Hidehito Matayoshi

Thermal Units Commitment Integrated with Reactive Power Scheduling for the Smart Grid Considering Voltage Constraints

Abstract Nowadays, deregulation and liberalization in the power market has increased the competition in the retail power sectors. As a result, power companies need to reduce the operational cost and maximize profits by operating generators with high efficiency. On the other hand, the all electric residences are increasing, so controllable loads such as the electric water heater, heat pump and electric vehicle are being introduced to the power systems. The conventional system does not operate using thermal units with controllable loads in a coordinated manner. Therefore, the smart grid has become very popular in all over the world. This paper focuses on the reactive power scheduling of controllable loads, and determines the optimal operation of thermal units by satisfying the voltage constraints. The proposed method can satisfy the voltage constraint and reduce the rate of the power cost for a power system. The optimal control algorithm has been determined by the Tabu search method. Simulation results verify the proposed method and validate the performance and effectiveness of the control algorithm applied to the controllable loads and batteries.

Comparison and Validation of Operational Cost in Smart Houses with the Introduction of a Heat Pump or a Gas Engine

Abstract Due to the concerns of global warming and the depletion of energy resources, renewable energies such as wind generation (WG) and photovoltaic generation (PV) are gaining attention in distribution systems. Efficient electric equipment such as heat pumps (HP) not only contribute low levels of carbon to society, but are also beneficial for consumers. In addition, gas instruments such as the gas engine (GE) and fuel cells (FC) are expected to reduce electricity cost by exhaust heat. Thus, it is important to clarify which systems (HP or GE) are more beneficial for consumers throughout the year. This paper compares the operational cost for the smart house between using the HP and the GE. Current electricity and gas prices are used to calculate the cost of the smart house. The system considered in this research comprises a PV, battery, solar collector (SC), uncontrolled load and either an HP or a GE. In order to verify the effectiveness of the proposed system, MATLAB is used for simulations.

Optimal Scheduling Method of Controllable Loads in DC Smart Apartment Building

Abstract From the perspective of global warming suppression and the depletion of energy resources, renewable energies, such as the solar collector (SC) and photovoltaic generation (PV), have been gaining attention in worldwide. Houses or buildings with PV and heat pumps (HPs) are recently being used in residential areas widely due to the time of use (TOU) electricity pricing scheme which is essentially inexpensive during middle-night and expensive during day-time. If fixed batteries and electric vehicles (EVs) can be introduced in the premises, the electricity cost would be even more reduced. While, if the occupants arbitrarily use these controllable loads respectively, power demand in residential buildings may fluctuate in the future. Thus, an optimal operation of controllable loads such as HPs, batteries and EV should be scheduled in the buildings in order to prevent power flow from fluctuating rapidly. This paper proposes an optimal scheduling method of controllable loads, and the purpose is not only the minimization of electricity cost for the consumers, but also suppression of fluctuation of power flow on the power supply side. Furthermore, a novel electricity pricing scheme is also suggested in this paper.

Voltage imbalance compensation by injecting active and reactive power using demand side inverter

In recent years, the increased use of renewable energy sources (especially photovoltaic (PV) systems) has been remarkable, and use is growing because of considerations for environmental problems. However, renewable energy sources dependent on weather conditions, such as PV systems, cause output power fluctuations. In an electric distribution system, many PV systems are connected with distribution lines, and PV systems generate unstable power and inject unbalanced power to each line. Therefore, it is possible for voltage imbalance to occur in three-phase distribution systems. In this paper, we propose a method of voltage imbalance compensation by injecting active and reactive power using inverters in Power Conditioning Systems connected to smart houses. If voltage imbalance compensation is executed considering only the distribution voltage, there is a concern that the voltage at the power receiving end will deviate. Therefore, the optimum quantity of power injection is decided depending on the proper rate ...

Improvement of power system voltage stability using battery energy storage systems

Recently, use of the electric vehicle (EV) has begun to spread rapidly. Fortuitously, there is a possibility that the EV can be connected to a smart house in order to control charging and discharging operations. In this case, the smart house must perform optimal load sharing control according to the state of charge of the storage battery and the battery capacity. In this paper, voltage control is accomplished by the use of energy storage systems which are controlled using an original voltage stability criterion. The voltage stability criterion is made possible using the (P, Q)-V limits of voltage stability for the IEEE 5-bus system model. The effectiveness of the proposed method is verified by simulation results in the Matlab environment.

System frequency control using emergency demand response in power systems with large-scale Renewable Energy Sources

Recently, the introduction of Renewable Energy Sources (RESs) has been remarkable. However, the RESs are the cause of output power fluctuation which depends upon the weather condition. It also causes system frequency to deviate that means reliability of system is decreased. In particular, RESs output power which varies steeply and significantly is a cause of concern. Due to these output power fluctuations, the supply-demand balance gets worse, in the worst case, massive blackout can occur. In this paper, we propose emergency demand response (EDR) method to prevent the steep output power fluctuation of the RESs. The EDR adjusts the supply-demand balance by changing the consumed power of controllable load depending on system frequency drop. When the system frequency drops steeply, the system frequency is restored rapidly within acceptable range using the EDR.

Uninterruptible smart house equipped with a single-phase dq-transformation system

This paper proposes an uninterruptible all-electric smart house equipped with photovoltaic system and storage battery. There is a control delay in the conventional control system, because the system uses root mean square or average values for the control method. Therefore, it causes transient currents when load variation and system faults occur. The transient current adversely affects the in-house loads (e.g., precision equipment). In this paper, the control delay is reduced by using a control system with single-phase dq-transformation information. Therefore, the smart house achieves a reduction of the transient current caused by load variation and system faults through the use of instantaneous inverter control. The effectiveness of the proposed method is verified by simulation results given by the Matlab/SimPowerSystems® environment.

Suppression of power system voltage and frequency fluctuations by decentralized controllable loads

A recent trend of the power system is the ever increasing number of distributed generators (DGs) utilizing renewable energy sources, which have output powers that fluctuate due to unpredictable weather and ambient conditions. This causes fluctuations in system frequency and bus voltages, resulting in poor quality power, higher prices for electricity, and increased chances of reverse power flow and voltage collapse. In order to allow higher levels of DG penetration, methods of reducing the effects of fluctuations must be implemented. This paper proposes a method to mitigate these fluctuations using controllable loads such as heat pump water heaters (HPs) and battery storage systems. The HPs are controlled using a decentralized bang-bang (on/off) control based on the cumulative distribution of water temperature of HPs in the local area and the local frequency. Battery systems are controlled using a smart frequency and voltage droop characteristics based control. The decentralized bang-bang control mitigates local frequency fluctuations by increasing active power consumption to lower frequency as well as decreasing active power consumption to increase the frequency. The smart droop characteristics based control applies a commonly used droop characteristics control to voltage and frequency; however, the control system monitors the state of charge (SOC) of the battery system and takes appropriate actions to prevent the SOC from reaching a critical level. The results of simulations show that fluctuations in frequency and bus voltage are mitigated by the application of the proposed control methodologies without adversely affecting the comfort level of consumers.

A Robust H∞ Controller Based Gain-scheduled Approach for the Power Smoothing of Wind Turbine Generator with a Battery Energy Storage System

Abstract Output power fluctuation of the wind turbine generator is a serious issue for power systems. The battery energy storage system is installed to the power system to solve this problem. However, the large battery energy storage system can increase the capital cost of the wind turbine generator system. Hence, the capacity of the battery should be reduced as much as possible. This article presents an H∞ based control method for the output power smoothing method of the wind turbine generator by using a battery energy storage system. The output power fluctuation of the wind turbine generator is considered in the frequency domain. Low-frequency fluctuations are smoothed by pitch angle control of the wind turbine generator, while high-frequency variations are smoothed by charge or discharge of the battery energy storage system, respectively. The battery energy storage system’s capacity and mechanical stress of wind turbine blades can be reduced by the proposed method. In addition, the gain-scheduled control theory is applied to the pitch angle control system of the wind turbine generator. Therefore, the robust control performance for high non-linearities of the wind turbine generator model can be achieved. The effectiveness of the proposed method is validated by numerical simulations.

Smart house-based optimal operation of thermal unit commitment for a smart grid considering transmission constraints

ABSTRACT This paper presents a smart house-based power system for thermal unit commitment programme. The proposed power system consists of smart houses, renewable energy plants and conventional thermal units. The transmission constraints are considered for the proposed system. The generated power of the large capacity renewable energy plant leads to the violated transmission constraints in the thermal unit commitment programme, therefore, the transmission constraint should be considered. This paper focuses on the optimal operation of the thermal units incorporated with controllable loads such as Electrical Vehicle and Heat Pump water heater of the smart houses. The proposed method is compared with the power flow in thermal units operation without controllable loads and the optimal operation without the transmission constraints. Simulation results show the validation of the proposed method.