Kejun Li

Distribution network reconfiguration for load balancing using binary particle swarm optimization

In this paper, a method based on modified binary particle swarm optimization (BPSO) is proposed for distribution network reconfiguration with the objective of load balancing. A novel model to simplify distribution network is presented. The feeder reconfiguration problem is formulated as a non-linear optimization problem, and BPSO is used to find the optimal solution. According to the characteristics of distribution network, some modifications are done to retain the radial structure and reduce searching requirement. Test results based on a sample network have shown that the proposed feeder reconfiguration method can effectively keep load balancing, and the BPSO technique is efficient in searching for the optimal solution.

Distributed energy storage system in wind power generation

With the rapid development of wind power generation during these years, many large wind farms were established, and the adverse impact of wind power fluctuations on power grid has become significant. In this paper, we put forward an improvement scheme of distributed energy storage system to cope with this effect, and to maximize the utilization ratio of wind power. Energy storage systems can smooth the fluctuations of wind power, and they perform better in larger wind farms. Unlike traditional methods, the energy storage systems are located besides load centers rather than wind farms, causing no more investment. In our plan, charging stations for electric vehicles are built within some of the energy storage stations and these electric vehicles can also be regarded as energy storage devices. Different kinds of devices are applied to improve the response speed and capacity of energy storage system. Furthermore, these distributed energy storage systems have a better performance if combined with other kinds of renewable energy generation. Our research is based on digital simulation and dynamic experiment, and the results show that this distributed energy storage plan is more effective than traditional methods.

Dynamic Simulator for Thyristor Controlled Series Capacitor

This paper presents an alternative approach to thyristor controlled series capacitor (TCSC) performance analysis. The approach is to interface a small-scale physical model of the TCSC with a classic physical power system simulation laboratory. The platform is capable to investigate the operation, protection, and control strategies of TCSCs. Furthermore, it can be used to investigate complex phenomena such as the breakdown of metal oxide varistor (MOV). Such phenomena are very difficult, if not impossible, to investigate using digital simulation methods.

A Study on Mode-Switching Control of TCSC Based on Conditional Firing of Thyristor

The mode-switching control method of thyristor-controlled series capacitor is of great importance to power system stability. It is very difficult, if not impossible, to realize mode-switching only by changing firing angles. A method of predicting current zero-crossing time is proposed first to provide line current synchronization signals for switching control in time. In the switching strategy from capacitive mode to inductive vernier mode, the thyristor conditional firing is put forward. The thyristor will be fired and conducted on condition that both line current and capacitor voltage are in phase. Simulation and experimental results show that the proposed switching method can make the switching process faster with improved dynamic performance.

Dynamic Simulator for Thyristor-Controlled Series Capacitor

This paper presents an alternative approach to thyristor-controlled series capacitor (TCSC) performance analysis. The approach is to interface a small-scale physical model of the TCSC with a classic physical power system simulation laboratory. The platform is capable of investigating the operation, protection, and control strategies of TCSCs. Furthermore, it can be used to investigate complex phenomena such as the breakdown of metal oxide varistors. Such phenomena are very difficult, if not impossible, to investigate using digital simulation methods.

Dynamic simulator for thyristor controlled series compensator

This paper presents an alternative approach to thyristor controlled series capacitor (TCSC) performance analysis. The approach is to build a small-scale physical model of the TCSC and to interface it with the classic power system physical simulator. The platform is capable to support the investigation of the operation, protection and control strategy of TCSCs. Furthermore, it can be used to investigate complex phenomena such as the breakdown of metal oxide varistor (MOV). Such phenomena are very difficult, if not impossible, to investigate using digital simulation methods

Theoretical and Experimental Investigation of Dual-impedance Phenomenon in Thyristor-controlled Series Capacitor

Abstract The desired impedance of thyristor-controlled series capacitors is usually obtained by adjusting the firing angle of the thyristor. It is of great importance to make a clear relationship between the firing angle and the equivalent thyristor-controlled series capacitor impedance. This article studies the impedance characteristics of a thyristor-controlled series capacitor, considering the influence of thyristor conduction and the equivalent resistance in the reactor branch. The dual-impedance phenomenon is obtained and demonstrated by both digital simulation and a dynamic simulation experiment.

An Experiment Device for Thyristor Controlled Series Compensator Dynamic Simulation

This paper introduces the design and completion of an experiment device for TCSC dynamic simulation and its controlling system. In this device, the hierarchical structure and the corresponding modular structure of TCSC controller are more flexible and liable to carry out the study on control strategies. The results of experiments show that the fast impedance control, damping the power oscillation and the accurate and flexible transition between inductive and capacitive modes can be realized by appropriate control strategies.

A multi-step dynamic equivalent method for urban power grid based on district-dividing

With the increasing demand of electricity, the development of urban power grid has drawn a lot of attention in China. In order to focus on the analysis of urban power grid, the remaining part of the large-scale power grid used to be reduced. The accuracy of the equivalence is key to urban power grid research. In this paper, a multi-step dynamic equivalent method based on district-dividing is proposed. Based on the electrical distance, voltage level and geographic location, the external system is divided into outer layer, inner layer and buffer subsystem. Each district is separately reduced by different methods. The proposed technique is illustrated by a real large-scale power grid in the south of China.

Impedance Control of Thyristor Controlled Series Capacitor to Improve the Transfer Capability of Remote Wind Farms

In this paper, we put forward a new impedance control method of thyristor controlled series capacitor (TCSC) by modifying variable structure PID feedback of firing angle, aiming at improving the transfer capability of remote wind farms. TCSC can get the best results with nonlinear closed-loop control method, but it is very difficult, if not impossible, to be implemented because a huge amount of data is required. The impedance controller with variable structure PID feedback of firing angle is designed as follows: the coefficient of its integral part is equal to zero before or around the moment that measuring impedance reaches the desired impedance first time, meanwhile its called PD controller; then add the integral part and it becomes PID controller. When TCSC steps from different impedance values to the same, the value of error accumulator changes a little, and so a better approximate control effect is obtained. Digital simulation and dynamic experiment results show that this control method can improve the transfer capability with good dynamic and static performance.