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In recent years, the amount of distributed generators in the power grid has increased. Most of these distributed generators are renewable energy facilities using wind turbine generators or photovoltaic power systems. The increase in distributed generators is mostly due to environmental issues, growing concern of resource depletion, and economic benefits for residents and homeowners. Along with the increase in distributed generators, all-electric apartment buildings and residential homes with electric vehicles are on the rise. This trend is beneficial for both the environment and the residents; however, the fluctuating power from renewable energy sources and unstable loads causes fluctuations in grid frequency and distributed voltage which become problematic. This paper presents a methodology to control system frequency and distributed voltage using distributed controllable loads such as the heat pump water heater (HP) and large capacity batteries such as those of the electric vehicle (EV). By applying a power consumption controller using decentralized control for heat pump water heaters and droop characteristics for batteries, fluctuations of grid frequency and voltage are suppressed to a desired value. In order to verify the effectiveness of the proposed system, MATLAB/Simulink is used for simulations. [ABSTRACT FROM AUTHOR]

In order to solve the problems of global warming and depletion of energy resource, renewable energy systems such as wind generation are getting attention. However, wind power fluctuates due to variation of wind speed, and it is difficult to perfectly forecast wind power. This paper describes a method to use power forecast data of wind turbine generators considering wind power forecast error for optimal operation. The purpose in this paper is to smooth the output power fluctuation of a wind farm and to obtain more beneficial electrical power for selling. [ABSTRACT FROM AUTHOR]

This paper deals with controlling the output power smoothing of a wind energy conversion systems (WECS) by using permanent magnet synchronous generator (PMSG). It uses the inertia control of the wind turbine and DC-link voltage control. The PMSG is connected to the grid through a generator-side converter and a grid-side inverter based on AC-DC-AC methods. The generator-side converter is used to control the torque of the PMSG while the grid-side inverter is used to control DC-Link voltage and grid voltage. Fuzzy logic is implemented to determine the torque command by using inertia of wind turbine. The inputs of the fuzzy logic are given by the operating point of the rotational speed of the PMSG and the difference between the wind turbine torque and the generator torque. From the proposed method, the generator torque is smoothed and kinetic energy generated by the inertia of the wind turbine is used to smooth the power fluctuations of PMSG. Also, a stable operation of WECS is achieved during the system fault by using the chopper circuit in the DC-link circuit. The output power smoothing is achieved with stability and low cost. The effectiveness of the proposed method is verified by the numerical simulations. [ABSTRACT FROM AUTHOR]

This paper presents the operation under fault and protection of multi DC smart grids connected to the DC transmission line. The smart grid consists of wind turbine and photovoltaic generators, controllable loads, generator side and grid side inverters. The voltage stability of the DC bus voltage is attained by applying the power consumption control of controllable loads, the power control of grid connected converter and power control of renewable plants. On the other hand, the fault protection for short-circuit and low resistance ground fault at the DC transmission line was sighted. Simulation results based on PSIM are provided to demonstrate the effectiveness of the system. [ABSTRACT FROM AUTHOR]

This paper presents a high efficiency drive strategy for micro-turbine generator (MTG) in which permanent magnet synchronous generator (PMSG) is used. PMSG operates at maximum efficiency point by optimizing the phase of armature current of PMSG; i.e., an optimum d-axis current in the rotor reference frame is analytically derived from mathematical model of PMSG taking iron loss into account. In addition, in order to use turbine output power effectively, compressor input power is minimized by optimizing revolving speed of PMSG. Simulation results confirm validity of the proposed method. [ABSTRACT FROM AUTHOR]

Currently, there are several published reports on wind farms (WFs) for controlling output power by using pitch angle control. In addition, to reduce the adverse effects of frequency deviations, battery energy storage systems (BESSs) are introduced to small power systems. In this context, this paper presents a frequency control method by the WF and the BESS using load estimation. The load is estimated by a disturbance observer. The frequency deviations in low and high frequency domain are reduced by the WF using pitch angle control and battery charge/discharge, respectively. By using the proposed method, the reduction of the rated capacity of the BESS is possible. Furthermore, for the pitch angle control system of each WTG in the WF, generalized predictive control (GPC) is applied to achieve robust control performance. The effectiveness of the proposed method is verified by numerical simulation. [ABSTRACT FROM AUTHOR]

This paper presents a determination methodology for finding optimal operation schedules of thermal units (namely unit commitment) integrated with an energy storage system (ESS) to minimize total operating costs. A generic ESS formulation along with a method for solving unit commitment (UC) of thermal units with ESS is proposed to serve this purpose. The problem of unit commitment with an ESS is solved using the Priority List method. Intelligent Genetic algorithm (GA) is included in the algorithm for generating new and potential solutions. The proposed method consists of two steps. The first step is to determine the schedule of ESS and the schedule of thermal units. The second step is to dispatch the hourly output of thermal units and the ESS which comply a minimized total production cost. The proposed method is applied to a power system with ten thermal units and a large ESS. The presented simulation results show that the schedule of thermal units with an ESS of a particular life cycle, achieved by the proposed method, minimizes the operating cost. The discussion regarding the determination of schedule thermal units (TU) along with the integrated ESS may interest many types of ESS due to their generalized formulations. [ABSTRACT FROM AUTHOR]

In recent years, renewable energy generation has been coming up for effective use of natural energy, such as wind energy. Induction generators consisting squirrel-cage rotors are widely used as wind generators because of their salient features like robust rotor design, simplicity in the construction, maintenance free operation, etc. In this paper, it is derived that the transient current, electromechanical torque, and active power taking into account rotor speed change of induction generators at three-phase fault conditions. The output equations of the induction generator has nonlinearity, and the speed-time characteristic in a fault period is also expressed by the nonlinear equation. The approximation to derive analytical formulas for transient conditions is proposed, and the transient behavior of the induction generator is analyzed by the developed equations. The simulation block diagram in MATLAB/SIMULINK is constituted using the system equation in consideration of the nonlinearity of the induction generator. The simulation results obtained from each theoretical analysis are in close agreement with that of results obtained using MATLAB/SIMULINK simulation. Furthermore, theoretical discussion also developed to determine the fault phase angle and the time at which maximum transient currents flow in the system. [ABSTRACT FROM AUTHOR]

In recent developments wind power has been gaining rapid usage as an alternative source of electrical power and there is need to formulate optimized control schemes for power generation. This paper presents a sensorless maximum power point tracking control methodology for a wind power generation system. For the sensorless vector control a sliding mode observer is utilized in the estimation of the rotor speed while the rotor position is estimated based on the flux linkage. The Powell method is introduced to improve the efficiency of the permanent magnet synchronous generator (PMSG) d-axis current optimization. To ensure robustness of the proposed paradigm to parameter variations, the windmill loss coefficients determining the optimal rotor speed are identified online. Results of simulations confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents an approach for short-term electricity price and load forecasting using the artificial neural network (ANN) computing technique. The described approach uses the three-layered ANN paradigm with back-propagation. The publicly available data, acquired from the deregulated Victorian power system, was used for training and testing the ANN. The ANN approach based on similarity technique has been proposed according to which the load and price curves are forecasted by using the information of the days being similar to that of the forecast day. A Euclidean norm with weighted factors is used for the selection of similar days. Two different ANN models, one for load forecasting and another for price forecasting, have been proposed. Test results show that average price and load MAPEs for the year 2003 by using the ANN approach are obtained as 14.29% and 0.95%, respectively. MAPE values obtained from the price and load forecasting results confirm considerable value of the ANN based approach in forecasting short-term electricity prices and loads. [ABSTRACT FROM AUTHOR]