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Summary: This paper presents a new concept for district energy (DE) systems using central battery storage and decentralized hybrid renewable systems. The proposed DE consists of five buildings integrated with centralized 300 (V), 6.5 (A.h) batteries, locally distributed generations such as 8.5 (kW) wind turbines and 10 (kW) solar cells rated at 110 (V) and three‐phase loads. The central battery can be connected to each home for exchanging power. To increase the resilience, the proposed control system connects home 1 to the external 380 (V) and 50 (Hz) network when the battery is operating above the limited power (ie, 50 [kW] for this case study). The connection to the external grid is done by assessing and confirming a set of necessary conditions. The proposed integrated control system for DE is designed to achieve the following objectives: maximum power extraction from local wind/solar units by maximum power point tracking, optimal charge‐discharge process for central battery, connecting DE to the upstream network under outages and supplying the loads under all operating conditions. These goals are investigated by implementing six different scenarios of performance. In scenario 1, wind and solar units produce 6.6 (kW) and 24 (kW), respectively. Therefore, to feed the total load of 42.5 (kW), the central battery produces 15 (kW). In scenario 2, the total load in the first step is 35 (kW) and it is 95 (kW) in the second step. The power of solar and wind units in both loading steps is constant. The battery power increases from 6.5 (kW) absorption in the first step to 22 (kW) injections in the second step. In scenario 3, the solar units are switched off and in scenario 4, both solar and wind units are switched off. In such conditions, the battery responds to supply loads of homes. Increasing the energy resilience of DE during grid outages is modeled in scenario 5; where the battery power increases from 21 to 51.7 (kW) to deal with such outages. The nonlinear simulations in MATLAB/SIMULINK software show that the developed control strategy is able to control local renewable energies as well as the central battery while increasing the resilience and harvesting maximum power from decentralized wind/solar units. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a novel control scheme on AC/DC ring bus islanded microgrid under unbalanced and non‐linear loads. The DC bus is integrated with the fuel cell, one wind turbine, and two batteries. The DC bus can be divided into two sub‐sections, where the first zone is supported by the fuel cell and battery 1, and the second zone is installed with the wind turbine and battery 2. The AC bus is also able to be sectionalized into two sub‐sections where the diesel generator and the unbalanced load are located on the first section and the non‐linear load with one wind turbine are placed on the other section. The DC bus is connected to the AC bus through two parallel three‐phase lines each one configured by three single‐phase inverters. The proposed control scheme in the ringed and separated modes presents several contributions including balancing the unbalanced loads, compensating the harmonics of non‐linear loads, improving the voltage stability and sag/swells, enabling partial operation under outages, and enhancing resilience. In the ring mode, wind turbine 1 and diesel generator inject balanced and linear P‐Q powers to the system as 39 kW/6 kVAr and 7 kW/9 kVAr, respectively. In the separated mode, the P‐Q powers of wind turbine 1 are 36 kW/9 kVAr and they are 15 kW/9 kVAr for diesel generators. In both modes, the unbalanced and non‐linear powers are supplied by the DC bus. The results verify that the developed control strategy efficiently deals with harmonic components, unbalanced currents and voltage issues. [ABSTRACT FROM AUTHOR]

This paper presents a control mechanism on high voltage direct current (HVDC) transmission line for frequency/voltage regulation, fault ride through (FRT) capability, and cyber‐attack/fault detection. The network under study consists of two areas with different frequencies that are connected through one 300 km HVDC line. The proposed control system regulates the frequency in both areas by managing power through HVDC line. The converters on both sides of HVDC line are controlled to handle faults on the DC and AC sections as well as improving fault ride through capability. The control strategies are implemented and operated depending on fault/cyber‐attack type and behaviour. In this respect, the control mechanism may change the firing angle of converters, switch their operating mode from rectifier to converter and vice‐versa or even block the converters. The proposed paradigm successfully distinguishes between the cyber‐attacks and faults. The simulations in MATLAB software validate that the proposed mechanism realizes all the objectives and the cyber‐attacks are completely identified and separated from the faults. [ABSTRACT FROM AUTHOR]

• The present study aimed to develop a new model of a smart PV inverter with novel control schemes. • The proposed LVRT control strategy improved the voltage drop caused by the line-to-line-to-ground fault. • The central control system changed the switching mode of the inverter in the islanded mode. This article proposes a central control system that communicates with both grid-tied and off-grid control systems to offer various control strategies for operating a smart photovoltaic (PV) inverter. The target is to connect two sets of PV panels and one set of battery storage unit to either a 440 V/60 Hz utility grid or to feed local loads at 380 V/50 Hz using a smart inverter. When the smart PV inverter is connected to the grid, on the one hand, it injects fixed and programmed active power into the grid under all operating conditions, both normal and critical conditions, and on the other hand, by reciprocal exchanging reactive power with the grid, it addresses balanced and unbalanced fluctuations of the grid voltage. Also, when the smart PV inverter is disconnected from the grid, it can operate as an islanded mode to feed time-varying three-phase loads. Nonlinear simulations of the time domain in MATLAB-Simulink software show that the set of control strategies offered for the smart PV inverter not only by controlling the active power leads to the sale of electricity to the grid, but also by controlling the reactive power problems on the grid side such as voltage drop as a result of single-line-to-ground (SLG) or line-to-line-to-ground (2LG) faults, balanced grid voltage fluctuations such as voltage sag-swell and unbalanced voltage conditions will be resolved. Also, variable three-phase loads are fed well in off-grid mode. [ABSTRACT FROM AUTHOR]

This paper presents an integrated control framework for islanded DC microgrid (MG) with electric vehicle (EV) charging stations, energy storage unit, and AC/DC loads. The proposed DC MG consists of two DC buses with different voltages, photovoltaic (PV) arrays as intermittent power generation sources, energy storage, three EV charging stations, and a three-phase inverter to power time-varying three-phase loads. Control strategies are proposed to select the charge-discharge mode of EVs that does not negatively affect the MG, as well as coordinate the production and demand management. A central control system enables the operation of MG under different working conditions by managing generation, consumption, and energy storage and also monitors the performance of the charging/discharging unit and the issues relevant to commands of different charging/discharging programs. A specific control strategy has also been implemented to provide fault ride-through (FRT). As a result, the MG feeds its loads in any operating condition. Nonlinear simulations are carried out in MATLAB/SIMULINK software to show that the proposed control methods easily and effectively achieve all objectives, including supplying DC/AC loads, managing battery/resources/charging stations, and detecting/dealing with AC faults. [ABSTRACT FROM AUTHOR]

• Large scale wind farm is designed including SCIG and DFIG units in two sites. • Proposed control strategy designs off-grid and grid-tied functionality for sites. • Sites and grid are supported by STATCOM and SVC to deal with voltage imbalance. • Fault ride through capability is enhanced by the proposed control strategy. • Frequency control is designed under grid-tied and off-grid operations. This paper presents a multi-objective control scheme on the interconnected wind farms which are formed by different wind turbines including doubly fed induction generators (DFIG) and squirrel cage induction generators (SCIG). The proposed control system aims to control voltage, frequency, and mechanical power in the wind farms under wind/load alterations, faults, and outages. The voltage stability and fault ride through capability are improved. The proposed model also deals with unbalanced loading and faulty conditions. All the aforementioned points are realized under both off-grid and grid-tied conditions. For voltage stability improvement, each wind farm is integrated with one static VAR compensator (SVC) and the grid-side is integrated with one static synchronous compensator (STATCOM). In the grid-tied, the resilience following events is improved by proper control of STATCOM. In the off-grid, the installed SVC at each site is responsible for increasing resilience. The proposed control systems are modeled and implemented on a typical test grid, and numerical simulations are carried out in MATLAB/SIMULINK software. It is demonstrated that the proposed multi-objective control scheme efficiently controls all individual wind farms, achieves a coordinated management between different wind farms, deals with stability/unbalanced operating condition/faults, increases resilience and improves fault ride through capability. [ABSTRACT FROM AUTHOR]

This paper presents a control scheme including resources and load management in the residential DC microgrid. The DC microgrid is supported by fuel-cell, solar-cell and battery. The DC, AC single-phase and AC three-phase loads with 50 Hz frequency are integrated. The DC microgrid is connected to the external 60 Hz AC three-phase network. An efficient multi-bus topology is proposed for the microgrid and it is formed by various AC/DC buses to supply the loads and managing the resources. The main bus of system is a 470 V DC bus and it is connected to the external 440 V/60 Hz AC grid. The main DC bus supplies three LV, MV and HV DC buses with 100, 220, and 110–380 V, respectively. The HV DC bus produces a variable output DC voltage between 110 and 380 V in order to regulate the load power (i.e., motor speed). The MV DC bus is connected to 220 V/50 Hz AC single-phase loads. The connections between DC microgrid with AC loads and AC external gird are made by single-phase or three-phase inverters. The interface inverters between DC bus and AC loads are operated to control power, torque, speed, frequency and voltage of loads. The unbalanced AC loads are appropriately balanced by proper control of interface inverters. The resources and inverters are efficiently controlled to enable operation of residential building under both off-grid or grid-tied conditions. The coordination of fuel-cell, solar-cell and battery can supply a fixed 8 kW power to external grid and supply the internal loads under all outages and off-grid conditions. The simulations demonstrate that the proposed control realizes all the objectives including AC/DC load management, unbalanced load amendment, frequency adaptation, and off-grid operation. • Designing residential DC microgrid with several voltage levels and frequencies. • Implementing multiple generation/load managements under off-grid and grid-tied. • Multi-bus topology for building including low, medium and high-voltage buses. • Balancing the unbalanced loads from the external network standpoint. • Implementing load shedding strategy in off-grid under critical situations. [ABSTRACT FROM AUTHOR]

• Integrated system including DFIG, battery storage, TCR and TSC is implemented. • Set of TCR-TSC-DFIG is controlled to compensate voltage sag-swell. • Set of DFIG-battery is controlled to damp out oscillations and power regulation. • Proper control loop is designed to improve DFIG resilience under three-phase fault. • Set of TSC-TCR-battery balances the unbalanced time-varying load. This paper presents a novel control scheme in doubly-fed induction generators (DFIG) wind turbine for operation under time-varying unbalanced loads. The proposed control scheme is implemented on a DFIG connected to the external grid. Additional equipment such as battery, thyristor-controlled reactor (TCR) and thyristor-switched capacitor (TSC) are integrated to the DFIG. These devices are integrated to DC link, grid side and rotor side converters. The developed control scheme aims to achieve several purposes simultaneously including voltage compensation, damping fluctuations, regulating frequency, increasing resilience, and balancing the unbalanced time-varying loads. Each purpose is realized by designing a separated control loop on DFIG, battery and TCR-TSC. All the designated control loops are operated coordinately. The non-linear time-domain modelling and simulations are carried out in MATLAB software and demonstrate that the proposed multi-purpose control plan can optimally utilize set of DFIG/battery/TCR/TSC and achieve all the objectives efficiently. [ABSTRACT FROM AUTHOR]

• Balancing the unbalanced and time-varying loads under grid-tied and off-grid. • Coordinated single phase control of diesel generator, battery and fuel cell. • Controlling and balancing both the active and reactive powers separately. • Improving the voltage profile following faults and events. • Stability improvement and resilient operation under events. This paper presents an advanced control strategy for balancing the time-varying and unbalanced loads by using the fuel cell and battery under the grid-tied and off-grid operations. In the grid-tied operation, the fuel cell and the battery are coordinately controlled to balance the three-phase unbalanced active and reactive powers of the loads. In this case, the received three-phase active-reactive powers from the grid become completely balanced by the given strategy. In the off-grid, the diesel generator supplies the active-reactive powers of load and the unbalances are handled by coordinated operation of fuel cell and battery. As well, the voltage of off-grid system is improved by injecting adequate reactive power to the system through the fuel cell, battery and diesel generator. The dynamic stability of the system is evaluated under non-linear disturbances like grid outage and single-phase fault. The time-varying unbalanced active-reactive powers are balanced under both off-grid and grid-tied states by implementing the proposed model. The purpose of the proposed control system is to balance the unbalanced load from point of view of the upstream grid at all time periods. In order to realize such function in the model, the load is modeled by two terms including the balanced and unbalanced parts. The unbalanced share is supplied by the inverters (DC bus) and the balanced term of load is supplied by the grid. The designed system is resilient under the events like grid outage and short circuits. As well, the system properly regulates and controls the load variations and unbalances. [ABSTRACT FROM AUTHOR]