Shunsuke Kawano

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.

Maximizing hosting capacity of distributed generation by network reconfiguration in distribution system

The maximization of distributed generation (DG) hosting capacity that takes into account network configuration is a complex, non-linear combinatorial optimization problem. The search space of the configurations becomes massively large in practical-size networks with several hundreds of switches. For this reason, no existing method can handle such large-scale networks. In this paper, we propose a novel exact solution method. Our method consists of two stages. In the first stage, the method divides the entire problem into a set of small subproblems. In the second stage, it converts all subproblems into a compressed data structure called a zero-suppressed binary decision diagram (ZDD), which expresses the combinatorial sets compactly. The proposed method avoids any combinatorial explosion by using the ZDD to enable operations of the weighted combinatorial item sets. We conducted experiments on a large-scale network with 235 switches. As a result, our method obtained the global optimal solution in 49 hours.

Distribution Network Verification for Secure Restoration by Enumerating All Critical Failures

If several feeders are interrupted in a severe accident, distribution networks should be restored by reconfiguring switches automatically with smart grid technologies. Although there have been several restoration algorithms developed to find the new network configuration, they might fail to restore the whole network if the network were critically damaged. The networks design has to guarantee that it is restorable under any possible failure for secure power delivery, but it is a computationally hard task to examine all possible failures in a large-scale network with complex electrical constraints. This paper proposes a novel method to find all the critical (unrestorable) line cuts with great efficiency to verify the network design. The proposed method first runs a fast screening algorithm based on hitting set enumeration; the algorithm selects suspicious cuts without naively examining all possible cuts. Next, unrestorable cuts are identified from the suspicious ones with another algorithm, which strictly tests the restorability of the network under each suspicious cut without redundantly repeating heavy power flow calculations. Thorough experiments on two distribution networks reveal that the proposed method can find thousands of unrestorable cuts from the trillions of possible cuts in a large 432-Bus network with no significant false negatives.

Evaluation of Annual Energy Loss Reduction Based on Reconfiguration Scheduling

In distribution network management, switch reconfiguration is an important tool for reducing energy loss. Recently, a variety of annual reconfiguration planning methods considering energy loss have been studied. However, no conventional methods address the reconfiguration periods in fine granularity. Practically, switch durability does not support high-frequency switching. Therefore, this paper proposes a new optimization method for annual reconfiguration scheduling. This method determines switch configurations and their reconfiguration periods with a constraint on the permissible reconfiguration times. In addition, this paper reveals the annual energy loss reduction effect of this optimization. Our method is based on partial network optimization with exhaustive enumeration of all feasible configurations. Experiments were conducted using a standard Japanese distribution network model with 468 switches. The results show that optimizing the reconfiguration periods reduces energy loss by up to 2.1 times, relative to that in a simulated conventional operation, which considers reconfiguration at equal intervals. We believe that this is the first quantitative report to address the difference between optimal reconfiguration scheduling and conventional reconfiguration.

Distribution automation system for service restoration involving simultaneous disconnection and reconnection of distributed generators

This paper presents a distribution automation system (DAS) for service restoration in the distribution network with photovoltaic (PV) generator systems, which are disconnected simultaneously after a fault and subsequently reconnected after service restoration. Because the reverse power flow of PVs affects voltage in the distribution system, voltage dips and surges occur during the service restoration. However, current DAS do not control voltage regulators such as an on-load tap changer (OLTC) and step voltage regulators (SVRs) during the service restoration. The proposed DAS estimates the voltage in a distribution network considering the simultaneous disconnection of PVs by performing power flow calculations, and it controls the tap position of OLTC and/or SVRs according to the predicted voltage deviation. The voltage after the disconnection of PVs is calculated by estimating the PV output utilizing square kilometer solar radiation data calculated using satellite image data in real time.

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.

Voltage Control Method Utilizing Solar Radiation Data in High Spatial Resolution for Service Restoration in Distribution Networks with PV

AbstractThis paper proposes a voltage control method during service restoration in the distribution networks with photovoltaic (PV) generator systems. In the current distribution automation system (DAS) process in Japan, voltage dips and surges occur during service restoration because PVs are disconnected simultaneously after a fault and subsequently reconnected after service restoration. However, in the current DAS, voltage regulators such as an on-load tap changer (OLTC) and step voltage regulators (SVRs) are not controlled during service restoration. The proposed DAS estimates the voltage in a distribution network during service restoration, and it controls the tap position of OLTC and/or SVRs according to the predicted voltage. The numerical simulation results using a real-world distribution system model on a real map and PV output profiles derived by actual square kilometer solar radiation data will be shown. Those results indicate that the proposed DAS prevents voltage deviation that occurs as long ...

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.

Centralized voltage control method using voltage forecasting by JIT modeling in distribution networks

This paper presents an enhanced centralized voltage control method of on-load tap changer (OLTC) and step voltage regulators (SVRs) in distribution systems with photovoltaic (PV) and evaluates its effectiveness. A conventional centralized voltage control is effective when its data acquisition period is short because tap operations of OLTC and SVRs are performed after the voltage values in the distribution lines are acquired. However, in distribution systems with high penetration rate of PVs, voltage deviation occurs between the data acquisition intervals because the tap positions can be changed only at the timing when the data are acquired. The proposed centralized voltage control method forecasts voltage fluctuation between the data acquisition intervals and changes to the tap position which maximizes the minimum voltage margin from the voltage limits. The numerical simulation results will be shown to compare the voltage control effectiveness of the proposed method with that of the conventional method.

Evaluation of coordinated energy management system for grid and home in distribution system with PVs

AbstractThis paper presents a coordinated energy management system (EMS) based on time-of-use pricing. The proposed EMS consists of prediction, operational planning, and control stages. To minimize amounts of curtailed PV output, operational costs, and voltage violations, line-drop compensation parameters are determined based on an input-output relationship database in the grid EMS. In the home EMS, an energy equipment operational plan is developed with a stochastic optimization problem (SP) to accommodate unavoidable uncertainties. Numerical simulations based on an actual distribution system model are performed, confirming the improved performance of the proposed method compared with the conventional method.