In this paper, the modeling and mitigation method of torque ripple are investigated for permanent-magnet synchronous motor (PMSM). A new torque ripple model is proposed for three-phase PMSM based on general airgap field modulation theory. The mapping relationship between the torque order and the current order has been revealed. The qualitative and quantitative relationship between the stator harmonic current and torque ripple is established directly without other intermediate variables. The phase and amplitude of the torque component are found to be proportional to the phase and amplitude of the injected harmonic current. Therefore, only a few constant coefficients are required by finite element analysis (FEA) simulation. With the proposed torque model, directional mitigation of torque ripple can be realized by harmonic current injection method with low computational burden by FEA. Repetitive control is employed for harmonic current injection. FEA simulation and experimental results at different operating conditions verify the validity of the proposed torque model and ripple mitigation method.

In the conventional finite control set model-based predictive current control, the dependence on PMSM parameters will seriously worsen the performance of this algorithm. To overcome this issue, this paper proposes a novel finite control set model-free predictive current control (FCS-MFPCC), with ultralocal model replacing PMSM model, which only considers the mapping relationship between the system input and output. Then, two recursive least squares (RLS) algorithms with different update conditions are applied to estimate the parameters in the ultralocal model. Thus, future current of PMSM can be predicted by using ultralocal model. At the same time, in order to balance the contradiction between the stability and rapidity of the RLS algorithm, the extended state observer (ESO) is used to eliminate the error of parameters estimation. The application of ESO also improves the convergence rate and robustness of the proposed algorithm. Experiment results verify the effectiveness of the proposed algorithm.

In this paper, a 6 stator-poles/19 rotor-teeth (6–19) in-wheel hybrid-excitation flux-switching (IW-HEFS) machine with E-shaped stator core units is proposed and optimized for light traction applications. The topology of 6-19 IW-HEFS machine and the main methodology are introduced, firstly. In order to achieve satisfactory overall performance of the proposed machine, a many-objective optimization issue with 6 objectives is presented and needs to be solved. Three optimization principles are put forward and utilized by transforming the many-objective optimization issue into 1) a single-objective optimization issue, 2) two multi-objective optimization issues, or 3) solving the many-objective optimization directly. Kriging models are established for each process to expedite the search for the optimal solution, and the optimal results of three principles are evaluated. The results reveal that the 6–19 IW-HEFS machine holds potential for further applications, and the methods proposed in this paper are effective.

Space vector pulse width modulation (SVPWM) technology is widely used in power converters as a modulation strategy that can effectively improve voltage utilization and reduce harmonics. However, as the number of levels increases, the number of space vectors suddenly increases, and the modulation algorithm design and implementation become more and more difficult. As a result, such application is hardly seen in three-phase multilevel current source rectifier (MCSR). This paper proposes a basic theory and control algorithm of SVPWM technology applied in 7-level rectifiers, which adopts a double closed-loop control strategy for inner current loop and outer voltage loop. System modeling and theoretical analysis with detailed vector selection method of the proposed control are provided. Simulation results show that both unit power factor and 7-level waveforms have been achieved, which has validated the proposed control.

The modular multilevel converter (MMC) is attractive for medium-or high-power applications because of the advantages of its high modularity, availability, and high power quality. Reliability is one of the most important challenges for the MMC consisting of a large number of submodules (SMs). The capacitor monitoring in each SM of the MMC is an important issue, which would affect the performance of the MMC. This paper proposed an effective monitoring method for the capacitance in each SM of the MMC. The proposed method reveals the relationship between the arm average capacitance and the capacitance in each SM of the arm, which can be used for capacitance estimation with a simple algorithm. The simulation studies with the professional tool PSCAD/EMTDC are conducted with the proposed method. The study results show the effectiveness of the proposed method.

This paper presents a smart DC network formed by a multi-terminal VSC-HVDC connecting various micro-grids, independent power generation stations, and passive loads. The corresponding deadbeat current control scheme based on coordinated strategy for multi-terminal VSC-HVDC systems is proposed. The current control scheme is easy to design, implement and has good dynamic response. the case of four-terminal VSC-HVDC interconnected with AC grids, wind farms, and passive loads is developed in MATLAB/Simulink to demonstrate the validity of the proposed control scheme and the united system. Simulation results have demonstrated that the proposed scheme enables optimal operation under conditions of voltage dip, power flow and load changes when used for a large DC smart network.

In this paper, a novel hybrid DTC scheme is proposed for asymmetric six-phase PMSM drives, which can achieve faster dynamic response of classical ST-DTC scheme and good steady-state performance of classical SVM-DTC scheme. The key is that a completely novel control strategy for torque and stator flux is designed. Different torque control methods are adopted under dynamic mode and steady-state mode without adding complexity of control algorithm. And a mode switching method is design to guarantee the smooth transition between the two modes. In addition, the proposed scheme can suppress current harmonics induced from inherent property of asymmetric six-phase motor effectively. Comparative experiments are carried out on a laboratory prototype to verify the effectiveness of the proposed scheme. The proposed hybrid DTC scheme applies equally to three-phase and other multiphase PMSM drives.

A novel topology is proposed for three-phase electric spring (TPES) to achieve specific functionalities. With respect to the existing one, the novel topology contains an additional three-phase transformer with the primaries located at the position of the non-critical three-phase load (NCL) of the existing topology and its secondaries connected to the new three-phase NCL, thus forming a new three-phase smart load (SL). To control the novel topology, the so-called modified δ control utilized for the single-phase electric springs is extended to the three-phase case. Thanks to these solutions, TPES exhibits a behavior entirely different from the existing ones. For instance, under a fluctuation of the line voltages, it exhibits a change of the voltages across NCL that has the same trend as the line voltages. Moreover, it regulates the voltages across the three-phase critical load even under both imbalanced and distorted grid conditions. The effectiveness of the novel TPES topology and of its control is validated by simulation results.

This paper proposes a non-symmetrical permanent-magnet linear motor traction system (PMLMTS), in which the primary permanent-magnet linear motor (PMLM) is employed. Four movers are mounted with same phase angles. There are nine legs, including eight independent legs and one common leg. All legs have same normal voltage but different normal currents. The normal current of the common leg is four times the normal current of the independent leg. Compared with axle-control topology, three legs are reduced in the non-symmetrical topology. As a result, the system complexity is simplified and the system reliability is enhanced. This paper also proposes the control method for the non-symmetrical PMLMTS. The effectiveness of the proposed topology and its control method are verified by simulation results.

This paper proposed an improved fault-tolerant control strategy for open winding fault-tolerant fractional-slot concentrated winding interior permanent magnet synchronous motor (FTFSCW-IPMSM) under switch open-circuit fault. When switch open-circuit fault occurs, the complementary switch located in the same leg is clamped. To maintain symmetry of the two inverters, the other inverter performs the same action. The new fault-tolerant method is presented based on the post-fault reconstruction topology. Compared with the reducing rating operating mode, the proposed method has the advantages of low switching frequency, low current harmonic, and balanced output power of two inverters. Simulation results validate the correctness and validity of the proposed fault-tolerant control method in this paper. In addition, the proposed method can easily be extended to other driving system under single switch open-circuit fault.

This paper is to study the control scheme for neutral-point-clamping three-level (NPC-3L) inverters fed dual three-phase permanent magnet synchronous motor (PMSM) drives based on vector space decomposition (VSD). The key is to propose a novel VSD based space vector modulation (SVM) strategy for the dual-three phase drives. The torque of the PMSM drive is controlled by voltage components on α-β plane while the current harmonics are suppressed by voltage components on x - y plane of the VSD-SVM. The upper and lower capacitor voltages are balanced well in DC link. Based on the proposed VSD-SVM strategy, a simple control scheme is presented for the dual three-phase PMSM drives. The principles of the proposed modulation strategy and control scheme are described in detail. The experiments are carried on a laboratory prototype to verify that the proposed VSD-SVM based control scheme can provide both good steady-state and dynamic performance for the dual three-phase PMSM drives.

A control scheme is proposed for the three-phase electric springs (TPESs), based on the recently introduced δ control and an improved phase locked loop (PLL). The scheme utilizes three independent δ controls, one for each phase, to stabilize the voltages across the critical loads (CLs) while handing over imbalance and distortion of the microgrid voltages, in addition to their fluctuations, to the non-critical loads (NCLs). Instrumental in achieving this outcome is the operation of the improved PLL that separates the fundamental component of the positive sequence of the microgrid voltages from the other sequences and harmonics. The scheme is also able to stabilize the CL voltages under imbalance of CLs and NCLs. Simulation results obtained under various conditions of imbalance of the microgrid voltages and/ or the loads, and of distortion of the microgrid voltages, taken individually and together, show the effectiveness of the proposed control scheme of TPESs.

A cascaded brushless doubly fed induction generator-based wind energy conversion system (CBDFIG-WECS), with the merits of high reliability, flexible power control and reduced power converter capacity, is presented in this paper. Based on the dynamic modeling of direct power control (DPC), two conventional DPC strategies are specifically introduced. Then an encoderless DPC strategy is proposed, in which the rotor current/position sensor is removed and only the parameter of control machine stator resistance is involved, contributing to simplicity, high reliability, and robustness of the controller. The effectiveness of the proposed DPC strategy is validated by simulations.

An interleaved current-fed bidirectional full-bridge DC/DC converter for on-board Electric Vehicle (EV) charger is proposed in this paper. This proposed DC/DC converter interleaves two isolated full-bridge converters. In the forward direction power flow, it is an input-parallel output-series (IPOS) voltage-fed construct with the merits that low input current ripple and output voltage ripple. The IPOS construct can also decrease the current stress on the primary side devices and voltage stress on second side devices. In the reverse direction power flow, it is an input-series output-parallel (ISOP) current-fed construct with the merits low input voltage stress and low output current stress. It can realize zero current switching (ZCS) by second-side voltage clamping technique without snubber circuit. Moreover, the boost topology can decrease the turn ration of the transformer and lower the input current ripple. These merits make the bidirectional converter suitable for electric vehicles charging and driving mode. Operation equivalent circuits, analysis, simulation results are presented in this paper. A 3.3KW on-board EV charger prototype is built to demonstrate the validity of the proposed topology.

Compared with the traditional microgrid, a smart transformer (ST)-based microgrid shows advantages in terms of higher efficiency, increased hosting capacity, and enhanced reliability. However, this novel microgrid presents challenges because of the complex resonances within the system and the interactions between ST and power converter-based distributed energy resources (DERs). Both the ST and DERs might be severely affected by each other and leads to performance degradation and system instability. To solve these problems, this paper first develops equivalent circuits of a ST-based microgrid. Then, the resonance and interaction problems are investigated based on the equivalent circuits. The active damping method is used to fully address the resonance issue and mitigate the coupling effects. To guarantee superior performance, this paper also designs high-performance control strategies for both the ST and DERs. Simulation and experimental results are provided to verify the validity of the proposed control strategy.

Firstly, in this paper we briefly review the control schemes for the VSC-HVDC system. Then, present conventional PI decoupling control, hysteresis current control and deadbeat current control schemes for the VSC-HVDC transmission system connecting two AC grids. Furthermore, compare their advantages and disadvantages in the VSC-HVDC control systems. Finally, Case of two-terminal VSC-HVDC system is developed in MATLAB/SimPowerSystems and the dynamic performance of the system is evaluated during system start up, grid voltage sags and power reversal changes. Simulation results show that these three control schemes for VSC-HVDC system can offer good dynamic performance when system start up, voltage sags in the grid and power reversal in the system. Different control schemes have different responses performance in the system. Thus, we can choose different control schemes according to the system control requirements and applications.

In this paper, a novel brushless machine with 12-stator-slot/8-rotor-pole having magnets surface-mounted in the stator instead of rotor is proposed, which can be regarded as an improved flux-reversal permanent magnet (FRPM) machine and is especially suitable for brushless DC operation. The topology, operation principle and static characteristics of the proposed three-phase 12/8 stator surface-mounted permanent magnet (SSPM) prototyped machine are analyzed based on 2-D finite element analysis. A comparison between the FRPM and SSPM machines having the same dimensions is presented including the field distributions, back-EMF, cogging torque and electromagnetic torque. In addition, an optimization on the key dimensions of the SSPM machine is explored to improve the characteristics of PM flux-linkage, back-EMF as well as to reduce cogging torque. The predicted results confirm that the SSPM machines with special stator slots and rotor poles combinations are attractive candidates in brushless DC drives.

This paper proposes a new magnetic-planetary-geared permanent magnet brushless (MPG-PMBL) machine for hybrid electric vehicles. The key is to integrate a magnetic planetary gear into permanent magnet brushless machine. Thus, the resulting machine can achieve both power split and mixing flexibly, and therefore, can obtain ultralow emission and high fuel efficiency at different operational modes. Moreover, by incorporating the concept of non-contact transmission mechanisms of magnetic gear, the proposed machine possesses the merits of small size, light weight, reliability, reduced maintenance and inherent overload protection. By using the finite element method, the electromagnetic performances are analyzed. Finally, multi-operational modes are analyzed to evaluate the proposed system.