Microgrids (MGs) are seen today as the solution to the challenge of meeting the ever-increasing demand of energy which is clean. A variety of challenges need to be overcome for these MGs to be successful varying from stability, power quality to protection, and management. Since the various control strategies are actively being researched and emerging challenges still being addressed, there has been a lot of interest related to the aspect of testing. The ever-increasing complexity of control mechanisms invokes the need for safer, faster yet reliable testing methods, which do not compromise on the degree of detail and at the same time are economical and require the minimum testing time. Off-line simulation, real-time (RT) simulation, hardware in the loop simulation, RT emulation, hardware test beds, pilot plants, and other integrated approaches are the major methods for testing in MGs. This paper gives an overview of the testing techniques and discusses the trends in the various technologies employed for testing MGs. First, the various methods are briefly discussed and a comparison is provided. Next, the various research efforts carried out on the aspect of MG testing are categorized and presented one-by-one. Furthermore, new methodologies and emerging approaches for the testing have also been highlighted, and the challenges and future research avenues have been presented.

Real-Time Testing Approaches for Microgrids

In this paper, a new active power control (APC) with enhanced maximum power point tracking (MPPT) algorithm are implemented to improve the performances of a solar photovoltaic system (SPV) based standalone water pumping station. The APC uses proportional resonant controller with antiwindup (AWPRC) for ac voltage regulation without saturation phenomena and with high power quality at the point of common coupling. Furthermore, the proportional resonant controller design method for optimal gains to achieve high performance during transition period in terms of phase margin and desired settling time is analyzed. To achieve the MPPT with less oscillation while protecting the battery energy storage system from overvoltage, an enhanced power ratio variable step based perturbation and observation algorithm is used. The effectiveness of the developed control strategies are validated through simulations and experimental results.

Experimental Implementation of an APC With Enhanced MPPT for Standalone Solar Photovoltaic Based Water Pumping Station

Three-phase induction (asynchronous) motors (IM) are industrial work-horses, making the protection of IM a very important topic. IM protection devices typically monitor the motor current and/or voltage to provide the motor protection functionalities like current overload, over/under voltage, etc. One of the interesting parameters to monitor is the operating power factor (PF) of the IM, which provides better underload protection compared to the motor current-based approaches. Traditionally, PF estimation would require both the voltage and the current measurements in order to apply the displacement method. In this paper, we present a method of determining the operating PF of the IM using only the measured current and the manufacturer data that are typically available from the nameplate and/or datasheet. Experimental results are presented to substantiate the feasibility of the proposed method, validated alongside the state of the art PF estimation methods. Operational PF can be effectively used for underload detection, like in a pump application, or PF compensation for improving the power quality.

Estimation of Induction Motor Operating Power Factor From Measured Current and Manufacturer Data

Milling is among the most energy-consuming technological stages of copper ore processing. It is performed in mills, which are machines of high rotational masses. The start of a mill filled to capacity requires appropriate solutions that mitigate the overloading. One method for increasing the energy efficiency of ball mills is to optimize their drive systems. This article looks at two variants of drive systems with efficiencies higher than the already existing solutions. The first variant is a low-speed synchronous motor with permanent magnets without a gearbox, and the second variant is an asynchronous high-efficiency motor with a gearbox and a fluid coupling. The energy performance analysis of the three solutions was based on the average energy consumption indicator per mass unit of the milled material and on the energy consumption per hour. The investigations required models of the drive systems and analyses with the use of the Monte Carlo methods. The highest energy efficiency is observed in the case of the solution based on the permanent magnet motor. However, the drive system with the high-speed motor offers a gentle start-up possibility owing to the fluid coupling.

https://www.mdpi.com/1996-1073/14/6/1786/pdf

Energy Efficiency Analysis of Copper Ore Ball Mill Drive Systems

Overheating is a negative effect that induction motors suffer under either mechanical or electrical anomalous conditions, which can decrement the motors' useful life or produce catastrophic damage. In this sense, a new approach for assisting in the analysis and solution of problems related to overheating in induction motors is the correlation of thermal effects between the abovementioned conditions. In this study, a methodology for the experimental extraction of mathematical models that correlate the thermal effect on the induction motor stator due to voltage unbalance and mechanical overload is developed. In general, the proposed methodology is based on thermal gradients at different points of an induction motor stator. These thermal gradients are generated from either voltage unbalance or mechanical overload. For voltage unbalance estimation, the definitions of IEEE standard 141, IEEE standard 1159, and NEMA norm are considered. The correlation models are carried out and validated experimentally on a three-phase induction motor of 746 W (1 hp). Results demonstrate effectiveness in the correlation at different stator points of both variables: unbalance voltage and mechanical overload.

Correlation Model Between Voltage Unbalance and Mechanical Overload Based on Thermal Effect at the Induction Motor Stator

Centrifugal pumps are the most widely used ac-motor-driven pump systems mainly for water pumping applications. Due to increasing and varying load demand, voltage variation and unbalance is a reality and has to be dealt with carefully. Studies on motor-driven systems under conditions of voltage unbalance have either neglected or maintained constant magnitude of the rotational loss component and focused only on the motor performance while system side performances have not been discussed generally. This paper presents the experimental results of a three-phase induction motor-pump system subjected to voltage and load variations with a view to justify that knowledge of voltage and load variations are very much essential for better result analysis.

Effect of Voltage and Load Variations on Efficiencies of a Motor-Pump System

Load emulation is the technique by which, different types of load characteristics can be realized without using the actual load modules. This is very useful for testing of power supply equipment under various load conditions. Further the technique of load emulation can be applied for micro grid design and power flow studies under various load conditions. A battery charger based regenerative load emulation technique is explained here which can be applied for emulated micro grids. The design is done in such a way that the system can emulate pure resistive, inductive and capacitive loads and regenerate the in phase power to store in battery. The stored energy can be further inverted and supplied back to the grid, thereby making the system regenerative in nature. The simulation results for the proposed load emulation technique, along with the application of the same in micro grids are presented in detail. The results show the required emulator waveforms and energy stored in to the battery.

Regenerative load emulator with battery charging for evaluation of energy management in microgrid with distributed renewable sources

Various converter topologies have been developed
from many years for the effective operation of solar photovoltaic (SPV) systems. Induction motor application using SPV source requires an efficient converter which can produce higher value of AC voltage output from the PV input and also implement v/f control with reduced losses and wide range of speed control. Here a modified Z- source inverter for V/f control of induction motor driven from a Solar PV system is presented. Using Z source network, voltage levels higher than the input value can be obtained without requiring a boost converter. This can be utilized in SPV applications for obtaining required DC voltage
for the inverter. An improved PWM inverter with HERIC
topology combined with Z source network is presented for the
induction motor application. The new topology is found to have better performance with reduced switching losses compared to the conventional inverters. The topology is evaluated for variable speed applications and it is found to give satisfactory results compared to conventional v/f control especially for low speeds

Modified Z-source inverter based three phase induction motor drive for solar PV applications

The demand for electrical energy has increased tremendously over the last 25 years; its importance is such that it is now a vital component of any nation’s economic progress. Increase in population has increased the energy requirements, coupled with the industrialization & socio-economic responsibilities; the energy supply has not kept pace with the demand. This has led to a bleak energy scenario whereby power generation and utilization from alternate energy sources has become very much a necessity. In the industrial context, electrical energy is used to produce a desired output, given the availability of all the relevant raw materials. For a nation to progress economically, the industrial sector has to be constantly encouraged and developed, but as the number of industrial units / sectors increase, energy demand and consumption also increases. The industrial sector is the largest consumer of all the electrical energy that is commercially generated for utilization, and process industries like fertilizer, cement, sugar, textile, aluminum, paper, etc.; are extremely energy intensive in nature. To reduce the increasing demand-supply gap, either more industrial energy has to be generated or the existing consumption of energy has to be brought down without any compromise on either product quality or quantity. The rate of growth in the domestic sector easily outnumbers the industrial sector. In the event of power shortage, industrial sector gains precedence over other sectors, thereby, domestic sector always bears the brunt of long or constant power cuts. The impact of rising energy cost has a disastrous impact on the day-today activities of industrial and domestic consumers wherein the prices of commodities, products and even essential services tend to cost more. One option is to improve the working efficiency of the process and systems. This will ensure the reduction in the product cost in addition to efficient energy management. The other option is the use of energy derived from non-conventional energy sources i.e.; ensure a balance between conventional and nonconventional energy sources in the process. With depleting coal reserves, it is very essential to develop the renewable energy technology so as to be an alternative option. Amongst the various renewable energy sources, solar energy is the best possible option and finds application in most of the domestic and industrial processes.

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Energy Efficiency in Industrial Utilities

Process industries are energy intensive in nature and are one of the largest consumers of electrical energy that is commercially generated for utilization Motor driven systems consume more than two-thirds of the total energy consumed by the industrial sector; among which, centrifugal pumps are the most widely used equipment mainly for the purpose of fluid transportation The efficiency of pumping units is around 40 to 50%, hence they offer tremendous opportunities of not only improving the efficiency of the process, but also ensure effective energy utilisation and management With the increasing use of power electronics equipment, power quality (PQ) has become a very serious issue of consideration On account of the random switching of single-phase loads in addition to time varying operations of industrial loads, PQ problem of voltage variation and unbalance is inevitable across three-phase systems Application of varying or unbalanced voltages across the three-phase motor terminals results in performance variations leading to inefficient operation For the purpose of study, the performance of a motor-pump system can be separately analyzed from the motor and pump points of view The motor efficiency may vary in a very narrow band, pump efficiency depends upon the system head and flow rate but the system efficiency is a combination of the two; hence, necessary to analyze separately As centrifugal pumps are classified under variable torque-variable speed load category, variation on the input side has a significant effect on the output side Therefore the system efficiency now becomes an important index for ensuring efficient energy utilisation and efficiency The main objective of the chapter is to put forward a methodology to analyze the working performance of a three-phase induction motor driven centrifugal pump under conditions of voltage and load variations by, defining additional factors for correct interpretation about the nature and extent of voltage unbalance that can exist in a power system network; define induction motor derating factors for safe and efficient operation based on operational requirements and devise energy management strategies for efficient utilization of electrical energy by the motor-pump system considering the voltage and load conditions

P. Giridhar Kini

Papers

Effect of Voltage and Load Variations on Efficiencies of a Motor-Pump System

Regenerative load emulator with battery charging for evaluation of energy management in microgrid with distributed renewable sources

Modified Z-source inverter based three phase induction motor drive for solar PV applications

Energy Efficiency in Industrial Utilities

An intelligent motor-pump system