Peter Wolfs

A Review of the Single Phase Photovoltaic Module Integrated Converter Topologies With Three Different DC Link Configurations

The annual world photovoltaic (PV) cell/module production is growing at almost an exponential rate and has reached 1727 MW in 2005. Building integrated PV (BIPV) projects are emerging as the strongest part of the PV market and grid interactive inverters are a key component in determining the total system cost. Module integrated converter (MIC) technology has become a global trend in grid interactive PV applications and may assist in driving down the balance of system costs to secure an improved total system cost. This paper concentrates on the topology study of the PV MICs in the power range below 500 W and covers most topologies recently proposed for MIC applications. The MIC topologies are classified into three different arrangements based on the dc link configurations. A systematic discussion is also provided at the end of the paper that focuses on the major advantages and disadvantages of each MIC arrangement. These are considered in detail and will provide a useful framework and point of reference for the next generation MIC designs and applications.

A current-sourced DC-DC converter derived via the duality principle from the half-bridge converter

A current-sourced switch-mode power supply topology is developed by applying a duality principle to a voltage-sourced half-bridge converter. The converter has boost converter characteristics and is suited to low-voltage high-current input applications. It is shown to compare favorably with the center-tapped transformer converter. Two optional enhancements-nondissipative snubber networks and inductor clamping windings-are also examined. Some results obtained with a low-power prototype are presented. >

A Current Fed Two-Inductor Boost Converter With an Integrated Magnetic Structure and Passive Lossless Snubbers for Photovoltaic Module Integrated Converter Applications

In this paper, a photovoltaic (PV) module integrated converter is implemented with a current fed two-inductor boost converter cascaded with a line frequency unfolder. The current source is a sinusoidally modulated two-phase buck converter with an interphase transformer. The boost cell operates at a fixed duty ratio and has an integrated magnetic structure. The two inductors and the transformer are integrated into one magnetic core. Passive lossless snubbers are employed to recover the energy trapped in the transformer leakage inductance and to minimize the switching losses. The two-inductor boost converter output interfaces with the mains via an unfolding stage, where the MOSFETs are driven by the PV gate drivers. Experimental results are provided for a 100-W converter developing a single phase 240-V 50-Hz output

An Analysis of the ZVS Two-Inductor Boost Converter under Variable Frequency Operation

The two-inductor boost converter has been previously presented in a zero-voltage switching (ZVS) form where the transformer leakage inductance and the MOSFET output capacitance can be utilized as part of the resonant elements. In many applications, such as maximum power point tracking (MPPT) in grid interactive photovoltaic systems, the resonant two-inductor boost converter is required to operate with variable input output voltage ratios. This paper studies the variable frequency operation of the ZVS two-inductor boost converter to secure an adjustable output voltage range while maintaining the resonant switching transitions. The design method of the resonant converter is thoroughly investigated and explicit control functions relating the circuit timing factors and the voltage gain for a 200-W converter are established. The converter has an input voltage of 20V and is able to produce a variable output voltage from 169V to 340V while retaining ZVS with a frequency variation of 1MHz to 407kHz. Five sets of theoretical, simulation and experimental waveforms are provided for the selected operating points over the variable load range at the end of the paper and they agree reasonably well. The converter has achieved part load efficiencies above 92% and an efficiency of 89.6% at the maximum power of 200W

Optimal PV Inverter Reactive Power Control and Real Power Curtailment to Improve Performance of Unbalanced Four-Wire LV Distribution Networks

The rapid uptake of residential photovoltaic (PV) systems is causing serious power quality issues such as significant voltage fluctuation and unbalance that are restricting the ability of networks to accommodate further connections. Based on the latent reactive power capability and real power curtailment of single-phase inverters, this paper proposes a new comprehensive PV operational optimization strategy to improve the performance of significantly unbalanced three-phase four-wire low voltage (LV) distribution networks with high residential PV penetrations. A multiobjective optimal power flow (OPF) problem that can simultaneously improve voltage magnitude and balance profiles, while minimizing network losses and generation costs, is defined and then converted into an aggregated single-objective OPF problem using the weighted-sum method, which can be effectively solved by the global Sequential Quadratic Programming (SQP) approach with multiple starting points in MATLAB. Detailed simulations are performed and analyzed for various operating scenarios over 24 h on a real unbalanced four-wire LV distribution network in Perth Solar City trial, Australia. Finally, smart meter readings are used to justify the validity and accuracy of the proposed optimization model and considerations on the application of the proposed PV control strategy are also presented.

Hybrid active filter for harmonically unbalanced three phase three wire railway traction loads

This paper investigates a hybrid active/passive topology and control strategy appropriate for removing harmonics caused by unbalanced nonlinear loads. Unbalanced loads such as railway traction loads may use static compensators to balance the fundamental frequency components. The harmonic currents produced by this combination are unlikely to be balanced. Purely passive structures are not sensitive to this harmonic imbalance, however some active structures are. Controllers aimed at balanced three phase loads using synchronous transformations will not remove all of the harmonic components. The controller presented in this paper uses harmonic sequence components to detect both balanced and unbalanced components and reduce both harmonic components to zero.

The Power Loss Optimization of a Current Fed ZVS Two-Inductor Boost Converter With a Resonant Transition Gate Drive

This paper develops a power loss optimization method in a current fed zero-voltage switching (ZVS) two-inductor boost converter, which is suitable for the module integrated converter applications in grid interactive photovoltaic systems. The paper conducts the numerical analysis of the variable power loss components and establishes a set of the circuit parameters for an optimized operating point with a minimized average power loss. The ZVS two-inductor boost cell is fed from a sinusoidally modulated two-phase synchronous buck converter with an interphase transformer and produces a rectified sinusoidal voltage, which can be applied to an unfolding stage to generate the grid compatible voltage. The boost cell is also equipped with a resonant transition gate drive circuit to reduce the power loss in the drive circuit under high frequency operations. The experimental results for a prototype 1-MHz 100-W ZVS two-inductor boost converter are presented at the end of the paper

Systematic identification and review of hybrid active filter topologies

Since the first installation of a passive tuned filter in the mid 1940s, the development of filter technology has advanced in incremental steps. The development of hybrid configurations to improve the performance of passive tuned filters has been quite ad hoc, building on the existing tuned links. This paper describes a process for systematically identifying all hybrid active filter topologies and their generalized characteristics. The paper first identifies generalised load categories which capture the dependence between harmonic voltage and current. The desirable attributes of filters for these loads are then discussed. The final step is to identify all possible combinations of active and passive elements and match these to the desirable attributes. The topologies are evaluated and those that offer significant advantages in rating are identified. The evaluation indicates those topologies that are known and those topologies that are relatively new.

Novel topology for correction of unbalanced load in single phase electric traction systems

Railway traction loads present large single phase loads to the supply system. Typically zero sequence components are removed using a phase to phase transformer connection, however a large negative sequence component remains. As the amount of rail traffic increases and the use of regenerative braking becomes higher, the issue of negative sequence becomes more critical. This paper presents a novel active filter approach to negative sequence compensation using single phase compensators at the track side of the system. The compensators for two separate track sections share a common DC bus, which allows power transfer between the sections. A control algorithm based on synchronous reference frame theory is proposed, with modified transformations to reflect the two phase nature of the system. The topology and control algorithm are verified using simulation and results are shown.

Survey of Wireless Communications Applications in the Railway Industry

Advances in information and communications technology have enabled the adoption of wireless communication techniques in all sectors for the transmission of information in all forms between any two points. Wireless communications and distributed computing have promoted the development of vehicle- monitoring systems to reduce the maintenance and inspection requirements of railway systems while maintaining safety and reliability. This paper surveys existing wireless techniques used in the railway industry for both communications and signalling purposes. Finally we present our work in progress on low-cost, low-power wireless sensor networking architecture to monitor the health of railway wagons attached to a moving locomotive.