Ren Zhigang

Community detection using Ant Colony Optimization

Many complex networks have been shown to have community structure. How to detect the communities is of great importance for understanding the organization and function of networks. Due to its NP-hard property, this problem is difficult to solve. In this paper, we propose an Ant Colony Optimization (ACO) approach to address the community detection problem by maximizing the modularity measure. Our algorithm follows the scheme of max-min ant system, and has some new features to accommodate the characteristics of complex networks. First, the solutions take the form of a locus-based adjacency representation, in which the communities are coded as connected components of a graph. Second, the structural information is incorporated into ACO, and we propose a new kind of heuristic based on the correlation between vertices. Experimental results obtained from tests on the LFR benchmark and four real-life networks demonstrate that our algorithm can improve the modularity value, and also can successfully detect the community structure.Many complex networks have been shown to have community structure. How to detect the communities is of great importance for understanding the organization and function of networks. Due to its NP-hard property, this problem is difficult to solve. In this paper, we propose an Ant Colony Optimization (ACO) approach to address the community detection problem by maximizing the modularity measure. Our algorithm follows the scheme of max-min ant system, and has some new features to accommodate the characteristics of complex networks. First, the solutions take the form of a locus-based adjacency representation, in which the communities are coded as connected components of a graph. Second, the structural information is incorporated into ACO, and we propose a new kind of heuristic based on the correlation between vertices. Experimental results obtained from tests on the LFR benchmark and four real-life networks demonstrate that our algorithm can improve the modularity value, and also can successfully detect the community structure.

An advanced adaptive backstepping control method for STATCOM

An innovative approach to high robustness and anti-interference performance for static synchronous compensator (STATCOM) control systems is proposed to address the problems including parameter uncertainties and external disturbances which often deteriorate system performance significantly. Improvement is made in three aspects. Firstly, the adaptive backstepping control has been adopted to design the state-feedback control law and improve the transient stability of the STATCOM recursively. Secondly, In order to reduce high degree of coupling between the states and the estimation error, the adaptive law and the state-feedback control law are designed separately by using the immersion and invariance adaptive (I&I adaptive) control. Thirdly, the dissipation inequality is constructed between energy storage function and an energy supply function in each step. This can get a certificate theoretically that the energy is dissipated and the robustness of the control system. Moreover, the compared simulations show that more rapid speed response and stronger robustness can be obtained by the proposed approach than other advanced algorithms under the same conditions.

Design and implementation of a real-time simulation test system for rectifying devices

In order to reduce the development costs and shorten the development period of power electronic experiments, a real-time digital simulation test system for rectifying devices is presented in this paper. This system combines the traditional simulation software SIMULINK with high-performance industrial personal computer (IPC). SIMULINK is used to create system model and the interface module. The RTW toolbox provided by SIMULINK is used to convert the model to C code, which is then uploaded to the IPC. When the C code runs, the test signals required by the control board are output through the I/O or Ethernet port. Whats more, the simulation model can be modified in real time according to the control signal fed back by the control board, and can also be used to carry on the hardware-in-loop simulation test. In this paper, many problems were solved or mitigated, such as numerical oscillation in the off-line simulation, the cumbersome process of the model converting to C code, and the real-time performance of the task scheduling strategy of the computing unit. At last, some experiments were done to show that the system has strong real-time performance and can be used in the experiment of rectifier.

Analysis of Fault Arc in High-Speed Switch Applied in Hybrid Circuit Breaker ⁄

The behavior of fault arc in a high-speed switch (HSS) has been studied theoretically and experimentally. A simplified HSS setup is designed to support this work. A two-dimensional arc model is developed to analyze the characteristics of fault arc based on magnetic-hydrodynamic (MHD) theory. The advantage of such a model is that the thermal transfer coefficient can be determined by depending on the numerical method alone. The influence of net emission coefficients (NEC) radiation model and P1 model on fault arc is analyzed in detail. Results show that NEC model predicts more radiation energy and less pressure rise without the re-absorption effect considered. As a consequence, P1 model is more suitable to calculate the pressure rise caused by fault arc. Finally, the pressure rise during longer arcing time for different arc currents is predicted.

Backstepping based direct power control for rectifier

A backstepping based direct power control (DPC) method is proposed for the three-phase voltage-source rectifier. In the proposed backstepping based controller, the feedback control laws associated with the Lyapunov functions are constructed recursively to lower the dimension of the overall system. The stability of the system is ensured by the designed power controller which provides the best switching states. The proposed DPC is verified with the simulation and experiment. The results show that, compared with the conventional DPC, the current Total Harmonic Distortion (THD) of the proposed DPC is less than 45% of that of the conventional DPC in the steady state, and the phase error between the voltage and current is reduced by 66.7%. The transient setting time of the proposed DPC is only half of that of the conventional DPC.