Jose Antonio Cobos

A multi-level boost topology based on a flying capacitor is compared in this work with the hybrid, multi-level, partial power processing topology already presented in the literature for use as a dc/dc stage in 1500-V, two-stage, grid-connected PV systems. Different variations of the resonant stage of the hybrid topology are analyzed and compared in terms of losses, volume and complexity. Full multivariable optimization is conducted for the multi-level boost topology with different number of levels and for all the analyzed variations of the resonant stage of the hybrid topology. Appropriately rated new classes of 650-V and 900-V WBG devices are included in the optimization algorithm. Results of the comparison show that losses of both topologies are in the same range, while hybrid, partial power processing topology provides lower occupied volume. All the analysis related to the resonant stage of the hybrid topology is confirmed by detailed and comprehensive measurements of two prototypes of 4kW of nominal and 7kW of maximal power with reported euro-efficiency of 99.79% and 12.1 kW/kg of specific power. Additionally, all the loss models applied in the optimization algorithms presented in this paper are confirmed by detailed measurements, thermal calibration and finite element thermal simulations of the wide bandgap devices and inductor designs employed in this work.

The design and optimization of coils for Inductive Power Transfer (IPT) systems is an iterative process conducted in Finite Element (FE) tools that takes a lot of time and computational resources. In order to overcome such limitations in the design process, new empirical equations for the evaluation of the self-inductance and mutual inductance values are proposed in this work. By means of a multi-objective genetic programming algorithm, the self-inductance, the mutual inductance and the coupling factor values obtained from FE simulations of IPT link are accounted by analytical equations, based on the geometric parameters defining the IPT link. The behavioral modeling results are compared with both FE-based and experimental results, showing a good accuracy.

This work presents a hybrid converter combining soft-charged switched capacitors and an autotransformer with DC current in the windings, optimized for 4:1 fixed voltage gain conversion (DCX) for high output current. By adding an additional output inductor, it can also regulate the output voltage to lower than of the input voltage by changing the duty cycle. The switched capacitors voltage and the two winding currents in the transformer are auto-balanced. Non-resonant operation of the circuit enables DC current in the windings and simplifies both transformer and circuit design. Experimental results for 48V-12V DCX operation achieve 98% peak efficiency and 97.8% full load (250W) efficiency. Regulation by using the output inductor is verified experimentally up to 48V-6V (8:1) voltage step down.

The analytical calculation of winding loss in gapped magnetic components is complex, and numerical analysis tools, such as finite elements analysis (FEA) tools, are commonly needed to characterize the windings. As FEA tools are used, the required design time of these types of components increases greatly when many simulations are needed to select the appropriate component for a given application, and simple analytical models become necessary to reduce the design time. In this paper, some analytical approaches for winding loss calculation in gapped magnetic components are reviewed and a general two-dimensional equivalent method, which aims to consider the frequency effects in conductors in a simplified manner, is proposed afterward. Due to its simplicity, it can be integrated into design and optimization tools in order to evaluate the influence of the air gap over the winding loss even at the early stages of the design process. The presented model shows good agreement with FEA simulations and measurements.

This paper reviews and classifies representative types of “Differential Power Processing, DPP” architectures, focusing on the aspect of how the processed power is reduced with DPP. Comparing to existing review works on this topic, this paper provides new viewpoints from three perspectives: (1) the differential power Pdiff at both architecture level and converter level is discussed. For the calculation of the total processed power in a power architecture, instead of summing up the output power Pout delivered by the DPP converters, we account for Pdiff inside the DPP converters, because direct power exists not only at the architecture level, but also at the converter level, so the power processed in a converter may be lower than Pout. (2) The VA area modeling is applied to the DPP architectures to illustrate and visualize the processed power in the power architectures and converters, thus analyzing and comparing them at high level. (3) The processed power of different DPP architectures is compared quantitively with statistical analysis for varied operating situations.

In this paper, analysis and design of a 3.3kW isolated single-stage three-phase buck-type rectifier for aircraft applications is presented. The operating principle and modulation method of the proposed rectifier are introduced. The advantageous Zero-Voltage Switching (ZVS) feature in all of the switching transitions is analyzed. A comparison with the VIENNA Rectifier III is done, being different both in the phase-leg implementation and the modulation sequence. A detailed rectifier design guideline is discussed and losses estimations are provided aiming at reaching 93.7% overall efficiency including the EMI filter. Simulation waveforms are presented. Finally, experimental results obtained with the designed 3.3kW hardware demonstrator are provided. The results verify achievement of ZVS in all of the switching transitions from full load down to 50% of nominal load, while exhibiting 1.9% THDi and 0.9996 PF at nominal power, ultimately showing very good agreement to the simulation results.

This paper presents a 6.78-MHz wireless power transfer (WPT) system, which is configured to automatically cancel the reactance in primary and secondary. In the WPT system, the detuning caused by the parameter variation, the implementation of the frequency control, and components tolerance will decrease a lot the system performance especially in very low coupling (k=0.06) and low power applications. The delivered power is sensitive to the reactance under low coupling and high-frequency conditions, accordingly, a novel self-adaptive WPT system to automatically retune the resonance is proposed. The proposed concept uses a Synchronous Series Compensator (SSC) instead of a capacitor in series with the secondary to tune it, which can automatically cancel the reactance caused by the inductor, non-resistive load or frequency variation, hence increases the system performance in terms of delivered power and efficiency. A prototype has been built and tested experimentally to validate the feasibility of the proposed concept. A constant power of 1.8W can be transmitted with 50% overall efficiency at a coil separation distance of 1.5cm between the printed-circuit-board transmitter (3×3 cm2) and receiver (1×2 cm2) under wide detuning conditions, being 0.95 the ratio between distance and the equivalent diameter of receiver.

This work presents a non-isolated hybrid topology targeting at 4:1 fixed ratio and high output current applications. This topology can be regarded as a compact integration of switched capacitor and autotransformer. The switched capacitors are soft charged and the two winding currents in the autotransformer are auto balanced. The transformer has quasi-DC current with negligible AC winding losses. To further study the performance of the transformer in the proposed circuit, the transformer is simulated with different current waveforms, and the results show that with quasi-DC current the winding losses do not increase with switching frequency, and they are at least two times lower than the losses generated from sinusoidal or square current. The proposed circuit is measured at 24V-6V step-down and up to 25A output current, achieving 96.7% peak efficiency. The same transformer is also tested in a full bridge testbench to compare winding losses with square current by measuring its temperature.

This paper presents a control linearization technique for a Single-Phase Single Stage (SPSS) inverter with multiple modulation strategies. The power topology is based on a FCML inverter, and the control is based on the plant inversion. The proposed technique allows decoupling the control of the input current and the output voltage, which simplifies the control in two ways: first, the control of both variables is independent and second, the controllers are independent of the modulation applied, thanks to the plant inversion. This control is implemented in an FPGA. Since the converter operates at variable frequency, two different data acquisition alternatives are explored: sampling at variable frequency (once per switching cycle) or sampling at constant frequency (higher than the switching frequency). The proposed control is validated by simulation and experimental results with a 1 kVA prototype.