Interview with Professor Phil Mawby, Department of Engineering
Published August 2010
Energy management is 'the dirty side' of electronics - it is needed to run every single electrical device, but people are not aware of just how sophisticated the system has to be. Silicon is already widely used to make the semi-conductors - an essential part of this process.
“There are two halves to electronics,” explained Professor Phil Mawby, of the Department of Engineering at the University of Warwick. “One half we are very familiar with: the processing of information. The other half, power electronics, is the processing of electrical energy. It is the less well known side. Everyone needs it but no one cares.” Different components that use electricity require that electricity to be in a certain form. Inside any one electrical device there will be lots of little conversations going on to maximise power-use efficiency and decrease the demand on the battery. There is a lot of thinking that goes into this design which is taken for granted by the consumer: “You don’t buy a laptop because of how smart the power supply is but the only reason we have such compact mobile phones is because the energy management is very sophisticated.”
Traditionally, stepping up electricity from one voltage to another would require a transformer, which is an electromechanical device. New semi-conductor technology provides an alternative method of performing the same function, but they are much smaller and they can be controlled by micro-processors introducing the capacity for intelligence into the system. “If micro-processes are the brains, power electronics is the brawn and silicon is the work horse.” Silicon is a material that is most often used where a semiconductor is required and the impact of silicon semiconductors should not be underestimated: "Silicon Valley” is so named because much of the vast wealth created there is from the semiconductor industry.
For very high voltages silicon switches have to be put in series which makes control of the system much more difficult. Silicon Carbide is the next-generation semiconducting material. It is very similar to silicon but a much smaller piece of the material can perform the same functionality, meaning space and weight are saved, and less heat is lost. The problem is the cost: “This material is very expensive. You can buy a 12 inch wafer of silicon for a few dollars but a 4 inch wafer of the silicon carbide is 1,000 dollars.
There are 200 different polytypes of the crystal and only one has the valuable properties. Intellectual property protects the process used to make this particular crystal shape and this is what drives up the price.” A company called CREE is currently a major producer of the material, which is still being developed: “They receive some money from government grants because the military are very interested in the potential for this material. Similarly the electric car producers in Japan are paying close attention. At the moment the Toyota Prius has to have one radiator to cool down the engine and one to cool down the power electronics. The second radiator would no longer be necessary if the silicon was replaced by silicon carbide.”
We have come to expect smaller and lighter from computer system updates but this material has another major application that would introduce totally new functionality into the biggest type of electricity distributing system: The National Grid. At the moment the electricity is transported in alternating current (ac). 5-6% is lost due to heat dissipated when electricity is transported over long distances. Semiconductors are not usually used in this process since transistors are able to offer the required functionality. “These losses are bearable; when a system is 95% efficient people are not so worried about taking that to 96% but the total energy lost is substantial.” The system was designed to transfer ac current because the transformers cannot perform the stepping-up/down function on dc current.
The requirements of The National Grid, however, are changing. In the future we will need a more distributed system, where electricity can not only be taken from, but also added to, the grid. As the demand for electricity increases it would be useful to introduce intelligent capabilities: “If everyone on a street plugged their electric car in at night the grid could not meet the required supply unless each car was charged in turn. This all requires power electronics.” Such improvements would require the use of advanced power electronics; electricity could be transferred at a higher voltage, increasing from 300-400V to 500-600V, which would improve the efficiency; the transfer could be made in dc current and intelligence could be introduced into the system to dictate exactly when electricity was being delivered from the grid. This can, and is, being done but using silicon not silicon carbide. The size of the substation required is a couple of acres big. If silicon carbide were used this space could be reduced to that of a room. Off-shore wind farms could certainly make use of this space saving.
Professor Mawby is currently working on creating devices out of this super-material Silicon Carbide. The first stage is to grow oxide on the surface of the silicon carbide to make it into a ‘MOSFET’. He has his very own clean room at Warwick University which is dedicated to researching this material and a high temperature furnace that is helping to solve a particular problem: “It is very difficult to grow an oxide which is high enough quality. When oxidising silicon a silicon dioxide layer forms but in silicon carbide the extra carbon atom is either released as CO gas or it clumps together to form uneven oxides on the surface.” At very high temperatures however, the likelihood that CO gas is formed increases and it is thought that this will be a key breakthrough in developing the technique for producing a unifrom oxide layer. “This particular piece of kit is creating a lot of industry interest.”
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Prof Mawby joined the University of Warwick School of Engineering having spent 19 years and the University of Wales, Swansea. He has built an international reputation in the area of power electronics and power device research. Whilst in Swansea Prof Mawby established the power electronics design centre, which carried work out in a whole range of areas relating to power electronics. The centre focussed on interaction with SME's in Wales as well as larger international companies. Whilst he was in Swansea he held the Royal Academy of Engineering Chair for power electronics. Prof Mawby is on Many international conference committees including, ISPSD, EPE, BCTM and ESSDERC. He is Chartered Engineer, a Fellow of the IET, and a Fellow of the Institute Physics as well as a Senior Member of the IEEE. He has published over 70 Journal papers and 100 conference papers, and is a distinguished lecturer for the IEEE Electron devices society.