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Standalone microgrids are used in various industrial operations to supply critical loads. The authors have proposed a stable and robust decentralized ac microgrid architecture that provides an automatic and equitable load sharing between distributed generators, without the use of droop control. To deal with faults or real-time changes in the distributed generation levels, a flexible reconfiguration of the microgrid can be advantageous. To achieve that, this article proposes the use of power line communication (PLC). Two PLC strategies are explored in this article: the first is based on using a single and constant PLC frequency, and the second is based on using a variable PLC frequency within a given range. This article details PLC injection, detection, and suppression methods, as well as the overall communication logic. It demonstrates the ability of the microgrid to adapt to changes while minimizing the amount of battery support. Findings of this article are supported by simulations and validated by experiments. [ABSTRACT FROM AUTHOR]

Common-mode-voltage (CMV) is a well-known source of bearing currents and electromagnetic interference (EMI) in industrial applications. In industrial environments with impedance-earthed IT earthing system, such as underground mining, CMV is additionally associated with potentially undetectable fault currents, due to their diversion away from a protection circuit. This article proposes a variable speed drive (VSD) solution that generates practically zero CMV and removes alternative paths for the fault currents. The VSD topology utilized in this article is a standard two-level inverter with active front end. The article develops a control strategy such that it eliminates CMV, minimizes EMI, and optimizes harmonic distortion at the drive input and output. Experiments conducted in physically emulated industrial environment have confirmed that CMV and EMI are practically eliminated, and the earth fault protection is effective. [ABSTRACT FROM AUTHOR]

Large induction motors used in variable speed industrial applications (digging, traction, etc.) undergo dynamic stresses at high power levels. Their lifetime is reduced as compared with constant speed motors and downtime costs are very high. To monitor the condition of such motors, advanced sensor instrumentation is considered, including installation of Hall effect flux sensors inside the motor airgap. Such an advanced instrumentation enables continuous measurement of the airgap flux in both time and space domains simultaneously. This allows for advanced fault detection algorithms. This paper presents a method for early diagnosis of stator turn-to-turn faults and static eccentricity, and differentiation between these two conditions. The paper demonstrates that the proposed method detects, localizes, and quantifies both faults with high accuracy and sensitivity. Furthermore, each fault can be detected at an incipient stage and its development can be predicted. The results of the presented study have been supported by both simulation and experimental results obtained on a laboratory scale induction motor. Based on the results presented in the paper, a real-time condition monitoring system has been developed. [ABSTRACT FROM AUTHOR]

The next big change in various industry applications is associated with power dense motors, such as permanent magnet synchronous motors (PMSMs). Utilization of multiphase PMSM can offer an additional fault-tolerant capability to their applications. Combining both advantages, this paper proposes a simple yet robust current control strategy for a five-phase PMSM under normal operation and in a case of a loss of one phase. Traditional linear current controllers successfully applied to reference tracking of a healthy motor may become less efficient during postfault operation due to additional unmodeled dynamics. This paper proposes a modified angular transformation to a special rotating frame in which the postfault permanent magnet flux linkage remains unchanged and the motor model remains decoupled. Following this, a nonlinear current control scheme based on sliding mode control is proposed, which successfully treats model inaccuracies and provides good dynamic performance and tracking accuracy. Feasibility of the proposed control strategy is experimentally validated on a laboratory scale PMSM motor with a digital signal processor/field programmable gate array based drive. [ABSTRACT FROM AUTHOR]

Most of the existing electrical techniques of condition monitoring and fault diagnosis are based on frequency analysis of signals measured externally to the motor. In this paper, it is proposed to add the space dimension to the measured signals by using an array of Hall effect flux sensors installed inside the motor air gap, and to explore the advantages brought by such an instrumentation. The paper presents analytical models of air gap flux density expressed in terms of time and space, for a healthy motor and for a motor with rotor bar faults and mixed eccentricity. Based on these models, the paper proposes a new technique for early detection of rotor bar faults and mixed eccentricity, and for discrimination between them. The paper demonstrates that, with the help of the proposed technique, the severity of each fault and its location relative to rotor or stator can be accurately established. The results of the presented study are supported by simulations and validated by experiments on a laboratory scale induction motor. The formulated fault diagnosis algorithm is suitable for real-time implementation. [ABSTRACT FROM PUBLISHER]

Traditional model predictive control cost functions, when utilizing long prediction horizons ( $N\geq 10$) in power inverter applications, have demonstrated harmonic performances approaching that of schemes based on offline-generated optimal pulse patterns. However, long prediction horizons often prohibitively increase computational load. A different approach to maximizing harmonic performance is taken in this paper. It is shown that shaping the output voltage spectra using a simple feedback mechanism can significantly reduce the length of the required prediction horizon, facilitating a feasible computational load. When a short-horizon cost function is augmented by the feedback mechanism an excellent tradeoff between harmonic performance and switching loss is achieved, even with a prediction horizon of one. It is also shown that the feedback mechanism can be used to improve input reference tracking. Experimental verification of the proposed modulator is performed on a two-level three-phase inverter. [ABSTRACT FROM AUTHOR]

This paper proposes a new design procedure for a bidirectional dc/dc LCL converter for potential megawatt range applications, including mobile mining equipment. This type of dc/dc converters employ two dc/ac converters and a passive LCL filter instead of a traditional high-frequency transformer. The exclusion of the transformer eliminates the core losses, while the switching losses are minimized by using soft switching operation. The proposed design method is different from previous publications as it ensures zero reactive power circulation, minimizes the size of the biggest capacitor, ensures stable and robust operation, and offers a good tradeoff between the capacitor size and the fault current in the converter under a dc fault condition. In addition to the proposed design, a simple and effective control strategy is proposed, which is based on single phase $pq$ theory. The converter design and control have been evaluated by a digital simulation in EMTP-RV software environment for a 100 MW 300 kV/20 kV converter. Experimental validation has been carried out on a laboratory 200W 100V/20V prototype converter. [ABSTRACT FROM AUTHOR]

When employed as a modulator in power inverters, model predictive control has an equivalence to a recently proposed modulation technique known as feedback quantizer modulation (FBQM). Both schemes produce a random-like switching pattern that can facilitate explicit control over the shape of frequency spectra associated with inverter output voltages and currents. This is useful to satisfy electromagnetic interference and acoustic noise requirements, and to avoid excitation of external system resonances. However, it will be shown in this paper that inverter deadtime introduces a disturbance into FBQM that significantly degrades the ability to shape the frequency spectra. Several compensation techniques, designed to model the effect of deadtime inside the formulation of FBQM, are proposed and experimentally verified on a two-level three-phase inverter. [ABSTRACT FROM PUBLISHER]

A new optimisation-based modulation and control design for matrix converters is proposed. The design uses a quadratic optimisation programme to seamlessly combine control requirements on the input and output sides of the converter. On the input side, the requirements are to keep the source voltage and current in phase with each other and to attenuate transient oscillations caused by a resonant RLC filter, which is used to protect the voltage source from undesirable harmonics. On the output side the requirement is to track a desired current to feed a load. The novel aspects of the scheme are that (i) the optimisation is posed in terms of the converter's modulation matrix, whose entries represent the duty cycles of each of the converter switches; and that (ii) the solution of the optimisation is obtained in closed form and shown to be implementable with a small number of elementary operations. Simulation results demonstrate the good performance of the proposed design. [ABSTRACT FROM AUTHOR]

Condition monitoring of induction motors is important for their efficient and reliable operation. Most of the existing electrical techniques of condition monitoring and fault diagnosis are based on current, voltage, vibration, or/and flux measurements external to the motor. This paper proposes an online fault diagnostic system, which is based on measurements of internal main air gap flux density of an induction motor by an array of Hall effect flux sensors. Such an instrumentation is justified for large specialized induction motors with particularly high-reliability requirements. Fundamental theory behind the air gap flux density as a function of time and space, and its distortions introduced by various faults, is reviewed in this paper. Based on this theory, this paper proposes a comprehensive condition monitoring approach to diagnose induction motor faults including stator turn-to-turn shorts, rotor bar damage, and static and dynamic eccentricity, which may be present individually or at the same time. Moreover, the proposed approach not only detects each fault at its early stage but also determines its exact location and severity. The principles proposed in this paper are illustrated by extensive simulations and are experimentally validated on a prototype online condition monitoring system based on National Instruments real-time platform. [ABSTRACT FROM PUBLISHER]

Model predictive control (MPC) has been widely advocated as a design strategy for many aspects of industrial electronics. The methodology has been strongly promoted by some researchers but has also attracted criticism from others. In this context, the purpose of this paper is twofold. First, we show that many existing and popular control strategies, including finite set MPC and linear controllers [proportional integral, proportional resonant (PR)], can be viewed as special cases of MPC. Second, we show that the predictive control framework allows one to embellish these classical control architectures with novel features and to design new and advanced control architectures to address various challenges posed by power electronics applications. The findings of the paper are supported by a practical example of designing of a novel form of PR controller with superior tracking performance and delay compensation, confirmed via simulation and experiments. [ABSTRACT FROM PUBLISHER]

Due to their robustness and simplicity of control, dc machines continue to be widely used in many applications, including mining. Although a mature technology, dc machines still require research attention to accommodate for heavier loads and harder operation conditions dictated by production needs. Recent advances in sensoring, data acquisition, and signal processing technologies allow for direct measurement of quantities that used to be theoretically modeled or indirectly measured in the past. Within a research project with industry partners, the research team obtained the measurements of flux densities inside the motor air gap under both static and dynamic conditions. A variety of valuable information about the motor performance can be derived from these measurements. This paper focuses on one particular aspect of the commutation performance of dc machines, namely, the magnitudes and uniformity of current density through a brush, which, to a large degree, dictate the wear rates of the dc motor commutating group. This paper revisits the classical commutation theory, presents a mathematical model for current density estimation across a brush, and applies this model to the experimental results obtained. The results are then discussed and related to the commutation quality of the machine. [ABSTRACT FROM AUTHOR]

This paper considers recent advances made within the field of electric drives and how this new technology might be best applied within the mining industry. A case study is presented showing simulated results of the performance of the electric drives in a coal preparation plant. The various starting methodologies (resistance starting, fluid coupling, V/f = const, and vector control) are compared within this application. The merits of each method are then discussed with regard to the specific application and other more generic applications within the mining industry. Application of a rotor flux orientation control drive is substantiated, and its superior performance under start and stall conditions to that of the currently implemented system is confirmed by theoretical analysis and simulations. Experimental results for a scale model of the candidate system are presented, which agree with the main conclusions of this paper. [ABSTRACT FROM AUTHOR]

Natural field orientation (NFO) is a technique for generating a rotating reference frame position for an induction machine aligned with the stator flux. The term "natural" is applied because there is an implicit tendency for the rotating frame to realign with the correct stator flux frame position if there is a perturbation away from this position. However, under regeneration conditions this realignment property does not occur, and the frame position, if perturbed, will move the control reference frame away from stator flux alignment. This paper examines this frame alignment stability problem and proposes a solution that retains the features and simplicity of the NFO concept. [ABSTRACT FROM AUTHOR]

The Matrix Converter is a power electronics topology that allows direct conversion of an alternating-current (AC) source to an AC load operating at a different frequency. The associated control problem is inherently difficult since it is both nonlinear and underactuated. This paper describes a novel control strategy for Matrix Converters based on Transient Power Balance. The scheme achieves the following design objectives: tracking of a desired load current, tracking of a desired supply (leading or lagging) power factor, rapid active damping of supply-current oscillations, arising from a supply-side resonant filter, without needing any additional resistance on the supply side, and mitigation of supply-current distortion arising from supply-voltage distortion. Achieving these goals simultaneously has hitherto been an open problem in this area. All of these goals are achieved in the face of significant errors in circuit component values. A proof of local asymptotic stability of the proposed algorithm is given and associated design constraints are addressed. The claims are illustrated by simulation studies. [ABSTRACT FROM AUTHOR]

This paper proposes a new method for measurement-based modeling of nonlinear loads in power systems. The proposed method includes a combination of a binary tree algorithm with nonlinear autoregressive with exogenous input (NARX) identification. This paper demonstrates that the new method performs well without any prior knowledge of the system structure. In contrast to other load modeling methods, which are typically aimed for particular studies or load types, the proposed method can be used with any load type and for any study. Accurate load modeling is particularly important for studies of industrial networks and grids. In the study described, a field data set was collected at a mine site from a large electrical rope shovel. This data set has been used to develop a model of the rope shovel based on the proposed binary tree—NARX algorithm. When compared to other known methods, such as wavelet and sigmoid networks, the proposed method has shown the fastest training time and the highest accuracy. Finally, the modeling results have been verified against another set of field measurements from an existing network and have shown a very good agreement. [ABSTRACT FROM PUBLISHER]

Open-loop poles on, or near, the imaginary axis in the complex plane are a common occurrence in feedback systems. They can occur as part of the model in systems containing lightly damped resonances or they can be deliberately introduced so as to ensure perfect tracking for sinusoidal or periodic signals. This paper establishes both time and frequency domain implications of such poles on system performance. Dual results for zeros on, or near, the imaginary axis are also discussed. Many practitioners are, at least heuristically, aware of the broad implications of these results but, to the best of the authors' knowledge, they have not previously been explicitly articulated nor quantified. [ABSTRACT FROM AUTHOR]

To reduce stored capacitor energy in modular multilevel converters (MMCs), previous papers propose injection of harmonics in the arm circulating currents and zero-sequence voltages. While this approach is effective, previously utilized combinations of injected harmonics significantly increase converter current ratings. In contrast, the optimization approach developed in this article identifies harmonics that simultaneously achieve capacitor energy optimization and reduced overrating of converter currents. In addition, the proposed approach eliminates the possibility of convergence to local minima, which is a significant improvement on previously proposed nonconvex optimization approaches. Experimental verification of the proposed approach is performed on a low-voltage three-phase modular multilevel converter. [ABSTRACT FROM AUTHOR]

Abstract: Control technology underpins the operation of many, and arguably all, modern high technology systems. Such systems include transportation (aircraft, high speed trains, marine vessels, automobiles), telecommunication systems, electricity networks, mining, minerals processing and agriculture. A particular area where control is playing an increasingly important role is industrial electronics. In this paper we will give a tutorial introduction to the application of control engineering concepts to such systems and reflect on the opportunities and challenges that exist in this area. [ABSTRACT FROM AUTHOR]