Mam Marcel Hendrix

Transformer-Coupled Multiport ZVS Bidirectional DC–DC Converter With Wide Input Range

Multiport dc-dc converters are particularly interesting for sustainable energy generation systems where diverse sources and storage elements are to be integrated. This paper presents a zero-voltage switching (ZVS) three-port bidirectional dc-dc converter. A simple and effective duty ratio control method is proposed to extend the ZVS operating range when input voltages vary widely. Soft-switching conditions over the full operating range are achievable by adjusting the duty ratio of the voltage applied to the transformer winding in response to the dc voltage variations at the port. Keeping the volt-second product (half-cycle voltage-time integral) equal for all the windings leads to ZVS conditions over the entire operating range. A detailed analysis is provided for both the two-port and the three-port converters. Furthermore, for the three-port converter a dual-PI-loop based control strategy is proposed to achieve constant output voltage, power flow management, and soft-switching. The three-port converter is implemented and tested for a fuel cell and supercapacitor system.

Three-Port Triple-Half-Bridge Bidirectional Converter With Zero-Voltage Switching

A three-port triple-half-bridge bidirectional dc-dc converter topology is proposed in this paper. The topology comprises a high-frequency three-winding transformer and three half-bridges, one of which is a boost half-bridge interfacing a power port with a wide operating voltage. The three half-bridges are coupled by the transformer, thereby providing galvanic isolation for all the power ports. The converter is controlled by phase shift, which achieves the primary power flow control, in combination with pulsewidth modulation (PWM). Because of the particular structure of the boost half-bridge, voltage variations at the port can be compensated for by operating the boost half-bridge, together with the other two half-bridges, at an appropriate duty cycle to keep a constant voltage across the half-bridge. The resulting waveforms applied to the transformer windings are asymmetrical due to the automatic volt-seconds balancing of the half-bridges. With the PWM control it is possible to reduce the rms loss and to extend the zero-voltage switching operating range to the entire phase shift region. A fuel cell and supercapacitor generation system is presented as an embodiment of the proposed multiport topology. The theoretical considerations are verified by simulation and with experimental results from a 1 kW prototype.

Line-Interactive UPS Using a Fuel Cell as the Primary Source

This paper proposes a line-interactive fuel-cell-powered uninterruptible-power-supply system. A three-port bidirectional converter connects a fuel cell and a supercapacitor to a grid-interfacing inverter. The system can operate in both stand-alone and grid-connected modes. Moreover, an active filtering function is integrated into the system. It is shown that a supercapacitor can serve as both an active and a reactive energy storage and can buffer the periodical low-frequency ripple in the requested power. For connecting the system to the utility grid, a high-performance single-phase phase-locked loop that incorporates an orthogonal filter is presented. Resonant controllers for both the voltage and current regulations eliminate steady-state error and implement selective harmonic compensation. Simulation and experimental results are provided to show the feasibility of the proposed system and the effectiveness of the control methods.

Pliant Active and Reactive Power Control for Grid-Interactive Converters Under Unbalanced Voltage Dips

During voltage dips continuous power delivery from distributed generation systems to the grid is desirable for the purpose of grid support. In order to facilitate the control of inverter-based distributed power generation adapted to the expected change of grid requirements, generalized power control strategies based on symmetric-sequence components are proposed in this paper, aiming to manipulate the delivered instantaneous power under unbalanced voltage dips. It is shown that active and reactive power can be independently controlled with two individually adaptable parameters. By changing these parameters, the relative amplitudes of oscillating power can be smoothly regulated, as well as the peak values of three-phase grid currents. As a result, the power control of grid-interactive inverters becomes quite flexible and adaptable to various grid requirements or design constraints. Furthermore, two strategies for simultaneous active and reactive power control are proposed that preserve flexible controllability; an application example is given to illustrate the simplicity and adaptability of the proposed strategies for online optimization control. Finally, experimental results are provided that verify the proposed power control.

Modeling and Analysis of Grid Harmonic Distortion Impact of Aggregated DG Inverters

This paper proposes an impedance-based analytical method for modeling and analysis of harmonic interactions between the grid and aggregated distributed generation (DG) inverters. The root cause of harmonic interaction/resonance problems is the impedance-network quasi-resonance between the effective output impedance of the inverter and the equivalent grid impedance at the connection point. Starting with the output impedance modeling of an inverter, a Norton model of the inverter is derived. Comparing with the switching model and the average model of the inverter, simulation results show the effectiveness of the model. This paper proposes that impedance limits should be specified and used as an extra design constraint for DG inverters in order to minimize the harmonic distortion impact on the grid. Assuming the impedance models of individual inverters and local loads within a distribution grid are known, especially in the case of new grids under construction, harmonic interactions between the grid and a certain number of DG inverters can be preliminarily estimated.

Acoustic Energy Transfer: A Review

Acoustic energy transfer (AET) is a relatively new form of contactless energy transmission that uses sound waves to wirelessly convey energy. In contrast to inductive coupling, it is suited for energy transmission over distances that are large in comparison to the transmitter and receiver dimensions. The frequencies that are used are low, minimizing losses and keeping the electronics simple. This review summarizes the work done on AET by various researchers.

Multiport converters for hybrid power sources

Multiport converters, a promising concept for hybrid power sources, have attracted increasing research interest recently. The use of a single power processing stage to interface multiple power inputs integrates power conversion for a hybrid power source. This structure removes redundant power stages that would exist in the conventional approach that uses multiple converters. The multiport structure is promising from the viewpoints of centralized control and compact packaging. The proposed basic bidirectional switching cells show several possibilities to construct a multiport converter. Several three-port topologies are discussed. Furthermore, based on the interleaving technology, topologies for higher power applications are also provided.

Control of grid-interfacing inverters with integrated voltage unbalance correction

This paper presents the control of a grid-interfacing inverter with integrated voltage unbalance correction. It is proposed to add an additional function to the inverter to decrease the negative-sequence voltage at the point of connection with the utility grid. Based on a symmetric sequence voltage decomposition and using an improved multi-variable filter, the grid-interfacing inverter intentionally absorbs a small amount of negative-sequence current from the grid, thereby helping to correct the negative-sequence voltage. Although the amplitude reduction contributed by each individual inverter system is small compared to the total negative-sequence component, grid-interfacing inverter modules can collectively achieve substantial results in the grid. The integrated function and proposed control has been verified in simulations and by experiments on a laboratory prototype.

Controlled HID Lamp-Ballast Interaction for Low-Frequency Square-Wave Drivers

High intensity discharge lamps are typically operated at low frequency to avoid damage from acoustic resonance. Accordingly, an electronic ballast normally comprises a buck converter to control the lamp current magnitude and a full-bridge to commutate the lamp current at a low frequency. In such a system, the negative dynamic lamp characteristic may interact with the power electronic driver may give a poorly damped response, sometimes resulting in an oscillatory lamp current. Furthermore, lamp aging and reduced power mode operation both tend to increase re-ignition voltage overshoot, which in turn may lead to reduced lifetime, or prematurely extinguishing lamps. In the present paper, a procedure for obtaining the small-signal dynamic characteristics of metal halide lamps is proposed. Using this dynamic model, the lamp-ballast interaction is simulated and analyzed. A fuzzy-logic control method is presented to cope with nonlinear behavior and improve the lamp-ballast performance. The simulation results are verified with practical measurements on a laboratory prototype

Contactless energy transfer through air by means of ultrasound

An alternative approach to the wireless transfer of energy is proposed, employing acoustic waves in air. Unlike conventional methods, acoustic energy transfer is able to achieve energy transfer at high efficiencies over distances that are large in comparison to the dimensions of the transmitter and the receiver. This paper gives an overview of the principle and explains the different loss mechanisms that come into play. A theoretically limit on the achievable efficiency is calculated. It exceeds that of a comparable inductively coupled system by an order of magnitude. First preliminary measurements indicate that AET is feasible, although the measured efficiency is lower than the predicted theoretical limit.