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Boundary conduction mode (BCM) or critical conduction mode (CrM) converter implementations have become very attractive since the introduction of gallium nitride (GaN) switches. This operation mode is characterized by an inductor current that operates in the boundary between continuous (CCM) and discontinuous conduction modes (DCM) making the converter switching frequency dependent on the converter operating conditions. The advantage of this operation mode versus CCM is achieving zero current switching (ZCS) conditions for the converter rectifier, which makes it possible to use silicon (Si) based rectifiers without having a penalty due to reverse recovery issues. Moreover, the main switch turn-on loss is decreased due to ZCS conditions and valley switching operation. However, the penalty is an increased current stress in the circuit, and an increased main switch turn-off energy loss. Implementation of synchronous rectifier in BCM converters makes it possible to achieve zero voltage switching (ZVS) conditions by extending the synchronous rectifier conduction time after zero current condition in the inductor. High power density, high efficiency MHz implementations have already been demonstrated in the literature; however, none of the proposed solutions solves the controllability issues of the synchronous rectifier switch. This work proposes and validates a ZVS self-regulating control method for BCM converters operating in the MHz switching frequency range.

High efficiency and low cost power converters for interfacing energy storage have become critical in renewable energy systems. In this paper a fractional charging converter (FCC) is proposed to reduce power rating as well as cost of the dcdc converter for hydrogen production by alkaline electrolyzer cells. The FCC configuration only processes the partial power resulting from the voltage difference between the source and the energy storage element. Moreover, the converter employed in such configuration can be either isolated or non-isolated, which simplifies topology selection. An analysis and comparison of two dcdc topologies using a high-frequency transformer based on component stress factor (CSF) is performed to determine the optimal solution for the evaluated application. Based on the results of the CSF analysis, and due to its capability of handling wide input voltage, the isolated full-bridge boost (IFBB) converter is designed, built and tested. Experimental results prove the feasibility of the fractional charging configuration with a reduction of 80% of the power rating compared to the traditional interconnection, which implies a reduction in cost, weight and an increase in efficiency. The converter’s maximum voltage gain achieved is 25 and the highest ½½½measured system efficiency is 98.2 %.

Designing a switched-mode power supply includes the calculation of the loss in all of the different components: inductor, transformer, switches and capacitors. By combining all of the loss calculations, and providing a graphical user interface to the designer, the designer is able to get an understanding of the loss distribution and thereby the influence of each component on the complete design.

This paper presents an analysis and comparison of dc/dc switched-mode power supplies (SMPS) for energy storage systems in partial power processing (PPP) configuration. The advantage of this configuration is that the SMPS only processes the partial power resulting from the voltage difference between the source and the energy storage element, thus allowing for a reduction of the converter power rating. Selection of an appropriate topology for a given system configuration is the key factor in achieving high efficiency power conversion. An analysis and comparison of dc/dc topologies based on component stress factor (CSF) is performed to determine the optimal solution for the evaluated application. Based on the results of the CSF analysis, a dc/dc converter is designed, built and tested. Experimental results prove the feasibility of the PPP configuration with a reduction of the 80% of the power rating compared to the traditional interconnection, which implies a reduction in cost, weight and an increase in efficiency.

A theoretical loss analysis is presented for GaN switches, for which conduction and switching losses are considered, and for planar transformers, where winding and core losses are considered. The analysis is then used to make a comparison of the losses in the partial parallel isolated full bridge boost converter and the isolated full bridge boost converter.

This paper presents two configurations of dualinput (DI) or three-port (TPC) isolated dc-dc converters for hybrid renewable energy systems such as photovoltaics and batteries. These two converters are derived by integrating an interleaved boost converter and a single-active bridge converter with an ac inductor as a power interfacing element or phase-shift softswitching converter with an output dc inductor. Both converters are controlled by a pulse-width modulation and phase-shift hybrid modulation scheme. The two converter topologies are, even though quite similar from the topological and control perspective, distinct in operation principles, voltage/power transfer functions, loss distributions, soft-switching constraints, and power efficiency under the same operating conditions. Moreover, the inductor design differs greatly between these two cases. In this paper, a comprehensive comparison is given for the first time and thereby the corresponding design tradeoffs are discussed. Finally, a laboratory 1 kW prototype is constructed and tested to verify the theoretical analysis

A review of high voltage gain, high efficiency bidirectional dc-dc topologies is presented. Each converters primary benefit is highlighted, and a summary of all the converters is presented. It is observed that voltage gains higher than 20 is only achieved with topologies using a transformer. The average efficiency of the topologies is slightly lower for isolated topologies. Different strategies are utilized in most of the topologies in order to achieve the high voltage gain, and high efficiency, for example charge pumps, resonant circuits, coupled inductors, and switching cells

This paper presents the design, modeling, and control of an isolated dc-dc three-port converter (TPC) based on an interleaved-boost full-bridge converter with pulsewidth modulation (PWM) and phase-shift control for hybrid renewable energy systems. In the proposed topology, the switches are driven by phase-shifted PWM signals, where both phase angle and duty cycle are the controlled variables. The power flow between the two inputs is controlled through the duty cycle, whereas the output voltage can be regulated effectively through the phase shift. The primary-side MOSFETs can achieve zero-voltage-switching (ZVS) operation without additional circuitry. Additionally, due to the ac output inductor, the secondary-side diodes can operate under zero-current-switching (ZCS) conditions. In this study, the operation principles of the converter are analyzed and the critical design considerations are discussed. The dynamic behavior of the proposed ac-inductor-based TPC is investigated by performing state-space modeling. Moreover, the derived mathematical models are validated by simulation and measurements. In order to verify the validity of the theoretical analysis, design, and power decoupling control scheme, a prototype is constructed and tested under the various modes, depending on the availability of the renewable energy source and the load consumption. The experimental results show that the two decoupled control variables achieve effective regulation of the power flow among the three ports.

In locations far from the equator achieving high conversion efficiency in low-power solar systems is challenging due to low solar irradiance levels. This paper presents a high efficiency three-port converter (TPC) for light-to-light (LtL) applications where no direct solar conversion is required. The separation of the power flows allows to replace the conventional solution of two cascaded converters into a single structure with shared components. A loss distribution analysis of the proposed structure is performed, which shows very good match with the experimental results. A prototype of the TPC demonstrates high efficiency in both power flow paths. At low irradiation level, the power flow from the photovoltaic panel to the battery shows a peak efficiency of 99.1% at at 1.5 W output power, and the LED driver stage presents a peak efficiency of 97.3% at 3 W output power.

This paper discusses some of the major challenges in the development of L2L (Light-2-Light) products. It’s the lack of efficient converter electronics, modelling tools for dimensioning and furthermore, characterization facilities to support the successful development of the products. We report the development of 2 Three-Port-Converters respectively for 1-10Wp with a peak efficiency of 99.1% at 1.5 W output power at PV to battery and almost similar characteristics for a 10-50 Wp. Furthermore, a modelling tool for L2L products has been developed and a laboratory for feeding in component data not available in the datasheets to the model is described. A living lab facility is realized to field test prototypes of L2L lighting products in their development state to validate the modelling tool and tweak the parameters in the system for optimized performance the product. Finally, the model was validated against a field test from the living lab over a four-day period with an offset of 5.3 %

Some major challenges in the development of L2L products is the lack of efficient converter electronics, modelling tools for dimensioning and furthermore, characterization facilities to support the successful development of the products. We report the development of 2 Three-Port-Converters respectively for 1-10Wp and 10-50 Wp with a peak efficiency of 97% at 1.8 W of PV power for the 10 Wp version. Furthermore, a modelling tool for L2L products has been developed and a laboratory for feeding in component data not available in the datasheets to the model is described.

DC microgrids or nanogrids have attracted increasing research interest in recent years. Therefore, as a critical component, dc-dc converters with multiple inputs are required. In this paper, a dual-input interleaved buck/boost converter is proposed and its corresponding power flow control methods are analyzed and designed accordingly. Furthermore, the design guidelines are discussed. Finally, in order to verify the validity of this study, the measurement results are presented.

This paper presents a performance evaluation and comparison of state-of-the-art low voltage Si MOSFETs for a stand-alone photovoltaic-LED Light to Light (LtL) system. The complete system is formed by two cascaded converters that will be optimized for a determined solar irradiation and LED illumination profiles. The comparison is performed based on dynamic characterization and evaluation of the devices energy loss at different current levels.

DC-DC converters for fuel cell applications require wide voltage range operation due to the unique fuel cell characteristic curve. Primary parallel isolated boost converter (PPIBC) is a boost derived topology for low voltage high current applications reaching an efficiency figure up to 98.2 %. This paper proposes a new operation mode for extending the input and output voltage range in PPIBC. The proposed solution does not modify PPIBC power stage; the converter gain is modified by short-circuiting one of the parallel connected primary windings in the topology. The change in operation mode divides by two the converter input-to-output voltage gain. This allows covering the conditions when the fuel cell stack operates in the activation region (maximum output voltage) and increases the degrees of freedom for converter optimization. The transition between operating modes is studied because represents a change in the converter steadystate conditions. A solution is proposed based on precalculation of the duty cycle prior to the transition.

This paper presents an an alysis and comparison of magnetics structures in a tapped boost converter for LED applications. The magnetic structure is a coupled inductor which is analyzed in a conventional wire-wound core as well as in a planar structure for different interleaving winding arrangements. The analysis is performed in term s of leakage inductance, winding capacitance and winding loss. Efficiency measurements are performed to verify the effect on the converter performance

This paper presents an analysis and comparison of isolated topologies for bidirectional fuel cell systems. The analyzed topologies are the dua l active bridge (DAB) and the isolated full bridge boost converter (IFBBC). The analysis is performed based on the component stress factor (CSF). Results highlight that the DAB has lower CSF than the IFBBC for narrow converter operating points. On the other hand the IFBBC presents a more homogeneous CSF over the entire converter operating range. Finally, experimental results obtained from a 30-80 V 80 A 6 kW 40 kHz IFBBC are presented. The converter achieves efficiencies up to 98.2% and 97.45% depending on the converter power flow.

PV-powered lighting systems, light-to-light systems (L2L), offer outdoor lighting where it is else where cumbersome to enable lighting. Application of these systems at high latitudes, where the difference in day length between summer and winter is large and the solar energy is low requires smart dimming functions for reliable lighting. In this work we have built a laboratory to characterize these systems up to 200 Wp from “nose to tail” in great details to support improvement of the systems and to make accurate field performance predictions.

A barrier for exploiting use of standalone solar lighting for the urban environment seem to be lack of knowledge and lack of available tools for proper dimensioning. In this work, the first part of the development of powerful dimensioning tool is described and initial measurements are presented.

This paper presents an isolated bidirectional dc/dc converter based on primary parallel isolated boost converter (PPIBC). This topology is an efficient solution in low voltage high power applications due to its ability to handle high currents in the low voltage side. In this paper, the converter has been modeled using non-ideal components and operated without any additional circuitry for startup using a digital soft-start procedure. Simulated and measured loop gains have been compared for the validity of the model. On-the-fly current direction change has been achieved with a prototype interconnecting two battery banks. A second prototype has been constructed and tested for supercapacitor operation in constant power charge mode.

The converter control scheme plays an important role in the performance of maximum power point tracking (MPPT) algorithms. In this paper, an input voltage control with double loop for a stand-alone photovoltaic system is designed and tested. The inner current control loop with high crossover frequency avoids perturbations in the load being propagated to the photovoltaic panel and thus deviating the operating point. Linearization of the photovoltaic panel and converter state-space modeling is performed. In order to achieve stable operation under all operating conditions, the photovoltaic panel is linearized at the maximum power point (MPP) and at the voltage and current source regions. A settling time under 1 ms is obtained which allows fast MPP tracking implementation.

Applications requiring wide input and output voltage range cannot often be satisfied by using buck or boost derived topologies. Primary paralleled isolated boost converter (PPIBC) [1]-[2] is a high efficiency boost derived topology. This paper proposes a new operation mode for extending the input and output voltage range in PPIBC. The proposed solution does not modify PPIBC power stage, the converter gain is modified instead by short circuiting one of the paralleled connected primary windings present in this topology.

In this paper state space modeling and closed loop controlled operation have been presented for primary parallel isolated boost converter (PPIBC) topology as a battery charging unit. Parasitic resistances have been included to have an accurate dynamic model. The accuracy of the model has been tested by comparing the calculated and measured loop gains. The designed controller has been implemented in a DSP based control circuit and stable operation of the converter has been achieved.