CN105048445A - Method for three phase state estimation in active distribution system taking multiple types of distributed generators (DG) into consideration - Google Patents

Abstract

The invention provides a method for three phase state estimation in an active distribution system taking multiple types of distributed generators (DG) into consideration. The method comprises the steps of: adding pseudo-measurements to the state variable in DG and boundary regions, which guarantees observability in each subregion of the active distribution system; establishing a DG grid connected three-phase model, which enables an accurate estimation of the real-time operation status of the DG and an AC node; selecting a Weighted Least Squares (WLS) estimator, which has efficiency higher calculation efficiency and convergence performance. The method provides guarantees for stability analysis of a smart power distribution system and application of advanced software, and has excellent potential in engineering application.

Description

Take into account the active distribution network three-phase state method of estimation of polymorphic type distributed power source

Technical field

The present invention relates to a kind of active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source, belong to distribution system analysis control field.

Background technology

Along with a large amount of accesses of distributed power source (distributedgenerator, DG), traditional passive power distribution network just progressively changes the active distribution network (activedistributionsystem, ADS) containing polymorphic type DG into.Meanwhile, for ensureing the application of intelligent distribution system high-level software, active distribution network state estimation is an indispensable part.In addition, due to the asymmetry of load, line parameter circuit value, power distribution network is generally asymmetrical three-phase, and the three-phase state thus studying active distribution network is estimated more to be of practical significance.

The research that conventional electrical distribution net state is estimated mainly comprises three aspects: 1) the choosing of state variable, except basic take node voltage as state variable, also can choose branch current, branch power is state variable, to improve state estimation efficiency, to reduce state estimation to the sensitiveness of line parameter circuit value; 2) suitable state estimator is chosen, Robust filter is applied at power distribution network by document, the literature research selection of state of electric distribution network estimator, and sum up for measuring the lower power distribution network of redundancy, it is the most rational estimator that weighted least-squares (weightedleastsquares, WLS) is estimated; 3) allocation optimum measured, on the basis ensureing system Observable and economy, the configuration of measurement should improve precision and the robustness of state estimation as far as possible.

Estimate compared to conventional electrical distribution net state, the maximum difference of active distribution network state estimation is the modeling to DG.The existing modeling method to DG mainly can be divided into 2 classes: 1) DG is regarded as general PQ and inject node, do not set up the physical model that DG is detailed.2) for the DG not configuring real-time measurement, according to the three-phase gross capability of historical data, real-time weather prediction DG, and suppose that DG three-phase injecting power is equal, obtain the pseudo-measuring value of DG each phase injecting power, although this process simplify the estimation of three-phase DG, but because the three-phase injecting power of DG under actual conditions is necessarily asymmetric, therefore the method is accurate not.

The distributed three-phase state of active distribution network that the present invention have studied based on WLS is estimated.First, establish the triphase flow that DG is grid-connected, be divided into two classes by grid-connected for DG: be direct grid-connected, grid-connected through pulse-width modulation (pulsewidthmodulation, PWM) converter.Be unpractical owing to configuring real-time measurement to all DG, for the DG not configuring real-time measurement, propose a kind of feasible program measured according to the interpolation puppet of Weather information or PWM control strategy.By adding pseudo-measurement to DG, adjacent boundary region, ensure that the observation of all subregion well.Finally, the test of example of calculation shows that context of methods have estimated DG exactly, exchanges the real-time running state of node.

Summary of the invention

Goal of the invention: the present invention proposes a kind of active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source, have estimated DG exactly, exchanges the real-time running state of node.

Technical scheme: the technical solution used in the present invention is a kind of active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source, comprises the following steps:

Obtain power distribution network and DG and the measurement amount of site, topological sum parameter information;

In power distribution network zero injects Joint Enterprise virtual measurement, and DG site arrange and pseudo-ly measure z _dG, the node sets puppet not configuring intelligent electric meter measures, all the other node sets real-time measurements;

Definition AC extended mode variable x _aC:

x _AC＝[xE ₀δ ₀] ^T

E ₀for single-phase voltage amplitude, δ ₀for single-phase voltage phase angle;

For the DG of direct grid-connected, its pseudo-measurement z _dG=[P ₀q ₀], wherein P ₀for exporting three-phase always meritorious process, Q ₀exert oneself for three-phase is always idle; Lower z is controlled for through the grid-connected DG of PWM, P-Q _dG=[P _inq _in], Udc-Q controls lower z _dG=[P ₀q _in];

Adopt weighted least-squares method as the target function of state estimation;

With Newton method linearizing non-linear measurement equation and iterative state variable x _aC;

Judge whether to reach convergence threshold, be, terminate AC iteration, otherwise continue iterative until convergence.

Preferably, the DG of described direct grid-connected, it exports the three-phase always meritorious P that exerts oneself ₀can obtain according to historical data, real-time weather information prediction, three-phase is the idle Q that exerts oneself always ₀can be obtained according to estimation by exert oneself P-Q curve or DG power factor (PF) of DG, direct grid-connected DG puppet measures and can be expressed as:

z _DG＝[P ₀Q ₀]

The non-linear relation that DG puppet measures between quantity of state can be expressed as:

In formula for DG export meritorious, reactive power mutually; for the grid-connected point voltage amplitude of phase DG and phase angle; G=r/ (r ²+ x ²), b=-x/ (r ²+ x ²).

Preferably, the DG adopting P-Q to control in the described DG grid-connected through PWM, its pseudo-measurement z _dGfor:

z _DG＝[P _inQ _in]

In formula, control PWM AC injects total active-power P _in, reactive power Q _infor definite value, DG puppet measures z _dGand the non-linear relation between quantity of state can be expressed as:

Preferably, U is adopted in the described DG grid-connected through PWM _dcthe DG that-Q controls, and meet:

P _DC＝f(U _DC)

As shown in Figure 2

Control PWM DC voltage U in formula _dC, AC inject reactive power Q _infor definite value, be illustrated in figure 3 PWM DC side power, f (g) describes the non-linear relation between DC voltage, power, P ₀for PWM AC power;

Pseudo-measurement is:

z _DG＝[P ₀Q _in]

The pseudo-non-linear relation measured between AC quantity of state can be expressed as:

Preferably, the optimization aim that described WLS estimates is:

$x=\underset{x}{\arg \min }{(z-h\left(x\right))}^T{R}^{-1}(z-h\left(\text{x}\right))$

In formula: for measurement amount; for state variable; for measuring weight matrix; H () describe z and between non-linear relation.

Preferably, in described Newton method linearizing non-linear measurement equation, the update equation of WLS iterative is:

$\left\{\begin{array}{c}{\mathrm{\Δx}}^{\left(k\right)}={\left[H^T\left(x^{\left(k\right)}\right)\mathrm{WH}\left(x^{\left(k\right)}\right)\right]}^{-1}{H}^T\left(x^{\left(k\right)}\right)W(z-h\left(x^{\left(k\right)}\right))\\ x^{(k+1)}=x^{\left(k\right)}+{\mathrm{\Δx}}^{\left(k\right)}\end{array}\right...$

Preferably, in described Newton method linearizing non-linear measurement equation, the threshold of iteration convergence is:

||x ^k+1-x ^k|| _∞＜ε

In formula: ε convergence precision, generally get ε=10 ^-4: 10 ^-6.

Preferably, described convergence precision ε=10 ^-4: 10 ^-6.

Preferably, described following formula solves PWM DC side running status:

P _DC＝f(U _DC)

P ₀＝P _DC

E ₀＝k ₀MU _DC

In formula: $k_0=\sqrt{3}/\left(2\sqrt{2}\right).$

Beneficial effect: the present invention proposes a kind of active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source, possesses following features: 1) by adding pseudo-measurement to DG, borderline region quantity of state, ensure that the observability of active distribution network all subregion; 2) establish the triphase flow that DG is grid-connected, accurately estimate the real-time running state of DG and interchange node; 3) choose WLS estimator, have higher computational efficiency and constringency performance.Thus the present invention provides guarantee for the steady-state analysis of intelligent distribution system, the application of high-level software, has engineering background well.

Accompanying drawing explanation

Fig. 1 is the inventive method flow chart;

Fig. 2 is direct grid-connected DG triphase flow;

Fig. 3 is the triphase flow through the grid-connected DG of PWM;

Fig. 4 is measure configuration and the topology of test example.

Embodiment

Below in conjunction with the drawings and specific embodiments, illustrate the present invention further, these embodiments should be understood only be not used in for illustration of the present invention and limit the scope of the invention, after having read the present invention, the amendment of those skilled in the art to various equivalents of the present invention has all fallen within the application's claims limited range.

As shown in Figure 1, the present invention includes following steps:

1, power distribution network WLS estimates

It is solve following optimization problem in essence that WLS estimates:

$x=\underset{x}{\arg \min }{(z-h\left(x\right))}^T{R}^{-1}(z-h\left(\text{x}\right))$

In formula: for measurement amount; for state variable; for measuring weight matrix; H () describe z and between non-linear relation; The observable necessary condition of system is: m > n.

Choose three-phase voltage amplitude U herein _abc, phase angle δ _abcfor state variable (root node voltage is considered as definite value), then there is x=[U _abcδ _abc] ^t.Power distribution network measures and generally comprises polytype: load power measures, branch current magnitudes measures, branch power measures, node voltage amplitude measures.For ease of the Analysis on Observability of power distribution network, defined amount is measured z and is made up of two parts:

z＝[z ₁z ₂] ^T

In formula: z ₁for three-phase load power measurement, z ₂for the set that branch current magnitudes measures, branch power measures, node voltage amplitude measures.

Wherein, z ₂be generally real-time measurement, z ₁comprise three types:

1) virtual measurement.Inject node for zero in networking, configurable virtual measurement, virtual measurement is actual true value, and thus its accuracy in measurement is very high, can give large weight;

2) pseudo-measurement.Pseudo-measurement, generally according to the historical data of load, is obtained by the method for prediction, although pseudo-measurement precision is lower, ensure that the observability of power distribution network;

3) real-time measurement.Compared to existing power distributing amount examining system, the maximum lifting of intelligent distribution network measurement system is the application of intelligent electric meter (smartmeters, SMs).Intelligent electric meter provides the real-time measurement of feeder line, secondary substation load power, even if the Measurement different step that SMs provides, its precision also measures apparently higher than traditional load puppet.

For traditional power distribution network, by configuring the measurement of above-mentioned three types, the load power obtaining all nodes (except root node) measures z ₁, then have:

$\dim \left(z_1^T\right)=\dim \left(x\right)$

In formula: dim () is the dimension of vector.

Z is measured according to load power ₁, by Load flow calculation, the real-time running state x of distribution network can be solved to obtain.Also there is the measurement of other type in general networking, then have:

dim(z)＞dim(x)

Now there is redundancy in system, can estimate according to WLS, obtains the optimal estimation value of x.

State estimation belongs to nonlinear optimal problem in essence, and after trying to achieve its First Order Optimality Condition, with Newton method linearisation measurement equation, then the state of electric distribution network based on WLS is estimated by following form iterative:

$\left\{\begin{array}{c}{\mathrm{\Δx}}^{\left(l\right)}={\left[H^T\left(x^{\left(l\right)}\right)\mathrm{WH}\left(x^{\left(l\right)}\right)\right]}^{-1}{H}^T\left(x^{\left(l\right)}\right)W(z-h\left(x^{\left(l\right)}\right))\\ x^{(l+1)}=x^{\left(l\right)}+{\mathrm{\Δx}}^{\left(l\right)}\end{array}\right..$

In formula: H is Jacobian matrix; L is iterations.

The grid-connected modeling of 2 three-phase DG

DG accesses in ADS generally two kinds of forms: 1) direct grid-connected (comprising synchronous, asynchronous wind driven generator); 2) through power electronics converter grid-connected (comprising photovoltaic, fuel cell, miniature gas turbine etc.), wherein voltage-source type PWM converter is most widely used power electronics converter, and DG through the grid-connected equivalent electric circuit of PWM as shown in Figure 3.

Generally speaking, blower fan, PWM converter port voltage three-phase symmetrical, thus its three-phase voltage can by single-phase variable E ₀, δ ₀represent; And the actual general asymmetrical three-phase of grid-connected side distribution network voltage that exchanges, thus its state variable needs to represent U with three-phase variable _abc, δ _abc.After DG accesses asymmetrical three-phase power distribution network, definition AC extended mode variable x _aC:

x _AC＝[xE ₀δ ₀] ^T

X _aCtake into account DG state variable E ₀, δ ₀if DG site does not configure real-time measurement, traditional measurement z is difficult to the observability of guarantee system.Hereafter will describe direct grid-connected respectively, add the pseudo-method measured through the DG that PWM is grid-connected.

The grid-connected interpolation puppet of 3 three-phase DG measures

The puppet of adding DG is measured and is defined as z _dG, exchange propagation survey and be defined as z _aC=[zz _dG] ^t.Compared to x, x _aCtake into account variable E ₀, δ ₀, thus DG grid-connected side puppet measurement number can not be less than unknown quantity number, i.e. z _dGneed satisfy condition:

dim(z _DG)≥dim([E ₀δ ₀])

Under the condition that above formula is set up, the grid-connected side of DG is observable, and the conventional electrical distribution net simultaneously taking no account of DG is also observable, and thus active distribution network is observable, namely meets:

dim(z _AC)＞dim(x _AC)

For direct grid-connected, through the grid-connected DG of PWM, its pseudo-measurement z _dGcan obtain respectively by with under type:

1) DG direct grid-connected

Such as, for the DG of direct grid-connected, wind-driven generator, it exports the three-phase always meritorious P that exerts oneself ₀can obtain according to historical data, real-time weather information prediction, three-phase is the idle Q that exerts oneself always ₀p-Q curve or DG power factor (PF) can be exerted oneself according to P by DG ₀estimation obtains, and thus direct grid-connected DG puppet measures z _dGcan be expressed as:

z _DG＝[P ₀Q ₀]

Measuring similar to load puppet, measuring z by predicting that the DG obtained exerts oneself _dGprecision is lower, need arrange less measurement weight.

The non-linear relation that the DG puppet of direct grid-connected measures between quantity of state can be expressed as:

In formula: for DG export meritorious, reactive power mutually; for the grid-connected point voltage amplitude of phase DG and phase angle; G=r/ (r ²+ x ²), b=-x/ (r ²+ x ²).

2) DG is grid-connected through PWM

The DG grid-connected through PWM can adopt different control strategies, and PWM can control AC and DC side quantity of state.Owing to controlling each single-phase power of AC, voltage relative difficult, the integrated value (such as three-phase gross power, positive sequence voltage) of PWM general control AC three-phase state amount.The puppet that the quantity of state that PWM controls can be used as DG measures.Consider two kinds of PWM control strategies herein:

1. P-Q controls, and namely controls AC and injects gross power P _in, Q _infor definite value, now pseudo-measurement z _dGcan choose:

z _DG＝[P _inQ _in]

And the non-linear relation that DG puppet measures between quantity of state can be expressed as:

2. Udc-Q controls, and namely controls DC voltage U _dC, AC inject reactive power Q _infor definite value.Work as U _dCtime known,

According to DC side power flow equation, DC side power P can be obtained _dC(now P _dChave nothing to do with AC running status):

P _DC＝f(U _DC)

In formula: f () describes the non-linear relation between DC voltage, power.

In addition, PWM Converter DC-side and AC need meet power, voltage retrains:

P ₀＝P _DC

E ₀＝k ₀MU _DC

In formula: $k_0=\sqrt{3}/\left(2\sqrt{2}\right).$

According to above formula, can by definite value U _dCbe converted into PWM and export meritorious P ₀, thus U _dcz under-Q control strategy _dGcan choose:

z _DG＝[P ₀Q _in]

The pseudo-non-linear relation measured between AC quantity of state can be expressed as:

Especially, for through the grid-connected DG of PWM, E is estimated to obtain by WLS ₀, P ₀after, PWM, DC side quantity of state M, U can be solved according to following formula _dC, P _dC.

P _DC＝f(U _DC)

E ₀＝k ₀MU _DC

4 sample calculation analysis

Shown in test example Fig. 4 herein.In Fig. 4, access DG respectively at the node 632,680,692 of IEEE13 node system, obtain active distribution network example ADS13 node system; The grid-connected type of all DG and pseudo-measurement are see table 1.Measuring value adds the random noise of Gaussian distributed on the basis of trend true value, compared to trend true value, measuring value worst error is respectively: 1.5% (voltage magnitude, branch current magnitudes, power measurement), 3% (real-time measurement that SMs provides), 40% (according to historical data, the load power of real-time weather prediction, the exerting oneself of direct grid-connected DG).

Table 1DG grid-connect mode and pseudo-measurement are arranged

For verifying the validity of the inventive method, table 2 gives and must compare based on the inventive method, conventional method (supposing that DG three-phase injecting power is equal) the grid-connected point voltage estimated value of DG.Table 2 is known, and based on DG model in this paper, the estimated accuracy of DG three-phase voltage quantity of state is obviously higher.DG three-phase injecting power is symmetrical due to existing DG model assumption, and the disequilibrium of DG three-phase injecting power is more serious, and DG injecting power evaluated error is larger, and then have impact on the estimated accuracy of the whole network quantity of state.Thus compared to existing DG model, more accurate to the modeling of DG herein, more can react the real time execution characteristic of DG.

Table 2 the inventive method, conventional method compare the grid-connected point voltage estimated value of DG

Claims (9)

1. take into account an active distribution network three-phase state method of estimation for polymorphic type distributed power source, it is characterized in that,

Comprise the following steps:

Obtain power distribution network and DG and the measurement amount of site, topological sum parameter information;

In power distribution network zero injects Joint Enterprise virtual measurement, and DG site arrange and pseudo-ly measure z _dG, the node sets puppet not configuring intelligent electric meter measures, all the other node sets real-time measurements;

Definition AC extended mode variable x _aC:

x _AC＝[xE ₀δ ₀] ^T

E ₀for single-phase voltage amplitude, δ ₀for single-phase voltage phase angle;

For the DG of direct grid-connected, its pseudo-measurement z _dG=[P ₀q ₀], wherein P ₀for exporting three-phase always meritorious process, Q ₀exert oneself for three-phase is always idle; Lower z is controlled for through the grid-connected DG of PWM, P-Q _dG=[P _inq _in], Udc-Q controls lower z _dG=[P ₀q _in];

Adopt weighted least-squares method as the target function of state estimation;

With Newton method linearizing non-linear measurement equation and iterative state variable x _aC;

Judge whether to reach convergence threshold, be, terminate AC iteration, otherwise continue iterative until convergence.

2. the active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source according to claim 1, is characterized in that, the DG of described direct grid-connected, and it exports the three-phase always meritorious P that exerts oneself ₀can obtain according to historical data, real-time weather information prediction, three-phase is the idle Q that exerts oneself always ₀can be obtained according to estimation by exert oneself P-Q curve or DG power factor (PF) of DG, direct grid-connected DG puppet measures and can be expressed as:

z _DG＝[P ₀Q ₀]

The non-linear relation that DG puppet measures between quantity of state can be expressed as:

In formula for DG export meritorious, reactive power mutually; for

the grid-connected point voltage amplitude of phase DG and phase angle; G=r/ (r ²+ x ²), b=-x/ (r ²+ x ²).

3. the active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source according to claim 1, is characterized in that, the DG adopting P-Q to control in the described DG grid-connected through PWM, its pseudo-measurement z _dGfor:

z _DG＝[P _inQ _in]

In formula, control PWM AC injects total active-power P _in, reactive power Q _infor definite value, DG puppet measures z _dGand the non-linear relation between quantity of state can be expressed as:

。

4. the active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source according to claim 1, is characterized in that, the DG adopting Udc-Q to control in the described DG grid-connected through PWM, and meets:

P _DC＝f(U _DC)

As shown in Figure 2

Control PWM DC voltage U in formula _dC, AC inject reactive power Q _infor definite value, be illustrated in figure 3 PWM DC side power, f (g) describes the non-linear relation between DC voltage, power, P ₀for PWM AC power;

Pseudo-measurement is:

z _DG＝[P ₀Q _in]

The pseudo-non-linear relation measured between AC quantity of state can be expressed as:

5. the active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source according to claim 1, is characterized in that, the optimization aim that described WLS estimates is:

In formula: for measurement amount; for state variable; for measuring weight matrix; H () describe z and between non-linear relation.

6. the active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source according to claim 1, is characterized in that, in described Newton method linearizing non-linear measurement equation, the update equation of WLS iterative is:

7. the active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source according to claim 1, is characterized in that, in described Newton method linearizing non-linear measurement equation, the threshold of iteration convergence is:

||x ^k+1-x ^k|| _∞＜ε

In formula: ε convergence precision, generally get ε=10 ^-4: 10 ^-6.

8. the active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source according to claim 7, is characterized in that, described convergence precision ε=10 ^-4: 10 ^-6.

9. the active distribution network three-phase state method of estimation taking into account polymorphic type distributed power source according to claim 4, it is characterized in that, described following formula solves PWM DC side running status:

P _DC＝f(U _DC)

P ₀＝P _DC

E ₀＝k ₀MU _DC

In formula: