<abstract xmlns="http://www.w3.org/1999/xhtml">With the fast development of power electronics techniques, electrification of shipboard power systems (SPS) is an unstoppable trend, and the concepts of electric ships (ESs) and all-electric ships (AESs) emerge. In order to meet the constantly increasing electricity demand in SPS, the medium voltage direct current (MVDC) SPS becomes a promising shipboard electrical network architecture. This paper aims to present a comprehensive review of the design, control, power management, system stability and reliability in ESs. The most recent technologies and academic achievements in these fields are discussed. In the near future, it is possible that the electric propulsion technology will be widely applied to various types of ships.</abstract>

An Overview of Design, Control, Power Management, System Stability and Reliability in Electric Ships

<abstract xmlns="http://www.w3.org/1999/xhtml">Properties and control of a doubly fed induction machine operating under unbalanced grid voltage conditions have been presented. The proposed method does not include symmetrical sequences decomposition and is realized in a rotating frame not synchronized either with the grid voltage vector or with the stator flux vector. The method uses a reference torque and the reference <italic>q</italic> component of instantaneous power for calculation of the reference stator current. Next, calculation of magnetizing current for a given unbalanced grid voltage is used to assign the reference rotor current. Due to the fact that the reference current contains both a positive and a negative sequence, a proportional-integral-resonant controller is used. The main control target is the non-oscillatory waveform of torque, whereas other separate strategies like symmetrical stator current or sinusoidal rotor current can be easily obtained by adequate filtration of the reference control signals of the stator or rotor currents, respectively. The simulation results of the 2 MW model have been presented for a doubly fed induction generator as well as the results of laboratory tests with the use of a small scale 7.5 kW machine.</abstract>

Control of a Doubly Fed Induction Generator at Grid Voltage Imbalance

<abstract xmlns="http://www.w3.org/1999/xhtml">A hybrid maximum power point tracking method has been proposed for the photovoltaic system using a stochastic evolutionary search and a deterministic hill climbing algorithm. The proposed approach employs the particle swarm optimizer (PSO) to solve a dynamic optimization problem related to the control task in a <italic>PV</italic> system. The position of the best particle is updated by the hill climbing algorithm, and the position of the rest of the particles by the classic PSO rule. The presented method uses the re-randomization mechanism, which places five consecutive particles randomly, but in specified intervals. This mechanism helps track the maximum power point under partially shaded conditions.</abstract>

Hybrid MPPT Algorithm for PV Systems Under Partially Shaded Conditions Using a Stochastic Evolutionary Search and a Deterministic Hill Climbing

<abstract xmlns="http://www.w3.org/1999/xhtml">The purpose of this paper is to show a new state observer for doubly-fed generator. A proposed <italic>z-</italic>type observer algorithm based on mathematical model of doubly fed generator with additional variables treated as a disturbances has been used. A nonlinear multiscalar control method has been proposed to control active and reactive power of the generator. All analyses were verified by simulations and experiments tests.</abstract>

State Observer for Doubly-Fed Induction Generator

<abstract xmlns="http://www.w3.org/1999/xhtml">The analysis of the influence of transfer function zeros on the parameters of state feedback controllers has been conducted. If a transfer function of a control object has zeros which are located closely to poles, the control object tends to singularity, and the influence of the input control signal to the states of the control object becomes weaker. The problem of the state feedback controller synthesis becomes ill-conditioned, which leads to the appearance of extremely large state feedback coefficients. In this case, the state feedback coefficients are sensitive to the parameters of the control object. As a result, the parametric robustness of the control system is reduced. Known methods of structural analysis of control object models are included amongst different methods of the numerical evaluation of the controllability and the observability, as well as methods of the model order reduction. These methods have some disadvantages, such as dependence on the state space representation form of the control object, ignoring a part of the control object model. In this paper, some ways of the preliminary structural analysis of the state space models of control objects have been proposed. The singular (Hankel) matrix is proposed for analyzing the properties of control object models. The singular matrix is the invariant characteristic of the control object in various state space forms and it characterizes the property of the control object completeness. As a result of the research, it was found that the coefficients of the state feedback controller are inversely proportional to the determinant of the singular matrix, and the determinant of the singular matrix is equal to the resultant of the transfer function polynomials. Thus the value of the determinant of the singular matrix depends on the location of the zeros of the transfer function. The method of the structural transformation (decomposition) of the control object for the defining the need of the reducing the order of the control object model is proposed.</abstract>

Problems of Designing State Feedback Controllers for Objects with Transfer Function Zeros

<abstract xmlns="http://www.w3.org/1999/xhtml">Classical voltage space vector modulation techniques cannot be efficiently applied in four-switch three-phase voltage inverter-fed electrical drives due to a voltage offset in DC-link capacitors. The capacitor voltages imbalance is a result of a bidirectional current which flows in a phase of an electric motor that is connected to a DC-link capacitor midpoint. To overcome this problem which leads to an incorrect inverter voltage modulation or even can affect the DC-link capacitors, predictive control algorithms considering the voltage offset in DC-link capacitors have been developed. Despite the predictive methods are highly effective, they require to adjust the cost function weighting factors which is normally an inexplicit task. In this paper, an on-line tuning method of the weighting factor related to the capacitor voltages imbalance incorporated in the cost function of the predictive algorithm has been proposed. According to the proposed approach, the weighting factor is self-adjusted so that the DC-link capacitor voltages are stabilized as well as a high quality of the drive control is remained simultaneously, regardless of its operating point. The proposed strategy has been validated by using simulation model of the induction motor drive system.</abstract>

Modified Scheme of Predictive Torque Control for Three-Phase Four-Switch Inverter-Fed Motor Drive with Adaptive DC-Link Voltage Imbalance Suppression

<abstract xmlns="http://www.w3.org/1999/xhtml">In the perspective of current trends in engineering education, aiming at meeting industry requirements, especially in the field of power electronics and motion control, the article presents a way of teaching electric drive control in undergraduate engineering programmes using experimental setups with AC motors equipped with industrial frequency converters. The setups consist of two motors: induction and PMSM (each one can act as a motor or a load machine) and a number of other elements necessary in contemporary drive systems: speed sensors, temperature sensors and braking resistors. While using such setups students can learn about various issues related to AC motor control, both in terms of scalar and field-oriented control methods in all three drive operating modes: torque, velocity and position control. The laboratory setups allow students to familiarize themselves with such detailed issues as: vector control without a speed sensor, various ways of voltage control in a DC input circuit of the voltage inverter during motor braking or the influence of the type and value of load torque on drive system operation. Classes can have a classical form or they can be taught in the open-laboratory system.</abstract>

Application of Industrial Frequency Converters for Project-Oriented Education of Controlled Electrical Drives

<abstract xmlns="http://www.w3.org/1999/xhtml">The proof of a concept for a new method of modulation has been presented which reduce switch count in a three-level neutral point clamped (3L-NPC) inverter. The method is an implementation of space vector modulation (SVM) by means of a prediction algorithm and sequences of transistors, which are not common in use. Those sequences make active use of clamping diodes of the inverter. The prediction algorithm analyzes possible sequences of transistors’ states and choose those which offers smaller switch count. Measurements of steady states were taken on prototype 3L-NPC.</abstract>

A Method of Reducing Switch Count in Three-Level NPC Inverter – Analysis in Steady States

<abstract xmlns="http://www.w3.org/1999/xhtml">Electromagnetic compatibility requirements for immunity tests have been presented and the emission levels of electromagnetic disturbances in adjustable speed power drive systems have been determined. The disturbances are divided into two groups: low-frequency (up to 50 harmonics of the power supply system) and high-frequency (above 150 kHz). The lack of legal regulations on permissible disturbance level in the frequency range from 2.5 kHz to 150 kHz has also been mentioned. This range is considered high frequency by the authors. Standarized compatibility levels and sample measured parameters of the electromagnetic environment have also been shown. An exemplary reaction of the drive to the most common disturbances in the power supply system has been presented.</abstract>

Wroclaw University of Science and Technology

Department of Electrical Machines, Drives and Measurements

Laboratory of Electromagnetic Compatibility

EMC Requirements for Power Drive Systems

<abstract xmlns="http://www.w3.org/1999/xhtml">The article presents the results of research on the use of an axial flux in the diagnostics of induction motor stator winding fed by a frequency converter. Voltage signal waveforms proportional to the axial flux were recorded during motor operation under various conditions and were analyzed with regard to the detection of stator winding short circuits. The taps of the selected coil turns of stator phases were introduced into the tested motor, which allowed to physical modelling inter-turn short circuits. The structure and operation of the computer system used to monitor the state of induction motor windings were discussed. The developed diagnostic system was made in the National Instruments LabVIEW environment. The analysis of faults of the axial flux was made in the detection of induction motor stator winding. The results of experimental research conducted using the developed diagnostic system have also been presented.</abstract>

Diagnostic System for Induction Motor Stator Winding Faults Based on Axial Flux

<abstract xmlns="http://www.w3.org/1999/xhtml">The possibility of using neural networks to detect eccentricity of induction motors has been presented. A field-circuit model, which was used to generate a diagnostic pattern has been discussed. The formulas describing characteristic fault frequencies for static, dynamic and mixed eccentricity, occurring in the stator current spectrum, have been presented. Teaching and testing data for neural networks based on a preliminary analysis of diagnostic signals (phase currents) have been prepared. Two types of neural networks were discussed: general regression neural network (GRNN) and multilayer perceptron (MLP) neural network. This paper presents the results obtained for each type of the neural network. Developed neural detectors are characterized by high detection effectiveness of induction motor eccentricity.</abstract>

Application of Neural Networks to Detect Eccentricity of Induction Motors

<abstract xmlns="http://www.w3.org/1999/xhtml">The article presents the results of the research on inductive current transducers in the form of a uniform winding non-magnetic ring with a rigid and flexible construction encompassing the flow of processed current in the frequency range of up to 150 kHz. The results for the developed transducer were related to the results obtained in simulations conducted on the transducer simplified model. The frequency tests of this type of transducers are of key significance in the assessment of the applicability of a given transducer in the measurements of network signals with high-order harmonics, and particularly in the assessment of the construction capacity of inductive current transducers in the form of the Rogowski coil.</abstract>

Inductive Current Transducers in the Frequency Range Up to 150 kHz

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Power Electronics and Drives

Special Section on: Advanced Control Methods of Electrical Machines and Drives  Power Electronics and Drives (PEAD) is an open access, peer-reviewed journal which aims to publish original scientific papers (research and survey papers) on new theoretical developments, novel applications, and case studies regarding advances in power electronics and electrical drive systems. Articles published in our journal cover full scope of power electronics and its applications in electrical drives, renewable energy systems and mechatronic systems. The published articles deal with the following subjects:    power electronic converters;  intelligent control in power electronics and drives;  state variable estimation for AC and DC drives;  diagnostics in power electronics and drive systems;  fault-tolerant control strategies in power electronic converters and drives;  industrial drives, renewable energy systems and smart grid technologies;  power consumption and energy efficiency of converter-fed drives;  electrical machines modeling, simulations and analysis;  motion control, mechatronics;  education issues in power electronics and drives;  other related topics.    The journal is an annual and is published in the open volume system. The basic version of the journal is the electronic version (eISSN: 2543-4292.  The publication in this journal is free of charge.  Power Electronics and Drives is specially oriented to young scientists, PhD students and young Doctors, who can publish (quickly and without any charge) their research results and extended summaries of their PhD dissertations (in this last case the number of pages should be consulted with the Editor-in-Chief).  The journal observes a code of ethics based on academic standards (see for details at the journal web site).  The full texts of articles are freely available from the Power Electronics and Drives web site according to Creative Commons Licence (CC BY-NC-ND) and, since 2018, through the DOAJ database serving the best interests of the scientific community.  Power Electronics and Drives (PEAD) has been published under this title since 2016. It continues the tradition of the journal entitled Scientific Papers of the Institute of Electrical Machines, Drives and Measurements of the Wroclaw University of Technology. Studies and Research, which has been published regularly since 2003 (occasionally from 1969), mainly in Polish. Since 2016 all papers in the whole journal has been published in English.  The journal is published and financed by the Faculty of Electrical Engineering and Department of Electrical Machines, Drives and Measurements at the Wroclaw University of Science and Technology. Since 2019 the journal is published under the patronage of the Electrical Engineering Committee of the Polish Academy of Sciences.  Journal homepage www.ped.pwr.edu.pl  Archiving Sciendo archives the contents of this journal in Portico - digital long-term preservation service of scholarly books, journals and collections.  Plagiarism Policy  The editorial board is participating in a growing community of Similarity Check System's users in order to ensure that the content published is original and trustworthy. Similarity Check is a medium that allows for comprehensive manuscripts screening, aimed to eliminate plagiarism and provide a high standard and quality peer-review process. 

Power Electronics and Drives

Volume 2 (2017): Issue 2 (December 2017)

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