Fuzzy logic has the power to save

A small firm in Enfield has developed a system that will reduce electricity consumption by 12 to 20% in any installation. Using fuzzy logic, it is designed to reduce power consumption by AC motors to exactly what is needed – and no more. Voltage is reduced in such a way that full functionality is maintained but energy consumption is minimised. The low cost technology is applicable to any electrical installation, whether it be a retail store, hotel, distribution centre or small factory. Presidio, a small Enfield-based company, started making safety motor control centres in 1996/7. It then went onto develop the PowerMiser, a motor controller with “some intelligence” which could reduce the power consumed by three-phase motors by adjusting motor torque to the minimum needed under whatever load it experienced. This led onto a second generation ACMiser product with more intelligence, which made the company overall winner in the 2001 London Innovation Awards. The ACmiser can be programmed to interact with the environment and a typical application on which the device has been applied is a machine for milling corn for breakfast cereal. In this case, the controller adjusts the position of a slide valve, so that the feed into the mill keeps the motor under a constant load condition. In this particular example, load is computed from motor power factor. If, for example, in normal operation, the power factor is 0.8, and power factor rises to 0.9, this indicates that the load has increased inside the mill and requires that the controller close the slide valve proportionally. The company’s latest idea is called the PowerCap. This tackles the problem of general electrical efficiency in a different way. According to managing director, Zia Shlaimoun, it arose when a large frozen foods retailer approached the company in late 2000, for a solution to cope with excessive supply voltages. Electricity companies are obliged to supply power at 230V, with a minimum set at 216V. But in order to ensure that all customers receive sufficient voltage, they generally supply at up to 253V (+10%) to cope with resistance losses in the transmission lines. As voltage increases, so does power consumption. The result is both wastage of power, and potential damage to and reduced life of equipment. Work carried out by some of the Country’s top experts in this field has confirmed this. Presidio Power decided that solid-state control was the answer to the problem. It was also decided that, by using fuzzy logic, it would be possible to take the idea further than just reducing voltage back down to 230V – it could be reduced to whatever voltage level minimised overall power consumption. It is fraught with complications though. For example, in the case of multiple motors driving refrigerator pumps, reducing voltage too much causes current to rise in order to maintain refrigeration load, and overall power consumption will go up. The controller therefore has to look for the optimum state. Fuzzy logic, which deals with uncertainties and probabilities is ideal for this kind of task, but requires the services of an engineer who understands it in order to get it to work. The PowerCap uses a combination of thyristors and IGBTs to regulate up to 250A per phase. It works by comparing input and output voltages and each phase can be set independently. The device can either be set to produce a preset output voltage or use its fuzzy logic to find the bottom of the membership function bell curve (see additional article below) and so the minimum power level. The device learns as it controls, recording its experience in Flash memory. It has a separate high voltage card and logic card, where logic is held on an FPGA. Customers use their own metering equipment to calibrate it, and then set the device to run. The human machine interface (HMI) has a small screen and six buttons. Four scroll through various functions, vertically or horizontally and the other two buttons are for “Yes” and “No”. The unit has two power supplies to give it redundancy, and a Telemecanique Square D by-pass contactor to maintain mains supply in the event of failure. The whole system fits in a box 650 x 400 x 260mm. Applications for the present unit are seen in manufacturing establishments, retail stores, distribution centres, hotels, shopping malls and offices. On-site tests show savings in the range 12 to 16%, and a small single-phase unit, suitable for domestic use, is planned for the future, as are higher power versions capable of operating with loads measured in thousands of amps. Fuzzy precision Fuzzy logic was an idea invented by Dr Lofti Zadeh in 1964. Instead of dealing with certainties, such as switching on below exactly 216V, or switching off above exactly 253V, it works in human-type concepts such as too little, or too much, or OK without having to define exactly what too little, too much or OK mean. This means it assigns a grade to the concept of too little, too much, or OK. Hence, while 253V might be considered too much and assigned a grade of one, 240 is only a bit too much and might be assigned a grade of 0.5, with OK also being assigned a grade of 0.5. The relationship between the controlled parameter, the different states and the grades of each state are usually represented as bell curves, although simple implementations, or ‘membership functions’ are more usually made to be triangular for ease of computation. First commercial implementations were on cement kilns in order to improve fuel efficiency. In June 1986, Eureka reported a successful implementation by SIRA on kilns operated by Blue Circle, but was asked not to reveal just how great the appreciable fuel savings were. Fuzzy logic was all the rage in Japan in the 1990s, and is commercially available in controllers supplied by both Omron and Fuji. Implementations in the UK are rare, mainly because so few engineers understand it, although the presence of Professor Ebrahim Mamdani, one of the world’s experts, at Queen Mary College for 11 years means there is a knot of engineers with the required knowledge in and around East London, hence the development by Presidio. Eureka says: The idea that small boxes of electronics could knock 12 to 20% off the nation’s £16 billion electricity bill and 200 millions tonnes of associated carbon dioxide emissions is staggering. Applied to the world, it means that meeting the requirements of the Kyoto Protocol could be achieved without pain and with very little effort.