Energy efficiency – thinking small
30 August 2011
Even equipment with a low output and correspondingly low power dissipation can make a significant contribution towards energy saving. CEE reports on a new range of power supplies that have been designed to be optimally energy efficient.
The cost of energy is becoming an increasingly important factor in the process and manufacturing environment. The addition of legislation has required leading industrialised countries to reduce their annual greenhouse gas emissions and has brought about the need to look at ever more energy efficient solutions when considering new products and equipment.
While many engineers are focusing on the biggest energy using systems, it is important that the smaller energy-hungry components are not overlooked in the search for greater energy efficiency.
For some time now switching power supplies have been specified for use in many production environments due to their inherent energy-efficiency compared to conventional linear power supplies. However, according to Siemens, there are still significant energy savings possible from switching power supplies.
Power supplies continue to be designed in such a way so that they offer the highest possible efficiency at maximum load. Simply stating the efficiency at nominal load is not an indicator for an efficient power supply. This is because power supplies are normally run in a load range between 30 and 70% of the nominal or maximum output – depending on the process. In addition, there are production-free or idle times when individual electricity consumers or plant sections are switched into a ‘standby mode’ to save energy. This requires the power supply to minimise the energy consumption during no-load times.
During the development of its new SITOP compact line of regulated power supplies up to 100 W - with DC output of 12 V or 24 V - Siemens focused on ensuring that the units could offer high efficiency over the entire load range and therefore a low power dissipation; that they were designed for input voltages between 85 and 265 V AC (wide-range) so they function on 1-phase 120 and 230 V AC power networks without switching; and that they could also be operational on DC power networks with 110 to 300 V DC. Finally, it was important that they had minimum no-load losses.
The quasi-resonant operation of a flyback converter was chosen for use inside the power supply, because of its wide-range input with power ratings of up to 100 W. Power dissipation is greatly reduced because the switching losses are low. Another benefit of the quasi-resonant topology is that the electromagnetic interference (EMI) is considerably lower than in applications with direct switching.
To keep the no-load losses to a minimum, a specially designed control IC was integrated into the switching electronics of the power supply. The IC itself is designed to only consume a fraction of the power, compared to earlier components, making the switching electronics more energy-efficient.
Adhering to industrial requirements concerning the output voltage regulation at partial to no load was another design challenge. Unlike the consumer sector, it is not specified from the outset which electricity consumers are to be supplied with electric power by the industrial power supply. This means that it is also unclear what kind of voltage fluctuations can be tolerated by the individual electricity consumers. Industrial devices therefore need to be prepared for any load. The power supply has to deliver a constant output voltage under all load conditions, with minimum energy losses, irrespective of their sensitivity to voltage fluctuations.
Measurements undertaken in real operating conditions have shown that, when compared to conventional power supplies, the regulated power supplies of the SITOP compact line can offer energy savings of around 28% during load operation and even approximately 53% during no-load operation. During normal use – consisting of a mixture of load and standby operation – up to 35% of energy can be saved. This confirms that SITOP compact can offer energy savings when installed in machines, plants or office buildings that are in standby mode temporarily, or for longer periods.
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