Complex military systems require efficient power electronics
High density power electronics with high efficiencies – typically more than 90 percent – are becoming the defacto requirement for high-end mission critical military platforms such as radar, fighter jets, UAVs, and weapon systems where size, weight, and power are limited. Meanwhile, Gallium Nitride based RF components are beginning to populate military RF applications.
Whether for unmanned or manned platforms in the air or on the ground, innovation in power electronics is driven by reduced requirements for Size, Weight, and Power (SWaP). However, it’s the last part of that acronym – power – that really enables the first two or, to be more precise, efficient power through higher density. Signal processing for modern military radars, weapon systems, avionics, Unmanned Aerial Vehicle (UAV) payloads, missile control, etc., use processing power that generates tremendous amounts of heat. Therefore the more efficient the power electronics – 90 percent is the norm today – the less heat that needs to be dissipated and the more performance system integrators can pack into the same footprint each time they upgrade.
“When discussing power electronics design trends there always seems to be variations on the same theme – increased efficiency of power and greater densities,” says Kai Johnstad, Product Marketing Manager at Vicor in Andover, MA. “There is also a need for smaller packages for portable applications, which also drives up efficiency demands on the primary power source.”
“The key characteristics military customers want from power components are high efficiency, high density, and high reliability over a long life. Very high reliability (high-rel) is needed in power electronics for aviation and military systems where products such as missiles that may sit in storage for as long as 20 years, but then still need to work when placed in mission critical applications,” says Martin Schlect, President and CEO of SynQor in Boxborough, MA. “The density of a power supply goes hand-in-hand with its efficiency, but often designers are limited by how much heat can dissipate from a product. For high-rel applications SynQor offers its MilQor series of high-rel DC-DC converters and EMI filters, which come in multiple input voltage ranges, have no opto-isolators, and operate at a fixed frequency. For military applications that do not have demanding high-rel requirements the company has a product family called Mil-COTS that includes DC-DC power converters, EMI filters, and PFC modules.”
“We see increased demand for more power in existing industry standard packages as opposed to smaller converters,” Schlect says. “Customers do not necessarily want a smaller physical brick, they want more power in the same physical footprint they are working with today. In other words they want more density in the same size and weight they have now. To accomplish this, the efficiency of the converter has to increase since heat removal from the package is the limiting factor.
“The density of a power supply goes hand in hand with its efficiency, but often designers are limited by how much heat can dissipate from a product,” he continues. “For customers there is a lot of expense associated with inefficiency, especially when it comes to removing heat from the board or system. Heat removal is a big endeavor as the heat removal system often adds weight. However, if your power supply is more efficient then you will not need that thick cold plate or a fluid/liquid cooled system. Improved efficiency also solves weight issues for systems running off batteries. They need to run for a certain amount of time and if you can get 10 percent more efficiency from a power supply your battery can last 10 percent longer. Therefore the need to carry extra batteries decreases, reducing the weight. This also applies to UAVs, which can stay on station longer for persistent surveillance missions if their power electronics are more efficient.”
“Radar, especially airborne radar with its SWaP and high efficiency requirements, is becoming a growing market for power component products, which has not traditionally been the case as power components were not ideal for the demands of dynamic loading common in radar systems,” says Tom Curatolo, Director of Global Defense and Aerospace Business for Vicor. “In radar, applications pulling large currents for various duration during the radar’s transmit and receive mode places a major demand on power supplies. Typically the transmit mode is short and requires a big burst of current and the power supply has to deliver that from a state of no load to near full load conditions. In the past, power supplies needed a huge amount of capacitance to address the demand for instantaneous current draw.
“Vicor’s Factorized Power Architecture leverages the Sine Amplitude Converter’s ability to deliver virtually instantaneous current by locating it at the point of load with the ZVS Buck-Boost regulator upstream where its control loop for regulation is not limiting the delivery of current for demanding dynamic loads,” Curatolo continues. “This is accomplished with the VI Chip’s fixed frequency PRM and VTM chip set. It enables designs to have efficient power components and also take advantage of capacitance multiplication – where less capacitance can be used on the input of VTM for the same impact that large levels of capacitance were previously used at the load, leveraging higher reliability. This means more PCB real estate and lower cost.” (See Figure 1.)
The power requirements for the Next Generation Jammer program are very similar to those for radar systems. “An offshoot of the radar market is the jammer,” Curatolo says. “The Next Generation Jammer program is an airborne jammer that has a variety of parameters that have to be met for the power section such as small size and light weight, which leads to efficiency. More than 90 percent efficiency is the baseline for the program.”
The VITA 46 standard – also known as VPX – is driving many signal processing intensive applications in military applications such as radar, sonar, image processing, etc. However, the power supplies for VPX systems lacked a standard to make them work with multiple VPX vendor solutions. Thus VITA 62 was created to enable that interoperability, and products based on this standard are growing in demand just like VPX systems.
“There has been much discussion around VITA 62 and OpenVPX in these circles. Embedded computing companies continue to use bricks in their power supplies for open computing standards,” Vicor’s Curatolo says. “Embedded designers are putting more and more power on these cards in a fixed form factor and are requiring more power density from their DC-to-DC converter devices.”
“We see the most steady demand for VPX, VME, and VXI power supplies,” says Gerry Hovdestad, Director of COTS Engineering at Behlman Electronics in Hauppauge, NY. Behlman Electronics offers a VITA 62 and OpenVPX compliant DC-to-DC power supply called the VPXtra 1000CM series. The 6U device is a conduction-cooled, switch mode unit designed for military and industrial applications. It uses SynQor bricks and provides 600 watts of DC power via five outputs, Hovdestad says.
Engineers at Advanced Avionic Technologies Corp. (AATC) in Medford, NY, are also developing a line of 3U and 6U VPX power supply products, says Russel Kittel, Business Development Manager at AATC. The 3U device will target reduced SWaP applications, he adds. “We can produce five to six variants on the same power supply by employing a toolbox approach, allowing the customer to pull from various subcomponents to meet his design requirements,” Kittel says.
SynQor, which already provides its Mil-COTS bricks to many embedded computing companies for their VITA 62-based power supply modules, is developing their own VPX power supply assembly, using their Mil-COTS devices. “We already have a VME-based power assembly, but are focused on VPX going forward as it is in demand for many military applications,” SynQor’s Schlect says. “We are releasing a 3U VPX assembly that will be standard, with six outputs running at 500 watts and a 6U VPX assembly running at 1,000 watts.”