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Pulsewidth-modulated (PWM) current-source converters (CSCs) have the features of simple configuration, reliable short-circuit protection, and sinusoidal ac output voltages. The conventional space-vector modulation (SVM) scheme usually generates high-magnitude low-order harmonics in CSCs with low switching frequency. In this article, two modified SVM schemes, namely MSVM1 and MSVM2, are proposed to improve the harmonic performance for PWM CSCs in the high-power applications with low switching frequencies. The MSVM1 scheme focuses on eliminating the average dwell-time error of current vectors within each sampling period, while the MSVM2 scheme is targeted to achieve the accurate dwell time of current vectors as that of the natural sampling-based SVM scheme. The theoretical analysis and the calculation equations of dwell time are derived for both MSVM1 and MSVM2. The experiments are given to verify the effectiveness of the two modified SVM schemes in improving the harmonic performance of high-power CSCs with low switching frequencies. [ABSTRACT FROM AUTHOR]

In this article, the control strategy is studied for the neutral-point-clamped three-level inverter-fed dual three-phase permanent-magnet synchronous motor (PMSM) drive with low switching frequencies. An interleaved finite-control-set model predictive control (MPC) scheme is proposed, where a two-layer MPC is designed to solve the multiobjective optimization problem. The two sets of windings in PMSM are sampled and controlled in an interleaved way so that the control delay and the prediction horizon of the drive system are reduced by half. Moreover, the proposed interleaved control scheme increases the equivalent sampling and control frequency from the perspective of the whole drive system, and thus provides better steady-state performance and dynamic performance. With the switching states of one inverter remaining unchanged, the cross traversal of vector candidate sets between two sets of windings is avoided, and the computational burden can be reduced effectively. Experimental results are given to verify the validity and effectiveness of the proposed interleaved control scheme. [ABSTRACT FROM AUTHOR]

A feedback linearization based direct torque control (FL-DTC) scheme is designed for interior permanent magnet synchronous motors drives. Several main aspects related to FL are studied thoroughly. A proper choice of two new state variables (the torque and the squared amplitude of stator flux) yields the exact input–output linearization decoupling of the closed-loop system. The FL-DTC frame is obtained after finding a feasible diffeomorphism. For the partially linearized subsystem, i.e., the independent torque and flux loops, two FL-DTC-based controller design solutions are provided. The control problem of internal dynamics is converted to an absolute tracking problem of an equivalent Lur'e system. [ABSTRACT FROM AUTHOR]

The silicon carbide (SiC) devices have attracted more and more attention due to the capability of withstanding higher blocking voltage, higher switching frequency, and higher temperature. However, challenges for SiC devices applied in voltage-source-inverter fed motor drives such as electromagnetic interference (EMI) issues and limited over-current capability still limit the further application of SiC devices. In this article, a novel SiC devices based zero-voltage-switching (ZVS) current-source-inverter (CSI) is proposed for permanent-magnet synchronous motor (PMSM) drive. The key is to propose an auxiliary resonant circuit, which achieves ZVS conditions for all switches in power circuits and reduces the dv/dt of high speed SiC devices. The resonant capacitor in the auxiliary circuit can clamp overvoltage caused by possible open-circuit faults. To further reduce the EMI, the random switching frequency pulsewidth modulation is designed for the proposed CSI motor drive. The system configuration, working principle, circuit design, and control schemes are described in detail. Both simulations and experiments are presented to verify the effectiveness of the proposed ZVS-CSI fed PMSM drive system. [ABSTRACT FROM AUTHOR]

The problem of leakage-inductor parameter in paralleled current-fed isolated dc/dc system has not been solved. Aiming at solving that problem, a leakage-inductor parameter compensation method is proposed without an additional sensor. It provides tunable reflected voltage for parameter difference individually and compensation loops for parameter uncertainty. Thus, the circulating current and the current stress are minimized, and the voltage spike is avoided. The experimental results are given to validate the effectiveness of the method. [ABSTRACT FROM AUTHOR]

The direct torque control (DTC) is widely used in motion control of electric drives, especially for the switching table based direct torque control (ST-DTC) and the space vector modulation (SVM) based DTC (SVM-DTC). The classical ST-DTC schemes can achieve fast dynamic response but may suffer from distinct torque and flux ripples in steady-state operation. On the other hand, the classical SVM-DTC schemes have lower ripples in torque and flux, but the methods slow down dynamic response of DTC. Different from them, a novel hybrid DTC scheme is proposed for dual three-phase permanent-magnet synchronous motor (PMSM) drives in this paper, which can achieve fast dynamic response of classical ST-DTC scheme and good steady-state performance of classical SVM-DTC scheme simultaneously. The key of the proposed scheme is to implement different torque control methods under dynamic operation mode and steady-state operation mode, respectively. A switching method has been designed to guarantee smooth transition between the two operation modes. Besides, the decoupling control of torque and stator flux is maintained with the proposed control scheme, and the stator flux is controlled stably all along. By experiments on a laboratory prototype, it has been verified that the proposed scheme can achieve both good steady-state and transient performance compared to other control methods for dual three-phase PMSM drives. [ABSTRACT FROM AUTHOR]

In this paper, a novel space vector modulation (SVM) strategy is proposed and designed for dual three-phase three-level motor drives based on vector space decomposition (VSD), which could be applied for high-power and high-reliability applications. The key of the proposed method is to design two decoupled groups of voltage vector candidates for synthesis on α − β subspace and x − y subspace, respectively. The two decoupled groups of voltage vectors will synthesize respective voltage references on α − β subspace and x − y subspace, while having no impact on each other. The redundant small voltage vectors and zero-sequence voltage vectors are utilized to mitigate voltage oscillation in midpoint of dc link and suppress zero-sequence current component for dual three-phase windings with a common neutral. For comparison, another VSD-SVM strategy is designed based on traditional solution, which cannot offer closed-loop control on x − y subspace. Both simulation and experiments have been given to verify that the proposed decoupled VSD-SVM can suppress harmonic components on x − y subspace besides tracking torque components on α − β subspace. Furthermore, the harmonic performance of the proposed decoupled VSD-SVM has been compared with the traditional VSD-SVM strategy and the carrier disposition based pulsewidth modulation. [ABSTRACT FROM AUTHOR]

This paper studies and proposes the vector space decomposition-based direct torque control (DTC) scheme for the T-type neutral-point-clamping (T-NPC) three-level inverters-fed double-stator-winding permanent magnet synchronous machine (PMSM) drive, which provides an effective solution for high-power high-reliability applications. The key is to propose a simple but effective space vector modulation (SVM) for DTC of T-NPC double-stator-winding drives-based two-step voltage vector synthesis, in such a way that good dynamic response and harmonic performance are obtained. The closed-loop controllers on harmonic subspace are incorporated to suppress the possible harmonics induced from back electromotive force and unbalanced parameters in phase windings of electrical machine. Furthermore, a hybrid current control is proposed for fault-tolerant operation of the T-NPC double-stator-winding PMSM drives under one-phase open-circuit conditions. In the hybrid current controller, the healthy winding still uses the SVM-DTC control while the faulty winding uses the closed-loop current controller to track the optimized current references. Both simulation and experimental results are presented to verify the performance of the proposed switching strategies and control schemes. [ABSTRACT FROM AUTHOR]

In this paper, three control schemes with variable switching frequencies are proposed and analyzed for the paralleled voltage source inverters (VSIs) fed permanent magnet synchronous motor (PMSM) drive. The proposed schemes could be applied in the low-speed operation region of high-power drive system, where the frequency modulation index is high. First, the field-oriented control (FOC) with phase-shifted chaotic space vector modulation (SVM) under synchronous frame and the FOC with phase-shifted chaotic sinusoidal pulse width modulation under stationary frame is proposed for the paralleled VSIs fed PMSM drive. The proposed phase-shifted chaotic PWM schemes not only eliminate specific switching harmonics completely but also suppress all remaining switching harmonic peaks in the spectrum. The avoidance of inherent circulating current is also considered in designing these two schemes. Second, the direct torque control (DTC) for the paralleled VSIs fed PMSM drive is proposed with circulating current suppression. Besides inheriting the advantages of DTC, the output currents of paralleled VSIs are kept balanced. The working principles of these three methods are presented in detail. Experimental results on a laboratory prototype are given to verify the validity of the three proposed control schemes for the paralleled VSIs fed PMSM with variable switching frequencies. [ABSTRACT FROM PUBLISHER]

In this paper, a hybrid pulsewidth modulation (PWM) scheme is proposed to suppress the LC resonance for the high-power current-source inverter (CSI) fed drives with low switching frequency. In CSI drive systems, the selective harmonic elimination (SHE) is selected due to the better performance of harmonics, but the LC resonance cannot be effectively damped due to the lack of control flexibility of SHE. In this paper, SHE is only used for the steady-state operation. The modulation scheme is then switched to space vector modulation with dynamic capacitor voltage control when the transient event occurs. The smoothed transitions between different modulation schemes are proposed. The proposed hybrid method effectively solves the resonant issues in CSI drives, while maintaining the power quality. Both simulation and experiments verify the performance of the proposed hybrid PWM scheme. [ABSTRACT FROM AUTHOR]

In this article, a dual-vector located model predictive control (DL-MPC) method based on a single dc-link current sensor is proposed for the permanent-magnet linear motor drive system. In DL-MPC, the phase currents are reconstructed by sampled dc-link current and selected active voltage vector (VV). Meanwhile, the sunk number of phase current is defined to evaluate the accuracy of current reconstruction. The first-optimal and second-optimal VVs are determined by dual-vector location. The second-optimal VV is selected for the voltage source inverter when the sunk number exceeds the threshold. Compared with traditional MPC schemes, DL-MPC has smaller current tracking error and better dynamic performance. Meanwhile, DL-MPC has more accurate current reconstruction and lower computation burden than that of the traditional MPC. The effectiveness of DL-MPC is verified by both theoretical analysis and experimental results. [ABSTRACT FROM AUTHOR]

This letter proposes a fast current control scheme for ac drives by minimizing the latency from current sampling to the updation of a pulsewidth-modulation (PWM) command. By reconstructing the architecture of a linear controller, the minimal necessary steps to obtain the output voltage are deduced as the primary calculation, and the other computation work of the current loop is done in the postcalculation after updating the PWM command. With the proposed method, the computational delay is reduced with negligible loss in the available modulation index, and a higher stability margin or system bandwidth is realized. Also, the developed controller structure exhibits inherited antiwindup characteristics. The technique has been validated by experimental investigations on a permanent magnet synchronous motor. [ABSTRACT FROM AUTHOR]

Based on the model predictive current control (MPCC), a dual-level located feedforward control (DLFC) is proposed for the five-leg dual-mover primary permanent-magnet linear motor traction system, in which, two three-phase movers are fed by one five-leg voltage-source inverter (VSI). In the proposed DLFC, the studied traction system is divided into dual-level subsystems, including mover level and system level. In the mover level, it is assumed that one mover is fed by one three-leg VSI. The reference synchronous currents are replaced by the reference static voltages, and the model current predictions are eliminated by the discrete mover voltage vectors (MVVs). Furthermore, the global optimal MVVs are determined by the mover-level geometrical location. If the implementation conflicts between two global optimal MVVs, two local optimal MVVs will be determined by the system-level geometrical location to replace one former global optimal MVV. Compared with MPCC, the computation burden of DLFC can be significantly reduced. If both control methods use the same sampling period, they have the same performances. On the other hand, DLFC can use shorter sampling period, and it can perform better than MPCC. All the theoretical analyses are verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is an attractive option for high-voltage and high-power applications. Fault localization is one of the most important challenges for the MMC consisting of a large number of power electronic switches. Existing literature has not provided a complete fault localization strategy for the MMC under submodule (SM) lower switch open-circuit fault, which only considers the MMC in inverter mode and neglects the MMC in rectifier mode. This article proposes a fault localization strategy for the MMC under SM lower switch open-circuit fault, which is suitable for the MMC not only in inverter mode but also in rectifier mode. This article analyzes the MMC fault characteristics under SM lower switch open-circuit fault, which considers the MMC in inverter and rectifier mode, respectively. Based on two modes’ common fault characteristic that the capacitor is charged all the time during the period when the arm current is positive, the faulty SM can be effectively located by the proposed fault localization strategy. The proposed strategy is not only implemented in simulation with professional tool PSCAD/EMTDC but also verified with a downscale MMC prototype in the laboratory. The results confirm the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]