Negative impedance stabilizing pulse adjustment control technique for dc/dc converters operating in discontinuous conduction mode and driving constant power loads

Multiconverter power-electronics-based power systems are being increasingly used in advanced vehicles. Stability of these power electronics-intensive systems is a significant design consideration because of the potential for negative impedance instability. In this paper, in order to mitigate the problem of negative impedance instability, pulse adjustment, which is a novel fixed frequency digital control technique for converters operating with constant power loads (CPLs), is presented. This novel digital control approach treats the converter as a digital system and achieves output voltage regulation by choosing high- and low-power pulses instead of using conventional pulsewidth modulation scheme. A comparator compares the actual output voltage with the reference voltage and then switches between the appropriate states. Therefore, the digital control task is to deliver the right amount of energy to the converter by right numbers of state operations so that the average power delivery matches the required power. It needs few logic gates and comparators to implement this digital control, thus making it extremely simple and easy to develop using low-cost application specific integrated circuits. It is simple, cost effective, and dynamically fast. In this paper, a model to analyze the dc/dc buck-boost converter that is controlled by the pulse adjustment approach in the discontinuous conduction mode is derived. Stability of the buck-boost converter driving CPLs is analyzed using the introduced model. Furthermore, comprehensive sensitivity analyses of applying the pulse adjustment method to control dc/dc converters that are loaded by CPLs are presented. In addition, this paper gives design considerations to assess performance and stability robustness of the pulse adjustment method to control buck-boost converters that are loaded by CPLs. Analytical, simulation, and experimental results are presented to describe and verify the proposed technique. Index Terms--Constant power loads (CPLs), control, modeling and analysis, multiconverter, negative impedance instability, power converters, stability, state-space averaging (SSA), vehicular systems.