Digitally controlled DC-DC converters for distributed power systems

Project abstract

The main aim of the project is to develop digitally controlled DC-DC converters for distributed power systems (DPS). The steady reduction of supply voltages (down to the Volt range), along with the steep increase of load currents (from 80 A to 190 A for microprocessors) and the quest for higher efficiency, demand for high-performance modular power supply systems. Digital architectures outperform traditional analog ones in a market that requires increasingly complex and reconfigurable controllers, sophisticated power management strategies, low costs and short time-to-market.
The research activities include:

• design of novel fully digital and mixed-signal control architectures;
• design of high-efficiency converter topologies;
• design of integrated converters in mixed technology (Bipolar-CMOS-DMOS (BCDVI)).

Research activity is carried out in collaboration with ST Microelectronics (Agrate and Castelletto) and the Universities of Udine and Padova. The monolithic integration of a digital controller for a six-phase buck converter in BCD VI technology is almost completed. This controller will be compatible with a “PMbus” communication protocol. At the same time we are developing a flexible digital platform including a DSP core and a DPWM converter, which can be easily configured for the control of different types of converters (symmetric Half bridge, Phase shift full bridge etc.).

Project results

A key result of this project is the development of mixed synchronous/asynchronous digital architectures that have been exploited for the control of non-isolated DC-DC converters (multiphase buck for VRMs, boost) and isolated DC-DC converters (full and half bridge). These digital controllers have been implemented on FPGA, showing an excellent immunity to quantization effects and dynamic performance comparable to that of the best analog controllers.

Most important publications

• Saggini, S.; Ghioni, M.; Geraci, A. “An innovative digital control architecture for low-Voltage, high-current DC-DC converters with tight voltage regulation” IEEE Transactions On Power Electronics, vol. 19, 210 - 218, 2004 (this paper received the “PELS TRANSACTIONS PRIZE PAPER AWARD” in 2004).
• W. Stefanutti, P.Mattavelli, S.Saggini, M.Ghioni, “Autuning of digitally controlled buck converters based on relay feedback” IEEE Transactions on Power Electronics, in press (2006).

Patents

• S. Saggini, M. Ghioni, A. Geraci, F. Villa “Digital controller for DC-DC switching converters”, US Patent n. 2004/005151A1, Mar. 18 2004.
• G. Garcea, M.Ghioni, C. Beia, S. Saggini, F. Villa, “Method for controlling a full bridge converter with a current-doubler and a corresponding digital controller”, European Patent n. EP 05022044.1, 10.10.2005.