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This article presents a multiobjective control scheme for a bidirectional interlinking converter (ILC) of renewable energy based ac–dc hybrid microgrid. The prime focus of the power management algorithm is to feed the ac loads, and dc loads from ac source, and photovoltaic battery energy storage (BES), respectively. The second objective is to utilize the solar power to maximum capacity, by feeding it to dc load, BES, and ac load, in the given order of priority. The ac and dc subgrids operate independently, while supporting each other in case of overloading/underloading, thus reducing the amount of power reserve required in each, and eliminating the need of dump loads. The ANFIS-MN-based power quality control is integrated in order to ensure the total harmonics distortion of ac source current remains below 5% as per IEEE 519 standard, irrespective of the nature of load connected. In addition, the ILC control prevents any negative sequence currents from entering the ac source, even if there is any open circuit fault leading to unbalanced loading on the three phases. The performance of ANFIS-MN-based ILC control is demonstrated to be superior when compared with the conventional and contemporary techniques under different scenarios. [ABSTRACT FROM AUTHOR]

In this article, islanding detection, control, grid synchronization, and power share techniques have been considered for the seamless operation of ac microgrid in grid-connected mode, islanded mode, and during the transition between both modes. A master–slave organization coordinates the power distribution among microgrid sources. The control scheme of each source is designed with a nested loop robust linear quadratic regulator and mixed $H_{2}/H_{\infty }$ optimal controller. The islanding detection algorithm is developed with synchro-extraction transform and optimal support vector machine (OSVM). An optimal linear Kalman filter-based synchronous reference frame phase locked loop (OLKF-SRFPLL) method is considered for the reconnecting of the microgrid to the utility grid. For optimal parameter tuning in the OSVM and LKF-SRFPLL methods, a particle swarm optimization technique is used. The seamless operation of the proposed ac microgrid system is verified in MATLAB/SIMULINK, and the practical feasibility is verified with an experimental photo-type setup and dSPACE 1202 control kit. Simulation and experimental results are presented to illustrate the seamless operation of the proposed ac microgrid system. [ABSTRACT FROM AUTHOR]

In this article, multiple parallel photovoltaic (PV) inverters based microgrid is developed to enhance the reliability and accessibility of electricity in remote areas. A self-adaptive control strategy is presented for a microgrid to ensure a seamless transition between the islanded mode (IAM) and grid-connected mode (GCM) of operation with a proportional power sharing. This microgrid consists of two solar PV inverters based on local distributed generation (DG) units. Each PV-inverter unit feeds an active power to support local loads and the power demand of each local load is shared between respective DG units and microgrid. The PV-battery-interfaced main unit with a self-adaptive control strategy in parallel with a PV array supported unit-2 is considered to operate in the IAM and GCM of operation. The control strategy achieves transient free operation during load disturbances, power variation at the PV array side, and off-grid operation. Moreover, the microgrid ensures high-quality performance at the point of common coupling and provides the seamless transition between GCM and IAM to guarantee a continuous power to critical loads. The microgrid simulation and experimental results are presented under various operating conditions, such as load variation, intermittent power generation, and automated mode transition between GCM and IAM. [ABSTRACT FROM AUTHOR]

With increased penetration of renewable power and the nonlinear loads in the distributed generation (DG) systems, increased power quality concerns are exhibited in the active distribution networks, especially the challenges associated with the current and voltage harmonics in the system. Various conventional harmonic compensation techniques are developed for voltage-controlled DG inverters in past, majority involve either multiple proportional-integral (PI) or proportional-resonant (PR) controllers in eliminating grid current harmonics. The current-controlled inverters, on the other hand, are not preferred in industrial applications, accounting to their wide variations in the switching frequency. A novel and adaptive harmonic voltage control is developed here, for voltage-controlled DG inverters, which neither uses any PI regulators nor imposes stability issues associated with nonideal implementation of infinite gains of PR controllers. Interestingly, the developed control logic can be used for DG inverters, both in grid-connected and off-grid operational modes. Furthermore, this strategy allows a network operator to use this as an additional supplement that can be enabled/disabled as per the network requirement. The control logic exploits the property of an optimal-switching-vector controller, i.e., accurate output voltage tracking. Simulations results demonstrate the effectiveness of the controller, to suppress grid current harmonics and load voltage harmonics in grid-interfaced (GI) and off-grid modes, respectively, ultimately satisfying the mandatory IEEE standard-1547. Experimental results verify the viability of the controller for practical applications. [ABSTRACT FROM AUTHOR]

This article presents an enhanced power quality solar photovoltaic (PV) inverter enabling common-mode leakage current elimination. A three-phase transformerless solar energy conversion system is considered here, which, along with peak active-power production from PV array, ensures different power quality improvement capabilities such as grid current harmonics mitigation, grid currents balancing while also offering the grid reactive power support. Unlike conventional power quality inverters, this strategy is robust with respect to abnormalities in grid voltages at far radial ends, and does not compromise with the leakage currents caused by parasitic capacitance of PV array with ground. Common practice in the PV inverter power quality control is to neglect the PV leakage currents; however, they considerably affect the system performance by deteriorating the power quality and causing the safety issues of operating personnel. The standards VDE-00126 and NB/T-32004, therefore, compel the transformerless PV systems to operate with leakage current under 300 mA range. Various simulation and test results show the satisfactory performance of the presented strategy, even under various grid-side abnormalities. The comparative analysis with the state-of-the-art techniques shows the effectiveness of the strategy. Under all test conditions, the harmonics in grid currents are observed within limits as per the IEEE-519 and IEC-61727 standards, whereas the PV leakage currents are maintained well within the range recommended by VDE-00126 standard. [ABSTRACT FROM AUTHOR]

This article aims to develop a solar- battery energy storage (BES) based system, which ensures an uninterruptable supply to loads irrespective of availability of the grid. This system comprises of a solar photovoltaic (PV) array, a BES, the grid and local residential loads. A new control is implemented such that the active power demand of residential loads, is fed from the PV array, a BES unit and the utility grid. In this system, the power control operates in different power modes, which delivers the benefits to the end users with an integration of BES and an excess of PV array power, which is sold back to the grid. For this, an effective control logic is developed for the grid tied voltage source converter. Moreover, this system deals with the issue of an integrating power quality enhancement along with the power generation from the solar PV source. The cascaded delayed signal cancellation based phase locked loop is implemented for grid synchronization during the grid voltage distortion. The developed control is easily implemented in a real time controller (dSPACE-1202). Test results validate the performance of the implemented control in different operating conditions such as varying solar power generation, load variations and unavailability of the grid. [ABSTRACT FROM AUTHOR]

The dual active bridge (DAB) converters have the capability of handling high power in compact form and it is one of the key elements for interconnecting different dc microgrid clusters. A DAB also offers bidirectional power transfer with galvanic isolation between two power buses of similar or different voltage levels, i.e., low voltage and high voltage buses. In microgrid applications, bus voltage regulation is necessary for an uninterrupted power flow and reliable operation of dc microgrids. Due to the galvanic isolation and modularity nature of a DAB, the output can be easily interconnected for efficient and reliable power sharing. In this article, taking the advantage of modularity property of the DAB, an efficient and improved power sharing scheme is developed to stabilize the bus voltage in microgrid applications. A robust bidirectional power sharing control strategy is developed between DABs from different high voltage buses to low voltage buses that improves the voltage stability. An advanced supervisory controller is designed by considering the nonlinearity and uncertainty that ensures stable dc bus voltage and reliable power sharing among DABs under different operating conditions. The controller is validated theoretically and a small-scale laboratory prototype is developed. The concept is verified experimentally at different possible scenarios. From theoretical and experimental results, it is found that the proposed DAB control provides excellent performance in terms of power sharing, dc-bus voltage regulation and power quality. [ABSTRACT FROM AUTHOR]

DC microgrids (DCMGs) are evolving into cyber-physical systems with advanced communication networks and computational methodologies, making them sensitive to cyber-attacks. These attacks can threaten the safe operation of a system. In this article, a virtual sensor-based framework is proposed for continuously monitoring and detecting malicious activities at the hardware level of a DCMG system. An adaptive state observer with a low computational burden is designed to estimate the voltage and current of a dc–dc converter. The proposed method considers the effects of cyber-attacks by injecting false data (FD) at targeted nodes in an attempt to affect the voltage regulation and current sharing by modifying the onboard voltage and current sensors. In the presented strategy, first, a DCMG is operated and controlled without any false data injecting attacks with different load conditions. Next, the DCMG is exposed to various cyber-attacks, and the output voltages and currents of dc–dc converters are estimated. Based on the error between the estimated and actual sensed signals, the cyber-attack is detected and corrected with the proposed framework. The proposed scheme is simple in design, efficient in operation, and easily implemented in a distributed control system. The effectiveness and robustness of the proposed method are illustrated by implementing it in real-time hardware using the LabView test bench by considering four dc systems (including a solar photovoltaic system) connected in a ringlike manner communicated via an ethernet-based local area network. [ABSTRACT FROM AUTHOR]

This article proposes a computationally simple strategy by using a three-sample-based technique for a grid-connected inverter in a single-phase active distribution system. The proposed control is to improve the performance during varying grid conditions such as voltage sag, swell, and frequency swing. A comparative analysis between the proposed controller and the conventional second-order generalized integrator phase-locked loop (PLL) based controller for dynamic grid conditions in weak-grid scenario has been presented. Additionally, a frequency domain analysis via describing function method is used to model the dynamics of nonlinear hysteresis current controller to analyze the closed-loop stability of the system. Further validation of the proposed control algorithm is simulated in MATLAB/SIMULINK environment for various scenarios. To establish the effectiveness of the proposed approach in real time, the proposed control strategy is tested in a 1 kVA based experimental setup. [ABSTRACT FROM AUTHOR]

The autonomous microgrid (MG) with multiple voltage source inverters (VSI) is operated in droop mode to share the load proportionally. These VSI controllers require higher droop constants if the feeder lines connecting the VSI to microgrid has a low X/R ratio. The higher droop gains and large loading conditions in the microgrid may exhibit instability with the low frequency power modes (LFPM). This paper details a systematic multivariable plant model of the MG using dynamic phasor modeling of power flow transfer functions to analyze the LFPM. Further, a robust supplementary multivariable controller is developed to stabilize the developed plant model, damp LFPM and improve transient power sharing performance of VSIs without affecting their steady-state power sharing. This stabilizer is developed based on Glover-McFarlane H∞ loop shaping robust stabilization technique with an additional pole placement constraints formulated in linear matrix inequality framework. A laboratory scale experimental validation is presented to evaluate the performance of proposed stabilizer under various operating conditions and uncertainties in the autonomous MG. Moreover, the transient power sharing performance of DGs with proposed controller was compared with that of widely used derivative droop controller. [ABSTRACT FROM AUTHOR]

In this work, a multifunctional control is implemented for a solar photovoltaic (PV) integrated battery energy storage (BES) system (PVBES), which operates both in the grid-connected mode (GCM) and a standalone mode (SAM). This system addresses the major issues of integrating power quality enhancement along with the solar PV generation. Thus, a multifunctional control of voltage source converter (VSC) is implemented to provide the load compensation, harmonics mitigation, unity power factor, and an automated transition between GCM and SAM in PVBES. A single VSC is used to control the active power and to maintain the power quality in this PVBES. Furthermore, due to an automated transition in the system, the local loads have continuous power irrespective of the grid accessibility. The main challenges addressed are the operation of an automated transition between GCM and SAM with the least disturbance to the nonlinear loads. The integration of a BES enables the SAM operation and improves the reliability of the PVBES. The charging and discharging of BES are controlled by using a dc–dc bidirectional converter. The performance of the implemented controls is tested using a real-time processor (dSPACE-1202) and validated through test results for steady state and dynamic conditions. In all operating conditions, the harmonics content of the grid current is maintained less than 5%, which follows the IEEE standard 519-2014. [ABSTRACT FROM AUTHOR]

A fully distributed hierarchical control strategy for multiple inverters‐based AC microgrid is proposed. The developed controller provides real‐time economic dispatch along with the network frequency and average voltage restoration. The controllers cooperate with neighbours using sparse communication network and perform local computations to achieve the assigned objectives. The economic dispatch control unit is embedded with the frequency restoration at the secondary level controller to change the active power supply from the inverter. The voltage controller along with reactive power controller ensures the proportional reactive power sharing as well as network average voltage regulation. The average voltage regulation aids the individual inverter to provide required reactive power demand, with a small, comprise at the terminal output voltages from the nominal values. The convergence of the proposed controller is proved using the Lyapunov stability criteria. The maximum allowable communication delay that obligate stable microgrid operation is derived. The simulation results verify the efficacy of the proposed controller. Experimental validation is also presented, and the controller ability to ride through communication failure and load perturbation condition is demonstrated. [ABSTRACT FROM AUTHOR]

For microgrids (MGs) owned by different utilities, it is always desirable that the steady state impact of load or generation changes in one MG, does not affect the generation cost in another MG. To ensure this, the power flow through the tie-line is typically regulated at a pre-scheduled value thereby enforcing the individual MGs to manage their respective load at steady state. To this end, this article presents a distributed control scheme to regulate tie-line power flow between two autonomous dc MG clusters. In this article, a unifying hierarchical control scheme based on distributed communication is proposed where the tie-line power flow control based on a pinning control strategy is unified with the distributed optimization and average voltage regulation control loops. The distributed optimization utilizes economic dispatch to minimize the operating costs of the DG, while the average voltage control regulates the MGs average voltage at its nominal value. With the application of this approach, the responsibility of tie-line regulation is distributed in an economic manner without degrading the voltage quality in the system. Time-domain simulations, real-time simulation using Ethernet-based transmission control protocol/internet protocol (TCP/IP) communication, and experimental results are presented to validate the performance of proposed distributed control under normal and faulty system conditions. [ABSTRACT FROM AUTHOR]

This article proposes a predictive optimal switching vector controlled virtual synchronous machine (VSM) for three-phase microgrid applications, which inherits self-synchronization and islanding detection technique within the controller. A novel synchronization signal is introduced here, to modify the frequency reference in VSMs. This integrates the synchronization and islanding detection within the control loop, thereby resulting in smooth system responses without causing stability issues associated with phase-locked loops. Moreover, it totally eliminates proportional–integral (PI) regulators in the system. The traditional pulsewidth modulation controllers use cascaded internal control loops, and they demand multiple PI regulators and synchronous coordinate transformations. They are associated with finite dynamic response time by PI regulators and necessitate rigorous tuning for practical implementation purposes. The proposed controller, however, estimates the behavior of output voltages and uses a minimization criterion to produce optimal inverter switching sequences. The voltage vectors that cause the overcurrents in the inverter are inherently avoided by the minimization function within the controller. The effectiveness of the proposed control strategy is verified through simulations and experiments validate the performance under different operating conditions. [ABSTRACT FROM AUTHOR]

It is well-known that distributed control can improve the resiliency of dc microgrids against multiple link failures as compared to centralized control. However, the control layer is still vulnerable to cyber attacks. Unlike widely studied false data injection attacks, which involve adding false signals on top of the existing ones in the controller or communication links, hijacking attacks completely replace the existing signals. As a result, the compromised agent(s) diverge from steady state owing to imbalance in the iterative rule of consensus algorithm. To detect hijacking attacks, a novel distributed screening (DS) methodology is proposed. In addition to that, a fault detection (FD) metric is provided to assist the proposed attack detection strategy in differentiating between hijacking attacks and sensor faults. This reduces the complexity of decision making in the attack mitigation approach. Furthermore, interoperability of the proposed detection metrics allows simultaneous detection of sensor faults and hijacking attacks. The performance of the proposed detection metrics is evaluated under simulation and experimental conditions to conclude that it successfully detects the attacked agent(s) as well as sensor fault(s). [ABSTRACT FROM AUTHOR]

This paper presents the design of a power system stabilizer (PSS) for stability improvement of a droop-controlled inverter-based microgrid systems. For faster power sharing, high droop gains are required, but increasing the droop gains degrades the system stability. Hence, there is a tradeoff between the faster load sharing and system stability. An answer to the given problem is presented in this paper by developing a PSS for inverter-based microgrid. The proposed stabilizer provides sufficient damping to the low-frequency oscillation even at higher value of droop gains which are usually unstable otherwise. The PSS designed in this paper is a generalized one and a step-by-step method to select the PSS parameters is also presented. Time domain simulation, experimental results, and eigenvalue analysis are presented for verification of the proposed controller. [ABSTRACT FROM AUTHOR]

This paper proposes a multilevel hybrid control scheme, including grid control and node control, for an islanded 48-V solar photovoltaic-based low voltage dc microgrid that aims to overcome the drawbacks of centralized and decentralized control schemes. The analyzed microgrid includes a 35-kW rooftop solar system as the main power source at bus-1 with battery storage, 5-kW hybrid energy storage system (Vanadium Redox flow battery with super capacitor) at bus-2, and variable loads such as electrical vehicles at bus-3. In the case of a central failure, the proposed hybrid control scheme is capable of seamlessly switching between high bandwidth communication and low bandwidth communication channels of communications to implement a distributed control scheme. The central supervisory controller is responsible for updation of grid characteristics and sending/receiving information to/from local node controllers, which are responsible for bus voltage regulation and energy management. The control hierarchy features optimized and safe operation (charge and discharge) of storage devices in dc microgrids. The paper also demonstrates the application of battery-supercapacitor systems to absorb system transients during load changes. The simulation showcases the continuous flow of information and decision processes via each level of control while simultaneously taking into consideration the constraints of each subsystem. The scheme has been simulated in MATLAB/Simulink environment for various case studies to evaluate system robustness. Further, the proposed scheme has been tested experimentally with its prototype and its results are explored. [ABSTRACT FROM AUTHOR]

The grid-connected photovoltaic (PV) system with battery energy storage (BESS) has been in use for many demand-related issues. This article discusses the use of grid-connected PV with BESS in case of open-phase condition in the distribution system. An open-phase condition at medium voltage (11 kV) will result in continuous voltage sag at low voltage (LV) voltage level (400 V), which may be detrimental to various kind of loads, especially for constant power loads. This article presents an approach to mitigate such a scenario by using a control strategy for voltage source converter of grid-connected PV connected to the distribution transformer terminal. The utility of the proposed configuration is demonstrated as the voltage is restored in all phases at the LV level during an open-phase fault at the MV level, and results obtained for selected possible loading conditions have been presented. For further validating the proposed control strategy in real-time conditions, experimental verification is also done on an NI-based PXI hardware setup along with an Opal-RT based hardware in the loop system, and results for the same have been presented. [ABSTRACT FROM AUTHOR]

This paper proposes an extended Kalman filter (EKF) based control strategy for fault ride-through operation in two-stage grid-connected photovoltaic (GPV) system. Unlike the conventional controllers for ride-through operation, the proposed strategy does not compromise with power quality improvement features in the system while enabling ride-through operation. The controller accounts for nonlinear loads in the system, grid harmonic-currents elimination, and grid-currents balancing even during the harmonic/distorted grid voltages. The IEEE Standard-1547.4 compels the distributed resource to ride-through during voltage disturbances caused by faults. For the ride-through operation, a limit is imposed on PV active power injection to prevent inverter overcurrents and dc-link energy aggregation, which reduces the lifetime of dc-link capacitor. The reactive power is fed to the grid, as per the depth in voltage-sag. The derated PV array power is supplied in cases where the inverter cannot handle the utmost PV-power. The power quality improvement is ensured using EKF state estimator, which precisely estimates the fundamental load currents. In distribution network with modern nonlinear loads, especially at far radial ends, the grid voltages are prone to huge diversions and the proposed controller provides a possible solution to maintain active/reactive power support and maintain power quality in the network. The effectiveness of the strategy is demonstrated through simulations and experiments. Under all disturbances, the harmonic content in grid currents is observed within limits, in accordance with the IEEE Standard-519. [ABSTRACT FROM AUTHOR]

This study proposes a modified decentralised droop controller for inverter‐based autonomous photovoltaics (PV) microgrids to address the problem of instability and slower power sharing between PV inverters. The proposed controller modifies the conventional droop mechanism in transient as well as in steady state by adding an auxiliary control signal in the power control loop of the inverters. The proposed approach offers three key benefits, i.e. improves active power sharing, enhances system stability and performs the secondary control action by nullifying the frequency deviation by using only one auxiliary signal in the control loop. The accuracy of the proposed modified droop controller is verified with the help of time‐domain simulations in MATLAB/SIMULINK. The results obtained show that the controller is able to improve the power sharing and stability of the microgrid as well as to restore frequency. The performance of the proposed control scheme is also validated by experimental results and small‐signal analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a cooperative mechanism for detecting potentially deceptive cyber attacks that attempt to disregard average voltage regulation and current sharing in cyber-physical dc microgrids. Considering a set of conventional cyber attacks, the detection becomes fairly easy for distributed observer based techniques. However, a well-planned set of balanced attacks, termed as the stealth attack, can bypass the conventional observer based detection theory as the control objectives are met without any physical error involved. In this paper, we discuss the formulation and associated scope of instability from stealth attacks to deceive distributed observers realizing the necessary and sufficient conditions to model such attacks. To address this issue, a novel cooperative vulnerability factor (CVF) framework for each agent is introduced, which accurately identifies the attacked agent(s) under various scenarios. To facilitate detection under worst cases, the CVFs from the secondary voltage control sublayer is strategically cross coupled to the current sublayer, which ultimately disorients the control objectives in the presence of stealth attacks and provides a clear norm for triggering defense mechanisms. Finally, the performance of the proposed detection strategy is simulated in MATLAB/SIMULINK environment and experimentally validated for false data injection and stealth attacks on sensors and communication links. [ABSTRACT FROM AUTHOR]

This work deals with an implementation of a unique control approach for the power quality enhancement in solar photovoltaic (PV) based grid interfaced system. In this work, a robust control technique with strong filtering capabilities is implemented. A single‐phase two‐stage grid interacted solar PV topology is considered with a second‐order sequence filter as a test system for the validation of the power quality enhancement features. The system constitutes a PV array, a boost converter, a DC link capacitance, a voltage source converter (VSC), an interfacing inductor and a ripple filter. A boost converter is used at a primary stage of proposed topology, which supports the extraction of maximum power from the solar PV array. In addition, the VSC feeds the solar PV power into the grid. It also provides harmonics elimination and power factor correction. A new maximum power point tracking technique avoiding a drift feature is adopted for the fast dynamic performance. The implementation of the solar PV system is performed and the harmonic profile of grid current is observed in compliance to the IEEE‐519 standard. [ABSTRACT FROM AUTHOR]

This paper presents a supervisory control scheme for the mitigation of voltage regulation issues in a ring dc microgrid with energy hub (EH). The EH is installed with battery banks, proton exchange membrane based fuel cell and electrolyzer stacks representing an energy source-storage unit. In a ring dc system, power injection and absorption at different buses can cause significant voltage deviations throughout the system. This situation is further aggravated due to the intermittent nature of PV power generation. To resolve this issue, a supervisory control scheme is proposed which utilizes a centralized communication system to estimate the network voltage profile and generates desired voltage and current references for the controllable sources. The proposed system consists of dispatchable and non-dispatcable energy sources. Conventionally, in a grid connected system, a bidirectional voltage source converter (VSC) maintains the network voltage while the energy storage system remains at standby/fully charged. This paper suggests to utilize both VSC and EH in a coordinated manner, so as to maintain the voltage at the load terminals within a tolerance band. The proposed ring dc microgrid model is simulated in MATLAB/Simulink environment and the simulation results validate the effectiveness of the supervisory control under wide variations in system operating conditions. [ABSTRACT FROM AUTHOR]

This study presents an optimal control operation of a photovoltaic‐battery based standalone microgrid, feeding non‐linear loads. To ensure continuous power supply to the critical loads during low insolation or low battery state of charge, a diesel generator (DG) is used as an auxiliary generator. This cost effective hybrid system with maximum utilisation of the renewable as well as fossil fuel based generators can be employed in hospitals, telecom stations in remote areas. In order to nullify the effect of non‐linear loads on the DG, modified enhanced phase‐locked loop (EPLL) based power quality conditioner is used. The characteristic equation of conventional EPLL is amplitude dependent, thus, the controller tuning parameters need to be modified if the input signal varies over a large range. The presented controller overcomes this problem making the system more robust in eliminating noise and harmonics and extracting fundamental component of a given signal. This component is drawn from the DG with the help of a voltage source converter, thus, making its current always distortion free. The proposed control scheme is simulated in MATLAB. Furthermore, experimental verification is done on a laboratory prototype of the same. The steady state and dynamic responses of the system validate its satisfactory performance. [ABSTRACT FROM AUTHOR]

For the effective operation of a dynamic voltage restorer (DVR), a control strategy plays a significant role. This paper presents an enhanced control strategy for DVR using dual role cascaded delay signal cancellation (CDSC)-based dual vector control (DVC) under unbalanced and distorted grid conditions. Based on the numerical analysis, it is found that the CDSC prefilter is a promising solution when grid voltage is distorted by symmetric, asymmetric harmonics, and unbalanced sag. Mainly, the CDSC prefilter extracts instantaneous symmetrical components of the grid voltage required for voltage sags detection and generation of fundamental component of reference voltage for the DVR. A CDSC-based DVC algorithm with inductor current and capacitor voltage feedback is implemented in a synchronous reference frame, which tracks the fundamental DVR reference voltages. An extractor based on the modified CDSC strategy is designed to extract harmonics from load voltage during distorted grid conditions. These extracted harmonic components (nonfundamental) are added in phase opposition with fundamental component and fed to pulse width modulation block to generate reference voltages. Experimental studies are conducted on scaled down (100 V, 0.5 kVA) laboratory prototype DVR to verify the effectiveness of the proposed control algorithm under unbalanced and distorted grid conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a distributed finite-time secondary controller to achieve average voltage regulation and proportionate current sharing within a finite settling time for autonomous network of dc microgrids. It is employed by using a distributed finite-time control approach which maintains average voltage regulation of the system facilitating proportionate current sharing simultaneously by virtue of dynamic consensus between its neighbors. The proposed scheme ensures an improved performance over the conventional distributed secondary methods by reducing overshoots and chattering which is significant for critical operation of the loads. The proposed control strategy is simulated in MATLAB/Simulink environment to test link-failure resiliency, plug and play capability, and controller performance under communication delays within a tolerable upper bound on delay determined using time-delay analysis. Moreover the effect of variable time delays in different transmission medium is also simulated to test the practicality of the approach. This strategy is further tested on a 500-W FPGA-based experimental prototype to validate the control approach under different scenarios. [ABSTRACT FROM AUTHOR]

The active power distribution network operation with the integration of various renewable distributed generations (DGs), storage units, and dynamic loads are attracting a lot of interest due to substantial benefits in maximizing the penetration of available renewable energy resources (RES). However, the risk of voltage violation in the active distribution system (ADS) is exacerbated due to increasing penetration of DGs. It has become a bottleneck to maximize the DG penetration into the system. This bottleneck can be handled by effective voltage regulation and reactive power support into ADS. Nowadays, power electronic devices are frequently used for voltage and reactive power support over the conventional approaches. In this paper, an approach to maximize the penetration of RES, such as solar, wind, etc., into ADS by maximum utilization of existing solar photovoltaic inverters (SPVI) in the system is presented. Optimal utilization of SPVI may enhance the voltage stability of the ADS and wind power penetration into the system. The proposed SPVI control approaches are depended on active power generation of solar photovoltaic (SPVG), rating and capability of SPVI, and required reactive power in the ADS. In this paper, the problem of maximum penetration of RES is formulated as an optimal power flow embedded nonlinear optimization problem subject to the physical limitations of the SPVI. The results of the analysis performed on an IEEE 33 bus system show that the proposed SPVI control strategies can improve the voltage profile of the ADS with minimization of curtailment of wind power generation. [ABSTRACT FROM AUTHOR]

Development of microgrids and wide spread deployment of renewable generation and energy storage systems have highlighted the need for distributed control schemes to achieve maximum utilization and coordination among all the connected resources. In DC microgrids, the key goals of system-wide control are droop-based current sharing and network dc-voltage regulation. These may be achieved using a consensus algorithm secondary control that a) averages all the node voltages dynamically and maintains them at a nominal value and b) based on information from neighboring source currents to converge to a consensus in current sharing. Achieving the dynamic consensus may impose significant communication burden when implemented using conventional periodic communication methods. In this paper, an event-triggered communication based dynamic consensus algorithm is proposed that helps achieve both the stated goals of proportional current sharing along with average DC voltage regulation in a DC microgrid. The convergence and stability of the modified dynamic consensus algorithm and event triggering condition is proven using Lyapunov's stability criterion. The proposed control is applied to a DC microgrid system for secondary control of voltage and current regulation, and the performance of the proposed technique is validated under various operating conditions and disturbance in the communication system in both simulation and hardware environment. [ABSTRACT FROM AUTHOR]

This paper presents a step in microlevel photovoltaic (PV) summation technology for combining unsymmetrical PV modules with differences in specification and age, relocation on nonfertile land, or multilocation mounting by designing an add-on modular hardware interface to a multi-input single-output (MISO) dc bus, using an MISO controller employing a suitable maximum power point (MPP) tracker under partial shading/long distance/mismatching PV module conditions along with a sensor-less PV vector control inverter (PV–VCI) driving a three-phase asynchronous squirrel cage induction motor dedicated to irrigation, with the facility of autoconfiguration/autotuning at the beginning. A PV source gets automatically added/removed in a ramp profile in proportion to the load in steps, thus keeping on only when required, enabling high efficiency, minimum heating, and prolonged life as that of a PV module. The contribution includes a reduced PV energy cost per watt by 24.10%, improved return on investment by 27.48%, improved water discharge yield by 11.06%, and improved MPP tracker impact by 14.59% with 90.88% MISO system efficiency compared to a normal scheme. [ABSTRACT FROM AUTHOR]

This paper presents a multi-objective adaptive power management scheme for an autonomous dc microgrid which consists of a novel adaptive gain-based proportionate charging/discharging strategy in order to provide energy balancing between battery energy storage systems (BESSs) of different capacities. As BESSs are a key component to maintain reliability and stability in an autonomous microgrid, control measures for longevity of these units should be properly investigated. Following the recommended way of charging for BESSs, i.e., constant current/constant voltage (CV) charging, the conventional methods undergo mode switching using a floating reference value to control CV charging which does not guarantee zero current when the battery is fully charged. To account for this issue, a novel progressive de-rating control scheme for PV in a seamless fashion to carry out CV charging of BESSs is done using the adaptive mechanism introduced by model reference adaptive control scheme for optimized power management between sources and loads. Furthermore, emergency events such as load shedding and load following operation of PV have also been discussed in detail. The proposed control strategy is simulated in MATLAB/SIMULINK environment and tested on a 1 kVA FPGA-based experimental prototype to validate the control approach under different scenarios. [ABSTRACT FROM AUTHOR]

Based on interaction with farmers, few post photovoltaic (PV) irrigation installation issues like diminishing water discharge due to increasing depth of ground water level, prolonged idleness (40%–60% time over a year) including morning/evening, no alternate use after irrigation, high maintenance cost of brushless dc pump, low return on investment (ROI), surrounding shading effect, etc., are identified. To address above issues, a co-operative movement for PV irrigation scheme-based solution is implemented by integration of PV arrays of two farmers (minimum) using multi-input dual-output controller with single-ended primary-inductance converter design. Control features like maximum power point tracking, energy transfer, optimum power utilization and sharing, vector control inverter, protections are adapted. MATLAB simulation and real-time field data result shows ROI per kilowatt improvement by 5.97%, reduced PV energy cost per watt by 14.89%, additional morning, evening PV extraction by 13.68%, and overall daily excess energy yield and water discharge by 18.75% and 24.74% for each farmer. [ABSTRACT FROM AUTHOR]

This paper presents a multipurpose three-phase double-stage grid interfaced photovoltaic (GPV) system using an adaptive nonlinear control strategy. Along with a peak power extraction from a photovoltaic array, the proposed system is capable of harmonics currents elimination, reactive power compensation, grid currents balancing, and adaptive dc-link voltage control. The fundamental and harmonics information from the polluted load current are precisely estimated using an adaptive observer. A strictly positive real Lyapunov function is used to derive update laws for an adaptive observer. The DC-link voltage is adaptively adjusted in proportion to the point of common coupling voltage to minimize switching losses in voltage source converter and to avoid its tripping in sensitive distribution grids. A feed-forward loop for PV contribution is included to improve system response under dynamic conditions. Simulated and test results depict the performance of the GPV system with aforementioned functionalities. Improved steady-state and dynamic performances are observed with the proposed nonlinear adaptive estimation based control approach. The total harmonic distortions in grid currents are found well within the limits prescribed by an IEEE-519 standard. [ABSTRACT FROM PUBLISHER]

A robust controller design for the voltage control of an autonomous three-phase voltage source converter (VSC) is proposed. As compared with the conventional proportional plus integral (PI) controllers, fractional order controllers make the VSC system robust due to their fractional characteristics. The fractional PI $\lambda$ controller has an additional degree of freedom $\lambda$ along with $k_p$ and $k_i$ gains of the conventional PI controller. Detailed modeling of a VSC is used in the controller design process so as it include inner current control and filter dynamics. The outer fractional voltage controller is designed such that the VSC system satisfies a required phase margin, with improved robustness in the system and capability to attenuate the noise. The overall system stability is analyzed using both bode plot and step response, and these responses are compared with a conventional PI controller. Further, the dynamic performance of the fractional controller is evaluated by simulating the nonlinear system. A hardware prototype is also developed to demonstrate the practical realization of the controller. [ABSTRACT FROM AUTHOR]

In this paper, a dynamic power management scheme (PMS) is proposed for a standalone hybrid ac/dc microgrid, which constitutes a photovoltaic (PV)-based renewable energy source, a proton exchange membrane fuel cell (FC) as a secondary power source, and a battery and a supercapacitor as hybrid energy storage. The power management algorithm accounts for seamless operation of the microgrid under various modes and state-of-charge limit conditions of hybrid energy storage when all the sources, storages, and loads are connected directly at the dc link. The PMS generates current references for dc converter current controllers of the FC, the battery, and the supercapacitor. The average and fluctuating power components are separated using a moving average filter. The dc-link voltage regulation under dynamic changes in load and source power variation is proposed. Also, PV power curtailment through control is formulated. The proposed power management is modified and extended to multiple PV generation systems and batteries, with all the sources and storages geographically distributed and operating under multitime-scale adaptive-droop-based control with supervisory control for mode transition. The proposed PMS is validated using simulation results. Also, field programmable gate array/Labview-based laboratory-scale experimental results are presented to validate the PMS under various critical conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a repetitive learning-based phase locked loop (RLPLL) to improve power quality of the grid-connected dc microgrids under distorted grid voltage in a weak grid. The harmonic component present in grid current in a high impedance network amplifies the distortion in voltage, which often leads to instability. Since the behavior of the conventional synchronous reference frame PLL (SRF-PLL) varies, owing to the proportional-integral gains constrained to harmonic rejection bandwidth ultimately leading to a sluggish response. However, RLPLL accommodates this limitation with a comparable dynamic performance and enhanced harmonic attenuation properties. This has been achieved by using a Lyapunov-based approach for harmonic estimation, which facilitates the periodicity and boundedness of the harmonic component to obtain an adaptive learning-based update. To deal with the computational burden, this paper also provides a low-computing alternative model of the proposed strategy. The dynamic response of RLPLL along with a comparative analysis with SRF-PLL is governed by many events directly affecting the dc voltage, which is critical for the operation of dc microgrids. Its performance is validated under different scenarios in a 1-kVA field programmable gate array-based experimental setup. [ABSTRACT FROM AUTHOR]

Unity power factor injection from single‐phase photovoltaics (PVs) located towards the end of a residential feeder leads to voltage rise problems. Also, unbalanced current injection due to variable solar insolation results in voltage unbalancing and makes the situation worst. A decoupled controller for a single‐phase PV inverter is proposed to improve the voltage profile of the distribution feeders. The proposed controller consists of the following components: voltage regulator (to control the amount of reactive power injection), outer voltage control loop (slow controller to set the reference for the inner current loop), inner current control loop (to control the PV inverters) and modified second‐order generalised integrator (to generate fundamental frequency). A sample distribution systems consisting of several PVs located in all three phases and a three‐phase induction motor load is considered. The real‐time hardware‐in‐the‐loop simulations are performed to test the efficacy of the proposed controller scheme. Results show the improvement in voltage regulation of different buses. [ABSTRACT FROM AUTHOR]

This study proposes a grid supportive control scheme for a single‐phase photo‐voltaic (PV)‐based inverter to mimic the behaviour of a synchronous generator during grid voltage/frequency variations. The converter embedded with the proposed controller, termed as a 'single‐phase synchronverter', transforms a large segment of rooftop PV, which is, in general, single phase, to an ancillary service provider in compliance with the grid code (i.e. if the grid code allows rooftop PV to provide inertial/primary frequency/voltage response). Owing to fluctuations in incident solar irradiation, a battery has been connected at the dc link to take care of the variability in PV output power. The challenges involved in extending the three‐phase synchronverter philosophy to a single‐phase converter have been discussed and the performance of the resultant single‐phase synchronverter to different values of virtual inertia and droop/regulation has been analysed. An experimental setup is developed and the system behaviour for different operating conditions has also been studied. [ABSTRACT FROM AUTHOR]

A control strategy is formulated for photovoltaic generators (PVG) operating in parallel in a Microgrid. A radial microgrid is considered and when it is isolated from the utility grid, the PVG's must operate in the voltage‐frequency control mode in the absence of a storage or a diesel generator unit. It is observed that the conventional P‐f and Q‐v droop control method fails to deliver correct power references for inverters operating in parallel when network impedance is unequal, and therefore an active power‐reactive power‐frequency‐derivative (PQFD) droop control is proposed to achieve an error free power sharing. Seamless operation from the grid connected mode to isolated mode and vice‐versa is achieved with the help of the aforementioned control, which in addition assists in the alleviation of sluggish response in the presence of Induction motor (IM) loads by providing appropriate damping. For a transient free transfer from isolated mode to grid connected mode, a synchronisation control is formulated which helps in the proper reconnection. The controller designed is tested in both Microgrid and the grid connected mode and during transition. The controller gains used in the paper have been obtained with the help of a small signal analysis of the system considered. [ABSTRACT FROM AUTHOR]