Digital control of DC/DC converters driving constant power loads in vehicular systems

Multi-converter power electronics based power systems are being increasingly used in many applications such as telecommunication systems, sea and undersea vehicles, international space station, aircraft, electric vehicles, hybrid electric vehicles, and fuel cell vehicles, where reliability is of prime concern. The number of power electronic converters in these multi-converter electrical power systems varies from a few converters in a conventional land vehicle to tens of converters in advanced aircraft, to hundreds of converters in the international space station.; In many advanced applications, power electronic converters need to be tightly regulated. From the output perspective, this property is highly desirable. However, since power electronic converters are efficient, tight regulation of the output makes the converter appear as a constant power load (CPL) at its input side. Dynamic behavior of constant power loads is equivalent to negative impedance and, therefore, can result in instability of the interconnected power system. Hence, stability of the power electronics intensive systems is a significant design challenge because of the potential for negative impedance instability.; In order to mitigate the problem of negative impedance instability, Pulse Adjustment, a novel fixed frequency digital control technique, for converters operating with constant power loads is presented in this dissertation. 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 pulse width modulation (PWM) scheme. A comparator compares actual output voltage with the reference voltage and then switches between the appropriate states. Therefore, the digital control task is to deliver 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. The proposed technique is applicable to all types of converters in all modes of operation. In addition to this theory and its analytical explanation, mathematical models as well as, simulation and experimental results of the proposed control technique, being applied to DC/DC converters, are presented in this dissertation.