Himanshu K. Patel

Voltage transient spikes suppression in flyback converter using dissipative voltage snubbers

The Flyback topology results in significant cost and space savings for multiple output power supplies for power levels up to 100 W. Flyback topologies store and transfer energy using a transformer, which due to physical limitations can cause large voltage transient spikes during the switching cycle at the drain of the power switch and at the secondary rectifier. This paper presents an overview of dissipative voltage snubbers and discusses their design guidelines to suppress the voltage transients on both the primary and secondary sides of a flyback converter. In particular, Snubbers used to reduce the stress on the switch and improve efficiency in a flyback topology are discussed.

Flyback Power Supply EMI Signature and Suppression Techniques

Flyback power supplies have a distinctive EMI signature caused by superposition of the transformer primary current (IPRI), drain voltage (VDrain), diode voltage (VDiode) and transformer secondary current (ISEC) waveforms; each generate emission currents which may exceed the desired EMI specification limits without proper EMI design technique. The primary current waveform causes primarily differential mode emission currents to circulate between the AC mains and the power supply input. It can also create common mode emissions due to radiated magnetic fields if the current path defined by the PC board layout encircles a large physical area. The drain voltage, diode voltage and secondary current waveforms are mainly responsible for the generation of common mode emission currents. Controlling EMI in SMPS requires attentions to following areas: 1. Differential mode filtering 2. Common mode filtering 3. Power cord damping 4. Transformer construction This paper addresses the concept of EMI signature in SMPS and presents conceptual techniques for EMI suppression. Differential mode filter analysis and common mode filter analysis are discussed in detail and an effective high frequency circuit model of the differential mode filter is obtained. Important aspects of power cord damping and transformer construction are also briefly covered. This paper is intended to be an efficient helping tool for the EMI filter designers.

Fuzzy logic based Decision Support System framework for irrigation scheduling

Decision Support System (DSS) is computerized tool to provide decision for partially known system. DSS for agriculture system gains popularity in recent past. Irrigation scheduling is one of the important aspects for profitably and sustainability in agriculture system. One of the widely used irrigation scheduling approach is ‘Water Balance Approach’ as it does not requires highly accurate and costly sensors for soil moisture, canopy temperature, and leaf thickness. However, implementation of this method involves extensive computation and accurate measurement of large numbers of variables. In agriculture system, it is seldom possible to get accurate measurement values of necessary variables. This paper proposes fuzzy logic based DSS framework for irrigation scheduling. It is proposed to use fuzzy rule base for soil characterization, calculation of evapotranspiration, and estimation of root zone. Use of fuzzy logic helps to reduce computation requirements as well as eliminates need of accurate measurement of parameters.

Analysis of Cryogenic Cycle with Process Modeling Tool: Aspen HYSYS

Cryogenic engineering deals with the development and improvement of low temperature techniques, processes and equipment. A process simulator such as Aspen HYSYS, for the design, analysis, and optimization of process plants, has features that accommodate the special requirements and therefore can be used to simulate most cryogenic liquefaction and refrigeration processes. Liquefaction is the process of cooling or refrigerating a gas to a temperature below its critical temperature so that liquid can be formed at some suitable pressure which is below the critical pressure. Cryogenic processes require special attention in terms of the integration of various components like heat exchangers, Joule-Thompson Valve, Turbo expander and Compressor. Here, Aspen HYSYS, a process modeling tool, is used to understand the behavior of the complete plant. This paper presents the analysis of an air liquefaction plant based on the Linde cryogenic cycle, performed using the Aspen HYSYS process modeling tool. It covers the technique used to find the optimum values for getting the maximum liquefaction of the plant considering different constraints of other parameters. The analysis result so obtained gives clear idea in deciding various parameter values before implementation of the actual plant in the field. It also gives an idea about the productivity and profitability of the given configuration plant which leads to the design of an efficient productive plant.

Design and Simulation of Optimum Triggering Scheme for a Series Switch in RF Heating

Plasma is the fourth state of matter. High temperature is essential to sustain the plasma in ionic form. The RF heating system used to provide the required temperature may get damaged due to occurrence of arcing. Series switch (circuit breaker) is one of the most effective and efficient methods of protecting RF generators. The series switch must be operated within stipulated time after the occurrence of electric fault and therefore the triggering circuit of series switch must be designed carefully to obtain optimum results. This paper presents an optimum triggering scheme based on fiber optic triggering. The importance of optical triggering and utilization of fiber optic has be justified. The design is well supported with the experimental results. Finally the system is designed to obtain the triggering with delay of only 4.8 muS as compared to the safety margin of 10 muS.

Critical Considerations for EMI Filter Design in Switch Mode Power Supply

Offline switching power supplies have high voltage and high current switching waveforms that generate electromagnetic interference (EMI) in the form of both conducted and radiated emissions. Consequently, all offline power supplies must be designed to attenuate or suppress EMI emissions below acceptable limits. EMI filters are actually simple combinations of inductors or chokes and capacitors but many key parameters need extra care and attention while designing the optimum EMI filter. This paper addresses this subject and presents a conceptual view of some critical design considerations for EMI filter optimization. Some important guidelines for the selection of EMI filter components are suggested to provide an efficient helping tool for the designers.

Automatic PID Control Loops Design for Performance Improvement of Cryogenic Turboexpander

Cryogenics field involves temperature below 123 K which is much less than ambient temperature. In addition, many industrially important physical processes—from fulfilling the needs of National Thermonuclear Fusion programs, superconducting magnets to treatment of cutting tools and preservation of blood cells, require extreme low temperature. The low temperature required for liquefaction of common gases can be obtained by several processes. Liquefaction is the process of cooling or refrigerating a gas to a temperature below its critical temperature so that liquid can be formed at some suitable pressure which is below the critical pressure. Helium liquefier is used for the liquefaction process of helium gas. In general, the Helium Refrigerator/Liquefier (HRL) needs turboexpander as expansion machine to produce cooling effect which is further used for the production of liquid helium. Turboexpanders, a high speed device that is supported on gas bearings, are the most critical component in many helium refrigeration systems. A very minor fault in the operation and manufacturing or impurities in the helium gas can destroy the turboexpander. However, since the performance of expanders is dependent on a number of operating parameters and the relations between them are quite complex, the instrumentation and control system design for turboexpander needs special attention. The inefficiency of manual control leads to the need of designing automatic control loops for turboexpander. Proper design and implementation of the control loops plays an important role in the successful operation of the cryogenic turboexpander. The PID control loops has to be implemented with accurate interlocks and logic to enhance the performance of the cryogenic turboexpander. For different normal and off-normal operations, speeds will be different and hence a proper control method for critical rotational speed avoidance is must. This paper presents the design of PID control loops needed for the efficient performance of cryogenic turboexpander (Radial Inflow type) to ensure that the control systems meet the technical conditions and constraints more accurately and ensure the equipment safety.

Design and development of high voltage scheme for a crowbar in RF heating

Plasma is a mixture of freely moving charged particles. To sustain these particles in ionic state, very high temperature is essential. RF heating systems are utilized for obtaining high temperatures. Arching phenomenon in these systems can cause enormous damage to the RF tube. Fast switching circuit breakers are used to cutoff the load from the supply in cases of arcing. The crowbar interrupts the connection between the high voltage power supply (HVPS) and the RF tube for a temporary period during which the series switch has to open. This paper presents the design and development of Crowbar based on fiber optic triggering for the protection of RF heating system. The importance of optical triggering and utilization of fiber optic has been justified. Protection techniques other than crowbar are briefly discussed. The design of Crowbar is well supported with the experimental results.

Role of optimization in pulverization process of thermal power plant

Every nation dreams for highly efficient and economical type of energy production units. The scenario of power sector is inversely proportional as far as the generation and demand of power is concern. In India, normally the power plants run on the availability of fuel and consumers. Majority of the power generation units are fuel based in Indian power sector. There are so many types of fuel but coal is cheapest and easily available fuel, therefore a large number of companies deal with the coal based thermal power plant. Thermal power plant have maximum efficiency around 32% to 42%. There are various losses associated in generation of electric power and to overcome or recover those losses, optimization is needed. Optimization can be considered at various stages of power generation. In pulverization process, the optimization is plays a crucial role. This paper presents overview of the pulverization process of the coal fired power plant and focuses on the optimization techniques which can be used to facilitate the power generation at optimal level. Different optimization techniques applied for coal pulverization are discussed and their relative comparison is presented which in turn may be helpful to the thermal power plant engineers for better and efficient operation of the plant.

Sensor Used in E-nose

“Electronic noses” are devices which consist of electronic-chemical sensors with specificity capable of recognizing simple or complex gas mixtures. The recent advances in sensor devices have allowed the development of new devices for various applications in many technological fields. This chapter describes the basic sensor design, technology, and mechanism implemented in the development of E-nose sensor and main characteristics of the sensors. The current state-of-the-art of sensors used in the development of E-nose sensor analysis system is also discussed.