This paper proposes a high-efficiency dimmable LED driver for light emitting diodes (LED). The developed LED driver consists of a full-bridge resonant converter and six buck converters. The function of the full-bridge resonant converter is to obtain a smooth dc-link voltage for the buck converters by phase-shift modulation (PSM) while that of the six buck converters is to drive six LED modules, respectively. The gate voltage of the active switch of each buck converter is a combination of high-frequency and low-frequency pulses. The duty ratio of the high-frequency pulse controls the LED voltage and thereby, controls the amplitude of LED current. LEDs are dimmed by low-frequency pulse-width modulation (PWM) to vary the average current flowing through LED. Circuit equations are derived and circuit parameters are designed. High circuit efficiency is ensured by operating the active switches at zero-voltage switching-on to reduce the switching loss. Finally, a prototype circuit was built to verify the accuracy and feasibility of the proposed LED driver.
To support the demand response function for smart grid, an intelligent power meter with hybrid communication module has been proposed in this paper. The circuit module consisting of VI measurement, power calculation chip, microprocessor and PLC/ZigBee/RS-485 communication is designed to support load control to achieve load reduction after receiving the demand response command of via two way communication. The load control function can also be activated by the real time pricing information, which has been downloaded from utility control center. The embedded power management system is developed to perform the management of intelligent power meters to monitor and control electrical appliances. Based on the field test, the intelligent power meter can be used for load shedding or power due to achieve energy conservation and enhance system stability for smart grid application.
The penetration level of a 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. 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 1-year period are determined according to the annual duration of solar irradiation. 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.
This paper investigates the impact of photovoltaic generation system (pvgs) on the distribution system. The installations of various types of distributed generators (dgs) on the distribution system have significantly changed the operating, planning and maintaining strategies of the utility. In this paper, one practical Taiwan Power Company (taipower) distribution system with a large-scale of pvgs is selected for study. Many power quality issues like steady state voltage variation, reverse power, voltage unbalance, short-circuit current and harmonic are analyzed by considering many different operation scenarios of the distribution system and pvgs. The simulation results are compared with the related standards and it is found that the pvgs impact on the concerned power quality and reliability issues are all within the limits. It is concluded that the simulation results of the paper are very helpful to the electric utilities and pv producers for providing better power quality as well as increasing photovoltaic (pv) penetration in distribution grids.
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