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This paper deals with stator-flux-oriented control of permanent-magnet (PM) synchronous motors and synchronous reluctance motors (SyRMs). The variables to be controlled are the stator-flux magnitude and the torque-producing current component, whose references are easy to calculate. However, the dynamics of these variables are nonlinear and coupled, potentially compromising the control performance. We propose an exact input–output feedback linearization structure and a systematic design procedure for the stator-flux-oriented control method in order to improve the control performance. The proposed controller is evaluated by means of experiments using a 6.7-kW SyRM drive and a 2.2-kW interior PM synchronous motor drive. [ABSTRACT FROM AUTHOR]

This paper addresses robust design of the active-power and dc-link control loops of power-synchronization control. Robustness is obtained by analytic gain selections, which give large enough stability margins. The proposed design allows robust stability irrespective of the grid strength and of the operating point, the latter with one exception. The proposed design is compared to design based on the principle virtual synchronous machine. Experiments show that the time-domain results correlate well with the frequency-domain results. [ABSTRACT FROM AUTHOR]

This paper deals with the speed and position estimation for synchronous reluctance motors (SyRMs) and interior permanent-magnet synchronous motors (IPMs). A unified design and analysis framework for a class of back electromotive force-based observers is developed and the links between apparently different estimation methods are brought out. State observers equipped with a speed-adaptation law are shown to be mathematically equivalent to voltage-model-based flux observers equipped with a position-tracking loop. The error signal driving the adaptation law or the tracking loop is presented in a generalized form. Using the framework, a stabilizing gain design is reviewed and detailed design guidelines are given. Selected observer designs are experimentally evaluated using a 6.7-kW SyRM drive and a 2.2-kW IPM drive. [ABSTRACT FROM AUTHOR]

This paper deals with grid-voltage sensorless synchronization and control under unbalanced grid conditions. A three-phase grid-connected converter equipped with an LCL filter is considered, and no signals other than the converter currents and the dc-link voltage are measured for control. An augmented adaptive state observer is proposed for estimation of the positive- and negative-sequence components of the grid voltage. Dynamic performance limitations of the proposed method and effects of parameter errors are analyzed. The proposed observer is tested as part of a sensorless control system. Experimental results show that the proposed method works well even under highly unbalanced grid conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a standstill method for the identification of the magnetic model of synchronous reluctance motors (SyRMs). The saturation and cross-saturation effects are properly taken into account. The motor is fed by an inverter with a short sequence of bipolar voltage pulses that are first applied on the rotor $d$- and $q$ -axes separately and then simultaneously on both the axes. The stator flux linkages are computed by integrating the induced voltages. Using the current and flux samples, the parameters of an algebraic magnetic model are estimated by means of linear least squares. The proposed method is robust against errors in the stator resistance and inverter voltage, due to the high test voltages (of the order of the rated voltage). The fitted model matches very well with the reference saturation characteristics, measured using a constant-speed method, and enables extrapolation outside the sample range. The method was tested with a 2.2-kW SyRM, whose shaft was uncoupled from any mechanical load, which is the most demanding condition for this method. The proposed method can be used for automatic self-commissioning of sensorless SyRM drives at standstill. [ABSTRACT FROM PUBLISHER]

Synchronization with the power system is an essential part of control of grid-connected converters. This paper proposes a grid-voltage sensorless synchronization and control scheme for a converter equipped with an LCL filter, measuring only the converter currents and the dc voltage. A discrete-time pole-placement design method is used to formulate an adaptive full-order observer for the estimation of the frequency, angle, and magnitude of the grid voltage. The proposed discrete-time design method enables straightforward implementation and suits low sampling rates better than its continuous-time counterpart. The analytically derived design is experimentally validated, and the results demonstrate rapid convergence of the estimated quantities. Moreover, the experimental tests show that grid-voltage sensorless operation is possible under balanced and unbalanced grid disturbances and distorted grid conditions. [ABSTRACT FROM PUBLISHER]

This paper deals with discrete-time models and current control methods for synchronous motors with a magnetically salient rotor structure, such as interior permanent-magnet synchronous motors and synchronous reluctance motors (SyRMs). The dynamic performance of current controllers based on the continuous-time motor model is limited, particularly if the ratio of the sampling frequency to the fundamental frequency is low. An exact closed-form hold-equivalent discrete motor model is derived. The zero-order hold of the stator-voltage input is modeled in stationary coordinates, where it physically is. An analytical discrete-time pole-placement design method for two-degrees-of-freedom proportional–integral current control is proposed. The proposed method is easy to apply: only the desired closed-loop bandwidth and the three motor parameters (\boldsymbolR_\mathbfs, \boldsymbolL_\mathbfd, \boldsymbolL_\mathbfq) are required. The robustness of the proposed current control design against parameter errors is analyzed. The controller is experimentally verified using a 6.7-kW SyRM drive. [ABSTRACT FROM AUTHOR]

State-space current control enables high dynamic performance of a three-phase grid-connected converter equipped with an LCL filter. In this paper, observer-based state-space control is designed using direct pole placement in the discrete-time domain and in grid-voltage coordinates. Analytical expressions for the controller and observer gains are derived as functions of the physical system parameters and design specifications. The connection between the physical parameters and the control algorithm enables automatic tuning. Parameter sensitivity of the control method is analyzed. The experimental results show that the resonance of the LCL filter is well damped, and the dynamic performance specified by direct pole placement is obtained for the reference tracking and grid-voltage disturbance rejection. [ABSTRACT FROM PUBLISHER]

This paper deals with methods for parameter estimation of two-mass mechanical systems in electric drives. Estimates of mechanical parameters are needed in the start-up of a drive for automatic tuning of model-based speed and position controllers. A discrete-time output error (OE) model is applied to parameter estimation. The resulting pulse-transfer function is transformed into a continuous-time transfer function, and parameters of the two-mass system model are analytically solved from the coefficients of this transfer function. An open-loop identification setup and two closed-speed-loop identification setups (direct and indirect) are designed and experimentally compared. The experiments are carried out at nonzero speed to reduce the effect of nonlinear friction phenomena on the parameter estimates. According to results, all three identification setups are applicable for the parameter estimation of two-mass mechanical systems. [ABSTRACT FROM PUBLISHER]

This paper deals with the design of a speed-adaptive full-order observer for sensorless induction motor (IM) drives. A general stabilizing observer gain matrix, having three free design parameters, is used as a design framework. A gain-scheduled selection of the free design parameters is proposed. Furthermore, the full-order observer is augmented with the stator-resistance adaptation, and the local stability of the augmented observer is analyzed. The performance of the proposed full-order observer design is experimentally compared with a reduced-order observer using a 2.2-kW IM drive. [ABSTRACT FROM AUTHOR]

This paper proposes a model-based two-degree-of-freedom (2DOF) state-space speed controller design for a two-mass mechanical system. Analytical tuning rules for a feedback gain, the reduced-order state observer, full-order state observer, and prefilter are derived. The proposed design rules enable the automatic tuning of the controller if the mechanical parameters are known. The prefilter is designed for step, ramp, and parabolic command tracking. The effects of the time delay, measurement noise, and parameter variations on controller tuning and control performance are studied by means of Nyquist diagrams, noise transfer functions, and time-domain simulations. It is shown that the full-order-observer-based controller is a preferable choice, particularly if the feedback loop is delayed and noisy. The proposed controller design is experimentally evaluated using two 4-kW servo motors coupled with a toothed belt; good reference tracking for step and dynamic commands, as well as robust and fast load-torque rejection, is demonstrated. [ABSTRACT FROM PUBLISHER]

A back-electromotive-force-based position observer for motion-sensorless synchronous reluctance motor (SyRM) drives is augmented with parameter adaptation laws for improved operation at all speeds, including standstill. The augmented observer is theoretically analyzed under various operating conditions. The analysis indicates that the stator-resistance adaptation should be enabled only at low speeds, the $d$-axis inductance adaptation should be enabled only at medium and high speeds near no load, and the $q$-axis inductance adaptation should be enabled only at high speeds under high load. The augmented observer is experimentally evaluated using a 6.7-kW SyRM drive. [ABSTRACT FROM AUTHOR]

This paper presents a state-space current control method for active damping of the resonance frequency of the LCL filter and setting the dominant dynamics of the converter current through direct pole placement. A state observer is used, whereupon additional sensors are not needed in comparison with the conventional L filter design. The relationship between the system delay and instability caused by the resonance phenomenon is considered. Nyquist diagrams are used to examine the parameter sensitivity of the proposed method. The method is validated with simulations and experiments. [ABSTRACT FROM AUTHOR]

The induction machine model parameters need to be estimated with good accuracy to ensure a good performance of the drive. Due to the magnetic saturation, the inductances vary as a function of the flux level. The magnetizing curve can be identified at standstill, but more accurate results are obtained if the identification is performed as the machine is running. In this paper, the magnetic saturation is modeled using a power function, and adaptation laws for the function parameters are proposed. The adaptation method is implemented in the control system of a sensorless drive. Experimental results on a 2.2-kW machine show that the identification of the stator inductance is rapid and the accuracy is good. [ABSTRACT FROM AUTHOR]

A back-electromotive-force-based reduced-order position observer with stator-resistance adaptation is analyzed for motion-sensorless synchronous reluctance motor (SyRM) drives. Analytical equations for steady-state estimation errors and stability conditions are derived (with and without resistance adaptation), taking into account errors in the parameter estimates. The effect of the observer gain on the noise reduction is studied by means of eigenvector analysis. A robust gain selection is proposed, which maximizes the allowed uncertainties in the parameter estimates. The proposed observer design is experimentally evaluated using a 6.7-kW SyRM drive; stable operation is demonstrated at low speeds under various parameter errors. [ABSTRACT FROM AUTHOR]

Two back-electromotive-force-based position observers are compared for motion-sensorless synchronous motor drives: the reduced-order observer and the adaptive full-order observer. A stabilizing gain is proposed for the adaptive full-order observer, which guarantees the local stability of the closed-loop system, if the motor parameters are known. Equations for the steady-state position error and for the linearized estimation-error dynamics under erroneous parameters are derived, and the robustness of the two observers against parameter errors is analyzed and compared. The observers are experimentally evaluated using a 6.7-kW synchronous reluctance motor drive in low-speed operation and under parameter errors. The gain selection of the reduced-order observer is easier, but the adaptive full-order observer can be made more robust against parameter variations and noise. [ABSTRACT FROM AUTHOR]

This paper deals with reduced-order flux observers with stator-resistance adaptation for speed-sensorless induction motor (IM) drives. A general analytical solution for the stabilizing observer gain is given. The gain has two free positive parameters (which depend on the operating point), whose selection significantly affects the damping, convergence rate, robustness, and other properties of the observer. The general stability conditions for the stator-resistance adaptation are derived. An observer design is proposed that yields a robust and well-damped system and requires a minimal amount of tuning work. The proposed observer design is experimentally tested using a 45-kW IM drive; stable operation at very low speeds under different loading conditions is demonstrated. [ABSTRACT FROM AUTHOR]

A small-signal model is derived for saturated induction machines. Inductances are allowed to saturate as a function of their own current (or flux), and the mutual saturation effect originating mainly from skewed or closed rotor slots is also included in the model. The model fulfills the reciprocity conditions, and it can be applied to parameter identification and to the analysis and development of flux-angle estimation methods. As application examples, the parameters of a 2.2-kW induction machine were identified using the data obtained from time-stepping finite-element analysis and locked-rotor measurements. The proposed model fits well to the data, and the fitted parameters are physically reasonable. [ABSTRACT FROM AUTHOR]

Saturation due to main flux and rotor leakage flux interaction appears in induction machines, particularly if rotor slots are skewed or closed. Conventional saturation models used in connection with dynamic equivalent-circuit models do not take this phenomenon into account. In this paper, explicit functions for modeling this mutual saturation are proposed. These functions are physically reasonable and are easy to fit, and the number of their parameters is small. The proposed functions can be used in real-time applications and in computer simulations if high accuracy and physical consistency are preferable. The model fits well to the data obtained from finite-element analysis or experimental data of a 2.2-kW motor. The model predicts the stator current with good accuracy both in steady state and in transients. [ABSTRACT FROM AUTHOR]

This paper proposes an online method for the estimation of the stator resistance and the permanent-magnet (PM) flux in sensorless PM synchronous motor drives. An adaptive observer augmented with a high-frequency signal injection technique is used for sensorless control. The observer contains excess information that is not used for the speed and position estimation. This information is used for the adaptation of the motor parameters: At low speeds, the stator resistance is estimated, whereas at medium and high speeds, the PM flux is estimated. Small-signal analysis is carried out to investigate the proposed method. The convergence of the parameter estimates is shown by simulations and laboratory experiments. The stator resistance adaptation works down to zero speed in sensorless control. [ABSTRACT FROM AUTHOR]

In this paper, reduced-order observers for flux and speed estimation of sensorless induction-motor drives are analyzed. All gain selections, which give stability for all operating conditions, including the regeneration mode (called complete stability), are found. Furthermore, it is shown that full-order observers, under the assumption of fast stator-current dynamics, have equivalent implementations as reduced-order observers. Consequently, all gain selections of the full-order observer gains for which complete stability is obtained, under the assumption stated, are also found. A number of previously proposed full-order observers are analyzed within the developed framework, generally showing agreement between the full- and reduced-order models. [ABSTRACT FROM AUTHOR]

This paper deals with a speed and position estimation method for the sensorless control of permanent magnet synchronous motors. The method is based on a speed-adaptive observer. The dynamics of the system are analyzed by linearizing both the motor model and the observer, and the observer gain is selected to give improved damping and noise suppression. At low speeds, the observer is augmented with a signal injection technique, providing stable operation down to zero speed. The experimental results, obtained using a 2.2-kW interior magnet motor, are in agreement with the results of the analysis. [ABSTRACT FROM AUTHOR]

This paper deals with the maximum torque and speed of permanent-magnet synchronous motor (PMSM) drives when the inverter output voltage is filtered by an LC filter with a cutoff frequency well below the switching frequency. According to steady-state analysis, the filter affects the performance of the motor drive, especially at high speeds. The stator current is not equal to the inverter current, and due to the inverter current and inverter voltage limits, the torque-maximizing stator current locus differs from that of a drive without the filter. A field-weakening method is proposed for PMSM drives with an inverter output filter. The method is implemented and tested in a 2.2-kW PMSM drive. The experimental results agree well with the analysis, and validate the high- speed performance of the proposed field-weakening method. [ABSTRACT FROM AUTHOR]

This paper deals with sensorless vector-controlled induction motor drives that are fed by a frequency converter that is equipped with a diode front-end rectifier. A small dc-link capacitance is used, which makes it possible to replace the electrolytic capacitors with film capacitors. The natural frequency of the dc link is chosen to be considerably higher than six times the mains frequency but lower than the switching frequency. A recently proposed sensorless controller can be exploited; only minor modifications for small capacitances are needed. The simulation and experimental results of a 2.2-kW drive that is equipped with a capacitance of only 24 µF demonstrate operation in a wide speed range. [ABSTRACT FROM AUTHOR]

This paper deals with sensorless vector control of pulsewidth-modulated inverter-fed induction motor drives equipped with a three-phase diode rectifier. An electronically controlled braking resistor across the dc link is not used. Instead, the power regenerated during braking is dissipated in the motor while a dc-link overvoltage controller limits the braking torque. Losses in the motor are increased by an optimum flux-braking controller, maximizing either the stator voltage or the stator current depending on the speed. Below the rated speed, the braking times are comparable to those achieved using a braking resistor. The proposed braking scheme is very simple and causes no additional torque ripple. Experimental results obtained using a 2.2-kW induction motor drive show that the proposed scheme works well. [ABSTRACT FROM AUTHOR]

This paper deals with the speed sensorless vector control of an induction motor in a special case where the output voltage of the pulsewidth-modulated inverter is filtered by an inductance-capacitance (LC) filter. The system states are estimated by means of an adaptive full-order observer, and no additional voltage, current, or speed measurements are needed. The rotor speed adaptation is based on the estimation error of the inverter output current. Quasi-steady-state and linearization analyses are used to design an observer that enables a wide operation region, including very low and very high speeds. A torque- maximizing control method is applied in the field-weakening region. Simulation and experimental results show that the performance is comparable to that of a drive without the LC filter. [ABSTRACT FROM AUTHOR]

This paper deals with the full-order flux observer design for speed-sensorless induction motor drives. An unstable region encountered in the regenerating mode at low speeds is well known. To remedy the problem, a modified speed-adaptation law is proposed. Instead of using only the current estimation error perpendicular to the estimated flux, the parallel component is also exploited in the regenerating mode. Using current estimation error loci in steady state, a linearized model, simulations, and experiments, it is shown that the observer using the proposed speed-adaptation law does not have the unstable region. It is also shown that the effect of erroneous parameter estimates on the accuracy of the observer is comparatively small. [ABSTRACT FROM AUTHOR]

This paper deals with the flux estimation for sensor-less induction motor drives. The linearized model of the speed- adaptive full-order flux observer is applied to help choosing the observer gain and the speed-adaptation gains. It is shown that the linearized model reveals potential instability problems that are difficult to find by other means. An observer gain and a method to vary the speed-adaptation gains in the field-weakening region are proposed. Experimental results show stable operation in a very wide speed range. [ABSTRACT FROM AUTHOR]

Presents the steady-state parameter sensitivity analysis of both the flux estimation and the torque production for rotor flux orientation controlled drives using a full-order flux observer. Description of the induction motor model; Information on the observer gain design; Results of the experiments.

This letter deals with voltage model flux estimators for sensorless induction motor drives. In order to eliminate the drift problems, the pure integrator of the voltage model is replaced with a first-order low-pass filter, and the error due to this replacement is compensated in a very simple way. [ABSTRACT FROM AUTHOR]

This article proposes a multifunctional cascade controller structure for voltage-source converters. The proposed structure contains a decoupling loop between the outer voltage control loop and the inner current control loop, and operation in either voltage or current control mode is possible. In voltage control mode, the current controller can be made completely transparent. In the case of faults, the proposed structure enables inherent overcurrent protection by a seamless transition from voltage to current control mode, wherein the current controller is fully operational. Seamless transitions between the control modes can also be triggered with an external signal to adapt the converter to different operating conditions. The proposed structure allows for integration of simple, accurate, and flexible overcurrent protection to state-of-the-art single-loop voltage controllers without affecting voltage control properties under normal operation. The properties of the proposed controller structure are validated experimentally on a 10-kVA converter system. [ABSTRACT FROM AUTHOR]

This article develops a dynamic model for six-degree-of-freedom bearingless linear motor systems by means of lumped-element modeling. A four-sided motor system, containing eight three-phase motor units fed by their own inverters, is considered as an example system, but the modeling approach can be applied to other motor systems as well. The mechanical subsystem of the model comprises the rigid-body dynamics. The electromagnetic subsystem governs the electrical dynamics of the motor units and the production of the resultant electromagnetic force and its associated torque. In order to model the unbalanced magnetic torque due to tilting of the mover, the motor units are spatially discretized into a number of identical submotor models having a uniform air gap. The submotor models of each motor unit are electrically connected in series, i.e., they share the same current, but their flux linkages and forces differ in tilted positions. The electromagnetic subsystem can be parameterized based on simple static two-dimensional finite-element method computations at a range of uniform air-gap and current values. The developed model is validated through a comparison between the time-domain simulation results and the experimental results. The model can be applied to time-domain simulations, real-time control system development, and various analyses of the system. [ABSTRACT FROM AUTHOR]

The stability of the converter-grid interconnection can be studied by analyzing the product of the converter output admittance and the grid impedance. For reliable stability analysis, it has been of interest to obtain accurate converter output admittance models for a wide range of frequencies, ideally also around and above the Nyquist frequency of the converter system. This article presents a modeling method for the output admittance of power converters defined in the Laplace domain that takes into account the discrete nature of the control system. The modeling method is based on analyzing the intersample behavior of sampled-data systems, a class of systems that includes the modern digitally controlled power converters. The proposed method is compared to conventional admittance modeling methods, and its accuracy is validated by means of simulations and experiments. [ABSTRACT FROM AUTHOR]

In this letter, an enhancement of power-synchronization control is proposed, whereby pole–zero cancellation in the closed-loop system is achieved. An effect thereof is that step-response ringing and overshoot are eliminated. For strong grids, the closed-loop bandwidth increases, allowing a shorter step-response rise time. [ABSTRACT FROM AUTHOR]

This paper deals with a dynamic model for three-phase induction machines equipped with closed rotor slots and deep rotor bars. The thin bridges closing the rotor slots saturate highly as a function of the rotor current. The impedance of the rotor bars also varies much as a function of the rotor current frequency. An extended dynamic model, which takes into account the slot-bridge saturation and the deep-bar effect, is developed. The model extensions can be plugged into a standard machine model and parametrized easily. The proposed model can be applied to time-domain simulations, real-time control, and identification. The model is validated by means of finite-element analysis and experiments using a four-pole 5.6-kW induction machine. The results show that the accuracy of the proposed model is superior to the standard model, particularly under transient excitation typically used in standstill self-commissioning tests of induction motor drives. [ABSTRACT FROM AUTHOR]

Magnetic saturation characteristics of synchronous reluctance motors (SyRMs), with or without permanent magnets, are highly nonlinear. These nonlinear effects can be included in the current controller by changing its state variable from the stator current to the stator flux linkage using the known saturation characteristics. A direct discrete-time variant of the flux-linkage-based current controller is developed in a state-space framework. If the magnetics are modeled to be linear, the proposed control structure reduces to the standard current controller in this special case. Experimental results on a 6.7-kW SyRM drive demonstrate that the proposed flux-linkage-based controller enables a higher closed-loop bandwidth and is more robust against parameter errors, as compared to the standard current controller. [ABSTRACT FROM AUTHOR]

An introduction to the periodical is presented in which the editor discussed various topics within the issue including a design strategy for ferrite-assisted synchronous reluctance machines, five-phase machine design and the use of bridges in the rotor lamination.

This paper proposes a method for estimating two inductances and capacitance of an LCL filter, connected between a converter and a grid. Only the dc-bus voltage and converter phase currents need to be measured. An excitation signal is fed into the converter voltage reference. The fundamental and selected harmonic components are removed from the stored identification data to prevent biases in the parameter estimates. The parameters of the hold-equivalent discrete-time model are estimated recursively. The inductance and capacitance estimates are calculated from the estimated discrete-time parameters using the corresponding closed-form model. The proposed method can be added to the existing converter control algorithms. It can provide the parameter estimates for the converter control. Further, it can be run occasionally during the normal operation in order to obtain an updated grid inductance estimate. Experimental results show that the proposed method yields very good parameter estimates and that it can also detect the changes in the grid inductance. [ABSTRACT FROM PUBLISHER]

A classical control approach to the design and analysis of proportional–integral (PI) speed controllers for electrical drives is presented. After vindicating the fact that traditional one-degree-of-freedom PI control generally gives unsatisfactory performance, a well-performing two-degree-of-freedom PI controller is designed, with analytical parameter selection. The robustness of the obtained closed-loop system is analyzed and is found to be satisfactory. All the proposed control designs are validated by means of experiments. [ABSTRACT FROM AUTHOR]

This paper applies a dynamic space-vector model to loss-minimizing control in induction motor drives. The induction motor model, which takes hysteresis losses and eddy-current losses as well as the magnetic saturation into account, improves the flux estimation and rotor-flux-oriented control. Based on the corresponding steady-state loss function, a method is proposed for solving the loss-minimizing flux reference at each sampling period. A flux controller augmented with a voltage feedback algorithm is applied for improving the dynamic operation and field weakening. Both the steady-state and dynamic performance of the proposed method is investigated using laboratory experiments with a 2.2-kW induction motor drive. The method improves the accuracy of the loss minimization and torque production, it does not require excessive computational resources, and it shows fast convergence to the optimum flux level. [ABSTRACT FROM PUBLISHER]

In grid-forming control, the swing equation of a synchronous machine is emulated by a power controller. Thereby, frequency droop, power-oscillation damping, and/or virtual inertia can be obtained. In this letter, it is shown that a phase-locked loop—which is normally grid following—can be designed so as to, in turn, emulate a generic power controller, thus, becoming grid-forming. [ABSTRACT FROM AUTHOR]

This article deals with discrete-time state-space current controllers for three-phase grid converters equipped with an LCL filter. The integral action in the controller can be implemented either using an integrator or a disturbance observer. The results show that the disturbance-observer-based and integrator-based controllers become mathematically equal if the feedforward gains are selected to be equal, the feedforward zero is placed to cancel the pole originating from the integral action, and the closed-loop poles are placed identically. The equivalent performance in both designs is verified by means of analyses and experiments. The equivalence is also shown for double-frequency current controllers. [ABSTRACT FROM AUTHOR]

This article deals with discrete-time state-space current control of three-phase converters equipped with an LCL filter. Either the converter or grid current is measured, and the unknown states are estimated using a reduced-order observer. The stability and dynamic performance of the control designs based on these two current measurement options are compared by means of analysis and experiments at different sampling frequencies and under varying grid conditions, ranging from strong to very weak. Equal reference-tracking performance under nominal conditions is used as a basis for comparison between these two options. If a strong grid is assumed in the control tuning, the controller based on the grid current measurement (GCM) is found to be more robust against varying grid conditions in a wide range of sampling frequencies than the controller based on the converter current measurement (CCM). The CCM leads to better dynamic performance as compared to the GCM if the resonance frequency of the system falls below the critical resonance frequency. [ABSTRACT FROM AUTHOR]

This article deals with dynamic models for three-phase bearingless flux-switching permanent-magnet (FSPM) linear machines. This machine type can be used to build a magnetically levitating long-range linear drive system, whose rail does not need any active materials apart from iron. A dynamic machine model is developed by means of equivalent magnetic models, taking into account air-gap variation and magnetic saturation. The effects of these phenomena are analyzed using finite-element method (FEM) simulations of a test machine. The parameters of the proposed model can be identified using the FEM or measured data. The model can be applied to real-time control and time-domain simulations. The model is validated by means of experiments. [ABSTRACT FROM AUTHOR]

This article presents a real-time identification method for LCL filters used with three-phase grid converters. The method can be applied to identify both the inductance and capacitance values of the filter and the series resistance seen by the converter. As a side-product, an estimate of the grid inductance seen from the point of connection is also obtained. A wideband excitation signal is added to the converter voltage reference. During the excitation, converter current and converter voltage reference samples are used for identification. The samples are preprocessed in real time by removing dc biases and significant grid-frequency harmonics. Parameters of two discrete-time models are estimated at each sampling instant with a recursive estimation algorithm. Depending on the estimated model, the model parameter estimates are translated to either the resistance or the inductance and capacitance values of the system. The method can be embedded to a control system of pulsewidth-modulation-based converters in a plug-in manner. Only the dc-link voltage and converter currents need to be measured. Simulation and experimental results are presented for a 12.5-kVA grid converter system to evaluate the proposed method. [ABSTRACT FROM AUTHOR]

In high-performance control of ac machines through variable frequency drives, the knowledge of machine parameters plays a decisive role. The accuracy with which machine parameters can be known is directly related to the time and effort put during the testing and commissioning process. In the ever-demanding industrial environments, the time spent on parameter identification translates into loss of production. To reduce commissioning times, research in this direction has focused on automatizing the identification procedure without loss of accuracy. This paper reviews different lines of research adopted over the past few decades for machine parameter identification. Parameter estimation of ac machines is considered because of their widespread applications from servomechanisms to traction to aviation. The surveyed works include self-commissioning schemes that have become an integral part and a salient feature of modern electric drives. This feature enables the drives to automatically identify machine parameters and tune the control loops. [ABSTRACT FROM AUTHOR]

This paper deals with the optimal state reference calculation for synchronous motors having a magnetically salient rotor. A lookup table computation method for the maximum torque-per-ampere locus, maximum torque-per-volt limit, and field-weakening operation is presented. The proposed method can be used during the start up of a drive, after the magnetic model identification. It is computationally efficient enough to be implemented directly in the embedded processor of the drive. When combined with an identification method for the magnetic model, the proposed method enables the plug-and-play startup of an unknown motor. Furthermore, a conventional reference calculation scheme is improved by removing the need for one two-dimensional lookup table. A 6.7-kW synchronous reluctance motor drive is used for experimental validation. [ABSTRACT FROM AUTHOR]

This paper deals with the speed and position estimation of interior permanent-magnet synchronous motor (IPM) and synchronous reluctance motor (SyRM) drives. A speed-adaptive full-order observer is designed and analyzed in the discrete-time domain. The observer design is based on the exact discrete-time motor model, which inherently takes the delays in the control system into account. The proposed observer is experimentally evaluated using a 6.7-kW SyRM drive. The analysis and experimental results indicate that major performance improvements can be obtained with the direct discrete-time design, especially if the sampling frequency is relatively low compared with the fundamental frequency. The ratio below 10 between the sampling and fundamental frequencies is achieved in experiments with the proposed discrete-time design. [ABSTRACT FROM PUBLISHER]

An interior permanent-magnet (PM) motor is modeled by a combined analytical–numerical approach, in which the relationships between the stator currents and flux linkages are identified with static finite-element (FE) analysis. In addition to the previous approaches using the current space vector as the state variable, new models are also developed using the flux-linkage space vector, which leads to more convenient time-integration of the voltage equations. In order to account for the zero-sequence effects in delta connection, the models also include either the zero-sequence flux or current as an additional state variable. Finally, the possibilities of deriving the required quantities as partial derivatives of the magnetic field energy are discussed. The energy-based approaches avoid inaccuracies related to torque computation and thus allow better satisfying the power balance in the state-space model. We show the ability of the developed state-space models to predict the currents and torque equally to a nonlinear time-stepping FE model with much less computational burden. The results are validated by means of measurements for a prototype machine in both star and delta connections. In addition, we also demonstrate the effect of the zero-sequence current on the torque ripple in case of a delta-connected stator winding. [ABSTRACT FROM PUBLISHER]