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This study presents a maximum torque per ampere (MTPA) control method for a mono inverter dual parallel (MIDP) surface-mounted permanent-magnet synchronous motor (SPMSM) drive system. The multimotor drive system has been extensively studied, because it can drive moreover two motors using only one inverter, reducing the costly power conversion circuit. However, existing studies concerning MIDP permanent-magnet synchronous motor drive systems focus on stabilizing the system, and studies regarding efficiency optimization are difficult to find. Some studies have shown the efficiency-optimizing method, but implementing is challenging because of the complicated calculations and algorithm. The proposed control method can achieve efficiency-optimizing operation using the angle difference controller. The angle difference controller controls the angle difference of two motors to an optimal value. Furthermore, the optimal angle difference of two motors can be easily obtained regardless of parameter errors, using the perturbation and observation algorithm. The proposed MTPA strategy is verified by performing simulations using matlab Simulink and applying the method to an actual MIDP SPMSM drive system. [ABSTRACT FROM AUTHOR]

Open-circuit fault is one of the common faults of multiphase motors. After fault occurrence, the control strategy needs to be modified in order to maintain smooth and uninterrupted operation. However, existing strategies with harmonic injection are unable to achieve effective decoupling of multiple planes. This letter proposes a novel fault-tolerant strategy with harmonic injection for the purpose of torque ripple reduction while enhancing torque operation range compared with state-of-the-art method. Since the higher order harmonic plane has less effect on torque ripple generation, the proposed strategy introduces harmonics into the higher order plane, thereby reducing its coupling to the fundamental plane. A seven-phase induction motor is utilized as the prototype to verify the effectiveness of the proposed fault-tolerant control technique. Furthermore, the design principles of the proposed strategy in this letter can easily be extended to multiphase motors with higher phase numbers. [ABSTRACT FROM AUTHOR]

A position-sensorless control is developed for doubly fed induction machines (DFIM). In this article, an adaptive reduced-order observer is used to estimate both rotor speed and position. The proposed reduced-order observer is based on the stator equation, and four issues are explored. First, the stator equation is used to realize the adaptive reduced-order observer, by which the structure is simple without flux calculation. Second, the stability of adaptive reduced-order observer is analyzed by the linearization method, which paves the way for design procedure of observer's feedback gain. Third, the tracking performance of the rotor-position estimation is investigated through the acceleration/deceleration of rotor speed; an explicit guideline is provided to design the adaptation integral gain to satisfy the specified tracking response. Fourth, sensitivity to machine's parameter variations is studied; the robust stability property is enhanced by the observer's feedback gain; and the robust sensitivity to inductance variation is strengthened by the adjustment of mutual inductance with stator voltage accordingly. Experiment is conducted with a 4-kW DFIM drive system to verify the validation of the proposed theoretical concepts. [ABSTRACT FROM AUTHOR]

Optimization-based control strategies are an affirmed research topic in the area of electric motor drives. These methods typically rely on the accurate parametric representation of equations of a motor. In this article, we present the transition from model-based to data-driven optimal control strategies. We start from the model-predictive control paradigm, which uses the voltage balance model of the motor. Then, we discuss the prediction error method, where a state-space model is identified from data, without parameterization. Moving toward data-driven controls, we present the subspace predictive control, where a reduced model is constructed based on the singular value decomposition of raw data. The final step is represented by a complete data-driven approach, named data-enabled predictive control, in which raw data are not encoded into a model but directly used in the controller. The theory behind these techniques is reviewed and applied for the first time to the design of the current controller of synchronous permanent magnet motor drives. Design guidelines are provided to practitioners for the proposed application, and a way to address offset-free tracking is discussed. Experimental results demonstrate the feasibility of the real-time implementation and provide comparisons between the model-based and data-driven controls. [ABSTRACT FROM AUTHOR]

This article proposes a novel method for detection of open-phase faults, which was specifically designed for usage in low-cost motor drives. The proposed algorithm uses analysis of current signals to detect the failure and it was developed for usage with conventional configuration of motor drives, where phase currents are measured with the shunt sensors placed in motor phases, or dc-link and which signals are corrupted with a noise. The author discusses the specifics of inverter hardware design for low-cost applications and explains why the conventional techniques are not applicable. After that a new method capable of operating at high noise to signal ratio is proposed and implemented. The experimental results verified feasibility of the developed technique and demonstrated its reliable operation under different load conditions. In order to perform comparative analysis, several conventional algorithms were implemented and their performance was compared to the performance of the proposed method. After experimental verification, this algorithm was included into the existing control scheme of commercial permanent magnet synchronous motors, as a part of the safety module. The modified motor drive successfully passed standardization according to UL 60730 safety standards and was put into mass production. [ABSTRACT FROM AUTHOR]

Common-mode voltage (CMV) is one of the major concerns in modern motor drive systems using pulsewidth modulation (PWM) controls. To alleviate the CMV issue, a series of different PWM methods have been proposed. However, due to the physical limits of the three-phase structure, none of those reduced-CMV PWMs (RCMV-PWMs) can fully eliminate the CMV. As the motor phases have been extended to even numbers, such as six phases, opportunities to eliminate the CMV by a proper modulation scheme emerge. This article proposes a new modulation method to fully eliminate or reduce the CMV for the full modulation span of a dual-three-phase motor drive system, thereby helping to shrink the CM filter. Mathematical models are built indicating its effectiveness of eliminating the CMV in the linearity range of the modulation index and reducing the CMV in the overmodulation range. Simulation results along with experiments implemented on field-programmable gate array controlled dual inverters validated the effectiveness of the proposed control algorithm. [ABSTRACT FROM AUTHOR]

Phase-locked loops (PLLs) and frequency-locked loops (FLLs) are of importance in power and energy applications. Both technologies have been introduced to speed-sensorless- controlled motor drives, and increasing applications of PLLs and FLLs for speed estimation are foreseen. To enable a proper and good design, a thorough review of the PLL- and FLL-based speed estimation schemes is then provided in this article. It is revealed through the review that many PLL- and FLL-based estimation schemes fail to accurately track a frequency ramp (i.e., obvious estimation errors appear), which may lead to a compromised estimation accuracy when these schemes that are applied in induction motor drives operating during acceleration and deceleration processes. To address this, the proven speed estimation schemes together with new attempts are also presented in this article. Moreover, various challenges to the PLL- and FLL-based speed estimation schemes, including harmonics, dc offsets, and parameter variations, are considered when evaluating these schemes. Solutions to tackle these disturbances are accordingly presented. In addition, two representative estimation schemes are exemplified through experimental tests. Finally, further challenges in using the PLL- and FLL-based schemes for speed estimation are discussed. [ABSTRACT FROM AUTHOR]

This article presents a direct model predictive control (MPC) method for drive systems with superior steady-state and dynamic performance. Specifically, the discussed MPC algorithm achieves a steady-state behavior that is similar or better than that of a linear controller with a dedicated modulator, and fast transient responses that characterize direct controllers. Moreover, it ensures a fixed switching frequency by allowing for one switching transition per phase and sampling interval. Furthermore, the controller utilizes the stator current gradient to predict the evolution of the drive system within the prediction horizon. To find the optimal switching time instants—and thus ensure favorable performance—the control and modulation problems are formulated in one computational stage as a constrained quadratic program (QP). To solve the latter within a few microseconds, a computationally efficient QP solver based on a gradient method is proposed that enables the real-time implementation of the presented algorithm. To further alleviate the computational demands of the proposed method, a mechanism that can identify suboptimal switching sequences at the very early stages of the optimization process is proposed. The effectiveness of the proposed control scheme is experimentally verified on a 3 kW drive system consisting of a two-level inverter and an induction machine. [ABSTRACT FROM AUTHOR]

Load commutated inverter (LCI)-based drives are quite popular in high-power, medium-voltage (MV) applications. However, the limited torque capability during starting and low-speed operation is a major drawback of these drives. This is due to the small back electromotive force (EMF) in the drive motor at low speeds, which is usually insufficient to commutate the silicon-controlled rectifiers in the LCI. A new technique to overcome this drawback for an LCI-fed active-reactive induction motor (ARIM) drive is proposed in this article. The ARIM is a dual-stator induction machine reported in literature, with one winding rated for MV and the other rated for low voltage (LV). The MV winding is fed with active power from the LCI, while the LV winding is supplied with reactive power from a lower rated LV voltage source inverter (VSI). In the proposed method, the VSI is used to apply a preselected voltage vector for a short time during each turn-off instant, such that a commutation voltage of sufficient magnitude is induced in the MV winding, providing safe commutation irrespective of the magnitude of the back EMF. Thus, the drawback of the low torque capability at starting and low speeds is overcome in the proposed method, which is also experimentally validated using a 75-kW, 3.3-kV prototype. [ABSTRACT FROM AUTHOR]

Model predictive control (MPC) represents an affirmed optimal control strategy, able to handle multivariable systems and their input–output constraints. However, MPC does not provide an integral control action for reference tracking control problems. Several methods have been proposed to overcome this limitation. Standard MPC methods include a disturbance observer to handle unmodeled uncertainties, such as external unknown disturbances and parameter mismatches. Among these formulations, the authors focus on the velocity form MPC, which considers the incremental formulation of the motor state-space model. This formulation gets rid of the bias errors in reference tracking problems. In this article, the MPC paradigm is applied to the current control of synchronous motor drives. The intent is to compare the velocity form and the MPC with disturbance observer. A theoretical analysis of the MPC coupled with disturbance observers and the equivalence between these formulations and the velocity form is presented. Input constraints are included in the MPC optimization process, thus requiring an online quadratic programming solver. Experimental tests consider a 1 kW anisotropic synchronous motor. Numerical aspects regarding the optimization problem are investigated for both methods. [ABSTRACT FROM AUTHOR]

Modulated model predictive current control techniques are considered an interesting option to control multiphase drives due to their control flexibility and fast dynamic response. However, a practical stability study of those techniques is still missing. This article presents an experimental stability study, to quantify the limits of stability, to modulated predictive current controllers applied to an asymmetrical six-phase induction machine. Experimental results are presented to verify the theoretical analysis results in terms of stability ranges regarding sampling frequency and rotor speed. [ABSTRACT FROM AUTHOR]

High-precision torque estimation and control of induction motor drives is an important research field due to the extensive use of these motors in torque controlled applications, for example, in electric vehicles. The open-loop torque control performance depends strongly on the accuracy of both the motor model and the flux estimation. To address this appropriately, an adaptive Kalman filter with offline parameter and observer design optimization is proposed in this article. Thereby, the basic induction motor model is extended by magnetic saturation, iron losses, and skin effect influences. All uncertain motor model and observer configuration parameters are offline identified by a global optimization technique, namely particle swarm optimization. The identification utilizes a comprehensive data set consisting of test bench measurements and leads to an optimized observer enabling precise torque estimation and control. In experimental validation, for both torque estimation and control, the root-mean-square error is below 1  % of the nominal torque over the entire operating range. With the help of an accurate gray-box inverter model for phase voltage estimation and a speed-adaptive Kalman filter tuning scheme, the proposed observer is able to operate also at slow speeds including standstill. [ABSTRACT FROM AUTHOR]

The standard converter concept employed in variable speed motor drives is the two-level three-phase Si insulated-gate bipolar transistor voltage source inverter with its switch nodes connected to the motor terminals via shielded cables to avoid excessive high-frequency noise emissions. However, high $dv/dt$ pulses of the inverter pose substantial stresses on the motor, which are further intensified by the ever-faster switching speeds of wide band-gap semiconductors, hence promoting interest in inverters with full-sinewave output filters, which potentially enable the use of inexpensive unshielded motor cables. However, the IEC 61800-3 standard dictates stringent conducted and radiated emission limits on unscreened power interfaces. In this article, a dc input and ac output filter structure allowing operation with unshielded cables is derived for a phase-modular 11-kW buck–boost Y-inverter motor drive system employing 1.2-kV SiC MOSFETs with a switching frequency of 100 kHz. First, regulations and measurement techniques for conducted and radiated emissions of motor drives are analyzed. Next, the operating principle of the Y-inverter is described and an electromagnetic interference equivalent circuit is derived, followed by a systematic filter design. Finally, measurements are conducted on an ultracompact hardware prototype of the converter system with 12 kW/dm3 (197 W/in3) power density, where the results indicate full compliance with the IEC 61800-3 conducted and radiated emission limits for operation with unshielded dc supply and motor cables in a residential area. [ABSTRACT FROM AUTHOR]

In the finite control set model predictive control (FCS-MPC) of induction motors, the mismatched motor parameters will inevitably lead to model predictive errors, and then reduce the control performance. At present, the evaluation methods of the prediction errors caused by mismatched parameters and of improving robustness have become the research hotspots of FCS-MPC of induction motors. In this article, an observer-predictor-based predictive torque control of induction machine is proposed in order to improve the prediction accuracy. In the stator current prediction equation, this article abandons the traditional open-loop prediction equation and proposes a closed-loop stator current prediction equation. In the stator flux prediction equation, this article abandons the traditional stator flux prediction model based on voltage model, and proposes a discrete hybrid prediction model combining voltage model and current model, where the proportional-integral regulator is used to switch the voltage model to the current model. Second, the stability and parameter design principles of the closed-loop stator current prediction model and the closed-loop stator flux prediction model are analyzed. Finally, the experimental results show that the proposed method is superior to the traditional method in dynamic performance, steady-state performance, and parameter robustness. [ABSTRACT FROM AUTHOR]

In this article, the predictive horizon of model predictive current control (MPCC) is extended for achieving better operational performance. However, the computational burden of MPCC exponentially increases with its predictive steps, and thus, the predictive step is usually chosen as one. In order to explore the potential advantage of multistep MPCC (M-MPCC), one simplified search method is proposed so that the M-MPCC can be executed in practice with greatly reduced complexity. In the proposed search method, a large number of possible voltage vector sequences can be excluded in advance with the guide of the defined reference voltage vector sequence. Then, one simplified M-MPCC is applied to two 3 kW arc induction machines with a large radius, which can make a full demonstration on the drive performance of linear induction machine in practice. The comprehensive simulation and experiments have clearly indicated the relationship between the predictive step and the performance of the proposed M-MPCC. It has persuasively verified the feasibility of low complexity and decreasing time consumption based on the proposed search method in this work. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous machines work with controllers and controller parameters affect the machine's voltages and currents and, thus, the diagnosis of stator winding fault. One such parameter is the current controller bandwidth that affects the harmonic content in these signals. In the literature, the second harmonics in both $dq$ -axis currents and voltages have been used for fault detection, and the main advantage is that interturn short-circuit (ITSC) winding fault with a few shorted turns, specially one turn, can be detected. One indicator that combines the fault information in voltages and currents is the instantaneous reactive power (IRP). However, it has been shown that IRP does not perform robustly with respect to current controller bandwidth. The main contribution of this article is that it proposes and validates a new mathematical function for ITSCs detection, Rayleigh quotient, which combines the fault information present in voltages and currents to make ITSCs detection robust to current controller bandwidth. The validations from both cosimulation and experiment show that the proposed method is robust to the bandwidth and can detect ITSC faults faster than IRP. [ABSTRACT FROM AUTHOR]

Overmodulation (OVM) techniques of asymmetrical six-phase induction machine (ASIM) achieve higher dc-bus utilization by applying nonzero average voltage in nonenergy transfer plane. This results into unwanted current and associated copper loss. Existing OVM techniques reduce this loss with pulsewidth modulation (PWM) techniques from six-dimensional space vector perspective, which is both conceptually difficult and computationally challenging. The computational complexity of space vector based techniques is reduced by few existing PWM techniques in linear region by splitting the six-phase inverter as two three-phase inverters and modulate these inverters with linear PWM techniques in 30 $^\circ$ phase shifted. This is referred as three-phase inverter based technique in the title. But, three-phase inverter based OVM technique does not exist in the literature due to lack of knowledge of the relationship between six-dimensional space vectors and space vectors of two three-phase inverters. This article first establishes this relation. Based on this relation, an OVM technique is proposed where the reference voltage vectors of two inverters are phase shifted by 30 $^\circ$ but of different magnitudes. The proposed technique achieves THD and WTHD performances similar to space vector based best technique of ASIM with reduced computational complexity, as shown in details. The proposed strategy is validated through experiments and simulations on six-phase induction machine at 4.2 kW. [ABSTRACT FROM AUTHOR]

This article presents a postfault control algorithm that minimizes the stator Joule losses in multiphase induction machines under an open-phase fault and for different star connection layouts. The key novelty is that the algorithm can be applied to any configuration of a multi-n-phase machine, independently of the connection of the neutral points. The latter is analytically derived and is based on the space vector representation of the machine model. In addition, it is shown that a low number of neutral points helps to reduce the winding losses in case of an open-phase fault but requires additional control regulators and computational efforts. The theory is applied to an asymmetrical quadruple-three-phase induction machine, which is configured to represent five different motor layouts. Finally, experimental results are presented to validate the control algorithm. The optimal solution that is given in this article can be employed for the control of symmetrical or asymmetrical multiphase machines with different star connection layouts and in any open-phase postfault operation. [ABSTRACT FROM AUTHOR]

Utilizing electromagnetic interference (EMI) filters is a major approach to reduce the conducted emissions from the power electronic converters. These filters enlarge the total volume and weight of the system. Many works have been done to integrate the filter components. In this article a new integrated choke with a certain winding structure, consists of two core, a toroid, and a solenoid is presented. Although the DM inductance of the proposed choke could be independently increased by designing the windings, the CM inductance value remains almost constant as the conventional choke. Theoretical analysis for modeling the choke and prediction of the inductances and saturation conditions is provided. Experimental measurements validate the analysis, and show a good filtering performance with rejecting conducted noise from an induction motor drive system while it decreases the overall filter size. [ABSTRACT FROM AUTHOR]

Finite control set model predictive control (FCS-MPC) of three-level neutral point clamped inverter-fed induction motor has received wide concern recently, thanks to its low switching frequency and fast dynamics. However, the performance largely depends on the accurate measurement and parameters which determine the feedback and control loops, respectively. Besides, FCS-MPC demands a large number of resources to perform the exhaustive search, which indicates that the computation burden increases exponentially with the increasing switching states. Aiming at improving the robustness under the condition of unavoidable measuring noises and parameter variation as well as reducing the computational burden, a passivity-based model predictive control (PB-MPC) scheme is presented in this article. For an ideal system, the PB-MPC has a similar character as that of the FCS-MPC. In real applications, where noises and disturbances impact the system more or less, PB-MPC outperforms FCS-MPC due to the power shaping and damping injection inherited from passivity-based control which ensures the asymptotic stability. A Lyapunov function is designed to prove the stability of the proposed scheme. The stability and efficiency are verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

An interturn short-circuit fault in the stator winding of an electric machine, denoted as turn fault, has been recognized as one of the most severe faults in permanent magnet machines, which require a swift and reliable detection, in order to implement appropriate mitigations. The asymmetry brought by a turn fault is widely used for fault detection. However, similar features also emerge in a less severe high-resistance connection (HRC) fault, which may lead to an incorrect fault identification. In this article, a more exclusive turn fault detection method with the ability to differentiate from the HRC fault is proposed. It injects high-frequency square-wave voltage signals and makes use of the difference in the high-frequency impedance under the two fault conditions. The sensitivity to the HRC fault is largely reduced. The proposed turn fault indicator is independent of the operating conditions and robust with respect to state transients. This method is validated in a fault-tolerant permanent magnet assisted synchronous reluctance machine drive. [ABSTRACT FROM AUTHOR]

This article presents an online data-driven diagnosis method for multiple insulated gate bipolar transistors (IGBTs) open-circuit faults and current sensor faults in the three-phase pulsewidth modulation inverter. The fast Fourier transform (FFT) algorithm is used to extract the fault frequency spectrum features of the three-phase currents. Then, a feature selection method named ReliefF is introduced to select the most critical features by removing redundant and irrelevant features. In addition, as novel fast learning technology, a random vector functional link network is applied to learn the faulty knowledge from the historical dataset. Based on the well-learned model, the fault type and location of the converter can be accurately identified as long as the three-phase current signals are measured. Offline test results verify that the proposed method can identify the IGBT and sensor faults with an accuracy of 98.83% and outperforms the state-of-the-art learning algorithms. Moreover, the real-time hardware-in-the-loop test results show that the proposed method can successfully identify the IGBT faults and current sensor faults within 22 ms. It is robust to the dc-link voltage fluctuations, model parameters, and speed or load variations. The extensibility of the proposed method is also validated based on the test results in terms of other fault modes and drive systems. [ABSTRACT FROM AUTHOR]

This article deals with a photovoltaic-grid integrated system operating an induction motor (IM) coupled to a water pump. A simple dc-link voltage regulation approach is adopted for the power transfer. This system is utilized to primarily feed the induction motor-driven water pump and when water pumping is not desired, the power is delivered to the utility. This system requires two current sensors and two voltage sensors in total for sensing and estimation purpose. Induction motor phase currents are estimated from dc-link current by modified space vector modulation (SVM) technique. The speed estimation in this system is achieved by artificial neural network-based model reference adaptive system with a third-order integrator for flux estimation and is capable of controlling the power flow as per demand. The field-oriented control is used for speed control of an IM-pump. A third-order integrator based unit voltage generation algorithm is used to control the power transfer in both the direction between utility and the IM drive with water pump by regulating dc-link voltage. The appropriateness of the system is justified by simulated results on MATLAB/Simulink platform and test results procured with the help of a developed prototype during varying solar irradiances. [ABSTRACT FROM AUTHOR]

Although the stability of a speed adaptive full-order observer (AFO) has been studied for a sensorless induction motor (IM) ultralow speed operation, few researchers concern its dynamic performance simultaneously. To address this problem, this article proposed a novel feedback gain selection principle of an AFO considering both stability and dynamic performance. Compared with the conventional stability-based feedback gain selection, the proposed method applied the zero-point locus diagram and Bode diagram to further limit the range of stabilized feedback gain, leading to improved dynamic performance. Moreover, the robustness of the AFO is guaranteed with the proposed feedback gain under IM parameter mismatch. The validity of the proposed method is confirmed by comparative experiments. [ABSTRACT FROM AUTHOR]

In this article, a concept of separation of an inverter-fed induction motor drive from its mains supply by two transistor switches inserted in the dc-link circuit is re-examined based on the proposed parallel quasi-resonant dc-link inverter (PQRDCLI). The objective of the article is to show an advantage of the proposed topology in limiting high-frequency common-mode voltage and bearing currents. In the laboratory setup, an induction machine was equipped with hybrid ceramic bearings and an insulated clutch to measure the shaft-to-frame bearing voltage and the shaft-grounding current. Experimental tests of the PQRDCLI confirm significant reduction of common-mode voltage and shaft-to-frame bearing voltage at dc-link zero voltage notches. By controlling the output voltage slopes, the shaft-grounding brush current and the ground leakage current are also reduced. The efficiency measurement and evaluation of the proposed topology, as compared with a two-level hard switched inverter, reveal comparable efficiency of around 95% and indicate loss distributions in both inverters. [ABSTRACT FROM AUTHOR]

The maximum-torque-output (MTO) trajectory can achieve optimal current distribution for induction motor (IM) field-weakening (FW) control. To provide the dynamic model for MTO, this letter proposes quantitative analysis of the current dynamic character in FW control. As the current vector moves along MTO trajectory, the current changing rate and voltage margin requirement are calculated to study the dynamic control objective and the realization condition of FW control. According to the summarized changing law of voltage margin requirement, the d-axis voltage margin priority approach is applied to the IM FW system for current dynamic optimization. The effectiveness of the studied method is verified through comparison experiments on an advanced RISC machine (ARM)-based 3.7-kW IM platform. [ABSTRACT FROM AUTHOR]

This article provides an interval type-2 fuzzy-based direct torque control (IT2FDTC) of the induction motor (IM) drive, (IMD) in which a hybrid duty ratio control (HDRC) technique is used to activate a two-level inverter. Moreover, it is implemented with the help of DSPACE-1104 controller in a real-time application using a 2HP IM and compared its overall performance with a conventional proportional-integral direct torque control (CPIDTC) using space vector modulation (SVM) technique. The IT2FDTC can be provided less torque and flux ripples with a faster dynamic performance of IMD over a CPIDTC. This due to the fact that a three-dimensional Mamdani type-2 fuzzy controller along with the centroid method is used in the defuzzification process, for the proposed control method. The proposed method of study effectively controls the gains of PI and HDRC. Also, HDRC has a total of five possible duty ratios in which two novel duty ratios are introduced including two clamping and one SVM duty ratios to further improve the current/flux/torque harmonic profile performance of IMD than CPIDTC. [ABSTRACT FROM AUTHOR]

This article proposes and demonstrates a fault-detection method to locate interturn short circuits (ITSCs) in the stator windings of a brushless doubly fed induction machine (BDFIM). The detection of ITSC is important in machine health prognostics as ITSC is an early stage fault that may lead to other faults such as coil-to-coil and coil-to-ground. BDFIM consists of power and control windings in the stator that are magnetically coupled through a nested-loop rotor winding. Existing ITSC detection algorithms use rotor slot harmonics in stator current spectra as fault indicators for only conventional doubly fed induction machines. However, these algorithms cannot be applied to BDFIM due to its different stator/rotor winding structure. This article primarily proposes a new analytical formulation for the nested-loop rotor slot harmonics (NRSHs) as ITSC fault indicators in BDFIMs. Using NRSHs, a detection algorithm is also proposed to detect and locate ITSC in power/control windings of BDFIMs. The proposed algorithm is verified based on numerical analysis of a BDFIM using the finite-element method. The accuracy of the proposed fault-detection algorithm is also experimentally investigated and demonstrated using a BDFIM test rig. Both numerical and experimental test results confirm effectiveness of the proposed ITSC fault-detection algorithm. [ABSTRACT FROM AUTHOR]

A control scheme is presented for a dual inverter drive with a floating capacitor bridge, with decoupled motor and capacitor dynamics. A stator current reference frame is used that decouples the real and reactive power components of the motor and enables the decoupling of the motor and capacitor dynamics. Apart from the high frequency voltage ripple due to the inverter switching pattern, the capacitor voltage can be kept constant even during large step changes in motor speed reference and load torque. This allows for the use of a significantly smaller floating bridge capacitor whose size depends only on the steady-state high frequency voltage ripple. Additionally, the number of PI regulators used compared to previous works and the dc-link voltage requirements are both reduced. [ABSTRACT FROM AUTHOR]

This article presents a progressive comparison of predictive torque control (PTC) algorithms for a five-phase induction motor fed with a two-level five-phase inverter. The extension of three-phase PTC to the five-phase motor, introduces current harmonics of the order 10n $\pm$ 3 (n = 0, 1, 2...), which are not responsible for torque/flux production. The inherent disadvantage of PTC is being a variable frequency algorithm, which adds complexity to the design of magnetic components. This disadvantage of PTC can be overcome by applying dwell time ($t_{s}$) to the voltage vectors obtained through a minimum torque ripple condition, which is determined based on the ripple equation. In the proposed algorithm, a set of synthetic voltage vectors are generated and used for reducing flux and torque error through cost function. The use of synthetic voltage vector simplifies the cost function and further reduces the computation time. A two-step delay compensation is adopted to improve the precision of the control algorithm further. In each control cycle, an optimal switching time is calculated to reduce the torque ripple and to maintain the constant switching frequency. In this article, a modified PTC is proposed, which targets to achieve constant switching frequency, eliminate the xy-subspace current harmonics, reduce the torque ripple, and minimize the computational burden involved in the conventional predictive torque control algorithm. The experimental study is carried out on a laboratory prototype. The results show compliance with all the experimental study with different PTC algorithms with different sampling frequencies, and the modified cost function. [ABSTRACT FROM AUTHOR]

The fault-tolerant ability is a significant advantage of multiphase machines over the three-phase ones. Parallel connections of stator windings or converter legs are preferred to enhance the power rating or drive performance. Open-circuit faults on parallel branches are reflected as the derating of current limits for the corresponding phases, and fault-tolerant strategies are required to keep the phase currents within asymmetrical current limits. This article analyzes the optimal phase current trajectories of a five-phase induction machine under three different faulty scenarios in parallel situations and then proposes the offline optimized current trajectory tracking (OCTT) fault-tolerant strategy, which can reach the maximum achievable fault-tolerant power while guaranteeing optimized ohmic losses over the full power range. Furthermore, based on the generalized symmetrical components theory, an extended rotor field-oriented control (RFOC) is proposed to realize the OCTT mode in field-oriented control. Experimental results confirm the efficiency improvement of the OCTT mode in the full-power-range operation and verify the asymmetrical current trajectory tracking ability of the extended RFOC. [ABSTRACT FROM AUTHOR]

Operation of the conventional modular multilevel converter (MMC) at low frequencies for the induction motor drive is difficult. The peak-to-peak voltage ripple of submodule (SM) capacitor increases abnormally at low frequencies of the drive. Recently, the problem of high voltage ripple has been solved by using back-to-back MMC without overloading the converter till very low frequency of the drive. In this back-to-back configuration, the grid-side MMC generates constant dc current source at its output instead of dc voltage source. Using this current source as input, the motor-side MMC drives a three-phase induction motor. It is shown that the voltage ripple of SM capacitor remains constant till very low frequency due to the dc current source. However, the average capacitor voltage controllers do not guarantee balanced operation of individual SM. In this article, the need for balancing controller of individual SM capacitors of back-to-back MMC is established experimentally. Therefore, this article proposes additional voltage-balancing controllers for the individual capacitor of grid-side MMC and motor-side MMC without disturbing the average controllers. The operating principle of this balancing controller has been presented analytically and verified experimentally. Finally, the operation of the drive with the proposed balancing controller is presented for wide speed range. [ABSTRACT FROM AUTHOR]

The induction motor (IM) drive with direct torque control scheme (DTC) turns prominent for industrial applications. However, it retains disadvantage of high torque ripples. The conventional look-up table for DTC scheme is structured with selection of reverse voltage vectors (VVs) when flux and torque errors crosses lower hysteresis boundary condition. This results in higher torque ripples and increase in switching frequency. In this article, modified look-up table for DTC of three-level dual voltage source inverter fed open-ended winding IM drive is proposed, where the VVs selection for lower hysteresis boundary conditions of torque and flux are restructured with null voltage states. The selection of suitable null voltage switching states from the various possible combinations of dual inverter switchings is based on minimization of switching state transitions. To nullify flux instability at zero speed, proper active VVs are placed at hysteresis flux +1 and torque 0 condition in the modified look-up table. These overall effective modifications in the proposed DTC scheme enjoys the benefits of reduction in torque ripple, switching frequency, and stable flux maintenance. The MATLAB simulations and practical investigations are conducted for existing and proposed DTC schemes. From these results, the benefits of the proposed DTC over existing DTC schemes are verified. [ABSTRACT FROM AUTHOR]

Starting in the rotating condition is an important technology for induction motor (IM) speed sensorless control. The key of this technology is that the initial speed of the IM in the rotating condition should be estimated quickly and accurately. In this article, an integral sliding mode control method based on the nonlinear model of the rotor back electromotive force is designed to start a speed sensorless controlled IM in the rotating condition. The stability is guaranteed by Lyapunov stability analysis, and the robustness to rotor time constant and disturbance are analyzed. Meanwhile, in comparison with the proposed control method, the existing input–output feedback linearization (IOFL) control method is introduced and the stability and robustness are also analyzed. Compared with the existing IOFL control method, the proposed control method can estimate the initial speed in the rotating condition without overshoot and has better dynamic performance and robustness. In addition, the proposed control method can be applied not only to the restart operation but also to the normal operation. Only a single control strategy is required from the restart operation to the normal operation. The proposed method is verified by simulation and experiments using a 7.5 kW IM. [ABSTRACT FROM AUTHOR]

This letter proposes a Luenberger model-based predictive torque control (LM-PTC) of induction machine to compensate prediction error caused by mismatched parameters. In the traditional predictive torque control (T-PTC), stator current, stator flux vector, and electromagnetic torque are predicted in one sampling period by open-loop prediction model, which will inevitably lead to prediction error by mismatched parameters, first. Inspired by the idea of closed-loop Luenberger observer, in the torque and flux prediction, the feedback correction part is introduced into prediction equations for LM-PTC. Second, the steady prediction errors of T-PTC and LM-PTC are, respectively, analyzed with mismatched parameter. Finally, the proposed LM-PTC is verified by the comparison experiments including dynamic-state, transient-state, and steady-state experiments. [ABSTRACT FROM AUTHOR]

This paper proposes a new approach for the capacitor balancing of a dual three-level T-type converter based on silicon carbide discrete semiconductors. This study is performed while the converter feeds an open-end induction motor. The model predictive control (MPC) scheme is developed to balance the dc-link capacitors and to control the machine torque simultaneously. The proposed technique for MPC reduces the number of redundant switching states that are used in computations without affecting the operating voltage vectors. This reduces the computational time substantially. In addition, the proposed control strategy mitigates the weighting factor tuning problem of capacitor balancing in addition to the conventional MPC cost function. MATLAB simulation results for the proposed drive system under different case studies are presented. Hardware experimental setup for the proposed converter is built, tested, and verified. A comparison between experimental and simulation results is presented. It is observed that the theoretical as well as the experimental results are in full agreement. [ABSTRACT FROM AUTHOR]

This paper proposes a novel polygonal voltage space vector structure (SVS) having 30 sides, for a star-connected induction motor drive. The SVS eliminates the presence of harmonics up to 25th order from motor phase voltage throughout the entire modulation range, providing a torque profile devoid of lower order pulsations. Linear modulation is extended till 99.63% of base speed without exceeding the motor phase voltage rating. Topology consists of a dc-link fed primary inverter and two equal low voltage modular capacitor fed secondary inverters. Here the harmonics generated by the primary inverter is canceled by the secondary inverter which acts as a switched capacitive filter. Detailed description of the SVS generation and timing calculations are provided in this paper. Effectiveness of the proposed scheme is validated using experimental results, inverter loss calculations, and harmonic analysis. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of active zero vector pulsewidth modulation (AZPWM-1) and space vector pulsewidth modulation (SVPWM) on the design of passive common-mode (CM) attenuation methods to reduce CM current and shaft voltage in inverter-fed V/f-controlled induction motor drives. The passive CM attenuation methods examined here are the CM choke, the CM electromagnetic interference (EMI) filter, and the CM transformer. The attenuation requirement of AZPWM-1 and SVPWM is identified to design the passive CM choke and EMI filter. Based on the attenuation requirement, the design guidelines are revisited for SVPWM, and design rules are proposed for AZPWM-1. However, the CM transformer is designed based on the step change in magnitude of CM voltage of both the pulsewidth modulations (PWMs). The limitations in design, regarding switching frequency and component size for each case, are also established. It is shown that to have a similar attenuation in the considered two PWM cases, AZPWM-1 requires smaller passive components compared to SVPWM. The proposed design guidelines are substantiated with experimental results on a 1.1-kW induction motor drive. [ABSTRACT FROM AUTHOR]

Health monitoring and fault detection are becoming more and more important in electrical machine systems due to the increasing demand for reliability. Winding turn fault is a common fault in permanent magnet (PM) machines, which can cause severe damages and requires prompt detection and mitigation. High resistance connection fault, which results in phase asymmetry may also occur but does not require immediate shutdown. Thus, apart from the fault detection, the classification between the two faults is also required. In this paper, a new technique for detecting and classifying turn fault and HRC fault by utilizing both the high and low frequency components of the zero sequence voltage is proposed with the enhanced sensitivity. The dependence on the operating conditions is minimized with the proposed fault indicators. The effectiveness of fault detection and classification has been verified by extensive experimental tests on a triple redundant fault tolerant PM assisted synchronous reluctance machine. The robustness of the turn fault detection in transient states and under no load conditions has also been demonstrated. [ABSTRACT FROM AUTHOR]

The conventional control methods for brushless doubly-fed induction generator (BDFIG) normally employ mechanical sensors to acquire the information of rotor speed, which brings many disadvantages in the cost, complexity, reliability, etc. This paper presents an improved rotor speed observer (RSO) for the sensorless operation of standalone BDFIGs, which is based on the power winding (PW) voltage and control winding (CW) current. In order to eliminate the impact of unbalanced and nonlinear loads on the RSO, second-order generalized integrators (SOGIs) and low-pass filters (LPFs) are introduced to pre-filter the PW voltage and CW current, respectively. Through comprehensive parameter design, the response speed of the improved RSO will be not lower than that of the basic RSO with ensuring the filtering effect of these additional filters. In addition, the proposed RSO is independent to machine parameters except the pole pairs. Comprehensive experiments are conducted and results verify the proposed improved RSO applied to the standalone BDFIG. Also, the applicability of the proposed RSO on another dual-electrical-port machine, doubly-fed induction generator, is confirmed by simulation results. [ABSTRACT FROM AUTHOR]

This paper presents a reduced component count five-level inverter topology based on the stacked cell approach to multilevel inverters. The proposed topology utilizes the fundamental properties of three-phase voltages to reduce the number of switches and flying capacitors to cut size, weight and costs while facilitating higher reliability, simpler wiring and lesser electromagnetic interference. The operational aspects of the topology such as circuit structure, modulation and capacitor balancing are explained, followed by an account of device stresses and reliability. A discussion of certain additional features such as fault tolerant operation, loss steering and common-mode elimination addresses the usefulness of the topology in practical situations. A comparison of the proposed topology with existing methods in terms of several parameters is then used to highlight its merits and features. Finally, experimental results obtained using an induction motor drive incorporating the topology are given, so as to validate the feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

The pole-phase modulated induction motor (PPMIM) drives facilitate the extended range of speed-torque characteristics, which is an essential requirement for traction and electric vehicle applications. For getting the wider speed-torque variations, $15-\Phi $ PPMIM drive is analyzed, which is capable to operate at 2-pole 15-phase, 6-pole 5-phase, and 10-pole 3-phase modes. In these pole-phase operations, in high-phase and low-pole mode of operation, the increment in the linear modulation range with space vector pulsewidth modulation (SVPWM) is not significant. In the low-phase and high-pole mode of operation, there will be higher torque ripples due to the higher magnitude of space harmonics. In this paper, these issues are addressed by using carrier phase-shifted SVPWM (CPS-SVPWM) and phase grouping concepts. In low-pole operation, the linear modulation is enriched by using conventional $3-\Phi $ SVPWM to drive 15-phase machine by appropriately reorganizing the phase winding connections. Similarly, in 6-pole 5-phase mode of operation, the linear modulation range of PPMIM drive is enriched by using $5-\Phi $ SVPWM. It is known that in high-pole mode of PPMIM drive operation, each effective phase is formed by the multiple number of equal voltage potential coils (EVPCs), which are electrically in phase. The carriers of these EVPCs per phase are phase shifted by an appropriate angle to minimize the harmonics in the effective phase voltage, which results in better torque ripple profile. In addition, the detailed comparison of three possible different CPS-SVPWMs is presented, with their pros and cons for selecting the proper carrier phase shift angle. The performance of the proposed scheme has been validated by ANSYS Maxwell two-dimensional as well as laboratory prototype on 5-hp, $15-\Phi $ PPMIM drive. [ABSTRACT FROM AUTHOR]

In self-commissioning, motor parameters are estimated by analyzing the measured currents and voltages. At standstill, the obtained voltages are low because the motor back EMF is zero. Therefore, the inverter nonlinearities are comparable with the estimated voltages and it is necessary to compensate for the nonlinearities. In order to model the inverters nonlinear characteristics, dc current test is conventionally used. However, this test results in a nonlinear equation that contains nonlinearities of two phases. Hence, a numerical solution must be carried out to achieve each inverter phase nonlinearity. Moreover, three-phase symmetry of the inverter is necessary in conventional methods, making them inappropriate to characterize the nonlinearities of multilevel inverters with bypassed cells. This paper proposes a novel characterization algorithm with no numerical solutions applied for motor self-commissioning of VSI-fed drives. Not only the proposed method improves the fundamental and the THD of the calculated phase voltage by 42% and 6% at low currents, respectively, but also it is suitable for characterizing the nonlinearities of multilevel inverters with bypassed cells. A prototype of a five-level cascaded H-bridge inverter and a two-level inverter feeding a 2.2-kW three-phase induction motor is provided to verify the superiority of the proposed method specifically at very low currents. [ABSTRACT FROM AUTHOR]

In this paper, two simple control methods are proposed for improving direct torque control (DTC) with a constant frequency torque controller (CFTC-DTC) in induction machines. The CFTC-DTC was initially introduced to reduce torque ripple and achieve constant switching frequency in inverters. However, when compared to the original DTC, the CFTC-DTC algorithm suffers from slow torque dynamic response owing to the selection of zero-voltage vectors during torque transient. In addition, when the motor operates at low speed, flux droop occurs at sector transitions, which leads to undesirable current distortions. The problem of flux droop occurs because of short-duty voltage cycles and small radial voltage components at low speeds. This paper has two main contributions—to eliminate zero-voltage vectors during torque dynamics in order to establish a fast torque response in the transient state, and to minimize the flux droop at the sector transitions by applying another triangular carrier and modifying the torque output in order to increase the duty voltage cycles at low motor speeds. A detailed analysis of the problems and proposed methods is presented. Experimental results are provided to validate the effectiveness of both proposed methods. [ABSTRACT FROM AUTHOR]

Due to the requirements of multiple working conditions for induction motor in high-speed flux-weakening operation, conventional “maximum torque oriented” flux-weakening controller reveals its own limitations. This paper focuses on holistic torque performance optimization for multi-condition operation. Torque ripple and dynamic response under two kinds of specific working conditions (high-speed braking and load step change) are explicitly analyzed. The theoretically precise maximum torque point is derived to extract the possible output torque for deep flux-weakening operation. Further, an operating point selected flux-weakening controller (OPS-FC) is proposed. It retains the maximum output torque capability for step acceleration and full-load conditions, as well as holding other novel features for the changing working conditions. First, the selected operating point is automatically manipulated for torque ripple alleviation under non-maximum torque condition. Second, since the voltage reference in proposed OPS-FC is directly constructed, the system robustness is enhanced. Finally, speed range is extended to the deep flux-weakening operation, and the complex vector decoupling part of d-axis current regulator is first applied and shared as a flux-weakening path for closed-loop control. Hence, the complicated PI regulator tuning is averted. The proposed scheme is experimentally verified on a 3.7 kW commercial platform. [ABSTRACT FROM AUTHOR]

In finite control set predictive torque control (FCS-PTC), mismatched parameters will lead to the electromagnetic torque prediction error. To solve the aforementioned problem, this paper proposes feedback-correction-based dual reference frame predictive torque control for induction machines, abbreviated as DRF-PTC. First, a DRF flux observer is proposed, which abandons a traditional model reference adaptive observer with rotor speed as adaptive variable. The proposed flux observer decouples the flux observation and the speed estimation and improves the estimation accuracy of flux linkage and rotor speed. Second, a DRF-PTC is proposed to eliminate the effect of speed estimation error on torque prediction. For the influence of mismatched parameters, a correction term is incorporated in double reference frame torque prediction equations, in which the correction term is derived from the correction term of the proposed flux observer. Finally, the proposed DRF-PTC in this paper is verified on the experimental platform of an induction machine. Experimental results show that the proposed DRF-PTC has excellent performance in speed estimation and electromagnetic torque prediction, compared with the traditional FCS-PTC. [ABSTRACT FROM AUTHOR]

The open-phase fault in vector-controlled drives is known as one of the most prevalent failures that require immediate detection. It is still challenging to develop a trustable fault diagnosis scheme at light load, transients, and low-speed regions. This paper presents a novel open-phase fault diagnosis strategy for three-phase induction motor drives over the entire speed range and for different load conditions. By taking advantage of the second-order rotational park transformation (SORP), new fault indices are proposed to identify the open-phase location without using any additional sensors or electric equipment. Comparing with root-mean-square (RMS) calculation-based methods, the proposed method detects the fault at least twice faster, with minimal system resources. The presented scheme may be implemented simply and is robust against the operating point changes. Proof of the proposed fault detection and localization method has been shown through experimental tests on a 250-W three-phase induction machine which is controlled by TI-DSP F28335. [ABSTRACT FROM AUTHOR]

The methodologies applied to speed sensorless induction motor drives (SSIMD) can be divided into two categories. The first category makes use of the fundamental model of induction motor to establish speed and flux observers. However, the rotor speed is unobservable with these methods when synchronous speed is close to zero. The second category makes use of anisotropies of induction motor to observe rotor speed. However, the anisotropies of induction motor are too weak to extract rotor speed information. Consequently, the unstable problem of SSIMD at low synchronous speed (including zero synchronous speed) has not been solved yet by now. In this paper, a virtual voltage injection method is proposed to solve this problem. The voltage is only injected into observer. The observability of rotor speed based on proposed virtual voltage injection is analyzed. Because the injected voltage into observer results in estimated speed error, a compensation method is proposed then. The stability of the system with virtual voltage injection and corresponding compensation method is analyzed by the input-state-stability concept. Finally, the feasibility of the proposed method is verified by experiments. [ABSTRACT FROM AUTHOR]

A novel pulsewidth modulation (PWM) scheme for the decoupled and coordinated control of two parallel connected split-phase induction machines is discussed in this paper for the first time. Both the motors are operated from a single six-phase voltage source inverter which acts as a power source, and two switched capacitor-fed auxiliary inverters to limit the flow of nontorque producing currents in each motor. Both the motors can be operated at its full rated power with low switching frequency, and decoupled control for full power range can be achieved with the proposed topology. This is possible because the individual machines do not carry the load/harmonic currents of other machine (unlike the conventional series or parallel connected systems). The converters can be modulated using sine-triangle PWM or space vector pulsewidth modulation (SVPWM). Furthermore, two different schemes of SVPWM techniques are proposed and compared in this paper. Exhaustive experimental results for all the modulation schemes are provided for steady state and transient operating conditions including start-up to validate the proposed topology and modulation schemes. [ABSTRACT FROM AUTHOR]

Generating dense multilevel voltage space structure using polygons of higher sides is one of the novel and elegant method to suppress low-order harmonics and to obtain refined sinusoidal voltages using voltage source inverters for variable frequency drive application without passive filters. Apart from the advantages of conventional multilevel inverter topologies, schemes generating polygonal voltage space vector structure can equip full dc-bus utilization, low switching frequency strategies to eliminate low-order harmonics, and increased linear modulation range. In this paper, an induction motor drive scheme generating a highly dense multilevel 24-sided polygonal voltage space vector structure using a single dc source, which can eliminate harmonics till 23rd order from phase voltages, is presented. Cascaded power circuit topology with a flying capacitor inverter fed with a dc source and two low voltage floating capacitor fed H-bridge inverters is used. Detailed experimentally validated results, under scalar as well as indirect rotor field oriented control of induction motor are provided. Studies on voltage ripple and reactive energy in various floating capacitors, harmonic performance of output voltage for wide range of speed operation, are also included. [ABSTRACT FROM AUTHOR]