Martin Ordonez

Improvements in Boundary Control of Boost Converters Using the Natural Switching Surface

A boundary control scheme for boost converters with enhanced performance using the natural switching surface (NSS) is presented in this paper. The derivation of the switching surface (SS) is performed in the normalized domain to obtain a general geometrical representation that is applicable to any combination of boost converter parameters. The resulting SS provides an excellent dynamic response during start-up and sudden load changes, achieving steady state in only one switching action. In order to illustrate the characteristic features and the superior performance of the natural SS, a geometrical analysis is fully developed and compared to other recent SSs. A design example is presented to illustrate the benefits of the normalization technique, and the qualities of the natural SS are confirmed with simulation and experimental results of a 30 W, 10 V/22 V converter.

Applying Response Surface Methodology to Small Planar Transformer Winding Design

Planar transformers provide a light-weight and low-profile solution for power electronic converters with highly reproducible parameters and simple manufacturability. Parasitic inductances, capacitances, and resistances in planar magnetics are difficult to model due to the complex interactions between the physical winding arrangement of each layer and the core geometry (track width, air gap, clearance, etc.). These nonlinear and multivariate magnetic devices play a key role in defining the performance of traditional, soft-switching, and resonant converters by ruling behaviors such as ringing, self-resonant frequency, conduction losses, and the current rate of change in these converters. In this paper, a methodology for determining parametric models for leakage and magnetizing inductance, inter- and intrawinding capacitances, and the winding resistance of small planar transformers is presented using a variety of winding arrangements. The models are employed to shape the winding design to control parasitic elements in order to optimize soft-switching and resonant converters. A central composite design based on the design of experiment methodology is employed on finite element simulations to provide the comprehensive models. Results from physical verification on a planar Ferroxcube ER18/3.2/10-3F3 core set are provided and show excellent correlation between models and verification tests. The method is later employed to effectively design an LLC resonant converter, which is also experimentally verified to illustrate the benefits of the proposed method. The methodology can be employed to characterize and design planar transformers and to predict their performances as part of a variety of power electronic converters.

High Performance Boundary Control of Boost-Derived PFCs: Natural Switching Surface Derivation and Properties

This study presents the application of the natural switching surface (NSS) to control single-phase power factor correctors (PFCs). The proposed boundary control scheme provides tight regulation and enhanced dynamic characteristics. The analysis is performed in the normalized geometrical domain to provide valuable graphical insight and generality. Low-frequency ripple effects are included as part of the converter reference to improve its behavior in steady state and load transient operation. In addition to the complete characterization of the system, a method to obtain fixed-frequency operation is presented by employing discrete-step references. The resulting switching surface (SS) provides fast output voltage regulation and input current dynamics, and low input harmonic distortion, achieving steady state in only a few switching actions under sudden load disturbances. The enhanced qualities of the natural SS are confirmed with simulation and experimental results of a 300 WPFC.

Integrated magnetic design of small planar transformers for LLC resonant converters

Integrating magnetic parasitics in the design of LCC resonant converters provides a solution to reduce parts count and increase power density. This paper provides an efficient design procedure for small planar transformers which integrate transformer leakage inductance and magnetizing inductance into the resonant tank by employing an accurate parasitic prediction model. Finite element simulations were used to create the models using Design of Experiment (DoE) methodology. A planar transformer prototype was designed and tested within a 2.5W LLC resonant converter and results under different operating modes are included to illustrate the resonant behaviour and to validate the presented design procedure.

Boundary control of buck-boost converters: normalized trajectories and the Natural Switching Surface

This paper derives the natural trajectories for buck-boost converters and defines the Natural Switching Surface (NSS) control law to obtain enhanced transient responses. The study performed in the normalized geometrical domain provides understanding of the transient behavior of the converter and generality to the equations. The analytical framework proves that the converter can be operated at the physical limits. As a result, an excellent dynamic response during start-up and large load disturbances is achieved using the resulting Switching Surface (SS), accomplishing steady state in only one switching action. The analysis presented in this paper completes the theory of control using natural trajectories for basic topologies - buck and boost, with the addition of buck-boost. A design procedure, along with experimental results are presented to confirm the benefits of the normalization method and illustrate the qualities of the Natural Switching Surface.

DSP-based marine current turbine emulator using a 3-phase inverter

This paper introduces a novel DSP-based emulator that employs a 3-phase current controlled inverter to reproduce the dynamic behavior of marine current turbines. The proposed marine current emulator provides a flexible platform to modify the resource conditions, test different combinations of the turbines parameters, and supervise the system variables in real time. These characteristics allow the emulation of steady and transient electrical behavior of turbines under various operating conditions and scenarios. The emulator is, therefore, a valuable R&D tool for this emerging and promising power generation technology. The elimination of mechanical parts and the simplicity of the design, two innovative aspects of the proposed architecture, introduce several advantages: low cost, free-maintenance, portability, and safety (characteristics often required in laboratory settings). Experimental results of the marine current emulator are presented to validate the system and illustrate the operation of the high-bandwidth inverter employed to drive its output. The emulator can be used for sizing analysis, site evaluation, testing power converter topologies, and evaluating control strategies.

Introducing the Natural Switching Surface for reference frame systems: Three-phase boost PFCs

This paper presents the boundary control of three-phase boost rectifiers, bringing unprecedented dynamic response to reference frame based systems. A novel approach using the Natural Switching Surface (NSS) in the normalized αβ domain is introduced, providing superior dynamic performance and low input harmonic distortion. The derivation of the natural trajectories in the aforementioned domain is first performed to gain insight into the behavior of the system, yielding a generalized analysis that is valid for any possible combination of converter parameters. The target operating trajectory produced by the varying references is also described and characterized. Based on the previous analysis, the control laws that rule the behavior of the active rectifier are proposed, achieving constant-frequency operation as part of the control scheme. The resulting strategy provides excellent transient behavior, reverting to steady state in a few switching cycles when the PFC is subject to sudden load disturbances. Experimental and simulation results of a small scale 50W converter are presented to verify the enhanced properties of the NSS.

Swinging bus technique for ripple current elimination in Fuel Cell power conversion

A swinging bus scheme is investigated in this work to eliminate undesirable low frequency ripple current reflection in Fuel Cells (FCs). The swinging bus is thoroughly characterized under various loading conditions to establish a behavioral model. As a result, a general control scheme and signal processing for buck- and boost- derived power converters is obtained. A digital filter in the form of a Moving Averaging Filter (MAF) proves to be a fundamental component of the control loop, a significant practical advancement in control for low frequency ripple elimination. A formal mathematical demonstration is included and experimental results are presented to validate the technique and illustrate its benefits.

Boundary control for isolated topologies: The Natural Switching Surface for Full-Bridge ZVS

This paper presents the use of a high performance boundary controller for a classic isolated topology: the Full-Bridge ZVS. An enhanced dynamic response is obtained by employing the Natural Switching Surface (NSS), which is thoroughly derived in the normalized geometrical domain. The advantages of the normalization are the simple graphical representation, the generality for any combination of parameters, and the mathematical simplicity. Recently, non-isolated basic topologies have benefited from advancements in boundary control. The analysis and derivation in this work bring the benefit of outstanding dynamic performance to this isolated topology. As demonstrated in this work, the relationship between the leakage and output filter inductances make possible the formulation of the natural trajectories for isolated converters. The resulting SS provides an excellent dynamic response during start-up, reference change, and sudden output loading conditions. Experimental results are presented to illustrate the characteristics and advantages of the control scheme, and the converter operation with fixed switching frequency.

Boundary control of boost-derived PFCs using the Natural Switching Surface: Derivation and enhanced properties

This work presents the application of the Natural Switching Surface (NSS) to control Power Factor Correctors (PFCs). The proposed boundary control scheme provides tight regulation and enhanced dynamic characteristics. The analysis is performed in the normalized geometrical domain to avoid inaccuracies and provide generality. Low frequency ripple effects are included as part of the converter reference to improve its behavior in steady state and load transient operation. In addition to the complete characterization of the system, a method to obtain fixed-frequency operation is presented by employing discrete-step references. The resulting SS provides an excellent dynamic response and low input harmonic distortion, achieving steady state in only a few switching actions under sudden load disturbances. The enhanced qualities of the natural SS are confirmed with experimental results of a 300 W PFC.