Motoki Tokudome

Frequency and voltage control of small power systems by decentralized controllable loads

From depletion of energy resources and consideration to natural environment, introduction of renewable energy facilities has been increasing annually. Moreover, introduction of photovoltaics has increased on the demand side. However, due to the fluctuating power from renewable energy sources, frequency and voltage fluctuations of power systems become problematic. At the same time, there has been a marked increase in the electrification of residential houses, as well as electric vehicles. Thus, capability for energy control has been increasing, with the load utilized as controllable load. This paper presents a methodology for grid frequency and voltage control by distributed controllable loads. The power system consists of diesel generators, wind generators, photovoltaics and loads. By applying power consumption control under droop characteristics, grid frequency and terminal voltage fluctuations are maintained around rated value. In order to verify the effectiveness of the proposed system, MATLAB/Simulink® is used for simulations.

Frequency and voltage control of isolated island power systems by decentralized controllable loads

From depletion of energy resources and consideration to natural environment, dispersed power system such as wind power generators are introduced. Moreover, all electrification in houses or residences and electric vehicles are increased in recent years. Again, introduction of photovoltaics has increased in demand side. However, due to the fluctuating power from renewable energy sources and loads, frequency and voltage fluctuation of power system become problematic. This paper presents a methodology for grid frequency and voltage control by distributed controllable loads. This system consists of diesel generators, wind generators, photovoltaics and loads. By applying power consumption controller adopted PI control, grid frequency and voltage fluctuations are maintained around rated value. In order to verify the effectiveness of the proposed system, MATLAB/Simulink is used for simulations.

Output power leveling of wind generation system using inertia of wind turbine

Wind energy is a significant and powerful natural resource that is safe, clean, and abundant. However, wind energy has a drawback of having only 1/800 density as compared to that of water energy, and it is not constant and wind turbine output is proportional to the cube of wind speed, which causes the generated power of wind turbine generator (WTG) to fluctuate. In this paper, a technique is proposed for output power leveling of a wind generation system. Wind turbine blades have a large inertia compared to the inertia of generator. The inertia of the rotor behaves like an inductor in an electrical circuit. It helps smooth the wind turbine output power, stores energy during acceleration, and restores energy during deceleration. The effectiveness of output power leveling control is verified by simulations for the wind power generation system.

A new control methodology of wind farm using short-term ahead wind speed prediction for load frequency control of power system

Currently, there are several published reports on wind power detailing various researches based on such subjects as pitch angle control, variable speed wind turbines, energy storage systems, and so on. These reports propose output power leveling to reduce the adverse effects of power system frequency deviation. In this context, it is desirable to decrease frequency deviations of power systems by output power control of wind turbine generator that has potential of effective utilization. This paper presents an output power control methodology for wind farm which can decrease frequency deviations of a power system using load power estimation. Load power is estimated by a disturbance observer and, output power command for wind farm is determined according to estimated load. Besides, each wind turbine generator can also be controlled well during wind turbulence since the power command is determined by considering short-term ahead predicted wind speed. In order to verify the proposed method, simulation results are presented to show the effectiveness of considering wind turbulence and sudden load variation.

Frequency control strategy for parallel operated battery systems based on droop characteristics by applying H ∞ control theory

Stand alone ac power supply system like that is designed for isolated islands is subjected to large frequency and voltage fluctuations caused by power deviation of wind turbine generator and load demand. An autonomous decentralized frequency control system of parallel operated decentralized generators based on droop characteristic is presented in this paper. The conventional droop control methods proposed in past researches exhibit slow and oscillating dynamic responses. Moreover, the conventional droop control is affected by measurement noise when the fast controllability of the system is emphasized. This paper proposes the improved droop control system for load sharing of multi operated decentralized generators by applying H∞ control theory, improving transient response of droop control and robustness against measurement noise and parameter variations. Simulation results validate the effectiveness of the proposed control system.

A frequency control approach by decentralized generators and loads in power systems

Many isolated small power systems are powered by diesel generators, which results in greater operating costs than interconnected large grids. It is therefore desirable to integrate renewable energy sources such as wind power into these small grids. However, due to the fluctuating power generation from renewable energy sources, frequency deviations of power systems become problematic. Distributed intelligent load control can be used to significantly increase renewable energy penetration and cut diesel fuel consumption. This paper presents a methodology for grid frequency control by electric water heaters as controllable loads. This system consists of diesel generator, wind farm, and loads. By applying a power consumption controller adopted from Hinfin control theory, grid frequency deviation is maintained around rated value. In order to verify the effectiveness of the proposed system, MATLAB/Simulink is used for simulations.

Torsional torque suppression of decentralized generators using H ∞ observer with parameter identification

The output power fluctuation of renewable energy power plants such as wind turbine generator and photovoltaic system result in frequency deviation and terminal voltage fluctuation. Furthermore, these power fluctuations also affect the turbine shafting of diesel generator and gas-turbine generators which are the main power generation systems in isolated islands. This paper presents a control strategy that achieves torsional torque suppression and power system stabilization. Since the measurement of the torsional torque is difficult technically, and there is uncertainty in mechanical constants of the shaft torsional system, the torsional torque is estimated by using developed H∞ observer with parameter identification system. The simulation results validate the effectiveness of the proposed control system.

Advanced digital control for the harmonization of wind-based energy in the electric power supply

As wind turbines continue to grow in size and flexibility and are deployed in more hostile environments, the need to develop advanced control schemes will be elemental to deliver the lowest possible energy costs. This paper explores controller design based on modeling the wind speed as a stochastic process, and the wind generating system (WGS) as a multi-mass system with a soft shaft linking the turbine with the asynchronous generator. The control objectives are to enhance reduction in stresses on the drive-train and to ensure operation geared toward optimal power conversion. A sophisticated control strategy incorporating a multi-objective, full-state feedback with state estimation linear quadratic Gaussian (LQG) for generator torque control is proposed. This study focuses on above rated wind speeds, and the LQGs main purpose is to add damping to the drive-train, thereby minimizing cyclic fatigue, while a pitch mechanism prevents rotor overspeed thus ensuring the maximum power constraint is respected. Simulations show the efficacy of the proposed paradigm in meeting the control objectives.

Torsional torque suppression of decentralized generators using LQR obsever with parameter identification

The output power fluctuation of renewable energy power plants such as wind turbine generator and photovoltaic system result in frequency deviation and terminal voltage fluctuation. Furthermore, these power fluctuations also affect the turbine shafting of diesel generator and gas-turbine generators which are the main power generation systems in isolated islands. This paper presents a control strategy that achieves torsional torque suppression and power system stabilization. Since the measurement of torsional torque is difficult technically, and there is uncertainty in mechanical constants of the shaft torsional system, the torsional torque is estimated by using LQR observer with parameter identification system. The simulation results validate the effectiveness of the proposed control system.

Torsional torque suppression of decentralized generators using H ∞ observer

Electric utility deregulation has made it possible for power producers and suppliers (PPSs) to enter the electricity market in Japan. PPSs are supposed to achieve 30-minute balancing control for stable supply of electrical power, in which energy demand and energy supply should be matched within thirty minutes. Meanwhile, load rejection and instantaneous voltage drop greatly affect turbine shafting, that is, torsional torque oscillation. Therefore, PPSs have to consider the reduction of torsional torque to prevent generator shaft damage. However, observation of torsional torque is technically difficult. Thus, this paper proposes an observation system for torsional torque based on Hinfin theory. This work also introduces a control system that achieves both the 30-minute balancing control as well as reduction in torsional torque by use of an Hinfin observer for the shaft torque. The effectiveness of the proposed control system is verified by using MATLAB.