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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]

The semicontrolled open-winding permanent magnet synchronous generators (OW-PMSGs) with a common dc bus system have received more attention in recent years due to its advantages of reduced cost and simpler power supply. Good control performances could be achieved under the zero power factor angle (PFA). However, current clamping problem is normally presented under non-zero PFA condition, resulting in unexpected torque pulsations and voltage pulse disturbances. Meanwhile, misjudgment of voltage vectors and subsequent deteriorations in steady-state performances can be observed at current zero-crossing points. In order to improve the control performances of semicontrolled OW-PMSGs, a virtual zero-crossing detection method is proposed in this paper to effectively suppress the oscillation of voltage vectors at current zero-crossing points. In addition, a segment injection strategy of third-order harmonic current is proposed. With the proposed strategy adopted, the current clamping problem can be successfully solved, and more importantly, the torque ripple and third-order harmonic current could be simultaneously suppressed. Relevant experimental validations and performance comparisons based on a 2.3-kW semicontrolled OW-PMSG system are presented to verify the proposed control strategies. [ABSTRACT FROM AUTHOR]

Optimal currents with appropriate harmonic components injected into the motor windings can effectively mitigate torque ripple for interior permanent magnet (IPM) type brushless dc motors (BLDCMs). However, existing approaches may fail to accurately inject the optimal currents into motors due to the limited current loop bandwidth. This paper proposes a simple enhanced generalized vector control strategy to mitigate the torque ripple for IPM-type BLDCMs. With the proposed vector control strategy, the control block diagram for IPM-type BLDCMs is as simple as that with traditional vector control for sinusoidal permanent magnet synchronous motors. First, an electromechanical energy conversion voltage (EECV), considering the effects of the non-sinusoidal back-EMF and the rotor salience property, is proposed in αβ-axis. Then, a novel coordinate frame is constructed with the proposed EECV, which is based on the arbitrary reference frame theory. As a result, the currents of IPM-type BLDCMs can be decomposed into two constant components, one being linked to the torque and the other one to the flux linkage. Thus, the bandwidth of current loop with simple proportional integral regulator can be equivalently expanded in the proposed coordinate frame. Finally, comprehensive experiments are conducted in different operation conditions to validate the effectiveness of the proposed vector control strategy. [ABSTRACT FROM AUTHOR]

This paper investigates open-phase fault modeling and fault-tolerant control (FTC) of dual three-phase permanent magnet synchronous machines (DT-PMSMs). A comprehensive fault model that considers both the permanent magnet torque and reluctance torque under the open-phase fault is proposed first. This model shows that under open-phase fault the average torque of DT-PMSM will decrease, while torque ripple will increase significantly. Then, a novel optimized FTC approach is developed based on the proposed model, in which genetic algorithm (GA) is applied to optimize the stator currents to maximize the average torque and minimize the torque ripple under open-phase fault. The proposed fault model and GA-based FTC are applicable to both surface-mounted and interior DT-PMSMs. However, existing approaches neglecting the reluctance torque are only applicable to surfaced-mounted DT-PMSMs. Moreover, the proposed approach is simple in implementation as it employs the original control structure and it is capable of smooth switching between the healthy operation and FTC without inducing noticeable torque pulses. The proposed approach is demonstrated with design examples, compared with existing one and validated with experiments on a laboratory interior DT-PMSM. [ABSTRACT FROM AUTHOR]

When many distributed parallel inverters are integrated into grid without switching sequence coordinated control capability, the high-frequency harmonics will accumulate randomly at the point of common coupling. Global synchronous pulsewidth modulation (GSPWM) method can significantly attenuate the accumulated switching ripples by intentionally assuming an intelligent optimization algorithm and a communication system. To avoid the dependence on low-latency communication system, this paper proposes a novel phase-locked loop based PWM carrier synchronization (PLL-CS) method for GSPWM system, where the switching sequences can be effectively synchronized as expected without using low-latency synchronization signals. By doing so, the operational reliability of the whole GSPWM system can be significantly improved, while the additional hardware cost of GSPWM can be dramatically reduced, which can enhance the implementation adaptability of GSPWM method. Experimental results have verified the performance of the proposed PLL-CS GSPWM method. [ABSTRACT FROM AUTHOR]

Traditionally, the communication between power converters connected in a microgrid is established using a wired method or a wireless droop method. The shortcomings of these methods have opened up the possibility of power-line-based communication between converters. However, the conventional power line communication systems have the disadvantages of using high-frequency data carrying signals that are prone to attenuation. These systems also make use of explicit couplers, transmitters, and amplifiers that adds to the overall cost and infrastructure. In this paper, a novel fractional harmonic $d\text{--}q$ domain based power line communication technique is proposed. A switched fractional harmonic current space vector is used to carry data. The primary control loop and the modulation algorithm of the converters are used for encoding and decoding of data. The proposed technique thus overcomes the disadvantages of the conventional power line communication systems and at the same time carries forward the advantages of it. The proposed technique is validated with sufficient experimental test results. [ABSTRACT FROM AUTHOR]

It is well known that spatial field harmonics will cause high eddy current losses in surface-mounted permanent magnets (PMs) especially for the fractional-slot PM motors. However, the influence of temporal current harmonics, especially of the high-order temporal harmonics caused by pulsewidth modulation voltages from an inverter, lacks attentions. This paper studies the eddy current losses of the PMs caused by high-order current harmonics. In order to simplify the calculation and save computation time, analytical methods are used to predict the current harmonics caused by the PWM inverter, and the armature reaction field, the eddy current density, and losses in the PMs generated by the current harmonics. Finite element analysis, coupling simulation, and experimental studies are used to verify the analytical results. The study results show that the high-order current harmonics cause much higher eddy current losses than those caused by slotting and fundamental current even though the amplitudes of the high-order current harmonics are much lower. [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]

Multiphase drives offer important advantages over three-phase ones, e.g., lower per-phase rating and enhanced fault tolerance. For multiphase machines, multifrequency current control (MCC) is often required, e.g., for harmonic cancellation or injection. In certain situations, converter output voltage (OV) saturation occurs, which can cause windup and additional OV distortion. For MCC, obtaining antiwindup and distortion-free OV saturation, with full dc-bus exploitation, entails extra complexity. Recent publications address this problem in three-phase and dual-three-phase (treated as two independent three phases) systems with one and two isolated neutrals, respectively. However, extending such solutions to drives of any phase number $n$ , winding arrangement (symmetrical or asymmetrical), and neutral configuration is not straightforward. This paper proposes a general MCC scheme, including antiwindup and distortion-free OV saturation with full dc-link utilization, for $n$ -phase machines with different winding arrangements (symmetrical or asymmetrical) and neutral configurations. The computational burden required by the proposed antiwindup and saturation strategy is studied; it is concluded that, although it is significant in comparison with the resources needed by the rest of the MCC, the total computational load is acceptable in most of the cases. Experimental results with two multiphase machines are provided, including a comparison with other approaches. [ABSTRACT FROM AUTHOR]

In ac motor drives, the fixed-frequency harmonic components of output voltage and current from the inverter with fixed-frequency pulsewidth modulation usually lead to electromagnetic interference (EMI). The spread spectrum clock generation (SSCG) is a widely used solution for this problem. Adjusting the switching frequency to reduce EMI is one kind of practicable scheme among SSCG methods. How to design an optimal or suitable modulation profile is a research emphasis of scholars and has been discussed in depth in many literatures. However, apart from the modulation profile, the mode and quality of carrier are also important and can be improved. In most frequency modulation methods, due to the limitation of the conventional carrier generation mode, the implementation of the new frequency instruction has to wait for the termination of the last switching period. In order to eliminate the waiting state and design a simpler algorithm, this paper has proposed a wait-free phase-continuous carrier frequency modulation (WPCFM) strategy by combining the direct digital frequency synthesizer theory and proper temporal planning of control interruptions. Besides, a theoretical analysis of WPCFM, including quantization error, frequency jitter, phase delay, and voltage distortion, has been finished. Moreover, compared with conventional methods, a more convenient, feasible, and simpler field-programmable gate array based algorithm implementation method and the control structure of WPCFM are also introduced. The analysis shows that, although WPCFM causes a slight increase of the current ripple, it can solve the partial frequency nonuniform distribution problem of the conventional method, and it has a potential value of applications in the wide band gap motor drive systems. The effectiveness of the WPCFM is verified by several sets of EMI reduction experiments where classical periodic carrier frequency modulations are applied. [ABSTRACT FROM AUTHOR]

The most prominent problem of the doubly fed induction generator-dc (DFIG-dc) system is the highly distorted stator voltage due to the diode bridge on stator side. The highly distorted stator voltage not only influences the stator voltage orientation control but also causes harmonic currents and torque ripples. In this paper, an enhanced stator fundamental voltage orientation method is proposed to deal with the highly distorted stator voltage. Furthermore, the relationship between torque ripples and harmonic currents is investigated. And then an improved direct resonant control strategy is proposed for suppressing the torque ripple and reducing the harmonic currents simultaneously. In this way, the loss of harmonic currents can be reduced while suppressing the torque ripple. Finally, the experimental results are presented to validate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical time and frequency domains evaluation of torque harmonics produced by high-power load-commutated-inverters (LCIs) and pulsewidth-modulated (PWM) voltage-source inverters for adjustable speed applications. These drive systems are used in petrochemical and mining industries, where driven loads have multi-inertia or long shafts that are potentially subject to torsional mode excitation. Such excitation may lead to accelerated fatigue, system failure, and loss of production, and in turbine-generator sets, to system blackout. The investigated power conversion topologies are multi-pulse LCIs (6/6 and 12/12-pulse systems), parallel connected three-level neutral-clamped-converters with non-interleaved and interleaved PWM signals, as well as series-connected H-bridge multi-level inverters, single thread and four threads supplying a 12-phase machine and parallel connection of four threads converter systems with interleaved PWM commands. They are the most used variable frequency drives in the megawatt range, both with synchronous and induction machines, in the petrochemical industry. The time and frequency domains of the machine's air-gap torque is calculated from the motor's voltage and stator's current waveforms, this proven method is independent from the type of ac machine. More than 50 simulated operating points are discussed and experimental results for NPC and cascaded inverters are also presented. [ABSTRACT FROM AUTHOR]

The impedance-based stability analysis of single-phase voltage source converters (VSCs) emphasizes the precise impedance modeling. Considering the complexity of $dq$ -frame impedance modeling and measurement, this paper proposes a mirror-frequency impedance modeling and measurement approach of single-phase VSCs in the stationary frame based on harmonic linearization. First, the mirror frequency definition is put forward and the dynamics of the second-order generalized phase-locked loop considering the mirror-frequency effects is validated by simulations. Next, the impedance model considering the mirror-frequency effects and dc-link voltage control loops is compared with the conventional one-dimension impedance model and a mirror-frequency impedance measurement method is presented, which are verified by experiments on the hardware-in-the-loop platform. The results indicate that the mirror-frequency impedance model considering the dc-link voltage control is more accurate and better captures the cross-coupling dynamics of VSCs. Finally, the different bandwidths of dc-link voltage control loops and different capacitances are designed to study the impacts of dc-link voltage control loops and ripples on impedance. The experiments and impedance-based analysis illustrate that the wider bandwidth of dc-link voltage control loops or the less capacitance with high dc-link voltage ripple will expand the frequency range of negative impedance in the low frequency. [ABSTRACT FROM AUTHOR]

This paper focuses on the analysis and development of low-current harmonics for a six-leg, three-phase inverter for permanent-magnet synchronous motor (PMSM) drives. Each phase of the PMSM is operating independently, the low-order harmonics appear in the back electromotive forces (EMFs) and currents. In this case, the standard vector control cannot handle the current harmonics. This harmonic enhances the current and causes the torque ripple. This paper presents a zero-axis current estimator auxiliary vector control method to compensate for three multiples of the voltage harmonic. This method can eliminate the zero-axis current. A prototype PMSM system was built using the TMS302F28335 digital signal processor. And the computer simulation and control method were completed. When the system operated at half load, the total harmonic distortion of current decreased from 20.89% to 4.42%. At full load, the total harmonic distortion of current decreased from 8.43% to 1.71%. [ABSTRACT FROM AUTHOR]

This paper presents a fault diagnosis technique for high-resistance connection (HRC) in a nine-phase flux-switching permanent-magnet (FSPM) machine based on zero-sequence voltage components (ZSVC), where the neutral-point connection mode is considered. A nine-phase FSPM machine topology is first introduced and no-load back electromotive force waveforms are analyzed. Moreover, the topologies of the nine-phase FSPM drive with different neutral-point connection modes are studied. Then, the mathematical model of a nine-phase FSPM machine with HRC is established with the consideration of the neutral-point connection mode and then the influence of the HRC on the ZSVC is analyzed based on the established model. It is shown that the HRC may be diagnosed by monitoring the change of the spectral contents of the ZSVC. Furthermore, this paper focuses on the situation of the nine-phase FSPM machine with one neutral point. In this case, to remove the influence of the FSPM machine operating point, an effective fault indicator is defined and used for HRC fault detection. Finally, the simulation and the experiment are carried out to validate the proposed method. Both the results show that the proposed method can be applied for the HRC fault diagnosis in a nine-phase FSPM machine. [ABSTRACT FROM AUTHOR]

This paper presents, initially, a systematic derivation of extended first harmonic approximation (FHA) analysis and, later, a comprehensive time-domain (T-D) analysis to study series–series compensated inductive power transfer (IPT) systems with a diode bridge rectifier. Further, the paper shows that both FHA and T-D methods predict four mutually exclusive and collectively exhaustive modes of operation. Explicit criteria for each operation mode and formulae for mode boundaries are derived and it is concluded that FHA can explain three of four modes. The proposed T-D analysis is capable of describing the quantitative behavior of the system in all four operation modes with closed-form equations for all the mode boundaries. This analysis provides an objective basis to assess the accuracy of FHA predictions under the entire operating conditions. Quantitative comparison of key variables revealed that the FHA results can be unacceptably inaccurate for certain operating points. It is shown that the T-D approach provides a comprehensive design base for series–series compensated IPT without a need to know the load value. The T-D predictions are validated by experiment. A mathematical design calculator tool is also provided to the reader to visualize the mode boundaries, all the waveforms and the numerical results from both methods. [ABSTRACT FROM AUTHOR]

In this paper, a new space vector pulse width modulation method to extend the linear modulation range of a cascaded five level inverter topology with a single dc supply is presented. Using this method, the inverter can be controlled linearly and the peak phase fundamental output voltage of the inverter can be increased from 0.577 to 0.637 V\text{dc} without increasing the dc bus voltage and without exceeding the induction motor voltage rating. This new technique makes use of cascaded inverter pole voltage redundancy and property of the space vector structure for its operation. Using this, the induction motor drive can be operated till the full speed range (0–50 Hz) with the elimination of lower order harmonics in the phase voltage and phase current. The five-level topology presented in this paper is realized by cascading a two-level inverter and two full bridge modules with floating capacitors. The inverter topology and its operation for extending the modulation range is analyzed extensively. Simulation and experimental results for both steady-state and dynamic operating conditions are presented in this paper. [ABSTRACT FROM AUTHOR]

Rotor position estimated with high-frequency (HF) voltage injection methods can be distorted by voltage errors due to inverter nonlinearities, motor resistance, and rotational voltage drops, etc. This paper proposes an improved HF square-wave voltage injection algorithm, which is robust to voltage errors without any compensations meanwhile has less fluctuation in the position estimation error. The average position estimation error is investigated based on the analysis of phase harmonic inductances, and deduced in the form of the phase shift of the second-order harmonic inductances to derive its relationship with the magnetic field distortion. Position estimation errors caused by higher order harmonic inductances and voltage harmonics generated by the SVPWM are also discussed. Both simulations and experiments are carried out based on a commercial PMSM to verify the superiority of the proposed method and the investigations in this paper. [ABSTRACT FROM AUTHOR]

The degradation in power quality causes adverse economical impact on the utilities and customers. Harmonics in current and voltage are one of the most commonly known power quality issues and are solved by the use of a hybrid series active power filter (HSAPF). In this paper, a new controller design using sliding-mode controller-2 is proposed to make the HSAPF more robust and stable. An accurate averaged model of a three-phase HSAPF is also derived in this paper. The design concept of the robust HSAPF has been verified through simulation and experimental studies, and the results obtained are discussed. [ABSTRACT FROM AUTHOR]

This paper presents a single-switch isolated dc–dc converter suited for a very high-frequency switching operation, especially above 10 MHz. The converter features a small number of passive components, low-switching loss, and low-voltage stress on the switch. In order to achieve low-voltage stress while maintaining zero voltage switching, the voltage waveform across the switch is shaped by designing the resonant network of the converter. The resonant network includes main parasitic components, such as leakage inductances of the transformer and the junction capacitance of the switch. Furthermore, some resonant elements are entirely replaced by these parasitic components under the specific condition. This paper derives the conditions and then minimizes the number of passive components. To validate the design procedure and the performance of the proposed converter, a GaN-based prototype was implemented. It operates at 10 MHz and provides the output power of 10 W from the dc input voltage of 50 V. The output voltage is regulated to 20 V by the ON–OFF control. Experimental results show that the peak voltage on the switch is reduced to 2.2–2.3 times the dc-input voltage and the efficiency of 69% is achieved under the full load. [ABSTRACT FROM AUTHOR]

This paper proposes a control strategy for a three-phase three-wire thyristor-controlled LC -coupling hybrid active power filter (TCLC-HAPF), which can balance active power and compensate reactive power and harmonic currents under unbalanced loading. Compared with TCLC-HAPF with conventional control strategy, active power filters and hybrid active power filters which either fail to perform satisfactory compensation or require high-rating active inverter part for unbalanced compensation, a control strategy was proposed for TCLC-HAPF to operate with a small rating active inverter part for a variety of loads with satisfactory performance. The control idea is to provide different firing angles for each phase of the thyristor-controlled LC-coupling part (TCLC) to balance active power and compensate reactive power, while the active inverter part aims to compensate harmonic currents. First, the required different TCLC impedances are deduced. Then, independent firing angles referenced to the phase angle of voltage across TCLC are calculated. After angle transformations, final firing angles referenced to phase angle of load voltages are obtained. In this paper, a novel controller for TCLC-HAPF under unbalanced loading is proposed. Simulation and experimental results are provided to verify the effectiveness of the proposed controller in comparison with a state-of-the-art controller. [ABSTRACT FROM PUBLISHER]

This paper proposes grid current shaping method using dc-link shunt compensator for three-phase diode rectifier system without electrolytic dc-link capacitor. In the proposed method, the diode rectifier system can satisfy the grid regulation IEC61000-3-12 without any power factor correction circuit or heavy grid filter inductor. The proposed grid current shaping method can be realized by applying DSC with reduced-rating components and without electrolytic capacitor, which is connected parallel to the dc link. Since DSC has no electrolytic capacitor, the system with DSC has high circuit reliability. Furthermore, DSC can enhance the system efficiency, especially in flux-weakening area, since the motor drive inverter recovers the reduced modulation index, which has been spent in the additional control for small passive components. This paper presents the control method for DSC and analyzes the effect of proposed method. The feasibility of proposed method is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

The single-phase diode rectifier system with small dc-link capacitor shows wide diode conduction time and it improves the grid current harmonics. By shaping the output power, the system meets the grid current harmonics regulation without any power factor corrector or grid filter inductor. However, the system has torque ripple and suffers efficiency degradation due to the insufficient dc-link voltage. To solve this problem, this paper proposes the dc-link shunt compensator (DSC) for small dc-link capacitor systems. DSC is located on dc-node in parallel and operates as voltage source, improving the system performances. This circuit helps the grid current-shaping control during grid-connection time, and reduces the flux-weakening current by supplying the energy to the motor during grid-disconnection time. This paper presents a power control method and the design guideline of DSC. The feasibility of DSC is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, the near-state pulsewidth modulation (NSPWM), adapted to be implemented in dual-voltage-source inverter (VSI) fed open-end motor, is proposed with the aim of mitigating low-order harmonics (which lead to current total harmonic distortion (THD) minimization). The following two proposed methods are studied in detail: 1) fixing phase angle displacement (PAD) between two VSIs to 120° while adjusting the modulation index (MI); and 2) fixing MI to the predetermined value (wherein low-order harmonics are highly mitigated) while adjusting PAD. Furthermore, the proposed approaches enhance efficiency by limiting the number of commutations within the switching interval. The paper also presents the mathematical approaches to accurately determine low-order harmonic components and switching losses for dual-VSI structure. The experimental setup, including dual-VSI and open-end induction motor, is assembled in the laboratory to evaluate performance of the proposed method. Finally, the simulation results, carried out in the MATLAB/Simulink environment, are found to be in close agreement with experimental data. [ABSTRACT FROM AUTHOR]

This paper extends the high-frequency transformer isolation concept to the Z-source (ZS) ac–ac converters and introduces a new family of high-frequency transformer isolated (HFTI) ZS ac–ac converters. The proposed HFTI-ZS converters retain all the benefits of their existing nonisolated counterparts, such as providing a larger range of output voltage with buck–boost functionality, reversing or maintaining the phase angle, reducing the in-rush and harmonic currents, and improving reliability. In addition to these benefits, the high-frequency (20 kHz) transformer (HFT) in the proposed ZS ac–ac converters provides the electrical isolation and safety with high power density as it eliminates the need for bulky and heavy line frequency (50 or 60 Hz) transformer for galvanic isolation, in applications such as dynamic voltage restorers, etc. The dc-blocking capacitor added in series with the HFT results in only ac voltage applied across its windings, which avoids its saturation. Various ZS-based HFTI ac–ac converters are proposed in this paper, and to verify their operation and advantages, example of quasi-ZS (qZS)-based isolated ac–ac converter is considered in detail. The commutation strategy is also developed to achieve the safe commutation, which avoids the current and voltage spikes without using any RC snubber. A 200-W laboratory prototype of HFTI-qZS ac–ac converter is fabricated and experiments are performed to validate the advantages of the proposed ac–ac converters. [ABSTRACT FROM PUBLISHER]

Modular multilevel converters (MMCs) are being developed for the grid connection of offshore wind or tidal farms. In order to reduce the construction and maintenance costs, it is desirable to reduce the weight and volume of the system. In current MMC submodule designs, the reservoir capacitor usually accounts for over 50% of the total volume and 80% of weight. This paper presents a new design concept and control principle for a submodule using the stacked switched capacitor (SSC) architecture that can significantly reduce the capacitor size in an MMC. Practical considerations for a high-voltage high-power SSC-based MMC submodule are presented in this paper, through the design of a 21-level, 40-kV (pole-pole dc), 19.1-MW, grid-connected system, and the concept is demonstrated experimenttally on a scaled-down 400-V, 12.3-Apeak laboratory prototype submodule. It is shown that with the proposed SSC architecture, the total volume of capacitors in each submodule can be reduced by more than 40% without significantly increasing the power loss. [ABSTRACT FROM AUTHOR]

This paper proposes a new control method of three-phase active power filters for reducing the dc capacitor voltage fluctuations in transient load change. The proposed control method introduces a new \boldsymbolk-step compensator, which maintains the mean active power flowing into the dc capacitor at zero every \boldsymbol1/(k-1) ac line period. Therefore, the compensator can suppress the transient voltage fluctuations across the dc capacitor even when a quick load change occurs. This paper theoretically reveals the relationship between the step number \boldsymbolk and the reduction effect of the dc voltage fluctuations. The experimental setup introducing the proposed seven-step compensator exhibits a good suppression effect of the dc voltage fluctuations and makes it possible to reduce the required capacitance value of the dc capacitor by a factor of seven. [ABSTRACT FROM AUTHOR]

This paper investigates the suitability of selective harmonic elimination (SHE) for low-loss multimegawatt grid-connected photovoltaic (PV) inverters. The proposed system is able to meet utilities regulations, IEEE and IEC standards. In an attempt to substantiate the potential superiority of SHE over carrier-based or space-vector pulsewidth modulation (PWM), this paper demonstrates that SHE may allow grid-connected PV inverters to be controlled using a switching frequency of less than 1 kHz, while the inverter is still able to provide necessary operation features such as independent control of active and reactive powers and operation control simplicity. For system validation, experimental results with SHE are compared to the case when the inverter is controlled using third-harmonic injection PWM, with a 2-kHz switching frequency. Furthermore, the paper proposes a new implementation technique for SHE that utilizes the third harmonics to spread the switching angles over 90° instead of being located in a narrow range as generated when using conventional techniques, along with increases in modulation index. The advantages of the proposed technique include simplicity in implementation and flexibility in PWM waveforms. Simulation and experimentation demonstrate agreement, which validates the practicability of the proposed system. [ABSTRACT FROM AUTHOR]

Power quality of inverter-based microgrids is a challenging issue due to nonlinearities of inverters, multiple resonance modes of network impedance, and unbalanced and nonlinear loading condition. The ideal solution is to assure the best power quality at the common bus to which loads are connected, and share the negative and harmonic sequence currents between the inverters without any communication. However, it is difficult to achieve this objective with existing virtual-impedance-based methods when nonlinearities of inverters, e.g., dead time, are not negligible. In this paper, a novel cost-function-based method is proposed to solve this problem. The proposed cost functions are optimized using continuous-control-set model predictive control. As unknown nonlinearities of inverters can be observed by introducing disturbance models, even when they are not negligible, the presented method can compensate bus voltage unbalance and harmonics and share the compensated current between inverters autonomously, with neither communication nor upper level controller. Parameter tuning of the proposed method is the key to achieve the balance between bus voltage quality and current sharing, and between stability and fast response. Experimental results demonstrate that the proposed control scheme is effective even under conditions of large inverter nonlinearities. [ABSTRACT FROM AUTHOR]

Torque ripple has been a critical issue for high-performance applications using permanent magnet synchronous machines (PMSMs). An efficient approach to minimize torque ripple is to control the stator current to follow an optimized current reference, which will produce an extra torque ripple to cancel the existing one. This paper proposes a multiple reference frame (MRF) based controller for torque ripple minimization (TRM), in which the measured speed ripple is explored as the feedback control signal. The proposed MRF-based controller consists of a TRM controller whose task is to find the optimal current reference and a current controller whose task is to control the actual current to follow the optimized current reference. In TRM controller, the control of reference current magnitude and phase angle is decoupled, and proportional integral (PI) controller is able to achieve TRM control. In current controller, MRF is adopted to convert harmonic current control into dc current control; thus, PI controller is able to achieve harmonic current control with the use of MRF. Compared with existing approaches, the proposed controller is capable of TRM under both steady-state and transient conditions. The proposed controller is experimentally evaluated on a laboratory PMSM drive system. [ABSTRACT FROM AUTHOR]

This paper presents a straight-forward method to compensate baseband distortion for regularly sampled pulsewidth modulation, for both sawtooth and triangular carrier, aimed at high-precision power electronics applications such as medical MRI and semiconductor lithography. The method adds correction signals to the modulator input to mitigate the distortion, which is computationally lightweight, and pseudo-code is given to simplify implementation. Measurements are conducted, which confirm the improvements offered by the method. It is shown that baseband distortion can be reduced by upto 60 dB. This improves the linearity and reduces audible noise of power converters. [ABSTRACT FROM AUTHOR]

In a three-stage cascaded modular solid state transformer (CMSST), unbalanced dc bus voltages at the output of cascaded multilevel rectifier is a common issue due to inevitable parameter mismatch in stage-2. To balance the dc bus voltages, either voltage balance control (VBC) in stage-1 or power balance control (PBC) in stage-2 is necessary. In this paper, an in-depth theoretical analysis to investigate the input power quality of the CMSST in the presence of voltage and PBC schemes is presented. The grid-side multilevel voltage of the CMSST is analyzed to highlight the limitation of using VBC in stage-1. It is then mathematically proven that the switching frequency based harmonics in the grid current are significantly reduced by using the PBC in stage-2. Simulation studies of a 3.3-kV, 50-kVA CMSST are carried out using the PLECS software to substantiate the proposed analysis. Experimental verifications are performed on a 750-VA single-phase CMSST laboratory prototype for a 20% parameter mismatch in stage-2. It is found that the grid current total harmonic distortion (THD) is reduced from 6.65% to 3.8% at 50% load by using PBC in stage-2. This paper provides guidelines for the designer to choose appropriate balance controllers for the CMSST. [ABSTRACT FROM AUTHOR]

The six-phase asymmetrical induction motors (SPIMs) are employed for high power medium voltage drive due to its attractive features of reduced stator copper loss, lower torque pulsation, higher torque per ampere, and higher reliability. In this paper, analysis of carrier-comparison-based pulse width modulation (PWM) techniques namely sinusoidal PWM and double zero-sequence injection PWM are carried out from a space vector perspective. Furthermore, new space vector pulsewidth modulation (SVPWM) techniques are developed by modifying the switching sequences of carrier-based PWM techniques. A comprehensive analysis of these PWM techniques is carried out in terms of harmonic flux trajectories, squared harmonic flux, and harmonic distortion factor (HDF). As a result, modified SVPWM technique namely 6ΦSVM3 is found superior to aforesaid PWM techniques, which significantly reduces HDF and provides lower current total harmonic distortion (THD). The experimental results of aforementioned PWM techniques are obtained and verified from six phase asymmetrical induction motor fed by dual two-level 3ΦVSIs. This paper is also accompanied by a video file of experimental test setup recorded while 6ΦSVM2 is running on SPIM. [ABSTRACT FROM AUTHOR]

Phase-to-neutral voltage or neutral-to-virtual neutral voltage zero-crossing points (ZCPs) detection method is usually used for sensorless brushless dc motor commutation control. Unfortunately, neither of them can be realized in lower speed range. In this paper, a simple commutation point detection method is proposed based on detecting inactive phase terminal to dc-link midpoint voltage. It eliminates the requirement of neutral wire or virtual neutral voltage and provides an amplified version of back electromotive force at the ZCPs which makes the lower speed range detection possible. As the speed increases, commutation point error is enlarged due to the low-pass filter. Utilizing the symmetry of the terminal to midpoint voltage, the phase error can be corrected. However, due to the nonlinear relationship between the detected voltage difference and phase error, it is difficult to regulate the error fast and robustly. Therefore, a novel phase regulator based on fuzzy neural network is proposed in this paper with simple structure and learning ability. The validity of the proposed ZCPs detection method and commutation instant shift correction method are verified through experimental results. [ABSTRACT FROM AUTHOR]

In the magnetically suspended rotor (MSR) system of the flywheel, harmonic current produced mainly by mass imbalance and sensor runout would cause undesirable harmonic vibration. Resonant control (RSC) is one of the remarkable performance alternatives for rejecting a set of selected frequency components of the periodic disturbance in a control system. Based on the intrinsic relationship between RSC and repetitive control, which is deduced and clarified, this paper proposes a novel quasi-resonant control (QRSC) scheme for a baseline prestable MSR system to suppress the harmonic current. By introducing a damping factor, QRSC achieves a good balance between stability and dynamic performance. With hybrid phase compensation, it provides system absolute stability and expands the stability margin of the MSR system. Further, as the domination of harmonic current, low-order frequency components are suppressed by parallel QRSCs (PQRSC). A stability criterion with rigorous proof for the plug-in PQRSC-controlled MSR system is addressed as well. Experimental results obtained with a magnetically suspended flywheel prototype corroborate the theoretical approach. [ABSTRACT FROM AUTHOR]

Electrolytic capacitor with a dc-side inductor is a typical dc-link filtering configuration in grid-connected diode rectified adjustable speed drives (ASDs). The criteria to size the dc-link filter are mainly from the aspects of stability and power quality. Nevertheless, the reliability of the dc-link filter is also an essential performance factor to be considered, which depends on both the component inherent capability and the operational conditions (e.g., electrothermal stresses) in the field operation. Nowadays, unbalanced voltage has the most frequent occurrence in many distribution networks. It brings more electrical-thermal stress to the component, affecting the reliability of the capacitors. In order to study the reliability performance of the LC filter in an ASD system quantitatively, this paper proposes a mission profile based reliability evaluation method for capacitors. Different from the conventional lifetime estimation, a nonlinear accumulated damage model is proposed for the long-term estimation, considering the nonlinear process of equivalent series resistor growth and capacitance reduction during the degradation. Based on the proposed lifetime estimation procedure, four case studies are investigated: first, lifetime benchmarking of capacitors in LC filtering and slim capacitor filtering configurations; second, scalability analysis for the lifetime of capacitors in terms of system power rating and grid-unbalanced levels; third, lifetime estimation of capacitors in the dc-link filter with long-term mission profile; and fourth, the impact of the capacitor sizing on the lifetime of the dc-link capacitor under grid-balanced and grid-unbalanced conditions. The results serve as a guideline for proper selection of dc-link configurations and parameters to fulfill a specification in ASDs. [ABSTRACT FROM AUTHOR]

This paper discusses an alternative to reduce harmonic current distortion in a 12-pulse rectifier. The circuit is based on a generalized autotransformer connection with low power-to-core that feeds two isolated SEPIC converters. Compared to other passive devices operating as conventional 12-pulse rectifiers, besides a tight dc bus, the use of static converters can, by means of an active current imposition, provide very low harmonic distortion of current. This paper presents a theoretical analysis which is corroborated by computational and experimental results. The results show that the performance of the proposed converter is similar to the performance provided by three-phase unity power factor PWM rectifiers, however, only two active switches are deployed. [ABSTRACT FROM AUTHOR]

Applications such as renewable energy generation, electric vehicles, and low-power UPS require single-phase ac/dc conversion. However, this conversion introduces a considerable amount of second-harmonic ripple on the dc link. If not filtered, this distortion hinders the converter's performance as well as the energy quality on both the ac and dc side. To mitigate this problem, a large electrolytic capacitor is usually the solution of choice, which mitigates the voltage ripple, but has drawbacks of its own, including the increased size and cost associated with the large capacitance and the limited lifespan of electrolytic capacitors. Alternative solutions to the problem include integration of an active filter circuit to the converter, which can utilize a storage element with the objective of mitigating power ripple. Such solutions have often been proposed alongside a control system, which is either highly complex or relies on open-loop feedforward techniques. This paper presents a control system, which adapts the single-input space vector concept for a single-phase application and leverages its simplicity and closed-loop architecture, allowing the controller to perform well in the presence of disturbances and parameter uncertainty. Experimental results are provided to elucidate the controller's performance on a single-phase grid-connected photovoltaic array application. [ABSTRACT FROM AUTHOR]

The small-signal impedance modeling of a modular multilevel converter (MMC) is the key for analyzing resonance and stability of MMC-based power electronic systems. The MMC is a power converter with a multifrequency response due to its significant steady-state harmonic components in the arm currents and capacitor voltages. These internal harmonic dynamics may have great influence on the terminal characteristics of the MMC, which, therefore, are essential to be considered in the MMC impedance modeling. In this paper, the harmonic state-space (HSS) modeling approach is first introduced to characterize the multiharmonic coupling behavior of the MMC. On this basis, the small-signal impedance models of the MMC are then developed based on the proposed HSS model of the MMC, which are able to include all the internal harmonics within the MMC, leading to accurate impedance models. Besides, different control schemes for the MMC, such as open-loop control, ac voltage closed-loop control, and circulating current closed-loop control, have also been considered during the modeling process, which further reveals the impact of the MMC internal dynamics and control dynamics on the MMC impedance. Furthermore, an impedance-based stability analysis of the MMC-high-voltage direct current connected wind farm has been carried out to show how the HSS-based MMC impedance model can be used in practical system analysis. Finally, the proposed impedance models are validated by both simulation and experimental measurements. [ABSTRACT FROM AUTHOR]

This paper proposed a novel method for two-segment three-phase motor to eliminate the harmonics nearby pulsewidth modulation (PWM) frequency. Due to PWM technique and switching losses considerations, ear-piercing high-frequency electromagnetic noise in drive system is common. By using magnetically coupled inductors (MCIs) and interleaved technique, the proposed novel method is able to remove the high-frequency harmonics located nearby the PWM frequency and other odd multiples in two-segment three-phase motor. With this method, the unpleasant acoustic noise could be removed when the PWM frequency is selected near 10 kHz. The size of MCIs mainly depends on the PWM frequency harmonic currents rather than the fundamental frequency currents. Thus, its size is very small compared with LC filter. Moreover, this method remains the control dynamics of two-segment three-phase motor without additional inductance for fundamental-frequency currents. The shift phase of two inverters PWM carriers is π, which is simple to implement. Finally, the effectiveness of the proposed method is verified by experimental results. [ABSTRACT FROM AUTHOR]

This paper introduces a new cross-correlation anti-islanding detection scheme for module-integrated converters (MICs) with pseudo dc-link. The proposed scheme periodically injects a second-order harmonic current component of low magnitude (in open-loop mode) and evaluates grid response by means of correlation. The proposed scheme is highly reliable, providing nondetection-zone free operation, fast detection, and compliance with the relevant power quality and anti-islanding standards. Additionally, it excels in lower computational cost, reduced fault detection zone, and higher output power quality, compared to the referenced anti-islanding schemes that are compatible with MICs. Last but not least, it can be implemented in MIC platforms without requiring an output current sensor, being an easily upgradable solution in software level. A firm theoretical framework that considers both high penetration levels of PV systems and weak grid conditions is also included in this paper. The theoretical framework, as well as the effectiveness of the proposed scheme, is verified through extensive experimental results for various electrical-network parameters and nonlinear loading conditions. Finally, a comprehensive comparison between the proposed method and the most common anti-islanding techniques (compatible with MICs) is performed, leading to some valuable conclusions from MICs perspective. [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]

This paper proposes a generalized design procedure for repetitive current controllers in distorted distribution grids to obtain good disturbance rejection properties and well behaved and robust system dynamics. Different implementation options for repetitive controllers (RCs) are discussed based on an accurate discrete time model. A simple control design is derived, which allows any desirable dynamics to be adjusted by one single parameter. Even a deadbeat design is possible. The impact of model inaccuracies and numerical errors on the dynamic and stability of the system is investigated. It is shown that the RC leads to low damping or even instability at high switching frequencies caused by modeling errors or numerical inaccuracies. Based on the stability analysis, it is discussed how to handle these design challenges, which exist especially for RCs of high order. The proposed control structure and control design concept is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

Flying-capacitor modular multilevel converter (FC-MMC) overcomes the zero/low-fundamental-frequency operation issues of conventional MMC without injecting common-mode voltage. However, the FC-MMC suffers from high current stress due to the large amplitude of inner high-frequency current. The square-wave design for the inner high-frequency components could effectively reduce the current stress, but the per-phaseLCcircuit (formed by arm inductor and flying capacitor) challenges the square-wave current control. This paper investigates the equivalentLCcircuit in FC-MMC, and proposes a control method to improve the performance of inner current control. Accordingly, the desired square wave is achieved for inner high-frequency current. The current stresses on semiconductor switches and flying capacitor are reduced by around 25% and 45%, respectively. Simulation and experimental results prove the effectiveness of the proposal. [ABSTRACT FROM AUTHOR]

This paper presents a two-segment motor system powered by two inverters with phase-shift pulsewidth modulation (PWM) to fulfill the purpose of low-torque ripple and vibration noise. Different from conventional multi-inverter structure, the inverters for this type of machine are electrically isolated between each other. First, the concept of multisegment machine is presented and the basic operation principle is analyzed with finite-element analysis (FEA) method. Then vibration caused by the switching device in machine is investigated and the control model of a two-segment motor is developed. Further, the principle of carrier phase-shift PWM is illustrated with the vibration analysis. Carrier phase shift can generate interleaved torque and force on the rotor for the two groups of windings in the machine and cancel each other for certain harmonics. Then simulation of control strategy for this type of machine has been done in MATLAB. Finally, based on the concept and principles mentioned before, a two-segment motor with its drive system is fabricated. Both the test of torque ripple and the vibration of the motor have been significantly improved. Compared with a normal three-phase motor driven by a paralleled inverter with interleaving, the proposed approach is with comparable vibration reduction but without using extra coupled inductors. [ABSTRACT FROM AUTHOR]

Rising power demands in more electrical aircraft (MEA) put power converters for commercial airplanes under increasing pressure to fulfill current harmonic distortion regulations as specified, for example, in DO-160G. Today, the implementation of filters is seen as an effective tool for dealing with harmonics; however, their increased weight and volume are not welcomed in the aerospace industry. This paper proposes a circuit, named forced commutation controlled series capacitor (FCSC-rectifier), which is able to maintain low individual harmonic current levels without the need for filter components. The FCSC-rectifier includes a variable capacitive line reactance that interacts in a controlled manner with the inductive line impedance. The result is that the converter input current is nearly purely sinusoidal with a power factor of almost unity. The FCSC-rectifier is to be used for stand-alone variable-voltage, variable-frequency generation systems and can, therefore, power the full authority digital electronic control system (FADEC) in an MEA. This paper shows that the FCSC-rectifier can maintain a high power factor and acceptable current harmonic levels without the use of filters, despite large voltage and frequency variations. A full description of the circuit modes of operation is presented in this paper together with simulation results showing circuit performance characteristics over a range of voltages and frequencies. Results are experimentally verified using a 1-kW test circuit. [ABSTRACT FROM AUTHOR]

In a low-voltage parallel inverter system, the active power, unbalanced power, and harmonic power generally cannot be properly shared among inverters with droop control due to the mismatch of output impedance. To address this issue, this paper proposes a two-stage adaptive virtual resistor (AVR) control scheme. In the first stage, a proportional-integral controller is applied to regulate the active power with the use of a synchronous maximum power bus (SMPB), and the reactive power is adjusted by means of aQ–ωdroop controller. In the second stage, all inverters switch to aP–Edroop control mode by introducing the AVRs at fundamental positive-sequence, negative-sequence, and harmonic frequencies. Not only can this method eliminate the active power, unbalanced power, and harmonic power-sharing errors, it can also reduce the voltage deviation caused by the droop control. Moreover, the synchronization between inverters can be guaranteed as long as the SMPB is present, without using voltage sensors at the point of common coupling. Simulation and experimental results are provided to verify the feasibility of this method. [ABSTRACT FROM AUTHOR]

The three-phase four-wire inverter with split dc-link capacitors can supply unbalanced loads. For the purpose of reducing the filter inductors, a neutral inductor could be introduced into the neutral line. This paper analyzes the operation principle of the three-phase four-wire inverter with split dc-link capacitors when a neutral inductor is introduced. It is illustrated that the neutral inductor can reduce the zero-sequence switching harmonics in the voltages between the phase-leg midpoints and the output neutral point, thus the filter inductors can be reduced. The optimized design of the neutral inductor and filter inductors is proposed with the considerations of the inductor current ripple, the ability of supplying unbalanced loads, and the total energy stored in the inductors. The equivalent circuits of the three-phase four-wire inverter with split dc-link capacitors and neutral inductor is derived in the α–β–0 frame, and the zero-axis voltage regulator is modified to suppress the third-order harmonic in the zero-sequence current caused by the deadtime of the drive signals for the power switches. Finally, the experimental results from a 9-kW prototype are provided to prove the effectiveness of the proposed optimized design of the neutral inductor and filter inductors and the control strategy of the inverter. [ABSTRACT FROM AUTHOR]

In this paper, a modified selective harmonic mitigation pulse amplitude modulation (SHM-PAM) is presented to be capable of canceling all triplen harmonic orders and suitable for single-phase application of five-level type of voltage source inverters. To this end, a new constraint is established for the two switching angles (α1, α2) to derive the new formula for the harmonics’ amplitude, which results in self-elimination of all triplen harmonics (e.g., 3rd, 9th, 15th, …). The fifth and seventh harmonic orders are mitigated through normal operation of the proposed SHM-PAM technique. It is also shown that the proposed technique is extendable to other multilevel voltage waveforms and a flowchart of self-elimination of all triplen harmonics has been presented. Mathematical analysis supported by experimental investigations show the desired performance of the proposed SHM-PAM algorithm on a two-cell single-phase cascaded H-bridge inverter as a typical five-level configuration in dealing with linear and nonlinear loads. Then, it is demonstrated that the maximum number of harmonic orders would be controlled with the minimum number of available angles in a low switching frequency voltage waveform. [ABSTRACT FROM AUTHOR]

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]