Galina Mirzaeva

Robust model predictive control: reflections and opportunities

The past three decades have witnessed important developments in the theory and practice of model predictive control (MPC). In particular, considerable effort has been devoted to robust MPC theory. There have also been many successful applications. This paper will give a brief overview of existing results and summarise experience gained in two real-world applications. We also present some reflections on issues which, in the authors’ opinion, deserve further attention.

Opportunities and challenges in the application of advanced control to power electronics and drives

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 adopt a control engineering perspective to reflect on the opportunities and challenges that exist in the application of advanced control to these systems.

A laboratory system to produce a highly accurate and uniform magnetic field for sensor calibration

This paper addresses one particular issue that the authors came across when developing a DC Motor Duty Meter - a comprehensive condition monitoring tool for large DC motors based on flux density measurement inside the motor air gap. This particular issue crucial for the project was how to calibrate, with high accuracy, a large number of flux density sensors to be used to measure the flux density distribution along the surface of the motor poles. From available literature and IEEE standards, the recommended and most common way to generate a calibration magnetic field is based on Helmholtz coil principle, which in practice is limited to small flux density magnitudes. A method used by the authors and described in this paper utilizes a step test and simple calculations based on Faradays Law. The novelty of the described method is in particularities of the system, measurements and calculations, which make the method highly immune to typical sources of errors. The method can be used to produce a very accurate and uniform magnetic field with densities ranging from fractions of Tesla to above one Tesla to calibrate flux sensors in this flux range. Its accuracy is only limited by that of a current source, a current probe and a digital oscilloscope. Uniformity of the generated field is discussed and experimentally confirmed. Experimental results obtained within the DC Motor Duty Meter project are included to illustrate correctness of the sensor calibration. Conditions that guarantee the maximum efficiency of the method are discussed. The paper is concluded by a step by step calibration procedure that other researchers may find useful.

An introduction to the control of switching electronic systems

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.

Active filtering and VAR control of a cascaded H-bridge multi-level StatCom

This paper investigates the control of a multi-level cascaded H-bridge STATCOM when used as a simultaneous active filter and VAR compensator. The control algorithms developed borrow heavily from control strategies used in variable speed drives, and use predictive current control and symmetrical PWM. A novel phase locked loop approach for the extraction of the harmonics and generation of the forward prediction of the harmonic reference currents is developed. Simulation results in this abstract are presented. The final paper will present experimental results as well.

Harmonic suppression and delay compensation for inverters via variable horizon nonlinear model predictive control

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.

An Improved Natural Field Orientation Control of a Current Fed Induction Machine

Natural field orientation (NFO) is a simplified version of stator flux oriented (SFO) control for an induction machine. The essential difference from traditional SFO is that NFO does not estimate the stator flux magnitude but assumes that its equal to the reference value. The NFO algorithm only requires knowledge of the stator resistance and is extremely simple to implement. However, it has been found that NFO has stability problems under regeneration. Also when implemented on a current fed induction machine, the control frame has an undesirable tendency to misalign with respect to the stator flux vector. This paper examines both the above issues in detail. It proposes a solution that mitigates this undesirable behaviour and, at the same time, retains the inherent simplicity of the NFO control scheme. The findings of the paper are substantiated by simulation and experimental results.

Analysis of frame alignment issues in natural field orientation including non-linear and leakage inductance effects

The natural field orientation (NFO) algorithm is a form of stator flux orientation (SFO) that has the desirable property that it does not use integration to determine the position of the stator flux reference frame. It is also supposed to implicitly correct reference frame errors. However, under certain modes of operation this does not occur. The purpose of this paper is to develop non-linear analytical expressions that accurately model this problem and then verify them against simulation and experimental results. This objective is achieved by using two non-linear modelling approaches - a simplified one which assumes that the machine has no leakage, and one where leakage is considered. The accuracy of two approaches are compared with each other. Furthermore, a solution to the frame instability is also proposed and analysed. The analytical results are verified by simulation and experiment.

A Generalized MPC Framework for the Design and Comparison of VSI Current Controllers

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.

Advanced noise shaping and filter design with Feedback Quantizer PWM

There has been a continuous development of PWM strategies addressing different inverter topologies, as well as requirements of efficiency and minimal distortion. One of such strategies recently proposed by the authors is Feedback Quantizer PWM (FBQ-PWM). In this paper we briefly describe FBQ-PWM. We present a detailed study of different feedback filter options for noise spectrum shaping. We illustrate our study with detailed simulations and experimental results. The paper is concluded by a summary of its main findings and notes on potential applications.