Dipanjan Das with advisor P. Krein

Power delivery to multi-core processors is becoming increasingly challenging with decreasing transistor sizes and, thereby, their operating voltages. With the increase in core number in each processor, the power requirements tend to remain the same with each new generation of microprocessors, and handling transient performance requirements along with efficiency has become much more difficult at lower voltages. Significant improvement in energy efficiency can be achieved by stacking the processor cores in series and regulating the core voltages by differential power processing (DPP). However, for practically achieving higher efficiency than the conventional parallel-connected processor cores, other (software) overheads are required to balance the power consumption of each processor core (such as communication between different voltage domains, scheduling processes to aid voltage balancing, etc.). A trade-off between these additional overheads and the actual power needed to be processed by the DPP converters must be optimized.

Presently control schemes for improvement in the dynamics of the DPP voltage regulator are being developed. One particular topology suitable for voltage regulation of a series-stack of digital loads is the hierarchical element-to-element topology, as shown in the schematic in Figure 1. It has been established that this topology provides improved dynamic performance compared to other non-isolated topologies in regulating stack voltages. Implementation of the bidirectional DPP converters has been one area of focus. A bidirectional multiphase buck/buck-boost converter with asymmetric current sharing was developed for improved efficiency over a wide load range. Higher light-load efficiencies of individual DPP converters is expected to significantly improve system-level efficiencies. Importance of light-load efficiency in the context of bidirectional power converters in various DPP applications is being highlighted and the applicability of the developed light-load controller to other series-stacked DPP topologies is being investigated. This research project is funded by the Grainger Center for Electric Machinery and ELectromechanics.

Figure 1: Schematic for hierarchical element-to-element topology