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Power Management

each IBC and POL using the least-squares- fit approach builds a polynomial model of the corresponding device, which the Simulink environment can import and manipulate.

number of iterations that follow the below sequence: I.II Simulate the power consumption that different load conditions create

II.I Verify the simulation with hardware tests

III. Validate the simulation model or adjust it to optimise the profile

When the sequence is qualified, the

Figure 4: Simple theory of the power losses in a switch-mode power supply

One strategy starts by running an algorithm that derives a baseline power loss value. The first control cycle then starts, monitoring relative power loss (see Figure 4) until reaching a threshold value that triggers an optimisation sequence. This complex algorithm performs

numerous iterations but ultimately drives the intermediate bus voltage to a value that minimises power loss for the present conditions, whereupon the sequence closes. The cycle repeats to minimise power losses within constraints that include hysteresis to ensure stable triggering conditions for the optimisation sequence, while also ensuring that the bus voltage does not fall below a level that maintains regulation for the load current profile.

A test system comprising an Advanced Intermediate Bus Converter supplying two 20A and four 40A digital POLs illustrates the efficiency improvement potential that results from dynamically adjusting the intermediate bus level compared with a fixed 12 VDC level. Improvements are estimated at between 3 and 10%,

depending on the average load per operation.

Simulation to application Simulation and verification

demonstrate the potential for saving energy by adjusting the intermediate bus voltage to match load conditions. Although running an onboard energy optimisation algorithm is a smart solution for small

profile is uploaded to the scenario library within a Board Power Manager, which controls the board’s bus voltage, among other possible tasks. Tests then run under best- and worst-case conditions before final implementation.

Profile examples

The following illustrates the value of the intermediate bus voltage relative to the influence that data traffic volumes exert on the power required by the equipment. The first profile corresponds to a normal traffic condition profile, taking into account residential, transit, and business operating hours before returning to lower traffic volumes. The second profile includes an event that demands high volumes of data traffic for a limited period.

Lower power consumption is achieved by adjusting the intermediate bus voltage to suit load conditions. In what is known as the ‘power cascading effect,’ every Watt saved at the board level results in an average saving of 2 to 3W at the system level. This ratio depends upon many factors, but is confirmed by users and power experts (see Figure 5).

Figure 5: Power Cascading Effect

systems, it may not always be the most appropriate approach for large and complex systems, such as datacenters or radio base stations. However, the concept is impossible to ignore in large systems as the amount of energy saved by DBV adjustment broadly scales with system size. The question is simply how best to assess and implement the technology in these circumstances. As data traffic levels have a profound effect on power consumption, one promising approach derives DBV levels from traffic flow statistics. In this case, controlling the bus voltage relies on lookup tables that reflect operational scenarios; the basic premise is to reduce the bus voltage with a fall in traffic and raise it again with increased volumes.

As is often the case with these types of

approaches, systems architects construct models that help to verify the accuracy of the profiles under consideration while they are compiling the lookup tables, and run a

Digital power control and management enables easy dynamic optimisation of the voltage delivered by a master DC/DC converter to a series of POL regulators, directly enabling reduced power consumption. Complementing the high efficiency offered by digital core controllers, the ability to optimise converter performance on-the-fly and adjust the intermediate bus voltage to match load conditions are just two of the wide range of opportunities made possible by digital power technology. The dynamic bus voltage is now a reality that represents the arrival of a new era of energy optimisation in ICT applications.

Ericsson Power Modules |

Patrick Le Fèvre, Marketing and Communication Director, Ericsson Power Modules

Components in Electronics December 2013/January 2014 25

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