Search

Active magnetic bearings (AMBs) provide reliable solution for high-speed rotors where oil-free and reliable operation are crucial. In high-power applications benefits of AMBs, compared to traditional rolling element bearings or fluid film bearings, are highly valued. Typical AMB rotors comprise 2 radial AMBs, which are designed with compressor or generator wheels integrated on the rotor. AMB dimensions and locations are carefully selected for each new application. The system design is being iterated such that the nodes of the lowest frequency rotor bending modes are sufficiently far away from the AMB and sensor nodes to ensure robust AMB control. The design is very challenging and cost sensitive. This work focuses on electromagnetic design, modelling, and control of fully levitated AMB-rotor with 3 radial AMBs. The additional bearing ensures that the same design can be re-used with different applications and regardless of the changes in locations of nodes of the first bending mode. The control plant is modelled based on flexible rotor dynamics; while bearing inductances and forces are modelled with 2D and 3D FEM electromagnetic simulations. The presented MIMO model-based control is coupled and centralized with 3 actuator-sensor pairs for radial suspension. The control design is verified in simulations using non-linear engineering models. Additionally, experimental identification results are included.

The paper addresses coupled loss and thermal analyses of a bearingless drive with an operating speed range of 17 00032 000 rpm. The drive is a part of a high-temperature heat pump system integrated in a high-speed compressor. This drive system comprises two bearingless motor units and an axial active magnetic bearing (AMB). The drive can be positioned horizontally or vertically. The positioning is directly related to the force necessary to raise and suspend the rotor. Furthermore, the amplitude of the suspension current has a significant effect on the motor winding and iron losses. The iron losses, eddy current losses in the magnets and losses in the bandage are investigated by 3D and 2D Finite Element Analysis (FEA). The influence of segmentation of the magnets on losses is analyzed. Friction losses of the coolant are calculated analytically, and all the losses obtained from the electromagnetic analysis are represented as distributed heat sources and coupled with the 3D thermal field analysis. The temperature fields are modelled under different motoring and suspension current conditions and evaluated for horizontal and vertical positions of the motor. As a precaution, demagnetization of the magnets is also considered.

The bearingless permanent magnet synchronous motor (BPMSM) is a compact motor structure that combines the motoring and bearing functions based on well-designed integrated windings for generating both torque and magnetic suspension force. In order to achieve a successful high-performance control design for the BPMSM, an adequate model of the rotor dynamics is essential. This paper proposes simplified multiple-input and multiple-output (MIMO) control approaches, namely the pole placement and the linear-quadratic regulator (LQR), that allow to carry out identification experiments in full levitation. Additionally, the stability of the MIMO levitation controller is verified with the rotation tests. Compared with other recently published works, the novelty of this paper is to experimentally demonstrate that a stable fully levitated five-degrees-of-freedom (5-DOF) operation of a bearingless machine can be achieved by the proposed approach, and thereby, options for commissioning of such a system are obtained.

High-speed solid-rotor induction machines (HSIMs) are popular within high-speed applications because of their high rotor structural integrity and their fairly well-established manufacturing process guaranteeing high quality series products. Designing a new high-speed electric machine requires a multidisciplinary team to accomplish the machine performance desired. In case of a high-speed machine design, the components and applied materials often reach their physical limits at the rated operating condition. Therefore, the design process is highly iterative and thus a systematic approach has a high potential to reduce the time of the design phase significantly. In this study, a systematic design process is proposed for a modular, multimegawatt (MMW) HSIM with three radial active magnetic bearings. The process includes a traditional multidisciplinary design flow with extra critical aspects of MMW high-speed machines: manufacturability, bearing system, housing and operating unit. In addition, the manufactured machine is reported. The proposed systematic design process is described, including several multidisciplinary critical design aspects of high-speed machinery. Post-print / Final draft

The integration of information and communication technologies (ICT) into energy power systems provides new applications and possibilities for grid control, operation, and protection. In this paper, a smart self-sustained off-grid concept based on photovoltaics- and battery energy storage system and low-voltage direct current (LVDC) power distribution network is studied. Due to small electrification and poor internet coverage, Sub-Saharan Africa is the target area of the concept realization. Focusing on the application of deep learning, this research presents new approaches to the power system's protection, as fault detection and classification are one of the most essential LVDC electricity distribution issues.

Artificial excitation signal based commissioning routines has been widely applied for the identification of the resonating mechanical system in electric drives. The commissioning tests encountered in the industry are mostly related to the detection of the first resonating mode, to be more specific, to the estimation of the two-mass-system model approximation needed for the velocity PI controller tuning. A standard identification procedure uses the torque reference as an input signal and the output is the measured velocity signal obtained from the encoder. However, most of the industrial drives are based on sensorless operation, thus there is no possibility to measure the velocity, but some information from the mechanical system is needed for the control design. This paper addresses to the issues related to the speed sensorless identification under closed loop control. A closed loop identification routine where a pseudo random binary sequence (PRBS) is superposed to the velocity control output is studied experimentally by considering a standard commercial frequency converter in sensorless mode driving an induction machine that is connected to resonating mechanical system.

Driveline resonances are one of the major reasons for poor vehicle drivability, passenger discomfort, and premature wear of the mechanical parts of the driveline. Therefore, adequate models generated by system identification are essential in order to analyze resonances, and especially to design solutions to mitigate these adverse effects by means of control. In this paper, the resonating mechanical driveline of a hybrid city bus is identified by feeding different excitation signals, such as a pseudo-random binary signal, stepped sine, and chirp to the driveline, and by measuring the frequency response at a standstill and during on-road experiments. The identification experiments are conducted by operating the bus in the series electric hybrid mode, that is, in an operating mode that corresponds to a full electric mode powered by energy storages. Resonating two-mass system models are parametrized based on the obtained frequency responses and used to validate the identification experiments.

For flux-switching PM (FSPM) motors, permanent magnets (PMs) are placed in the stator and not in the rotor structure as in the majority of PM motor designs. Recently, FSPM bearingless motors have been developed for special applications. The FSPM concept can be adapted to linear motors. For linear motors, magnets or windings located on the mover significantly decrease the complexity and cost for longer tracks. Following the ideas from the rotating bearingless motors, this work focuses on combining the motoring and levitation functionalities in a linear machine. Still, to separate the controls of air gap and torque (thrust), two sets of windings or multiphase windings are required for both rotating FSPM and linear PM machines. A linear FSPM-levitated motor solution, which integrates the magnets, winding structure, and all the driving and control electronics on the mover is desired in many applications. However, because of electromagnetic unbalances, the machine design is intertwined with the control limitations and requirements. We propose a modeling methodology for accurate derivation of the machine dynamic and static force parameters as a function of air gap, control currents, and track position in an extended operating range. Model-based control simulations based on accurate plant models determine the achievable machine performance and levitation limitations. The design and modeling methodology is universal and can be applied to various PM bearingless motors and magnetic levitation systems. In the case study of a linear FSPM-levitated motor (mover), air gap control is possible in a manner equivalent to classical active magnetic bearings, where it is linearized and independent of the thrust control.

Active magnetic bearings (AMBs) offer frictionless suspension, vibration insulation, programmable stiffness, and damping, among other advantages, in levitated rotor applications. However, AMBs are inherently unstable and require accurate system models for the high-performance model-based multi-input multi-output control of rotor position. Control electronics with high calculation capacity and accurate sensors of AMBs provide an opportunity to implement various identification schemes. A variety of artificial excitation signal-based identification methods can thus be achieved with no additional hardware. In this paper, a selection of excitation signals, namely the pseudorandom binary sequence (PRBS), chirp signal, multisine, and stepped sine are presented, applied, and compared with the AMB system identification. From the identification experiments, the rotor-bearing system, the inner current control loop, and values of position and current stiffness are identified. Unlike recently published works considering excitation-based identification of AMB rotor systems, it is demonstrated that identification of the rotor system dynamics can be carried out using various well-established excitation signals. Application and feasibility of these excitation signals in AMB rotor systems are analyzed based on experimental results.

Active magnetic bearing (AMB) supported rotor systems require advanced control strategies to meet the increased performance requirements of more and more demanding applications. To meet the particular requirements for the performance under changing dynamics, an adaptive control structure is a task worth pursuing. This paper studies adaptive multi-input multi-output (MIMO) pole placement applied to the control commissioning of an AMB-supported rotor system. The control tuning approach is based on a rigid body model, and the parameter estimation is carried out with a recursive extended least squares (RELS) based algorithm for the MIMO system. The proposed approach is studied by simulations and validated with both a 2-degree-of-freedom (2-DOF) and a 4-DOF AMB system. Post-print / Final draft

High-speed machine technology with magnetically levitated rotor systems is gaining attention in the industry. Control electronics with high calculation capacity together with accurate displacement sensors are of key importance in the quest for high-performance machines. In the most critical industrial processes, it is vital to have a remote monitoring system capable of providing measurement data for analysis. This paper proposes an Internet of Things (IoT) based monitoring concept for a high-speed machine with a magnetically levitated rotor system that employs the measured rotor position data for diagnostics. The unbalance in the rotor system is monitored by the sliding discrete Fourier transform (SDFT), and the processed data are stored in the cloud.

This paper proposes an energy management methodology for a Fusion Grid concept. The Fusion Grid concept integrates a Long-Term Evolution (LTE) base station and a power system based on photo-voltaic (PV) power generation and a battery energy storage (BES). The Fusion Grid concept can be scaled up to an off-grid system. The system studied in this paper provides connectivity in the form of an LTE mobile network and electricity access in the form of a charging station for mobile devices. The energy management and control methods are applied as part of the system. The methods are aimed at the effective use of the installed BES capacity and reducing the total life cycle costs (LCC) of the system. Furthermore, the implemented methods will prevent overdimensioning of the system, thereby having an effect on the system capital expenditure costs (CAPEX). The developed methods are evaluated in a simulation environment with quantification of their effects on the life span of the BES.

In control engineering education, interactive learning material is important to support the student to actively engage with the learning material. Especially, during the computer class exercises the given problem to be solved should be easy-to-follow and as visual as possible. Instead of using traditional problem description in paper-form, the so-called Matlab Live Script files give the possibility to make interactive learning material with visual problem statement that can be combined with the Matlab functions normally. In this paper, it is shown what kind of exercise material can be built with Matlab Live Scripts to support control engineering learning. Based on the student feedback, the implications of visual learning material in the course development is analyzed in brief.

This paper assesses the performance of a private LTE wireless network in an industrial automation setup. Our goal is to study the impact of communication latency in a robot arm position control application when the position feedback signal is transmitted via a commercial LTE wireless link. An Ethernet link scenario is considered as our benchmark. We show that even under very specific conditions (no network load, high signal power), the wireless link cannot achieve a satisfactory performance. The proposed demonstration provides a simple visualization of how LTE network latency disturbs the robot behavior, leading to undesired overshoots, oscillations and even stopping its movements. These results demonstrate that even a private LTE network is still incapable of providing the low latency required by industry automation applications, which shall be incorporated in the upcoming 5G wireless systems. Post-print / Final draft

It is beneficial to use model-based control approaches for the position control of high-speed machines with a magnetically levitated rotor system, as the system inherently involves multiple inputs and outputs. There is always uncertainty in the model parameters, and thus, a robust control approach is a preferable choice. In this paper, an $H_{\infty}$ loop-shaping method for bearingless machine control synthesis is studied and compared with the widely used PID control approach. System identification experiments are conducted to validate the results and the controller performance in the prototype system.

High-speed electric machines require dedicated bearings. Active magnetic bearings (AMBs) provide economical solution for high-power rotors where oil-free operation and low operational costs are crucial. In high-power and high-speed applications benefits of contactless rotor suspension, e.g. compared to traditional rolling element bearings, as well as online monitoring and diagnostics are highly valued. AMBs offer low losses and balancing capabilities in integrated package. The design of the high-speed high-power induction machine rotor is very challenging and cost sensitive. Manufacturing limitations, thermal and cooling constraints, stress and rotor dynamic issues and total efficiency are interdependent. The space and power electronics are limited for bearings and control design, which have to provide robust rotor suspension. This work presents electromagnetic design, modelling, and control of fully levitated AMB-rotor for demanding application. The machine design offers very limited space but 3 radial bearing planes and separate axial AMB are used. The control plant is modelled based on flexible rotor dynamics; while bearing inductances and forces are modelled with 2D and 3D FEM electromagnetic simulations. The presented LQG model-based control is scalable from single axis axial suspension to coupled centralized 3 actuator-sensor pairs radial suspension. The control has to deal with considerable plant parameter variations because of saturation and high destabilizing position stiffness because of small airgaps. The control design is verified in simulations using non-linear engineering models.

Non-contact rotor position sensors are an essential part of control systems in magnetically suspended high-speed drives. In typical active magnetic bearing (AMB) levitated high-speed machine applications, the displacement of the rotor in the mechanical air gap is measured with commercially available eddy current-based displacement sensors. The aim of this paper is to propose a robust and compact three-dimensional position sensor that can measure the rotor displacement of an AMB system in both the radial and axial directions. The paper presents a sensor design utilizing only a single unified sensor stator and a single shared rotor mounted target piece surface to achieve the measurement of all three measurement axes. The sensor uses an inductive measuring principle to sense the air gap between the sensor stator and rotor piece, which makes it robust to surface variations of the sensing target. Combined with the sensor design, a state of the art fully digital signal processing chain utilizing synchronous in-phase and quadrature demodulation is presented. The feasibility of the proposed sensor design is verified in a closed-loop control application utilizing a 350-kW, 15,000-r/min high-speed industrial induction machine with magnetic bearing suspension. The inductive sensor provides an alternative solution to commercial eddy current displacement sensors. It meets the application requirements and has a robust construction utilizing conventional electrical steel lamination stacks and copper winding.

This study presents current distribution modelling methods for a dual pack insulated-gate bipolar transistor (IGBT) module, which is operating under short-circuit conditions. The parasitic components of the commutation circuit current conductors and the internal busbars of the module are modelled by a three-dimensional finite-element method and the IGBT chips by a behavioural semiconductor model. The lumped IGBT chip model is characterised by using datasheet information only and without fine tuning of the model parameters. The mechanical dimensions of the IGBT module and the experimental setup are used to define the parasitic components for the commutation circuit. The model accuracy is investigated by comparing simulated dynamic and steady-state short-circuit parameters with experimental ones. Furthermore, uneven current distribution in the module main current terminals is observed in the simulations, and the behaviour is verified by experimental tests. The phenomenon may cause additional mechanical and electrical stresses in the device for instance because of thermal expansion and current couplings. The results show that the proposed methods are suitable to model the IGBT short-circuit behaviour and current distribution inside the module and can be used for example in the virtual design of power electronic inverter or switched power supply.

A proper real-time system identification method is of great importance in order to acquire an analytical model that sufficiently represents the characteristics of the monitored system. While the use of different time-domain online identification techniques has been widely recognized as a powerful approach to system diagnostics, the frequency-domain identification techniques have primarily been considered for offline commissioning purposes. This paper addresses issues in the online frequency-domain identification of a mechanical system with varying dynamics; particular attention is paid to detect the changes in the system dynamics. A closed-loop online identification method is presented that is based on a sliding discrete Fourier transform at a selected set of frequencies. The method is experimentally validated by a closed-loop controlled servomechanism with a limited stroke and time-varying parameters.

Wind is one of the fastest-growing renewable sources of electricity. As with most renewables, the economic viability relies on public subsidies. Even among renewables, the economic evaluation of wind projects is particularly challenging due to the unpredictability of the energy source, wind, and the high sensitivity of the project profitability to changes in a number of parameters. This makes the uncertainty analysis an important topic of research in the wind power sector. This study presents a method of combining two uncertainty analysis methods, sensitivity study and the Monte Carlo method, together with a technical and economic model of a wind farm, in an effort to improve the understanding of the practical effects of the uncertainties, and how they affect the financial risks of wind projects.

Many waste heat recovery and biomass applications offer opportunities for small-scale steam turbines to produce electricity and to improve systems’ energy efficiency. However, the currently used axial turbine-based technology is generally characterized by a relatively large physical size and poor design and off-design performances. To overcome these challenges, a new compact water-cooled high-speed radial outflow turbine concept is proposed. While the previous understanding of the chosen novel rotor water cooling approach indicates general system feasibility, improved turbine performance, and good potential, the scientific literature lacks relevant information. Since the design of high-speed machines is always case-dependent, every concept must be verified. Hence, to provide verification and new scientific information, this study combines analytical, numerical, and experimental analyses. The results predict turbine performance levels comparable with the previous radial outflow design, and its efficiency was found to exceed those of conventional turbines. During the experiments, the turbine also produced electricity from poor-quality steam, and its rotor dynamic behavior and magnetic bearing performance were close to the predicted results. These findings are considered a verification of the proposed concept. Furthermore, the rotor water cooling approach improved the stability of the system operation and although its physical behavior was not fully resolved, the study was able to verify its feasibility. In addition, at below 200 € /kW, the turbogenerator costs are competitive against competing technologies. Post-print / Final draft

Visual educational tools are important in contributing to skills in the electrical engineering profession. This paper introduces an active magnetic bearing (AMB) design tool used to teach important skills in modern high-speed technology to undergraduate students. The proposed tool is based on MATLAB, and it has a visual and easy-to-understand graphical interface. The paper describes how to use the tool and gives a design example of an axial AMB. The tools provide an opportunity to import the design directly to a finite element method (FEM) software in order to enable further analysis. The tool is also discussed from the perspectives of research and education. Post-print / Final draft

The bearingless machine construction is optimal for high-speed machines as it reduces the axial length of the machine. It is crucial that the vibration levels of the rotor are under control during rotation. In the bearingless machine, the rotor is magnetically levitated with an integrated winding system alongside a standard motor winding. In this paper, a control approach is presented to regulate the rotor position in the radial and axial directions together with the speed control of the machine. The rotor vibration levels are verified by rotational tests.

Many control schemes rely on an analytical model of the servomechanism to be controlled, and hence, accurate knowledge about the position- and time-dependent parameter variability becomes crucial in many contexts, such as robust control methods. Although a properly designed robust controller can cope with a large parameter variation, real-time identification of the system parameter behavior could lead to several advantages by means of monitoring the varying dynamics, e.g., the predetermined uncertainty region around the nominal value. This paper addresses issues in online parameter estimation of a linear tooth belt drive with a limited stroke. Particular attention is paid to detecting the position-dependent changes in the system dynamics by using recursive least squares algorithm and exciting the system in different cart positions in order to identify the varying dynamics. The algorithm used is based on an indirect output-error identification scheme. The experimentally estimated parameters are compared with the corresponding two-mass model parameters. The results show an acceptable agreement and demonstrate the feasibility of the estimation method to estimate the parameters of a closed-loop controlled servomechanism with a limited stroke and time-varying parameters.

A method is presented for tooltip tracking in active magnetic bearing (AMB) spindle applications. The proposed tool tracking approach uses control of the AMB air gap to achieve the desired tool position. A μ-synthesis-based controller is designed for the AMBs with the goal of robustly minimizing the difference between the tool reference and estimated tool position. In such a way, the model-based control approach concurrently addresses the tracking problem and the inability to directly measure real-time tool position in the presence of machining disturbances. To ensure the tractability of the control problem, a model of the desired tracking dynamics is included in the plant. The method is demonstrated on a high-speed AMB boring spindle. To confirm the tool tracking capability, characteristic part geometries are traced including stepped, tapered, and convex profiles. Tool tracking is demonstrated for the rotating AMB spindle in the range of 90 μm. Also, static and dynamic external loading is applied to the spindle tool location to confirm the disturbance rejection ability of the closed-loop system.

Traditionally, active magnetic levitation systems in rotor applications comprise separate motor for torque production, two or more radial active magnetic bearings (AMBs) and one axial AMB. Such an arrangement produces long rotors. Resulting AMB-rotor systems are often supercritical making the levitation control challenging. The centralization of the torque and force producing actuators shortens the rotor and allows for better control of unbalance magnetic pull from the rotor eccentricity. However, traditional bearingless motors employ separate windings for torque and for force production using a single actuator. This in turn lengthens the motor flux paths, increases the stator diameters, and reduces efficiency. This work studies performance and limitations of three current injection methods applied for active levitation control where the same winding is used for torque and for levitation force production. The FEM time stepping simulation results are presented and quantitative comparison is given. The case study bearingless motor system is of considerable power and high speed ratings. The use of the single winding system with the current injection control is suitable for the high-power and high-speed bearingless motor applications.

This paper presents an online nonparametric frequency response estimation approach for the identification of rotor dynamics of a high-speed machine supported by an active magnetic bearing (AMB) system. The closed-loop identification estimation approaches (direct and indirect) are based on a sliding discrete Fourier transform (SDFT) method that is applied in conjunction with a known multisine excitation signal design. The feasibility of the proposed identification approach is verified with experimental results on an AMB system. According to the results, the SDFT-based identification approach is applicable to online identification of rotor system dynamics in a computationally efficient manner.

This paper presents design optimization of high-speed and high-power bearingless motor/generator. Because of absence of separate suspension windings, in addition to the motor windings, and tooth coil arrangement a compact and axially short actuator can be achieved. A surface PM and inset PM rotor geometries are compared. The twin bearingless solution with separate axial active magnetic bearing delivers 6 degrees of freedom self-bearing motor system suitable for pumps, compressors and blower applications with considerable loads and precise clearance control in every direction. Both torque and suspension radial forces are induced with superimposed bearing and motor currents. Optimal design in terms of motor and suspension performances is investigated using finite element method and time stepping simulations.

High-speed (HS) electrical machines provide high system efficiency, compact design, and low material consumption. Active Magnetic Bearings (AMBs) bring additional benefits to the high-speed system, such as elimination of the friction losses, reduced wear and maintenance, and a built-in monitoring system. High-speed drivetrains are usually designed for specific applications and require a high level of integration. This paper describes a design method of the HS electrical machine supported by AMBs, considering their mutual influence on the system performance. The optimization procedure, which takes into account both the electrical machine and bearing designs is developed. The optimization is based on a multiobjective differential evolution (DE) algorithm. The selected optimization parameters include the AMB and machine dimensions. The optimization objectives cover the electrical machine performance and the rotordynamics. The results of the proposed optimization algorithm are implemented in the constructed 350kW, 15000rpm induction machine with a solid rotor supported by AMBs. The prototype tests verify the design and optimization results.

Accurate and updated knowledge of the electric machine parameters provides benefits in many applications, such as model-based control methods. This paper presents an online parameter estimation method for double-star interior permanent-magnet (IPM) machines supplied with voltage-source inverters (VSI). The estimation method is based on a decoupled D-Q model of the machine and a recursive least-squares (RLS) algorithm. Initial machine parameters are estimated at a standstill. Then, in the rotating operating state, the inductances and the flux linkage produced by the PMs are updated. The estimation in the operating state is performed with a flux-linkage-based approach. The experimental results are compared with the corresponding values obtained from finite-element analyses. The results show an acceptable agreement and demonstrate the feasibility of the estimation scheme to estimate the parameters of double-star PM machines. The parameters are validated by comparing experimental and simulated open-loop responses and steady-state torques.

Dual three-phase electric machines have many advantages compared with conventional three-phase machines. However, the properties of such machines present challenges for current control that make it difficult to produce sufficient performance for the electric drive. This paper introduces an improved vector control scheme for dual three-phase permanent magnet synchronous machines. The study includes detailed solutions for key parts of the control such as reference frame transformations, decoupling of the current control loops, and modulation. The performance of the suggested control scheme is evaluated using finite-element analyses and experimental results. The results show that the scheme can produce desired dynamics for the current control and guarantees balanced current sharing between the winding sets. In addition, the proposed solution is capable of reducing current harmonics produced by the internal structure of the machine. This problem is, however, only partly solved since complete elimination of harmonic components is not achieved. Nevertheless, the suggested control scheme overcomes many of the disadvantages found with other control solutions. Improved control performance allows the full benefits of dual three-phase drives to be utilized even in demanding applications.

Rapid development of wind power technologies is enabling many nations to increase the share of wind energy in total electricity production. Finland, in common with many other countries, has a target of raising the contribution of wind resources to national energy production. The majority of existing and planned turbines in Finland are located in coastal areas, where the wind resources can provide favorable conditions for wind farms. However, considerable wind potential may exist in inland areas of the country. This paper presents a wind resource analysis of the southeast of Finland. The wind data, consisting of meteorological mast and LIDAR measurements at several heights, were collected in 2009 – 2011. The analysis includes monthly average wind speed, diurnal wind behavior and wind shear assessment. The energy output is estimated for a 3 MW wind turbine based on real wind speed distributions. Capacity factors are calculated to assess 3 MW wind turbine feasibility at the site. The obtained results demonstrate that inland wind conditions have sufficient potential to allow wind energy to thrive.

Analytical models are the key tools in the model-based control design of electric drives. The inductances together with the stator resistance are the fundamental parameters of these models. In this study three methods to determine the inductances of the decoupled d–q model of double-star permanent-magnet (PM) synchronous machines are studied. These methods have commonly been used to determine the inductances of conventional three-phase PM machines. Two of the evaluated methods are based on the phase-variable inductance waveforms and flux linkages and are thus analysed with finite-element analyses only. The third method, based on the analytical stator voltage equations, can be applied straightforwardly with the real drive system supplied with voltage-source inverters (VSIs). This method requires only the knowledge of the rotor position and the existing current measurements of the VSIs that are used for the current control. Experimental results are provided to verify the applicability of the voltage-equation-based method to determine the inductances. On the average, the presented methods provide similar values, but also some discrepancies between the obtained values can be observed. The measured inductance parameters are validated using model-based closed-loop controllers.

The paper reports on the implementation and the design of a controller for a fuel cell blower (FCB) with active magnetic bearings (AMBs). The cascaded position-fluxcentralized controller is comprised of a centralized position control loop and an inner flux control loop. The last one is based on state estimation without explicit flux measurements. As the position control is not dependent on the magnetic field nonlinearities, such a control structure enables operation under a zero bias. The practical working implementation of a flux control for the industrial levitated rotor is shown for the first time. The flux control gives better results than current control for both normal and zero bias operation. The system is analyzed fully, combining rotor dynamics and power amplifier analyses simultaneously. The importance of using the coil voltage in addition to current and practical treatment of the flux control is revealed. The centralized position-flux controller is compared with a state-of-the-art cascaded position-current control, which has inner current control loops. The proposed control solution with a zero bias can achieve a dynamic performance comparable that of a controller with the classical bias current.

High-speed machine technology with magnetically levitated rotor systems has become interesting solution in modern compressor, pump and turbo applications. Often, the commissioning of such machines is system identification-based with injected artificially generated excitation. In this paper a statistically uncorrelated PRBS design is proposed for multi-input multi-output MIMO system that gives the possibility to utilize same PRBS signal for all inputs. The proposed routine is validated with an experimental high-speed generator with active magnetic bearings (AMBs). The obtained frequency responses are validated by comparing the results with the mathematical model.

A part of the wind farm layout optimization is the design of the wind farm infrastructure, that includes roads and the electrical collector system. The cost of the wind farm infrastructure is a minor part of the total cost. However, its variability with different layouts influences the optimal layout of the wind farm. The aim of this paper is to develop a realistic model for the wind farm infrastructure and propose a fast algorithm for solving the problem. First, the road layout is found using the Dijkstra's shortest path algorithm, considering the existing roads. After that, the collector system is optimized using metaheuristic Cuckoo Search algorithm, taking into account information about previously found road layout and the lifetime costs of the cables, power losses and outages. A Genetic algorithm is used as a benchmark for comparing the performance of the Cuckoo Search algorithm.

This paper studies an online nonparametric identification method that is based on a time-frequency representation of signals using Kalman filter. The method utilizes swept excitation signal by synchronizing the Kalman filter to the frequency of the excitation signal generator and updating the filter gains on a sample-by-sample basis. Four different closed loop identification configuration are studied and experimentally compared by considering direct and indirect identification approaches. Moreover, this paper studies loop transfer function estimation from the closed loop controlled servomechanism and discusses the possibility to use the result for loop diagnostics. The experimental results illustrate the effectiveness of the studied online identification method to estimate nonparametric frequency response of the closed loop-controlled servomechanism at a selected band of frequencies.

This paper proposes and investigates the application of the gradient heat flux sensor (GHFS) for measuring the local heat flux in power electronics. Thanks to its thinness, the sensor can be placed between the semiconductor module and the heat sink. The GHFS has high sensitivity and yields direct measurements without an interruption to the normal power device operation, which makes it attractive for power electronics applications. The development of systems for monitoring thermal loading and methods for online detection of degradation and failure of power electronic devices is a topical and crucial task. However, online condition monitoring (CM) methods, which include heat flux sensors, have received little research attention so far. In the current research, an insulated-gate bipolar transistor (IGBT) module-based test setup with the GHFS implemented on the base plate of one of the IGBTs is introduced. The heat flux experiments and the IGBT power losses obtained by simulations show similar results. The findings give clear evidence that the GHFS can provide an attractive condition monitoring method for the thermal loading of power devices.

This paper presents a novel analytical method for electro-mechanical design of a high speed long-term flywheel energy storage system and thermal evaluation of possible operating modes of the system. Flywheel’s composite shell rotor along with the motor/generator unit are assumed to be placed into a sealed vacuum chamber, which presents a challenge of heat transfer, produced by rotor losses. Developed method takes into account thermal radiation properties of the rotor and is realised using Mathcad software, which allows for quick investigation of any flywheel configuration. The method involves calculations for preliminary rotor sizing and determining achievable operation modes, while keeping the rotor under a specified temperature limit. Results of using this method for studying dependencies of thermal performance on initial system parameters are presented and conclusions are drawn. Based on the conducted study, recommendations on system design considerations are given.

Some of the most widely recognized online parameter estimation techniques used in different servomechanism are the extended Kalman filter (EKF) and recursive least squares (RLS) methods. Without loss of generality, these methods are based on a prior knowledge of the model structure of the system to be identified, and thus, they can be regarded as parametric identification methods. This paper proposes an on-line non-parametric frequency response identification routine that is based on a fixed-coefficient Kalman filter, which is configured to perform like a Fourier transform. The approach exploits the knowledge of the excitation signal by updating the Kalman filter gains with the known time-varying frequency of chirp signal. The experimental results demonstrate the effectiveness of the proposed online identification method to estimate a non-parametric model of the closed loop controlled servomechanism in a selected band of frequencies.

An improved duty-cycle modulation scheme for multilevel inverters is introduced. The scheme exploits two-to-three axis coordinate transformation to achieve duty-cycles of each phase directly from the location of the reference vector in the Cartesian coordinate system. There is no need for trigonometric functions, which makes the applicability of the algorithm very good in a digital signal processor or a field-programmable gate array. The method also guarantees a low common-mode voltage output, because a zero-component is added only when operating at a voltage amplitude larger than 75% of the maximum amplitude of the reference vector. The selection of zero-component is also simple and mathematically easy. The pulse-formation is formulated in such a way that the modules of the inverter are equally loaded, and the balance of the individual DC link voltages is maintained throughout the voltage region. The methods are verified with simulations and experimental tests on a seven-level 100 kVA, 3 kV prototype induction motor drive.

In this work a design optimization of the high-speed buried-type interior permanent magnet bearingless motor with significant power for such machines is presented. The geometry, windings arrangement and magnets are adjusted from the non-levitated motor design to avoid the significant magnetic saturation and achieve the performance target without oversizing the machine. The analytical design is optimized in finite element method analysis. The effect of stator skew on machine performance is thoroughly investigated.

Bearingless motors combine the torque generation of electrical motors and the radial suspension force capabilities of traditional magnetic bearings. The magnetomotive force (MMF) distribution in the motor generates radial force interference. The interference force affects the angle between the actual and desired radial force. This angle is called the force error angle. For stable levitation of the rotor of the bearingless motor the force error angle must be minimized in the design phase of the machine. This paper presents an optimal rotor structure for minimization of the error angle in a high-speed interior permanent magnet bearingless motor with magnets embedded in the rotor surface.

A method is presented for tool tracking in active magnetic bearing (AMB) spindle applications. The method uses control of the AMB air gap to achieve the desired tool position. The reference tracking problem is transformed from the tool coordinates into the AMB control axes by bearing deflection optimization. Therefore, tool tracking can be achieved by an off-the-shelf AMB controller. The method is demonstrated on a high-speed AMB boring spindle with a proportional integral derivative (PID) control. The hypothetical part geometries are traced in the range of 30 μm. Static external loading is applied to the tool to confirm disturbance rejection. Finally, a numerical simulation is performed to verify the ability to control the tool during high-speed machining.

Modern high power grid inverters use usually LC-or LCL-filter at grid interface. Simpler L-filter does not prove sufficient harmonic attenuation without resulting in to very large and bulky filter components. Higher order filters realize better attenuation with smaller components. However, these filters introduce additional resonances to the system, which may cause instabilities without proper care. Connecting more than one inverter with individual LC- or LCL-filters in parallel will result in shifted resonances. The identification of the resonances in parallel connected LC- and LCL-filter system is essential for proper operation of the grid-connected inverter. For instance the efficiency of active damping is highly depended on the accurate knowledge of the filter resonances. In this paper the transfer functions for parallel-connected filter systems are derived and resonances analyzed. A method for resonance identification is presented.

In the paper a nonlinear load control method is developed and implemented for a permanent magnet linear synchronous motor (PMLSM). The purpose of the controller is to track a flexible load to the desired velocity reference as fast as possible and without awkward oscillation. The control method is based on an adaptive backstepping algorithm whose stability is ensured by the Lyapunov stability theorem. The states of the system needed in the controller are estimated by using the Kalman filter. The proposed controller is implemented and tested in a linear motor test drive and responses are presented.