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The ability to use actuator and load models online in combination with experimental data becomes increasingly important in future electrical drives. Among the applications of such online model in torque and flux controllers, model predictive control (MPC) has gained increasing interest, allowing to deal in real time and in a suboptimal way with drive variations captured by the model used. For such ability, sufficient processing power is required to handle the model in real time, which appears to be less of a problem in recent drives. This article contributes to the current prediction in MPC, applied to an interior permanent-magnet synchronous machine (IPMSM) drive. The study aims at improving the prediction, through an online estimation of the current time gradient coefficients, and this by considering consecutive space vector step responses. Through measuring the resulting current responses, an online correction of the current gradients is realized. A two-step method, which consists of an estimation step and a prediction step, will be described in order to improve the current prediction. Experimental results obtained from a 3.7-kW IPMSM drive will verify that the proposed geometrical approach effectively improves the conventional short window current predictions.

Magnetostrictive behavior of the electrical steel cores of transformers and electrical machines has been studied under well-known excitation waveforms, e.g., purely sinusoidal. However, the magnetization may contain higher harmonics due to the grid harmonics for the application in transformers or due to pulse width modulation excitation in the case of induction machines. We have reported the presence of a single low-order harmonic in magnetization, but in reality, a superposition of several low- and high-order harmonics is present, which needs to be studied. Thus, in this paper, the magnetostrictive behavior of electrical steel is measured under a sinusoidal magnetization with high-order harmonics. A macroscopic description of the magnetostrictive behavior is presented afterward.

Model-based predictive control is a powerful control strategy to drive electrical machines. Conventional cascade proportional–integral (derivative) [PI(D)] controllers are often used to control speed, torque, and current. However, for low-inertia machines, achieving a high-performance and wide speed range is far beyond the application conditions for which these controllers are designed for. Using two cascaded PI(D) controllers for the speed/current control of a low-inertia machine, changes in the speed set point should be slowly applied in order to avoid stability problems. In this paper, a model predictive control algorithm that is able to control the speed of a low-inertia brushless direct-current machine with a high bandwidth and good disturbance rejection properties is proposed. The algorithm is implemented on a SPARTAN 3E 1600 field-programmable gate-array board, and experimental results verify the performance of the proposed algorithm.

By predicting future phase-current commutation instants of brushless dc (BLDC) machines, self-sensing control is achieved. Detection of the back electromotive force (EMF) zero-crossing moments is one of the methods used to predict the phase-current commutation instants. Most of the techniques based on back-EMF zero-crossing detection have the inherit disadvantage of an indirect prediction of commutation instants. This is the result of the commutation instant occurring at the $30^{\circ}$ electrical position after zero-crossing of the induced back-EMF in the unexcited phase. Often, the time difference between the zero-crossing of the back-EMF and the current commutation instant is assumed constant. This assumption can be valid for steady-state operation; however, a different time span should be taken into account during transient operation of the BLDC machine. To overcome this problem, an enhancement is proposed here, which improves the performance while keeping the simplicity of the back-EMF zero-crossing detection method.

This paper presents a load torque estimation method for self-sensing brushless dc drives. Torque ripples in brushless dc machines can be reduced using load torque information. This method uses the terminal voltage, the virtual neutral point voltage, and the dc bus current of the machine. The algorithm uses the variation of successive back electromotive force (back EMF) samples to estimate the rotor speed. The rotor position is estimated by defining an intermediate function of estimated speed and back EMF samples. An estimate of acceleration is used to estimate load torque. The load torque information is used for increasing the dynamic stiffness of the drive. The mathematical background is given and discussed, and the simulations and the experimental results prove the performance of the proposed method.

The effect of multilevel inverter supply on power losses in magnetic cores and electrical machines is studied. A dynamic numerical model for the hysteresis, eddy current, and excess losses in a core lamination is first developed. By both measurements and simulations for a ring-core inductor, we demonstrate how increasing the number of inverter voltage levels decreases the iron losses when compared with traditional two-level supply. Although the switching frequency has a significant impact on the iron losses in the case of a traditional two-level inverter, using three or five voltage levels makes the losses almost independent of the switching. Finally, finite-element simulations show that simi-lar reductions are also possible for the core losses of 150-kVA and 12.5-MW wound-field synchronous machines, in which rather low switching frequencies are typically used. Calorimetric loss measurements are also presented for the 150-kVA machine in order to confirm the significant effect of switching frequency on the core losses with two-level inverter supply.

As inverters are often used in critical applications, reliability is an important issue. In particular, the power electronic switches and gate drivers, the most essential components of the inverter, are vulnerable parts in real live operation. Therefore, this paper focuses on open-switch fault detection for multilevel inverters. When a single-switch open-circuit fault occurs in one of the power electronic switches, the algorithm can detect the fault and the switch that is causing it. The detection is worked out for both a linear resistive inductive load and an induction motor. The proposed algorithm is an extension of an already available finite-set model-based predictive control algorithm. Therefore, no extra hardware or measurements are required. This paper also discusses a suggested method for reconfiguration after fault detection. Computer simulation and experimental verifications validate the proposed methods.

For large synchronous machines, the excitation is usually provided by a DC-fed field winding in the rotor. For small synchronous machines, however, this is undesirable, on the one hand because of the complications for supplying DC to the rotor (i.e. slip rings, rectifier), on the other hand because the smaller the dimensions, the less efficient a field winding is in producing a magnetic flux.

As is clear from the previous chapters, DC commutator machines are ideal machines to obtain controlled torque and speed. To obtain similar properties, rotating field machines require more complicated supplies and control circuits. In this chapter we derive the basic control methods for rotating field machines, with as starting point the DC commutator machine characteristic properties.

While the previous chapters analysed the local stability of electrical machines, here we study a typical case of large transients, i.e. the sudden short-circuit of a synchronous generator. The model used is a simplified constant saturation machine model.

In this chapter we discuss some transient phenomena in simple electrical circuits (resistive, inductive, capacitive), as an introduction to the later chapters on (local) stability and dynamics of electrical machines and drives.

Traditional rotating field machines have no (for synchronous motors) or poor and limited (for induction motors) possibilities for variable speed operation when power is supplied from a fixed frequency source. In this chapter, we will discuss the open-loop variable frequency voltage supply of rotating field machines. These kinds of drives are commonly denominated as V/f drives, because both the voltage and the frequency are controlled together in open loop, so as to control both the speed and the flux. The aim of the open-loop variable frequency operation of rotating field machines is to obtain a cheaper and more reliable variable speed drive than the expensive and high-maintenance DC drive. Drives that are even more demanding in terms of speed, position or torque control will be discussed in later chapters.

In this chapter (which is mainly based on Novotny, Equivalent circuit steady state analysis of inverter driven electric machines, [30]), we will study a method for the fundamental harmonic modelling of inverter supplied rotating field machines. First, we derive fundamental harmonic equivalent circuits for the inverter. These fundamental harmonic circuits are then combined with the steady-state equivalent circuits of rotating field machines to derive the basic characteristics of these inverter-supplied machines. For the modelling of the inverters, the resistive voltage drop over the switches will not be taken into account. Commutation will also be simplified, as most transients will be disregarded.

In Chap. 17 of Part III, vector control and field orientation have already been presented. However, the dynamics have not been analysed. In this chapter we discuss vector control and field orientation more thoroughly, including an analysis of their dynamic behaviour.

Not only induction machines, but synchronous machines as well may exhibit dynamic problems when fed by a variable frequency supply. In this chapter we analyse and represent the dynamic behaviour of synchronous machines in an analogous way as we have done for the induction machine. The results are quite similar. However, for synchronous machines such scaling laws do not exist to the same extent as for induction machines.

This chapter aims to give an overview of the main power electronic components for application in electrical drives and electrical grids. It is not at all intended as a power electronics components course, but rather as the basis for the later chapters on the main power electronic circuits like rectifier, chopper or inverter. In addition to the traditional components (for example: diode, thyristor, IGBT) also a section is devoted to new developments regarding Si-C and GaN components.

Nowadays, the induction machine is by far the most commonly used electrical machine in electrical drives (for applications that require a highly dynamic behaviour or where energy efficiency or compactness is primordial the permanent magnet synchronous motor may be preferred, however). The main reasons for this are its straightforward and robust construction and its quite efficient energy conversion. Moreover, the last 30 or so years variable speed operation of induction machines using power electronic converters has ousted almost completely the DC commutator machine in variable speed applications. This chapter starts from the traditional transformer properties of an induction motor at standstill. Then, the operating principle of an induction machine is explained both intuitively and from a more mathematical point of view. In the subsequent sections we treat the energy conversion and torque, equivalent circuits and equations for an induction machine, the current locus and single-phase induction machines. Much attention is paid to per-unit values and scaling laws as these determine the behaviour of the machine to a great extent.

For many induction machines with pulsating loads, the pulsation frequency is rather low. Therefore, a quasi-stationary approach can be used to study the behaviour of the induction machine. In this chapter it is shown that a simple mathematical averaging cannot be used for dimensioning the machine.

In this chapter we discuss the synchronous machine mainly from its traditional function as generator. Motoring, in particular with permanent magnet synchronous motors, is treated in a later chapter. The first section gives an overview of the main two rotor types and their properties. In the following section, the smooth rotor synchronous machine is treated in detail, including armature reaction, phasor diagrams, equivalent circuits, current diagram, torque but also a thorough discussion of the non-linear generator characteristics. In the next section, salient pole synchronous machines are treated. One of the last sections is devoted to the operation (mainly as generator) on an infinitely strong grid.

As an introduction to the later chapters on the dynamics of induction and synchronous machines, in this chapter we study the modelling and dynamic behaviour of DC commutator machines. The traditional machine model, using a simplified modelling of the main field saturation, permits to derive the basic dynamic properties. A more accurate model for main field saturation is also presented. It is shown that the dynamic properties derived using this model are slightly different from those using the traditional model, but also somewhat more realistic.

Single-phase AC commutator machines are nowadays mostly used in (small) household machines, such as coffee grinders, mixers, or vacuum cleaners. Larger AC commutator machines also used to be applied in traction, for example in trains, but are now replaced by inverter-fed rotating field machines. In this chapter we review the basic properties of these single-phase AC commutator machines.

Windings of transformers and electrical machines are often subject to voltage surges, either by switching in the grid or by atmospherical phenomena. The resulting voltage waves may propagate into the windings of transformers and rotating machines, causing voltage stresses in the winding. In this chapter we present two simplified models to calculate these voltage stresses. Although nowadays computer models exist to rather accurately predict these voltage stresses, the simplified models offer valuable insight into the physical causes of the localised voltage stresses.

Although DC commutator machines are nowadays largely being replaced by rotating field machines, they remain an interesting study object. The basic principles for energy conversion are similar to those of other machines. Moreover, their excellent control properties (e.g. speed control, torque control) are the inspiration for modern drive control schemes for rotating field machines. Starting from the basic electromagnetic laws, the electromagnetic energy conversion in DC machines is explained. Attention is paid also to commutation and armature reaction. Motoring and generating characteristics are discussed in detail.

For rotating field machines supplied by a constant frequency supply, there are almost no acceptable means of speed control (and none whatsoever for synchronous machines). This section will mainly focus on starting, accelerating and braking, and speed control will be discussed in later chapter. Pure synchronous machines fed from a constant frequency supply cannot start and accelerate, as should be clear from Chap. 5 in Part 1. However, when starting and accelerating is required, the damper winding of a synchronous machine (which is usually required for stability) can be adapted to give a starting and accelerating torque, operating as an asynchronous machine. When approaching synchronous speed, the DC supply of the field winding can be switched on and the machine will synchronise when the load is not too large. The asynchronous starting, accelerating and braking discussed in the first section below is therefore also important for synchronous machines which are not too large. In the next section, speed control and cascade connections for slip-ring induction motors are reviewed. Other sections discuss the behaviour of rotating field machines at voltage variations and power-electronic voltage control for rotating field machines.

Rotating fields are the basis for most electric drives (induction and synchronous machines). First, the generation of a rotating field is discussed. As in the previous chapters, we start again from the basic electromagnetic laws. Both using a graphical depiction and a more mathematical method the rotating field generation is explained. Next, the emf is discussed. Finally, the torque on a (rotating) current layer in a (rotating) field is discussed.

Electric machines cover an extremely wide range of power ratings, from 1 mW (\(10^{-3}\) W) or less, to 1 GW (\(10^{9}\) W), which is a ratio of \(1:10^{12}\). The power range of 1 kW may be considered as the boundary between small and large machines.

In the past, the DC machine was the only motor that could provide easy speed control. Nowadays, since the advent of power electronics, rotating field machines offer cheaper and more powerful possibilities for speed control. Nevertheless, in older industrial installations and environments, DC motor drives may still be used. As a result, and also because of their excellent characteristics, it remains instructive to shortly review the possibilities of DC machines for speed control, including braking in particular.

In this chapter we shortly review the well known principles and definitions of stability and dynamics of systems.

The switched reluctance machine (SRM or also SWRM) started to receive much attention at the end of the 20th century. Its operation principle had already been known since 1838 but had not been able to find a practical use because no (fast) power electronic switches were available. Nowadays, the switched reluctance motor is applied in many industrial applications like washing machines or looms and even in more demanding applications like the starter-generator of jet turbines in airplanes. The most important advantages of the SRM are its simple and rugged construction, its inherent redundancy, and its suitability for high speeds. Its most negative aspect is the high level of noise and vibrations that it brings along.

An ideal current supply (i.e. a current independent of the load) is not feasible. In fact, most sources come close to more or less ideal voltage sources. In the (distant) past, a DC current supply was sometimes used for the supply of a group of machines, as will be illustrated in the next section. In the subsequent two sections, a purely theoretical discussion will be given of the ideal current supply of induction and synchronous machines, respectively. Primarily, the aim of this discussion is to point out the practical issues that would arise if an ideal current source existed. In reality, modern controlled drives make use of a controlled current source inverter or a voltage source inverter with a current control loop, as will be discussed in the following chapters.

To improve the accuracy of stator flux estimator in Direct Torque Control (DTC) of Interior Permanent-Magnet Synchronous Machine (IPMSM), a pulse response based rotor position estimator is proposed. The current ripples caused by active voltage vectors in DTC are utilized by the rotor position estimator. Then, the estimated rotor position serves as an input for a model-based stator flux estimator in order to steer the switching state generator. The proposed rotor position estimator exhibits a good accuracy without introducing additional test signals. This approach preserves many advantages of DTC in controlling electromagnetic torque and stator flux, such as the absence of a motion state sensor and pulse width modulation strategy. Furthermore, the effect of varying steady-state voltage vector on estimation of rotor position is studied. The rotor position estimation error has positive correlation with the rotational speed when the switching frequency remains constant. Simulation results verify the feasibility and effectiveness of the method in estimating the rotor position and controlling both the electromagnetic torque and the stator flux and the effects of varying steady-state voltage vector on rotor position estimation.

This paper studies the performance of the dual 3-level T-type converter topology, as an advanced 5-level converter, applied to an open-ends induction machine. The performance is evaluated based on harmonic analysis, converter power loss and the steady-state machine performance. An advanced technique based on space-vector pulse-width modulation is proposed to reduce the converter switching stress as well as switching losses. A simulation based on a Matlab/Simulink program for the proposed topology as well as for some conventional multilevel converter topologies is performed. A practical implementation, based on a field-programmable gate array, for the proposed topology is presented, discussed and analyzed. A comparison between experimental and simulation results is conducted. The results show that the advanced topology reduces the harmonic content, the machine torque ripple, and the overall drive losses compared to three-level converters. Also, the proposed topology and the proposed switching technique reduce the converter losses by 40% compared to conventional five-level diode clamped converter.

Multilevel converters, which are supplied by cascaded capacitors and non-isolated DC sources, can not operate without capacitor voltage balancing. This paper proposes a capacitor voltage balancing technique for the dual three-level T-type advanced converter topology. The reason behind the capacitor voltage unbalance, of this topology, is discussed and clarified by using the converter power circuit connected to an open-end three-phase load. The converter switching states are studied and classified to three different groups according to their effect on the capacitor balancing. The proposed capacitor balancing algorithm is implemented based on switching state redundancy. This algorithm was tested by simulation through Matlab/Simulink and implemented experimentally using a field programmable gate-array digital controller. The proposed capacitor voltage balancing technique has applied to a dual three-level T-type converter AC drive system. The simulation and the experimental results were compared and analysed. Both the simulation and the experimental results are in agreement verifying the proposed algorithm.

In this paper, a comparative study of the effect of different converter topologies on the iron loss of nonoriented electrical steel is presented. Three converter topologies are considered in this investigation; namely: two-, three-, and five-level power converters. Moreover, the effect of the carrier frequency on both the iron loss and converter loss is introduced. The experimental results show a dramatic increase of the iron loss for the two-level converter, especially for low levels of the carrier frequency. Furthermore, the increase of the iron loss is negligible for the multilevel converter topologies. Specifically, the use of the five-level converter, even at a low value of the carrier frequency, results in lower iron losses than the three-level converter at a relatively higher carrier frequency.

Attempts to lower the noise of electrical machines in general and the noise of transformers in particular have gained more attention during the last years. The deformation of the magnetised ferromagnetic materials, known as magnetostriction, is a significant contributor to this noise. The aim of this work is to model such deformation by means of numerical tools. To this end, first the magnetostrictive behaviour of the material is required to apply it further for the calculations. We start with an overview of the magnetostriction strain measurement setups developed at the Electrical Energy Laboratory of Ghent University. A recently developed setup using a heterodyne laser interferometer is compared with a strain gauge setup that has been developed in the past. The results obtained by the laser setup prove to have a higher accuracy than those obtained by the strain gauge setup. In the next step, the laser measurement results are applied to the numerical magnetostrictive deformation technique. Such technique is based on finite element approach and requires a model of the magnetostrictive behaviour of the core material, which is made on the basis of the experimental results. For the computation, continuum description of magnetoelastic materials based on Chu model formulations is considered. In this method, a set of forces are introduced, which in fact induce the same strain in the material as the magnetostriction does. Applying the measurement results obtained by the laser setup in the computation method enables us to better identify the core deformation. Copyright © 2013 John Wiley & Sons, Ltd.

Model-based predictive control (MBPC) for power-electronic converters offers fast and accurate control. Based on the prediction of the future system states the optimal control input sequence is obtained by calculating a cost for each sequence. The control objectives are expressed as terms in the cost function which are weighted to divide the control effort. However, selecting good values for the weight factors is not a trivial task. In this paper a method is discussed for the weight factor selection based on extensive system simulations. The simulation approach for the hybrid system of power electronic converter and its load is discussed as well. In this paper a specific application is considered: the combined output current and capacitor voltage control of a 4-level flying-capacitor converter (FCC). This inverter topology possesses important advantages, but the control is also challenging. The high computational burden of MBPC is often restrictive for a good implementation. In this paper the implementation in a field-programmable gate array (FPGA) of an efficient prediction and optimization calculation core for finite-set MBPC is discussed. The core is fully implemented in programmable digital logic and a good performance is obtained by exploiting the strong points of the FPGA: parallelism and pipe-lining. The calculation core can be used in three applications: for hardware co-simulations, for hardware acceleration with processor-based implementations and for full FPGA implementations. Experimental results obtained with an FPGA implementation are presented.

Recently, there has been an increase in the use of finite-set model-based predictive control (FS-MBPC) for power-electronic converters. However, the computational burden for this control scheme is very high and often restrictive for a good implementation. This means that a suitable technology and design approach should be used. In this paper, the implementation of FS-MBPC for flying-capacitor converters in field-programmable gate arrays (FPGAs) is discussed. The control is fully implemented in programmable digital logic by using a high-level design tool. This allows us to obtain very good performances (both in control quality, speed, and hardware utilization) and have a flexible, modular control configuration. The good performance is obtained by exploiting the FPGA's strong points: parallelism and pipelining. Furthermore, an improved cost function for the voltage control of the flying capacitors is proposed in this paper. Typical cost functions result in tracking control for the flying-capacitor voltages, although this does not correspond with the desired system behavior. The improved cost function offers a capacitor voltage control that corresponds more closely with the desired behavior and adds a limitation on the capacitor voltage deviation. Furthermore, the selection of the weight factor in the cost function becomes less critical.

Space-vector pulse-width modulation (SVPWM) computations are complex particularly for multilevel converters. This paper introduces a novel SVPWM computation method for multilevel converters. General formulas for the region identification as well as for PWM intervals calculation are proposed. Then, the proposed formulas are applied to the advanced dual three-level T-type converter topology. The operation of this advanced topology applied to an open end winding induction machine (OEWIM) is discussed in more details. A simulation study for the proposed AC drive system is performed by using Matlab™/Simulink®. A hardware implementation based on a field-programmable gate array (FPGA) for the advanced topology supplying an OEWIM is presented, discussed and analysed. The computation algorithm is built within the FPGA digital controller. A comparison between experimental and simulation results is performed. It is observed that the simulation and the experimental results are agreed and verified the proposed algorithm.

The deformation of magnetic origin in ferromagnetic cores is due to both magnetic forces and magnetostricion. The deformation of closed magnetic circuits, such as transformers, is commonly analysed by considering magnetostriction only, while in systems with an airgap, such as rotating electrical machines, only magnetic forces are considered for the analysis of vibrations and noise of magnetic origin. Nevertheless, both phenomena, magnetic forces and magnetostriction are present in both types of magnetic cores. In this paper, both magnetic forces and magnetostriction and their resulting stresses and strains in rotating electrical machines are illustrated by means of finite element computations.

In this article a control strategy for an induction machine (IM) based electric variable transmission (EVT) for hybrid electrical vehicles (HEV) is presented. Such electrical machines consists out of two rotors resulting in a power split and a decoupling of the internal combustion engine (ICE) speed and wheel speed. The proposed control method relies on a finite-set model based predictive control (FS-MBPC) algorithm to steer the torque of both rotors as well as the flux level within the machine. The advantage of this controller is the inherent feature of field weakening and strong reduction of Joule losses as a result of the optimisation routines within this controller using a cost function. As the focus of this paper is on the control method, simulation runs in Matlab/Simulink are performed to asses the feasibility and effectiveness of the proposed control method.

At low speed, the rotor-position estimation in sensorless control is often carried out based on the evaluation of the phase-current ripples resulting from the supply of high-frequency voltage test signals. However, the rotor-position estimation is affected by cross-saturation in the machine, resulting in less accurate position estimations at higher loads. As the importance of sensorless control of interior permanent-magnet synchronous machines (IPMSMs) increases, it is useful to design IPMSMs in such a way that they are optimized for accurate sensorless control. The goal of this paper is to determine design aspects in the rotor geometry of an IPMSM to minimize the position estimation error due to cross-saturation. Simulations of a sensorless drive are usually based on a state-space model with constant q- and d-axis inductances and no mutual inductances. In this paper, this technique is improved by calculating the inductance matrix from several finite-element models, which allows the study of the effect of variable q- and d-axis inductances and cross-saturation on the performance of the sensorless control. The rotor design is discussed, for both IPMSMs with and without flux barriers, in order to reduce the estimation error caused by cross-saturation.

Flying capacitor converters (FCCs), as most multilevel converter topologies, require a balancing mechanism of the capacitor voltages. FCCs have the valuable property of natural voltage balancing when a special modulation technique is used. The classic methods, like Phase-Shifted Pulse Width Modulation (PS-PWM), result in very slow balancing for some duty ratio ranges. Previous work showed that for a single-leg five-level FCC one time constant is infinite for a zero desired output voltage. In this paper, a modified PS-PWM scheme for a single-leg fivelevel FCC is presented which results in faster balancing over the total duty ratio range. The modified PS-PWM scheme is studied, resulting in an averaged voltage balancing model. This model is verified using simulations and experiments. The modified PS-PWM scheme solves the slow balancing problems of the normal PS-PWM method for odd-level FCCs, while maintaining the passive control property, and it provides a self-precharge capability.

PurposeFlying‐capacitor multilevel converters (FCC) need a passive or active regulation of the capacitor voltages. Recently the trend is towards active control, often implemented separately from the current control. The advantages of a true multi‐variable control sparked the interest to apply Model Based Predictive Control (MBPC) for FCC. In this paper an objective analysis method to evaluate the effects of several design choices is presented. The effects of the weight factor selection, model simplification, and prediction horizon expansion for MBPC of a 3‐level FCC are analyzed in a systematical way.Design/methodology/approachThe analysis is mainly based on the mean square error (MSE) of current and capacitor voltage. The results are analysed for different lengths of the prediction horizon and for a wide range of weight factor values. Similarly the effect of a model simplification, neglecting the neutral point voltage, is studied when implementing MBPC for FCCs while considering the computational aspects. Validation of the simulation results is done by experiments on an FPGA‐based setup.FindingsIncluding the effect of the neutral point voltage considerably increases the current control quality and a much wider range of good values for the weight factor exists. As this good range is not critically dependent on the current amplitude it is possible to select one weight factor value for all operating points. Furthermore, it is concluded that increasing the prediction horizon increases the computational load without improving the control quality.Research limitations/implicationsThe effects of increasing the prediction horizon when including other controlled variables is to be investigated, as well as the robustness to modeling errors. The MSE analysis methodology is very suitable for this further research.Practical implicationsFor practitioners of MBPC in power electronics the paper proves that by means of simulations and the MSE one value for weight factor can be chosen for all operating points. The paper clearly shows that a practical implementation is feasible and demonstrates that neglecting the neutral point voltage is not good practice.Originality/valueThe MSE‐based analysis is shown to be a systematical and unbiased methodology to evaluate the effects of design choices. The results from this analysis can be directly applied in practical setups.

Flying-capacitor (FC) converters need, besides an output current control, a control of the FC voltages to be able to produce appropriate output voltage levels. The output currents and capacitor voltages can be actively controlled by model-based predictive control (MBPC). This MBPC has several control parameters such as weight factors in the cost function. The selection of these weight factors and other control parameters of MBPC is not trivial and needs an objective criterion. A method using mean square error (MSE) values of the controlled variables is proposed. The feasibility of the MBPC and the MSE analysis method for multilevel inverters is demonstrated by experiments. The good correspondence between simulations and experiments clearly shows that the results from a design analysis of MBPC in simulation is applicable on the practical setup. Two models in the prediction step of the MBPC are discussed in this study: using a simplified model, where the star-point voltage is neglected, and using an unsimplified model. The simplification, although reducing the computational requirements, results in suboptimal control quality and more importantly a less robust control. The experiments validate the conclusion that using the unsimplified model extends the range of good weight factors and improves the control quality of the current and capacitor voltages.

In switched reluctance motors, rotor position information can be extracted from the measurement of position-dependent phase voltage resonances. Due to hysteresis in the magnetic core of the machine, subsequently triggered resonances can exhibit different resonance waveforms, even when the rotor is held at a constant angular position. In order to analyze the influence of hysteresis, a finite-difference model of a magnetic lamination is coupled with a scalar Preisach model and with an electric circuit comprising an air gap and an equivalent capacitance associated with the converter, power cable and phase winding. A good correspondence is obtained between simulated and measured time-domain resonance waveforms. The model is used to predict the impact of hysteresis on the initial position estimation at start-up of the drive.

For electrical machines, accurate position estimations at low speed can be obtained from current responses on high-frequency voltage test pulses. Nevertheless, to apply these voltage test pulses the current controller is often interrupted. In this paper, a modified test pulse sequence is discussed for which the current can be controlled without interruption. To generate the modified test pulse sequence, an asymmetric pulse-width modulator is required. The improvement in the dynamic behaviour of the sensorless drive is discussed by simulations including a salient-pole permanent-magnet synchronous machine, the current control loop, the pulse-width modulator and the position estimator.

The rotor position of a salient-pole permanent-magnet synchronous machine (PMSM) at standstill or rotating at low speed is often estimated by measuring the responses on high-frequency test signals. In some drives, the rotor position is computed by measuring important current ripples that are generated by supplying the PMSM periodically with high-frequency voltage test pulses. Besides these ripples, undesired distortions in the average-current samples have been measured. Simulation results have revealed that these distortions are caused by a test signal, as it produces a nonzero voltage deviation from the steady-state stator voltage. In this paper, a low-speed sensorless strategy is discussed where a strong reduction of the aforementioned distortions is obtained by adapting the test signals to the steady-state stator voltage. The main assumption is that an accurate estimation of the steady-state voltage is made by using the controller output. The computation of the adaptive test signals is done by taking into account the voltage restriction of the dc-bus voltage. Simulation results, as well as experimental measurements, indicate the effectiveness of the adaptive test signals in a sensorless controlled interior PMSM.

The aim of the research is to investigate how much the losses in a permanent-magnet synchronous machine (PMSM) increase by the test pulses that are injected for sensorless control, i.e., to obtain rotor position information without using a position sensor. The current responses to the voltage test pulses in the machine are used as input of a 2-D transient finite element model (FEM) of the PMSM, to compute the field distribution. The magnet losses are calculated by a 3-D FEM of one magnet and a part of the rotor yoke only. To find the iron losses in the SiFe part of the magnetic circuit, quasi-static and dynamic BH-loops were measured at various amplitudes by using an excitation winding and a measurement winding around the stator yoke of the PMSM. For field waveforms recorded in the 2-D FEM, the corresponding induction is calculated by a static Preisach model. The dynamic field is added based on the theory of loss separation. The test pulses cause minor hysteresis loops. Measurements and simulations show that losses due to the test pulses are usually small and have the same order of magnitude in the permanent magnets and the yoke.

Sensorless control of permanent-magnet synchronous machines (PMSMs) at low speed and standstill is often based on a difference between q- and d-axis inductances. By determining the inductances, i.e., by evaluating current responses that result from the supply of voltage test vectors, an estimation of the rotor position is obtained. These inductances are dependent on the stator current-because of (cross-)saturation-and on the geometry of the PMSM. Changing inductances strongly affect the accuracy of the rotor position estimation. This paper investigates the influence of geometrical parameters of the rotor on the inductances and on the position estimation. First, for several angles, widths, heights, and radial positions of the buried magnets in the rotor, finite element models (FEMs) calculate the inductances and the torque as a function of the stator current. Second, to study the effect of the variable q- and d-inductances on the position estimator, time-domain simulations are carried out in combination with FEM evaluations. The simulated control is validated on an experimental interior PMSM. The FEM is not needed by the controller in the experiments.

PurposeTo study the magnetic shielding of buried high‐voltage (HV) cables by adding conductive metal plates on the ground surface above the cables.Design/methodology/approachThe field is calculated with eight rectangular conductive plates above the cables, positioned with their long edge either parallel to the cables or transversal to the cables. Here, the circuit method is used. In this method, the shield is replaced by a grid of straight filaments in which the unknown currents are searched by solving an electrical circuit.FindingsIt is observed from the calculation results that it is important to have a perfect electrical connection between adjacent plates. In the area above the shield, an “infinite” contact resistance between neighbouring plates results roughly in double field amplitude compared to the situation with contact resistance zero. The positioning of the rectangular plates (parallel or transversal to the cables) has not much influence on the shielding. The shielding efficiency as a function of the shield size is studied as well. The circuit method is validated by measurements on an experimental setup at reduced scale.Research limitations/implicationsThe circuit method is applied to conductive objects and not to ferromagnetic objects.Practical implicationsAs the circuit method is rather fast also for 3D geometries with thin plates, the shielding of HV cables can be evaluated in a computationally more efficient way than by using, e.g. finite elements.Originality/valueThe circuit method is already described in the literature. The originality of this paper is the study – by this circuit method – of the effect of several parameters (size of the shield, contact resistance, orientation of the plates) on the shielding efficiency.