Philip T. Krein

Sensorless current mode control-an observer-based technique for DC-DC converters

Sensorless current mode (SCM) control is an observer method that provides the operating benefits of current mode control without current sensing. SCM has significant advantages over both conventional peak and average current-mode control techniques in noise susceptibility and dynamic range. The method supports both line and bulk load regulation, and reduces control complexity to a single loop. The static and dynamic performance of SCM are analyzed and verified experimentally for DC-DC converters. Performance in continuous and discontinuous modes compares favorably to conventional techniques when noise is not a factor, but is significantly better when noise and wide load ranges are a concern. The SCM method encompasses one-cycle control as a special case; the general SCM method is introduced here as a public domain control technique.

Dynamic maximum power point tracker for photovoltaic applications

A dynamic process for reaching the maximum power point of a variable power source such as a solar cell is introduced. The process tracks maximum power nearly cycle-by-cycle during transients. Information from the natural switching ripple instead of external perturbation is used to support the maximizing process. The method is globally stable for DC-DC power converters, provided that a switching action is present. A prototype boost power converter that uses this method for control can follow power transients on time scales of a few milliseconds. This performance can be achieved with a simple analog control structure, which supports power processing with minimum loss.

Continuous-time optimization of gate timing for synchronous rectification

Synchronous rectifiers, which use a controlled MOSFET in place of a standard p-n or Schottky rectifier, are an important technology for low-voltage power converters. Conventional control techniques for synchronous rectification are often very conservative, however, leaving room for improvement. This paper presents a method for monitoring current flow to adaptively optimize the relative timing of two gate signals for a buck converter with synchronous rectification. Theoretical development is given, along with experimental results for two low-voltage converters.

Real-time optimization of dead time for motor control inverters

A correlation-based control technique was used previously to optimize dead time in synchronous rectifier-based buck converters. Here, the correlation method is applied to the problem of optimizing dead time in motor drive inverters. The approach works on each inverter leg. It optimizes dead time to minimize input current either to each leg or to the inverter bridge as a whole. This in turn minimizes switching loss as current commutates between inverter devices. The approach is shown to be stable whenever switching action takes place. An experimental implementation is given. Results show a significant reduction in switching loss for the test inverter.