10/03/2024While configuring energy sources in a parallel arrangement may amplify the available output power, it can either augment or diminish the reliability of the energy system. The alteration in the reliability of the energy delivery system due to the interconnection of energy sources in parallel cannot be universally generalized, as it hinges on the system’s design and the characteristics of individual energy sources.
FIG. 1 – Power units with their outputs linked in parallel.
We shall commence by elucidating the term „failure rate“ and subsequently examine its application to components and systems comprising said components. A failure rate denotes a statistical parameter describing the incidence of failures within a specified timeframe.
A prevalent failure rate utilized in reliability assessments for electronic products is FIT (Failure In Time), denoting the anticipated number of failures within one billion (109) hours of operation.
A methodology for computing the failure rate (FIT) of a system entails computing the FIT of each component within the system, followed by summating the FIT values for all components in the system.
For a system constituted of n components, each possessing a FIT of f, the system’s FIT equates to n*f. It’s imperative to note that a higher FIT value denotes a less dependable system, implying more failures within a specific duration.
FIG. 2 – N power supplies, each having a FIT = f.
Applying the aforementioned to energy sources with interconnected outputs in parallel suggests that the system’s failure rate may escalate (corresponding to decreased reliability) with an increase in the number of supplies. Several mechanisms through which the failure of a solitary energy source within a bank of paralleled supplies can lead to a system failure include:
The direction in which the employment of multiple energy sources with interconnected outputs in parallel influences system reliability hinges upon the relative reliability of the supplies employed in distinct configurations. As exemplified below, additional information is imperative before discerning the impact on the reliability of the energy delivery system attributable to multiple energy sources.
Design 1 – A system necessitates a total power delivery of 128 W, and two power supplies, each offering 80 W output power, are to be employed with their outputs interconnected in parallel. Though in actuality, load current sharing may not be precise, for analytical purposes, let’s assume each supply provides 64 W of output power (equivalent to 80% of rated output power) at a 128 W system load power.
FIG. 3 – Two power supplies operating at 80% of their rated output power.
Design 2 – Alternatively, four supplies each offering 40 W output power could be chosen, with each supply furnishing 32 W of output power, operating once more at 80% of rated output power. Presuming the designs of the 80 W and 40 W power supplies are analogous, it’s plausible to assume that the FIT for both designs will be akin when operated under similar conditions.
With these assumptions, the power supply segment of the system in design one, employing two power supplies in parallel, would be more dependable, with half the FIT (twice the reliability) compared to the system in design 2, employing four power supplies in parallel.
FIG. 4 – Four power supplies functioning at 80% of their rated output power.
The calculations above presuppose that the power supplies are selected such that the FIT of each supply remains constant as the number of supplies in the system escalates. If the system entails a fixed load, and identical supplies are utilized as the number of supplies escalates, each supply would operate at a reduced load current with the addition of more supplies.
For numerous power supply designs, the FIT diminishes (implying increased reliability) as they operate at lower output power levels. Consequently, augmenting the number of power supplies interconnected in parallel would reduce the system’s FIT (enhance system reliability) if each supply’s FIT decreases more rapidly than the sum of FITs escalates.
Design 1 – In this scenario, the identical 128 W system load is employed, and the same initial design of two power supplies, rated at 80 W each, is evaluated. The power supply system’s FIT (and reliability) would mirror that of the first design in the preceding example.
FIG. 5 – Two power supplies operating at 80% of their rated output power.
Design 2 – If a configuration featuring four 80 W power supplies is selected, each supply would deliver 32 W, thereby operating at 40% of rated power.
FIG. 6 – Four power supplies functioning at 40% of their rated output power.
At this juncture, generalizations become inadequate, necessitating the verification of assumptions. If the FIT of the power supply operating at 40% of maximum power is less than half that of the FIT at 80% of maximum power, then employing four power supplies rather than two would enhance the reliability of the power delivery system.
It’s a customary practice to interconnect the outputs of power supplies to augment the power supplied to the load. In numerous such configurations, the failure of any individual supply precipitates the failure of the entire power delivery network. To ascertain the reliability of the power delivery network, it’s imperative to comprehend the efficacy of load current balancing and the reliability of individual supplies under prevailing operating conditions.
