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EETE SEP 2014

ENERGY HARVESTING The wireless option Wireless control has increased in popularity in the last decade due to advances in radio technology and the emergence of standards such as ZigBee or EnOcean protocol, which standardise communication between different devices. The key advantage of wireless control is the ease of upgrading existing buildings. No new control wiring is required for existing lights; rather they only have to be upgraded with wireless control units. Wireless control systems can potentially also provide greater installation flexibility if units within the system do not require dedicated Fig. 3: Components of Energy Harvesting Wireless Control cabling for power supply. There are three different types of wireless control: 1. Wireless devices requiring an external power supply Such devices can increase system performance by enabling advanced control schemes but rely on an existing cabling infrastructure. The flexibility of such solutions is therefore limited and the cabling cost remains a factor. A suitable application would be a line-powered light control system such as light ballast or relay. 2. Wireless devices requiring a battery Wireless controls with batteries combine the advantages of system performance and flexibility. They require no dedicated cabling meaning that switches and sensors can be freely placed during initial installation and subsequent reconfigurations. The key challenge with battery-powered devices is the aspect of maintenance, specifically the need for battery replacement. Acceptance for non-working light switches tends to be low so battery maintenance must be carefully planned and systematically executed. The associated cost needs to be carefully considered. 3. Self-powered wireless devices Advances in electronics and dedicated research have made self-powered wireless sensors and switches feasible for over a decade. They offer the advantages of wireless devices while at the same time eliminating the issue of maintenance – see figure 3. For lighting control purposes, the two main energy sources for battery-less wireless devices are motion and light. Selfpowered switches use kinetic energy to generate a wireless signal for controlling and dimming. The press of the switch activates an electro-mechanical energy harvester, which converts the motion into electricity to power a wireless module. One press is sufficient to send three telegrams. The second energy source is opened up by miniaturised solar cells, which harvest ambient light already from 200 Lux and convert it to electrical energy. This approach is particularly suitable for light intensity or occupancy sensors. Standardised communication The amount of energy harvested from these two environmental sources is lower than battery power. Therefore, the wireless communication and the protocol in use respectively need to be optimised for ultra-low power operation. The international standard ISO/IEC 14543-3-10 is a protocol which is particularly suited for energy harvesting applications, using only 7 bytes of protocol overhead for the transmission of 1 byte of sensor data - see figure 4. RF reliability is assured because wireless signals are less than one millisecond in duration and are transmitted multiple times for redundancy. The range of the protocol is approximately 300 metres in an open field and up to 30 metres inside buildings. These characteristics make the ISO/IEC standard well suited for wireless lighting control in larger buildings with a few hundred wireless sensor nodes up to several thousand. There are also sub protocols from other existing wireless standards that offer ultra-low power radio to be operated by energy harvesting. The sub protocols of the worldwide opened 2.4 GHz ISM band are a good example. The range is only one third compared to the ISO/IEC standard but it is ideally suited for consumer LED lighting control. Here, 2.4 GHz protocols are of common use and, therefore, enable the user to integrate self-powered wireless control in his intelligent lighting scenery environment. The batteryless switch in 2.4 GHz is the ideal fit for domestic LED lighting systems. It is the missing link between the LED bulb and the user, anytime the use of a smartphone app is not possible or is inconvenient. Today, lighting control is much more than just switching lights on and off. It is an integrated system which supports the users’ comfort, influences their perception of goods and is a significant energy saving factor in buildings. There are several ways of realising lighting control to match individual needs. LED lighting, in particular, offers a wealth of new possibilities. Choosing wired or wireless control is not a question of faith. Local conditions, time and installation effort as well as initial investment and operational costs all have to be taken into consideration to reach an optimal solution. In most cases, a combination of both will be the perfect fit. Fig. 4: Protocol Structure of ISO/IEC 14543-3-10 24 Electronic Engineering Times Europe September 2014 www.electronics-eetimes.com


EETE SEP 2014
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