DC-DC conversion in electric vehicle chargers can require a single or multiple stages depending on both electrical architecture and amount of processed power. When isolation is provided by an output stage, a unidirectional isolated DC-DC converter is required. Among the possible candidates, the LLC resonant converter and the phase shifted full-bridge (FSFB) converter show several advantages which has made them preferred choices in recent literature. This paper compares the efficiency of both converters on equal basis under the variable load conditions imposed by a cycle of the conventional constant-current constant-voltage (CC-CV) charging protocol. To support the study, scale-down experimental prototypes of both converters have been implemented and evaluated in laboratory showing the superiority of the LLC resonant converter for almost the entire range of operation.

This paper presents the detailed design of an active damping system for the stabilization of an open-loop boost converter in constant-power load (CPL) operation. The reported work analyzes the steady-state regime of the interconnection of a boost converter supplying a CPL, and a loss-free resistor (LFR) in series with the converter input port (SLFR) performing the active damping. The LFR behavior is obtained by peak current mode control (PCMC) imposing proportionality between the steady-state average values of current and voltage in the SLFR input port. The isolated SEPIC fulfills the topological constraints of the interconnection and is selected to implement the SLFR. Finally, PSIM simulations and measurements from a 500 W prototype are in good agreement with the theoretical predictions and illustrate the system stabilization around the specified steady-state operating point for different values of the CPL power.

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.

Small grid-connected PV-systems are quite usual in domestic roofs, but urban integration is still an open issue for wind systems. Similarly to grid PV systems, direct grid injection in a wind system requires two stages, a PFC boost rectifier and a grid-tie inverter. Nevertheless, although a buck inverter is a common choice in many grid PV systems, this topology imposing a minimum DC-Link voltage complicates the boost stage design, because the voltage variation range of a wind alternator, greater than the variation margin of a PV-array, would be absorbed only by the first converter. Consequently, we propose to share the voltage gain between both processor stages, using step-up voltage inverter instead of a buck one. In this work, boost and buck-boost based inverters are analyzed, and finally, a sliding mode controlled boost inverter with bipolar operation is proposed. To demonstrate the feasibility of this proposal, some relevant experimental results from a 1kW inverter prototype are given.

A battery-supplied, DC-HID lamp ballast, inspired on the Loss Free Resistor (LFR) concept is presented here. It consists of two stages. The first one, a boost converter, behaves like a constant power source. The second one, a switched capacitor boost converter is the ignitor circuit. The cascade connection of both converters results in a transformerless ballast able to reach a voltage of 6 kV from 12 V batteries. Among the ballast advantages we find: no light flickering, warm-up time reduction, no aging effects on lamp power, easy dimming control, and absence of acoustic resonance (AR) problems. The proposed system is compared with other existing solutions in the literature. After, the ballast dynamics, at both operation modes, is analyzed and simulated. The results achieved with one DC-HID lamp of 250 W demonstrate experimentally the feasibility of the proposed approach, where extreme voltage gains are achieved without a transformer. Besides of the expected functions of ignition and steady-state operation, the proposed circuit also includes other usual ballast features as diverse protections.