The widespread introduction of functionally-smart inverters will be an indispensable factor for the large-scale penetration of distributed energy resources (DERs) via the power system. On the other hand, further smartization based on the data-centric operation of smart inverters (S-INVs) is required to cost-effectively achieve the same level of power system operational performance as before under circumstances where the spatio-temporal behavior of power flow is becoming significantly complex due to the penetration of DERs. This review provides an overview of current ambitious efforts toward smartization of operational management of DER inverters, clarifies the expected contribution of machine learning technology to the smart operation of DER inverters, and attempts to identify the issues currently open and areas where research is expected to be promoted in the future.

Distributed energy resources (DERs) such as photovoltaics (PV) and battery energy storage system (BESS) are effective for improving the target renewable energy (RE) rate in a region. Furthermore, it is expected that distribution system operators (DSOs) will promote their installation in the future. However, it is not enough for DSOs to simply install large-capacity PV and BESS. They need to determine these capacities by taking into account the cost reduction of equipment and the constraints on grid operation. In this paper, we propose a DER installation capacity optimization method based on linear programming using annual data and a layout method from the operator's perspective. This method determines the capacity of DERs based on the target RE utilization rate in a controlled area of a distribution system. Furthermore, we report the results of an analysis of power flow when the DER is introduced. Moreover, we estimate the actual required capacity of DERs for a real 2-feeder distribution system model. In addition, power flow calculations are performed for a typical day where that amount of DERs were installed. The results were evaluated in terms of grid voltage, thermal capacity of line, and distribution losses, and the necessary controls were discussed.

This study proposes an output curtailment method for determining the output curtailment of renewable energy sources (REs) to mitigate grid congestion in transmission systems with a significant influx of REs. To manage congestion, minimizing the total REs output curtailment while avoiding the concentrated output curtailment on a specific RE is crucial. As a means of identifying effective curtailment targets for congestion mitigation, sensitivity analysis is being used for quantifying the congestion mitigation effect with curtailment. Furthermore, equality in output curtailment can be ensured by grouping REs of similar sensitivity and uniformly curtailing each group. Minimizing the curtailment of REs under the grouping-based approach requires forming a group of REs that is sensitive to frequently congested lines, considering the tendency of congestion occurrence in the whole grid. Consequently, this study proposes a method for determining the output curtailment rate of REs using grouping based on weighted sensitivity, considering the sensitivity of each RE and grid congestion. The effectiveness of the proposed method was evaluated by numerical simulation of congestion management over one year on a grid in the northern area of the Tohoku region in Japan. The results indicated that the proposed method was superior in terms of total REs curtailment and equality compared to the comparison method that does not consider the grid congestion amount.

Voltage violations in distribution systems (DS) with large photovoltaic (PV) installations must be cleared. To regulate the voltage, Chubu Electric Power Grid has implemented a grid control system (GCS) that aggregates measurement information from switches with sensors, smart meters, step voltage regulators (SVRs), and on-load tap changers (OLTCs) to determine their control parameters. The GCS is characterized by its function to separate measured currents into load and PV currents for the consideration of measured power flow conditions with and without PV generation. Based on the results of numerical simulations using a real grid model, we evaluated the effect of separating functions on increasing the PV hosting capacity in this study.

In this study, we comprehensively evaluated the impacts of popularizing electric vehicles (EVs) and the time shift of EV charging on voltage regulation in distribution systems. Although the popularization of photovoltaics (PVs) and EVs is required to realize a sustainable society, the generation from PVs and the charging demand of EVs may cause voltage violations in distribution systems. To combat these challenges, distribution system operators (DSOs) must upgrade the facilities and management of distribution systems. To verify the strategies for future operations, DSOs evaluate the impact of distributed energy resources (DERs) installation and the effectiveness of the countermeasure candidates on voltage regulations. Therefore, this study assesses the impacts of EV popularization on voltage regulation using an actual distribution system model in the Hokuriku area of Japan. In the numerical simulation, EV and PV popularization levels are set from 0 % to 100 % in 20 % increments. Additionally, the effectiveness of the time shift of EV charging as a countermeasure for voltage regulations is evaluated. To validate the effectiveness, ratios of time-shift EVs are set to 20 % and 50 %. The results reveal the effectiveness and limitation of the time shift of EV charging.

Grid congestion is expected owing to the interconnection of massive renewable energies within the transmission system. Power system operators need to resolve the problem by controlling the output of thermal and renewable generators, such as curtailment, which should be the smallest possible for efficient utilization. Moreover, the equality of generation opportunities should be maintained among renewable energies. However, achieving the two objectives simultaneously is challenging, because the output curtailment effect on grid congestion in a loop system varies depending on its configuration. Further, the thermal generators are curtailed before renewable energies in the merit order scheme necessitating adjustments in the thermal generator output considering the renewable energy curtailment. This study proposed a method to determine the output curtailment ratio of thermal power and renewable energies employing sensitivity analysis, aiming to ensure equality, and maximize the power generation opportunities of renewable energies for the mitigation of grid congestion. The effectiveness of the proposed method was verified via numerical simulations using a power system model based on an actual power system in the northern Tohoku area of Japan. The results indicate that the proposed method can reduce the total amount of curtailment and improve the equality of generation opportunities. (c) 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

To utilize renewable energy systems (RES) as main generators in power system, power system operators need to maintain reserve power to compensate the uncertain output of RES, such as wind farms (WF). This paper focuses on the balancing group (BG) composed of WF and a pumped-storage hydro generator (PSHG). In the BG operation, power system operators need to schedule the operation of PSHG to minimize the imbalance risk caused by the prediction error of WF output while considering the system specific constraints of PSHG, e.g. the mechanical constraint on pump-up/down switching. This paper proposes a method to schedule the PSHG operation using the interval prediction results of the WF output for alleviating the imbalance risk the proposed scheduling scheme is formulated based on the linear programming. To verify the effectiveness of the proposed method, the amount of imbalance and the net generation of the BG were evaluated based on numerical experiments under two types of situations with different characteristics in WF output. The experimental results reveal the effectiveness of the proposed method.

Transmission system operators (TSO) are responsible to manage the power quality within a proper range and to reduce power loss. Voltage reactive power control (VQC) is mainly utilized to manage the power flow. In the conventional VQC scheme, the static condenser (SC) and shunt reactor (ShR) is generally adjusted based on the target value determined for the heavy load condition in each voltage class. On the other hand, the installation of the massive photovoltaic (PV) systems into transmission systems cause the complex power flow such as the short-term fluctuation of power flow and reverse power flow from the lower transmission system to the upper transmission system. Thus, in the future power system with PV systems, the target values of the VQC devices need to be updated in the short-time period considering the interaction between the upper and lower transmission system to manage the power quality and to the reduce power loss efficiently. This paper proposes the optimization methodology for VQC devices in two-voltage class of transmission system using tabu-search and optimal power flow based on the central VQC methodology. To verify the effectiveness of the proposed methodology, the numerical simulation was performed based on the revised IEEJ EAST 30-machine system model.

This paper proposes a method to determine the Line Drop Compensator (LDC)-control parameters of an On-load Tap Changer (OLTC) and step voltage regulator (SVR) using a database with measured data from offline IT-switches. In a conventional determination method, the parameters are calculated based on the relationship between the sending voltage and the absolute value of current at the secondary side of the OLTC/SVR with a fixed power factor. However, the power factor changes with the interconnection of the photovoltaic (PV) system. Hence, in the proposed method, LDC-control parameters are determined by the relationship between active current, reactive current, and sending voltage. In other words, the parameters are determined from the plane by taking these values as axes. The plane is determined by four measured data extracted from the database which have large voltage fluctuations in response to severe power flow. The effectiveness of the proposed method is verified by numerical simulations using a distribution system model with PV systems. Our results show that the proposed method can improve the amount of voltage violation by 35% compared to a conventional method.

This paper proposes a method to determine an optimal radial-loop configuration to minimize power loss in a distribution network with photovoltaic (PV) systems and evaluates the effectiveness of this configuration. Due to the disaggregation of transmission and distribution in a deregulated power system, stable and efficient operations in terms of voltage regulation and power loss reduction utilizing existing equipment is becoming more important for distribution system operators (DSOs). Japanese DSOs operate distribution networks in a radial configuration while supplying power to customers with high reliability. One method to reduce further power loss is to upgrade the network topology to a radial-loop configuration, which achieves partial loop structures by closing the tie-switches of the radial configuration. To implement a radial-loop configuration, DSOs must first evaluate the reliability, as a loop configuration can cause a feeder circuit breaker (FCB) malfunction and an expansion of the nonsupplied area during fault conditions. However, the impact of a radial-loop configuration on reliability and effectiveness has not been verified. Therefore, this paper proposes a method to determine an optimal radial-loop configuration that minimizes active power loss and maintains high reliability. In a numerical simulation, the reliability of radial-loop configurations is verified, and the effectiveness of the configuration is analyzed in terms of active power loss and voltage regulation under several PV system penetration conditions. A 6.6 kV distribution network consisting of 6 feeders and 11 tie-switches is modeled based on an existing Japanese distribution network and used for numerical simulation.

Recently, a multiarea system operation utilized a tie-line has been verified to resolve a shortage of a control capacity of frequency control generators output due to a widespread penetration of renewable energy systems (RES). In order to determine the proper dispatch of the generators output to compensate RES fluctuation in the multiarea system operation, the power system operators should consider power flow constrains and indexes of power system conditions such as the speed of dispatch, the balance of reserved control capacity in each area, and the stability of power supply. In this paper, we propose a methodology to determine multiobjective dispatch candidates of frequency control generators output to compensate RES fluctuation in multiarea system operation considering three indexes, a speed of dispatch, a reserved control capacity, and a transient stability based on optimal power flow and multiobjective particle swarm optimization. The methods determine the dispatch based on Euclidean norm of the indexes in the calculated candidates in order to consider all indexes well-balanced. The effectiveness of the proposed methodology is verified by a numerical simulation used IEEJ EAST 30-Machine Grid Model with much RES, and the effectiveness of the dispatch minimized Euclidean norm is confirmed by comparison to single-objective solution in each index among the calculated candidates.

In this paper, we propose a comprehensive scheme to determine a suitable method and timing for upgrading the voltage control method. Voltage control methods are expected to be upgraded in accordance with the photovoltaic (PV) penetration in distribution systems. The suitable method and timing detailed in this paper are based on the limit of the PV penetration rate, which is constrained by the regulated voltage deviation. The upgrade process involves moving the on-load tap changer (OLTC) control method from the conventional scalar line drop compensator (LDC) method to the vector LDC method or centralized control method. Then, a static var compensator (SVC) or step voltage regulator (SVR) is installed. The locations of the SVR and SVC are determined to maximize the PV penetration rate. The suitable method and timing are demonstrated using a general distribution system. In addition to the numerical simulations, experiments are performed using an active network system with energy resources. The experimental results are consistent with the numerical simulation results, thus validating the proposed scheme. The maximum PV penetration rate obtained using the OLTC control method is 55%. Whereas, the installation of the SVR and SVC increased the rate to 95% and 100%, respectively.

Recently, a multi area system operation utilized a tie-line has been verified to resolve a shortage of a control capacity of frequency control generators output due to a widespread penetration of renewable energy systems (RES). In order to determine the proper dispatch of the generators output to compensate RES fluctuation in the multi area system operation, the power system operators should consider power flow constrains and indexes of power system conditions such as the speed of dispatch, the balance of reserved control capacity in each area and the stability of power supply. In this paper, we propose a methodology to determine multi-objective dispatch candidates of frequency control generators output to compensate RES fluctuation in multi area system operation considering three indexes, a speed of dispatch, a reserved control capacity and a transient stability based on OPF and MOPSO. The methods determine the dispatch based on Euclidean norm of the indexes in the calculated candidates in order to consider all indexes well-balanced. The effectiveness of the proposed methodology is verified by a numerical simulation used IEEJ EAST 30-machine system model with much RES, and the effectiveness of the dispatch minimized Euclidean norm is confirmed by comparison to single-objective solution in each index among the calculated candidates.