Guillermo O. Garcia

Switching Control Strategy to Minimize Dual Active Bridge Converter Losses

A switching control strategy to control the power flow and minimize the total power losses of the dual active bridge converter topology is proposed in this paper. The control strategy consists of driving the bridge with the largest DC voltage to generate a three-level pulsewidth-modulated (PWM) voltage waveform. This PWM is ruled by two manipulated variables: the phase shift between the primary and secondary transformer voltages and the modulation index. These variables are calculated using an algorithm that is deduced on the basis of particular calculation and analysis of converter losses, which are also presented in this paper. An experimental prototype was implemented to validate the theoretical analysis and feasibility of the proposal. The experimental results revealed that the overall efficiency of this converter can be improved up to 10% using the control strategy instead of the conventional one.

Optimization of power management in an hybrid electric vehicle using dynamic programming

Hybrid electric vehicles are those powered from two different sources. Typically, they are equipped with an internal combustion engine, and also with an electrical storage system, such as a bank of batteries or ultra-capacitors. While braking, these vehicles may convert kinetic energy to electrical energy and send it back to the electrical storage system (regenerative braking). The whole vehicle system may be abstracted to one consisting of two energy sources, one of them rechargeable and the other consumable, that feed or receive energy from an energy consumer. A centralized control strategy is required to define the instantaneous power flows among these three main components. In this work, we derive the power split between the two sources such that fuel consumption is minimized, while the vehicle performs a given velocity cycle. Bounds on the power flows from both sources are considered. There is also a constraint of an integral nature that arises from the fact that the energy of the electrical storage system must remain between proper limits, in order to avoid physical damage. The problem is posed as a finite horizon dynamical optimization problem with constraints and solved by a dynamic programming (DP) approach. The hybrid electrical vehicle being developed in the University of Rio Cuarto, Argentina is taken as the case study.

Modulation strategy to operate the dual active bridge DC-DC converter under soft switching in the whole operating range

A new modulation strategy that allows operating the dual active bridge (DAB) dc-dc converter under soft switching in the whole operating range is proposed. This strategy is ruled by imposing a certain modulation index in one of the two bridges and a phase shift between the transformer primary and secondary voltages. Moreover, the proposed algorithm reduces the reactive power and thus reducing the converter conduction losses. An experimental prototype was implemented and some experimental results are presented to validate the theoretical analysis. The experimental results reveal that the overall efficiency of the DAB topology can be improved up to 20% by implementing the proposed modulation strategy instead of the conventional one.

An efficient controller for an adjustable speed induction motor drive

The induction motor (IM) is a high-efficiency machine when working close to its rated operating point. However, at torques and/or speeds far from the rated values the efficiency is greatly reduced. In this work a new approach is proposed that minimizes the total copper and iron losses in a variable speed and/or torque IM drive, while keeping a good dynamic response. This method is based on a simple IM model that includes iron losses. The model, which only requires the knowledge of conventional IM parameters, is referred to a field-oriented frame. Using this model, the IM losses are quantified and an algorithm, based on a field-oriented scheme, is deduced. Simulation and experimental results are presented to validate the proposed method. >

Extending the ZVS Operating Range of Dual Active Bridge High-Power DC-DC Converters

A switching control strategy to extend the soft-switching operating range of the dual active bridge (DAB) dc-dc converter under the zero-voltage-switching (ZVS) operating mode is proposed. The converter topology consists of two active bridges linked by a high-frequency transformer. One drawback of this strategy is that soft-switching is only possible in a restricted converter operating region. A novel pulse width modulation strategy to extend the conventional soft-switching operating mode region and its analysis are presented in this paper. Experimental results are given in order to validate the theoretical analysis and practical feasibility of the proposed strategy.

Adaptive Observer for Sensorless Control of Stand-Alone Doubly Fed Induction Generator

A sensorless control strategy for a doubly fed (wound rotor) induction machine working in variable-speed stand-alone power systems without using mechanical sensors is presented in this paper. Stator voltage magnitude and frequency are regulated using two field-oriented control loops. A Luenberger observer is used to estimate the stator flux, while an adaptive scheme modifies the rotor position required in the stator flux estimation. Stator voltage magnitude and frequency control loops behave very well for steady state as well as for transient states like startup, speed variations, or electric load changes. Experimental results are presented to validate this proposal.

Online Model-Based Stator-Fault Detection and Identification in Induction Motors

In this paper, a model-based strategy for stator-interturn short-circuit detection on induction motors is presented. The proposed strategy is based on the generation of a vector of specific residual using a state observer. The vectorial residual is generated from a decomposition of the current estimation error. This allows for a fast detection of incipient faults, independently of the phase in which the fault occurs. Since the observer includes an adaptive scheme for rotor-speed estimation, the proposed scheme can be implemented for online monitoring, by measuring only stator voltages and currents. It is shown that the proposed strategy presents very low sensitivity to load variations and power-supply perturbations. Experimental results are included to show the ability of the proposed strategy for detecting incipient faults, including a low number of short-circuited turns and low fault current.

Field-oriented controlled induction generator with loss minimization

In this paper, a strategy to control an induction generator (IG) working with variable speed and load is presented and discussed. An inverter and a field-oriented controller are used in order to excite the induction machine (IM) efficiently, minimizing copper and iron losses, and to regulate the generated voltage. The proposed IG system is a stand-alone (not grid connected) system. It is used to produce electrical DC energy, to charge a battery bank, and/or to supply DC loads with maximum efficiency. A laboratory setup, based on a conventional 4 kW squirrel-cage IM, has been implemented. Experimental results are presented in order to validate the proposed strategy.

Induction generator controller based on the instantaneous reactive power theory

A novel control strategy for a stand-alone induction generator (IG), working with variable speed and load, is proposed. The IG is simultaneously excited by a capacitor and an inverter. The capacitor provides the rated reactive current needed to excite the IG while the inverter adds the reactive current needed to regulate the IG output voltage. The control strategy is based on the instantaneous reactive power theory. A 4 kW laboratory prototype has been built to validate the proposal and experimental results are presented.

A 2-D model of the induction machine: an extension of the modified winding function approach

A new method to calculate the inductances of induction machines considering axial nonuniformity is proposed. The proposed method, an extension of the modified winding function approach, allows considering nonuniformity due to skew and static and dynamic air-gap eccentricity. Theoretical fundamentals and experimental results that validate the proposed method are presented.