Voltage Regulation In Microgrids Research Articles

Voltage Deviation Improvement in Microgrid Operation through Demand Response Using Imperialist Competitive and Genetic Algorithms

In recent decades, with the expansion of distributed energy generation technologies and the increasing need for more flexibility and efficiency in energy distribution systems, microgrids have been considered a promising innovative solution for local energy supply and enhancing resilience against network fluctuations. One of the basic challenges in the operation of microgrids is the optimal management of voltage and frequency in the network, which has been the subject of extensive research in the field of microgrid operational optimization. The energy demand is considered a crucial element for energy management due to its fluctuating nature over the day. The use of demand response strategies for energy management is one of the most important factors in dealing with renewables. These strategies enable better energy management in microgrids, thereby improving system efficiency and stability. Given the complexity of optimization problems related to microgrid management, evolutionary optimization algorithms such as the Imperialist Competitive Algorithm (ICA) and Genetic Algorithm (GA) have gained great attention. These algorithms enable solving high-complexity optimization problems by considering various constraints and multiple objectives. In this paper, both ICA and GA, as well as their hybrid application, are used to significantly enhance the voltage regulation in microgrids. The integration of optimization techniques with demand response strategies improves the overall system efficiency and stability. The results proved that the hybrid method provides valuable insights for optimizing energy management systems.

Piece-wise Droop Control Algorithm in Renewable Fed DC Microgrid Voltage Regulation using Super-capacitors

Piece-wise Droop Control Algorithm in Renewable Fed DC Microgrid Voltage Regulation using Super-capacitors

Enhancing Hybrid Wind-Solar-Battery System Efficiency through Artificial Neural Network-Based Energy Management and Voltage Regulation in Micro Grids

Energy management in micro grids involves an integrated information and control system pivotal for optimizing energy flow from generation and distribution, minimizing operational costs. Energy Management Systems (EMS) are crucial for leveraging distributed energy resources, especially amidst variable generation and pricing. This paper introduces an Artificial Neural Network (ANN)-powered approach for managing a hybrid wind, solar, and Battery Storage System (BSS). Additionally, a 3 Port DC-DC Converter is proposed to sustain DC voltage. While renewable energy systems offer numerous benefits, their intermittent power generation poses challenges, resulting in grid power fluctuations. EMS seeks to mitigate these fluctuations while preserving the battery state of charge (SOC) within permissible limits to extend battery life. Implementation is conducted using the Simulink/Matlab platform. The efficacy of the proposed approach is demonstrated by comparing the Total Harmonic Distortion (THD) of the suggested controller (1.52%) against conventional controllers: ZSI-based PID (3.05%), PI (4.02%), and FO-PI (3.32%).

Comparative Performance of DVR and STATCOM for Voltage Regulation in Radial Microgrid with High Penetration of RES

In recent years, the penetration of renewable energy sources (RES) in microgrids and distribution system feeders has increased manifold. Moreover, the advancement of power electronics-based devices in the distribution system has significantly increased the number of sensitive loads. Variations in the voltage under intermittent RES create functional problems with sensitive loads, necessitating voltage regulators (VR) installation. In this paper, two custom power devices: dynamic voltage restorer (DVR) and static synchronous compensator (STATCOM), used for voltage regulation in a microgrid, are investigated under different operating conditions. The efficacy of DVR and STATCOM for voltage regulation in an 11-node radial microgrid with high penetration of RES is simulated under a MATLAB Simulink environment. Furthermore, the simulated microgrid voltage profile results are analyzed to evaluate the efficacy of both voltage regulators.

Unfalsified Switching Adaptive Voltage Control for Islanded Microgrids

Microgrid's voltage regulation is of particular importance during both grid-connected and islanded modes of operation. Especially, during the islanded mode, when the support from the upstream grid is lost, stable voltage regulation is vital for the reliable operation of critical loads. This paper proposes a robust and data-driven control approach for secondary voltage control of AC microgrids in the presence of uncertainties. To this end, unfalsified adaptive control (UAC) is utilized to select the best stabilizing controller from a set of pre-designed controllers with the minimum knowledge required from the microgrid. Two microgrid test systems are simulated in MATLAB to verify the effectiveness of the proposed method under different scenarios like load change and communication link failure.

Direct Model Reference Adaptive Control of a Boost Converter for Voltage Regulation in Microgrids

In this study, we present a Direct Model Reference Adaptive Control (DMRAC) algorithm in a boost converter used in islanded microgrids (MG) with a solar photovoltaic (PV) system. Islanded types of microgrids have very sensitive voltage and frequency variability; therefore, a robust and adaptive controller is always desired to control such variations within the MG. A DC–DC boost converter with a modified MIT rule controller is proposed in this paper, which stabilizes output voltage variations in islanded MG. Since the boost converter is a non-minimum phase, the controller design that relies only on output voltage feedback becomes challenging. Even though output voltage control can be achieved using inductor current control, such current mode controllers may also require prior knowledge of the load resistance and more states, such as output and inductor currents in feedback. Here, two control loops are used to achieve a stable output voltage; a PID controller can regulate the output voltage at a fixed level, and the outer loop is designed to implement the MIT rule for a DMRAC. To ensure that the actual system is following the desired reference model, using only an output voltage feedback sensor, a DMRAC is devised to update the PID controller parameters in real-time. Compared to a DC–DC boost converter connected to the MG, a controller, such as the one introduced in this paper, is more successful in dealing with unknown parameter fluctuations and disturbance changes. The MATLAB/SIMULINK is used to design and simulate the controller with different load disturbances and input voltage variances. The hardware validation is also carried out to show the performance of the proposed controller. Our results suggest that the DMRAC provides robust regulation against parameter variations.

DOBC-based frequency & voltage regulation strategy for PV-diesel hybrid microgrid during islanding conditions

The integration of renewable energy sources (RES) based distributed energy resources (DER) lead to reduction in overall system inertia which causes large voltage and frequency fluctuations during any intermittency. This necessitates the integration of fast and robust controllers for low-inertia microgrids. Therefore, this paper proposes disturbance observer based control (DOBC) approach for frequency and voltage regulation of microgrid consisting of solar PV and diesel generator (DG) based hybrid microgrid under islanding situations. The DOBC is included as feed-forward control to the synchronous generator-based DG, which handles the real-time power mismatches and regulates frequency and voltage of islanded microgrid. To demonstrate the operational resilience of the designed controller under real-time uncertainties in PV and load, the controller has been evaluated under the most extreme uncertainty scenarios. The suggested controller has been implemented on a MATLAB/Simulink platform, and results have been validated utilising the real-time simulator OPAL-RT. In addition, the efficacy of the suggested control strategy has been evaluated in the presence of communication delays and noisy load circumstances. Results demonstrate the controller's dynamic performance in regulating the frequency and voltage for low-inertia microgrids. Finally, the proposed control technique has been executed on laboratory-scale microgrid to demonstrate the potential of developed controller.

Resiliency-Driven Approach of DC Microgrid Voltage Regulation Based on Droop Index Control for High Step-Up DC-DC Converter

Regulation of DC microgrid voltage in presence of variable sources and loads is quite challenging. The ability of a microgrid to pay off the critical loads when subjected to disturbances, such as utility grid outage/poor climatic conditions, has gained importance recently. To address the above issues, we propose a resiliency analysis of a DC microgrid interconnected with 400 V and 200 V buses. The interconnected microgrid system is fed with solar PV along with the energy storage system and is integrated with a utility grid. Boost and high step-up DC-DC converters are employed for DC bus voltage regulation with droop index control. Here, the droop coefficient is optimized using particle swarm optimization (PSO) while maintaining uninterrupted service to critical loads and for satisfactory voltage regulation. The effectiveness of the droop index control method is tested in comparison to other optimization techniques and also with the conventional method. The resiliency analysis of the overall system, aiming for continuous power supply to the critical loads while maintaining the grid voltage unaffected, is carried out in grid outage, low solar insolation, and grid restoration conditions. The reliability of the interconnected DC microgrid test system is evaluated using the loss of power supply probability index for normal, grid outage, and grid restoration conditions. The system is implemented using PSCAD/EMTDC platform. Finally, the experimental prototype of a high step-up DC-DC converter is developed and tested to validate the effectiveness of the droop index controller with an optimized droop coefficient.

Centralised and decentralised data communication scheme for voltage regulation in DC Microgrids

Voltage regulation is one of the main control issues in DC Microgrids (MGs). To achieve voltage regulation in MGs, exchange information between distributed generation units (DG) is inevitable. There are two types of data exchange proposed and discussed, centralised and decentralised data communication schemes. Many papers in the literature did not give attention to the type of data communication infrastructure that will have a significant impact on both centralised and decentralised schemes. This paper proposes centralised and decentralised data communication scheme and their impact on voltage regulation in DC MGs. The dynamic performance of a DC MG with loads fluctuations, operating with the proposed technique, is evaluated through simulation analyses, realized in MATLAB. Both the proposed centralised and decentralised methods are able to maintain the voltage within acceptable limit during loads fluctuations; however the centralised method is around five times faster than the decentralised method. The results show the superiority of the proposed method for the DC MGs operations during load demands fluctuations, loads varieties, communication delays and structures.

A Review of Recent Advances on Hybrid Energy Storage System for Solar Photovoltaics Power Generation

The use of hybrid energy storage systems (HESS) in renewable energy sources (RES) of photovoltaic (PV) power generation provides many advantages. These include increased balance between generation and demand, improvement in power quality, flattening PV intermittence, frequency, and voltage regulation in Microgrid (MG) operation. Ideally, HESS has one storage is dedicated for high energy storage (HES) and another storage for high power storage (HPS) purpose. HES is used to fulfill long-term energy demand, while HPS is used to handle power transients and fast load fluctuations. This paper examines HESS comprehensively for PV power generation and focuses on its ability to combine two storage technologies. The two storage technologies include high energy and high power. This paper also analyzes the important aspects of advance HESS in PV power generation in the context of capacity sizing, power converter topology and strategies management energy. Several capacity sizing methods were critically reviewed and tabulated. Power converter (PC) topologies are classified and briefly discussed regarding their advantages and disadvantages. Furthermore, energy management strategies with various control techniques are critically classified and evaluated for better future direction. In addition, the implementation of HESS on PV power generation in current real projects is presented and evaluated. Finally, this paper can be considered as useful guide for the use of HESS in PV power generation including features, limitations, and real applications.

A New DC Microgrid Voltage Regulation Control Strategy for Photovoltaic Power Plant Based on Variable Power Reserve Level

With the gradual increase of photovoltaic power penetration, in order to ensure the voltage quality of DC micro-grid, photovoltaic power plants need to be able to participate in voltage regulation tasks to cope with the impact of photovoltaic power fluctuations and load fluctuations on voltage quality. Researches show photovoltaic power plants under load-reduction operation can participate in voltage regulation without using energy storage equipment. In this paper, a photovoltaic voltage regulation control strategy with variable load-reduction rate considering photovoltaic power fluctuation is proposed, which can change the load-reduction rate of photovoltaic plants according to the fluctuation of photovoltaic. Then, aiming at the problem of fast voltage change caused by small inertia time constant of DC micro-grid, the method of using photovoltaic backup capacity to provide inertia control for the system is adopted, so that photovoltaic power plants can cope with both photovoltaic fluctuation and load fluctuation at the same time. Finally, a simulation model is established in PSCAD/EMTDC. Simulation results verify that under the proposed control strategy, grid-connected converters for the PV can participate in the DC voltage regulation.

A study of voltage regulation in microgrid using a DSTATCOM

A well-prepared abstract enables the reader to identify the basic content. This paper presents the solution of voltage fluctuations in urgent situations by providing voltage and reactive support from a distribution static synchronous compensator (DSTATCOM) in the grid. Also, it analyses the influences of DSTATCOM as a voltage controller and compares the system performance with and without DSTATCOM. The DSTATCOM is used in the study to maintain voltage in the microgrid (MG) to be around the rated value after Microgrid disturbance. A successful simulink model of the photovoltaic (PV) system and the proposed DSTATCOM are illustrated to work together as the Microgrid. Microgrids could provide unique resilience and reliability when the environment encountered with less water, higher temperatures, more frequent and harsh wildfires, and severe weather events. The proposed DSTATCOM was installed in different locations in the MG and the best location was chosen to achieve the goal of improved power quality and efficiency. In this paper, two scenarios are discussed with and without DSTATCOM. The simulation results show the difference between the MG with and without DSTATCOM and how the DSTATCOM can amplify power quality in the Microgrid. The proposed DSTATCOM has the capability to improve dampen power oscillations during transit events.

A Virtual-Impedance Droop Control for Accurate Active Power Control and Reactive Power Sharing Using Capacitive-Coupling Inverters

Capacitive-coupling inverters (CCIs) have low operation voltage and enhanced reactive power control capability. It is a promising alternative to provide reactive power and voltage regulation in microgrids (MGs). Droop control is one of the most widely used primary controllers under a hierarchical framework in an MG. However, conventional droop control performance needs improvement since the droop curve assumption is not valid in part of CCI's operational area. At the same time, reactive power sharing error due to the uncertainty factor of feeder impedance needs to be minimized. In this article, virtual-impedance droop control is proposed for CCIs to solve the two issues. A virtual impedance selection method is developed with consideration of CCI's second-order LC coupling branch. First, the virtual impedance is selected for reducing the coupling between the active and reactive power of CCIs. The stability and sensitivity of the system are also evaluated based on a small-signal model to provide guidelines for virtual impedance selection. The proposed control varies the equivalent impedance via a feedback loop in CCI's control for accurate power control and sharing in MGs under mismatched feeder impedance. The validity of the proposed virtual-impedance droop control is verified through simulation and experimental results.

Control Scheme of Photovoltaic Inverter for Voltage Improvement in Isolated AC Microgrids

This paper presents a control scheme for a PV inverter in isolated three-phase AC microgrids. The proposed control scheme allows performing the voltage regulation by reactive power control of the PV inverters without communication systems. The PV inverter in the microgrid commits to supply the active power generated from the PV array first, and then the remaining capacity of the PV inverter represents the available reactive power that can contribute in the microgrid voltage regulation. The proposed control scheme allows the PV inverters to deliver or to absorb the reactive power depending on the measured voltage at the connection point of the PV inverter and the available reactive power of the PV inverter. The tested microgrid consists of two power inverters, one for interfacing energy storage batteries controlled by a droop control scheme in order to regulate the voltage and the frequency of the microgrid. The second inverter interfacing the PV array controlled by the proposed control scheme in order to support the microgrid by the active power generated from the PV array and the available reactive power. The results obtained from the simulations show that the proposed approach provides the expected voltage regulation in the tested microgrid under different operating conditions.

Research on Voltage and Frequency Regulation of Micro-Grid with Distributed Energy Storage

Aiming at the increasingly widespread use of distributed energy storage, building a model of distributed energy storage for Micro-Grid voltage regulation and frequency modulation. The waveforms of the frequency, active power, reactive power and bus voltage of the Micro-Grid are given. Firstly, the control method of distributed energy storage inverter - droop control is introduced. Secondly, based on MATLAB/Simulink platform, a Micro-Grid model with distributed energy storage system output to adjust voltage and frequency is built. Through the simulation, the role of distributed energy storage in the Micro-Grid is verified, which lays a foundation for the research of distributed in the Micro-Grid.

Distributed Predictive Control for Frequency and Voltage Regulation in Microgrids

Distributed control schemes have transformed frequency and voltage regulation into a local task in distributed generators (DGs) rather than by a central secondary controller. A distributed scheme is based on information shared among neighboring units; thus, the microgrid performance is affected by issues induced by the communication network. This paper presents a distributed predictive control applied to the secondary level of microgrids. The model used for prediction purposes is based on droop and power transfer equations; however, communication features, such as connectivity and latency, are also included, thus making the controller tolerant to electrical and communication failures. The proposed controller considers the frequency and voltage regulation control objectives and consensus over the real and reactive power contributions from each power unit in the microgrid. The experimental and simulation results show that the proposed scheme (i) responds properly to load variations, working within operating constraints, such as generation capacity and voltage range; (ii) maintains the control objectives when a power unit is disconnected and reconnected without any user updating in the controllers; and (iii) compensates for the effects of communication issues over the microgrid dynamics.

Hybrid energy storage system for microgrids applications: A review

Abstract Energy storages introduce many advantages such as balancing generation and demand, power quality improvement, smoothing the renewable resource’s intermittency, and enabling ancillary services like frequency and voltage regulation in microgrid (MG) operation. Hybrid energy storage systems (HESSs) characterized by coupling of two or more energy storage technologies are emerged as a solution to achieve the desired performance by combining the appropriate features of different technologies. A single ESS technology cannot fulfill the desired operation due to its limited capability and potency in terms of lifespan, cost, energy and power density, and dynamic response. Hence, different configurations of HESSs considering storage type, interface, control method, and the provided service have been proposed in the literature. This paper comprehensively reviews the state of the art of HESSs system for MG applications and presents a general outlook of developing HESS industry. Important aspects of HESS utilization in MGs including capacity sizing methods, power converter topologies for HESS interface, architecture, controlling, and energy management of HESS in MGs are reviewed and classified. An economic analysis along with design methodology is also included to point out the HESS from investor and distribution systems engineers view. Regarding literature review and available shortcomings, future trends of HESS in MGs are proposed.

Robust AC Voltage Regulation of Microgrids in Islanded Mode with Sinusoidal Internal Model

This paper shows that the H∞ control is an effective tool for electric voltage regulation. We here consider robust AC voltage regulation of microgrids in an islanded mode. When a microgrid is disconnected from a utility grid, it automatically switches to an islanded mode to provide necessary power using a battery system until the grid is recovered. In the islanded mode, it is important to regulate the electric voltage generated in the grid to track a predetermined AC voltage reference. A difficulty is that there exits unmodeled dynamics in the grid that may cause large power fluctuations. To resolve this problem, we adapt the H∞ control with a sinusoidal internal model to robust AC voltage regulation in microgrids. Simulation and experimental results confirm that the proposed H∞ control can achieve robust tracking performance.

Sensitivity-Analysis-Based Sliding Mode Control for Voltage Regulation in Microgrids

This paper presents a sliding mode controller to address the problem of voltage regulation in microgrids involving doubly fed induction wind generators (DFIGs). The control objective is to achieve terminal voltage regulation while ensuring maximum power point tracking (MPPT). The control development is based on voltage sensitivity analysis to eliminate the possibility of interference with the other voltage regulation devices in the microgrid. The proposed method: 1) does not require synchronous coordinate transformation, 2) eliminates the need for decoupled proportional-integral (PI) loops, and 3) is local and can be implemented in the absence of widespread communication systems or remote measurements. Additionally, its control performance is not degraded by errors in system parameters. The performance of the method is illustrated on the IEEE 13-bus distribution network. Dynamic models are considered for the DFIG, converters, and internal controllers along with their operational limits. Stochastic fluctuations in wind speed are modeled with NREL Turbsim while accounting for the tower shadow and wind shear. Dynamic simulations (in PSCAD/EMTDC) are presented to assess the control performance with voltage fluctuation compensation and control system robustness.

Reactive Power Management of a DFIG Wind System in Microgrids Based on Voltage Sensitivity Analysis

This paper addresses the problem of voltage regulation in microgrids that include doubly fed induction generator (DFIG)-based wind generation. Due to significant line resistances in microgrids, active power variations produced by wind turbines can lead to significant fluctuations in voltage magnitudes. This paper proposes a voltage sensitivity analysis-based scheme to achieve voltage regulation at a target bus in such microgrids. The target voltage can be of an important central bus, or a bus with sensitive voltage loads. The method is local and can be implemented in the absence of a widespread communication system or remote measurements. The performance of the method is illustrated on the IEEE-13 bus distribution network. Dynamic models are considered for the DFIG, converters, and internal controllers along with their operational limits. Stochastic fluctuations in wind speed are modeled with NREL Turbsim while accounting for tower shadow and wind shear. Dynamic simulations (in PSCAD/EMTDC) are presented to assess the voltage regulation characteristics under different load conditions and network contingencies.