Hong-Chan Chang

An efficient approach for reducing harmonic voltage distortion in distribution systems with active power line conditioners

This paper presents a combined differential evolution/multiple gradient summation approach for reducing harmonic distortion with active power line conditioners (APLCs). The purpose of this approach is to minimize the total injection currents of APLCs while satisfying harmonic standards and practical constraints such as the individual harmonic voltage distortion, total harmonic voltage distortion limits, and the commercially available discrete sizes of the APLCS. The proposed approach was tested on an 18-bus radial distribution system. Results obtained show that the proposed approach can effectively solve the APLC installation problem.

Composite reliability evaluation model for different types of distribution systems

The paper develops a set of composite distribution system reliability evaluation models that can be applied to a nonradial type system. The developed models reflect the effect of distribution substations, primary distribution systems, and the interaction between them. First, reliability assessments for five configurations of distribution substation are performed using minimal cut-set technique. Next, the interaction between distribution substation and primary distribution system is modeled according to the tripping behavior of feeder circuit breakers. Last, the contribution of reliability indices evaluated from the primary distribution system is added to the previous two effects, and then the composite load point reliability evaluation models are developed. The developed models are demonstrated on five types of distribution system modified from a reliability test system. Comparisons of reliability indices are made and discussed.

Partial discharge pattern recognition of power cable joints using extension method with fractal feature enhancement

Highlights? The proposed method has high recognition rate and provides fast recognition speed. ? The PD defect types can be directly identified by the degree of correlation. ? The fractal theory could extract the important features from PD 3D patterns. ? This technology can application in power station partial discharge detection. This paper proposes a new partial discharge (PD) pattern recognition using the extension method with fractal feature enhancement. First, four common defect types of XLPE power cable joints are established, and a commercial PD detector is used to measure the PD signal by inductive sensor (L-sensor). Next, the feature parameters of fractal theory (fractal dimension and lacunarity) are extracted from the 3D PD patterns. Finally, the matter-element models of the PD defect types are built. The PD defect types can be directly identified by the degree of correlation between the tested pattern and the matter-element based on the extension method. The extension method needs representative features to define the interval of the matter-element. In order to enhance the extension performance, we add fractal features that are extracted from the PD 3D patterns. To demonstrate the effectiveness of the extension method with fractal feature enhancement, the identification ability is investigated on 120 sets of field-tested PD patterns of XLPE power cable joints. Compared with the back-propagation neural network (BPNN) method, the results show that the extension method with fractal feature enhancement not only has high recognition accuracy and good tolerance when random noise is added, but that it also provides fast recognition speed.

Gas-insulated switchgear PD signal analysis based on Hilbert-Huang transform with fractal parameters enhancement

This study proposes a novel method of partial discharge (PD) electrical signal analysis based on the Hilbert-Huang transform (HHT) with fractal feature enhancement. Firstly, this study establishes four defect types of 15 kV gas-insulated switchgear (GIS) and uses a commercial high-frequency current transformer (HFCT) to measure the electrical signals caused by the PD phenomenon. Second, the authors applied HHT for the PD electrical signal process. The HHT can represent instantaneous frequency components through empirical mode decomposition (EMD) and then transform to a 3D Hilbert energy spectrum. Finally, this study extracts the fractal parameters from the 3D energy spectrum and uses a neural network (NN) for PD recognition. To demonstrate the effectiveness of the proposed method, this study uses 160 sets of field-tested PD patterns generated by GIS, and then compares the recognition rate of the signal with and without the EMD process. The result shows that the proposed method can easily separate various defect types. The method can also be employed by the construction unit to verify the GIS quality and determine the GIS insulation status.

Generation Dispatch Strategy under Environment Protection Consideration

An optimal generation dispatch strategy method while considering CO2 emissions is presented in this paper. Firstly, different CO2 equivalent models for fuel generated thermal units are derived. Secondly, the Cost-CO2 emission Tradeoff Curve (CCTC) and Incremental Cost for CO2 Reduction (ICCR) curve, are introduced to assess the impact of CO2 emissions on power generation costs. Incorporating these two indexes, the single-objective and bi-objective programming methods are employed to establish a generation dispatch strategy. The salient feature of the strategy allows the decision-maker to consider both environmental and economic factors at the same time. Since generation dispatch belongs to large-scale non-linear planning problems, this study employs a particle swarm approach with novel coding scheme for generation dispatch solution, which can quickly find an optimal solution with higher probability. Finally, taking the 27-unit system from Taiwan power company as an example, simulation result of the study reveals that the proposed dispatch strategy can effectively take into consideration CO2 reduction impact on cost during off-peak, half-peak and peak load conditions to achieve environmental protection and economic purpose.

Implementation of a power supply with the characteristics of solar panels under partially shaded

This paper aims at producing a power supply with the characteristics of solar panels under partially shaded. Temperature and solar illumination can be set up on the power supply to emulate the characteristics of a solar panel, which can be provided for exploring the effect of a solar panel when it is shaded by clouds or polluted by dust. In this paper, uniform solar illumination model and partial shading model with two solar modules in series are proposed. A buck converter is adopted to adjust the output of power supply. The adjustments are made in accordance with the quiescent points of solar panels obtained from a digital signal processor on a basis of the load impedance and the characteristics of solar panels. Finally, this study develops a power supply with the maximum short circuit current of 5A and maximum open circuit voltage of 60V. Load is changed time after time so as to depict V–I curve and verify the practicability of the power supply.

Emergency Dispatch Strategy Considering Remaining Lives of Transformers

An emergency dispatch strategy (EDS) is proposed as a power system operational support tool following a transformer malfunction. First, a revised model based on IEEE C57.91 provides a method to calculate the remaining life of a transformer from the data of current load and elapsed life. Second, the life function and the constraints of transformers and the system are constructed to formulate the dispatch model. Finally, a realistic test case based on the Taiwan power system is used to demonstrate the practical applications of the EDS method. The results, when compared with those obtained using the traditional balance loads method (BLM), indicate that the EDS method is beneficial because power operators would have more time to replace a damaged transformer and successfully defer a power outage.

Application of automated mapping system to distribution transformer load management

This paper develops an application program that is based on the automated mapping and facility management system (AM/FM) to provide load forecasting and power flow calculation capability in distribution systems. First, the database and related data structure used in the Taipower distribution automation pilot system is studied and thoroughly analyzed. Then, our program, developed by the AM/FM ODL software, is integrated into the above pilot system. This program can predict future load growth on distribution feeders, considering the effects of temperature variation, and power needed for air conditioners. In addition, on the basis of load density and diversity factors of typical customers, the saturation load of a new housing zone can be estimated. As for the power flow analysis, it can provide three-phase quantities of voltage drop at each node, the branch current, and the system loss. The program developed in this study can effectively aid public electric utilities in distribution system planning and operation.

Optimal installation of three-phase active power line conditioners in unbalanced distribution systems

Abstract In this paper, a new solution algorithm based on a multiple gradient summation (MGS) and differential evolution (DE) approach for optimal three-phase active power line conditioners (APLCs) installation in unbalanced distribution systems is proposed. The active power line conditioners installation problem considers the individual and total harmonic voltage distortions as well as the commercially available discrete sizes of the APLCs limits to minimize the total sizes of three-phase APLCs. The imbalance of systems resulting from using asymmetrical connection transformers was taken into account. The effectiveness of the proposed method was demonstrated by its application to a 23-bus unbalanced radial distribution system.

A novel electric energy management strategy applied in hybrid PV system

This paper presents a hybrid PV system operated in accordance with an electric energy management strategy for public lighting equipments in apartment buildings. We attempt to alternate PV with grid-connected power systems to avoid the occurrences of islanding, safe protection and the low reliability of power supply in standalone PV system through implementing the electric energy management strategy presented herein. The power conversion devices included in the proposed system contain buck-boost, push-pull, full-bridge inverter, switches and high-efficient digital signal controller as means of achieving MPPT, power charging and power system switching. A 100W experimental prototype of hybrid PV system was built in the lab. Experimental results are shown to verify the effectiveness of proposed energy management strategy.