S.P. Chowdhury

Modelling, simulation and performance analysis of a PV array in an embedded environment

Photovoltaic (PV) generation involves the direct conversion of sunlight into electrical energy. In recent years it has proved to be a cost-effective method for generating electricity with minimum environmental impact. Due to the environmental and economic benefits PV generation is now being deployed worldwide as an embedded renewable energy source and extensive research is being performed in order to study and assess the effectiveness of PV arrays in Distributed Generation (DG) systems either as a potential energy source or as energy reserve in combination with other types of distributed energy resources. This paper presents the modeling and MATLAB simulation of a stand-alone polycrystalline PV Array system and investigates load following performance efficiency under various loading and weather conditions as well as suitability with regard to enhancing power supply reliability to critical loads. The modeling of the PV array that has been performed in this research using MATLAB Simulink is based on the calculation of parameters for the Thevenins equivalent circuit of each cell of the array. The standard double exponential polycrystalline cell model has been adopted for this research with solar irradiance E and ambient temperature T as the input and Thevenins voltage Vthar and Thevenins resistance Rthar as the output.

Mathematical modelling and performance evaluation of a stand-alone polycrystalline PV plant with MPPT facility

Photovoltaic (PV) generation has now-a-days proved to be a cost-effective method for renewable power generation with minimum environmental impact. Due to environmental and economic benefits, PV is now being widely deployed as a distributed energy resources (DER) in distributed generation systems or microgrids. Extensive laboratory-based research and simulation studies are being performed for assessing its effectiveness as DER in microgrids. Simulation studies mostly involve development of mathematical models which can account for the variation of PV output with solar irradiance and ambient temperature as well as the simulation of MPPT feature that is built in the inverters usually interfaced with the PV arrays. Simulation studies of microgrids with interconnected DERs and elaborate control schemes often warrants the development of simple and robust mathematical models for PV arrays that would pose low mathematical burden on the system, have low data storage requirements and which can be represented by standard block sets of a modelling software. At the same time, the models should be able to simulate the weather dependent electrical behaviour of the PV modules. This paper reports on the development of a DC voltage source model of a polycrystalline PV Array in MATLAB Simulink and its performance analysis under various loading and weather conditions as well as the application of the model to develop a load shedding scheme for a stand-alone PV system.

Islanding protection of distribution systems with distributed generators — A comprehensive survey report

Anti-islanding protection schemes currently enforce the DGs to disconnect immediately for grid faults through loss of grid (LOG) protection system. This greatly reduces the benefits of DG deployment. For preventing disconnection of DGs during LOG, several islanding protection schemes are being developed. Their main objectives are to detect LOG and disconnect the DGs from the utility. This allows the DGs to operate as power islands suitable for maintaining uninterruptible power supply to critical loads. A major challenge for the islanding protection schemes is the protection co-ordination of distribution systems with bi-directional fault current flows. This is unlike the conventional overcurrent protection for radial systems with unidirectional fault current flow. This paper presents a comprehensive survey of various islanding protection schemes that are being developed, tested and validated through extensive research activities across the globe.

Setting of market clearing price (MCP) in microgrid power scenario

Microgrid comprises an interconnection of various low voltage, small-scale distributed generators (DGs), energy storage devices and controllable loads interfaced through fast acting power electronic devices in an isolated remote area as islanding operation where conventional grid is not available. Combined heat and power (CHP) produced by DGs may be utilized in the local market making the microgrid most efficient and economic. Like deregulation regime in conventional power market, multi agent generator providers also may be considered to make the microgrid market equal competitive. The basic objective of a competitive electricity market is to serve the consumers at a reduced price. The objective of this paper is to analyze and propose the pricing mechanism for microgrid energy in the competitive electricity market where the microgrid central controller (mucc) is made to participate in the bidding process to settle market-clearing price (MCP). Two important market settlement techniques, day-ahead and real-time, have been considered with the marketing strategies of renewable DGs like photovoltaic (PV) and wind generation.

ANFIS based automatic voltage regulator with hybrid learning algorithm

In this paper, the authors propose a design methodology of adaptive neuro-fuzzy inference system (ANFIS) based automatic voltage regulator (AVR) using hybrid learning algorithm to improve the small-signal performance of power system. Here, a zero order Sugeno fuzzy model is considered, whose parameters are tuned off-line through hybrid learning algorithm. This algorithm is a combination of least square estimation and error backpropagation method, where the least square method is applied for the tuning of linear output membership function parameters and the backpropagation method is used to tune the nonlinear input membership function parameters. The proposed method is verified through digital simulation with a single machine infinite bus system. It is found that the AVR is performing well in restoring the terminal voltage instantaneously and the damping characteristics of the rotor angle are also improved. The simulation results establish that the design of ANFIS based AVR employing hybrid learning algorithm can be very useful in small signal stability of power system.

Performance analysis of Z - source Inverter based ASD system with reduced harmonics

This paper presents the Z - source inverter for adjustable speed drive system. The Z - source inverter employs a unique impedance network couple with inverter main circuit. By controlling the shoot through duty cycle, the Z - source inverter system using MOSFETS provide ride - through capability during voltage sags, reduces line harmonics, improves power factor and high reliability, and extends output voltage range. Analysis and simulation results will be presented to demonstrate new features. It reduces harmonics, electromagnetic interference.

Key energy management issues of setting market clearing price (MCP) in micro-grid scenario

Micro grid is an epitome of a macro grid but works in low voltage comprising of various small-distributed energy resources (DERs), energy storage devices, and controllable loads being interfaced through fast acting power electronic devices. Combined heat and power (CHP) produced by DERs are utilized in the local market where Micro Grid operates either in island mode or in grid-connected mode. The CHP mode of operation makes the Micro Grid most efficient and economic. Like deregulation regime in Micro Grid market, multi agent generator providers may be considered to make the Micro Grid market competitive. The reason for competitive electricity market is to serve the consumers at a reduced price. The main purpose of this paper is to analyze and propose the pricing mechanism for Micro Grid energy in the competitive electricity market. Central controller of the Micro Grid (mucc) is the main brain behind all energy management system (EMS) activities, which includes participation in the bidding to settle market- clearing price (MCP). Two important market settlement techniques - Day-ahead and Real-time - have been discussed briefly in this paper. Uniform and Pay-as-bid pricing rules have been discussed separately for electricity pricing fixation in the context of Micro Grid. In this paper marketing strategies of some of the renewable DERs - mainly Photovoltaic (PV) and wind generator - have been considered. Wind power is now a potential candidate in non-conventional power generation family. Power available from wind and PV system cost high and is of intermittent in nature. Participation of these two renewable DERs along with Micro turbine, Diesel generator, fuel cells etc. in the bidding for market clearing price (MCP) make the market complex. This paper gives a brief guideline for marketing of PV and wind power. Consumers in the Micro Grid system are categorized as shed-able and non-shed-able according to their priority. How these loads affect demand curve have also been discussed. This paper presents a case study on price determination based on demand and supply side bidding strategies. The impacts of congestion management, market power, carbon taxation, price volatility, etc. on pricing have also been discussed in the context of Micro Grid.

Voltage stability analysis and real power loss reduction in distributed distribution system

The development of DGs will bring new changes to traditional power systems. Distributed generation has important consequences for the operation of the distribution networks. Appropriate size and location of distributed generation (DG) play a significant role in minimizing power losses in distribution systems. This paper represents techniques to minimize power losses and improves voltage stability in a distribution feeder by optimizing DG model in terms of size, location and operating point of DG through sensitivity analysis. The methods have been developed with considering load characteristics and representing loads with constant impedance and constant current models, separately. A DG injection into the distribution system improves the voltage profile with minimum loss. The proposed techniques have been tested on IEEE 37 bus distribution system and TNEB 11 KV distribution feeder.

CONTROL & RELIABILITY ISSUE OF EFFICIENT MICROGRID OPERATION USING HYBRID DISTRIBUTED ENERGY RESOURCES

In this paper, the authors deal with the issue of power quality phenomena in the distribution system that affects the reliability of the power supply to sensitive loads. Traditional solutions to power quality problems have been discussed here and the use of a microgrid as a preferred solution is presented. When the conventional and non-conventional micro sources are combined with energy storage devices, they are called distributed resources (DR). The energy storage device of the DR provides the ride-through for the transient load demand. The DR is capable of providing reliable power supply to sensitive loads when connected in the form of a microgrid. The customer solution of UPS typically provides AC voltage to the load when the grid fails. Backup generation systems based on rotating machines may be used as an alternative to a UPS system to supply power to sensitive loads during temporary interruptions in grid power supply. However, such systems require a start-up time to deliver power, which would cause a brief interruption in the operation of sensitive loads. More recently, electrical generation systems that are dispersed and located near the load centers, commonly known as micro sources, distributed generation (DG) etc. are gaining popularity

Reliability study of a micro-grid power system

Deregulation and restructuring of old centralized power system has brought a renaissance in the history of electric power system. It has unleashed an open competition among the utility service providers in the respective sector of electric power system, i.e. generation, transmission, and distribution. Also, it gives birth to the new concept of micro-grids, which is an epitome of larger grid, called macro-grid, in general. Small utility service providers having generating capacity less than 10 MW are the main players in the micro-grid market. Micro-grids works, generally, at low voltage (415 V). Added advantages of micro-grids are its CHP (combined heat and power) operation, less emission of dasiaSOx and NOxpsila, reduction of dasiaTransmission line congestionpsila, easy installation and control of its small distributed energy resources etc. to name a few. Like macro-grid, main motto of the micro-grid system is to cater reliable and quality power to its customers. This paper presents a 6-bus system to study the reliability of the system in four different case studies. To judge the best reliable condition in each of the cases, four parameters, such as bus voltages, maximum line flow, slack bus injection, and system line loss, are considered and in each case study, these parameters are compared in different changing situations for getting the best result out of those situations. Fast de-coupled load flow (FDLF) method in Compaq visual FORTRAN is used to analysis the various cases. In all the analysis, macro-grid is considered as a large virtual generator and is used as a slack bus.