Srikanth Kotra

Bio: Srikanth Kotra is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Microgrid & Electric power system. The author has an hindex of 5, co-authored 8 publications receiving 195 citations.

A Supervisory Power Management System for a Hybrid Microgrid With HESS

Abstract: This paper proposes a supervisory power management system (PMS) for a grid interactive microgrid with a hybrid energy storage system. The key feature of the proposed PMS is reduced number of sensors required to implement the PMS. The PMS considers renewable power variation, grid availability, electricity pricing, and changes in local loads. It can detect the operating mode of system without measuring load currents and powers. A single-phase voltage source converter (VSC) transfers real power between dc grid and utility grid besides offering ancillary services such as harmonic mitigation, reactive power support, and unity power factor at the point of common coupling (PCC). In the proposed system, a better dc-link voltage regulation is achieved and the usage of supercapacitors reduces the current stress on the battery. The PMS also addresses extreme operating conditions such as load shedding, off-maximum power point tracking operation of photovoltaic, elimination of critical oscillation of hybrid energy storage systems power, islanded operation, and resynchronization with grid. The performance of the proposed PMS is verified by digital simulation and experimental studies.

Design and Stability Analysis of DC Microgrid With Hybrid Energy Storage System

Abstract: This paper deals with the design and stability analysis of a dc microgrid with battery-supercapacitor energy storage system under variable supercapacitor operating voltage. The conventional design method reported in the literature considers the rated supercapacitor voltage in the modeling and design of controllers. However, the supercapacitor unit can discharge as low as 10% of its rated voltage due to self discharge. It is observed that the conventional method of controller design can potentially make the system unstable or introduce ringing in the dc link voltage at low supercapacitor voltage. In this paper, the sensitivity of dc microgrid stability with respect to supercapacitor voltage variation is analyzed, an optimal supercapacitor voltage to be considered in the design is calculated and a design method is proposed to ensure the stability of dc microgrid in all operating modes. The stability of the dc microgrid with controllers designed using the proposed method is evaluated with digital simulation and experimental studies.

Energy management of hybrid microgrid with hybrid energy storage system

Abstract: This paper proposes a unified energy management system (EMS) for a grid interactive hybrid microgrid with a hybrid energy storage system (HESS). The proposed EMS achieves a continuous and reliable power supply to local loads and exports/imports power to/from grid. The proposed EMS considers the PV power variations, grid availability, electricity pricing and variations in local loads. A single phase voltage source converter (VSC) transfers real power between DC grid and utility grid and provides ancillary services such as reactive power support, unity power factor and harmonic mitigation at point of common coupling (PCC). The EMS also addresses extreme operating conditions like load shedding, off-MPP operation of PV, critical oscillation of HESS powers, islanded operation and resynchronization with grid. The efficacy of proposed EMS is verified by time-domain simulation.

Design and small signal analysis of DC microgrid with hybrid energy storage system

Abstract: This paper presents the small signal analysis and two loop control design of a DC microgrid with control strategy based on the output of DC link voltage controller. The employed control strategy generates current references to PV, grid, battery and supercapacitor converters based on the average of DC link voltage controller output. In this control strategy, a single DC link voltage controller maintains the DC link voltage in all operating modes. Thus, designing a DC link voltage controller which is stable in all operating modes is a crucial aspect of DC microgrid. The design and stability analysis of DC microgrid employing this control strategy is not discussed in literature. In this work, a detailed two loop control design of a DC microgrid employing this control strategy is presented. The DC link voltage controller is designed such that it is stable in all operating modes and the effect of low pass filter introduced to obtain the average value of DC link voltage controller output is considered. Simulation study with the designed control parameters is performed to verify the stability of the system in various operating modes. Results show the satisfactory transient and steady state performance of the DC microgrid in all operating modes with the designed control parameters.

Power management based on the operating conditions of grid, mircogrid and hybrid storage

Abstract: Distributed generation (DG) is nowadays increasing in the power sector at a level that it is reducing the conventional power generation. The increased usage of these systems near to the load centers has several power quality aspects to deal with. In order to elicit the maximum power from the renewable energy sources (RES) many control algorithms are available, but these methods lack the impact of sudden load changes and unpredictable behaviour of RES. To support the system during these dynamic changes additional power units are necessary to meet the condition of overall power balance. A combination of battery and supercapacitor based hybrid storage can be employed in this scenario. Also with these abnormalities of RES and loads, the voltage and frequency profiles at the customer end will also be affected. Under such a condition of grid, RES and loads an appropriate algorithm with all these conditions taking into consideration need to be formulated to operate the RES, storage based converters and grid interfacing converter to act as per the situation of the system. This improves the reliable operation of the interconnected system under any kind of variations. Hence an adaptive control algorithm is proposed and it is implemented on the grid integrated RES system along with the energy storage devices (ESD) in the MATLAB/Simulink and the various cases validate the results.

Optimal Scheduling of an Isolated Microgrid With Battery Storage Considering Load and Renewable Generation Uncertainties

Abstract: By modeling the uncertainty of spinning reserves provided by energy storage with probabilistic constraints, a new optimal scheduling mode is proposed in this paper for minimizing the operating costs of an isolated microgrid (MG) by using chance-constrained programming. The model is transformed into a readily solvable mixed integer linear programming formulation in general algebraic modeling system (GAMS) via a proposed discretized step transformation approach and finally solved by applying the CPLEX solver. By properly setting the confidence levels of the spinning reserve probability constraints, the MG operation can achieve a tradeoff between reliability and economy. The test results on the modified Oak Ridge National Laboratory Distributed Energy Control and Communication lab MG test system reveal that the proposal significantly exceeds the commonly used hybrid intelligent algorithm with much better and more stable optimization results and significantly reduced calculation times.

Optimal Scheduling of an Isolated Microgrid with Battery Storage Considering Load and Renewable Generation Uncertainties

Abstract: By modeling the uncertainty of spinning reserves provided by energy storage with probabilistic constraints, a new optimal scheduling mode is proposed for minimizing the operating costs of an isolated microgrid (MG) by using chance-constrained programming. The model is transformed into a readily solvable mixed integer linear programming (MILP) formulation in GAMS via a proposed discretized step transformation (DST) approach and finally solved by applying the CPLEX solver. By properly setting the confidence levels of the spinning reserve probability constraints, the MG operation can be achieved a trade-off between reliability and economy. The test results on the modified ORNL DECC lab MG test system reveal that the proposal significantly exceeds the commonly used hybrid intelligent algorithm with much better and more stable optimization results and significantly reduced calculation times.

Supercapacitors: Electrical Characteristics, Modeling, Applications, and Future Trends

Abstract: Energy storage systems are playing an increasingly important role in a variety of applications, such as electric vehicles or grid-connected systems. In this context, supercapacitors (SCs) are gaining ground due to their high power density, good performance, and long maintenance-free lifetime. For this reason, SCs are a hot research topic, and several papers are being published on material engineering, performance characterization, modeling. and post-mortem analysis. A compilation of the most important millstones on this topic is essential to keep researchers on related fields updated about new potentials of this technology. This review paper covers recent research aspects and applications of SCs, highlighting the relationship between material properties and electrical characteristics. It begins with an explanation of the energy storage mechanisms and materials used by SCs. Based on these materials, the SCs are classified, their key features are summarized, and their electrochemical characteristics are related to electrical performance. Given the high interest in system modeling and a large number of papers published on this topic, modeling techniques are classified, explained, and compared, addressing their strengths and weaknesses, and the experimental techniques used to measure the modeled properties are described. Finally, SCs are successfully used in the market sectors, as well as their growth expectations are analyzed. The analysis presented herein gives the account of the expansion that the SC market is currently undergoing and identifies the most promising research trends on this field.

Energy Management and Control for Grid Connected Hybrid Energy Storage System Under Different Operating Modes

Abstract: DC-coupled microgrids are simple as they do not require any synchronization when integrating different distributed energy generations. However, the control and energy management strategy between the renewable energy sources and the energy storages under different operating modes is a challenging task. In this paper, a new energy management scheme is proposed for the grid connected hybrid energy storage with the battery and the supercapacitor under different operating modes. The main advantages of the proposed energy management scheme are effective power sharing between the different energy storage systems, faster dc link voltage regulation to generation and load disturbances, dynamic power sharing between the battery and the grid based on the battery state of charge, reduced rate of charge/discharge of battery current during steady state and transient power fluctuations, improved power quality features in ac grid and seamless mode transitions. The effectiveness of the proposed method is validated by both simulation and experimental studies.