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This paper presents a contemplate study on online voltage control strategy with different loading conditions in a DC microgrid using particle swarm optimization (PSO). DC microgrids consist of many converters and it is an important issue to stabilize network voltage by properly designing their controllers. Conventional feedback controls have been often used as a primary control for voltage stabilization with optimizing control parameters such as droop gains. Moreover, the optimal control parameters should be flexibly updated when the system condition dynamically changes so as to maintain high voltage control performance under sudden and unexpected changes in system conditions. In that context, this paper introduces an online voltage control using an advanced PSO technique to frequently update control gains. The primary control was modeled as a proportional‐derivative controller, and the optimization problem was defined based on the eigenvalue analysis. A parallel operation of local and global searches is conducted in the proposed method to search optimal control gains by allocating a part of particles to move in a random pattern. The validation of the proposed method was performed using a simplified 3‐bus DC microgrid model with two generator sets and two constant power loads. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This paper deduces the quantitative relationship between the flux vectors and the power of power winding (PW) in brushless doubly‐fed reluctance generator (BDFRG). On this basis, the direct power control (DPC) theory of BDFRG is established, which makes up the deficiency that the DPC theory of BDFRG is only based on qualitative analysis in the existing literature. The power derivative expression is derived for accurately analyzing the effect of voltage vector of control winding (CW) on the power of PW, concluding that the control effect of DPC is related to the operation point of a BDFRG. The number of basic voltage vectors of CW connected with two‐level converter is limited, resulting that under some operation conditions, a BDFRG controlled by DPC could present a time interval where the power cannot be controlled satisfactorily. Therefore, the space vector modulation‐based direct power control (SVM‐DPC) strategy of BDFRG is proposed, which can solve the above problem and fix the switching frequency. Experimental results prove the correctness of the elaboration and the proposed method. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This paper examines the impact of different voltage unbalance definitions on voltage control in unbalanced distribution systems. Traditional voltage regulation methods for unbalanced systems rely on a single voltage unbalance definition with inconsistent adoptions. In such a situation, voltage control performance can vary between definitions, and improper choice leads to control failures. In this study, we perform numerical analysis and simulations to investigate the impact of different definitions. In the numerical analysis, two definitions quantifying negative and zero sequence components are used as reference definitions, and the theoretical error range of the remaining definitions is identified. The results are further verified by the simulations on the IEEE 123 node test system with phase‐by‐phase controlled three‐phase step voltage regulators and smart photovoltaic inverters. The control of the devices is optimized to minimize or limit a specific definition. The results show that the values of each definition at the same voltage condition can differ significantly, and inappropriate definitions may lead to significant uncertainty in the voltage control. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

In order to fill the blank of practical engineering application of inductive control in ozonizer power supply, this paper probes into a scheme of high frequency and high voltage inverter for the control, and analyses operation modes to form a reasonable theoretical result, and introduces a new current zero crossing and phase locking method to adjust the address deviation and ensure that the address pointer directs to the last value of inverter current by changing the sampling period and adjusting the error of practical reference address pointer at each zero crossing point. The results from theoretical derivation, numerical simulation, and power experiment prove that the scheme can suppress the current spike caused by diode reverse recovery and reduce the power loss of switch devices, which is conducive to cost reduction. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This paper proposes a control method for step voltage regulators (SVRs) to avoid voltage violations in distribution systems with unbalanced voltages due to photovoltaic (PV) generation and electric vehicle (EV) charging. Distribution system operators must effectively address voltage problems resulting from the widespread installation of distributed energy resources under the optimizing the utilization of existing voltage regulators to establish an efficient and rational infrastructure. Therefore, this study focused on advancements in voltage control using SVR based on line‐drop compensator (LDC) control, which is widely used in actual operations. We propose a method that utilizes voltage data from information technology switches to detect and address voltage unbalances in the control section, allowing for the sequential adjustment of the monitoring target in LDC control to maintain appropriate voltage limits under unbalanced conditions. We conducted power flow calculations using a distribution system model that represents an actual distribution system in the Hokuriku area. The effectiveness of the proposed method was evaluated in terms of its impact on PV and EV hosting capacity, as well as the frequency of tap operations. © 2023 The Authors. IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

In recent years, with the large‐scale access of distributed generation (DG), the line voltage of the distribution network will be offset, which will adversely affect users. This paper aims at the voltage adjustment of the distribution network. Firstly, the reactive power control methods of distributed static synchronous compensator (DSTATCOM) and electric spring (ES) are studied separately, and then a layered cooperative control strategy based on them is proposed, which combines centralized compensation and distributed compensation to stabilize the entire line voltage. The upper layer aims at optimizing the comprehensive factors including voltage offset, user comfort and cost, and applies the dynamic adaptive particle swarm optimization (DAPSO) algorithm to study the optimal scheme of voltage adjustment. The lower layer designs the control loops of the compensation devices in response to the reactive power instruction. Finally, simulation results show that the voltage of the distribution network is effectively controlled. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

With increase in the number of photovoltaic system installations, the prospect of voltage deviation from the acceptable range in a distribution system is increasing. Voltage distribution can be controlled using step voltage regulators (SVRs) and static var compensators (SVCs); however, for their coordination, it is necessary to stringently adjust the set value for each distribution line. In this study, a method of applying model predictive control to the coordination between an SVR and an SVC is investigated. In this paper, we first describe the proposed method and subsequently present the results of the performance comparison of the proposed and conventional methods to validate the effectiveness of the proposed method. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

At present, intermittent control is a main method to solve the problem of pumping output voltage with light load of LLC resonant converter, which can not only solve the problem of high pumping output voltage, but also, to a certain extent, improve the efficiency of light load to a certain extent when converter is operating. However, in extremely light‐loading, especially in no‐ loading, with the intermittent cycle increasing and the low‐frequency ripple being introduced, which cannot meet the demand of high‐quality output voltage, and is not conducive to the converter's stable operation. Due to the extremely small power transferred by the converter, in this case, efficiency is not the main factor considered. In this paper, a voltage regulation strategy based on energy feedback is proposed for LLC resonant converter in extremely light‐loading. The output voltage is controlled by adjusting the feedback energy to the source. Compared with the uncontrollable burst off mode of the intermittent control, the proposed control method can effectively improve the output voltage quality due to the controllability in voltage drop mode and the independence from the load. It also can eliminate low frequency ripple and extend battery charging life. The output voltage ripple is minimized by optimizing the duty cycle and the phase shift angle. The correctness and feasibility of the proposed method are verified by experiments. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This paper proposes a predictive voltage control scheme baseda on short‐time‐ahead voltage fluctuation estimation in a distribution system for achieving high penetration of photovoltaic generation. In the proposed control scheme, the short‐time‐ahead voltage fluctuation is estimated from the previously measured voltage of the sensor, and the voltage regulator operates to minimize the expected voltage violation risk in the entire distribution system. Because there is no requirement for real‐time sensor‐measured voltage values, as required in centralized voltage control schemes, the proposed scheme is an autonomous control scheme that uses only the present secondary voltage of the voltage regulator. The proposed control scheme was tested on a large‐scale distribution system model to which thousands of customers are connected, and the voltage control performance was evaluated using the monthly measurement data that was in terms of voltage violation amount and number of tap operations. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

In this paper, we propose a semicentralized voltage control method utilizing past voltage measurements obtained with sensors in a distribution network (DN) to improve the voltage control performance of a single‐step voltage regulator (SVR). In this method, the SVR basically performs autonomous voltage control referring to the control parameter, the reference voltage, but the parameter is updated with a specific interval via communication. To determine a time series of the reference voltage using the past voltage measurements, the simple averaging method and the probabilistic weighting method are considered. The effect of these methods on the voltage control performance is evaluated with a power flow simulation using a realistic 6.6 kV DN model with photovoltaic systems. The results show that the proposed semicentralized SVR control with these advanced parameter‐updating methods dramatically mitigate voltage violation compared to the conventional SVR operation in which the constant reference voltage is used for 1 year. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

In recent years, a rapid spread of residential photovoltaic power systems (PVs) causes voltage imbalance in distribution systems. For this reason, it has become difficult to control voltage in distribution systems to within the allowable range. Therefore, the authors have proposed a system for suppressing the voltage unbalance using single‐phase static capacitors (SCs). The purpose of the system (SC system) is to suppress voltage imbalance by controlling single‐phase SCs in each phase, and its effect has been confirmed by the previous authors' study. On the other hand, as a result of analyzing the voltage measured on some distribution lines, the authors found that it is not necessary to control single‐phase SCs in each phase because the voltage imbalance hardly changes throughout a day. In this paper, an alternative method for suppressing the voltage imbalance by constantly installing single‐phase SCs on distribution lines is proposed in order to realize at a lower cost than the previous SC system. In addition, the authors verify the effect of the method on the actual distribution lines. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

In order to compensate voltage unbalance at the point of common coupling (PCC) for the islanded microgrid, a novel strategy based on PCC negative‐sequence voltage feedforward is proposed. Through the PCC negative‐sequence voltage feedforward, a virtual voltage source is added to the DG terminal at the negative‐sequence. Then, the effective impedance between the distributed generation (DG) unit and the PCC can be reduced proportionally to the compensation coefficient, thereby reducing the unbalanced voltage caused by the unbalanced load. On this basis, an adaptive mechanism of the compensation coefficient is proposed to achieve compensation effort equalization among parallel DGs. Different from the widely adopted virtual impedance method, the additional unbalanced voltage droop (caused by the virtual impedance) can be avoided. In addition, the H∞ repetitive controller is designed to obtain good voltage control performance for the parallel operation. Finally, microgrid simulations are provided to demonstrate the effectiveness of the proposed control strategy. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Approximately 50% of natural lightning flashes make multiple contacts on the ground. Lightning-induced voltage by nearby lightning stroke is the major cause of overvoltage. The electromagnetic waves emitted by lightning flashes with multiple ground strike points (GSPs) increase new risks to damage electronics information devices located in the vicinity of the GSPs. Therefore, it is very important for electromagnetic compatibility engineering to clarify the characteristics of lightning flashes with multiple GSPs. We have observed lightning discharges over the whole area of Japan detected by the Japanese Lightning Detection Network (JLDN). Specifically, we analyzed negative cloud-to-ground (CG) flashes observed by JLDN within 80 km of Sagamihara in summer. We investigated the median location accuracy of the JLDN in the observation area to evaluate characteristics of spatial distribution of subsequent strokes hitting the GSPs. The median location accuracy varied between 0.2 and 0.4 km in the observed area. The mean multiplicity of negative CG flash observed by JLDN was 3.5. The average inter-stroke interval of new ground contact (NGC) strokes was longer than that of pre-existing channel (PEC) strokes. The ratio of peak current to the first return stroke was higher in the NGC than that in the PECs. Some of flashes hit the ground at several points. The mean number of GSPs was 2.0 per flash, with the mean number of 1.6 subsequent strokes per a GSP. Furthermore, the number of strokes per a GSP has not been previously reported. We also observed that the subsequent strokes altered between different GSPs. [ABSTRACT FROM AUTHOR]

In this study, we propose a new optimization method to determine the control parameters of a step voltage regulator (SVR) to maximize its voltage control characteristic in distribution networks (DNs) with photovoltaic systems. Considering the service life of an SVR, the proposed method evaluates the expected number of tap operations and the voltage control performance based on the past voltage measurements obtained with sensors in the DN. Subsequently, the time series of two control parameters, that is, the reference voltage and the dead bandwidth, are determined for the most improved voltage control characteristic of the SVR, maintaining the number of tap operations within the upper limit. Voltage control simulation using a realistic 6.6‐kV DN model is conducted to show that the proposed method significantly reduces the voltage violation compared with the conventional SVR control using fixed parameters, as well as the alternative SVR operation developed in our previous study, in which the reference voltage was temporally updated. In addition, the simulation results demonstrate that the proposed method realizes efficient tap operations to mitigate the voltage violation, whereas the conventional method requires a much larger number of tap operations to mitigate the voltage violation to the same degree. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]