Shinya Yoshizawa

Detection of Cyber Attacks Against Voltage Control in Distribution Power Grids With PVs

In this paper, we consider the impact of cyber attacks on voltage regulation in distribution systems when a number of photovoltaic (PV) systems are connected. We employ a centralized control scheme that utilizes voltage measurements from sectionizing switches equipped with sensors. It is demonstrated that if measurements are falsified by an attacker, voltage violation can occur in the system. However, by equipping the control with a detection algorithm, we verify that the damage can be limited especially when the number of attacked sensors is small through theoretical analysis and simulation case studies. In addition, studies are made on attacks which attempt to reduce the output power at PV systems equipped with overvoltage protection functions. Further discussion is provided on how to enhance the security level of the proposed algorithm.

On detection of cyber attacks against voltage control in distribution power grids

In this paper, we consider the impact of cyber attacks on voltage regulation in distribution systems. We employ a centralized control scheme which utilizes voltage measurements from sectionizing switches equipped with sensors for connecting distributed generation. Through detailed case studies by simulations, it is demonstrated that if measurements are falsified by an attacker, voltage violation can occur in the system. However, by equipping the control with a detection algorithm, we verify that the damage can be limited especially when the number of attacked sensors is small. Further discussion is provided on how to enhance the security level of the proposed algorithm.

Distributed Energy Management for Comprehensive Utilization of Residential Photovoltaic Outputs

The introduction of photovoltaic power systems is being significantly promoted. This paper proposes the implementation of a distributed energy management framework linking demand-side management systems and supply-side management system under the given time-of-use pricing program for efficient utilization of photovoltaic power outputs; each system implements a consistent management flow composed of forecasting, operation planning, and control steps. In our framework, demand-side systems distributed in the electric distribution network manage individual energy consumption to reduce the residential operating cost by utilizing the residential photovoltaic power system and controllable energy appliances so as not to inconvenience residents. On the other hand, the supply-side system utilizes photovoltaic power maximally while maintaining the quality of electric power. The effectiveness of the proposed framework is evaluated on the basis of an actual Japanese distribution network simulation model from both the supply-side and demand-side viewpoints.

Centralized voltage control method of load ratio control transformer and step voltage regulator for bank fault restoration

This paper presents and verifies a method for centralized voltage control of load ratio control transformers and step voltage regulators for bank fault restoration. In conventional methods, voltage control in distribution systems primarily serves to alleviate voltage violations. Conventional methods remain imperfect, however, so it is necessary to evaluate how to minimize the number of violations during bank fault restoration. Thus, the proposed method adjusts the tap position of voltage regulators to minimize the number of affected customers in consideration of the power factor control of photovoltaic generation systems. We perform numerical simulations of bank fault restoration to verify the effectiveness of the proposed method, and visually compare the results with those of the conventional method.

Voltage control of multiple step voltage regulators by renewing control parameters

This paper presents a novel method of determining the control parameters and a voltage control method for multiple step voltage regulators (SVRs) in a single feeder. The main feature of the proposed method is the updating of the control parameters at constant intervals to minimize the amount of voltage violations and the tap operation times of the SVRs while maximizing the voltage margin from the proper limits in the distribution system. To determine the SVR control parameters, a combined method of a greedy algorithm and a tabu search is used. To verify the proposed method, numerical and experimental simulation studies based on an actual distribution model with photovoltaic (PV) sources are carried out. The results show that the proposed control method can reduce the amount of voltage violations and tap operation times of the SVRs compared with the conventional voltage control method.

The basic study for development of a method for determining the LDC parameters of LRT and SVR using PV output forecasting

This paper proposes a new method for determining the LDC (Load Drop Compensator) parameters of LRT (Load Ratio Transformer) and SVR (Step Voltage Regulator). Since the voltage control effect of LRT and SVR depends on the LDC parameter, the proper parameters should be chosen in order to control voltage within proper range. When the photovoltaic generation system is installed in the distribution system, voltage control becomes difficult and the optimal parameters in the daytime differ from those in the nighttime. In the proposed method, the parameters are reset every hour. The parameters are determined by choosing from the database including all the optimal parameters for each time period in the past. The database also includes the PV output profiles and load profiles in the past, and the proposed method searches the similar time periods in the database to the next one hour period by comparing forecasted PV output profiles with that in the database. And the common parameters among the similar time periods are chosen for the next one hour. The simulation results will be shown to evaluate the performance of proposed method.

Novel voltage control of multiple step voltage regulators in a distribution system

This paper presents a novel method for determining the control parameters and a voltage control method for multiple step voltage regulators (SVRs) in a single feeder. The main purpose of the proposed method is to reduce the amount of voltage violation and the tap operation times and to extend the voltage margin from the upper and lower voltage limits by updating the control parameters of the SVRs. To determine the control parameters of the SVRs, an improved greedy algorithm is used. In order to verify the proposed method, a numerical and experimental simulation study based on an actual distribution model is carried out. The results show that the proposed control method has the capability to reduce the amount of the voltage violation in a distribution system and the tap operation times of the SVRs.

Versatile Modeling Platform for Cooperative Energy Management Systems in Smart Cities

With growing attention to sustainability and recognition of the impact of global warming problems, energy supply and consumption have become critically important. This paper presents the construction of a modeling platform accommodating cooperative energy management systems (EMSs), which virtually produces the model of a smart city with a distribution network (DN) by using a wide range of data obtained from the real world. The platform involves models of various EMSs, governing the operation of a power system or controlling consumer-installed devices, and simulating the power flow, electrical losses, and voltage in the DN. In addition, indices measuring the sustainability of the model city, such as CO2 emission, are estimated from scenarios, for example, photovoltaic system installation, electric vehicle penetration, etc. The results can be visually displayed and the platform is highly versatile and applicable to various types of issues associated with smart cities. Two case studies are presented in detail.

Electric Vehicle Charge-Discharge Management for Utilization of Photovoltaic by Coordination between Home and Grid Energy Management Systems

This paper proposes an electric vehicle (EV) charge-discharge management framework for the effective utilization of photovoltaic (PV) output through coordination based on information exchange between home energy management system (HEMS) and grid energy management system (GEMS). In our proposed framework, the HEMS determines an EV charge-discharge plan for reducing the residential operation cost and PV curtailment without disturbing EV usage for driving, on the basis of voltage constraint information in the grid provided by the GEMS and forecasted power profiles. Then, the HEMS controls the EV charge-discharge according to the determined plan and real-time monitored data, which is utilized for mitigating the negative effect caused by forecast errors of power profiles. The proposed framework was evaluated on the basis of the Japanese distribution system simulation model. The simulation results show the effectiveness of our proposed framework from the viewpoint of reduction of the residential operation cost and PV curtailment.

Method for enumerating feasible LDC parameters for OLTC and SVR in distribution networks

This paper presents a method for enumerating the feasible load drop compensator (LDC) parameters of on-load tap changer (OLTC) and step voltage regulators (SVRs) in distribution networks utilizing data acquired by SCADA. Deriving the feasible combinations of LDC parameters is becoming important because voltage control is becoming difficult due to the introduction of photovoltaic generation systems, and the voltage control effectiveness of OLTC and SVRs depends on their three LDC parameters: the target voltage, the dead-band, and the impedance. However, an exhaustive search takes a lot of time and heuristics or metaheuristics provide no guarantee on the quality of the solution. The proposed method derives all the feasible LDC parameters, with which tap operation keeping voltage within the proper range is performed, within practical time. To evaluate the performance of the proposed method, the numerical simulation results of the proposed method will be compared with those of the metaheuristics.