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Four pillars of power management to consider when selecting your next PDU

Fri, 01/04/2013 - 1:43pm
Dave Proli, Director of Engineering, Marway Power Solutions

As consumer, commercial and industrial electronic systems become more advanced; they require more precise and reliable power sources to function at optimum levels.  System integrators and designers are turning to more sophisticated power distribution units (PDUs) with customized specifications to better tackle power hurdles.

Today’s advanced PDUs can implement multiple functions into a single package to help reduce space, weight, and cost. Understanding the four key pillars of power management is vital to designing a system with optimal performance while maintaining minimal cost and packaging space.  Those four pillars are:

• Power conditioning
• Power conversion
• Power control
• Power monitoring

Power conditioning
Sensitive electronic equipment such as computers, communications hardware, security systems, data acquisition systems,and others require clean, stable power free of noise in order to perform their functions optimally and reliably. Voltage spikes, brownouts, and electromagnetic interference (EMI) can wreak havoc with sensitive electronic systems. A clean alternative current (AC) signal has a perfectly smooth sine wave (Fig.1) when viewed on an oscilloscope. Any imperfections in this signal can adversely affect electrical equipment causing poor performance, incorrect functionality, or even damage to circuitry.

Most electronic equipmentwill have some minor power conditioning capabilities built in, but there’s a basic assumption that incoming power is pretty close to a perfectly clean signal. However, that’s not always the case. Mobile power sources (i.e., generators) and power utilities in some locations will not deliver smooth clean signals. Even the clean power supplied by a robust power utility will become degraded within a facility. This degradation is caused by the very devices using the power such as air conditioners and compressors, electric heating equipment, motor-driven industrial machinery, elevators, conveyors, computers, printers, copy machines, ballasts for fluorescent lights, and other equipment.

Since signal problems such as voltage spikes and electromagnetic interference (EMI) are introduced to power lines throughout a facility’s wiring, it is beneficial to add power conditioning at points throughout the facility.  Specifically, PDUs are an excellent place to implement several types of mitigation techniques.  A surge protective device (SPD) provides an effective means to prevent transients from reaching load equipment.  There are multiple technologies available, with metal oxide varistors (MOVs) being the most common.  EMI filters reduce the amplitude of noise, notching, and harmonics on the power line, thus protecting downstream equipment from their damaging effects.  And transformers are useful for providing isolation as well as providing protection against common mode noise.

Power conversion
In many types of equipment, the loads require different voltages or phase configurations from each other or from the facility feed.  In this situation, some type of power conversion is needed to satisfy the discrepancy.  This can be as simple as a step-down transformer to reduce the voltage provided from the facility so that it is compatible with the load.  Sometimes, a delta source is available, but the load(s) require a wye supply.  Or the conversion may involve changing an AC source to a DC feed as needed by the load equipment.  In legacy equipment, power conversion products were installed and wired as separate devices.  But it is often convenient and cost-effective to implement the power conversion requirements inside the power distribution unit, especially when the requirements of the various loads differ from each other. 

Transformers can be integrated into the PDU to provide voltage scaling or phase reconfiguration.  Power supplies can also be integrated to provide DC outputs when needed.  And for situations where only a DC power source is available, DC to DC converters can be integrated to change the voltage as needed, and in some cases inverters can even be added to provide AC outputs.  With this philosophy, the PDU itself manages the task of accepting the available facility power, and then providing the specific power configuration needed by each load device without the need for external components.  And of course PDUs can be specified to provide the specific connector type that is most convenient for each device in the system.

Power control
The simplest of PDU designs distribute power and usually include some kind of overcurrent protection (circuit breaker).  For many applications, it is convenient to include additional power control features.  These features may simply support user convenience or may be implemented to provide a safe response to dangerous conditions.  Some common examples include emergency power off (EPO) circuits, over-temperature or cooling interlocks, and power quality interlocks which shut off critical circuits during undesirable conditions such as over/under-voltage or improper phase rotation.  Sequencing is an automated control feature often implemented to power up circuits in a staggered order.  This helps avoid excessive inrush current load on the PDU input which could be caused if all of the output circuits were to turn on at the same time.  Remote control of power switching can also benefit the overall design.  Typical remote control interfaces include dry contact, command line via serial or TCP/IP, and webpage. Implementing these types of power control features within the PDU can improve the design while helping to reduce the overall cost and complexity of an application.

Power monitoring
A growing trend is to monitor all aspects of electrical power. In the vein of “you can’t manage what you don’t measure,” facility managers and engineers are looking to decrease their carbon footprint by utilizing energy efficiency initiatives that reduce costs without sacrificing reliability and system uptime. At the PDU level, it’s not only important to know how the PDU is performing but it’s also useful to view specific parameters such as input voltage to be assured that the power for the application is within acceptable limits. In cases with sensitive downstream equipment or processes, it may be important to monitor a wide range of parameters regarding power quality and status.  With some equipment designs, the PDU is not visible to the user, so a method of remotely monitoring this information is desired.  Since the PDU is the focal point of power in a design, it is the most logical place to implement some kind of power monitoring.

Overall advantages
As mentioned above, the benefits of advanced PDUs are many and go beyond the standard feature-set of common PDUs. Integrating power conditioning, conversion, control and monitoring into the PDU itself provides many advantages:

• The convenience of a single solution to solve multiple power needs
• Reduction of packaging space
• Improvement in wire/cable management by reducing system complexity (all power is distributed by the PDU via appropriate connection types)
• Control and monitoring directly at the focal point
• Lower overall system cost (eliminating the cost of separate enclosures for separate power management devices).

Whether an off-the-shelf, modified or a complete custom power design is required, today’s PDUs offer a smarter, lighter and more cost-effective solution over PDUs of the past. A combination of performance, power management,packaging efficiency and reliability are key attributes to consider when choosing your next PDU.

www.marway.com

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