Electric motors make things go

 

Electric motors make things go. Better motors mean better go power. What constitutes “better” and what to do about it, is the subject of a great deal of investigation. Better motors generally mean 2 things, higher efficiency and greater torque produced for a given amount of input power.

The Department of Energy has spent incredible sums of money on the problem in several different forms. The DoE segmented very high volume applications of electric motors to see if any of the applications could be improved by a few percentage points. For example, the US builds and buys washing machines at the rate of a few million a year. So small changes in the performance of washing machine motors has the potential to impact electrical consumption in the US.

Similar applications exist in air conditioning compressor motors and air handling motors. These applications occur by the millions of production units every year in many parts of the world. US and other governments spend lots of research dollars looking for improvements, but very few make it into the real world.

This fact should give us pause for reflection.

New technology cannot gain widespread acceptance unless a significant benefit can be realized. Environmental impact may be a factor for some consumers, but generally environmental impact attributes are product preferences that require paying a cost premium. Products that embody preferential features are generally more expensive and are suited to a limited consumer audience.

Products which are critical in widespread systems, like gasoline in the transportation system, are extremely sensitive to pricing and preferential features are not easy to support. Decreasing sulfur in fuels as a way to decrease emissions in combustion costs somewhere around 15 cents a gallon. So a legislative decision about emissions results in a cost impact that is tolerable for some and a burden for others.

Tangible benefits are most often those embodied in reduced operating cost. Widespread adoption of new technology requires a significant cost reduction, either in the direct price or the operating expense. And it has to be significant enough to be compelling.

There is a well known electrically commutated motor for moving air in central air conditioners. The motor is very efficient by virtue of the fact that there is a small inverter in the end bell of the motor. It is an otherwise simple ac motor. It has taken 20 years for industry to come up with a better solution.

Why is change in technology so slow? Because it takes lots of people, lots of time and lots of money to come up with better solutions.

 

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The new age in solar inverter conversion efficiency

Why efficiency is so important to solar ?

Power conversion efficiency has certainly been a very popular topic in solar industry. PV inverter manufacturers have invested significant amount of effort to achieve even a 0.1% higher efficiency year over year. But just how important is efficiency to a solar system?

The U.S. installed more than 7 GW of solar in 2014. Every single installation required some type of power conversion from DC (solar panel) to AC (grid). To simplify the discussion, if we assume 98% efficiency for the inverter loss, that equals about 6.86 GW of AC power generated. If all the inverters performed at 99% power conversion efficiency, and all else being equal, that number would be 6.93 GW. That is a 70-MW difference and equivalent to a large utility-scale PV plant! Higher efficiency equates to more energy harvest and is therefore critically attributed to the total revenue stream of the PV system.

 

Reaching 99% conversion efficiency

The PV inverter is a complex piece of equipment made up of thousands of components. Roughly 80% of losses come from a switching device and AC inductors. One of the most critical components within PV inverter is this “switching device” or semiconductor device being used to perform DC to AC conversion. Historically, the solar industry has relied on an IGBT (Insulated Gate Bi-polar Transistor) for this device. The IGBT is the heart of the PV inverter where power conversion really takes place.

PV inverter manufacturers have provided innovative solutions in the configuration methodology of IGBT, but one of the most innovative solutions is advanced NPS (Neutral Point Switch) 3-level topology. Conventional PV inverter technology typically uses a 2-level inverter system with a lower number count of IGBTs. The 3-level power conversion incorporates at least twice the number of IGBTs distributing power stress among individual devices. In fact, the total loss of IGBT and AC inductor in 2-level topology inverter ranges from 80% to about 85%, while the 3-level topology inverter is able to achieve 75% to 80%.

Additionally, NPS 3-level topology is able to achieve better power quality due to its unique switching characteristics. This allows reducing AC inductor size by half. This 50% reduction would also mean reducing the total inductor ohmic loss, and also 50% reduction in core-loss as constant loss attributes to significant improvement in efficiency at lower load conditions. Lower stress on individual IGBTs and reduction in AC inductor size inevitably equates to lower total losses contributing to an increase in efficiency and reliability.

 

 

 

All inverters need cooling because a significant amount of heat is exhausted out of PV inverters, especially in large utility-scale central inverters. Most large PV inverters size range from 1 MW to 1.9 MW, and the amount of heat directly correlates with conversion efficiency. For an example, a 1-MW inverter with a 98% conversion efficiency equates to about 20 kW of heat. That is enough heat to comfortably warm 10 homes! In essence, as we achieve higher efficiency less heat is required to be exhausted out of the inverter, therefore requiring a simpler cooling system. Some of the recent advancement in the inverter cooling system, such as an advanced hybrid cooling solution, requires significantly less air-flow in the system without an auxiliary fan power load. This lower load condition allows the inverter to further increase conversion efficiency.

 

IGBT design and the cooling system are two of the most important aspects in achieving 99% inverter conversion efficiency. They are also intimately related. Inefficient IGBT design will result in lower efficiency with higher heat exhaust. This in turn, will require more complex and/or a higher air-speed cooling system. Technology optimization in the switching device and cooling system is key to entering the next era of PV inverter efficiency, beyond 99%.

 

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100 Gb speed with Li-Fi

Soon you will get 100 Gbps speed into your computer with Li-Fi Like Systems.

Earlier the data which was transferred to our computer was not accurate and had drops while travelling a long way to its final destination that is you.  The data which travelled in the form of light has certain drops in midway due to various reasons. Now, researcher believe it’s all over.

How would it sound if we take the light all the way to the computer or TV, projecting it through the air over the last few meters and only converting it to an electronic signal at the end? That sounds amazing isn’t. The researches at Oxford University is  working on the similar technique with a system that takes light from the fiber, amplifies it, and beams it across a room to deliver data at more than 100 gigabits per second.

Ariel Gomez, a Ph.D. student in photonics at Oxford University who describes the system in IEEE Photonics Technology Letters says that such indoor optical wireless probably wouldn’t replace Wi-Fi, but if compared with data rates of 3 terabits per second and up, it’s certainly amazing and could find its uses. Wi-Fi, by contrast, can give a maximum top speed of about 7 Gb/s. And with light, there’s no worry about sticking to a limited set of radio frequencies. “If you’re in the optical window, you have virtually unlimited bandwidth and unlicensed spectrum,” Gomez says.

 

 

So to use this feature, you need to install a base station on the ceiling of a room, which would project the light toward the computer and also receive data heading out from the computer to the Internet.

The transceivers should be mounted with a wide field of view to make the alignment task easier, because the device relies on wavelength division multiplexing, which splits the signal into slightly different colours of light.  Just like a prism, which diffracts the light into several colours, the diffraction grating of the beam steerer bends each wavelength a different amount. With a 60° field of view, the team was able to transmit six different wavelengths, each at 37.4 Gb/s, for an aggregate bandwidth of 224 Gb/s. With a 36° field of view, they managed only three channels, for 112 Gb/s.

The system requires a direct line of sight, and for now the receiver must be in a fixed position. The next step is to develop a tracking and location system so that a user could place a laptop at a random spot on a table and have the system find it and create a link.

The team which is working on this technology also included researchers from University College, London, accomplished this using so-called holographic beam steering at both the transmitter and receiver ends. These use an array of liquid crystals to create a programmable diffraction grating that reflects the light in the desired direction. The device is similar to that used in projectors, says Dominic O’Brien, a photonics engineer at Oxford who directed the work.

Brien is a member of the Ultra-Parallel Visible Light Communications project, with colleagues at the Universities of Edinburgh, Strathclyde, St. Andrews, and Cambridge.  Among several goals one of their goals is to develop LiFi, which uses the light that’s also illuminating a room as a way to send data signals. He says LiFi usually refers to schemes based on visible wavelengths of light, whereas this system relies on infrared light at 1550 nm, which is used in telecommunications.

All these technologies - Wi-Fi, Li-Fi, optical wireless - may wind up being part of how people link devices to the Internet. There is no limitations in the field of technology and today or some other day the most advanced and reliable technology has to come and replace all others. The fact that remains is the time which the technology would take to develop.

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