Power Quality Improvement In Microgrids Research Articles

Adaptive Harmonic Impedance Reshaping Control Strategy Based on a Consensus Algorithm for Harmonic Sharing and Power Quality Improvement in Microgrids With Complex Feeder Networks

In islanded microgrids with complex feeder networks, distributed generation units (DGs) and loads can be freely connected to any node, leading to changes in the feeder impedance between nodes and the microgrid structure. However, traditional harmonic sharing control methods encounter difficulties with microgrids with complex topologies. Additionally, existing techniques essentially require constructing additional harmonic virtual impedance, possibly resulting in conflict between voltage quality and harmonic sharing effectiveness. To address this issue, this paper proposes an adaptive harmonic impedance reshaping method based on a consensus algorithm. The proposed method adaptively reshapes the inverter harmonic impedance by introducing harmonic current feedforward compensation control and impedance reshaping factor adaptive control, which can achieve accurate harmonic sharing while greatly improving the voltage quality of the microgrid. The proposed method avoids constructing additional harmonic virtual impedance and can be applied to microgrids with complex feeder networks and variable structures without acquiring prior microgrid configuration knowledge. Moreover, the proposed method is a fully distributed control, where the microgrid central controller (MGCC) is not required. Furthermore, the control parameter design method based on modeling and stability analysis is discussed in detail. Finally, simulations and experiments verify the feasibility and effectiveness of the proposed method.

A Novel Sliding Mode Based UPQC Controller for Power Quality Improvement in Micro-Grids

A Novel Sliding Mode Based UPQC Controller for Power Quality Improvement in Micro-Grids

Power Quality Improvement in Microgrids using STATCOM under Unbalanced Voltage Conditions

A large number of single-phase loads and sources create unbalanced voltage in microgrids. Voltage unbalance reduces the power quality, which results in misoperation or failure of customer equipment and microgrid. Also, voltage unbalance negatively impacts induction motors, power electronic converters, and adjustable speed drives. Static synchronous compensator (STATCOM), as an influential segment of the Flexible Alternative Current Transmission Systems (FACTS), has been extensively utilized as shunt compensators for controlling reactive power and regulation voltage in transmission and distribution networks. Under unbalanced conditions, an oscillating couple between the positive and negative sequence components of control loops emerge in the d-q frame. This paper suggests an innovative point of common coupling (PCC) voltage controller in Decoupled Double Synchronous Reference Frame (DDSRF) to compensate for an unbalanced PCC voltage and reduce the oscillating couple using STATCOM. Implementation of the proposed DDSRF involves several steps. Firstly, unbalance signals are rotated counterclockwise to split up the positive sequences. Secondly, those signals are rotated clockwise to separate negative sequences. Finally, by utilizing mathematical equations, the proposed DDSRF is introduced, which enables independent control of positive and negative sequence components. This study controls DC capacitor voltage for unbalanced conditions. Furthermore, the regulation voltage at PCC is performed. The control system scheme is also designed under unbalanced conditions, and simulation results guarantee the suggested control strategy.

Smart branch and droop controller based power quality improvement in microgrids

Abstract This paper presents two unique smart branch controller for compensating several power quality disturbances. The first proposed intelligent branch controller comprises a series transformer with its indirectly controlled impedance by secondary voltage injection. Further, the smart controller is made adaptive and flexible. It is installed at the point of common coupling (PCC), where PCC voltage & load current can be locally acquired without the presence of a communication channel, which then tracks its references as pure sinusoidal waveforms. Therefore without any filter requirement, harmonic elimination is done by the smart branch controller. The proposed smart controller can be applied in microgrids (MGs) for multi-objective optimization of power quality (PQ). For proper elimination of harmonics and to enhance the quality of power supply, the smart branch is optimized by a droop controller, which delivers power to a constant current source and eliminates harmonics by providing an appropriate quantity of harmonic voltage to the inverter voltage. The total harmonic distortion (THD) becomes 23.06% for the voltage and 6.24% for the current with droop controller, whereas, with an only smart branch into the power network, the THD becomes 26.47% for the voltage and 12.30% for the current. The simulation result concludes that the discussed optimized smart branch-based droop controller reduces drastically THD. Also, a separate study has been performed on the improvement of PQ by second proposed smart controller called as Photovoltaic Distribution Static Compensator (PV-DSTATCOM) grid-tied system using an adaptive reweighted zero attracting (RZA) control algorithm with perturbation and by applying maximum power point tracking technique (MPPT) for a three-phase system. The converter with PV array along with an active filter feature known as PV-DSTATCOM is required to convert the DC voltage into AC and for the improvement of the PQ by limiting harmonic distortions. It is concluded from the simulation results that the use of the RZA strategy presents an excellent steady state and transient response. The proposed PV grid-tied system is capable of working round the clock for both constant and variable irradiation and linear loads. The system is termed as smart as it can perform both modes automatically sensing the PV power and is capable of multi-directional power flow. The proposed method performs dual functions of improving PQ by working as DSTATCOM and also transfers power to the load and the grid obtained from PV array.

Sliding mode controller‐based voltage source inverter for power quality improvement in microgrid

Development of control technologies facilitates the integration of renewable energy sources to the grid through power electronic converters. In this study, the inverter acts as shunt active power filter along with the power conversion operation. Various sliding mode control (SMC) techniques namely relay and signum method, hysteresis method and equivalent control method are implemented to control the real, and reactive power flow between Renewable Energy System (RES), load and grid using an inverter. To reduce the complexity, the control law (u eq) for equivalent control method is derived using a simple single-phase equivalent circuit of a three-phase voltage source inverter. In this study, the robustness is enhanced by choosing the integral sliding surface. These controllers are used to reduce the total harmonic distortion (THD) and to ensure unity power factor (PF) in the grid during balanced and unbalanced grid voltage conditions even in the existence of nonlinear loads. The SMC using equivalent control function outperforms the other methods in terms of chattering, THD and PF. To illustrate the effectiveness, three different modes are considered: (i) no RES power, (ii) insufficient RES power and (iii) excess RES power. The performance of controllers is validated by the simulation and experimental results.

Application of mathematical morphology for power quality improvement in microgrid

Application of mathematical morphology for power quality improvement in microgrid

An Intelligent Battery Energy Storage-Based Controller for Power Quality Improvement in Microgrids

Modern power systems rely on renewable energy sources and distributed generation systems more than ever before; the combination of those two along with advanced energy storage systems contributed widely to the development of microgrids (MGs). One of the significant technical challenges in MG applications is to improve the power quality of the system subjected to unknown disturbances. Hence innovative control strategies are vital to cope with the problem. In this paper, an innovative online intelligent energy storage-based controller is proposed to improve the power quality of a MG system; in particular, voltage and frequency regulation at steady state conditions are targeted. The MG system under consideration in this paper consists of two distributed generators, a diesel synchronous generator, and a photovoltaic power system integrated with a battery energy storage system. The proposed control approach is based on hybrid differential evolution optimization (DEO) and artificial neural networks (ANNs). The controller parameters have been optimized under several operating conditions. The obtained input and output patterns are consequently used to train the ANNs in order to perform an online tuning for the controller parameters. Finally, the proposed DEO-ANN methodology has been evaluated under random disturbances, and its performance is compared with a benchmark controller.

A novel “Smart Branch” for power quality improvement in microgrids

A novel “Smart Branch” is introduced in this paper which compensates for various power quality disturbances. This “Smart Branch” includes a series transformer which its impedance is controlled indirectly by voltage injection to its secondary. By using a finite control set-model predictive controller (FCS-MPC), the “Smart Branch” can be controlled adaptive, flexible and straightforward. The “Smart Branch” is installed at the PCC, where the load current and the PCC voltage can be measured locally without using a communication channel. The “Smart Branch” controller tracks pure sinusoidal waveforms as its references. Thus the “Smart Branch” hardly produces harmonics and therefore its output filter can be eliminated. The controller can be used for multi-objective optimization of power quality in power systems and especially in microgrids. A droop based method is developed for adjusting the objectives’ weightings in the cost function of the MPC. In the last part of the paper, by using the extensive simulations and scenarios, the figure of merits of the “Smart Branch” is proved.

Controllable AC/DC Integration for Power Quality Improvement in Microgrids

Renewable energy sources can be connected to utility grids by using AC and DC integration methods. The AC integration is a practical and cost-effective method thanks to its simple stru ...

Power Quality Improvement in Microgrids Under Critical Disturbances Using an Intelligent Decoupled Control Strategy Based on Battery Energy Storage System

The concept of microgrids (MGs) provides the flexibility to integrate renewables into the power network. Nevertheless, the transience of most renewable energy sources (RESs) exacerbates the power quality of the grid network. Furthermore, the unpredictability of RESs additionally becomes challenging in case of high magnitude disturbances. The deployment and optimal utilization of energy storage systems, to act as an energy buffer are hence pertinent. In this paper, a control strategy for a battery energy storage system (BESS) is formulated based on two intelligent decoupled controllers. The objective is the restoration of system voltage and frequency considering a wide range of disturbances and hence circumvent the power quality degradation. The proposed controller is based on hybrid differential evolution optimization and artificial neural network (DEO-ANN). The controller parameters are tuned online by training the ANN with the sets of input and output data obtained during the process of optimizing the two controllers under low and high disturbances using DEO. Finally, the effectiveness of the proposed controller is validated on a power network consisting of a synchronous generator, photovoltaic power system, and BESS. The simulation results prove the robustness of the proposed control approach as compared with a benchmark controller.

A Review: Control Strategies for Power Quality Improvement in Microgrid

Power generation through the renewable energy sources has become more viable and economical than the fossil fuel based power plants. By integrating small scale distributed energy resources, microgrids are being introduced as an alternative approach in generating electrical power at distribution voltage level. The power electronic interface provides the necessary flexibility, security and reliability of operation between micro-sources and the distribution system. The presence of non-linear and the unbalanced loads in the distribution system causes power quality issues in the Microgrid system. This paper explores and reviews different control strategies developed in the literature for the power quality enhancement in microgrids. Also comparisons of different control methods are presented with suggestions for future research.

A Review of Distributed Control Techniques for Power Quality Improvement in Micro-grids

Micro-grid is typically visualized as a small scale local power supply network dependent on distributed energy resources (DERs) that can operate simultaneously with grid as well as in standalone manner. The distributed generator of a micro-grid system is usually a converter-inverter type topology acting as a non-linear load, and injecting harmonics into the distribution feeder. Hence, the negative effects on power quality by the usage of distributed generation sources and components are clearly witnessed. In this paper, a review of distributed control approaches for power quality improvement is presented which encompasses harmonic compensation, loss mitigation and optimum power sharing in multi-source-load distributed power network. The decentralized subsystems for harmonic compensation and active-reactive power sharing accuracy have been analysed in detail. Results have been validated to be consistent with IEEE standards.

Power quality improvement in microgrid using custom power devices

Power quality may be caused when maximum AC loads consume reactive power. Distribution STATCOM is a custom power device (CPD) which is used to control the flow of reactive power in the microgrid. Compensation of reactive power and the other power quality issues are being analysed with the help of model predictive control (MPC) algorithm. The detailed modelling and simulations of MPC with DSTATCOM are presented and implemented along with necessary equations in the MATLAB simulink using the Simpower systems tool boxes.

Power quality improvement in microgrid using custom power devices

Power quality may be caused when maximum AC loads consume reactive power. Distribution STATCOM is a custom power device (CPD) which is used to control the flow of reactive power in the microgrid. Compensation of reactive power and the other power quality issues are being analysed with the help of model predictive control (MPC) algorithm. The detailed modelling and simulations of MPC with DSTATCOM are presented and implemented along with necessary equations in the MATLAB simulink using the Simpower systems tool boxes.

Power Quality Conditioning of PV-Wind Microgrid to Provide Harmonic Reactive Power Compensation using Series APF

Objectives: In this analysis, PV-Wind Microgrid with real time environmental conditions is compensated for harmonics and reactive power. Methods/Analysis: Microgrids suffer from many power quality problems which require harmonic and reactive power compensation being connected with different sources and loads. In this regard, initially a microgrid has been developed using the data from the weather monitoring system in BITS Pilani, Hyderabad Campus. Later compensation requirement has been identified and Series APF with its unique control is applied to provide power quality enhancement. Findings: The microgrid suitable for all practical conditions is developed to give an equivalent output of conventional 3 phase distribution system and the variations in the power flows causing power quality issues are observed when connected to dynamically varying reactive loads. By using Series APF in microgrid, these issues like voltage swells and sags are mitigated and thus the reactive power compensation is provided. The % THD of voltage harmonics in the microgrid is effectively improved using the novel control technique that has been implemented. Novelty/Improvement: Power quality improvement in microgrids using active power filter topology specifically in islanded mode, Identity Vector Template Generation Approach specifically towards harmonic compensation.

A GPS-Based Control Framework for Accurate Current Sharing and Power Quality Improvement in Microgrids

This paper proposes a novel hierarchical control strategy for improvement of load sharing and power quality in ac microgrids. This control framework is composed of a droop-based controller at the primary level, and a combination of distributed power sharing and voltage conditioning schemes at the secondary level. The controllers in the primary level use GPS timing technology to synchronize the local reference angles. The voltage reference of each distributed generation is adjusted according to a voltage–current (V–I) droop characteristic to enable proper current and power sharing with a fast dynamic response. The droop coefficient, which acts as a virtual resistance, is adaptively changed as a function of the peak current. This strategy not only simplifies the control design but also improves the current sharing accuracy at high loading conditions. The distributed power sharing scheme uses consensus protocol to ensure proportional sharing of average power. The voltage conditioning scheme produces compensation signals at fundamental and dominant harmonics to improve the voltage quality at a sensitive load bus. Experimental results are presented to validate the efficacy of the proposed method.

Design of Filters for Power Quality Improvement in Microgrids

This paper deals with the design of filters for power quality enhancement in microgrid. The voltage source inverters (VSI) fed from microgrid requires filter across them to detect the unbalance and harmonics in the system. The performances of various filters are compared and the improved negative sequence filter is found out to be the best solution. The stability of these filters are also studied and simulations are carried out to validate the results.