High-voltage fixed-ratio bus converters have been around for some time, adequately serving the needs of intermediate bus architectures (IBAs). But the emergence of a variety of new high-voltage, high-power dc-dc market applications is driving demand for a new generation of bus converters with input ranges higher than 400 V.
High-Voltage DC Applications
With power consumption and the cost of power increasing exponentially, datacenters around the globe are rapidly migrating toward high-voltage dc power distribution because of their increasing need to substantially reduce power distribution losses and improve overall system efficiency.
In the event of an ac line power outage, the dc distribution system can run directly off of a battery plant eliminating the need for the dc-ac inverter and its associated losses. Regulatory standards are prompting telecom facilities to incorporate strategies that provide overall system efficiency, density, and scalability.
In a recent study, Lawrence Berkeley National Laboratories highlighted the benefits of using high-voltage dc power distribution schemes in datacom facilities versus the use of traditional 480-V ac power distribution systems. Similar needs are also emerging in the industrial market, green commercial buildings, and other such applications.
Open industry associations like the EMerge Alliance and the Electric Power Research Institute (EPRI) are jointly promoting the energy efficiency benefits of using high-voltage dc versus ac power distribution in green buildings, datacenters, and datacom facilities.
Likewise, to minimize the use of copper for high-power transmission, three-phase circuits are popular in datacenters and datacom facilities in Europe. Such applications revolve around three-phase distribution at 380 or 415 V ac with a basic ac-dc front end connected to each phase. The high dc voltage generated from this scheme is distributed throughout the system for further conversion.
High-voltage dc power distribution is gaining traction in the military and commercial electric-vehicle/hybrid electric-vehicle (EV/HEV) market. Traditionally operated by a stack of Li-ion type batteries, application designs for these vehicles are incorporating power distribution systems driven by input voltages in the 600-V range. As a result, such systems must incorporate bus converters that down-convert the high-voltage input from the batteries to 28-V dc output as a bus for powering other functions in the vehicle.
The military, which has stringent standards for ruggedness, transient response, safety, and other factors, has generated specifications that define the characteristics of the 600-V dc electrical system. Labeled MIL-PRF-GCS600A and approved by the Department of Defense (DoD), these specifications provide a system of requirements for the electrical characteristics and safety of high-voltage power distribution subsystems in military ground vehicles.
Possible Solutions
Power suppliers can meet the needs of these emerging applications in a number of ways. First, today’s high-voltage intermediate bus converters can provide a good starting point for the development of new bus converters that meet these requirements. High-voltage dc power distribution in any of the applications mentioned must offer greater power density and efficiency.
The technology exists within existing high-voltage fixed-ratio dc-dc solutions to pave the way for the development of bus converters that can handle up to 600-V input applications. There are currently 360- to 400-V input range fixed-ratio bus converters that may be upgraded to handle 600-V input while maintaining high conversion efficiency, power density, and power throughput.
Another quick, cost-effective, and proprietary approach from Vicor is to stack the inputs of high-voltage off-the-shelf dc-dc converters in series. By using field-proven power blocks designed for high efficiency, density, and overall performance, the end solution can be realized with a minimum of design effort.
Even though this approach seems straightforward, it may involve more than just connecting two modules’ inputs in series. With high-voltage power distribution, one must address key issues such as reliability, safety, and compliance for creepage and clearance.
With voltages as high as 600 V, safety becomes paramount. The designer must ensure that dc-dc converters used in these systems meet the isolation requirements of the application. If needed, new transformers would have to be designed to replace the existing ones in the converters to meet the new isolation requirements of higher-voltage applications. In addition, the need for miniaturized high-voltage fusing and protection components is critical from the safety perspective.
In addition, minimizing electromagnetic interference (EMI) and curbing transients and surges at high voltages raises its own set of engineering challenges. In fact, tackling such issues in high-voltage circuits can present a significant barrier to entry for most power-supply vendors.
With the advancement of power components such as higher-voltage miniaturized switching elements with a better figure of merit and high-breakdown voltage capacitors, existing designs can be upgraded to meet the dc-dc conversion needs of high-voltage applications with 400-V and higher dc input voltages. The concept of selectively strapping the primary of two power trains in series or parallel to accommodate wide input ranges is another Vicor proprietary approach worth exploring.
Ultimately, power-supply makers need to understand more fully the market opportunities and then choose to either re-examine and rework existing approaches or develop a brand new power scheme to enable power system designers to efficiently and cost effectively meet these new power challenges.