Gayatri Agnihotri

Control Strategies for Distribution Static Compensator for Power Quality Improvement

Abstract Distribution Static Compensator is an important device in correcting power factor, maintaining constant distribution voltage, and mitigating harmonics in a distribution network. This paper focuses on the comparative study of the control techniques for voltage source converter based Distribution Static Compensator, broadly classified as voltage controlled and current controlled. Under the former, phase shift control is compared with the latter, considering indirect decoupled current control and regulation of AC bus and Dc link voltage with hysteresis current control. The first two schemes have been successfully implemented for Static Compensator control at the transmission level for reactive power compensation and voltage support, and are recently being incorporated to control a Distribution Static Compensator employed at the distribution end. The following indices are considered for comparison - measurement and signal conditioning requirement, performance with varying linear/nonlinear load, total harmonic distortion, DC link voltage variation and switching frequency. The paper briefly describes the salient features of each strategy, with their merits and demerits. A dynamic simulation model of the Distribution Static Compensator has been developed for various control strategies, in Matlab/SimPower System environment.

Inverter topologies and control structure in photovoltaic applications: A review

The inverter is an integral component of the power conditioning unit of a photovoltaic power system and employs various dc/ac converter topologies and control structure. It has to meet various international standards before it can be put in commercial use. The function of inverter in distributed power generation system on top of photovoltaic generation includes dc-ac conversion, output power quality assurance, various protection mechanisms, and system controls. The requirements in terms of low cost, high efficiency, high reliability, and tolerance over wide range of input voltage variations have driven the inverter development toward simpler topologies, lower component counts, and tighter modular design. Historically, the inverters employed in PV technology may be classified based on number of power processing stages, type of power decoupling, types of interconnection between the stages, and types of grid interface. Based on power processing stage, the inverter may be classified as single stage and multip...

Control Algorithms for Distribution Static Compensator

Reactive power compensation in a power distribution network plays a vital role in improving power quality, correcting power factor and maintaining constant distribution voltage. Among the various compensation devices available voltage source converter (VSC) based controllers offer very fast response to reactive power demand and thus can be effectively used for power factor correction and voltage regulation. One such VSC based controller called the distribution static compensator (DSTATCOM) proves to be a viable alternative to the conventional static var compensators (SVC). Further, the control algorithms applied to the DSTATCOM play a vital role in its performance. In this paper, the control algorithms applied to a DSTATCOM for reactive power compensation and power factor correction are reviewed and analyzed through digital simulations

Estimation of Hourly Temperature at a Site and its Impact on Energy Yield of a PV Module

This paper discusses a method for estimating the hourly temperature at a location, if the ambient maximum and minimum temperatures of a particular day, along with the maximum temperature on the previous day and the minimum temperature of the following day, are known. The impact of estimated temperature on the energy yield of a photovoltaic (PV) module is also discussed with the help of a mathematical model. Algorithms have been developed for relevant computations and implemented using MATLAB. Hourly meteorological data of Bhopal and Trivandrum, India, have been considered for studying, analyzing, and validating the results. A PV module (BP 3215) manufactured by BP Solar Ltd. has been considered for analyzing the results in terms of energy generation. The statistical error parameters calculated for the estimated hourly temperature indicate a reasonable degree of accuracy of estimation. The values of mean absolute error (MAE) and root mean square error (RMSE) are superior to those of other models and that of R2 is comparable. The estimated values of yearly and monthly average of hourly temperature are invariably found to be more than the corresponding measured values. At these two locations, there is a reasonable linear fit between monthly averages of hourly temperature, calculated from the estimated and measured values of hourly temperature. The deviation between the two values of annual energy generated, one calculated from the estimated values and the other from the measured values of hourly temperature, is nominal. Thus, the estimated values of hourly temperature can be used for energy estimation and feasibility analysis of PV system, with a fair degree of accuracy.

Design of voltage controller for parallel operated self excited induction generator — Micro grid

Micro-grid system is currently a conceptual solution to fulfill the commitment of reliable power delivery for future power systems. Renewable power sources such as wind, hydro offer the best potential to supply free power for future micro-grid systems. A micro grid consists of six parallel operated self excited induction generators driven by either wind or hydro system. The self excited induction generators (SEIG) with reactive power compensator are used for improving voltage regulation. An adjustable reactive power source is required to maintain constant grid voltage with varying load. The required reactive power can be provided by VAR compensator which consists of solid state self-commutating devices along with DC sources. Selection and ratings of these components for self commutating devices are quite important for optimal design of VAR compensator. In this paper design of micro grid is proposed which consist of six parallel operated systems. If a fault occurs in any one of the generating unit then the VAR compensators has to maintain constant voltage of micro grid at varying load.

Analysis of a Microgrid under Transient Conditions Using Voltage and Frequency Controller

This paper presents an investigation of voltage-and-frequency-(VF-) based battery energy storage system (BESS) controller used in micro grid for analyzing the optimum capability of plant. Microgrid is formed by using three hydropower plants feeding three-phase four-wire load. The proposed controller is used for load balancing, harmonic elimination, load leveling, and neutral current compensation. The proposed BESS controller permits the selection of an optimum voltage level of battery and allows independent current control of each phase. The main emphasis is given on maintaining constant voltage and frequency within the micro grid during transient conditions. Micro grid with power plant and its controller is modeled in MATLAB/Simulink using Power System Blockset (PSB) toolboxes.

Comparison of Power flow control: TCSC versus UPFC

In an AC transmission system power flow can be controlled by injecting a compensating voltage in series with the line. Thyristor controlled series compensator (TCSC) are utilized as a conventional means for the purpose while unified power flow controller (UPFC) is the latest converter based devices employing fast power electronic equipments. This paper utilizes the steady state model of thyristor controlled series capacitor and a unified power flow controller for series voltage compensation, and evaluating their range of power flow control for simple network. The models are incorporated into the existing Newton Raphson load flow algorithm. The iterative equations of the Newton Raphson load flow algorithm are modified by the device parameters and the combined set of power flow equations and UPFC or the TCSC control equations are solved for convergence of the formula. Matlab codes are utilized for the implementation of the two devices in the Newton-Raphson algorithm. Power flow control ranges are evaluated for few IEEE bus systems and standard 5 bus system. Results are reported and studies are presented to illustrate and compare the effectiveness of the UPFC and TCSC.

Real-Time Implementation of Islanded Microgrid for Remote Areas

Islanding is a condition in which a microgrid or a portion of power grid, consisting of distributed generation DG sources, converter, and load, gets disconnected from the utility grid. Under this condition the DG sources in a microgrid must switch to a voltage control mode, in order to provide constant voltage to local loads. In grid connected mode, the microgrid works as current controller and injects power to the main grid, depending on the power generation and local load with suitable market policies. Providing constant voltage at a stable frequency with proper synchronization amongst each DG in a microgrid is a challenge. The complexity of such grid requires careful study and analysis before actual implementation. These challenges of microgrid are addressed using real time OPAL-RT simulation technology. Thus the paper describes an islanded microgrid with master slave controller for power balance, voltage/frequency regulation, and synchronization. Based on an advanced real-time platform named Real-Time Laboratory RT-LAB, the impacts of the micro sources, load, and converters in an islanded microgrid is studied in this paper. The effectiveness of the proposed controller is analyzed through experimental results under balanced/unbalanced nonlinear loads condition.

Soft Computing Technique-Based Voltage/Frequency Controller for a Self-Excited Induction Generator-Based Microgrid

Microgrids (MGs) are small scale energy unit networks that can offer an adequate energy supply to cover local demand by incorporating renewable energy and storage technologies. The system capacity is generally between several kW to several MW. They work in terms of low voltage (LV) level or medium voltage (MV) level. They can also be connected/disconnected from main grid whenever it is necessary. This paper presents a comparison of two soft computing (SC) techniques fuzzy logic (FL)/artificial neural network (ANN) over a conventional proportional integral (PI)-based voltage frequency controllers used for improving the performance of MG under islanding mode. Microgrid is formed by using three 7.5kW, four pole, 50Hz, self-excited induction generators (SEIGs) driven by small hydro turbine feeding three-phase four-wire consumer load. The proposed topology functions excellently in maintaining phase angle, voltage and frequency (VF) regulation of the micro sources (MSs) in islanded mode as well as in resynchronization when one of the MSs is turned off due to fault or unavailability of resources. The conventional PI controller is replaced by a controller based on SC techniques, as it has disadvantages like explicit description of mathematical model, affected by variations in consumer loads and sources, thus the proposed SC techniques enhance the performance of VF controller. A comparative analysis of PI/FL/ANN controller is also carried out to highlight the superiority of AI controller. The performance of controller with proposed configuration is verified for balanced/unbalanced non-linear load. Microgrid and control schemes are simulated in MATLAB Sim Power Systems environment.

Design of reduced rating VFC for a micro grid

The day-by-day increasing demand for energy can create problems for the power distributors, like grid instability and even outages. The necessity of producing more energy combined with the interest in clean technologies yields in an increased development of power distribution systems using renewable energy. In this purview, several types of Distributed Generations (DGs), local loads, storage system and voltage source converter can be connected together to form a small local power generation system called as micro grid (MG). MG can operate in grid connected mode or in islanding mode. The paper discusses islanding control of power electronics interfaced with DG systems in micro grid. Further, a new topology is introduced with zigzag/star transformer, which reduces the size of battery connected parallel to DC link of the voltage source converter, hence reducing the cost of the system. The proposed topology works well in maintaining phase angle, voltage and frequency of the micro sources in islanded mode as well as in resynchronization when one of the micro sources is off due to fault or unavailability of resources. The proposed topology is verified in MATLAB environment.