Cheng-Ting Hsu

Optimization of Photovoltaic Penetration in Distribution Systems Considering Annual Duration Curve of Solar Irradiation

The penetration level of a photovoltaic (PV) system is often limited due to the violation of voltage variation introduced by the large intermittent power generation. This paper discusses the use of an active power curtailment strategy to reduce PV power injection during peak solar irradiation to prevent voltage violation so that the PV penetration level of a distribution feeder can be increased to fully utilize solar energy. The PV power generation is simulated according to the hourly solar irradiation and temperature data provided by the weather bureau. The voltage variation at the point of common coupling (PCC) is also derived by executing the 3-φ load flow analysis to investigate the maximum PV power injection without causing a voltage violation problem. When using the proposed voltage control scheme for limiting PV power injection into the study distribution feeder during high solar irradiation periods, the total power generation and total energy delivered by the PV system over a one-year period are determined according to the annual duration of solar irradiation. The annual cash flow from sales of PV power, the O&M cost over the system life cycle, and the capital investment in the PV system are then used to calculate the payback years and the net present value (NPV) of the PV project. With the proposed voltage control to perform the partial generation rejection of PV systems, the optimal installation capacity of PV systems can be determined by maximizing the net present value of the system so that better cost effectiveness of the PV project and better utilization of solar energy can be obtained.

Financial Analysis of a Large-Scale Photovoltaic System and Its Impact on Distribution Feeders

To promote the photovoltaic (PV) installation, a large-scale PV system installed in the Main Stadium of the 2009 World Games has been investigated for the design of selling price of PV power generation. The PV power generation is simulated according to the hourly solar irradiation and temperature provided by the weather bureau. The cash flow of annual power generation, the O&M cost, and the capital investment cost of the PV system is then used to derive the payback years and the internal rate of return for the PV system under different selling price of PV power generation. The voltage variation and the power system loss of the distribution feeder, which serves the Main Stadium, are also performed by executing the 3-φ load flow analysis for the impact analysis of the PV system. The results indicate that the reduction of voltage drop and power system loss can be obtained with the PV system installed to provide the dispersed generation for the local loads. However, the PV system penetration is limited due to the violation of voltage variation introduced by the large intermittent PV power generation. The selling price of PV generation has to be designed according to the conditions of solar irradiation and temperature so that sufficient incentives can be provided to encourage more customers to participate the PV program.

Artificial Neural Network Based Adaptive Load Shedding for an Industrial Cogeneration Facility

This paper presents the design of adaptive load shedding strategy by executing the artificial neural network (ANN) and transient stability analysis for an Industrial cogeneration facility. To prepare the training data set for ANN, the transient stability analysis has been performed to solve the minimum load shedding for various operation scenarios without causing tripping problem of cogeneration units. Various training algorithms have been adopted and incorporated into the back- propagation learning algorithm for the feed-forward neural networks. By selecting the total power generation, total load demand and frequency decay rate as the input neurons of the ANN, the minimum amount of load shedding is determined to maintain the stability of power system. To demonstrate the effectiveness of the ANN minimum load-shedding scheme, the traditional method and the present load shedding schemes of the selected cogeneration system are also applied for comparison and verification of the proposed methodology.

Electric Power System Analysis and Design of an Expanding Steel Cogeneration Plant

This paper presents the electric power system analysis and design of an expanding steel cogeneration plant. The site and capacity of shunt capacitor banks as well as the tap position of transformers are determined according to the power flow analysis. Also, to comply with the restriction of circuit breaker capacity, the high-impedance transformers are designed. In addition, the voltage fluctuation resulted from the dramatic reactive power variation of hot strip rolling mill can be greatly reduced if proper static var compensator is installed. The significant voltage sag due to the starting of induction motor can be effectively improved by applying wye-delta transformer starter. Furthermore, the total voltage harmonic distortion and the total current demand distortion are both acceptable if the proper filters are installed. It is also found that the cogeneration system can keep stable operation in autonomous mode by applying the governor control action and the load-shedding scheme after tie line tripping. It is concluded that the power system analyses are important for the steel plant with cogeneration unit to identify hidden problems and remedy strategy to ensure the system power quality and operation performance.

Adaptive load shedding for an industrial petroleum cogeneration system

Abstract This paper presents the design of adaptive load-shedding strategy by executing the artificial neural network (ANN) and transient stability analysis for an Industrial cogeneration facility. ► To prepare the training data set for ANN, the transient stability analysis has been performed to solve the minimum load shedding for various operation scenarios without causing tripping problem of cogeneration units. Various training algorithms have been adopted and incorporated into the back-propagation learning algorithm for the feed-forward neural networks. ► By selecting the total power generation, total load demand and frequency decay rate as the input neurons of the ANN, the minimum amount of load shedding is determined to maintain the stability of power system. ► To demonstrate the effectiveness of the ANN minimum load-shedding scheme, the traditional method and the present load shedding schemes of the selected cogeneration system are also applied for comparison and verification of the proposed methodology.

Impact of PV generation to voltage variation and power losses of distribution systems

To promote the PV installation in Taiwan, a large scale photovoltaic (PV) system with total capacity of 1000kWp has been installed in a sporting complex in Kaohsiung, which is connected to the Taiwan Power Company (Taipower) distribution feeder. This paper is to investigate the impact of large PV system to the operation of distribution feeders. The PV power generation is simulated according to the hourly solar irradiation and temperature provided by the weather bureau. The voltage variation and the power system loss of the study distribution feeder are simulated by executing the three-phase load flow analysis for the impact analysis of the PV system. The results indicate that the reduction of voltage drop and power system loss can be obtained with the PV system installed to provide the dispersed generation for the local loads. However, the PV system penetration is limited due to the violation of voltage variation introduced by the large intermittent PV power generation.

Transient Response of an Incinerator Plant by Considering Boiler Model With Dynamic Steam Variation

This paper investigates the effect of boiler steam system on transient response of turbine generators for an incinerator plant. By performing the test of cogeneration units, the mathematical models of turbine generator, governor, and boiler have been identified, which are used in the computer simulation to solve the steam pressure and system frequency of the cogeneration system for islanding operation after tie line tripping. Due to the variation of trash heat value, the power output of the cogeneration unit is stochastically varied with the steam generation for normal operation, which will cause the dynamic change of tie line power flows. For the severe fault contingency of external power systems, the cogeneration system will be isolated by tie line tripping, and the system frequency response is then determined by including the boiler effect to represent the dynamic steam generation. Because of more sluggish response of the boiler system caused by unstable trash heat value, the transient response of the incinerator governor system is inferior to that of conventional industrial cogeneration systems. To maintain the system stability for successful islanding operation of the incinerator plant, the amount of load shedding after tie line tripping has to be properly determined based on the transient stability analysis by considering the response of boiler system.

Power Quality Assessment of a Hot Strip Mill with Cycloconverter Drive Systems

This paper presents the power quality assessment of a hot strip mill with cycloconverters for an integrated steel- making facility. Due to the stochastic operation characteristics of cycloconverters, the electric power consumed by the hot strip mill fluctuates dramatically with the harmonic currents of different integer orders and non-integer orders. Both of the harmonic distortion and voltage flicker problems have been introduced to deteriorate the power quality of the industrial customer. To mitigate the harmonic pollution and provide proper reactive power compensation at the same time, two single-tuned and three high-pass passive filters have been therefore applied according to the harmonic load flow analysis. After removing the resistor due to flash over damage, the 6.8th order high-pass filter has been converted to be a single-tuned filter. The impact of harmonic distortion on the existing filters and other equipments is investigated in this paper to ensure the harmonic distortion of the hot strip mill to be within the tolerance limit with the new configuration. To represent the harmonic current injection more accurately for the harmonic load flow analysis, the harmonic currents generated by cycloconverters are determined by field measurement. It is found that the total voltage harmonic distortion THDv solved by computer simulation is very close to the actual harmonic distortion. According to the harmonic load flow analysis, the serious harmonic pollution problem introduced by the cycloconverter drive system can be mitigated effectively by the implementation of proposed harmonic filter banks. Besides, the voltage flicker problem due to dramatic variation of large reactive power consumption of the hot strip mill can be solved by proper control of cycloconverters.

Transient stability study of the large synchronous motors starting and operating for the isolated integrated steel-making facility

This paper presents the influences of the large motor starting and the large rolling mill operation on the isolated integrated steel cogeneration facility by executing the transient stability analysis. The system configuration of the steel facility will be introduced first. Furthermore, the proper mathematical models and the accurate parameters of the co-generators, excitation systems and governor systems are investigated in detail. Both the static and dynamic load models are applied in this paper. To reduce the starting current of large motors, the conventional step-down voltage method by adjusting the suitable tap position of the autotransformer and the constant magnetic flux control method by using the VVVF inverter are considered in the computer simulations. Also, the system voltage and frequency fluctuations due to the operation of the rolling mill will be observed and investigated carefully to verify the isolated cogeneration can be operated well and safely.

Capacity expansion planning of distribution substations considering PV penetration

This paper presents the capacity expansion planning of distribution substations to meet the criterion of customer service reliability by considering the impact of photovoltaic (PV) systems. The historical solar radiation data are collected and applied to derive the probability distribution of PV power generation using the Markov random procedure. With the land use available for PV system installation and the growth rate of PV penetration, the total capacity of PV systems within the service territory of a distribution system is determined for each study year. By the integration of probabilistic PV power generation model and the risk model of main transformer outage, the loss of load expectation (LOLE)of the study distribution system is analyzed according to the load growth of various types of customers. It is found that the capacity expansion of distribution main transformers to maintain the service reliability can be deferred effectively when the annual PV penetration is included in the distribution system planning.