Jianguo Zhao

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.

Power load forecasting algorithm based on wavelet packet analysis

This paper investigates the application of wavelet packet in power load forecasting, and it proposes a novel forecasting algorithm based on wavelet packet decomposition and reconstruction. The algorithm uses the biorthogonal wavelet that has linear phase to decompose the load data to extract load components of different frequencies, and then neural network is used to predict the load component of each wavelet packet space. Finally, the load forecasting values of all the spaces are added up to produce the load forecasting result. It is advantageous in analyzing the load characteristics in each time-frequency zone to achieve accurate modeling and forecasting. Case study shows that the proposed algorithm improves forecasting accuracy and it is superior to traditional back-propagation neural network.

Impact evaluation of IEC 61850 process bus architecture on numerical protection systems

The deployment of IEC 61850 process bus in substations calls for an impact evaluation of possible process bus architecture scenarios on the performance of numerical protection systems. Six alternative system architectures are proposed based on a component redundancy perspective. The functionality of each system is assessed using reliability block diagrams based on a success-oriented network. System reliability is calculated using the minimal tie sets method determined by the connection matrix. Sensitivity analysis is then carried out on the results using two approaches. One highlights those components with the greatest impact on system reliability and the other the importance of the task performed by each component in terms of how it affects the functionality of the system.

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

Single-phase-to-ground fault feeder detection based on transient current and wavelet packet

Single-phase-to-ground fault is the most frequently occurred short-circuit fault in distribution network, and it is urgent to develop new methods to detect fault feeder correctly. The paper compares the fault-feeder selection theories using transient signals with those of using steady signals, and the application of transient signal is emphasized. By analyzing the characteristics of the Peterson-coil-grounded system, the paper proposes a novel algorithm to select fault feeder based on the transient signals and wavelet packet. It records the post-fault transient zero-sequence current of each feeder, and wavelet packet is used to extract the supply fundamental frequency and high frequency components. Finally the current and its components are used to detect fault feeder. This method is accurate and adaptive for the Peterson-coil-grounded system. Case study validates the effectiveness of the new algorithm for various fault modes in neural ineffectively grounded systems.

A new data compression algorithm for power quality online monitoring

The increasing application of power quality data acquisition devices produces large amount of data that should be compressed. The paper investigates the characteristics of power quality data and delta modulation technique, and it proposes a lossless power data compression algorithm based on high-order delta modulation. The compression algorithm carries on multiple differential operations on power quality data, so it could reduce the magnitude of data and requires fewer bits for coding. The proposed algorithm has high compression ratio and little computation requirements. Furthermore, it is suitable for dealing with the power quality data measured at high sampling frequency, and it can work well with traditional compression methods such as Huffman coding. Simulations for several kinds of power quality data confirm its effectiveness and advantages over traditional Huffman coding method.

Impact of interharmonics on the measurement error of AC sampling

Interharmonics exists in power system and it brings negative effect to power quality. The problem of interharmonics has received more and more attention. The paper investigates the impact of interharmonics on measurement error of AC sampling, which is widely used in power data acquisition system. The research reveals that interharmonics, even if its amplitude is small, will bring considerable error, and makes it impossible for data acquisition instruments to assure acceptable accuracy. Traditional one-period sampling method could do little to reduce the measurement error, even if it traces the supply fundamental frequency and increases the sampling rate. The paper suggests adopt multiperiod sampling to reduce the negative effect of interharmonics and measurement error. Simulation validates the effectiveness of the proposed method.

On-Line Stability Control of Power Systems Integrated with Distributed Generation Systems

Because of the certain stochastic nature of renewable generation, large-scale distributed generation systems can impose unpredictable impact on the stability of their integrated transmission systems. This paper demonstrates that power system oscillations can be caused by unpredictable changes of operating conditions of integrated distributed generation systems and hence presents a novel method of power system damping control by applying the operational principle of immune system. The proposed immune damping control is to mimic the immune response, to identify and respond to disturbance, and keep a healthy level of power system oscillation damping. The proposed artificial immune control acts by monitoring the health index in real time and performing immune feedback to maintain required healthy level of power system damping such that oscillations are suppressed effectively. It does not need to establish detailed parametric model of studied power system, neither its operating conditions, for the design of the damping controller. Hence it is a robust and modeling-free scheme of power system damping control. In the paper an example power system integrated with large-scale distributed generation systems is presented. Simulation results demonstrate the effectiveness and robustness of the artificial immune control method in variable circumstances of power system operation.

Effects of the Quality Factor of reactor on the TCSC characteristics and the Dual Impedance Solution Phenomenon

This paper investigates how the reactors quality factor (labeled as Q at power frequency) affects the characteristics of TCSC and what principle should be followed in designing an experimental TCSC setup. Since no close-form representation of the fundamental frequency impedance (EFFI) against the firing angle can be obtained considering the quality factor of the reactor, detailed electromagnetic transient simulation is employed for the investigation. Results show that, under the same firing condition, the EFFI of TCSC using reactor with low Q value may present considerable resistance component compared with that of the ideal case when Q is infinite. Moreover, it is found that the EFFI of the TCSC using a reactor with limited Q can be either inductive or capacitive for a specified firing angle when it is fired in a line current reference mode. This so-called dual impedance solution phenomenon is analyzed in detail in the paper.

A Wide Area Protection System and Division of Protection lED Associated Area Based on Petri Net

In wide area protection system the operation performance of relaying protection IED is improved by receiving and utilizing wide area fault information. The utilization of wide area fault information should be selective. That is, when fault occurs, corresponding protection lEDs only accept and utilize information that is related closely with fault, ignore that contributes little to fault calculation. So it is necessary to divide associated area for protection IED. Operation manner of wide area relaying protection system are discussed first in this paper. The principle to divide protection IED associated area is determined based on Petri net theory. Double-bus and double-circuit connection and one and a half circuit breaker connection are taken as the examples to study network topology to meet the requirements of protection associated area division. Analysis results show that the method to divide protection associated area is effective, which can meet information transmission requirement of wide area relaying protection system