Smart grid : An overview

A smart grid is a modernized electrical grid that uses information and communications technology to gather and act on information, such as information about the behaviors of suppliers and consumers, in an automated fashion to improve the efficiency, reliability, economics, and sustainability of the production and distribution of electricity. Electric power generated by wind turbines and hydroelectric turbines by using induction generators can cause variances in the frequency at which power is generated. Power electronic devices are utilized in these systems to convert the generated ac voltages into high-voltage direct current (HVDC). The HVDC power can be more easily converted into three phase power that is coherent with the power associated to the existing power grid. Through these devices, the power delivered by these systems is cleaner and has a higher associated power factor. Wind power systems optimum torque is obtained either through a gearbox or direct drive technologies that can reduce the size of the power electronics device. Electric power can be generated through photovoltaic cells by using power electronic devices. The produced power is usually then transformed by solar inverters. Inverters are divided into three different types: central, module-integrated and string. Central converters can be connected either in parallel or in series on the DC side of the system. For photovoltaic "farms", a single central converter is used for the entire system. Module-integrated converters are connected in series on either the DC or AC side. Normally several modules are used within a photovoltaic system, since the system requires these converters on both DC and AC terminals. A string converter is used in a system that utilizes photovoltaic cells that are facing different directions. It is used to convert the power generated to each string, or line, in which the photovoltaic cells are interacting.

Power electronics application in a laptop

A lithium battery powers the system and several dc-dc converters change the battery voltage into the voltages required by the loads. A buck converter produces low voltage dc  required by the microprocessor. A  boost converter increases the battery voltage to the level needed by the disk drive. An inverter produces high voltage high frequency ac to drive the lamps that light the display. A transformer isolation converts the ac line voltage into dc to charge the battery. The  converter switching frequencies are in the range of several 100 KHz which leads to the substantial reduction in weight and size of the reactive elements. Power management is used to control sleep modes in which power consumption is reduced and battery life is extended.

Renewable energy : What to Expect!

Energy is essential to our society to ensure our quality of life and to underpin all other elements of our economy. Renewable energy technologies offer the promise of clean, abundant energy gathered

from self-renewing resources such as the sun, wind, earth, and plants. Virtually all regions of the world have renewable resources of one type or another. Currently  most of renewable energy  comes from hydro power and traditional biomass sources. Wind, solar, biomass, and geothermal technologies are cost-effective today in an increasing number of markets, and are making important steps to broader commercialization. Each of the renewable energy technologies is in a different stage of research, development, and commercialization, and all have differences in current and future expected costs, current industrial base, resource availability, and potential impact on greenhouse gas emissions. The technical status, cost, and applications of major renewable energy technologies and implications for increased adoption of renewable is being reviewed.

From the dawn of human civilization to about 100 years ago, the sources of energy used by mankind were predominantly human and animal muscle and wood, with lesser amounts of solar, wind, hydro, and geothermal. With the discovery of oil, the development of natural gas fields, and the widespread distribution of electricity from coal-powered central power plants, fossil fuels became the predominant sources of energy in the United States and the world. Is there another major transition ahead for energy? Can the renewable resources that sustained early civilization be harnessed with enough efficiency and availability and at a cost to meet a significant portion of the much higher energy needs of today’s society? Although there are always risks in predictions, the convergence

of some of today’s trends suggests interesting possibilities. In summary, today’s converging trends related to renewable energy include:

• relevant scientific discoveries and engineering progress;

• emergence of a new economic structure in the electricity sector;

• trends toward decentralization and modularity;

• explosive advances in computers, information, and telecommunications;

• globalization of markets;

• persistent, pervasive support for a clean environment;

• limited future availability of inexpensive fossil fuels.

Do these converging trends mean that we are on the brink of a new energy transition from fossil fuels to renewables? Several independent entities have recently developed scenarios indicating that renewable energy will play a major role in the energy mix for the world, with increasing impacts beginning as early as 2000–2010 and major impacts by 2050. In both of the Shell International scenarios, energy contributions from conventional energy resources begin to level off in 20–30 years, with petroleum consumption actually decreasing . According to these scenarios, the increases in world energy demand will be supplied by renewable energy technologies, which will provide 30%–50% of world energy by 2050.

Power electronics and its motives

Power electronics refers to control and conversion of electrical power by power semiconductor devices wherein these devices operate as switches. Advent of silicon-controlled rectifiers,abbreviated as SCRs, led to the development of a new area of application called the power electronics. Prior to the introduction of SCRs, mercury-arc rectifiers were used for controlling electrical power, but such rectifier circuits were part of industrial electronics and the scope for applications of mercury-arc rectifiers was limited. Once the SCRs were available, the application area spread to many fields such as drives, power supplies, aviation electronics, high frequency inverters and power electronics originated.

Power electronics has applications that span the whole field of electrical power systems, with the power range of these applications extending from a few VA/Watts to several MVA /MW. The main task of power electronics is to control and convert electrical power from one form to another. The four main forms of conversion are:

(1) Rectification referring to conversion of ac voltage to dc voltage,
(2) DC-to-AC conversion,

(3)DC-to DC conversion and

(4)AC-to-AC conversion.

"Electronic power converter" is the term that is used to refer to a power electronic circuit that converts voltage and current from one form to another. These converters can be classified as:

1.  Rectifier converting an ac voltage to a dc voltage,

2. Inverter converting a dc voltage to an ac voltage,

3. Chopper or a switch-mode power supply that converts a dc voltage to another dc voltage, and

4. Cycloconverter and cycloinverter converting an ac voltage to another ac voltage.
In addition, SCRs and other power semiconductor devices are used as static switches.