Search

Circulating current can be decomposed into double line-frequency positive-, negative- and zero-sequence components under unbalanced voltage conditions. First, in order to decrease peak/rms value of arm current, double line-frequency circulating current should be eliminated. Second, ac-side current that consists of positive- and negative-sequence components under unbalanced voltage conditions should be regulated to track the reference signal. Furthermore, fundamental frequency circulating current caused by asymmetry of the upper and lower arm should be also removed. To effectively control ac-side current and eliminate all circulating currents, an arm current control strategy based on a decoupler and proportional-integral controller plus the vector proportional integral (VPI) controller is proposed in this paper. The proposed control strategy works well under balanced and unbalanced voltage conditions as well as asymmetry of the upper and lower arm. In addition, this paper proposes a design procedure for the VPI controller to reduce the uncertainty of this process. A three-phase modular multilevel converter simulation model is set up on PSCAD/EMTDC to verify the effectiveness of the proposed control strategy.

In this paper, the authors develop multiple Lyapunov functions for hybrid power systems which have generators and dynamic reactive loads. They first introduce the model of hybrid power systems, and then construct multiple Lyapunov functions. They use Lyapunov functions theory as a tool to analyze the stability of hybrid power systems. Finally, they give an example of a hybrid power system with a tap changing transformer, and simulate and analyze the multiple Lyapunov functions switching stability when tap discrete actions occur. They also simulate and analyze limit cycle phenomena due to system parameter altering.

This paper devotes research to the single phase to ground fault line detection problem in neutral nondirect earthed power systems. A concept of fault measures is introduced to quantitatively describe the degree of the fault indication in each line for flexible and reasonable fusion of multi criteria. A wavelet based transient method is proposed to extend the use of fault information. Fault measure algorithms for transient, steady state magnitude and steady state phase angle are formulated respectively. D-S evidence theory is introduced to deal with the fusion of multi criteria. An example obtained from a practical fault is provided to verify the effect of the fault measures, the transient detection method and the D-S combination. The example shows that the novel resorts proposed in this paper can really improve the performance of fault line detection.

The research on a new RTU is introduced in this paper. The new RTU is based on LonWorks LAN technique. It can be used in the integrated automation substation system. The authors analyse the limitation of the traditional RTU used in the integrated automation substation. The technical feature of the RTU used in the integrated automation substation is provided. The scheme of the software and hardware of the new RTU is provided.

Electric power engineering design tasks are ill-defined, with results that considerable design knowledge cannot be described in forms of rule, logic and mathematical models, even data. Therefore it is very difficult to accomplish entire tasks by applying existing AI techniques. Fortunately, case-based reasoning is a promising way to solve these problems. In this paper, the authors present a case representation approach for electric power engineering design knowledge, which can describe data, tables, even drawings. So CBR could represent graphic design knowledge conveniently.

The development and study of substation automation is an ongoing activity in China. This paper is presented as material of the study. Some problems, such as the preferred methods for information transmission, the application of expert systems, the use of distributed busbar differential protection, distributed control and monitoring using IEDs and clock synchronization are discussed in this paper.