Design of Loss-Free Resistors Terminated at a Generic Nonlinear Static Load

Modern DC-DC power conversion represents an important challenge because connected loads are not purely resistive as it has been conventionally considered. Furthermore, the corresponding power converters perform functions which are not limited to regulate either a specific output voltage or output current. One of these new functions is the transfer of a regulated power to different types of loads, which emerge in the context of microgrids and electric vehicles, in which the sliding-mode control (SMC) is an important actor because of its versality, robustness and systematic design. This paper presents SMC of a boost converter operating as a loss-free resistor (LFR), which supplies a constant power to the parallel connection of three canonical elements, namely, a constant power load (CPL), a constant current load (CCL) and a dc voltage source with internal resistance. The studied load is defined as a generic nonlinear static load (GNSL). The subsequent analysis of the connection of the controlled power converter and the GNSL reveals the existence of a single equilibrium point, which is unconditionally stable. This feature is preserved when the GNSL is particularized in the single load cases of battery, current source or resistor, and in all cases of two-element and three-element load combinations. The exception is the supply of a single CPL, which results in an infinite number of equilibrium points with marginally stable behavior. Simulation and measurements in a 1 kW prototype are in perfect agreement with the theoretical predictions.