Search

The majority of existing models for estimation and control of switched reluctance machines (SRMs) ignore the dynamic effects of mutual coupling between different phases. Although this may be acceptable for some common industrial applications, such a simplification may degrade significantly the performance of the drive and the precision of the estimated quantities. In this work an enhanced representation of the SRM is introduced, by defining an appropriate finite element model of the machine. This model enables accurate estimation of rotor position and electromagnetic torque, for any current configuration. The necessity as well as the feasibility of this approach is illustrated in the ease of a three-phase, 6/4 SRM. Torque and position estimation accuracy provided by the proposed methodology is validated by measurements on a prototype three-phase 6/4 SRM. Index Terms--Angular position estimation, electromagnetic torque estimation, finite-element-based estimator, switched reluctance machine (SRM) drives.

In this paper, a novel four-level inverter will be presented and analyzed. The proposed inverter topology, which is composed of a conventional two-level and a three-level neutral-point clamped (NPC) inverter, is suitable for high-voltage and high-power applications. The proposed inverter, when it is compared with the conventional four-level NPC pulsewidth modulation inverter, exhibits the following advantages: a) ability of changing the power losses distribution profile among the devices by selecting a suitable switching strategy; b) reduction of total inverter power semiconductor device losses; c) ability of bidirectional operation for all power semiconductor switches; and d) easy implementation using existing power semiconductor modules. The effect of conduction and switching losses profiles of the proposed inverter for different switching strategies is examined under different loads, power factors, and modulation indices. The dc-link capacitors voltages are effectively balanced via a proposed self-voltage balancing topology, without the need of isolated dc voltage sources or additional voltage stabilizing circuits. Finally, the theoretical results are confirmed by simulation and experimental results. Index Terms--DC-Link capacitor voltage balance, multilevel voltage source inverter (VSI), semiconductor device power losses, sinusoidal pulsewidth modulation (SPWM).

This paper presents a methodology for a convenient modification of induction motor equivalent circuit parameters, taking into consideration switching frequency iron losses in case of inverter supply. The method is based on the determination of harmonic iron losses in laminated iron cores under nonsinusoidal excitation by using a particular three-dimensional (3-D) finite-element model adopting a reduced scalar potential formulation. Eddy currents in iron laminations are considered by means of convenient surface current densities. Experimental verification is performed in case of a 20-kW experimental setup. Index Terms--Eddy currents, finite-element methods, harmonic analysis, iron losses.

Battery management systems (BMSs) are used in many battery-operated industrial and commercial systems to make the battery operation more efficient and the estimation of battery state nondestructive. The existing BMS techniques are examined in this paper and a new design methodology for a generalized reliable BMS is proposed. The main advantage of the proposed BMS compared to the existing systems is that it provides a fault-tolerant capability and battery protection. The proposed BMS consists of a number of smart battery modules (SBMs) each of which provides battery equalization, monitoring, and battery protection to a string of battery cells. An evaluation SBM was developed and tested in the laboratory and experimental results verify the theoretical expectations. Index Terms--Batteries, error analysis, fault diagnosis, fault tolerance, protection, reliability.

In this paper an analytical method is presented which allows the exact calculation of the rms value of the state space variables of a switching power converter, whose starting point is the unified state-space representation of the switched networks and end result is a complete form of equations that include both the DC and RMS values. The method proposed in this paper, bridges the gap, which exists between the state-space technique and the small signal approximation that departures from the steady state ripple values are negligible, compared to the steady state values themselves. A new extended circuit model is proposed whose fixed topology contains all the elements of any DC-to-DC converter, regardless of its detailed configuration, and by which different converters can be characterized in the form of a table conveniently stored in a computer data bank to provide a useful tool for computer aided design and optimization. Finally, examples are given for Buck, Boost, and Buck-Boost regulator topologies. Index Terms--Buck-boost regulator, capacitor, DC-to-DC converter, inductor, semiconductor.

In maritime industry, high fuel costs encourage use of variable-frequency drives (VFDs) for energy-saving applications. However, introduction of such nonlinear loads in the vessel's power distribution network induces harmonics, which can lead to potential risks if are not predicted and controlled. In this paper, a systematic power-quality assessment and monitoring methodology is proposed to calculate VFD contribution to voltage distortion at the point of common coupling (PCC), considering the source short-circuit capacity and the existing vessel's power system harmonics. According to voltage harmonic distortion limits set by marine classification societies, design and sizing of appropriate harmonic attenuation filters is made, including ac and dc chokes and frequency-tuned passive filter options. The effectiveness of the proposed power-quality analyzing procedure is evaluated through a real practical example, which includes harmonic filter design for VFD retrofit application to fan and pump motors that operate constantly during sea-going operation in a typical tanker vessel. Power-quality field measurements obtained through a harmonic monitoring platform implemented on board verify that total voltage harmonic distortion and individual voltage harmonics at PCC are maintained below 5% and 3%, respectively, showing that design complies with relevant marine harmonic standards even in the worst operating case. [ABSTRACT FROM PUBLISHER]

In this paper, new expressions are introduced for the determination of the maximum power point (MPP) of photovoltaic (PV) systems as explicit functions of the five parameters of the single-diode model employing the Lambert W function. These equations provide the voltage and current at MPP in a direct and straightforward manner, thus dispensing with any need for iterative solution. They are initially derived for a PV system operating under uniform conditions, and subsequently extended for mismatched conditions at the PV string level. The novelty of these formulae lies in their solid theoretical foundation, which supports their validity in the general case and offers a well-founded symbolic formulation for the MPP evaluation problem. Extended simulations and experimental validation are performed to verify the accuracy and computational efficiency of the proposed equations compared with other methods available in the literature. [ABSTRACT FROM AUTHOR]

In this paper, a data-driven process controller is designed and implemented onboard a typical marine vessel for optimal variable-speed pump operation, leading to the energy efficiency optimization of its central cooling water system. To match variable flow rate requirements due to changes in the vessel's operational profile with respect to plant limitations, real-time process measurements are used as feedback signals to adjust the parameters and set-points of a data-driven process controller with self-tuned proportional–integral–differential control loops, which is realized through a commercial programmable logic controller and regulates the speed of sea water cooling pumps in order to maximize power saving potential during sea-going and cargo unloading periods. Data-driven control establishes system dynamics according to process parameter variation and ensures system reliability through parameter monitoring, regardless of the controlled plant model. The plant power saving potential is initially examined through a practical case study, whereas experimental results provided after the proposed control system retrofit installation onboard a tanker vessel show significant power balance improvement and reduction of diesel generator fuel consumption compared to existing pump throttle control methods, verifying that marine industry can be greatly benefited from this energy efficiency upgrade. [ABSTRACT FROM PUBLISHER]

The power losses, current and voltage stresses in semiconductor devices in voltage source transformerless multilevel inverters (VSTMLIs) topologies are unequal, depending on the switching states, the duty ratio, the levels of output voltage, the load power factor and the depth of modulation index. Non-uniform power loss profiles mean both unequal junction temperature and power rating in semiconductors. In this study, a comparison of power losses, current and voltage stresses in semiconductors of VSTMLIs is performed. Initially, the structural characteristics and operating principles of dominant VSTMLIs with sinusoidal pulse width modulation are analysed. Then, modifications of existing VSTMLIs and simplified multilevel topologies are proposed, which achieve a further reduction in switch count and power losses in semiconductors. The proposed modified circuitries are suitable for converting existing four-level VSTMLI topologies into five-level ones. This conversion is desirable, when a zero output voltage level under no-load conditions or low modulation indices should be obtained. Power losses in semiconductors are calculated analytically and then confirmed by simulation. A comparative presentation of profiles of power losses, current and voltage stresses in semiconductors of the examined VSTMLIs is analytically carried out. The obtained results are valuable for sizing and selecting the semiconductors in VSTMLIs. [ABSTRACT FROM AUTHOR]

In this paper, a photovoltaic (PV)-system maximum power point (MPP) tracking (MPPT) control strategy employing a predictive digital current-controlled converter implemented in conventional hardware resources is presented. Two current programmed controllers (finite-state predictive control and valley current control) have been integrated into a system with current- or voltage-oriented MPPT. The modifications applied to the perturb-and-observe algorithm enable the MPP tracker to interact rapidly with the controller accounting also for abrupt irradiance drops by considering voltage and current limitations. The implementation of digital control in PV systems entails significant advantages of speed and accuracy, although the controller converges correctly at the MPP under irradiance variations featuring fast dynamic response. The proposed controller scheme has been experimentally demonstrated on a digitally current-controlled boost converter delivering power from a PV system. [ABSTRACT FROM PUBLISHER]

The majority of existing models for estimation and control of switched reluctance machines (SRMs) ignore the dynamic effects of mutual coupling between different phases. Although this may be acceptable for some common industrial applications, such a simplification may degrade significantly the performance of the drive and the precision of the estimated quantities. In this work an enhanced representation of the SRM is introduced, by defining an appropriate finite element model of the machine. This model enables accurate estimation of rotor position and electromagnetic torque, for any current configuration. The necessity as well as the feasibility of this approach is illustrated in the case of a three-phase, 6/4 SRM. Torque and position estimation accuracy provided by the proposed methodology is validated by measurements on a prototype three-phase 6/4 SRM. [ABSTRACT FROM AUTHOR]