Professor Galina Mirzaeva

This paper provides an extensive review of control strategies for Matrix Converters (MC), starting from early research in 1980s and including the most recent and ongoing developments. The paper identifies and discusses four main approaches, namely: direct control; linear (PI) control with pulse width modulation (PWM); model predictive control (MPC); and state feedback control. Two novel control strategies for MC (fixed division MPC and state feedback control with power matching), proposed by the authors, are included in the paper scope. The paper compares performance of the selected control schemes by simulation. It demonstrates the benefits of state feedback control for MC and outlines future directions of its improvement.

The advantages of high efficiency and reliability, as well as weight and loss benefits, make matrix converters an attractive option for AC/AC power conversion. This paper reviews the existing AC/AC converter solutions in mining industry and provides a detailed discussion of the main features and techniques associated with matrix converters. The paper explains the fundamental difficulties in satisfying the load side and the supply side performance objectives, simultaneously. The paper then discusses and compares several control options for matrix converters, including the recently proposed Comprehensive control. The latter shows advantages over other options and can be recommended for demanding industry applications. Findings of the paper are supported by detailed simulations.

This paper proposes a new method for measurements-based modeling of nonlinear loads in power systems. This method includes a combination of a binary tree algorithm with Nonlinear Auto-Regressive with Exogenous Input (NARX) identification. The 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 this study, a field data set was collected in 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.

This paper proposes a new interpretation of Finite Set Model Predictive Control (FS-MPC) for inverters. This interpretation gives insights into the existing limitations of FS-MPC and suggests mitigation strategies. Consequently, significant improvements of FS-MPC performance are achieved, including elimination of steady state error, improved harmonic spectrum, reduced control delays, etc. The proposed new MPC interpretation also establishes relationships between various control schemes, including FS-MPC and PWM-MPC, FS-MPC and MPC with integral action, etc. Additionally, the paper proposes further embellishments to FS-MPC based on its more efficient and accurate implementation. The findings of the paper are supported by simulations and experimental results.

Model Predictive Control (MPC) has received significant attention from the power electronics research community. In this paper we apply MPC approach to designing optimal current regulators for voltage source inverters (VSI), in the sense of tracking references and rejecting disturbances of interest. In particular, we present a detailed derivation of optimal current regulators for tracking references and rejecting disturbances of constant and harmonic types. We compare these to the existing control structures, such as proportional integral (PI) and proportional resonant (PR) current regulators. We further propose a strategy to improve their performance based on matching their structure and parameters to the optimal controllers. The findings of the paper are supported by PSIM simulations and preliminary experimental results.

Recently, DC microgrids have become a viable option for mining distribution systems. Fault diagnostics and protection are known challenges in DC microgrids. In this paper, we present an overview of the existing strategies for fault diagnostics and protection of a DC microgrid and apply them to an open cut DC mine scenario, which includes large electric excavators. We propose a comprehensive fault tolerance strategy based on analysis of electrical and mechanical operations of an electric rope shovel and identification of its working cycle. Based on this strategy, in case of a fault, the electric rope shovel will be able to perform required actions to avoid collisions and safely finish its working cycle, while maintaining electric safety.

Model Predictive Control (MPC) has attracted significant attention from the power electronics community. In this body of work it is usual to utilize a linear load model. Also, to deal with computational complexity, it is common to deploy horizon 1 optimization. A major difficulty with these standard approaches is that modelling errors, e.g. those arising from non-linear effects such as magnetic saturation, lead to poor tracking performance. In this paper we show that perfect tracking is achievable provided that MPC controller is augmented by a suitable observer.

A new fault diagnosis scheme based on the monitoring of main air gap flux of the three phase squirrel cage induction motor is proposed. Most of the existing electrical techniques of condition monitoring are based on the stator current and/or leakage flux measurement outside the motor. Besides, most of these methods only concentrate on the time harmonics analysis of the acquired signal. We propose to analyse the space harmonics of the main air gap electromagnetic flux along with the time domain analysis. To this aim, we propose to monitor the main air gap flux using Hall Effect Flux Sensors (HEFS) at all the stator slots of an induction motor, which can be used to address the stator and rotor slot effects not only through frequency analysis of the time varying magnetic flux, but also by magnitude and phase shift comparison of sensors located at different geometric positions around the stator. Moreover, by using HEFS in all the stator slots, the flux density along the circumference of the stator can be acquired and the space harmonics of the flux can be analysed, which shown promising results in detecting and locating different faults. In this paper, we concentrate on detecting different types of rotor faults such as broken rotor bar fault and eccentricity.

A new fault diagnosis scheme based on the monitoring of main air gap flux of squirrel cage induction motors is proposed. Most of the existing flux monitoring techniques are based on the leakage or stray flux measurement outside of the motor. A few methods, however, use the main air gap flux as the fault signature, where search coils are used to monitor the derivative of the flux, which eventually introduces noise in the signal. Moreover, the diagnosis methods are mainly based on detecting a fault, whereas very little initiative has been taken to locate a fault precisely. To address these problems, a sophisticated yet robust condition monitoring and fault diagnosis method is needed. To this aim, we propose to monitor the main air gap flux using Hall Effect Flux Sensors (HEFS) at all the stator slots of an induction motor, which can be used to address the stator and rotor slot effects not only through frequency analysis of the magnetic flux, but also by magnitude and phase shift comparison of sensors located at different geometric positions around the stator. We have successfully detected the stator turn-to-turn fault at a very incipient stage and detected the location of the fault precisely. Promising results have been obtained through simulation in the case of broken rotor bar faults as well.

Condition monitoring of an induction motor may be based on measuring the electrical signals, such as stator current, electromagnetic flux etc. or mechanical signals such as vibration, noise etc. from the motor. Most of the existing electrical techniques of condition monitoring and fault diagnostics are based on the stator current and/or leakage flux measurement outside the motor. Besides, most of these methods only concentrate on the time harmonics analysis of the acquired signal. But the main air gap flux consists of both time and space harmonics. The latter is overlooked by most of the existing researches. We propose to analyse the space harmonics of the main air gap electromagnetic flux along with the time domain analysis. But to do so, a thorough knowledge of the space harmonics of the stator flux, the rotor flux and their insights is needed to be obtained. To this aim, we present the space harmonics analysis of the main air gap flux of a healthy induction in this paper. Then the applicability of the space harmonics analysis to detect the faults is discussed. Two types of rotor faults, i.e. eccentricity and the broken rotor bar fault are discussed.

Various modern control concepts have been developed over the last decades. Despite that, due to real-time computational constraints, standard linear controllers continue to dominate in industry applications of power converters. On the other hand, demanding applications (for example, mining excavating machines) can benefit from advanced performance offered by modern control schemes. To this aim, the current paper develops advanced control structures using principles of Optimal control, Predictive control, State Feedback control and Kalman Observer. Advantages of the proposed control schemes are demonstrated by simulation and experiment. Implementation of the proposed control in variable speed drives is discussed in detail, including examples of the software code.

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.

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.

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.

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.

Matrix converter is an attractive choice for motor drives with weight/size restrictions and high efficiency requirements, such as electric haulage vehicles used in mining. However, the use of matrix converters requires addressing a potential issue with input resonance, which can be exacerbated when using long feeders or trailing cables. This article addresses this problem by proposing a novel solution based on principles of modern control but shaped as a classical feedback architecture. Along with high quality reference tracking, the proposed solution utilizes the frequency changing properties of matrix converters to attenuate the input filter resonance by spectral shaping of the output current. This article shows that the solutions achieves its goals. Design and implementation details are discussed. This article results are validated by simulations and experiments.

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.

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.

© 2014 Taylor and Francis. Inverters play a central role in modern society including renewable energy integration and motor drives. Due to the inherent switched nature of the inverter waveforms harmonic distortion is an issue. Additionally, the switching patterns are perturbed by unavoidable switching delays. Amongst those, nonlinear and load-dependent switching delays (known as inverter dead-time delays) are the most difficult to compensate. In this paper, we propose a new approach to delay compensation and harmonic suppression in inverter voltage. The proposed approach is based on variable prediction horizon nonlinear model predictive control.