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In this paper, a new modulation strategy based on the carrier-based switching strategy for the non-square direct matrix converters (MC) is proposed to control the active power of distributed generation (DG) units. In this strategy, the active power of DGs is controlled by the central input current control of the non-square direct MC independent from the voltage and frequency. Conventionally, each DG has a converter, and for supplying a load with N number of DGs, N number of converters are needed and each converter has its own modulation switching and control strategy to control the power output of each DG. Needless to say, in a microgrid with N number of DGs, the control strategy of each converter has more complex structure than that of a microgrid with one converter, and surely the former strategy entails more volume and price. Using the proposed converter in this paper, it is possible to supply a load with N number of DGs through one converter. Also, the power outputs of all DGs are controlled by a central control strategy. The proposed central control strategy is described and simulated for a typical microgrid. Experimental and simulation results validate the effectiveness of the proposed converter and the proposed strategy. The results demonstrate the applicability and efficiency of the system and verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of efficiency for passive magnetic gear resulting from the selection of materials and structures in the magnetic circuit. A particular attention is paid to the structure of modulator, which forms the crucial element of the system, and which can be designed in a variety of ways. In this paper, the considered alternatives include a modulator design manufactured from soft magnetic composite material and from circumferentially and axially stacked lamination. Based on the experimentally determined efficiency versus load curves, the study demonstrates that the soft magnetic modulator has similar performance as for the case of a circumferentially and axially stacked lamination. The physical reasons of this result are explained by means of the finite element analysis of magnetic flux waveforms in the crucial parts of the systems. [ABSTRACT FROM AUTHOR]

This article investigates energy storage requirements in the submodules of a class of converters known as hybrid cascaded modular multilvel converters (HC-MMCs). The complexities arising from the usage of different submodule types and their non-conventional arrangement necessitate detailed analysis of submodule capacitor voltage ripples, which are needed for development of guidelines for sizing submodule capacitors. This paper characterizes electric charge variations in the submodule capacitors to derive expressions for capacitor voltage ripples, and to determine the energy storage requirements of the converter. The paper uses detailed electromagnetic transient (EMT) simulations and experimental results on a laboratory-scale MMC setup to verify and validate its findings. [ABSTRACT FROM AUTHOR]

The open-end winding permanent magnet synchronous motor (OW-PMSM) with common DC bus configuration provides a path for zero-sequence current (ZSC). Apart from the zero-sequence voltage (ZSV) generated by inverters modulation, ZSC also comes from the third harmonic back-EMF. However, the third harmonic back-EMF contains the position information of the rotor, which can be extracted by an appropriate strategy to achieve position sensorless drive. In order to achieve sensorless drive and ZSC suppression simultaneously, this paper proposes a novel general-integral extended state observer (GI-ESO) based method. The third harmonic back-EMF of the OW-PMSM is estimated and calculated in three-phase stationary coordinate system by GI-ESO. And then, a single-phase phase lock loop observer (SPLL) is exploited to extract the position and speed information of the rotor. Meanwhile, the estimated third harmonic back-EMF is directly fed forward to SPWM as the ZSV reference, then the output voltages of the inverters contains the ZSV that can exactly counteract the third harmonic back-EMF, so as to realize the suppression of ZSC. Compared with the method of combining the fundamental back-EMF detection and proportional resonance (PR) regulator, this method can realize sensorless drive and ZSC suppression at the same time with only one scheme. Benefiting from the use of GI-ESO, the observer bandwidth can be relatively low, which helps suppress noise and extend the speed range of sensorless operation. Moreover, this method has strong robustness against motor parameters. The proposed strategy is validated by experiments. [ABSTRACT FROM AUTHOR]

Finite-control-set model predictive current control (FCS-MPCC) always has large steady-state fluctuation and computational burden. In this paper, a novel FCS-MPCC without a modulator to drive permanent magnet synchronous hub motors (PMSHMs), which combines virtual vectors expansion scheme and duty cycle control was proposed. The lack of a modulator reduces the complexity of the control system. The virtual vectors are synthesized by using active vectors, which improve the accuracy of voltage selection, and further improve PMSHM's steady-state performance and reduce current harmonics. The duty cycle control uses a zero vector to obtain better steady-state performance. However, the duty cycle of the virtual vectors is limited by the synthesis method, and further analysis is needed. A new calculation process is proposed to reduce the amount of calculation. The deadbeat principle is used to get reference voltage which determines sectors. Then, the best voltage vector in the selected sector is determined by the predetermined cost function. The traditional MPCC and the duty cycle MPCC (DCMPCC) are used as a comparison item to compare with the proposed method to illustrate its effectiveness. Results confirm that improved MPCC has good steady-state performance while maintaining a fast dynamic response. [ABSTRACT FROM AUTHOR]

The conventional model predictive power control suffers from heavy computational burden and large power ripple. To address the problem, this paper proposes a simplified three-vector-based model predictive direct power control, which can greatly optimize the control set. Firstly, a switching table is designed to exclude the redundant virtual voltage vectors (VVs). Only half of the candidate VVs are retained. Then, the effect of each VV on power is analyzed in detail. The deviation of reactive power is used as the evidence to further simplify the control set. In this way, the prediction behavior is reduced from 12 to 2, which effectively reduces the computational burden. In addition, the concept of power deadbeat is employed to determine the duty cycles of the two virtual VVs and one zero VV. Thus, the power ripples and current harmonics can be considerably suppressed. With this proposed method, the calculation complexity is reduced, and the steady-state performance is improved. The simulation and experimental results are given to verify the proposed method. [ABSTRACT FROM AUTHOR]

A phase-locked loop or phase lock loop (PLL) is, essentially, a closed loop control system, where its output signal (regulated) maintains a direct (chosen) relationship to the input signal (unregulated). If the phases of the input and output signals remain the same, their frequencies will also match. In its usual way, a PLL is an electronic circuit with filters and controllers that must be tuned each time, according to the input signal parameters. As a contribution and novelty, this paper introduces a new, easy, fast and highly efficient PLL algorithm, that it does not need to adjust every time the input signal changes. This makes it independent of the input signal it receives and, therefore, and in a certain way, universally applicable. In addition, the proposal is implemented exclusively by software, housed in a microcontroller, which also represents another novelty. As another remarkable feature, the proposed algorithm is very simple, with a very low computational cost, which makes it very stable, practically insensitive to noise, and very fast. These characteristics and the performance shown over a wide range of input signal frequencies, make the proposed algorithm suitable for use in different applications, from the electricity grid synchronization to the demodulation of frequency modulation, DC motor drives, etc. In addition to frequency and phase tracking, the developed algorithm generates the signal corresponding to the fundamental frequency of the input signal. Furthermore, the algorithm behavior is not affected by the input signal distortion and is independent of its initial phase. The performance and excellent behavior of the developed algorithm are evaluated through simulations and experimental tests. [ABSTRACT FROM AUTHOR]

The implementation of finite-control-set model predictive control (FCS-MPC) in voltage source inverters (VSIs) can make the system suffer from poor current harmonics performance, which may complicate the design of the required AC filter. To overcome this shortcoming, a carrier-based modulated model predictive control (CB-MMPC) strategy is proposed in this paper. This method enables the utilization of existing PWM modulation techniques with FCS-MPC, where a modulation waveform with zero-sequence signal injection is generated and compared to a triangular carrier wave, while optimizing the selection of the switching states. As it is shown, the studied CB-MMPC strategy not only considerably improves the current total harmonic distortion (THD) but also attains the performance of fast current dynamic response and robustness as the traditional FCS-MPC. Herein, the detailed implementation of the CB-MMPC control strategy is given, while considering its application to the current feedback control loop of a three-phase three-wire two-level VSI modulated at constant switching frequency. Finally, PLECS circuit simulation and a 3-kW VSI prototype are used to verify the superiority and the effectiveness of the presented CB-MMPC strategy. This is also benchmarked to the FCS-MPC and dead-beat based controllers. [ABSTRACT FROM AUTHOR]

The brushless doubly fed machine (BDFM), which eliminates slip rings and brushes, shows great potential in application fields where reliability is a prime concern. This paper presents the generalized design methodology of the novel three-phase Y-connected wound rotor for both additive modulation BDFM and differential modulation BDFM with specific schemes. First, the above two types of BDFMs are explicated by magnetic field modulations of two main magnetic fields. Then, design principles are illustrated to further improve the conductor utilization ratio of the rotor winding (RW) and reduce harmonic contents of the magnetomotive force (MMF) with a three-phase AC winding. Design examples and specific procedures of the proposed novel three-phase Y-connected wound rotor are also presented for both additive and differential modulation BDFMs, respectively. Finally, finite element models of two types of the BDFM are established and a differential modulation prototype is manufactured. Proposed design schemes are verified by comparative simulation and experimental results at different speeds and load conditions. [ABSTRACT FROM AUTHOR]

An isolated single sourced multi-output dc/dc converter with a high-frequency link was proposed before to feed different cells of the Asymmetrical Cascaded H-bridge (ACHB) inverter. One of the fundamental advantages of the ACHB is that the main H-bridge is commutated with fundamental frequency, passing the majority of the inverter power. However, the isolated dc/dc converter needs to be connected to the main voltage source with high-voltage/high-frequency switches, which limits the power capability and the efficiency of the converter. In this paper, a switching pattern based on nearest level modulation method is proposed to command all the power to be transferred through the main H-bridge. Therefore, the power circulates between the auxiliary H-bridges with no need for high-voltage switches. As a result, a single-input single-output auxiliary converter is needed with only 5% of the power rating. This solution reduces cost and size while it improves the efficiency of the converter. Furthermore, the architecture makes the inverter more suitable for high power and high-voltage applications. The inverter switching strategy is based on programmable firing angles. The main dc-link of the grid connected inverter is controlled to achieve maximum power point tracking, while the dc/dc isolated converter is controlled to regulate the auxiliary dc-links. The proposed topology is verified by simulation and experimental results using a 1.5 kW hardware prototype. [ABSTRACT FROM AUTHOR]

In braking operation, when the unipolar modulation pattern is adopted by brushless DC motor (BLDCM), there exists not only the commutation torque ripple, but also a problem concerning controllability of braking torque. This paper conducts a research into eight unipolar modulation patterns and proposes a smooth braking torque control strategy for BLDCM. First, the controllability principle of braking torque is theoretically analyzed under different modulation patterns. Then, this paper derives and compares the speed ranges of each pattern where the braking torque is controllable and the commutation torque ripple can be reduced. On this basis, according to the torque control performance of each modulation pattern in different speed ranges, an optimized combination modulation method is developed in full-speed range. During the whole braking process, the proposed control strategy ensures that the braking torque is controllable, and meanwhile the commutation torque ripple can be reduced, thus obtaining good braking torque control performance. The effectiveness of the proposed strategy is verified by experimental results. [ABSTRACT FROM AUTHOR]

The stator-PM variable reluctance (VR) resolver has been proposed as a new position sensor for a wide speed range. The high-frequency (HF) signal injection is only required to measure the rotor position at low-speeds. Alternatively, at higher speeds, without requiring the HF excitation, the position measurement can be achieved by the back-EMF generated by the stator-PM. This novel resolver has a simple rotor structure and the analog signals can be efficiently decoded at high-speeds. In the first proposed stator-PM VR resolver, the prototype must have even number of rotor salient poles. However, the resolvers with odd number of rotor poles are also useful in many scenarios. To complete the design scheme of this resolver category, this article practices a solution on the basis of the theory of field modulation. The design issue and solution are illustrated and addressed in this paper. The winding function approach is applied to analyze the signals. With the low-cost materials, the proposed resolver measurement system is prototyped. [ABSTRACT FROM AUTHOR]

The hard switching operation of the insulated gate bipolar transistor (IGBT)-based multilevel converters (MLCs) in the transformer less direct integration of renewable power plants produces a considerable amount of switching and conduction power loss. This eventually causes higher junction temperature and lower thermal stability. The symmetrically designed MLC using third harmonic sixty-degree bus-clamped pulse width modulation (BCPWM) technique demonstrates reduced switching losses and better harmonic spectra. However, the development of analytical power loss model is a complex and challenging issue due to the discontinuous switching mode of IGBTs for the BCPWM in MLC. In this regard, an analytical model for calculating the average and the rms currents for the hard switching operation of IGBTs and antiparallel diodes (APDs) with BCPWM is proposed. Furthermore, to calculate the device turn-on and turn-off losses, a discrete form of equation is presented to evaluate the transition times of switching more precisely. The numerical power loss values of IGBTs and APDs found from the derived analytical equations for MLC are compared with the simulation and experimental results. The numerical results agree well with the simulated and the experimental outcomes, which validate the proposed analytical loss model. Moreover, an advanced three dimensional thermal impedance model with chip-wise interdependent multilayer thermal coupling effect is also considered in this paper to realize the critical thermal loading condition of the switching devices. [ABSTRACT FROM AUTHOR]

This paper proposes a simplified deadbeat based predictive torque control (DB-PTC) for interior permanent magnet synchronous machine (IPMSM) drives using space vector modulation (SVM). The proposed DB-PTC is implemented in stationary reference frame, which simplifies the design. It contributes to greatly diminish the torque and flux ripples by using SVM and predictions. Low computational complexity is achieved since iterative optimization is not needed in the proposed method. Moreover, one cycle delay is compensated through predictions. In addition, to further reduce the torque and flux ripples, three-level simplified neutral point clamped inverter (3L-SNPCI) is employed. It features fewer switching devices and less DC-link capacitor voltage imbalance problem compared to the other types of three-level inverters. A novel SVM scheme is proposed to fully exploit the advantages of this inverter while ensuring smooth voltage vector transition. Experimental results are provided to verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

This is Part II of a two-part paper on the extension of a previously developed parameterized linear 2D magnetic equivalent circuit (MEC) for radial flux magnetic gears with surface permanent magnets to a 3D model. Part I explains the implementation of the 3D MEC. This section, Part II, evaluates the 3D MEC model's accuracy relative to 2D and 3D nonlinear finite element analysis (FEA) models. First, analysis of three base designs illustrates the impacts of the axial discretization parameters and stack length. This leads to the development of guidelines for selecting the axial discretization parameters. Additionally, the MEC is shown to accurately match 3D FEA in predicting the axial variation of flux densities. Finally, 3D MEC, 2D FEA, and 3D FEA models are deployed for a 144,000 case parametric study. The 2D FEA model significantly overpredicts the torques of designs with short stack lengths. However, the 3D MEC provides a much better agreement with 3D FEA, with less than 1% average absolute discrepancy. Additionally, the 3D MEC model is much faster than the 3D FEA model, with average 3D MEC model evaluation speeds ranging from about 100 times to 300 times faster than the 3D FEA for the base designs. [ABSTRACT FROM AUTHOR]

In this paper, the interactions of the torsional dynamics of the wind turbines and power modulation for oscillations in DFIG-based wind generators are investigated. One major concern of active power modulation is its interaction with wind turbine’s torsional dynamics. A study case with wind turbine torsional dynamics modeled is derived from our earlier work. Both active power modulation and reactive power modulation controls are developed in this paper. The paper successfully demonstrates the presence of interaction between active power modulation and torsional dynamics and the absence of such interaction in the case of reactive power modulation. Linear system analysis and root loci approach are employed to demonstrate such interaction. Simulation results in MATLAB/Simulink further verifies the analysis. The major contribution of this paper is: 1) the demonstration of the potential disadvantage of wind generation's active power modulation; and 2) the identification of reactive power modulation in wind generation as an alternative for interarea oscillation damping. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of eccentric magnet design on sideband electromagnetic force (SEMF) and hence high-frequency vibroacoustic performance of integral-slot surface-mounted permanent magnet (SPM) machines. Also, the tangential SEMF components are considered to investigate their contribution for high-frequency vibration and acoustic noise. Firstly, the mechanism of sideband current harmonics introduced by space vector pulse-width modulation technique of open-winding drive system is derived. Moreover, the critical components of sideband synthetic magnet field in air-gap are derived to obtain the radial and tangential SEMF density components, and the effects of concentric magnet design of that is discussed. Then, the vibration synthesis model and acoustic radiation model are used to predict the vibroacoustic performance of machines. The results shows the eccentric magnet design can reduce the high-frequency vibration and noise of integral-slot SPM machines. Finally, two integral-slot SPM machines with concentric and eccentric magnets are manufactured and tested to validate the theoretical investigations. [ABSTRACT FROM AUTHOR]

This paper presents an investigation into sideband vibro-acoustics suppression of the permanent magnet synchronous motor (PMSM), associated with several periodic signal-based dithering modulations. Mathematical derivations of four typical periodic signal-based schemes are deduced with the power spectral density (PSD) method. The individual modulation parameters, such as bandwidth and modulation ratio, are determined the values to minimize the sideband vibro-acoustics. The frequency distributions of the sideband components are discussed by the analytical derivations. The relationship between the electromagnetic components and mechanical responses is reconstructed by coupling with temporal features. For verification, the experimental tests with a prototype PMSM are introduced under different operational conditions. According to the results and figures, both magnitude suppression and frequency distribution are accurately correlated with sideband harmonic components as well as vibro-acoustic responses. This investigation thus clearly holds promise for the evaluation and optimization in powertrain used by electric vehicles. [ABSTRACT FROM AUTHOR]

Flux-modulation machines operate based on the so-called magnetic-gear effect. The modulator of the flux-modulation machine is one of the key elements. In this paper, a design method to obtain the distribution of modulators on split-pole flux-modulation machine is proposed to improve output performance. First, the operation principle of the flux-modulation machine is briefly discussed. Then, taking surface-mounted flux-modulation machines as examples, the air-gap flux density model is established by taking the distribution of the modulator into account. Besides, the formula of back-electromotive force of the flux-modulation machine is derived for both concentrated and distributed windings to determine the modulator distribution. Then, according to extreme equation, the optimal pole arc coefficient and distribution of the modulators can be obtained. Finally, the correctness of the proposed method is verified by both simulated and experimental results on a prototype machine. [ABSTRACT FROM AUTHOR]

Biased flux machines (BFMs) have biased magnetic flux in the core and allows flexibility to adjust the field with a dc current. The conventional topology exploration methods for BFMs are based on the flux observation. It is time consuming and ineffective since the initial structure searching process is guideless. Meanwhile, BFMs usually work with arbitrary magnetic field harmonics instead of the fundamental one. The torque components of these machines and their essential operation principle have not been fully revealed. To solve these issues, in this paper, a topology exploration method for BFM based on magnetic field modulation mechanism is proposed, and the torque generating principle is analyzed. With this method, some new BFM structures have been developed and their torque components have been developed. It is shown that various space harmonics have contributed to constant torque rather than the fundamental one. To verify the feasibility of this design method, one double stator BFM is selected as a case study. Simulation and experimental results have verified that this design method is feasible and effective since the prototype has good sinusoidal back electromotive force waveforms and well performance. Besides, it is practical to realize flux weakening and strengthening the control with biased current. [ABSTRACT FROM AUTHOR]

In this paper, a novel coaxial magnetic gear (MG) is proposed, in which both permanent magnet and consequent poles are employed on the inner and outer rotors. The MG is expected with improved torque transmission capability by increasing the effective magnetic flux and offering additional reluctance torque. Air-gap field distribution and torque–angle characteristic of this MG are analyzed and compared with the conventional MG, which adopts dual surface-mounted permanent magnet rotors. To maximize the torque density, several key design parameters are investigated using finite-element method. Analysis results indicate that the proposed MG with ferrite magnets can largely improve the pull-out torque. In addition, end effect and power losses with different rotor structures are analyzed. Performance of two optimized MGs is then validated with test. Also, the MG cost effectiveness with different magnet materials is presented. [ABSTRACT FROM AUTHOR]

For power conversion systems interfaced to four-wire supplies, four-leg converters have become a standard solution. A four-leg converter allows good compensation of zero-sequence harmonics and full utilisation of the dc-link voltage. These are very important features when unbalanced and/or nonlinear loads are connected to the system. This paper proposes a three-dimensional space vector modulation (SVM) algorithm and provides a comprehensive analysis of the algorithm implemented on a three-level, four-leg neutral-point-clamped converter. The algorithm allows a simple definition of the different switching patterns and enables balancing of the dc-link capacitor voltages using the redundancies of the converter states. A resonant controller is selected as the control strategy to validate the proposed SVM algorithm in a 6 kW experimental rig. [ABSTRACT FROM AUTHOR]

With the development of power system electronization, distributed new energy generation-based DC microgrid system has become a hot spot of the current research. Aiming to implement the collection, transformation and transmission of the new energy sources, the dual active bridge (DAB) converter has become a key energy conversion device. Aiming to promote the transmitted efficiency for such DAB converter, a deep reinforcement learning (DRL) optimization scheme with the triple-phase-shift (TPS) is proposed. Specifically, the deep deterministic policy gradient (DDPG) algorithm is used for solving optimal solutions with the minimum power losses. Then, the trained DDPG agent is used as a fast surrogate predictor, which giving the suitable control decisions under whole operation conditions. The main control objective is to minimize the power losses for getting the target maximum efficiency. Besides, the soft switching constrains are added to the DDPG algorithm. Based on this, the proposed optimized method can be used for different operation conditions with excellent performance. The operation principles, the loss analyses, and the training consideration and evaluation of the DDPG algorithm are given. Finally, simulation and experimental results using a 200 W hardware prototype are displayed and compared to prove to effectiveness of theoretical analysis. [ABSTRACT FROM AUTHOR]

Magnetic gears perform the same fundamental power conversion as mechanical gears. However, magnetic gears have significant potential benefits due to their noncontact operation. This paper compares three different ways to achieve high gear ratios using coaxial magnetic gears by evaluating trends for radial flux coaxial magnetic gears with surface mounted permanent magnets. First, a single-stage design can be used, but the torque density and efficiency both decline as the gear ratio increases. Additionally, the gear ratio achievable with a single-stage coaxial magnetic gear is limited by practical considerations, such as the maximum number of modulators and pole pairs that can be used within the given space. Second, a multistage design can be formed by connecting single-stage designs in series. Multistage designs can achieve much higher net gear ratios with much less of a torque density penalty, especially as the number of stages increases, but this entails greater complexity. Third, the compound differential coaxial magnetic gear (CDCMG) is proposed. The CDCMG is formed by interconnecting two single-stage coaxial magnetic gears and can achieve gear ratios much higher than the product of the gear ratios of the individual stages. However, the circulating power in the CDCMG leads to poor efficiencies. [ABSTRACT FROM AUTHOR]

This paper provides a thorough, parametric comparison of axial and radial flux coaxial magnetic gears with surface-mounted permanent magnets. While both topologies share similar operating principles and can achieve comparable shear stresses, they exhibit different scaling trends with respect to key design parameters. Both topologies’ volumetric torque densities (VTDs) increase with the outer radius, but the axial flux topology's VTD increases with the radius at a much faster rate than the radial flux topology's VTD. Another difference between the topologies involves their cross-sectional scaling parameters. The stack length axially scales radial flux gear cross sections, and, as it increases, the impact of end-effects decreases, which improves the performance. For axial flux gears, the radii ratio scales the cross section's radial width between different radii. This fundamentally changes optimal parameter values and design performance tradeoffs. Finally, axial flux rotors experience significant axial forces, but the radial forces on radial flux rotors can be balanced out. Based on these trends, radial flux gears are superior to axial flux gears for most applications; however, axial flux gears have a significant advantage when a large radius and a small axial length are permissible or when mechanical power needs to be transmitted across a flat barrier. [ABSTRACT FROM AUTHOR]

This is Part II of a two part paper on the development of a parameterized linear magnetic equivalent circuit (MEC) for radial flux magnetic gears with surface permanent magnets. Part I describes the MEC implementation. This section, Part II, evaluates the MEC model's accuracy by comparing its results against those produced by a nonlinear finite-element analysis (FEA) model. Simulation results demonstrate that the linearity approximation does not prevent the MEC from accurately matching the torque and air-gap flux densities predicted by a nonlinear FEA model for three diverse magnetic gear base designs. The impacts of the MEC discretization parameters introduced in Part I are also investigated using the same base designs, and guidelines for those settings are developed. Additionally, single design parameter sweeps illustrate the MEC's ability to track these changes over most practical design ranges and reveal where the MEC's accuracy degrades due to the linearity approximation. Finally, the results of a 46,656 case parametric optimization study demonstrate the MEC's ability to match the nonlinear FEA model's torque predictions within a few percent over a wide range of designs while achieving average simulation speeds 44 to 271 times faster than those of the FEA model. [ABSTRACT FROM AUTHOR]

This paper presents a novel dual-flux-modulator coaxial magnetic gear (DFM-CMG) characterized by high torque capability and high permanent-magnet (PM) utilization efficiency. The DFM-CMG adopts spoke-type outer PM rotor and introduces an auxiliary flux modulator placed in the outermost layer. The harmonic analysis with detailed theoretical derivation is performed to reveal that the ferromagnetic pole shoes on the spoke-type outer PM rotor could modulate the flux density distribution as well and realize a nested magnetic-gearing effect. More effective magnetic harmonics are, thus, led into the air gaps to make contribution to the torque production. The effect of the auxiliary flux modulator on the flux density distribution is also studied by the finite-element (FE) analysis. Due to the presence of the auxiliary flux modulator, the flux leakage is suppressed and the useful harmonics are amplified. A quantitative comparison among the surface-mounted CMG (SM-CMG), spoke-type CMG (ST-CMG), and DFM-CMG is made to verify the performance improvement of the proposed CMG. With the same amount of consumed PMs, the torque capability and PM utilization efficiency of the DFM-CMG shows a 73% growth over the SM-CMG and a 44% growth over the ST-CMG. The ST-CMG and DFM-CMG are finally prototyped and tested to verify the FE analysis. [ABSTRACT FROM AUTHOR]

Magnetic-geared machines are based on the flux-modulation principle and typically constructed with a flux-modulated double rotor (FMDR). The modulator experiences high torsional stresses when designed for high torque transmission. As a result, the FMDR has high probability of failure if not designed appropriately. In this paper, the FMDR design options are investigated with mechanical and electromagnetic finite element (FE) modeling. The addition of filler material in between the poles of the modulator pole-pieces is found to reduce the shear stresses by $61.7\%$ to $87.2\%$ at the cost of $2.6\%$ to $3.2\%$ lower pull-out torque. Possible shear stress reduction with the design of bridged modulators is investigated. Increase in pole number is shown to increase localized stress levels in bridged modulators. Electromagnetic simulations show that for a given FMDR specification, the highest pull-out torque is at an optimal pole number. The tradeoff between FMDR weight, losses, and shear stress are discussed. A scaled-size prototype FMDR with a bridged modulator is constructed. The FMDR is tested and is shown to achieve comparable results with the FE simulations. At field intensity levels above 600 kA/m in the periphery, the FMDR achieves reduced pull-out torque $28.7\%$ lower in comparison with three-dimensional simulations. The losses at different load levels of the FMDR are also compared with experimental and FE simulation result and are shown to confirm the FE simulation results. [ABSTRACT FROM AUTHOR]

Open-end winding three-phase variable speed drives with dual-inverter supply have been extensively investigated for various applications, including series hybrid powertrains and propulsion motors. The topology is simple to realize while offering a higher number of switching states without the need for capacitor voltage balancing algorithms, when compared to the standard multilevel converters. This paper extends the open-end winding concept to a five-phase drive. A relatively simple space-vector modulation (SVM) algorithm, based on the already well-understood five-phase two-level drive SVM method, is developed. The proposed modulation technique has the advantage of being straightforward to implement and, like its two-level counterpart, is able to generate output voltages with minimum low-order harmonic content. The method generates up to 17-level output phase voltage and, therefore, offers superior harmonic performance when compared to the two-level five-phase modulation. The developed scheme is verified via detailed simulations and experiments, using a five-phase induction machine operating under open-loop V/f control. [ABSTRACT FROM AUTHOR]

In this paper, a wind energy conversion system interfaced to the grid using a dual inverter is proposed. One of the two inverters in the dual inverter is connected to the rectified output of the wind generator while the other is directly connected to a battery energy storage system (BESS). This approach eliminates the need for an additional dc–dc converter and thus reduces power losses, cost, and complexity. The main issue with this scheme is uncorrelated dynamic changes in dc-link voltages that results in unevenly distributed space vectors. A detailed analysis on the effects of these variations is presented in this paper. Furthermore, a modified modulation technique is proposed to produce undistorted currents even in the presence of unevenly distributed and dynamically changing space vectors. An analysis on the battery charging/discharging process and maximum power point tracking of the wind turbine generator is also presented. Simulation and experimental results are presented to verify the efficacy of the proposed modulation technique and battery charging/discharging process. [ABSTRACT FROM AUTHOR]

The partitioned stator switched-flux permanent magnet (PM) (SFPM) (PS-SFPM) machine is a novel stator-PM machine in which PMs and armature windings are separately placed in two different stators. Compared with the conventional SFPM machine with a single stator in which both PMs and armature windings are located, the PS-SFPM machine can generate higher torque density due to the utilization of the machine's inner space. In this paper, the magnetic gearing effect in the PS-SFPM machine is investigated in terms of air-gap field harmonics based on a simple magnetomotive force (MMF)-permeance model. It is found that the PS-SFPM machine is one type of magnetically-geared machine, in which the modulations of rotor iron pieces to the open-circuit PM and armature reaction fields are similar to those found in the magnetic gear and the conventional magnetically geared machine. The pole-pair numbers and rotating speeds of the air-gap field harmonics obtained by the MMF-permeance model are verified by finite element (FE) analysis. More than 93% of the average electromagnetic torque is contributed by the main air-gap field harmonics having pole-pair numbers (2i - 1)\boldsymbol p PM and \rm| N\rm{r} \,\pm \, (2i-1)pPM| ( i = 1,2,3) in a PS-SFPM machine with pPM-pole-pair PMs and Nr-rotor-pole. A prototype machine is fabricated and tested to verify the FE analysis. [ABSTRACT FROM PUBLISHER]

Apart from the basic voltage vectors of a inverter, virtual vectors can be generated by discrete space vector modulation (DSVM) technique. Thus, DSVM based-model predictive control (MPC) can achieve reduced torque ripples and current harmonics for a permanent magnet synchronous machine (PMSM) drive. However, the computational burden is also significantly increased due to a large number of candidate voltage vectors. In this article, a novel DSVM-based MPC is proposed, which can select the optimal voltage vector and calculate three-phase duty ratios in an efficient way without enumerating all the candidate voltage vectors, hence achieving good performance with low computational burden. The effectiveness of the proposed method is validated by the presented experimental results. [ABSTRACT FROM AUTHOR]

In order to improve the robustness and torque performance of a dual-flux-modulator magnetic-geared machine (DFM-MGM) considering simultaneously both random and interval uncertainties of design parameters, a multi-objective robust optimization (MORO) method with multiple Monte Carlo simulations (MCSs) is proposed. In this method, the multiple MCSs are adopted to evaluate the effects of parametric hybrid uncertainties on the robustness of optimization results. To build a MORO model of the DFM-MGM, the three-dimensional finite element model is established firstly and then validated by the experiment. Through a parametric study, it is found that five dimensional parameters of the permanent magnets (PMs) and stator have more significant effects on the stall torque (ST) and ST per PM volume (STPPV). Finally, a multi-objective particle swarm optimization algorithm with surrogate models, sigma criteria design and multiple MCSs method is implemented to solve the MORO problem. Both the average standard deviations and standard deviation differences of the ST and STPPV are used to deal with hybrid uncertainties during MORO. The optimized DFM-MGM by MORO has a STPPV 6.3% higher than that of the initial design under the same ST constraint. Moreover, the average standard deviations and standard deviation differences obtained by MORO are much smaller than those achieved by the deterministic optimization, indicating that the robustness of optimal results can also be significantly improved by the MORO. [ABSTRACT FROM AUTHOR]

This paper proposes a new modulation strategy that balances the neutral-point voltage for three-level neutral-clamped inverter systems. The proposed modulation replaces the P-type or N-type small switching states with other switching states that do not affect the neutral-point voltage. The zero and medium switching states are employed to help the neutral-point voltage balancing. This method little bit increases the switching events and output total harmonic distortion. However, this method has a strong balancing ability at all regions. Further, it is very simple to implement in both space vector modulation and carrier-based PWM methods. Simulation and experimental results verify the validity and feasibility of the proposed new modulation strategy [ABSTRACT FROM AUTHOR]

This paper is concerned with the low-frequency harmonies which originate from the rotor inverter of a doubly-fed induction generator (DFIG). By including the mechanical speed response, it expands the transformer approach previously taken to analyze the harmonic transfer in the machine. A numerical method is proposed to calculate the stator current sidebands, which can be used to predict the voltage fluctuation at the system busbar. It is shown that the pulsating torque associated with the rotor harmonics can induce speed ripple depending on the inertia, causing a significant change in the stator current spectrum. Experiment and simulation verify the analysis and the proposed calculation method. [ABSTRACT FROM AUTHOR]

Sensorless control technologies based on rotor saliency may not operate well due to the effect of magnetic saturation. In this work, a rotor backend (RB) is attached to an existing rotor structure of a permanent magnet synchronous motor (PMSM) to enhance anisotropic features. The geometry of the RB is further optimized to achieve greater current amplitude induced by the RB saliency modulation. The phase sequence direction of the modulation is not electrically synchronized with the rotor reference frame. A fractional slot/pole combination is selected and analyzed to strengthen the saliency modulation signal. Hence, the sensorless techniques will be immune to saturation effect in highly exploited machines. Both low and high-speed performance of the proposed method is verified through the experimental tests. It is demonstrated that the position estimation using saliency modulation of the RB is unaffected by machine saturation due to its electrical asynchronous property. [ABSTRACT FROM AUTHOR]

In order to better address the problem of many high-order harmonics’ concentration in the output voltage, a novel five-phase piecewise-random-switching-frequency space vector pulse width modulation (PRSF-SVPWM) strategy is proposed for a five-phase voltage source inverter. Compared to the conventional random switching frequency SVPWM (RSF-SVPWM), the entire fundamental period of this method is divided into two half-fundamental periods, so the original switching frequency in a single fundamental period is randomized in segments respectively. During this process, parameters named the offset frequency and random frequency are defined and assigned reasonably. In this way, high-frequency harmonics in one period are spread into a wider range. Subsequent simulation and experimental results verify that the proposed random modulation strategy can further reduce amplitudes of harmonics near switching frequency and its integer multiples, even though within a narrow switching frequency range, and a satisfactory effect of high-order harmonic dispersion is finally obtained, which contributes to the application and popularization of random pulse width modulation strategies. [ABSTRACT FROM AUTHOR]

This article presents an energy regulator based on a Model Predictive Control (MPC) algorithm for a Voltage Source Converter (VSC). The MPC is formulated to optimise the converter performance according to the weights defined in an objective function that trades off additional features, such as current harmonic distortion, reactive power tracking and DC bus voltage oscillation. Differently from most approaches found in the research literature, the MPC proposed here considers the coupling dynamics between the AC and DC sides of the VSC. This study is focused on the example case of a single-phase VSC, which presents a nonlinear relationship between its AC and DC sides and a sustained double-line frequency power disturbance in its DC bus. To reduce the burden of the MPC, the controller is formulated to benefit from the slow energy dynamics of the system. Thus, the cascaded structure typically used in the control of VSCs is kept and the MPC is set as an energy regulator at a reduced sampling frequency while the current control relies on a fast inner controller. The computational burden of the algorithm is further reduced by using a linear time-varying approximation. The controller is presented in detail and experimental validation showing the performance of the algorithm is provided. [ABSTRACT FROM AUTHOR]

A charge balancing method for series voltage source feeding multilevel inverters (MLI) based on current allocation control is presented. Unlike those MLIs based on isolated dc sources, the series-connected elements in a voltage source string, such as a battery or supercapacitor stack, cannot be by-passed individually. This brings the problems of source imbalance and limited redundant switching states for current allocation control at high modulation index. In this article, the source balance in the switch-ladder inverter is achieved by allocating the current distribution. Furthermore, the balancing effectiveness is enhanced by a novel configuration combining a switched-capacitor (SC) circuit. The working principle and modulation index limit for the current allocation method is elucidated with a flow diagram and mathematical representation. The feasibility and operation of the proposed method and topology are successfully validated by a simulation study and the experimental results. [ABSTRACT FROM AUTHOR]

The torque production mechanism of switched reluctance machines (SRMs) is investigated from the perspective of air-gap field modulation principle. The unipolar stator current excitations can be divided into DC and AC components and they induce the air-gap magneto-motive force (MMF) respectively. Meanwhile, thanks to the salient structure in SRMs, the air-gap MMFs induced by the two sources above can be modulated to obtain the synchronized air-gap fields for torque production. It is revealed that a multitude of field harmonics contribute to the torque together. The MMF-permeance model is built and the analytical deduction of the field modulation effect is provided, with which the orders of the field harmonics contributing to the torque output can be identified. Moreover, finite element method is employed to verify the predictions on various SRM topologies. Finally, aprototype machine is fabricated and measuredfor validation. [ABSTRACT FROM AUTHOR]