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

Abstract

The invention discloses a real-time online prediction method of characteristic parameters of a DC micro-grid, which includes the following steps: 1) Real-time collection of a disturbance current value I _k of a disturbed node in a DC micro-grid system, and the sampling time interval is T _s ; according to the The disturbance current value I _k collected is used to construct the disturbance current value array ARRAY[I ₁ , I ₂ , I ₃ , I ₄ , I ₅ ]; 2) Calculate the fourth-order differential derivative of the current value in the disturbance current value array ARRAY in real time: If the first-order differential derivative f ⁽¹⁾ is greater than ε, it is determined that the DC micro-grid system has entered a transient process; if the derivatives of each order are less than the preset small amount ε, it is determined that the DC micro-grid system is stable, and continue to collect the current at the next moment value, and continue to calculate the fourth-order differential derivative of the current value at the next moment. Compared with the prior art, the method of the present invention has better real-time and simplicity, and can be applied to the suppression of transient impulse current and online testing of motor parameters , Fault online diagnosis, online detection and suppression of low frequency power oscillation and many other fields.

Description

A Real-time Online Prediction Method of Characteristic Parameters of DC Micro-grid

technical field

The invention belongs to the research field of power quality and signal analysis and processing, and in particular relates to a real-time online prediction method for characteristic parameters of a direct current micro-grid.

Background technique

Microgrid is the most effective measure to realize the distributed application of new energy, and it is also the main content of future interactive smart grid. The system integrates distributed energy sources such as wind power, photovoltaics, and fuel cells through a large number of power electronic interface circuits, and uses energy storage devices such as batteries, supercapacitors, and high-speed flywheels as power adjustment methods. Under the coordination of the system and protection devices, clean, continuous and interactive power is provided to local loads through the micro-local power supply network.

By analyzing the system structure, networking mode, operation mode, and control strategy of the microgrid, it can be seen that it has the following important characteristics: 1. It contains a variety of intermittent energy sources, and there are inevitably continuous and random external inputs source disturbance. 2. The characteristics and forms of the load in the micro-grid are diverse, and a large number of random load changes lead to continuous changes in the characteristic parameters of the network. 3. The types of components vary widely, including current-type power electronic converters and voltage-type converters; both resistive and capacitive loads, as well as resistive and inductive loads; there are both static devices and moving ones device of. 4. There are various operating modes, which can be operated not only in the grid-connected mode, but also in the island mode. 5. A typical multi-scale coupling system includes both small-inertia power electronic converters and large-inertia rotating mechanical equipment; there are energy storage devices with low power and main grid systems with huge capacity; there are power frequency level The energy exchange also has power oscillations at the switching frequency level.

The above characteristics determine the complexity of microgrid stability analysis. Existing stability studies are almost all based on a definite network and a specific control strategy. However, the analysis method based on the mathematical model relies heavily on the accuracy of the system parameters and the model, so the theoretical analysis results may have a large deviation from the actual situation. More importantly, the micro-grid system is always subjected to a large number of random disturbances, and its control strategy, working mode, and characteristic parameters of the structure are also constantly changing. Therefore, in the microgrid system under disturbance conditions, the stability analysis methods based on parameters and models have great limitations, and the existing research results are difficult to meet the needs of online stability analysis of microgrids.

Contents of the invention

In view of the above defects or deficiencies, a real-time online processing method of the characteristic parameters of the DC micro-grid is provided, which can measure the state of the system in real time.

For achieving above object, technical scheme of the present invention is:

Include the following steps:

1) Collect the disturbance current value I _k of a disturbed node in the DC microgrid system in real time, and the sampling time interval is T _s ; according to the collected disturbance current value I _k , construct a disturbance current value array ARRAY[I ₁ , I ₂ , I ₃ , I ₄ , I ₅ ], and the initial value of each element in the disturbance current value array ARRAY is 0, and each time a point is collected, set I ₅ =I _k ; I ₄ =I ₅ ; I ₃ =I ₄ ; I ₂ =I ₃ ; I ₁ =I ₂ ;

2) Real-time calculation of the fourth-order differential derivative of the current value in the disturbance current value array ARRAY: If the first-order differential derivative f ⁽¹⁾ is greater than ε, it is determined that the DC microgrid system has entered a transient process; Assuming a small amount ε, it is determined that the DC micro-grid system is stable, continue to collect the current value at the next moment, and continue to calculate the fourth-order differential derivative of the current value at the next moment, wherein the fourth-order differential derivative of the current value in the array ARRAY of the disturbance current value The differential derivatives are f ⁽¹⁾ , f ⁽²⁾ , f ⁽³⁾ , f ⁽⁴⁾ :

${\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}$

${\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

${\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}$

${\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 6</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; ;</span>$

3) When the first-order differential derivative f ⁽¹⁾ is greater than ε, continue to collect the current value at the next moment, calculate the first to fourth-order differential derivatives of the current value at the next moment, and calculate the intermediate variables a, b, and c:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}\\ \mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>}\\ \mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>}\end{array}\right.$

(1) If the calculation result a=0, it is judged that the transient process of the DC microgrid system is a stable non-oscillating transient process, and the transient process contains only one main mode, and the time domain characteristics of the main mode are exponential regular changes;

(2) If the calculation result a≠0, then calculate the discriminant formula of the transient process type Δ=b ² -4ac:

(2.1) If Δ>0, it is determined that the transient process of the DC microgrid system is a stable and non-oscillating transient process, and the stable and non-oscillating transient process contains two main modes, and the time domain of the two main modes The characteristics are all exponential changes;

(2.2) If Δ<0, it is determined that the transient process of the DC microgrid system is a transient process of oscillation change, and the transient process of oscillation change contains a main oscillation mode, and the time domain characteristic of the oscillation mode is period The oscillation amplitude changes exponentially.

In (1) of step 3), the characteristic parameters of the stationary non-oscillating transient process with one main mode are characterized by the attenuation coefficient σ of the exponential mode, and the calculation formula is as follows:

$\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; .</span>$

The steady current value i _A after the end of a stationary non-oscillating transient with one dominant mode:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>\frac{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; .</span>$

The characteristic parameters of the stationary non-oscillating transient process containing two main modes in (2.1) are represented by the attenuation coefficients ρ, μ, and the calculation formulas of the attenuation coefficients ρ, μ are as follows:

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

If ρ>0 and μ>0, it is determined that the transient process of the DC microgrid system is convergent;

Otherwise, it is determined that the transient process of the system diverges, which will eventually lead to system instability.

If ρ>0 and μ>0, it is determined that the transient process of the DC microgrid system is convergent, and the stable current after the transient process is i _B , and the calculation formula of i _B is as follows:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&rho;\&mu;I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;\&mu;</span>}}<span\; class="notranslate">\; .</span>$

The characteristic parameters of the transient process of oscillation change in (2.2) are the oscillation period ω and the attenuation coefficient λ. The calculation formula is as follows:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; =</span>\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; ac</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; a</span>}}\\ \mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; b</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; .</span>\end{array}\right.$

When Δ<0, and λ>0, it can be judged that the transient process of the system is convergent, and the stable current after the convergent transient process ends is i _C :

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; .</span>$

Compared with prior art, the beneficial effects of the present invention are:

The invention detects the transient current of a disturbed node in the DC micro-grid, constructs the real-time detected current into a disturbance current, and then calculates the array of real-time disturbance current values to realize the real-time online prediction of the DC micro-grid and obtain The real-time state of the system, thereby realizing the separation of transient components and steady-state components; compared with the prior art, the method of the present invention has better real-time and simplicity, and can be applied to the suppression of transient surge currents, motor parameters On-line testing, on-line fault diagnosis, on-line detection and suppression of low-frequency power oscillations, and many other fields.

Furthermore, the present invention can quickly and accurately calculate the variation of local characteristic parameters of the micro-grid system based on the transient current measured in real time, thereby predicting the characteristic value and stability of the transient response process after the system undergoes a disturbance. Furthermore, the control system of the micro-grid can determine the disturbance suppression strategy and control instructions according to the predicted disturbance influence law, quickly determine the signal components in the shortest time at the initial stage of the oscillation hazard, and perform signal separation for subsequent additional The device performs real-time and online processing and other work to provide information support, thereby reducing power loss and harm to the power grid.

Description of drawings

Fig. 1 is the real-time online prediction method of DC micro-grid characteristic parameter of the present invention;

Fig. 2 is a schematic structural diagram of the DC micro-grid system of the present invention;

Fig. 3 is the simulation model diagram of the direct current microgrid of the present invention;

Fig. 4 is a predicted waveform diagram of the load current according to the present invention.

detailed description:

The present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the present invention provides a real-time online prediction method of DC micro-grid characteristic parameters, comprising the following steps:

1) Collect the disturbance current value I _k of a disturbed node in the DC microgrid system in real time, and the sampling time interval is T _s =0.01s; according to the collected disturbance current value I _k , construct the disturbance current value array ARRAY[I ₁ , I ₂ , I ₃ , I ₄ , I ₅ ], and the initial value of each element in the disturbance current value array ARRAY is 0, and each time a point is collected, set I ₅ =I _k ; I ₄ =I ₅ ; I ₃ =I ₄ ; I ₂ =I ₃ ; I ₁ =I ₂ ;

2) Real-time calculation of the fourth-order differential derivative of the current value in the disturbance current value array ARRAY: If the first-order differential derivative f ⁽¹⁾ is greater than ε, it is determined that the DC microgrid system has entered a transient process; Assuming a small amount ε, it is determined that the DC micro-grid system is stable, continue to collect the current value at the next moment, and continue to calculate the fourth-order differential derivative of the current value at the next moment, wherein the fourth-order differential derivative of the current value in the array ARRAY of the disturbance current value The differential derivatives are f ⁽¹⁾ , f ⁽²⁾ , f ⁽³⁾ , f ⁽⁴⁾ :

${\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}$

${\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

${\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}$

${\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 6</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; ;</span>$

Among them, the small amount ε is taken as ε=0.001 after considering calculation accuracy requirements and measurement errors and other factors.

3) Judging the specific state of the DC microgrid system entering the transient process:

If the first-order differential derivative f ⁽¹⁾ is greater than ε, it is determined that the DC microgrid system has entered a transient process, including:

Continue to collect the current value at the next moment, calculate the first to fourth order differential derivatives of the current value at the next moment, and calculate the intermediate variables a, b, and c:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}\\ \mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>}\\ \mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>}\end{array}\right.$

(1) If the calculation result a=0, it is judged that the transient process of the DC microgrid system is a stable non-oscillating transient process, and the transient process contains only one main mode, and the time domain characteristics of the main mode are exponential The characteristic parameters of a stationary non-oscillating transient process with one main mode are characterized by the attenuation coefficient λ of the exponential mode, and the calculation formula is as follows:

$\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; .</span>$

The steady current value i _A after the end of a stationary non-oscillating transient with one dominant mode:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>\frac{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; ;</span>$

(2) If the calculation result a≠0, calculate the discriminant of the transient process type, namely: Δ=b ² -4ac:

(2.1) If Δ>0, it is determined that the transient process of the DC microgrid system is a stable and non-oscillating transient process, and the non-oscillating transient process contains two main modes, and the time domain characteristics of the two main modes Both change exponentially; the characteristic parameters of a stationary non-oscillating transient process containing two main modes are represented by attenuation coefficients ρ and μ, and the calculation formulas of attenuation coefficients ρ and μ are as follows:

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

When Δ>0, if ρ>0 and μ>0, it is determined that the transient process of the DC microgrid system is convergent, and the stable current after the transient process is i _B , and the calculation formula of i _B is as follows:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&rho;\&mu;I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;\&mu;</span>}}<span\; class="notranslate">\; .</span>$

Otherwise, it can be judged that the transient process of the system diverges, which will eventually lead to system instability. At this time, urgent human intervention measures are needed to ensure the safety and stability of the whole system.

(2.2) If Δ<0, it is determined that the transient process of the DC microgrid system is a transient process of oscillation change, and the transient process of oscillation change contains a main oscillation mode, and the time domain characteristic of the oscillation mode is period The oscillation amplitude changes exponentially; the characteristic parameters of the transient process of oscillation change are the oscillation period ω and the attenuation coefficient λ. The calculation formula is as follows:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; =</span>\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; ac</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; a</span>}}\\ \mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; b</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; .</span>\end{array}\right.$

When Δ<0, and λ>0, it is determined that the transient process of the DC microgrid system is converged; the stable current after the converged transient process is i _C :

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; .</span>$

Otherwise, it is determined that the transient process of the system diverges, which will eventually lead to system instability.

As shown in Figure 2, the current real-time detection device is on a load branch of the micro-grid. Figure 3 shows a simulation model of a DC micro-grid. For the convenience of description, the DC micro-grid is simplified here. The DC bus is powered by the public power grid through a PWM (PulseWidthModulation, pulse width modulation) rectifier, and the DC bus voltage is stable through a voltage closed loop. Several loads are connected in parallel to the DC bus. At a certain moment, a large inertial load is connected to the micro-grid, and its capacity is unknown. The prediction method proposed by the invention can calculate the steady-state operation value of the system after the disturbance in real time and predict the stable performance of the DC micro-grid system.

Fig. 4 shows the measured load current waveform and the waveform of the load current steady-state value calculated and predicted by the method of the present invention. It can be seen from the figure that the online prediction value calculated by the method of the present invention can predict the steady state value well, and can further calculate the disturbance load power put into operation.

It can be known that the method of the present invention can be applied to the suppression of transient surge current. At the moment when the oscillation process just occurs, according to the characteristics of the transient process, an early and appropriate control strategy is adopted to realize the correction of the transient process, so as to achieve good dynamic and static characteristics, especially to avoid the impact of transient current and the miniature grid Larger voltage fluctuations occur, thereby increasing the stability margin of the microgrid.

The present invention provides a method for predicting the characteristic parameters of the real-time online calculation system in the DC micro-grid. The method is verified by simulation using MATLAB/Simulink. From the simulation results, it can be seen that the characteristic parameter calculation method given in this paper has already calculated the important parameters of the transient process on-line when the transient process has just begun, and realized the separation of transient components and steady-state components. separate. Compared with other methods, it has better real-time and simplicity. The proposed method can be applied to many fields such as the suppression of transient inrush current, online testing of motor parameters, online fault diagnosis, online detection and suppression of low-frequency power oscillation, etc.; , quickly determine the signal components, and separate the numbers, and provide information support for the follow-up additional devices to perform real-time and online processing, thereby reducing power loss and harm to the power grid.

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:

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