More efficient power supplies using health monitoring
Continuous monitoring is a more valid way of testing, often giving more insight into the failure modes and interaction with the rest of the system.
Intelligent power supplies for military applications are providing users with the ability to monitor faults, often in real time, thereby allowing warfighters to make quick decisions during critical missions. Meanwhile, standardization and commercial-off-the-shelf (COTS) technology are enabling flexibility.
Power is always a primary concern in military systems: Designers constantly balance size, weight, power, and cost (SWaP-C) requirements in order to boost efficiency. While each application may be different, power supplies that share information with the operator enable better understanding of what is wrong with the system. Monitored power supplies reduce troubleshooting and down time for the system, as well as enable smarter decision-making during evolving battlefield situations.
“Customers who in the past have typically resisted ‘intelligent power supply units’ (PSUs) are now warming to the benefits that improved built-in-test (BIT) signaling and overall control of the power supply provided by microcontrollers,” says Graham Jefferies, managing director of XCEL Power System, Ltd., a U.K. business unit of Data Device Corp. “Many requirements now call for a PSU that can perform self-diagnostic tests, to ensure that it is within its own parameters and to constantly pass the information via the aircraft or vehicle data bus, to the relevant systems, commonly referred to as health monitoring.”
“Fault reporting is a common requirement,” states Vito D’Erasmo, engineering manager of North Atlantic Industries, Inc. (NAI) Power Products in Bohemia, New York. A lot of what [customers] are requesting is part of the standard, things like input/output and temperature monitoring,” he says.
The basics of power management are there and are driving better efficiency in all military platforms. These trends are leading to “higher density, higher efficiency, and more communication type features. Continuous BIT test, power on BIT testing, so basically a lot of telemetry with power supply in terms of health status,” according to Lou Garofolo, product manager of NAI Power Products.
“Power supplies can share, sense, and monitor. Customers are looking more for intelligence, or power supplies that can gather information from the entire system,” says Jerry Hovdestad, director of COTS engineering, Behlman Electronics in Hauppauge, New York. “In the past when you had four cards, it was difficult to determine which one was misbehaving, now a complete check can tell you which one is not working.”
As the efficiency of each system rises, warfighters have the option of not taking the system offline for testing. Military applications such as unmanned systems, airborne electronic warfare (EW), and land-based platforms performing critical missions can opt to continue running if the issue is minor.
While it could be a minor issue, the software would tell the user that taking the equipment offline is necessary, thereby making the decision process faster and easier, says Christopher J. Stabile, marketing communications manager at Data Device Corp. in Bohemia, New York. With older systems, troubleshooting could take hours; with newer system-health monitoring devices, it only takes seconds, he adds.
“Digitized power supplies mean that diagnostic data is continuously available to the operator, enabling them to know the power status of all active system loads, and to know in advance if any are experiencing issues that may lead to a power failure,” Stabile says. “Prior to the availability of health and diagnostics data, vehicles and other equipment were required to have regularly scheduled – often costly – maintenance programs that required significant downtime to replace parts, whether they needed to be replaced or not, based on the parts’ theoretical life cycle. With vehicle health and diagnostic data, the operator is now provided with a real-time understanding of the whole power system, enabling them to make informed mission-critical decisions as needed, utilize the full operating capacity of the system, and potentially experience less time out of the field. Maintenance costs are lower, as well.”
Decisions made easier through fault monitoring
“If the systems have the performance information relating to the PSU, a decision can be made to prioritize the critical functions supported by the unit,” Jefferies says. “If the functions are mission-critical, ongoing operation would be allowed regardless of the effect on the PSU. Circuit-health monitoring avoids users having to take the unit out of service and test it on a bench; aside from the financial implications and system down time, continuous monitoring is a more valid way of testing, often giving more insight into the failure modes and interaction with the rest of the system.
“This tends to be found more with custom power supplies, rather than standard power supplies, because it is a specific feature,” he continues. “That capability generally needs to be tailored into a certain application.”
Standardization paves the way for flexibility
Standardization is not completely out of the picture, however. Manufacturers are still following the SWaP requirements set by the Department of Defense (DoD). For example, the VITA 62 standard still acts as a guideline for power supplies that support the VITA 62 slot on VPX backplanes and brings COTS components into power-supply modules. The perk about setting a standard is that engineers are able to not worry about the basics.
“We have been seeing a lot of airborne applications – both fixed-wing and rotary helicopter – going toward the newer VPX platforms,” D’Erasmo notes. “We are part of the VITA 62 committee; we finished updating the first specification for the VITA 62 specification. We see a lot of requirements from military customers asking for VPX products.”
There’s the addition to the VITA requirements which outlines communications – many customers want those capabilities of the VITA extension,” Garofolo adds.
“Everything we do is COTS. Our VPX is COTS. We repackage our designs into various custom form factors. Our customers are looking for high reliability,” Hovdestad says. “I’m part of the VITA 62 committee, where we are attempting to make an open standard, so anyone can buy, plug it into a system, and play.”
However, “our customers are looking for flexibility, to be able to change this and that and enhance what they like,” he continues. “They want standard, but they also want flexibility.” Engineers at Behlman Electronics have developed the VPXtra 100CD-IQ, which is designed to power Open VPX modules and is also VITA 62-compliant (Figure 1).
Behlman’s VPXtra 1000CD-IQ has the capability to monitor all input and output voltages as well as input/output current. “It gathers information from the entire system. If it has a temp issue or input problem, it collects and reports that information,” Hovdestad says.
NAI’s VPX57-31, a 3U DC/DC VPX product, includes remote error sensing, current share, and a built-in EMI filter. Engineers designed it to have VITA 62-compatible outputs, signaling, user programmability, inter-integrated circuit (I²C) communication, and temperature monitor (Figure 2).
“The 3U VPX power supply has a 270 volt DC (VDC) input,” D’Erasmo says. “The 270 VDC is used by aircraft. They take the AC and rectify right down to 270 DC. They’ll have an AC distribution system where they can put 270 into the power supply and we’ll make the voltage as they need for the rest of the system. The input and the features that we put in this power supply – programmability, BIT, temperature monitor, current share, higher efficiency – all come in a small package that’s 400 to 500 watts.”
NAI designs are also 100 percent discrete component designs, which “gives us a lot more flexibility to address special needs because we are not confined to a certain footprint of a brick. We can lay things out, we can reuse proven parts of a circuitry, and we can add new features a lot easier. We do nothing with prepackaged bricks,” he adds.
Testing challenges come with software
While the software that monitors power supplies’ faults benefits the users, giving them the ability to know exactly what is wrong, it can bring additional testing requirements in systems that are deemed safety-critical by the government.
As of right now, “Software has been mainly restricted to fault reporting and simple ON/OFF control and sequencing; this may change, however,” Jefferies says.
Installed software will be different from every manufacturer. “Customers need a standard,” Hovdestad explains. “The software from the manufacturer may be different, and so we need software standardization.”
Unlike with VITA 62, there are no set guidelines for software in power supplies. Engineers can innovate and take it to the next level, but within the boundaries the DoD has set, it could prove difficult. “We haven’t observed requirements for software control over PSUs in terms of altering output voltages on the fly,” Jefferies notes.
“In the military environment, introducing software and firmware triggers additional design hurdles and the requirement for testing becomes onerous,” he continues. “Once you start to build software into these units, you start to get into a vicious cycle: You bring digital control, which then brings the complication of certifying this software, which is a requirement all its own.”