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Considering the periodic disturbances caused by nonideal factors like dead time effect, permanent magnet flux harmonics, and current sampling errors in the permanent magnet synchronous motor (PMSM) drives, this paper establishes an augmented state space model (SSM), which contains information of periodic disturbances, and then more accurate description for the PMSM system is achieved. Meanwhile, since the three augmented state variables related to periodic disturbances in the augmented SSM cannot be measured directly, a novel periodic disturbance observer (PDO) depending on the Kalman filter is designed to estimate these state variables. On the basis of the augmented SSM and PDO, a linear-quadratic-regulator (LQR)-based state feedback controller is established, which can achieve a successful suppression of periodic disturbances and at the same time ensure a more smooth speed output. Finally, the proposed PDO-LQR is tested in a 6 kW PMSM, and the experimental results show that the proposed controller can efficiently improve the steady-state performance of the PMSM system without sacrificing dynamic-state performance. [ABSTRACT FROM AUTHOR]

In this paper, an improved flux-barrier geometry configuration of transversally laminated rotor synchronous reluctance machine (TLR-SynRM) is proposed to suppress the torque ripple. The flux-barrier geometry configuration has two remarkable features. First, its flux barriers are step shaped and their shapes could be described by the parameter X. Second, the widths of multi-flux barriers in the middle regions are changing in a gradient style. The conformal mapping method is introduced to calculate the reluctances of the improved flux-barrier geometry configuration, and the corresponding magnetic equivalent circuit is established to analyze how the parameter X influences air-gap flux density distribution in order to obtain the minimum torque ripple. Based on the above analysis, the results are used to improve the flux-barrier geometry configuration. Last, the effectiveness of the improved flux-barrier geometry configuration is verified by finite-element analysis. [ABSTRACT FROM AUTHOR]

This paper first presents a novel boost front end simply with a diode, a MOSFET, and a DC-link capacitor. Without extra inductors or other power components, the boost font end could boost the capacitor voltage with the motor stator inductances, thus reducing the influence of the limited DC-link voltage on commutation torque ripple reduction to a large extent. A unified commutation torque ripple suppression strategy is further proposed with the front end adopted based on the analysis about the effects of four switching vectors on motor speed regulation and DC-link capacitor voltage regulation. The proposed strategy can boost the DC-link capacitor voltage via properly selection of switching vectors under the premise of guaranteeing normal speed regulation in noncommutation period, and reduce both the commutation torque ripple and commutation time by two consistent switching vectors with the boosted DC-link capacitor voltage in commutation period. Finally, the proposed method is theoretically analyzed with respect to the capacitance selection and the boot capacity of noninductive boost front end. The correctness of the analysis and the effectiveness of the presented method are validated by the experimental results. [ABSTRACT FROM PUBLISHER]

This study proposed a direct self‐control (DSC) strategy with reduced torque ripple for brushless DC motor (BLDCM). Taking the inherent advantage of DSC, sensorless control can be easily achieved from the relationship between commutation points of BLDCM and the hexagon‐shape flux linkage locus. Furthermore, in the premise that position sensor is absent, excellent steady‐state torque performance can also be achieved by the proposed strategy, which is achieved by increasing the degrees of control freedom through translation of switching point. In addition, another attractive feature lies in its relatively simpler control structure. Detailed analysis of torque ripple is carried out by deriving the expressions of torque variation rate through solving differential equations. Durations of voltage vectors are calculated to ensure the minimisation of torque ripple. The superiority of the proposed method is confirmed by comparative experiments. [ABSTRACT FROM AUTHOR]

The performance of a standard model predictive controller (MPC) is directly related to its predictive model. If there are unmodeled periodic disturbances in the actual system, MPC will be difficult to suppress the disturbances, thus causing fluctuations of system output. To solve this problem, this paper proposes an improved MPC named predictive-integral-resonant control (PIRC). Compared with the standard MPC, the proposed PIRC could enhance the suppression ability for disturbances by embedding the internal model composing of the integral and resonant loop. Furthermore, this paper applies the proposed PIRC to PMSM drives, and proposes the PMSM control strategy based on the cascaded PIRC, which could suppress periodic disturbances caused by the dead time effects, current sampling errors, and so on. The experimental results show that the PIRC can suppress periodic disturbances in the drive system, thus ensuring good current and speed performance. Meanwhile, the PIRC could maintain the excellent dynamic performance as the standard MPC. [ABSTRACT FROM AUTHOR]

When the interior permanent magnet (PM) machine operates under load condition, the armature current is ahead of the back electromotive force. However, the advanced armature current produces the demagnetizing field, which makes the irreversible demagnetization appeared in PMs easily. In this paper, aiming at the U-type PM structure, the expressions of the flux density components in the corresponding magnetizing directions of PMs at each node of PMs are derived. A calculation model to analyze the demagnetization in PMs is established in the Finite Element software by utilizing the derived expressions. Several improved geometries for rotor are proposed in this paper to strengthen the anti-demagnetization ability of PM. Based on the established calculation model, effects of variables in the improved geometries on the demagnetization in PMs and the rated electromagnetic torque are analyzed in detail. Based on the analysis results, optimized improved rotor geometry is achieved giving consideration to the anti-demagnetization ability of PM and rated electromagnetic torque. [ABSTRACT FROM AUTHOR]

To reduce the steady-state torque ripples for permanent-magnet synchronous motor drives with predictive torque control (PTC), this paper proposes a modified PTC algorithm based on the extended control set (ECS-PTC). In the proposed algorithm, more candidate voltage vectors are extended to the control set, which forms the ECS, and then, the torque control precision could be improved and the torque ripples will be reduced. More attractive thing is that a new voltage vector synthesis method is deigned in ECS-PTC, and the corresponding predictive model and cascaded predictive algorithm are set up on the basis of this method. With the help of them, the optimal vector can be selected from ECS in a shorter control period of time, and its amplitude is also optimized at the same time to achieve high-precision control effects for torque and flux. In addition, the three-phase duty ratios of the output vector can be determined in ECS-PTC directly, without the help of space vector pulse width modulation. The experimental results show that ECS-PTC has excellent dynamic torque performance, and it also has more stable torque control performance and better execution efficiency at the same time. [ABSTRACT FROM PUBLISHER]

Due to the complicated rotor structure and nonlinear saturation of rotor bridges, it is difficult to build a fast and accurate analytical field calculation model for multilayer interior permanent magnet (IPM) machines. In this paper, a hybrid analytical model suitable for the open-circuit field calculation of multilayer IPM machines is proposed by coupling the magnetic equivalent circuit (MEC) method and the subdomain technique. In the proposed analytical model, the rotor magnetic field is calculated by the MEC method based on the Kirchhoff’s law, while the field in the stator slot, slot opening and air-gap is calculated by subdomain technique based on the Maxwell’s equation. To solve the whole field distribution of the multilayer IPM machines, the coupled boundary conditions on the rotor surface are deduced for the coupling of the rotor MEC and the analytical field distribution of the stator slot, slot opening and air-gap. The hybrid analytical model can be used to calculate the open-circuit air-gap field distribution, back electromotive force (EMF) and cogging torque of multilayer IPM machines. Compared with finite element analysis (FEA), it has the advantages of faster modeling, less computation source occupying and shorter time consuming, and meanwhile achieves the approximate accuracy. The analytical model is helpful and applicable for the open-circuit field calculation of multilayer IPM machines with any size and pole/slot number combination. [ABSTRACT FROM AUTHOR]

In order to meet the high performance and efficiency requirements, a new space vector-based discontinuous modulation strategy for neutral-point clamped three-level inverter is presented in this paper. Different from the conventional discontinuous PWM (DPWM) strategies, a new clamping state is applied to synthesize the reference voltage under the condition of low modulation index. The rms value of output current ripple for different clamping states are calculated, and then the distribution of the new clamping state and the other two clamping states adopted in conventional DPWMs is optimized based on the calculation results. The switching sequences are redesigned according to the new distribution of the three clamping states. The output voltage and current, switching loss, neutral-point voltage ripple and the common mode voltage of the proposed DPWM strategy and DPWM0–DPWM3 are compared by simulation and experimental results. The results show that by the use of the proposed strategy, the values of total demand distortion of output current (ITDD) and weighted total harmonic distortion of output voltage (\boldsymbolV{\mathbf{WTHD}}) are the lowest. Furthermore, the product of switching loss and ITDD of the proposed strategy maintains the lowest within a large range of modulation index-load angle plane. It can be concluded that the utilization of the new clamping state and optimal distribution of different clamping states could enhance the output performance of the inverter. Moreover, the high-efficiency requirement can also be realized at the same time. [ABSTRACT FROM AUTHOR]

In this paper, a space-vector overmodulation strategy for an ultrasparse matrix converter (USMC) is proposed. The maximum output voltage vector, which has the same phase as reference voltage, is derived accurately in space-vector modulation. According to the maximum output voltage vector, the overmodulation mode I and mode II are re-divided, the boundary voltage transfer ratio (VTR) of which is extended to 0.954, whereas the maximum VTR of USMC remains 1, and the low-order harmonic components are reduced effectively. The overmodulation strategies in both modes are realized, respectively, by the linear superimposed principle. In addition, the harmonic characteristics of output voltage in overmodulation mode are analyzed by the double Fourier integral transform method. It is shown that the output voltage contains not only (6 z1\pm 1) f\rm{out} harmonics, but also \rm\vert f\rm{out} \pm 6 z2f\rm{in}\rm\vert and \vert (6z1\pm 1) f\rm{out} \pm 6 z2f\rm{in}{\rm{\vert }} harmonics. The effectiveness of the proposed overmodulation strategy and the correctness of harmonic analysis method are verified by experiments. [ABSTRACT FROM AUTHOR]

The multi‐step direct model predictive control (M‐DMPC) could reduce the switching frequency and improve the efficiency of the motor drive system while ensuring good steady and dynamic performance. However, the conventional M‐DMPC, which uses the exhaustive optimisation method is with exponential time complexity, so it is difficult to realise in a short sample period. This study proposes a multi‐step direct predictive torque control (M‐DPTC) algorithm for two‐level voltage source inverter fed surface‐mounted permanent magnet synchronous motor (SPMSM) drive system. In the proposed algorithm, first, in order to reduce computation time in multi‐step predictive process, a simplified multi‐step predictive model is established. Compared with the complex operations, like square root and trigonometric function used in the conventional predictive model, only look‐up table and addition operation are utilised in the proposed model for multistep prediction. Second, compared with the exhaustive searching method, the proposed optimisation method avoids the exploration of all possible switching sequences and has logarithmic time complexity. Combining the above two measures, the proposed M‐DPTC can be achieved in a relatively shorter sample period. Simulation and experimental results for a 6‐kW SPMSM are presented to validate the proposed algorithm. [ABSTRACT FROM AUTHOR]

The disturbance voltage of voltage-source inverter operation exerts significant influences on the accuracy of motor parameter identification. In this paper, an accurate model is established for estimating the disturbance voltage that includes current harmonics and their derivative. The conclusion is drawn that the derivative of the d -axis current harmonics plays a major role in causing estimation error of the disturbance voltage. Based on this, two methods are proposed to reduce the estimation error of the disturbance voltage. One employs an iterative learning controller in the d-axis current control loop to suppress the harmonics of d-axis current, thus reducing their influence on the estimation of the disturbance voltage. The second estimates the disturbance voltage on the basis of the average value of the variables in q-axis equation of the motor, so that the estimation result is immune to current harmonics. Motor parameter identification accuracy is consequently improved by both. [ABSTRACT FROM AUTHOR]

In this paper, an analytical field calculation model is built for surface inset permanent magnet (SIPM) machines with high saliency ratio. The high saliency ratio of SIPM machine is obtained using unequal $d$ - $q$ axis air-gap length based on the SIPM rotor structure. High saliency ratio can produce large reluctance torque and wide speed range. To get a fast and exact knowledge of flux distribution and operation parameters of the SIPM machine with high saliency ratio, the field solving domain is divided into five subdomains, i.e., stator slots, stator slot openings, air-gap, rotor air slots, and rotor magnets. The vector potential in each subdomain is governed by Maxwell’s equation and can be solved using the variable separation method and boundary conditions between adjacent subdomains. In addition, the cogging torque, back electromotive force (EMF), inductance, output torque, and unbalanced magnetic force (UMF) are calculated based on the field model. All the field calculation results are compared with those of finite element analysis (FEA), and it is shown that analytical field calculation model is fast and accurate. Furthermore, the effects of $q$ -axis air-gap length and pole arc ratio on machine parameters, such as cogging torque, back EMF, saliency ratio, output torque, and UMF, are also investigated using the analytical field calculation model. [ABSTRACT FROM PUBLISHER]

Based on the Z-source inverter, this paper proposes a novel commutation torque ripple reduction strategy for brushless DC motor (BLDCM). The proposed strategy employs the same modulation mode in both the normal conduction period and the commutation period, and the commutation torque ripple is reduced by regulating the shoot-through vector and active vector duty cycles. The proposed detection method acquires the end point of commutation by comparing the clamped terminal voltages with reference zero level, and the signal-noise-ratio of the detection is improved by avoiding the attenuation of the terminal voltages. Furthermore, a certain pulse width of the shoot-through vector can not only reduce the commutation torque ripple but also provide a new opportunity to detect the end point of commutation. Moreover, Z-source inverter provides the buck–boost ability for BLDCM drive system, then the dc voltage utilization can be improved, and the safety of the drive system can also be improved. In addition, this paper analyzes the terminal voltages during each vector. The experimental results verify the correctness of the theories and the effectiveness of the proposed approach. [ABSTRACT FROM PUBLISHER]

In this paper, a direct torque control using a four-dimensional switching-table (4D-ST) is proposed for the voltage source inverter–permanent magnet synchronous motor drive system. The proposed strategy takes a number of virtual vectors, of which magnitude and angle can be configured freely, as candidate vectors. By taking advantage of the variety of the virtual vector, the proposed strategy can obtain superior steady-state and dynamic performance. To choose the optimal vector from all of virtual vectors, first quantify the change rule of the torque and stator flux generated by each different virtual vector, and then take the magnitude and angle of the virtual vector, stator flux angle, and the quantificational factor as four dimensions to establish 4D-ST; by analyzing the distributed laws of quantificational factors in 4D-ST, we can compress 4D-ST and propose a quarter selector to choose the optimal vector accurately and rapidly. By taking the step function instead of the hysteresis comparator as the torque and flux controller, the direct torque control using 4D-ST can be realized. Finally, numerical simulations and experiments with prototype are carried out to validate the feasibility and effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

In this paper, a direct torque control (DTC) using vector evaluation factor table (VEF-Table) is proposed for voltage source inverter (VSI)-permanent magnet synchronous motor (PMSM) drive system. In this approach, the candidate vectors can expand from six active vectors to 3\times N\text {d} vectors with duty cycle, and the change trends of torque and flux generated by all candidate vectors can be quantified and stored in the VEF-Table offline. In order to choose the output vector from the VEF-Table, a “Two-Step” selection algorithm is established based on the cost function, which can select two vectors with duty cycle sequentially. By synthesizing two vectors, the proposed approach is capable of adjusting the magnitude and angle of the output vector, so as to reduce the undesirable ripples of torque and flux. The feasibility and effectiveness of the proposed approach is verified by both numerical simulations and experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, a current control scheme with switching-gain adaptation is proposed for brushless DC motors. The scheme includes two components, namely a continuous control component and a switching control component. The continuous control component is employed with model reference adaptive control (MRAC) to approximate the parametric uncertainties, and the switching control component is used with integral sliding-mode control (ISMC) to eliminate the general disturbance caused by both the approximation errors and the unstructured uncertainties. Due to the variation in general disturbance in different operating conditions, a switching-gain adaptation method based on the unknown disturbance estimation is proposed, which improves the transient performance of the current controller and eliminates the high-frequency noise of current caused by chattering. Finally, the effectiveness of the proposed method is verified by experimental results. [ABSTRACT FROM AUTHOR]

In this paper, equal torque effect (ET‐effect) is discovered, which means that the same torque can be obtained by applying different voltage vectors whose terminals locate on a special curve called the equal torque curve (ET‐curve). By means of ET‐effect, an improved predictive torque control (PTC) without weighting factor is proposed. First, to obtain the volt‐sec vectors whose terminals locate on the ET‐curve, the proposed PTC calculates the duty cycles of all the voltage vectors intersected with the ET‐curve, and then establishes finite control set by accumulating those volt‐sec vectors. Second, a cost function that includes only the flux error is defined to select the optimal volt‐sec vector, and thus to avoid weighting factor adjustment since the torque error no longer exists in the cost function. Because of the two‐step optimisation of torque and flux, the proposed PTC can avoid the problem that the duty cycle cannot be fully utilised in standard PTC. As a result, the proposed PTC achieves better performance of torque and flux than standard PTC and PTC with duty cycle. Finally, experiments have been carried out to validate the proposed PTC strategy. [ABSTRACT FROM AUTHOR]

Many existing research works of ultrasparse matrix converter (USMC) show that the maximum linear output voltage transfer ratio (MLO-VTR) is less than 0.866, however, this paper proves that based on space vector modulation, MLO-VTR for USMC can break the ultimate value. First, based on the condition that input power factor is one, the maximum output voltage within one carrier period and the maximum linear output voltage are derived. Further, the mathematical equations among MLO-VTR, the output/input frequency ratios, and the output voltage initial phase are also derived. After that, by solving the operating limits of the mathematical relationship of the MLO-VTR, we can obtain the maximum value of MLO-VTR under different output/input frequency ratios which can be more than 0.866. Finally, all of theoretical derivations are verified by experiments. [ABSTRACT FROM PUBLISHER]

This study proposes a speed control scheme to improve the speed control performance of the permanent magnet synchronous motor (PMSM) servo system which is equipped with an absolute optical encoder. A two‐degree‐of‐freedom proportional integral speed controller is utilised to make a good compromise between tracking and disturbance rejection performance. Properties of the controller are analysed using the root locus method. As the controller performance is prone to be deteriorated by speed measurement noise and time delay, a novel Kalman filter is used to optimise the speed measurement process. The proposed Kalman filter modifies gain matrix based on the position residue error. By this means it improves dynamic response speed without damaging steady‐state precision. Experimental researches are carried out on a 5.2 kW PMSM drive prototype and the results prove the feasibility and effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

The iron loss of the interior permanent magnet (PM) machine is larger when the machine runs at a higher speed. The great stator and rotor iron loss have a negative effect on the machine, so the PM cavity of the interior PM machine with a single-layer $U$ -shaped PM geometry is improved to reduce the iron loss of the machine in this paper. Meanwhile, the Taguchi method is utilized to optimize the improved PM cavity at the rated point, maximum torque point, and flux-weakening point, respectively. The effects of each optimization variable on the iron loss and electromagnetic torque of the machine are analyzed. Then, the optimization scheme of the improved PM cavity is achieved at each selected operating point, respectively. The final optimization scheme of the improved PM cavity will be concluded after the overall consideration of optimization schemes at the selected operating points. In addition, the electromagnetic torque ripple and cogging torque are also effectively reduced by adopting the improved PM cavity, which improves the running stability of the machine. [ABSTRACT FROM PUBLISHER]

In this paper, an analytical model is developed for surface mounted permanent magnet (SMPM) machines with skewed slots via the subdomain technique and the multislice method. It takes the nonuniform distribution of flux density along the axial direction caused by slot skewing into account and can be used to obtain air-gap flux density distribution in the 3-D space. The cogging torque, flux linkage, back electromotive force (EMF), and output torque are calculated with the obtained air-gap flux density. The results calculated by the analytical model are validated by the 3-D finite element analysis. The convergence and computation time of the analytical model are investigated, and good convergence and fast calculation speed can be achieved. Based on the developed analytical model, the effects of slot skewing angle and pole arc on back EMF and output torque are researched. The analytical model can be applied to the fast optimal design and performance analysis of SMPM machines with skewed slots. [ABSTRACT FROM AUTHOR]

This paper proposes a speed and current proportional–integral–resonant (PIR) control strategy to realize smooth speed control of the low-speed high-torque permanent-magnet synchronous motor (PMSM) drive system by minimizing the periodic torque ripples. Some nonideal factors causing periodic torque ripples, such as harmonics of rotor flux, cogging torque, current measurement errors, and dead time of inverter, are mathematically modeled, and their effects on current and speed control are analyzed, according to their locations in the system. Stability analysis is carried out, considering the delays caused by current loop and speed measurement as they may make the whole system unstable under the proposed PIR control strategy, and the optimal phase adjustment parameters for resonant item to keep the system stable are then obtained through theoretical analysis and numerical simulations. Finally, experimental results achieved on a 10-kW setup prove that the proposed strategy effectively minimizes the periodic speed ripples of PMSM drive. [ABSTRACT FROM PUBLISHER]

The Halbach array permanent magnet machine has several advantages. Most notably, it has more sinusoidal air-gap flux density distribution, higher air-gap flux density amplitude, and self-shielding magnetization property. In engineering, the segmented Halbach array is usually used considering the complexity of fabrication, and certain gap exists between segments inevitably. To analyze the effect of the gap between segments on air-gap flux density, an analytical model of the Halbach array permanent magnet machine considering the gap between segments is established in this paper. The finite element model is adopted to validate the established analytical model. Furthermore, effects of the parameters of the segmented Halbach array, including gap between segments, segment number per pole, and pole pair number on the fundamental amplitude, and waveform distortion factor of the radial component of air-gap flux density are analyzed using the established analytical model. [ABSTRACT FROM AUTHOR]

Two types of eccentric magnetic pole shapes for optimizing conventional surface-mounted permanent-magnet (PM) synchronous machines with radial magnetization are presented in this paper. An analytical method based on an exact subdomain model and discrete idea is proposed for obtaining the air-gap flux density distribution in the improved motor. Cogging torque and back EMF analytical models are further built with the field solution, which provide useful tools for investigating motor performances with unequal thickness magnetic poles. The accuracy and feasibility of the models have been validated by a finite element method. Based on the analytical models, the effects of pole shape parameters on motor performance are investigated. Results show that both pole shapes can perfect magnetic field distribution, decrease harmonic content of back EMF, reduce torque ripples, and improve the utilization of PMs. [ABSTRACT FROM AUTHOR]

A novel direct torque control (DTC) strategy using duty cycle optimization is proposed for matrix converter (MC)-based permanent-magnet synchronous motor (PMSM) drive system, which is characterized by low torque ripples, no need for rotational coordinate transformation, and fixed switching frequency. Analytical expressions of change rates of torque and flux of PMSM as a function of MC voltage vectors are derived. An enhanced switching table is established by means of discretization and averaging, in which changes of torque and flux caused by voltage vectors are shown explicitly. Then, the proposed MC-fed DTC algorithm is implemented based on the table. Numerical simulation and experiments with a prototype are carried out. Both simulation and experimental results demonstrate that remarkable torque ripple reduction, more than 30%, has been achieved. As a result, the proposed strategy is proved to be effective in reducing torque ripples for MC-based PMSM drives. [ABSTRACT FROM AUTHOR]

In this paper, a current optimization control method for reducing torque ripple in brushless dc drives using integral variable structure control (IVSC) is proposed. The conventional current control method will result in torque ripple if the back electromotive force (EMF) is a nonideal trapezoidal waveform. Based on back-EMF waveforms, the proposed method can optimize the reference currents in both two-phase conduction mode and commutation mode. A Luenberger full-order estimator is designed in order to estimate back-EMF waveforms. During commutation, commutation control with two-phase or three-phase switching mode is employed to reduce torque ripple by controlling the currents of noncommutated windings to trace the optimized reference current, and a three-phase inverter is switched between the two switching modes according to the current rate of change and the difference between the reference current and the actual current. Current controllers using IVSC, which exhibits broadband noise-suppressing capacity and strong robustness against external disturbances, are designed to obtain optimal phase currents, and the experimental results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Neutral-point (NP)-clamped three-level inverter, which is a widely used topology of multilevel converters, suffers from the NP voltage drift as its main technical drawback. The nearest-three-virtual-vector (\NTV^2) modulation method can control the NP voltage balance for any load over the full range of inverter output voltage. However, compared with the nearest-three-vector (NTV) modulation method, \NTV^2 increases the switching frequency. This paper combines \NTV^2 with NTV, and the two methods are used alternately in a fundamental cycle. The duty-cycle coefficients of the redundant small vectors are analyzed to explore the intervals where NTV can control the NP voltage balance in a fundamental cycle. The proportional parameter, which represents the combination of the two methods in hybrid space vector pulsewidth modulation, can be selected to achieve a high-performance NP balance control and low switching frequency. The steady- and transient-state behaviors of the proposed strategy are analyzed in this paper. The experimental results verify the validity of the proposed strategy. [ABSTRACT FROM PUBLISHER]

Cogging torque is one of the emphases and difficulties of research on permanent magnet (PM) machines. In this paper, an improved analytical model, based on an exact subdomain model idea and Maxwell stress tensor, is applied for calculating a cogging torque of surface-mounted PM machines with auxiliary slots. It can accurately take account of the interactions between slots and the influence of finite slot depth and can be widely applied to internal/external rotor topology and radial/parallel/segmented-Halbach magnetized machines. The finite-element (FE) method is adopted to validate the proposed model. The results show good agreement in both flux density and cogging torque waveforms. Furthermore, the effects of auxiliary slot parameters on cogging torque are investigated. Conclusions are derived from the analysis and indicate that the analytical model provides a useful tool for PM motor design. [ABSTRACT FROM PUBLISHER]

In the wind energy conversion system (WECS) based on the permanent magnet synchronous generator, the topology that a wind generator is connected to a voltage source inverter through a diode rectifier and a boost chopper is widely adopted for its low cost and high reliability. However, with the increasing power level of the WECS, the power switch device of a boost chopper in the topology has to endure high instantaneous voltage and current stress, thus reducing the system reliability. Although the traditional multiple boost converter reduces the transmission power level of single circuit units in terms of structure, it is still limited by narrow speed regulation range. Thus, a novel switchable-cascaded-mode boost chopper is proposed in this paper. The operation principle of the new converter and the generator speed control strategy are analyzed. At last, the effectiveness of the new converter is verified with an experimental prototype. The experimental results demonstrate that speed range is extended by using the new topology as generator-side converter in the permanent magnet wind generation system. [ABSTRACT FROM AUTHOR]

This study presents a novel three effective vectors (TEV) current control scheme for four‐switch three‐phase inverter in cost‐effective brushless DC motor drive with improved performance. This scheme overcomes the possible distortion of three‐phase currents caused by phase C back‐EMF, and quasi‐square current waveforms are attained by inserting two adjusting vectors in each control period based on the conventional switching modulation scheme. The duty cycles of the two adjusting vectors are further calculated using a simple P controller. Integral variable structure control principle with advantages of high bandwidth and strong robustness against external disturbance is used to control the tracing of reference current by actual currents. The stability of the proposed TEV current control scheme is demonstrated by selecting a candidate Lyapunov function, based on which the range of duty cycles of adjusting vectors are also determined. Experimental results verify that the proposed scheme is simple and can provide small current ripple, with good performance in speed. [ABSTRACT FROM AUTHOR]

In this paper, the operation principle of a multiple converter, which is composed of the traditional two-level six-switch voltage source converter and constructed in line-voltage cascaded mode, is analyzed. The equivalent switching circuit model of the multiple converter is built based on its operation characteristic. By analyzing the feature of the multiple converter control, an improved voltage–current double-loop control strategy based on the proportional–resonant (PR) controller is proposed. The control strategy, which has the merit of the integrated control, can also realize the independent control of the transmission power of each unit of the multiple converter by adding the voltage-sharing compensation control. Meanwhile, a PR controller is adopted in the current loop. By giving a suitable current reference value for the controller, the problem of ac-side line-current asymmetry can be solved, and the effect of unbalanced grid voltages on the system can be avoided as well. The availability of the proposed control strategy is verified by the experimental results. [ABSTRACT FROM PUBLISHER]

A predictive current controller with an extended-state observer (ESO) is proposed for grid integration of wind energy systems. In each sampling period, the proposed strategy calculates the converter switching time that minimizes a cost function defined as a sum of squared current errors, leading to constant switching frequency. To achieve excellent dynamic performance, the impact of sampling delay is analyzed, and detailed compensation methods are proposed. In addition, an ESO is constructed to suppress parameter variations and modeling errors, which affect the performance of the controller. The parameter tuning and the stability of the observer are analyzed. The proposed strategy not only presents rapid dynamic response due to the use of the predictive current controller but also possesses robust control performance as a result of the observation algorithm. Simulation and experimental results are given to validate the effectiveness of the proposed solution. [ABSTRACT FROM PUBLISHER]

This paper presents the design and analysis of a variable arc magnet array comprising two segments per pole for permanent magnet (PM) spherical motor. The harmonic model for radial air-gap flux density distribution is solved by magnetic scalar potential equation using spherical harmonic series and validated by finite-element method. After the influence of magnet array parameters on the fundamental harmonics amplitude and higher harmonic content of the air-gap flux density is analyzed, the optimization of four-pole magnet array is performed in which the higher harmonics of the radial air-gap flux density are minimized. The final design is compared with iron-cored classical array and air-cored equal arc Halbach array, and the result shows that for a given relative volume of magnetic material the proposed variable arc magnet array produces lower higher harmonic content than the other two arrays. [ABSTRACT FROM AUTHOR]

A strategy based on finite-state model predictive control is proposed for permanent-magnet brushless dc motors (BLDCMs) to reduce commutation torque ripple. The main contribution is a detailed description of the algorithm design process applied to BLDCM for commutation torque ripple minimization, which points out that the optimal conduction status is directly selected and the exact duration of each conduction status is not required in control process. This method proposes a unified approach for suppressing commutation torque ripple over the entire speed range without distinguishing high speed and low speed and overcomes the difficulties of commutated-phase-current control, avoiding complex current controllers or modulation models. A discrete-time noncommutated-phase-current predictive model of BLDCM during commutation is established. According to the predefined cost function, the optimal switching state is directly selected and applied during the next sampling period so as to make the slope rates of incoming and outgoing phase currents match in the course of commutation, thus ensuring the minimization of commutation torque ripple. The simulation and experiment results show that the proposed method can effectively reduce commutation torque ripple within the whole speed range and achieve good performance in minimizing commutation torque ripple in both dynamic and steady states. [ABSTRACT FROM PUBLISHER]

The unstable oscillation of autonomous dynamic system of a matrix converter (MC) is studied based on nonlinear dynamic theory, and its chaotic characteristic is analyzed. Analysis based on the fundamental-harmonic nonlinear state equations shows that the system loses stability via a Hopf bifurcation. The behavior of the system near the critical power is examined through simulation. The trajectories obtained by the fundamental-harmonic nonlinear state equations show some typical chaotic characteristics such as extreme sensitivity to initial values and self-similarity. Power density spectrum and Lyapunov exponents of the MC are obtained from simulation results. Finally, the trajectories drawn based on experimental data show some behaviors very similar to those from simulation results, which implies a possible chaotic status in the electrical drive system fed by MC. [ABSTRACT FROM PUBLISHER]

The subseafloor structure offshore South China Sea was imaged using first-order water-layer multiples from ocean-bottom seismometer data and the results were compared to conventional imaging using primary reflections. The mirror-imaging method employs a primaries-only reverse time pre-stack depth migration algorithm to image the receiver ghosts. The additional travel path of the multiples through the water layer is accounted for by a simple manipulation of the velocity model and processing datum: the receivers lie not on the sea floor but on a sea surface twice as high as the true water column. Migration results show that the multiple-migrated image provides a much broader illumination of the subsurface than the conventional image using the primaries, especially for the very shallow reflections. The resulting image from mirror imaging has illumination comparable to the vertical incidence surface streamer (single-channel) reflection data. [ABSTRACT FROM AUTHOR]

A strategy based on internal model control (IMC) is proposed for a matrix converter-based permanent magnet synchronous machine (PMSM) drive system to reduce the adverse impact on drive performance caused by nonlinear output characteristics of matrix converter in the case of input voltage disturbance. Based on the duty-cycle space vectors and small-signal model, the relationship between output and input disturbances is obtained in the synchronous reference frame. Output characteristics of matrix converter are analyzed, and practical considerations are discussed for the purpose of controller design. A general design procedure of the robust IMC controller is described, and parameters of the controller are determined. Numerical simulations and experiments with a 10-kW prototype are carried out. The results show that good dynamic and steady-state performance on PMSM speed regulation is achieved under the unbalanced and distorted input voltage conditions, and the immunity of the drive system is verified to be improved. [ABSTRACT FROM AUTHOR]

With the increase of wind energy conversion system (WECS) capacity, conventional two-level voltage source converters tend to be replaced gradually by multilevel neutral-point (NP)-clamped converters. In this study, the topology of a boost three-level (TL) chopper on the front of a TL diode-clamped inverter is used for direct-driven WECSs. The switch-signal phase delay control (SSPDC) is proposed for NP potential balancing of TL inverter based on the characteristics of boost TL chopper. As the boost chopper is also used for maximum power point tracking, the controller with dual PI regulators is designed for the chopper. Parameters of the two PI regulators are determined according to the state space averaging model of the boost TL chopper using SSPDC. In addition, the proposed NP balancing method is compared with two methods based on redundant vector selection. The validity of the proposed method is verified by analysis and simulation results. [ABSTRACT FROM PUBLISHER]

Abstract: With increasing wind power penetration, transient responses of doubly-fed-induction-generator (DFIG) based wind turbines gain attentive focus. Accurate prediction of transient performance of DFIG under grid faults is required with increasing wind power penetration. Taking into account the main flux saturation and deep-bar effect, this paper concentrates on transient responses and stability of the DFIG system under symmetrical grid faults. Their roles played in the enhancement of system transient stability are clarified. The analyses proposed contribute greatly to proper selection, design and coordination of protection devices and control strategies as well as stability studies. [Copyright &y& Elsevier]

High‐frequency (HF) square‐wave voltage injection position sensorless control method for interior permanent magnet synchronous motor (IPMSM) is widely utilised in zero and low speed range due to its good dynamic performance and easy implementation. However, this method relies on the sampling accuracy of current sensors for rotor position estimation. To overcome this restriction, an HF square‐wave voltage injection position sensorless control method for IPMSM using a single current sensor (SCS) is proposed. Firstly, the impact of current sampling errors on HF square‐wave voltage injection position sensorless control is analysed, and it is concluded that the scaling errors of current sensors will cause the estimated position to oscillate at twice the fundamental frequency. Based on this conclusion, the phase currents reconstruction technology with SCS is adopted to avoid the impact of scaling errors on rotor position estimation. To reconstruct the phase currents containing HF component, a PWM cycle is divided into two parts, sampling stage and injection stage. By this way, the impact of HF square‐wave voltage injection on current reconstruction can be avoided. Then, the rotor position estimation is realised. The experiments are performed on a 20‐kW IPMSM platform and the results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A correction to the "A case study: travel time inversion for P-wave velocity using OBS data of South China Sea" that was published online in the July 30, 2015 issue is presented.

In this paper, the analytical relationship among supply voltage, current, and structure parameters of the permanent magnet (PM) motor is cleverly deduced by using an intermediate‐flux linkage. After further consideration of boundary conditions, the direct field‐circuit coupled analytical model in integrated matrix form is subsequently constructed. Using this model, the vector potentials and currents of the motor can be calculated simultaneously, and the electromagnetic performance, such as the output torque, winding flux linkage, and so on can be further calculated by the vector potentials. Because the control parameters and motor structure parameters are both considered in the derivation process, the proposed analytical model can be used to analyse the motor operation performance under different control strategies. Its validity is finally verified on a 10‐pole/12‐slot PM motor. The results of the proposed direct field‐circuit coupled analytical model are compared with those of field‐circuit coupled time‐stepping finite element model and experiment under speed‐current double closed‐loop and current closed‐loop control strategies, respectively. The results of the proposed model are proved well with finite element simulation and experimental results. [ABSTRACT FROM AUTHOR]

The purpose of this case–control study was to examine possible links between NLRP3 gene polymorphisms and the risk of developing posttraumatic osteomyelitis (PTOM) in the Chinese population. A total of 306 patients with PTOM and 368 normal controls were genotyped for NLRP3 (rs35829419, rs10754558, rs7525979, rs4612666), ELP2 (rs1785929, rs1789547, rs1785928, rs12185396, rs681757, rs8299, rs2032206, rs559289), STAT3 (rs4796793, rs744166, rs1026916, rs2293152, rs1053004), CASP1 (rs501192, rs580253, rs556205, rs530537), NFKBIA (rs696), NFKB1 (rs4648068), CARD8 (rs204321), and CD14 (rs2569190) using the genotyping technique SNaPshot. The genotype distributions of NLRP3 gene rs10754558 (p = 0.047) and rs7525979 (p = 0.048) significantly differed between the patients and the healthy controls. Additionally, heterozygous models indicated a significant association between NLRP3 rs10754558 and the likelihood of developing PTOM (OR = 1.600, p = 0.039), as did recessive and homozygous models of NLRP3 rs7525979 (OR = 0.248, p = 0.019 and 0.239, p = 0.016, respectively). Collectively, our findings suggest that, in the Chinese population, the risk of developing PTOM was increased by the association between NLRP3 rs10754558 and rs7525979. Therefore, our findings may provide novel insights and guidance in the prevention and development of PTOM. [ABSTRACT FROM AUTHOR]

In marine seismic exploration, ghost wave and bubble effect reduce the vertical resolution and interpretation accuracy seriously. Here firstly the far-field wavelet including source wavelet, ghost wave and bubble effect recorded by the vertical cable system (VCS) is extracted. Then, filters are designed using the extracted far-field wavelet to eliminate ghost wave, bubble effect and source wavelet. At last, the designed filters are applied to the seismic data of VCS. The results show that this method can eliminate ghost wave, bubble effect and source wavelet effectively and the vertical resolution of the seismic data is improved obviously. [ABSTRACT FROM AUTHOR]

In this paper, a novel model predictive control (MPC) scheme is proposed for field-oriented control of permanent magnet synchronous motor fed by voltage-source inverter, in which a hybrid control set (HCS) including active-vectors with duty cycle and virtual vectors with duty cycle can be established. Since more vectors with different angles and duty cycles are available, the proposed approach is capable of adjusting the magnitude and angle of the output vector finely. However, the duty cycle of vectors in HCS is countless, so the total of elements in HCS is actually infinite. In order to select the optimal vector from HCS, we transform the original MPC optimization problem. By means of finite enumerations and evaluations online, the optimal solution can be obtained, which includes both angle and duty cycle of the output vector. In addition, a simplified solving algorithm is also presented, which can further reduce the computational cost. Finally, the feasibility and effectiveness of the proposed approach can be validated by experimental results. [ABSTRACT FROM PUBLISHER]

In this article, a novel method is proposed to reduce the dc-link capacitance of the brushless dc motor (BLDCM) system. In the proposed strategy, the charging mode of dc-link capacitor is designed to improve the energy stored by dc-link capacitor in the charging process instead of reducing the discharge time of dc-link capacitor used in previous article. The new modulation strategy and controller is designed to pump the dc-link capacitor voltage and ensure that it exceeds the ac voltage peak. The proposed modulation strategy has three vectors. The charging vector is used to improve the dc-link capacitor voltage, and the effective vector and zero vector are used to adjust the motor speed. For practical application, we provide an engineering calculation method to get the dc-link capacitance, and prove that the dc-link voltage can exceed the average voltage of the BLDCM. The experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

In the low-speed operating range of sensorless interior permanent magnet synchronous motor (IPMSM), this article proposed an ultrahigh frequency (UHF) sinusoidal voltage injection method supplied by the control power supply, and the corresponding signal injection and detection system topology are designed. The proposed method replaces the traditional high-frequency injection method to continuously detect the rotor position by injecting UHF sinusoidal detection voltage into the three-phase motor windings during the main power supply (MPS) down, thereby avoiding the loss of rotor polarity information. When the MPS is restored, there is no need to wait for the convergence process of the position observer and the rotor polarity determination process. The sensorless IPMSM can immediately resume normal operation at low speed. For applications with low load inertia, the proposed method improves the rapidness of rotating restart, realizes zero-wait operation after MPS is restored, and reduces the speed drop during the power down. For electric vehicle (EV) applications, the proposed method meets the requirements of EVs event data recorder to continuously record the motor speed when the MPS is off. The experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a model predictive current control (MPCC) method based on current augmenter prediction model (CAPM) appropriate for interior permanent magnet synchronous motor (IPMSM) under high-speed condition. The accuracy of CAPM is improved by considering rotor movement during one control period especially under high-speed condition. Meanwhile, the use of the permanent magnetic flux linkage is eliminated. In order to further improve the robustness of the MPCC method, an adaptive observer based on CAPM is designed to estimate the model error. The proposed adaptive observer also eliminates the use of the permanent magnetic flux linkage, so the whole implementation process of the MPCC method with adaptive observer is independent of the permanent magnetic flux linkage. Moreover, since the adaptive observer with fixed adaptive integral gain cannot achieve satisfactory performance under different operating conditions of the motor, this paper designs a calculation method for the variable adaptive integral gains by considering the current estimation error, the amplitude of current and the angular velocity of the IPMSM. Finally, the proposed method is validated by means of the experimental results on a 20-kW test platform. [ABSTRACT FROM AUTHOR]

This paper proposes a self-adaption Kalman observer (SAKO) used in a permanent-magnet synchronous motor (PMSM) servo system. The proposed SAKO can make up measurement noise of the absolute encoder with limited resolution ratio and avoid differentiating process and filter delay of the traditional speed measuring methods. To be different from the traditional Kalman observer, the proposed observer updates the gain matrix by calculating the measurement noise at the current time. The variable gain matrix is used to estimate and correct the observed position, speed, and load torque to solve the problem that the motor speed calculated by the traditional methods is prone to large speed error and time delay when PMSM runs at low speeds. The state variables observed by the proposed observer are used as the speed feedback signals and compensation signal of the load torque disturbance in PMSM servo system. The simulations and experiments prove that the SAKO can observe speed and load torque precisely and timely and that the feedforward and feedback control system of PMSM can improve the speed tracking ability. [ABSTRACT FROM PUBLISHER]