改進電磁暫態仿真中數值振蕩消除方法的研究

解笑蘇，王　帆，張學凱（.國網山東省電力公司電力科學研究院，濟南　5000；.國網山東省電力公司濟南供電公司，濟南　500；.國網山東省電力公司，濟南　5000）

·專題論述·

改進電磁暫態仿真中數值振蕩消除方法的研究

解笑蘇1，王帆2，張學凱3
（1.國網山東省電力公司電力科學研究院，濟南250003；2.國網山東省電力公司濟南供電公司，濟南250012；3.國網山東省電力公司，濟南250001）

在不采取任何修正措施的情況下，電磁暫態仿真計算在開關動作時可能會出現數值振蕩現象。目前，線性插值法是消除這種振蕩最常用的方法。但是，如果插值法采用的初始數值存在誤差，數值震蕩可能無法被完全消除。提出一種改進的線性插值法，通過調整計算方法排除誤差影響來解決這一問題，并通過仿真對結果進行了驗證。

電磁暫態仿真；數值震蕩；線性插值

0　Introduction

Electromagnetic transient simulation has characteristics of accurate phenomenon portray and good numerical stability，and thus plays a key role in power system design and planning，analysis and operating control，online dynamic security assessment and so on.As a result of the trapezoidalmethod's own flaw，the computing process has a risk of numerical oscillation at the same time of switches action when nomeasures are taken［1］.

The CDA method［2-4］was firstly used to solve the problem.This method uses 2 steps of the backward Euler method to replace the trapezoidal method when switches act，and it performs well without using the value before changes happen.But facing themore and more complex simulation models such as power electronic devices，its complication and low efficiency expose.

The linear interpolation method replaced the CDA methodbecauseofthehigherefficiencyand flexibility［5-9］. As the simulating step of integration is small enough，the part of curve between two points can be regarded as a straight line approximately，and any points in this part can be calculated according to this line.This method provides a shortcut for calculating any point in range of one step and eliminating numerical oscillations.

The existing linear interpolationmethod has a defect that the oscillation may not be eliminated when error existing in the calculation progress.Although this case may not happen at usual time，it does have a big in-fluence on the simulation result.

1Generation of NumericalOscillation

The numerical oscillation is caused by the sudden change of non-state variables when the state variables crossing zero，owing to the defect of trapezoidal method.

Figure1　A Simple System

Figure 1 shows a simple system as an example.If the switch breaks at t=1，i and vLshould change along the real line in Figure 2.

Figure 2　Cause of NumericalOscillation

Butusing the trapezoidalmethod，we can get

Aswe know，when t≥2，i（t）=i（t-1）=0.And then we can get

As a result，the wave of vLbecomes the dotted line in Figure 2（b），and the numerical oscillation arises.

2　The Defectof Linear Interpolation Method

The steps of the linear interpolationmethod to eliminate numerical oscillation are as follows：

1）Calculate the unmodified result of t=2 using the trapezoidalmethod based on the result of t=1；

2）Calculate the result of t=1.5 using the interpolationmethod based on the resultof t=1 and the unmodified result of t=2；

3）Calculate the result of t=2.5 using the trapezoidalmethod based on the result of t=1.5；

4）Calculate the modified result of t=2 using the interpolation method based on the result of t=1.5 and t=2.5；

Generally，thismethod is correct and efficient，but the result may be as Figure 3 when error existing in the result of t=1.

Figure 3　The result of interpolation method when error existing

Assuming thatwemade amistake of i（1）=Δi not 0，the unmodified result should be

Using the linear interpolationmethod，we can get

According to the trapezoidal method and the linear interpolationmethod，we can get

Themodified v（3）≠0，and i（3）=0.Ifwe continue the calculation，we will get v（4）=-v（3）and v（5）=v （3）… .The numerical oscillation will never be eliminated.

3　The Improved Linear Interpolation Method

Facing the defect above，the numerical oscillation will be easily eliminated if we just change the order of calculation as follows:

1）Calculate the unmodified result of t=2 using the trapezoidalmethod based on the result of t=1；

2）Calculate the result of t=1.5 using the interpolationmethod based on the result of t=1 and the unmodified result of t=2；

3）Calculate the unmodified result of t=3 using the trapezoidal method based on the unmodified result of t=2；

4）Calculate themodified result of t=2.5 using the interpolationmethod based on the unmodified result of t=2 and t=3；

5）Calculate the modified result of t=2 using the interpolation method based on the result of t=1.5 and t=2.5；

As same as the assumption above，we can get the same resultas Equation（7）and Equation（8）.And according to the trapezoidal method and the improved method，we can calculate

Themodified v（3）=0，and i（3）=0，the numerical oscillation is eliminated.The simulation results comparison of the twomethods is as Figure 4.

Figure 4　The resultof new method when error existing

4　Conclusions

The existing linear interpolation method may not be efficient in eliminating the numerical oscillation when error existing in the calculation progress.We provide an improved linear interpolation method，and prove its correctness in frontof errors.

Reference

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［2］J.R.Marti，J.Lin.Suppression of Numerical Oscillations in theEMTP［J］.IEEE Transaction on Power Systems，1989，4（2）：739-747.

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［5］P.Kuffel，K.Kent，G.Irwin.The Implementation and Effectiveness of Linear Interpolation within Digital Simulation［J］.Electrical Power and Energy System，1997，19（4）：221-227.

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［7］Zou Ming，Mahseredjian Jean，Joos Geza，et al.Interpolation and Reinitialization in Time-domain Simulation of Power Electronics Circuits［J］.Electric Power Systems Research，2006，76 （8）：688-694.

［8］Wang Chengshan，Li Peng，Huang Bibin，et al.An Interpolation Algorithm for Time-Domain Simulation of Power Electronics Circuit Considering Multiple Switching Events［J］.Transactions of China Electrotechnical Society，2010，25（6）：84-88.

［9］Liu Tao，Yan Yipeng，Jin Na，et al.Interpolation Algorithm for ElectromagneticTransientSimulationConsideringMultiple Switching Events［J］.Proceedings of the CSU-EPSA，2013，25 （6）：144-147.

Accepted date：2016-03-09

Xie Xiaosu（1987），received master degree in Engineering from North China Electric Power University in 2013.He is now working in State Grid Shandong Electric Power Research Institute.His main research interest is generator excitation.

Im proved Numerical Oscillation Elim ination M ethod in Electromagnetic Transient Simulation

XIE Xiaosu1，WANG Fan2，ZHANG Xuekai3
（1.State Grid Shandong Electric Power Research Institute，Jinan 250003，China；2.State Grid Jinan Power Supply Company，Jinan 250012，China；3.State Grid Shandong Electric Power Company，Jinan 250001，China）

Electromagnetic transient simulation has a risk of numerical oscillation at the same time of switches action when no measure is taken.The linear interpolation method ismostwidely used to eliminate the numerical oscillation at present.But in the case of error existing in the initial value，the numerical oscillation may not be eliminated completely.We put forward an improved method of linear interpolation by adjusting the calculation method to eliminate the influence of errors to solve this problem，and prove the results through simulation.

electromagnetic transient simulation；numerical oscillation；linear interpolation

TM744

A

1007－9904（2016）04－0026－03