Analysis of a Smith-predictor-based-control concept eliminating the right-half plane zero of continuous mode boost and buck-boost DC/DC converters

It is pointed out that the small-signal transfer function of a boost or a buck-boost converter shows a zero located in the right-half complex plane for continuous operation. This zero makes the stabilization of the system considerably difficult. The authors use a boost converter as an example to show that application of the principle of linear prediction (as originally proposed for the control of systems with dead times) yields the mirror image of the control circuit zero. This shift of the zero into the left-half s-plane is achieved with unchanged location of the poles. Thereby the small signal transfer function is split into two parts: a phase-minimum system and a nonphase-minimum system. The latter can be interpreted as a linear Pade approximation of a dead-time element. For the design of a robust control system it is necessary to investigate the shift of the poles of the closed system depending on the change of the operating point. How the predictor influences the small- and large-signal system disturbance responses for changes of the load and for input voltage changes is also analyzed