Ram Shankar Yallamilli

Bio: Ram Shankar Yallamilli is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Microgrid & AC power. The author has an hindex of 4, co-authored 7 publications receiving 50 citations.

Instantaneous Symmetrical Component Theory Based Parallel Grid Side Converter Control Strategy for Microgrid Power Management

Abstract: This paper proposes a centralized control strategy for power management of hybrid microgrid connected to the grid using a parallel combination of grid side converters (GSCs). An improved version of instantaneous symmetrical component theory is developed and is used for the control of parallel operated GSCs, which results in reduced sensor requirement, control complexity, and communication bandwidth. In addition, a simple power management algorithm is developed to test the efficacy of the proposed parallel grid side converter control strategy for all the microgrid modes considering state of charge limits of hybrid energy storage system, load changes, and renewable power variations. In the proposed system, a better dc link voltage regulation is achieved and usage of supercapacitor reduces the current stresses on the battery. With the proposed control strategy, the essential features of grid side converters like power quality, power injection, bidirectional power flow, and proportional power sharing are achieved. The effectiveness of the developed control strategy for the proposed system is tested using MATLAB based simulink environment and validated experimentally using a laboratory prototype.

Power management of grid connected hybrid microgrid with dual voltage source inverter

Abstract: This paper proposes a grid connected hybrid microgrid system with dual voltage source inverter (DVSI) using modified instantaneous symmetrical component theory (MICST) for power sharing among inverters. In this paper a reduced DC link voltage has been achieved, efficient, simple power management algorithm (PMA) is proposed and new method is introduced for DVSI control parameter extraction which reduces control complexity and overall system cost. The Proposed topology consists of a three phase dual voltage source inverter (DVSI) which transfers the active power between grid and microgrid based on renewable power availability and state of charge (SOC) limits of hybrid energy storage system (HESS). Besides, offering ancillary services such as harmonic mitigation, reactive power support and unity power factor at the point of common coupling (PCC). The proposed system is tested and validated using MATLAB based Simulink environment.

Dynamic Energy Management in DC Microgrid using Composite Energy Storage System

Abstract: This paper describes the power management in DC microgrid system which consists of solar energy system, Wind Energy Conversion System and Composite Energy Storage System. Both the sources are operated in Maximum Power Point Tracking (MPPT) mode to extract maximum energy from the respective sources. The intermittent nature of solar/wind power makes the output power fluctuating. To make it reliably available, a composite energy storage system is used. In the proposed scheme, off-MPPT control and dump load scheme are compared. A simulation study is carried out in MATLAB/Simulink to validate the proposed Power Management Algorithm (PMA).

Cost Savings Oriented Microgrid Control Strategy Considering Battery Degradation

Abstract: In this paper a cost savings oriented centralised control strategy for grid connected hybrid microgrid consisting of renewable energy sources and energy storage systems is proposed. In this work, cost savings are achieved by a power management algorithm (PMA) which takes battery degradation cost and grid pricing into account. In-addition the proposed PMA always operates battery within SOC limits and also ensures microgrid reliability. The cost savings are computed as the difference between battery degradation cost and electricity cost. However, the battery degradation cost is calculated using depth of discharge (DOD) which is computed on a real time basis. In this work, hybrid energy storage system (HESS) is introduced to absorb the sudden transients and oscillations in battery current thereby increasing battery performance and life span. Apart from cost savings analysis, power quality aspects such as harmonic mitigation, reactive power support and unity power factor are achieved. The proposed control strategy is simulated using a MATLAB based simulink environment during both excess and deficit modes of microgrid by taking PV variations into account.

Effective Current Based Inverter Loss Computation and its Application for Energy Savings in a Microgrid Environment

Abstract: In this paper an effective current based inverter efficiency computation method for a hybrid microgrid system consisting of renewable energy sources and energy storage systems is proposed. Using the proposed inverter efficiency computation method, the efficiency curve of a single inverter is obtained. Then, particle swarm optimization is used to solve the loss minimization function of a parallel inverter setup. In this work, instantaneous symmetrical component theory and power management algorithm (PMA) are used for generating reference quantities for various power electronic converters. Once, the reference quantity for the parallel inverter setup is obtained, the reference quantity sharing among parallel inverters is determined by particle swarm optimization to achieve optimal conversion efficiency. Apart from energy savings analysis, power quality aspects such as harmonic mitigation, reactive power support and unity power factor are achieved. The proposed control strategy is simulated using a MATLAB based simulink environment only during excess mode of microgrid by taking PV variations into account.

A Review on the Selected Applications of Battery-Supercapacitor Hybrid Energy Storage Systems for Microgrids

Abstract: This paper presents a comprehensive categorical review of the recent advances and past research development of the hybrid storage paradigm over the last two decades. The main intent of the study is to provide an application-focused survey where every category and sub-category herein is thoroughly and independently investigated. Implementation of energy storage systems is one of the most interestingly effective options for further progression in the field of alternative energy technology. Apart from a meticulous garnering of the energy resources regulated by the energy storage, the main concern is to optimize the characteristic integrity of the storage devices to achieve a practically techno-economic size and operation. In this paper, hybrid energy storage consisting of batteries and supercapacitors is studied. The fact that the characteristic of batteries is mostly complementary to that of supercapacitors, hybridizing these storage systems enhances their scope of application in various fields. Therefore, the objective of this paper is to present an inclusive review of these applications. Specifically, the application domain includes: (1) regulation of renewable energy sources, (2) contributions to grid regulation (voltage and frequency compensation, contribution to power system inertia), (3) energy storage enhancements (life cycle improvement, and size reduction), (4) regenerative braking in electric vehicles, (5) improvement in wireless power transfer technology. Further, this review also descriptively highlights the control strategies implemented in these domains of applications. The application-oriented review explicates the principle advantages with the hybridization of battery and supercapacitor energy storage systems that can be used as an insight for further development in the field of energy storage technology and its applications.

An Adaptive Virtual Impedance Control for Improving Power Sharing Among Inverters in Islanded AC Microgrids

Abstract: Several drawbacks of the conventional and inverse droop control based decentralized techniques for islanded microgrids are being addressed actively, over the years by various researchers. One of the prominent issues is the inaccurate power sharing (reactive power in the conventional droop and real power in the inverse droop) among the distributed generators (DGs) due to the feeder/line impedances. Virtual impedance (VI) is a popular technique to overcome impedance mismatches but the challenge is in the setting of the appropriate value. This paper presents an adaptive decentralized technique for adjusting the virtual impedance in the controller of a DG, based on its output current, without the need of communication, extra sensors or network parameter/load estimations. The methodology is tested through simulations for a wide variety of cases including unbalanced, harmonic, constant power and induction motor loads, DG plug and play functionality and performance in larger networks (modified 13 and 33 bus systems) under meshed configurations. The range for parameter stability is verified through modelling and small signal eigenvalue analyses. Further, improved power sharing performances using the proposed scheme is validated through implementation on a laboratory experimental setup.

A Grid-Connected Dual Voltage Source Inverter with Power Quality Improvement Features

Abstract: This paper presents a dual voltage source inverter (DVSI) scheme to enhance the power quality and reliability of the microgrid system. The proposed scheme is comprised of two inverters, which enables the microgrid to exchange power generated by the distributed energy resources (DERs) and also to compensate the local unbalanced and nonlinear load. The con- trol algorithms are developed based on instantaneous symmetrical component theory (ISCT) to operate DVSI in grid sharing and grid injecting modes. The proposed scheme has increased relia- bility, lower bandwidth requirement of the main inverter, lower cost due to reduction in filter size, and better utilization of micro- grid power while using reduced dc-link voltage rating for the main inverter. These features make the DVSI scheme a promising option for microgrid supplying sensitive loads. The topology and control algorithm are validated through extensive simulation and experimental results.

Unbalance mitigation strategies in microgrids

Abstract: Unbalance or asymmetry in the distribution network is a well-known power quality issue. In the modern active distribution system, with the increasing penetration of renewables, this phenomenon becomes more pronounced. In the context of microgrids (MGs), several works have been proposed for the management and mitigation of the unbalance, for both the sharing of unbalanced load and maintaining the voltage quality in the islanded mode and for the control of distributed generators in the grid-connected mode during unbalanced conditions. This study comprehensively reviews, summarises, and classifies the various strategies of the unbalance mitigation techniques for the islanded and grid-connected modes of operation for three-phase MGs and presents the possible challenges and avenues for future investigations on the topic.

A Review on DC Microgrid Control Techniques, Applications and Trends

Abstract: The DC Microgrid concept has been flourishing in the recent times due to its intrinsic advantages like Renewable Energy Source (RES) compatibility, easier integration with storage utilities through Power Electronic Converters (PECs) and distributed loads. In-depth researches are going on in this field, as the concept of DC Grid can be considered as a master foundation in the realization of Smart Grid (SG) technologies. To achieve this, a number of constraints such as voltage regulation, islanding detection, allowable transient levels, etc. are to be met in accordance with globally accepted standards. The system should have a proper control scheme to keep the things reliable, fault-free and interoperable. In order to meet the constraints as per globally recognized standards, quite a few classes of control algorithms are adopted namely, Centralized, Decentralized and Distributed control. A standardized review of these control strategies is discussed as part of this work. A comparative study among these techniques is made so as to help a designer to choose the apt technique for controlling the microgrid.