A switched-inductor (SL) multi-cell boost converter is analyzed in this paper for a high-voltage gain application, stepping up a dc voltage from 36 V to 380 V in the first stage of a photovoltaic (PV) conversion chain. A fast maximum power point tracker (MPPT), processing the system input voltage, is used to extract the maximum power from the PV generator regardless of atmospheric conditions. A single sliding-mode control (SMC) loop forces the PV generator voltage to follow the maximum power point (MPP) voltage provided by a Perturb and Observe (P&O) algorithm. The sliding-mode analysis uses the equivalent control approach to demonstrate that the linearized ideal sliding dynamics are unconditionally stable. Theoretical predictions are corroborated by simulations and experimental measurements of the system under step-type changes in input irradiance and output load. The MPPT performance is experimentally evaluated against two classical approaches applied to a canonical boost converter: a current-based SMC and a voltage-based PWM. Both approaches track the MPP current and voltage, respectively, as given by the P&O algorithm. The proposed system outperforms the two classical systems, showing a better tracking accuracy.

This paper outlines a detailed design methodology for a digital multi-loop control strategy for an electric vehicle (EV) battery charger based on interleaved buck converters. The proposed control strategy implements the constant-power constant-voltage (CP-CV) protocol. Specifically, a first outer loop regulating the output voltage, enforces the CV phase, and a second outer loop controlling the battery power imposes the CP phase. An inner loop implements the democratic current sharing technique for the regulation of the inductor currents. Proportional-integral (PI) controllers are designed via the root locus method using a discrete-time model that considers parasitic resistances on the converter. A multi-rate sampling strategy is employed to follow conventional rules of cascade control systems ensuring that each control loop operates at the appropriate sampling frequency according to its dynamic characteristics. The entire proposal is validated through numerical simulations performed in PSIM© software.

In this paper, a control strategy is proposed to implement the constant power (CP)-constant voltage (CV) charging protocol for the ultrafast charging of electric vehicles (EV). The battery charger consists in a four-phase interleaved buck converter, with a multiple-loop controller in cascade configuration. Each of the three loops has its dedicated proportional integral (PI) controller for the control of a specific variable of the system. Namely, i) an inner loop to control the inductor current of each leg, ensuring equal distribution of the current between the four phases, ii) a first outer loop regulating the output voltage and providing the reference of the inner loop, and iii) a most outer loop to regulate the battery power by modifying the reference of the voltage loop. The correct operation of the system is validated by means of numerical simulation performed using the switched model implemented in PSIM©software.

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.

A constant power (CP)-constant voltage (CV) protocol for battery charging is implemented in a conventional boost converter with output filter (BOF) by imposing loss-free resistor (LFR) behavior during the CP phase. To compare on equal basis the performance of the new CP-CV technique with the classical constant current (CC)–CV protocol, the latter is also implemented in the same power stage. The CC phase in BOF is attained by imposing a G-gyrator of type II behavior to the converter. A versatile controller uses the same voltage regulation loop for both protocols during the CV phase and a slightly different loop for the CP and CC phases. The latter loop is based in both CP and CC phases on the sliding-mode control (SMC) of the input inductor current of BOF, which in steady-state is made proportional to the input voltage in the LFR case or to the output voltage in the gyrator implementation. To compensate for the slow variations of the battery voltage during the CC phase, a proportional-integral (PI) current regulator has been added in the gyrator realization. The comparison of the corresponding experimental results shows identical behavior in both approaches in the measured waveforms, component stress, efficiency and external temperature. The simplicity of the CP-CV implementation based on LFR allows the extension of the proposed protocol to other hard-switching converters.

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.

The unstable ON and OFF state trajectories of a boost converter supplying a constant power load (CPL) are appropriately combined using sliding-mode control (SMC) with a suitable surface to yield a stable trajectory that reaches a specified equilibrium point. Selecting the optimum surface involves a comparative analysis among potential candidates in terms of stability, disturbance rejection, conduction losses and inrush current. The performance as switching function of polynomials of degree zero (non-zero constant), degree one (affine function) and degree 2 (quadratic function) are analyzed in depth to conclude that the affine function leads to the best static and dynamic results. The theoretical predictions are verified by means of simulations and measurements in a prototype.

This paper presents a systematic approach to synthetize constant power loads using switching converters under sliding-mode control. The generation of sliding motions is analyzed in converters with a series inductor in the input port and a switching function representing the error between the input power and a suitable power reference. The analysis establishes the existence conditions for sliding-mode and the stability of the resulting ideal dynamics. Simulation and experimental results verifying the theoretical predictions in boost, Ćuk and SEPIC converters illustrate the proposal. The design procedure yields a simple, economical and small-size prototype that can be useful in the experimental validation of converters supplying constant power loads.

An implicit first-order non-dimensional model of open loop dc-dc boost converter operating in Discontinuous Conduction Mode (DCM) with Constant Power Load (CPL) is derived. Analysis of this model shows that successive period doubling bifurcations and subharmonic oscillation take place when certain parameters such as the switching period, the operating duty cycle and the load power are varied. The resulting typical period-doubling route to chaos is confirmed by numerical simulations under the mentioned operating conditions.

This paper presents a strategy to control the dynamic power sharing in a hybrid energy-storage system (HESS). The HESS is composed of a battery array of 24 V, a supercapacitor module of 16 V and 2 DC-DC converters allowing the connection of the system to an extra low voltage DC (ELVDC) bus of 48 V within a hybrid microgrid. The proposed strategy consists in a nested loop controller per converter enforcing charge and discharge regimes of the energy storage devices (ESD). The charging modes of the ESD are independent, whereas the discharging modes are coupled. Namely, the supercapacitor module injects power and regulates the ELVDC bus voltage, while the battery array injects the energy into the bus to maintain the levels imposed by the supercapacitor module until its contribution is cancelled. Furthermore, the battery array slowly injects the additional energy needed to restore the optimal supercapacitor voltage. Operation modes and transitions of the HESS control strategy are synthesized in a secondary control level. The entire proposal is validated through simulation results with scenario-based tests, where the modes of operations and the transient response to different loads and boundary conditions are verified.

Switching converters may exhibit unsuitable inrush current and an unacceptable transient response during startup. This phenomenon is mainly due to saturation of the duty cycle at the initial switching cycle and is more pronounced with nonlinear loads and reactive components and in the presence of unavoidable delays in the feedback. This paper proposes solutions to mitigate such problems in a digitally sliding-mode controlled dc-dc boost converter loaded with a constant power load and taking into account nonlinearities in the inductor. Numerical simulations from a detailed switched model validate the proposed approach and experimental measurements verify the mathematical analysis and the numerical simulation showing a good agreement.

In this paper, a systematic approach is presented to synthesize constant power loads using switching converters under sliding mode control. The study shows that switching converters with a series inductor at the input port may behave as an instantaneous constant power load under sliding-mode control based on a nonlinear switching surface representing the error between the input power of the converter and a suitable power reference. With the proposed approach, the synthesis and design of constant power loads is simple. The synthesized loads can offer an inexpensive alternative to analyze switching converters feeding constant power loads such as in dc distributed power systems and electric vehicles. The theoretical derivations are validated by numerical simulations performed on the detailed switched model of boost, SEPIC and Cuk converters.

This paper deals with the global dynamical analysis of a self-oscillating resonant inverter which is based on switching between two symmetrical circuit configurations. The analysis predicts coexisting steady-state solutions, which are increasingly relevant for low values of the quality factor of the resonant circuit, thus likely driving to an improper system operation. A repelling sliding region is found to be connected with the two unstable limit cycles that split the phase plane in three basins of attraction. To avoid the presence of multiple steady-state solutions, a viable solution consisting of a modification of the control is proposed and validated by numerical simulations.

A combination of two switching surfaces for the sliding-mode control of a boost converter feeding a constant power load is presented. It allows the converter start-up with small inrush current and permits the output voltage regulation by minimizing the effect of external perturbations on the steady-state operation. The resulting sliding-regime for each switching surface is analyzed and the conditions for the existence of sliding-mode are derived. PSIM simulations are in perfect agreement with the theoretical predictions.

Commercial photovoltaic microinverter topologies are normally composed of two stages: a step-up dc-dc stage and a step-down dc-ac stage. Nevertheless, to achieve high-ratio conversion, a high frequency transformer is used in the dc-dc stage, resulting in a bulky configuration with a high cost of implementation. To minimize these issues, a single stage boost inverter is proposed, composed by two bidirectional boost dc-dc converter. The control of this topology is complex due to its high non-linearity behaviour. Therefore, this paper presents a control methodology based on Finite Control Set Model Predictive Control (FCS-MP) algorithm with predictions of the system variables through the inverter model and an optimization process. Each boost dc-dc converter of the inverter is regulated to achieve an output signal composed of the sinusoidal wave with a dc bias. The main features of the boost inverter and predictive control are analysed. Simulations are shown in order to validate the proposed control and the converter for grid-connected PV applications.

The dynamic behavior and stability analysis of a quadratic boost converter for high conversion ratio applications is addressed. After studying the stability of the system by using the monodromy matrix, a closed form stability condition is used for predicting the boundary of subharmonic oscillation in the system in terms of the duty cycle and the slope of the ramp modulator. The derived theoretical conditions are validated by numerical simulations using a system-level switched model obtaining a good matching between the results. This work provides a convenient means of stability boundary determination in the parameter space hence facilitating the design of quadratic boost converters.

This paper discusses the influences of non-ideal current sensor on the stability and subharmonic oscillation boundaries in current mode controlled switching converters. First, a general-purpose simplified model is built applicable to any switching converter working in continuous conduction mode. Then, a steady-state asymptotic Fourier-series-based method is applied to obtain a boundary condition in the frequency domain and expressed in terms of the system state-space matrices. Using the Poisson sum formulae, this condition is transformed into the time-domain. The approach is applied to dc-dc switching converters with current mode control (CMC) taking into account finite current sensor bandwidth. Design-oriented equations describing the occurrence of subharmonic oscillations are derived for any single-switch dc-dc converter. These equations are expressed explicitly in terms of operating converter parameters and duty cycle making them directly applicable for design purposes. Some problems with influence of the limited bandwitdh of the current sensor on the ramp compensator design and system dynamics are discussed, along with some proposed solutions.

The significant improvements that have been recently achieved in HBLEDs technology in terms of lifetime, luminous efficacy, and power rating, make these devices one the most promising candidates to replace conventional light sources in various residential and industrial applications, despite their high cost. The efficiency requirement should be completed by means of the voltage conversion stage by performing Power Factor Corrector. In this paper we consider the problem of Power Factor Corrector and output current regulation for a group of HBLEDs by using a Ćuk converter under a Sliding-Mode Control which must be ultimately implemented by a hysteretic comparator to limit the switching frequency to practical values. However, with a constant hysteresis width, the system exhibits harmful harmonic distortion in the input line current waveform. Therefore, a variable hysteresis window is used thereby avoiding this distortion near the zero crossing of the input current. Using the Ćuk converter under a Sliding-Mode Control with variable hysteresis window, the converter will be forced to behave as a Loss Free Resistor. Simulation and experimental results are presented in this paper to demonstrate the functionality of the proposed technique.

In this paper, a system consisting of two cascaded dc-dc boost converters under sliding-mode control, working as loss free resistors, connected to a PV panel is studied. The modeling, simulation and design of the system are addressed. First, an ideal reduced-order sliding-mode dynamics model is derived from the full-order switched model taking into account the sliding constraints and stability analysis is carried out. It is shown that the cascade connection of boost-based loss free resistors can be a good solution for the impedance matching in PV systems with the standard 380 V dc bus voltage.

In this work a Loss-Free Resistor (LFR) based on a semi-bridgeless boost rectifier is synthesized using sliding mode control. A better efficiency can be obtained from bridgeless boost converters because of their reduced conduction losses in comparison the traditional PFC boost converters. Although different bridgeless topologies have been presented, the semi-bridgeless topology presents less common-mode noise and its practical implementation is more suitable. Sliding mode control is proposed to achieve a LFR behaviour and, therefore, its application in power factor correction is possible.

The synthesis of a Digital Loss-Free Resistor (DLFR) based on a boost converter in Pulse-Width-Modulation (PWM) operation is presented. The proposed control law is obtained by applying discrete-time sliding mode control theory on the discrete-time model of the boost converter to control the input current. The control law calculates the duration of the switch on-time at the beginning of each switching period in order to reach the proposed discrete-time sliding surface. The resulting digital Loss-Free Resistor (DLFR) can be used as a preregulator for power factor correction in one-phase circuits. Simulations are in good agreement with theoretical predictions.

Microgrids consist of distributed electrical generation architectures which have some instability problems due to the cascade interconnection of the converters and their related negative impedance effect. In electric power distribution system, a point of load converter behaves as constant power load (CPL) which result in a well known destabilizing effect. In this paper, different strategies that have been used to eliminate this undesirable behavior will be discussed. Then, an alternative approach based on sliding mode control (SMC) and using canonical elements for power processing will be proposed to stabilize cascaded converters. The proposed approach will be illustrated using a system consisting of two cascaded boost converters behaving as Loss Free Resistors (LFR) supplied from a PV panel and connected to a 380 V dc bus of a microgrid. It will be shown that using LFRs and SMC could be a good strategy to stabilize cascaded boost converters. The theoretical results are verified using simulations and experimental measurements.

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.

In this paper a SEPIC converter, operating as an AC-DC adaptation stage, is studied. It is shown that the system has high efficiency and good power factor being able to work both as a boost (step-up) or buck (step-down) converter. To impose a loss free resistor (LFR) behavior, sliding-mode control is applied. It is shown that the LFR acts as an ideal rectifier with a power factor near the unity. The output of the system is used to power supply a group of HBLEDs, and its brightness (luminosity) is controlled by the output current. The design and the models are validated by mathematical, numerical and experimental results.

The synthesis of a boost-converter-based loss-free resistor (LFR) operating in PWM is presented. The resulting LFR can be used as a preregulator for power factor correction in one-phase circuits. PSIM simulations are in good agreement with the theoretical predictions.

The main drawback of the discrete time models reported in the literature for predicting nonlinear phenomena in power electronic circuits is their complexity which make their use in system design very minted. The availability of approximated discrete time models that retain the accuracy of the exact model and at the same time makes the system design simple would give new perspectives in the control design of such systems. In this paper we give a detailed analytical study of a two-cell DC-DC buck converter for high voltage applications by using discrete time formulation. Different operating modes are possible and they can be modeled by a unified discrete time model. A digital controller is considered for the system. This controller includes a dynamic compensator in the form of digital integrator for the output variable regulation. An approximated discrete time model in the form of current recurrence equation which accurately describes the dynamical behavior of the system is derived. This model is use to predict instabilities when some design parameters are varied. The Jury test is applied to the characteristic polynomial in order to obtain boundary of stability in the design parameter space. Numerical simulations confirm the theoretical predictions

In this work, the describing function technique is applied to a two-rules fuzzy controller for switching regulators, in order to establish the scaling factors boundaries for which the system presents an oscillatory behavior, thus facilitating the fuzzy controller design. Simulation results for a boost converter are presented to illustrate the method.