Incorporated in 1989, today Uniline is the third largest Indian manufacturer of UPS solutions and is one of the fastest growing UPS companies in India in IGBT technology. RK Bansal, founder and managing director, Uniline Energy Systems spoke to Uma Bansal of Electronics Bazaar, about green UPS and advanced IGBTs
EB: What is the role of IGBT in a UPS? And what’s next after IGBTs?
Earlier, UPS were manufactured with a simple transistor that acted like a switch. The switching frequency was very low. Then came MOSFETs, which had a very high switching frequency resulting in higher efficiency and low noise in the system. However, the online resistance of MOSFETs was very high, requiring the use of more MOSFETs for the same power output and another dissipation mechanism for the heat generated.
IGBTs have the advantages of both transistors and MOSFETs. They offer the benefit of a high switching frequency and low online resistance, without the disadvantages of MOSFETs and transistors.
IGBTs themselves are going through a lot of changes. Currently, the IGBT being used is of the sixth generation. Earlier, IGBT ratings and DC voltage were low. Now IGBTs are available at up to 600A and 1200V. Also, two IGBTs are being packaged into a single chip.
Talking of the technology to follow IGBT, intelligent power modules have just started appearing. These are IGBTs with a complete electronic circuit that takes care of output voltage, output frequency and the driver.
EB: What techniques are being used to maximise the efficiency of UPS?
The efficiency depends on two to three factors. The more the switching frequency, the better the efficiency. The more the DC voltage, the better the efficiency. The type of transformer core and wires also affect the switching frequency.
EB: What is a multifunction UPS?
There are many applications in a plant that cannot wait for power. A multifunctional UPS can provide backup for almost all the load required in a plant, not just for the computers. So there is no need for the generator to be started. This is particularly useful for medical electronics.
EB: How green is the ‘green UPS’?
‘Green UPS’ is designed to save the environment from pollution. For IGBT based rectifiers, the input power factor is 0.99. Earlier thyristor based SCRs had a maximum power factor of only 0.8. Also, these had up to 25 per cent input current harmonics, which distorted the line. With IGBTs, the input current harmonics are less than 3 per cent and the input current drawn from the electricity grid is lower by around 20 per cent.
EB: What improvements are being made in energy storage systems? There is talk about battery alternatives like ultra capacitors and flywheels.
Ultracapacitors are currently being used in hybrid (electric+diesel) cars, besides wind and solar power systems. When you apply the brakes in a speeding car, a lot of energy is generated, which is fed to the capacitor. Ultracapacitors charge almost instantly, while batteries require 8-10 hours to charge. Also, the life of an ultracapacitor is more than 25 years, compared to not more than three years for a battery. So ultracapacitors are being used not only for the automotive industry but also for wind and solar power generation.
But, whenever any technology is launched, the initial cost is high. For example, earlier, solar cells were available for Rs 250/watt, now they are available for Rs 80/watt. With India’s requirements, the cost may come down to Rs 50/watt.
Similarly, the current cost of ultracapacitors is high. Once there are more manufacturers and more demand, the cost will automatically come down. Then the ultracapacitors could be used for UPS as well.
Flywheel UPS of the rotary kind, consisting of a motor, generator and flywheel. When the mains power is available, the motor rotates the flywheel. When the mains fail, the flywheel keeps rotating and generating power. In the meantime, the generator turns on and starts rotating the motor. So, practically, you have uninterrupted power.
Flywheel technology is very costly and is generally used for critical power systems of more than 500 kVA.
EB: When will we see solar backup systems for computers?
Solar powered laptops, mobile phones and other devices are already available in the market. At present, these are not very popular because their cost is high. But with government subsidies and other support, by the end of 2012, many such devices will be in use.
The government has asked all the banks to have a particular fixed number of their ATMs powered by solar systems. It is also thinking about bringing the concept of grid tied inverters. In this system, you install a solar system on the rooftop or any other place in your home. During the daytime, the extra power generated can be fed to the electricity grid and redrawn at night when you need it.
EB: What are the key challenges faced when designing UPS solutions for Indian conditions?
Every 50 km in India, you’ll find different challenges. Some states have surplus power, while some states don’t have power at all. Power cuts in states like Delhi are only for two hours a day, but 50 km away, in Faridabad or Gurgaon, it could be for six to eight hours a day. Also, you never know the input voltage at your end. In India, the power has to be a minimum of 230V±10 per cent. But, in many areas, the input power is not even 120V at night, so you have to use double stabilisers so that you can operate your AC.
Also, the Indian environment is dusty and hot, which adds to the heat generated by the system. Then, there is the issue of the time period for which backup power is required. When you buy any UPS from Europe, the standard backup time available is for not more than five minutes. But here, the power backup requirement can even be for up to eight hours.
EB: How does one select the battery for UPS?
There are various types of batteries—automotive, tubular and SMF. Each has its own advantages and disadvantages. Some are low cost, others are expensive, but have a longer life. Then there is the issue of gases. For AC environments, one should go for SMF batteries, not the automotive and tubular batteries.
To determine the load, ascertain your requirements. For example, in a room with only lights, count the total number of bulbs and add up the power consumed by each to arrive at the total load. Similarly, if you want to connect any particular device, go through its technical manual. Or, you can use a power meter to measure the current running load.
EB: What is a UPS-cum-inverter?
Batteries should then be chosen as per the total load on the UPS. Online UPS are UPS-cum-inverters because the inverter is ‘on’ 100 per cent of the time and the load is always through the inverter. In line interactive systems, there is a changeover time.
Any system with a changeover time of more than 10 minutes is not a UPS in the true sense. For your home application, in case power fails, there is a changeover and you get power. For you, it’s uninterrupted power. But, for office applications running on computers, at the changeover, systems reboot. So it’s not uninterrupted power.
