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Examining power module redundancy issues

Posted: 13 Nov 2014 ?? ?Print Version ?Bookmark and Share

Keywords:MicroTCA? Advanced Mezzanine Cards? embedded systems? Power Modules? redundancy?

MicroTCA (?TCA) is designed to build flexible and reliable (high availability) embedded systems. A?TCA system consists of up to 12 Advanced Mezzanine Cards (AMC), 2 cooling units (CU), 2 MicroTCA Carrier Hub (MCH) and 4 Power Modules (PM). A single power module is unlikely to meet the power requirements of a fully loaded?TCA system; hence load sharing mode is used in these systems, where the power requirements are met by having multiple PM.

Power Modules can also be configured to improve reliability by redundancy, but this will increase the number of PMs required in a system. Often load sharing is required, and PM redundancy is very desirable to improve the reliability of the system. However PM redundancy is sometimes disregarded due to increased costs, and in some cases it is not possible to achieve redundancy due to system constraints C for example, a chassis which has 2 PM slots and require them to be in load-sharing mode. For these systems, we discuss the additional costs of having PM redundancythe number of additional PMs required, and how a cost-effective solution can be achieved. In many cases PM redundancy can be achieved at no additional cost.

The power module is an integral part of the?TCA system. The PM's primary function is to provide management and payload power, but like any other FRU, it must be Intelligent Platform Management Interface (IPMI) compliant. Although the PM has the intelligence to autonomously bring up the MCH and the CU, the MCH is required to provide sophisticated features such as PM redundancy. Figure 1 shows a typical?TCA system consisting of 12 AMCs, 2 MCHs and 2 CUs and highlights the parts of the power system.

Figure 1: ?TCA System with 12 AMCs, 4 PMs, 2 MCH, 2 CU.

Conventional solution
Consider the system in figure 1, with each of 12 AMCs drawing 80W of power. Today's PMs are able deliver between 400 to 600W of power in the single module size; some very good ones are able to deliver up to 792W. So the total power required (~1000W) can't be met by a single PM, load-sharing mode is adopted where the total power requirements can be satisfied by having 2 PMs. We could configure the PM1 to power AMCs1-6, MCH1, CU1 and PM2 to power AMC7-12, MCH2 and CU2. To achieve PM redundancy we could have PM3 and PM4 which mirrors PM1 and PM2 respectively. So in order to have a fully populated power hungry system, with PM redundancy, we will require 4 PMs for these systems. Using a N+1 redundancy, we can bring this down the number of PM to 3. In this case PM3 would be a redundant PM to either PM1 or PM2.

Problem
Both load sharing and redundancy are very important concerns for building a system, but redundancy increases the number of power modules required, and hence increases the total costs.

Scenario 1
Let's suppose that we would like to have AMC6, AMC7, MCH1, MCH2, CU1, and CU2 to have redundant power supply in the system shown in figure 1.

We need one additional PM to achieve this using conventional solution (N+1 redundancy scheme), where:
PM1 to power AMC1-6, MCH1, CU1
PM2 to power AMC7-12, MCH2, CU2
PM3 (Redundant) AMC6, AMC7, MCH1, MCH2, CU1, CU2

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