CN103698629B - A kind of real-time online Forecasting Methodology of direct current micro grid characteristic parameter - Google Patents

Abstract

The invention discloses the real-time online Forecasting Methodology of a kind of direct current micro grid characteristic parameter, comprise the following steps: 1), Real-time Collection direct current micro grid system one is by the current perturbation value I of disturbance node_k, sampling time interval is T_s；According to the current perturbation value I gathered_k, construct current perturbation value array ARRAY [I₁、I₂、I₃、I₄、I₅]；2), the Four order difference derivative of current value in real-time calculation perturbation current value array ARRAY: if first-order difference derivative f⁽¹⁾More than ε, then judge that direct current micro grid system enters transient process；If all-order derivative is respectively less than default small quantity ε, then judge that direct current micro grid system is steady, continue to gather subsequent time current value, and continue to calculate the Four order difference derivative of subsequent time current value, compared with prior art, the inventive method has better real-time and simplicity, it is possible to suitable in the suppression of transient state dash current, parameter of electric machine on-line testing, on-line fault diagnosis, low frequency power oscillation the numerous areas such as on-line checking and suppression.

Description

A kind of real-time online Forecasting Methodology of direct current micro grid characteristic parameter

Technical field

The invention belongs to the quality of power supply and signal analysis and processing research field, be specifically related to the real-time online Forecasting Methodology of a kind of direct current micro grid characteristic parameter.

Background technology

Micro power network is the most effective measure realizing new forms of energy Distributed Application, is also the main contents of following interactive intelligent electrical network.Wind-powered electricity generation, photovoltaic, fuel cell distributed energy integration are got up by this system by substantial amounts of power electronics interface circuit; with energy storage devices such as accumulator, super capacitor and high speed flywheels for power adjustments means; under the coordinative role of micro power network central control system, dcs and protection device, provide cleaning, lasting, interactively electric energy by miniature local supply network for local load.

By analyzing the system structure of micro power network, networking mode, operational mode, control strategy it can be seen that it has following key property: 1, containing diversified intermittent energy, be inevitably present persistence, randomness external input sources disturbance.2, in micro power network, the characteristic of load is various, form is changeable, and the characteristic parameter that load variations substantial amounts of, randomness result in network constantly changes.3, the type of each assembly varies, the converters of existing current mode, also has the current transformer of voltage-type；The load of existing capacitance-resistance, also has the load of resistance sense；The device of existing silent oscillation, also has the equipment of motor type.4, operational mode is various, both can run on grid-connect mode, it is possible to be operated in island mode.5, typical multi-scale coupling system, the converters of existing little inertia, also there is the rotating machinery of big inertia；Existing lower-powered energy storage device, also has the major network system that capacity is huge；The energy exchange of existing power frequency rank, also has the oscillation of power of switching frequency rank.

These characteristics determines the complexity of micro power network stability analysis.Existing stability study is nearly all based on certain network determined and the control strategy adopting certain concrete.But based on the accuracy of the analysis method heavy dependence systematic parameter of mathematical model and model, therefore theoretical analysis result may have bigger deviation with practical situation.The more important thing is, micro power network system always constantly suffer from the disturbance of substantial amounts of randomness, and therefore and constantly the characteristic parameter of its control strategy, mode of operation and structure also changes.Therefore, in the micro power network system under disturbed conditions, the method for analyzing stability based on parameter and model has significant limitation, existing achievement in research to be difficult to meet the needs of micro power network stability on-line analysis.

Summary of the invention

For drawbacks described above or deficiency, it is provided that the real-time online processing method of a kind of direct current micro grid characteristic parameter, it is possible to the state according to real-time measurement system.

For reaching object above, the technical scheme is that

Comprise the following steps:

1), Real-time Collection direct current micro grid system one is by the current perturbation value I of disturbance node_k, sampling time interval is T_s；According to the current perturbation value I gathered_k, construct current perturbation value array ARRAY [I₁、I₂、I₃、I₄、I₅], and in current perturbation value array ARRAY, each element initial value is 0, often gathers a point, makes I₅=I_k；I₄=I₅；I₃=I₄；I₂=I₃；I₁=I₂；

2), the Four order difference derivative of current value in real-time calculation perturbation current value array ARRAY: if first-order difference derivative f⁽¹⁾More than ε, then judge that direct current micro grid system enters transient process；If all-order derivative is respectively less than default small quantity ε, then judge that direct current micro grid system is steady, continue to gather subsequent time current value, and continue to calculate the Four order difference derivative of subsequent time current value, wherein, the Four order difference derivative respectively f of current value in described current perturbation value array ARRAY⁽¹⁾、f⁽²⁾、f⁽³⁾、f⁽⁴⁾:

$f^{\left(1\right)}=\frac{I_5-I_4}{T_s}$

$f^{\left(2\right)}=\frac{I_5-{2I}_4+I_3}{{\left(T_s\right)}^2}$

$f^{\left(3\right)}=\frac{I_5-{3I}_4+{3I}_3-I_2}{{\left(T_s\right)}^3}$

$f^{\left(4\right)}=\frac{I_5-{4I}_4+{6I}_3-{4I}_2+I_1}{{\left(T_s\right)}^4};$

3), as first-order difference derivative f⁽¹⁾More than ε, then continuing to gather subsequent time current value, calculate subsequent time current value one arrives Four order difference derivative, calculates intermediate variable a, b, c:

$\left\{\begin{array}{c}a=f^{\left(1\right)}{f}^{\left(2\right)}-f^{\left(1\right)}{f}^{\left(3\right)}\\ b=f^{\left(2\right)}{f}^{\left(3\right)}-f^{\left(1\right)}-f^{\left(4\right)}\\ c=f^{\left(3\right)}{f}^{\left(3\right)}-f^{\left(2\right)}{f}^{\left(4\right)}\end{array}\right.$

(1) if result of calculation a=0, then judging that the transient process of direct current micro grid system is as steady dead-beat transient process, and transient process is only containing a primary modal, the time domain specification of described primary modal is exponential law change；

(2) if result of calculation a ≠ 0, then the discriminant Δ=b of transient process type is calculated²-4ac:

(2.1) if Δ > 0, then judge that the transient process of direct current micro grid system is as steady dead-beat transient process, and steady dead-beat transient process contain two primary modal, the time domain specification of two master modes is exponential law change；

(2.2) if Δ < 0, then the transient process of judgement direct current micro grid system is change in oscillation transient process, and described change in oscillation transient process contains a main Oscillatory mode shape, the time domain specification of Oscillatory mode shape is mechanical periodicity, and oscillation amplitude exponentially changes.

In (1) in step 3), the attenuation quotient σ of the characteristic parameter index mode of steady dead-beat transient process containing a primary modal characterizes, and its computing formula is as follows:

$\mathrm{\&sigma;}=-\frac{f^{\left(2\right)}}{f^{\left(1\right)}}.$

Steady dead-beat transient process containing a primary modal terminate after stabling current value i_A:

$i_A=I_5-\frac{{\left(f^{\left(1\right)}\right)}^2}{f^{\left(2\right)}}.$

(2.1) characteristic parameter attenuation quotient ρ, μ of the steady dead-beat transient process containing two primary modal in represent, attenuation quotient ρ, μ computing formula is as follows:

$\left\{\begin{array}{c}\mathrm{\&rho;}=\frac{\sqrt{b^2-4\mathrm{ac}}-b}{2a}\\ \mathrm{\&mu;}=\frac{\sqrt[-]{b^2-4\mathrm{ac}}-b}{2a}\end{array}\right.$

If ρ > 0 and μ > 0, judge the convergence of direct current micro grid system transient modelling process；

Otherwise, it is determined that the transient process of system is dispersed, cause system unstability the most at last.

If ρ > 0 and μ > 0; judge direct current micro grid system transient modelling process convergence, and transient process terminate after stabling current be i_B, i_BComputing formula as follows:

$i_B=\frac{{\mathrm{\&rho;\&mu;I}}_5+(\mathrm{\&mu;}+\mathrm{\&rho;})f^{\left(1\right)}+f^{\left(2\right)}}{\mathrm{\&rho;\&mu;}}.$

(2.2) in the characteristic parameter of change in oscillation transient process be cycle of oscillation ω and its computing formula of attenuation quotient λ as follows:

$\left\{\begin{array}{c}\mathrm{\&omega;}=\frac{\sqrt{4\mathrm{ac}-b^2}}{2a}\\ \mathrm{\&lambda;}=\frac{b}{2a}.\end{array}\right.$

When Δ<when 0, and λ>0, then can determine that the transient process of system restrains, the transient process of convergence terminate after stabling current be i_C:

$i_C=I_5+\frac{f^{\left(1\right)}{f}^{\left(1\right)}{f}^{\left(4\right)}-{2f}^{\left(1\right)}{f}^{\left(2\right)}{f}^{\left(3\right)}+f^{\left(2\right)}{f}^{\left(2\right)}{f}^{\left(2\right)}}{f^{\left(3\right)}{f}^{\left(3\right)}-f^{\left(2\right)}{f}^{\left(4\right)}}.$

Compared with the prior art, the invention have the benefit that

The present invention adopts the transient current of a certain disturbed node in detection direct current micro grid, the current flow configuration detected in real time is become current perturbation, then pass through and real-time current perturbation value array is calculated, realize the real-time online of direct current micro grid is predicted, the real-time status of acquisition system, and then achieve the separation of transient state composition and stationary component；Compared with prior art, the inventive method has better real-time and simplicity, it is possible to suitable in the suppression of transient state dash current, parameter of electric machine on-line testing, on-line fault diagnosis, low frequency power oscillation the numerous areas such as on-line checking and suppression.

Further, the present invention according to the transient current measured in real time, can calculate the situation of change of the local feature parameter of micro power network system, thus the system that dopes stands characteristic value and the stability of the transient response process after disturbance quickly and accurately.And then, the control system of micro power network can according to the disturbing influence rule doped, determine strategy and the control instruction of disturbance suppression, within the shortest time of vibration harm early period of origination, judging signal component rapidly, line number of going forward side by side separates, and carries out the work such as process in real time, online for follow-up attachment device, Informational support is provided, and then reduces the loss of power and the harm to electrical network.

Accompanying drawing explanation

Fig. 1 is the real-time online Forecasting Methodology of the direct current micro grid characteristic parameter of the present invention；

Fig. 2 is the direct current micro grid system structure schematic diagram of the present invention；

Fig. 3 is the phantom figure of the direct current micro grid of the present invention；

Fig. 4 is the prediction oscillogram of the load current of the present invention.

Detailed description of the invention:

Below in conjunction with accompanying drawing, the present invention is described in detail.

As it is shown in figure 1, the invention provides the real-time online Forecasting Methodology of a kind of direct current micro grid characteristic parameter, comprise the following steps:

1), Real-time Collection direct current micro grid system one is by the current perturbation value I of disturbance node_k, sampling time interval is T_s=0.01s；According to the current perturbation value I gathered_k, construct current perturbation value array ARRAY [I₁、I₂、I₃、I₄、I₅], and in current perturbation value array ARRAY, each element initial value is 0, often gathers a point, makes I₅=I_k；I₄=I₅；I₃=I₄；I₂=I₃；I₁=I₂；

2), the Four order difference derivative of current value in real-time calculation perturbation current value array ARRAY: if first-order difference derivative f⁽¹⁾More than ε, then judge that direct current micro grid system enters transient process；If all-order derivative is respectively less than default small quantity ε, then judge that direct current micro grid system is steady, continue to gather subsequent time current value, and continue to calculate the Four order difference derivative of subsequent time current value, wherein, the Four order difference derivative respectively f of current value in described current perturbation value array ARRAY⁽¹⁾、f⁽²⁾、f⁽³⁾、f⁽⁴⁾:

$f^{\left(1\right)}=\frac{I_5-I_4}{T_s}$

$f^{\left(2\right)}=\frac{I_5-{2I}_4+I_3}{{\left(T_s\right)}^2}$

$f^{\left(3\right)}=\frac{I_5-{3I}_4+{3I}_3-I_2}{{\left(T_s\right)}^3}$

$f^{\left(4\right)}=\frac{I_5-{4I}_4+{6I}_3-{4I}_2+I_1}{{\left(T_s\right)}^4};$

Wherein, small quantity ε takes ε=0.001 after considering the combined factors such as computational accuracy requirement and measurement error.

3) judge that direct current micro grid system enters the particular state of transient process:

If first-order difference derivative f⁽¹⁾More than ε, then, after judging that direct current micro grid system enters transient process, also include:

Continuing to gather subsequent time current value, calculate subsequent time current value one arrives Four order difference derivative, calculates intermediate variable a, b, c:

$\left\{\begin{array}{c}a=f^{\left(1\right)}{f}^{\left(2\right)}-f^{\left(1\right)}{f}^{\left(3\right)}\\ b=f^{\left(2\right)}{f}^{\left(3\right)}-f^{\left(1\right)}-f^{\left(4\right)}\\ c=f^{\left(3\right)}{f}^{\left(3\right)}-f^{\left(2\right)}{f}^{\left(4\right)}\end{array}\right.$

(1) if result of calculation a=0, then judging that the transient process of direct current micro grid system is as steady dead-beat transient process, and transient process is only containing a primary modal, the time domain specification of described primary modal is exponential law change；The attenuation quotient λ of the characteristic parameter index mode of the steady dead-beat transient process containing a primary modal characterizes, and its computing formula is as follows:

$\mathrm{\&sigma;}=-\frac{f^{\left(2\right)}}{f^{\left(1\right)}}.$

Steady dead-beat transient process containing a primary modal terminate after stabling current value i_A:

$i_A=I_5-\frac{{\left(f^{\left(1\right)}\right)}^2}{f^{\left(2\right)}};$

(2) if result of calculation a ≠ 0, then the discriminant of transient process type is calculated, it may be assumed that Δ=b²-4ac:

(2.1) if Δ > 0, then judge that the transient process of direct current micro grid system is as steady dead-beat transient process, and nonoscillating transient process contain two primary modal, the time domain specification of two master modes is exponential law change；Characteristic parameter attenuation quotient ρ, μ of steady dead-beat transient process containing two primary modal represent, attenuation quotient ρ, μ computing formula is as follows:

$\left\{\begin{array}{c}\mathrm{\&rho;}=\frac{\sqrt{b^2-4\mathrm{ac}}-b}{2a}\\ \mathrm{\&mu;}=\frac{\sqrt[-]{b^2-4\mathrm{ac}}-b}{2a}\end{array}\right..$

When Δ > 0 time, if ρ > 0 and μ > 0, judge direct current micro grid system transient modelling process convergence, and transient process terminate after stabling current be i_B, i_BComputing formula as follows:

$i_B=\frac{{\mathrm{\&rho;\&mu;I}}_5+(\mathrm{\&mu;}+\mathrm{\&rho;})f^{\left(1\right)}+f^{\left(2\right)}}{\mathrm{\&rho;\&mu;}}.$

Otherwise, can determine that the transient process of system is dispersed, cause system unstability the most at last, now need to take urgent human intervention measure, to guarantee system-wide safety and stability.

(2.2) if Δ < 0, then the transient process of judgement direct current micro grid system is change in oscillation transient process, and described change in oscillation transient process contains a main Oscillatory mode shape, the time domain specification of Oscillatory mode shape is mechanical periodicity, and oscillation amplitude exponentially changes；The characteristic parameter of change in oscillation transient process be cycle of oscillation ω and its computing formula of attenuation quotient λ as follows:

$\left\{\begin{array}{c}\mathrm{\&omega;}=\frac{\sqrt{4\mathrm{ac}-b^2}}{2a}\\ \mathrm{\&lambda;}=\frac{b}{2a}.\end{array}\right.$

When Δ,<when 0, and λ>0 judges the convergence of direct current micro grid system transient modelling process；The transient process of this convergence terminate after stabling current be i_C:

$i_C=I_5+\frac{f^{\left(1\right)}{f}^{\left(1\right)}{f}^{\left(4\right)}-{2f}^{\left(1\right)}{f}^{\left(2\right)}{f}^{\left(3\right)}+f^{\left(2\right)}{f}^{\left(2\right)}{f}^{\left(2\right)}}{f^{\left(3\right)}{f}^{\left(3\right)}-f^{\left(2\right)}{f}^{\left(4\right)}}.$

Otherwise, it is determined that the transient process of system is dispersed, cause system unstability the most at last.

As in figure 2 it is shown, on a certain load branch of real-time current detection device micro power network.Fig. 3 gives the phantom of a direct current micro grid, for sake of convenience, direct current micro grid has been simplified herein.Dc bus is passed through PWM(PulseWidthModulation, pulse width modulation by public electric wire net) rectifier power supply, guarantee that DC bus-bar voltage is stable by voltage close loop.Some load parallel connections access dc bus.At a time, large inertia load being accessed micro power network, its capacity is unknown, and the Forecasting Methodology that the present invention proposes can the steady-state operation value of system after real-time online calculation perturbation, it was predicted that the stability of direct current micro grid system.

Fig. 4 is given the load current waveform of actual measurement and is calculated the waveform of the load current steady-state value predicted by the method for the invention.As seen from the figure, the calculated on-line prediction value of the method for the invention steady-state value can be predicted well, it is possible to and then calculate the perturbation load power put into operation.

It follows that the method for the invention can be applicable to the suppression of transient state dash current.That shift to an earlier date, suitable control strategy is taked according to the characteristic of transient process in the moment that oscillatory process has just occurred, realize the correction of transient process, to reach good static and dynamic performance, especially the impact of transient current can be avoided, avoid micro power network that voltage pulsation by a relatively large margin occurs, thus improving the stability margin of micro power network.

The present invention gives the Forecasting Methodology of real-time online computing system characteristic parameter in a kind of direct current micro grid.And utilize MATLAB/Simulink that the method has been carried out simulating, verifying.From simulation result it will be seen that transient process just just, calculation of characteristic parameters method given in this article has just online calculated the important parameter in this transient process, and achieves the separation of transient state composition and stationary component.Compared to additive method, there is better real-time and simplicity.Proposed method can apply to the numerous areas such as on-line checking and the suppression of the suppression of transient state dash current, parameter of electric machine on-line testing, on-line fault diagnosis, low frequency power oscillation；The method that the present invention proposes can within the shortest time of vibration harm early period of origination, judging signal component rapidly, line number of going forward side by side separates, and carries out the work such as process in real time, online for follow-up attachment device, Informational support is provided, and then reduces the loss of power and the harm to electrical network.

Claims (7)

1. the real-time online Forecasting Methodology of a direct current micro grid characteristic parameter, it is characterised in that comprise the following steps:

1), Real-time Collection direct current micro grid system one is by the current perturbation value I of disturbance node_k, sampling time interval is T_s；According to the current perturbation value I gathered_k, construct current perturbation value array ARRAY [I₁、I₂、I₃、I₄、I₅], and in current perturbation value array ARRAY, each element initial value is 0, often gathers a point, makes I₅=I_k；I₄=I₅；I₃=I₄；I₂=I₃；I₁=I₂；K is positive integer；

2), the Four order difference derivative of current value in real-time calculation perturbation current value array ARRAY: if first-order difference derivative f⁽¹⁾More than ε, then judge that direct current micro grid system enters transient process；If all-order derivative is respectively less than default small quantity ε, then judge that direct current micro grid system is steady, continue to gather subsequent time current value, and continue to calculate the Four order difference derivative of subsequent time current value, wherein, the Four order difference derivative respectively f of current value in described current perturbation value array ARRAY⁽¹⁾、f⁽²⁾、f⁽³⁾、f⁽⁴⁾:

$f^{\left(1\right)}=\frac{I_5-I_4}{T_s}$

$f^{\left(2\right)}=\frac{I_5-2I_4+I_3}{{\left(T_s\right)}^2}$

$f^{\left(3\right)}=\frac{I_5-3I_4+3I_3-I_2}{{\left(T_s\right)}^3}$

$f^{\left(4\right)}=\frac{I_5-4I_4+6I_3-4I_2+I_1}{{\left(T_s\right)}^4};$

3), as first-order difference derivative f⁽¹⁾More than ε, then continuing to gather subsequent time current value, calculate subsequent time current value one arrives Four order difference derivative, calculates intermediate variable a, b, c:

$\left\{\begin{array}{c}a=f^{\left(1\right)}{f}^{\left(2\right)}-f^{\left(1\right)}{f}^{\left(3\right)}\\ b=f^{\left(2\right)}{f}^{\left(3\right)}-f^{\left(1\right)}{f}^{\left(4\right)}\\ c=f^{\left(3\right)}{f}^{\left(3\right)}-f^{\left(2\right)}{f}^{\left(4\right)}\end{array}\right.$

(1) if result of calculation a=0, then judging that the transient process of direct current micro grid system is as steady dead-beat transient process, and transient process is only containing a primary modal, the time domain specification of described primary modal is exponential law change；

(2) if result of calculation a ≠ 0, then the discriminant Δ=b of transient process type is calculated²-4ac:

(2.1) if Δ > 0, then judge that the transient process of direct current micro grid system is as steady dead-beat transient process, and steady dead-beat transient process contain two primary modal, the time domain specification of two primary modal is exponential law change；

(2.2) if Δ < 0, then the transient process of judgement direct current micro grid system is change in oscillation transient process, and described change in oscillation transient process contains a main Oscillatory mode shape, the time domain specification of Oscillatory mode shape is mechanical periodicity, and oscillation amplitude exponentially changes.

2. the real-time online Forecasting Methodology of direct current micro grid characteristic parameter according to claim 1, it is characterized in that, step 3) in (1) in the attenuation quotient σ of characteristic parameter index mode of steady dead-beat transient process containing a primary modal characterize, its computing formula is as follows:

$\mathrm{\&sigma;}=-\frac{f^{\left(2\right)}}{f^{\left(1\right)}}.$

3. the real-time online Forecasting Methodology of direct current micro grid characteristic parameter according to claim 1 and 2, it is characterised in that the steady dead-beat transient process containing a primary modal terminate after stabling current value i_A:

$i_A=I_5-\frac{{\left(f^{\left(1\right)}\right)}^2}{f^{\left(2\right)}}.$

4. the real-time online Forecasting Methodology of direct current micro grid characteristic parameter according to claim 1, it is characterized in that, (2.1) characteristic parameter attenuation quotient ρ, μ of the steady dead-beat transient process containing two primary modal in represent, attenuation quotient ρ, μ computing formula is as follows:

$\left\{\begin{array}{c}\mathrm{\&rho;}=\frac{\sqrt{b^2-4ac}-b}{2a}\\ \mathrm{\&mu;}=\frac{-\sqrt{b^2-4ac}-b}{2a}\end{array}\right.$

If ρ > 0 and μ > 0, judge the convergence of direct current micro grid system transient modelling process；

Otherwise, it is determined that the transient process of system is dispersed, cause direct current micro grid system unstability the most at last.

5. the real-time online Forecasting Methodology of direct current micro grid characteristic parameter according to claim 4, it is characterised in that if ρ > 0 and μ > 0, judge direct current micro grid system transient modelling process convergence, and transient process terminate after stabling current be i_B, i_BComputing formula as follows:

$i_B=\frac{{\mathrm{\&rho;\&mu;I}}_5+(\mathrm{\&mu;}+\mathrm{\&rho;})f^{\left(1\right)}+f^{\left(2\right)}}{\mathrm{\&rho;}\mathrm{\&mu;}}.$

6. the real-time online Forecasting Methodology of direct current micro grid characteristic parameter according to claim 1, it is characterised in that in (2.2), the characteristic parameter of change in oscillation transient process is ω and attenuation quotient λ cycle of oscillation, and its computing formula is as follows:

$\left\{\begin{array}{c}\mathrm{\&omega;}=\frac{\sqrt{4ac-b^2}}{2a}\\ \mathrm{\&lambda;}=\frac{b}{2a}\end{array}\right..$

7. the real-time online Forecasting Methodology of direct current micro grid characteristic parameter according to claim 6, it is characterised in that when Δ<when 0, and λ>0, then can determine that the transient process of system restrains, the transient process of convergence terminate after stabling current be i_C:

$i_C=I_5+\frac{f^{\left(1\right)}{f}^{\left(1\right)}{f}^{\left(4\right)}-2f^{\left(1\right)}{f}^{\left(2\right)}{f}^{\left(3\right)}+f^{\left(2\right)}{f}^{\left(2\right)}{f}^{\left(2\right)}}{f^{\left(3\right)}{f}^{\left(3\right)}-f^{\left(2\right)}{f}^{\left(4\right)}}.$