Sensorless Current Sharing Analysis and Scheme For Multiphase Converters

Current sharing control in multiphase converters is essential for stable and safe operation under variable conditions or applications. It is usually used to maintain equal or desired current sharing between converter phases. In conventional current sharing schemes, this requires the sensing and processing of each phase current through a current sharing/balancing controller, which adds complexity, size and cost to the converter design. In most cases, conventional schemes are usually based on achieving a preset current sharing ratio between phases (usually equal current value among different phases), assuming that the design of phases is known (or symmetric in the case of equal sharing ratio), which may not result in achieving the optimum efficiency. Moreover, the accuracy of achieving the preset current sharing ratio is sensitive to the current sensing accuracy in all phases, which requires careful and tedious calibration of sensing circuitries. Furthermore, when digital controller is used, in order to achieve equal current sharing or desired current distribution among different phases, more analog-to-digital converters (ADCs) are required to obtain digital information on equivalent phases´ currents. In this paper, theoretical analysis results are presented to derive or prove a sensorless current sharing method. The analysis is further expanded to reveal the boundary conditions that result in not achieving the desired current sharing ratio. For example, it provides the conditions under which certain phases may carry negative current, resulting in overloading the other phases. The presented method is described and verified with experimental results from a proof of concept prototype based on digital controller implementation.