adjusting amount are calculated; and output voltage of each controllable power supply in a DC micro network is adjusted through sagging control parameters such that the output of each power supply is controlled, the trend on each distribution branch is adjusted accordingly, and the line loss is reduced. According to the invention, the line loss of the DC micro network is optimized under the condition that line impedance and enormous operation information are measured without reliance on high-sensitivity sensors. Experiment results indicate that compared to a conventional DC micro network control method, the control method provided by the invention can effectively reduce the line loss, and the specific reduction amplitude is determined according to the distribution condition of the line impedance and loads.

Description

Based on the direct-current micro-grid Secondary Control control method that line loss is optimized

Technical field

The invention belongs to distribution network technology and power electronic technology crossing domain, particularly relate to a kind of direct-current micro-grid Secondary Control control method optimized based on line loss.

Background technology

Different from the form of conventional electrical distribution net system single power supply, tree, there is multiple direct voltage source in direct-current grid.This makes to realize line loss optimization by load disturbance in power distribution network becomes possibility.DC micro power grid system just progressively rises in recent years, is optimized the method for control at present also rare for its line loss.In interchange microgrid, part research is carried out progressive alternate by measurement circuitry impedance and through-put power and is realized line loss optimization, but the method is too high depends on sensor accuracy, is difficult in practice realize, even runs counter to desire.

Direct-current micro-grid power supply is run and controls, generally adopt distributed droop control method at present.Some researchs propose to adopt the sagging parameter of LF communication system to converter to carry out Secondary Control on the basis of each power source base layer substrate operation droop control method.Some are researched and proposed and stablize busbar voltage by Secondary Control, offset the busbar voltage fluctuation that droop control brings, but do not consider line impedance problems; Some researchs propose the control method of each power supply current-sharing on the basis considering line impedance, but the method does not have optimization function to line loss, even can improve line loss.

Conventional droop control is such as formula shown in (1):

U ^*＝U ₀-Ik (1)

Droop control can be regarded system as and do closed loop droop control by converters to the voltage that each power supply exports.Its voltage-current characteristic exported is a straight line obliquely, and being similar to and sealing in a size at power output end is the virtual resistance of k.Do the common bus that can realize multiple direct voltage source like this to run, avoid backflow, realize current-sharing.But the method can cause floating of DC bus-bar voltage, accurately cannot control, therefore also cannot realize power flowcontrol and line loss optimization to the output voltage of each power supply.For realizing power flowcontrol, and then realizing the line loss optimization of direct-current micro-grid, in microgrid, LF communication system and top level control center must be introduced between each converter.Realize controlling it to the Secondary Control of each port output voltage and exerting oneself by sharing of operation information, thus control the trend of whole microgrid.Even if but introduce Secondary Control, how load disturbance can realize system loss minimization does not still have related ends at present.The main purpose of current Secondary Control is stable busbar voltage, and offset the busbar voltage skew that droop control causes, its control block diagram as shown in Figure 1a.Some researchs propose Secondary Control method for the purpose of each power supply current-sharing based on the object of battery management in micro-capacitance sensor, control block diagram as shown in Figure 1 b, specifically such as formula (2),

$\begin{array}{cc}{\mathrm{\δu}}_i=\mathrm{Gs}(U_{\mathrm{dc}}^{*}-u_{\mathrm{ave}})& {\mathrm{\δu}}_i=\mathrm{Gs}(U_{\mathrm{dc}}^{*}-u_{\mathrm{ave}})\\ {\mathrm{\δi}}_i=\mathrm{Gs}(\stackrel{\‾}{i}-i_i)& \mathrm{\δ}{i}_i=\mathrm{Gs}(\stackrel{\‾}{i}-i_i)\\ U_i^{*}=U_0+\mathrm{\δ}{u}_i+\mathrm{\δ}{i}_i-i_{i}k& U_i^{*}=U_0+\mathrm{\δ}{u}_i+\mathrm{\δ}{i}_i-i_{i}k\end{array}---\left(2\right)$

Formula (2) although in represented each power supply current equalizing method can realize each power supply torque equilibrium, this mode of exerting oneself obviously is unfavorable for the optimization of line loss.Such as, when respectively there is a power supply at a certain load two ends, and connect two power supplys line impedance small one and large one time.For reducing line loss, the large power supply of line impedance obviously should be made to exert oneself less, and another power supply is exerted oneself greatly.And method injunction two power supply in formula (2) is exerted oneself identical, line loss must be increased like this.

In the control of some AC network, part is had to realize optimizing the method for line loss by load disturbance, but these methods need to do difference by sensor measurement line impedance or by the method for line loss iteration to adjacent twice line loss, these methods depend on sensor accuracy unduly, cannot reach theoretical effect in practice.

Summary of the invention

In order to adopt Transient Electromagnetic principle of energy balance to implement the multivariable Control of converter, the present invention proposes a kind of direct-current micro-grid Secondary Control control method optimized based on line loss, comprising:

Step 1, build a direct current micro-grid system, this system comprises multiple controllable voltage source, multiple current source or power source load, many transmission lines, multiple converter, low bandwidth communication system, top level control center; Wherein, top level control center is connected with each controllable voltage source by low bandwidth communication system, converter bottom control platform successively, and top level control center is connected with current source or power source load by low bandwidth communication system; Transmission line is divided into power branch and trunk transmission line, and together with multiple controllable voltage source is linked with current source or power source load by power branch, each bar power branch and multiple current source or power source load are linked together by trunk transmission line;

The operation of each converter and sample information are uploaded to top level control center by step 2, low bandwidth communication system;

Step 3, top level control center, according to the operation information that each converter transmits, calculate direct current micro-grid system line loss power;

Step 4, top level control center set up the condition of direct current micro-grid system optimal route loss power;

Step 5, top level control center calculation each controllable voltage source droop control intercept common and different mode regulated quantity;

Regulated quantity by passing to each converter under low bandwidth communication system, being regulated by droop control parameter and realizing the control of direct current micro-grid system Secondary Control by step 6, top level control center.

Described calculating direct current micro-grid system line loss power comprises the loss power of each bar power branch and each bar trunk transmission line, and total formula is:

$\begin{array}{c}{P}_l=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{P}_{\mathrm{li}}+{(i_1+i_2-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j})}^2{R}_1+...+{(i_1+i_2-\underset{j=1}{\overset{a}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b}{\mathrm{\Σ}}}{I}_{2j}-\underset{k=1}{\overset{q}{\mathrm{\Σ}}}{I}_{q-1})}^2{R}_q\\ +{(i_1+i_2+i_3-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j}-\underset{j=1}{\overset{c-1}{\mathrm{\Σ}}}{I}_{3j}-\underset{q=1}{\overset{p}{\mathrm{\Σ}}}{I}_{q-1})}^2{R}_{q+1}+...\end{array}$

The wherein line loss P of i-th power branch _libe calculated as follows formula:

$P_{\mathrm{li}}=i_i^2{R}_{i1}+{(i_i-I_{i1})}^2{R}_{i2}+...+{(i_i-\underset{m=1}{\overset{q}{\mathrm{\Σ}}}{I}_{\mathrm{im}})}^2{R}_{i(q+1)}$

Wherein, P _lfor direct current micro-grid system line loss power, i _ibe the output current of i-th controllable voltage source, i=1,2 ..., n, n are the number of controllable voltage source, I _ijbe the jth load rating electric current on i-th controllable voltage source branch road, j=1,2 ..., m, m are the load number on this power branch, R _{i (q+1)}be the q+1 section transmission line impedance on i-th controllable voltage source branch road, q=1,2 ..., p, p are the transmission line segmentation number on this power branch; I _q-1for q-1 load rating electric current on trunk transmission line, R _qfor the q section transmission line impedance on trunk transmission line; A, b, c are respectively the load sum on the 1st, 2,3 controllable voltage source branch road.

The condition process of establishing of described optimal route loss power comprises:

Direct current micro-grid system line loss power P _lobtain minimum value then to need to meet: for i ₁, i ₂,

$\begin{array}{c}\frac{\∂P_l}{\∂i_1}=\frac{\∂p_{l1}}{\∂i_1}+2(i_1+i_2-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j})R_1+...+2(i_1+i_2-\underset{j=1}{\overset{a}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b}{\mathrm{\Σ}}}{I}_{2j}-\underset{k=1}{\overset{q}{\mathrm{\Σ}}}{I}_{q-1})R_q\\ +2(i_1+i_2+i_3-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j}-\underset{j=1}{\overset{c-1}{\mathrm{\Σ}}}{I}_{3j}-\underset{q=1}{\overset{p}{\mathrm{\Σ}}}{I}_{q-1})R_{q+1}+...=0\\ \frac{\∂P_l}{\∂i_2}=\frac{\∂P_{l2}}{\∂i_2}+2(i_1+i_2-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j})R_1+...+2(i_1+i_2-\underset{j=1}{\overset{a}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b}{\mathrm{\Σ}}}{I}_{2j}-\underset{k=1}{\overset{q}{\mathrm{\Σ}}}{I}_{q-1})R_q\\ +2(i_1+i_2+i_3-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j}-\underset{q=1}{\overset{c-1}{\mathrm{\Σ}}}{I}_{3j}-\underset{q=1}{\overset{p}{\mathrm{\Σ}}}{I}_{q-1})R_{q+1}+...=0\end{array}$

Draw $\frac{\∂P_{l1}}{\∂i_1}=\frac{\∂P_{l2}}{\∂i_2},$

Again because $U_1=U_{12}+\frac{\∂P_{l1}}{\∂i_1}$

$U_2=U_{12}+\frac{\∂P_{l2}}{\∂i_2}$

Then draw and work as P _lwhen obtaining minimum value, there is U ₁=U ₂; In like manner can obtain, work as P _lwhen obtaining minimum value, U ₁=U ₂=U ₃=...=U _n, wherein, P _l1, P _l2be respectively the line loss of the 1st, 2 article of power branch, i ₁, i ₂be respectively the output current of the 1st, 2 controllable voltage source, U ₁, U ₂be respectively the current voltage measured value of the 1st, 2 controllable voltage source, U _nbe the current voltage measured value of the n-th controllable voltage source, U ₁₂be the 2nd responsible operating voltage on the 1st controllable voltage source branch road.

The computing formula of described intercept common mode regulation amount is:

$\mathrm{\δ}{u}_{\mathrm{com}}^{*}={\mathrm{Gs}}_{\mathrm{com}}(U_{\mathrm{dc}}^{*}-u_{\mathrm{ave}})$

Wherein for intercept common mode regulation amount, Gs _comcommon mode regulation device, adopts PI to regulate. for the specified busbar voltage of direct current micro-grid system, u _avefor the mean value of each controllable voltage source busbar voltage, each converter voltage source droop control intercept common mode regulation amount is identical.

The computing formula of described intercept differential mode regulated quantity is:

$\mathrm{\δ}{u}_i^{*}=G{s}_{\mathrm{dif}}(u_{\mathrm{ave}}-u_i)$

Wherein Gs _diffor differential mode adjuster, PI is adopted to regulate.U _avefor the mean value of each controllable voltage source busbar voltage, u _ibe i-th controllable voltage source current voltage measured value, each converter voltage source droop control intercept differential mode regulated quantity is different.

The computing formula that described converter droop control parameter regulates is:

$U_i^{*}=U_0+\mathrm{\δ}{u}_{\mathrm{com}}^{*}+\mathrm{\δ}{u}_i^{*}-i_{i}k$

Wherein, be the output voltage of i-th controllable voltage source, U ₀for droop control intercept, for intercept common mode regulation amount, for intercept differential mode regulated quantity, i _ibe the output current of i-th controllable voltage source, i=1,2 ..., n, n are the number of controllable voltage source, and k is drop wire slope, and the drop wire slope of each converter of initial setting is identical, and remains unchanged in running.

The communication frequency passing to each converter under described low bandwidth communication system is level second.

The present invention has following advantage:

1, microgrid line loss reaches theoretical optimum: solving analysis result according to the calculating of direct-current micro-grid line loss with optimum loss can find out, controls according to institute's extracting method the theoretical minimum value that each power grid voltage can realize line loss.

2, do not rely on high-precision sensor: the step that the physical quantity not having size close in institute's extracting method implementation procedure is subtracted each other, therefore can not introduce because of sensor accuracy problem the deviation that cannot ignore.

3, each controller operand is little: due to described method do not relate to line loss identification calculate and each power supply, load output calculation, substantially reduce the calculation resources of each controller, be conducive to raising control frequency;

4, reliability is high: each converter of institute's extracting method still runs droop control, top level control center only provides the parameter regulated quantity of droop control, even if therefore communication system or top level control central fault, power supply in whole direct-current micro-grid still operates in droop control state, can not cause the problems such as power supply circulation.

Accompanying drawing explanation

Fig. 1 a is the direct-current micro-grid Secondary Control control method flow chart based on voltage stabilization.

Fig. 1 b is the direct-current micro-grid Secondary Control control method flow chart based on power supply current-sharing.

Fig. 2 is direct-current grid structure chart.

Fig. 3 is direct-current grid circuit theory reduced graph.

Fig. 4 is the direct-current micro-grid Secondary Control control method flow chart optimized based on line loss.

Fig. 5 is the circuit example direct-current grid structure chart that organon adopts.

Fig. 6 a is for institute's extracting method line loss is with line parameter circuit value situation of change schematic diagram.

Fig. 6 b is with line parameter circuit value situation of change schematic diagram based on the direct-current micro-grid Secondary Control control method of voltage stabilization.

Fig. 6 c is with line parameter circuit value situation of change schematic diagram based on the direct-current micro-grid Secondary Control control method of power supply current-sharing.

Fig. 7 a is for being intended to based on the direct-current micro-grid Secondary Control control method of voltage stabilization and institute's extracting method line loss differential.

Fig. 7 b is for being intended to based on the direct-current micro-grid Secondary Control control method of power supply current-sharing and institute's extracting method line loss differential.

Embodiment

Build a direct current micro-grid system, as shown in Figure 2, this system comprises multiple controllable voltage source, multiple current source or power source load, many transmission lines, multiple converter, low bandwidth communication system, top level control center; Wherein, top level control center is connected with each controllable voltage source by low bandwidth communication system, converter bottom control platform successively, and top level control center is connected with current source or power source load by low bandwidth communication system; Transmission line is divided into power branch and trunk transmission line, and together with multiple controllable voltage source is linked with current source or power source load by power branch, each bar power branch and multiple current source or power source load are linked together by trunk transmission line; Its reduced graph as shown in Figure 3.

In specific implementation process, be reduce Financial cost, low bandwidth communication system recommendations adopt bus form, as 485, CAN etc.Communication protocol suggestion participates in upper strata poll, the communication mode of bottom response.Owing to adopting the mode of poll one by one, if each converter returns the operation information of polled time, then in a communication cycle, in fact each transducer information that top level control center obtains is not synchronization.This will produce considerable influence to institute's extracting method.Therefore each converter storage running information is simultaneously adopted, then the communication mode uploaded one by one.Concrete implementing procedure is as follows:

After the q-1 time communication cycle completes, each converter before the order of latching operation information for receiving top level control center the q time, the control command passed down according to q-1 control centre exports converter carries out droop control, such as formula (1):

$U_i^{*}=U_0+\mathrm{\δ}{u}_{\mathrm{com}(q-1)}^{*}+\mathrm{\δ}{u}_{i(q-1)}^{*}-I_{i}k---\left(1\right)$

In a certain moment, the latches command that top level control center sends received by each converter simultaneously, and now all converters latch operation information output voltage u simultaneously _1q, u _2q..., u _nqwith output current i _1q, i _2q..., i _nq

Poll is carried out to each converter in top level control center, is returned its information u latched by the converter i of inquiry operation information of calling the roll _iqand i _iq

The calculating of the q time droop control regulated quantity is carried out at top level control center after the complete all converters of poll according to the operation information of feedback, specifically such as formula (2):

$u_{\mathrm{ave}\left(q\right)}=\frac{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{u}_{\mathrm{iq}}}{n}$

$\mathrm{\δ}{u}_{\mathrm{com}\left(q\right)}^{*}={\mathrm{Gs}}_{\mathrm{com}}(U_{\mathrm{dc}}^{*}-u_{\mathrm{ave}\left(q\right)})$

$\mathrm{\δ}{u}_{i\left(q\right)}^{*}=G{s}_{\mathrm{dif}}(U_{\mathrm{ave}\left(q\right)}-u_{\mathrm{iq}})---\left(2\right)$

The q time droop control regulated quantity that top level control center will calculate with send to each converter successively, converter is only preserved after receiving the q time droop control regulated quantity, does not regulate at once;

Top level control center under passed all converter kth time droop control regulated quantity after, send synchronized update order, all converters are unified in synchronization and upgrade droop control regulated quantity after receiving more newer command with then this process is repeated.

According to above-mentioned input active power controller amount calculation procedure, build the direct-current micro-grid Secondary Control optimized based on line loss and control as shown in Figure 4.

Fig. 5 is the circuit example that organon adopts.Wherein each parameter is as shown in table 1.

Table 1 example circuit parameter is chosen

Fig. 6 a-c and Fig. 7 a-b is droop control, sharing control compares with institute extracting method line loss.Wherein Fig. 6 a-c is the situation of change of line loss with line impedance and load of three kinds of methods.Be not difficult to find out that institute's extracting method obviously can reduce line impedance.The line loss that Fig. 7 a-b is other two kinds of methods in same parameter situation and institute's extracting method line impedance difference.Can find out, institute's extracting method line loss is always less than other line loss of two kinds, even can optimize loss about 50% under certain situation.

The above; be only the present invention's preferably embodiment, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (7)

1., based on the direct-current micro-grid Secondary Control control method that line loss is optimized, it is characterized in that, comprising:

Step 1, build a direct current micro-grid system, this system comprises multiple controllable voltage source, multiple current source or power source load, many transmission lines, multiple converter, low bandwidth communication system, top level control center; Wherein, top level control center is connected with each controllable voltage source by low bandwidth communication system, converter bottom control platform successively, and top level control center is connected with current source or power source load by low bandwidth communication system; Transmission line is divided into power branch and trunk transmission line, and together with multiple controllable voltage source is linked with current source or power source load by power branch, each bar power branch and multiple current source or power source load are linked together by trunk transmission line;

The operation of each converter and sample information are uploaded to top level control center by step 2, low bandwidth communication system;

Step 3, top level control center, according to the operation information that each converter transmits, calculate direct current micro-grid system line loss power;

Step 4, top level control center set up the condition of direct current micro-grid system optimal route loss power;

Step 5, top level control center calculation each controllable voltage source droop control intercept common and different mode regulated quantity;

Regulated quantity by passing to each converter under low bandwidth communication system, being regulated by droop control parameter and realizing the control of direct current micro-grid system Secondary Control by step 6, top level control center.

2. method according to claim 1, it is characterized in that, described calculating direct current micro-grid system line loss power comprises the loss power of each bar power branch and each bar trunk transmission line, and total formula is:

$\begin{array}{c}{P}_l=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{P}_{\mathrm{li}}+{(i_1+i_2-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j})}^2{R}_1+...+{(i_1+i_2-\underset{j=1}{\overset{a}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b}{\mathrm{\Σ}}}{I}_{2j}-\underset{k=1}{\overset{q}{\mathrm{\Σ}}}{I}_{q-1})}^2{R}_q\\ +{(i_1+i_2+i_3-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j}-\underset{j=1}{\overset{c-1}{\mathrm{\Σ}}}{I}_{3j}-\underset{q=1}{\overset{p}{\mathrm{\Σ}}}{I}_{q-1})}^2{R}_{q+1}+...\end{array}$

The wherein line loss P of i-th power branch _libe calculated as follows formula:

$P_{\mathrm{li}}=i_i^2{R}_{i1}+{(i_i-I_{i1})}^2{R}_{i2}+...+{(i_i-\underset{m=1}{\overset{q}{\mathrm{\Σ}}}{I}_{\mathrm{im}})}^2{R}_{i(q+1)}$

Wherein, P _lfor direct current micro-grid system line loss power, i _ibe the output current of i-th controllable voltage source, i=1,2 ..., n, n are the number of controllable voltage source, I _ijbe the jth load rating electric current on i-th controllable voltage source branch road, j=1,2 ..., m, m are the load number on this power branch, R _{i (q+1)}be the q+1 section transmission line impedance on i-th controllable voltage source branch road, q=1,2 ..., p, p are the transmission line segmentation number on this power branch; I _q-1for q-1 load rating electric current on trunk transmission line, R _qfor the q section transmission line impedance on trunk transmission line; A, b, c are respectively the load sum on the 1st, 2,3 controllable voltage source branch road.

3. method according to claim 1, it is characterized in that, the condition process of establishing of described optimal route loss power comprises:

Direct current micro-grid system line loss power P _lobtain minimum value then to need to meet: for i ₁, i ₂,

$\begin{array}{c}\frac{{\∂P}_l}{{\∂i}_1}=\frac{{\∂P}_{l1}}{{\∂i}_1}+2(i_1+i_2-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j})R_1+...+2(i_1+i_2-\underset{j=1}{\overset{a}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b}{\mathrm{\Σ}}}{I}_{2j}-\underset{k=1}{\overset{q}{\mathrm{\Σ}}}{I}_{q-1})R_q\\ +2(i_1+i_2+i_3-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j}-\underset{j=1}{\overset{c-1}{\mathrm{\Σ}}}{I}_{3j}-\underset{q=1}{\overset{p}{\mathrm{\Σ}}}{I}_{q-1})R_{q+1}+...=0\end{array}$

$\begin{array}{c}\frac{{\∂P}_l}{{\∂i}_2}=\frac{{\∂P}_{l2}}{{\∂i}_2}+2(i_1+i_2-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j})R_1+...+2(i_1+i_2-\underset{j=1}{\overset{a}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b}{\mathrm{\Σ}}}{I}_{2j}-\underset{k=1}{\overset{q}{\mathrm{\Σ}}}{I}_{q-1})R_q\\ +2(i_1+i_2+i_3-\underset{j=1}{\overset{a-1}{\mathrm{\Σ}}}{I}_{1j}-\underset{j=1}{\overset{b-1}{\mathrm{\Σ}}}{I}_{2j}-\underset{j=1}{\overset{c-1}{\mathrm{\Σ}}}{I}_{3j}-\underset{q=1}{\overset{p}{\mathrm{\Σ}}}{I}_{q-1})R_{q+1}+...=0\end{array}$

Draw $\frac{\∂P_{l1}}{{\∂i}_1}=\frac{{\∂P}_{l2}}{{\∂i}_2},$

Again because $U_1=U_{12}+\frac{{\∂P}_{l1}}{{\∂i}_1}$

$U_2=U_{12}+\frac{{\∂P}_{l2}}{{\∂i}_2}$

Then draw and work as P _lwhen obtaining minimum value, there is U ₁=U ₂; In like manner can obtain, work as P _lwhen obtaining minimum value, U ₁=U ₂=U ₃=...=U _n, wherein, P _l1, P _l2be respectively the line loss of the 1st, 2 article of power branch, i ₁, i ₂be respectively the output current of the 1st, 2 controllable voltage source, U ₁, U ₂be respectively the current voltage measured value of the 1st, 2 controllable voltage source, U _nbe the current voltage measured value of the n-th controllable voltage source, U ₁₂be the 2nd responsible operating voltage on the 1st controllable voltage source branch road.

4. method according to claim 1, it is characterized in that, the computing formula of described intercept common mode regulation amount is:

${\mathrm{\δu}}_{\mathrm{com}}^{*}={\mathrm{Gs}}_{\mathrm{com}}(U_{\mathrm{dc}}^{*}-u_{\mathrm{ave}})$

Wherein for intercept common mode regulation amount, Gs _comfor common mode regulation device, PI is adopted to regulate, for the specified busbar voltage of direct current micro-grid system, u _avefor the mean value of each controllable voltage source busbar voltage, each converter voltage source droop control intercept common mode regulation amount is identical.

5. method according to claim 1, it is characterized in that, the computing formula of described intercept differential mode regulated quantity is:

${\mathrm{\δu}}_i^{*}={\mathrm{Gs}}_{\mathrm{dif}}(u_{\mathrm{ave}}-u_i)$

Wherein Gs _difdifferential mode adjuster, adopts PI to regulate, u _avefor the mean value of each controllable voltage source busbar voltage, u _ibe i-th controllable voltage source current voltage measured value, each converter voltage source droop control intercept differential mode regulated quantity is different.

6. method according to claim 1, is characterized in that, the computing formula that described converter droop control parameter regulates is:

$U_i^{*}=U_0+{\mathrm{\δu}}_{\mathrm{com}}^{*}+{\mathrm{\δu}}_i^{*}-i_{i}k$

Wherein, be the output voltage of i-th controllable voltage source, U ₀for droop control intercept, for intercept common mode regulation amount, for intercept differential mode regulated quantity, i _ibe the output current of i-th controllable voltage source, i=1,2 ..., n, n are the number of controllable voltage source, and k is drop wire slope, and the drop wire slope of each converter of initial setting is identical, and remains unchanged in running.

7. method according to claim 1, it is characterized in that, the communication frequency passing to each converter under described low bandwidth communication system is level second.