Constant switching frequency techniques for sliding mode control in DC-DC converters

Sliding mode is a very effective control strategy for switch mode DC-DC converters. However, its widespread adoption has been hampered by some of the drawbacks inherent to this control technique. Among these, the most important is apparently the varying operating frequency, which can cause electromagnetic-interference (EMI) problems. This problem is particularly critical in portable devices (e.g. smartphones, e-readers) where it is highly desirable that the DC-DC converters operate at a constant switching frequency to avoid interferences with other parts of the system. Several methods have been proposed in previous literature to stabilize the operating frequency of sliding mode controllers. In this paper, some of the most promising techniques are evaluated and applied to a specific test-case, i.e. a Buck converter for a wireless system. A detailed model of the DC-DC converter has been developed in order to obtain realistic results. The system parameters have been chosen to reflect an actual commercial application.