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This paper proposes a voltage control method based on a multi-agent system (MAS) for a distribution system to reflect the intentions of owners of distributed generators (DGs) with regard to voltage regulation. The proposed voltage control system consists of three types of agents: monitoring agents, DG agents, and a moderator. If a voltage violation is detected by a monitoring agent, DG agents send bidding data which represent the intentions of their owner to the moderator. The moderator determines the reactive power references of the DGs based on the voltage sensitivity and the bidding data. In order to interpret the complex relationship between the input and output and to reduce the calculation burden, a fuzzy inference system (FIS) is used for determining the reactive power reference. In addition, this paper proposes a method to compensate for voltage sensitivity. The proposed voltage scheme is validated by a pilot system.

Nowadays, due to the development of power electronic technology, nonlinear electronic loads using power electronic circuits are widespread in power grids. The loads can consume more reliable and high-quality power through the power conversion circuits. However, the power grids can suffer significant harmonic currents caused by these power electronic circuits. This paper proposes a new harmonic compensation method of utilizing multiple power inverters that integrate distributed resources (DRs) to a microgrid. Therefore, harmonic problems can be solved without installing additional power filters to the grids. To coordinate multiple various DGs such as small distributed generators (DGs) and battery energy storage systems (BESSs), the proposed method considers multiple objectives in terms of energy cost, generation margins of DGs and energy margins of BESSs. The optimization algorithm is constructed based on fuzzy multi-objective optimization model so that the proposed method assigns the additional output power of each DR that is needed for harmonic elimination. Simulations of the suggested coordination strategy for harmonic compensation using multiple DRs are conducted in the microgrid including two inverter-based DGs and one BESS to verify the performance of the proposed method.

Image rejection and harmonic rejection are important performance parameters in wideband low-IF TV system. In this paper, double quadrature harmonic rejection architecture insensitive to gain and/or phase mismatch is proposed to satisfy stringent image rejection ratio (IRR) and harmonic rejection ratio (HRR) for analog/digital TV tuner ICs. Fabricated in 0.13µm CMOS process, more than 60dB of the IRR is achieved over 42–864MHz RF frequency and more than 69dB of the 3rd HRR is achieved over 42–306MHz RF frequency without any calibration.

This paper proposes a new method to determine the droop of the inverter-based distribution generations (DGs). Conventionally, inverter-based DGs have droop controller with fixed slope according to their capacity. Some additional control methods have been proposed in order to enforce the maximum or minimum limit of a unit. However, in some severe cases, the frequency deviation during the islanded mode becomes larger with the existing methods. To overcome this problem, the proposed method, namely “variable droop,” determines the droop of DGs according to their operating points. Using the proposed method, the frequency can be maintained within the predetermined limits and the load demand can be properly shared by the DGs. The effectiveness of the method is verified by the PSCAD/EMTDC simulation.

This paper presents a grid-connected photovoltaic (PV) system with the new operation method considering voltage regulation in distribution system. In proposed system, PV system adjusts real power and reactive power injection at connection point, in order to maintain the overall system voltage within acceptable range and improve power quality. It consists of modeling of PV array, inverter and inverter controller using PSCAD/EMTDC, and development of operation method of PV generation for voltage regulation in distribution system. PV array modeling is accomplished using 2-diode model which is generally used, and inverter with control system is implemented using proposed operation method based on instantaneous power theory and hysteresis current control. Proposed operation method consists of 3 stages control and using that operation method, overall system effectiveness is improved. To validate the effectiveness of the proposed system, it is compared with system with conventional operation under variable case such that connection, disconnection, load changes and voltage sag using PSCAD/EMTDC.

By introducing the concept of simulated annealing into the conjugate gradient algorithm, we propose a stochastic conjugate gradient algorithm which has an increased probability of obtaining a global minimum, and the determination of the weights of the cost function becomes easier due to the wider feasible scope of its parameters. We apply the proposed algorithm to an optimal task partitioning and compare the scope of the parameters and the probability of obtaining a global minimum with those of the Boltzmann machine. Simulation results show characteristics in favor of the proposed algorithm. We also present a hardware for the proposed algorithm.