Wei-Lin Hsieh

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.

Enhancement of PV Penetration With DSTATCOM in Taipower Distribution System

The PV penetration level of a distribution system is often limited by the violation of voltage variation caused by large intermittent power generation. This study investigates the use of a distribution static compensator (DSTATCOM) in reactive power compensation for system voltage control, during peak solar irradiation, in order to increase the PV installation capacity of a distribution feeder and avoid the voltage violation problem. PV power generation is simulated using 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 determine the maximum PV power injection without causing voltage violation. By applying the proposed voltage control scheme of DSTATCOM during high solar irradiation periods, the total power generation and the total energy delivered by the PV system over one year are determined according to the annual duration of solar irradiation. The annual sales of PV power, the system O&M cost, the cost of DSTATCOM installation and the initial capital investment for a PV system are then used to calculate the cash flow over the system life-cycle and the final net present value (NPV) of the PV project. With the proposed DSTATCOM voltage control to perform reactive power compensation, the optimal installation capacity of PV systems can be determined by maximizing the net present value of the system to ensure the best cost-effectiveness of the PV project and to better utilize solar energy.

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

To promote the PV installation, a large scale photovoltaic (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.

Loading Balance of Distribution Feeders With Loop Power Controllers Considering Photovoltaic Generation

For the operation of distribution systems, loading balance of distribution feeders is important for reducing power loss and mitigating power flow overloading. In this paper, a loop power controller (LPC) is applied for the control of real power and reactive power flows by adjusting voltage ratio and phase shift so that the loading balance of distribution feeders can be obtained. To incorporate photovoltaic (PV) power generation in feeder loading balance, a Taipower distribution feeder with large PV installation is selected for computer simulation. Daily loading unbalance is determined by analyzing PV power generation recorded by the SCADA system and by constructing daily power load profiles based on distribution automation system (DAS) data. The load transfer required to achieve loading balance and the line impedance of distribution feeders are used to derive the voltage ratio and phase shift of the LPC. Computer simulations indicated that loading balance can be achieved in distribution feeders with large PV system installation by using loop power controllers according to the variation of solar energy and power loading of study feeders. The system power loss reduction resulting from feeder loading balance by LPC is also investigated in this paper.

Development of smart distribution grid

To enhance the service reliability and increase the penetration level of distributed generation in power systems, the smart grid has been under development for many power companies in the whole world. This paper describes the implementation of the distribution automation system (DAS) in Taiwan Power Company and how it is used to improve the service reliability of distribution systems in Taipower. With the operation of DAS system, the customer outage duration has been reduced dramatically for the fault contingency on the distribution feeders to achieve the resilient function of smart grid by reforming the function of fault detection isolation and restoration (FDIR) automatically. To support more functions of smart distribution, the advanced distribution automation system (ADAS) is proposed in this paper to cover the application of PV inverter control to reduce the system impact due to intermittent power generation by renewable energy such as wind and solar power. The ADAS will also perform the asset management of transformers to improve the utilization of distribution facilities; the FDIR function of ADAS system proposed will be extended to cover the distribution laterals and customers.

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.

Optimal penetration level of PV generation for distribution system load transfer

This paper is to investigate the impact of load transfer operation to the reduction of PV installation capacity so that the limit violation of voltage fluctuation caused by PV generation can be prevented. To determine the constraint of PV installation capacity when the load transfer is executed for distribution operation, the large scale PV systems installed in two feeders of the Feng-Shan District of Taiwan Power Company (Taipower) have been selected for computer simulation. The PV power generation is simulated according to the hourly solar irradiation and temperature provided by the weather bureau. The voltage variations of the distribution feeders are also performed by executing the 3-φ load flow analysis for the impact analysis of the PV system. To solve the reduction of PV installation capacity due to load transfer operation of distribution system, the advanced distribution automation system (ADAS) may be considered to perform the control of PV inverter for generation curtailment during the load transfer for service restoration. With the control of PV power generation to prevent over voltage problem, the PV installation capacity of distribution feeders can be increased to improve the penetration level PV system to make full use of renewable solar energy.

Advanced distribution automation system for control of PV inverters to enhance PV penetration

The PV penetration level of a distribution system is often limited by the violation of voltage variation introduced by large intermittent power generation. This study investigates the control of PV inverters. To achieve better control of PV inverters, the Advanced Distribution Automation System is proposed in this paper to monitor the system voltage variation due to large ramping rate of real power injection by PV systems. The ADAS system is also considered to support the fault detection, isolation and service restoration (FDIR) for enhancement of system reliability. In reactive power compensation for system voltage control during peak solar irradiation in order to increase the PV installation capacity of a distribution feeder without causing voltage violation problem.

Coordination control of PV inverters for load transfer operation of distribution feeders with high penetration of PV installation

This paper presents the dispatch of reactive power compensation and real power curtailment of PV systems to prevent the over voltage violation when load transfer between distribution feeders is executed. The voltage sensitivity factors of reactive power injection at all PV buses are derived according to the configuration of distribution network. The Advanced Distribution Automation System (ADAS) issues the control command to each PV inverter for adjustment of PV power generation according to the sensitivity coefficients and PV installation capacity so that the ancillary service of voltage support can be provided by all PV systems in a fairer manner. The practical Taipower distribution feeders are selected for computer simulation to verify the effectiveness of the proposed control method to mitigate the voltage violation problem for the operation of load transfer between distribution feeders with high penetration of PV installation.