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This article proposes a novel flux weakening scheme for five-phase PMSM with active harmonic currents injection. The conventional flux weakening control schemes applied in the five-phase PMSM do not consider the voltage limit drop in the fundamental subspace due to the harmonic current controller. Thus, the derivation between the reference current trajectory and actual current trajectory would cause the current distortion when applying deadbeat current controller (DBCC). This article analyses the precise voltage limit circles considering the voltage drop caused by the resistance and harmonic currents control at first. Then, a feed-forward flux weakening control algorithm is designed to optimize the current trajectory online. The gradient descent method is used to ensure the converge speed and stability of the optimized current trajectory. Thirdly, the peak value of phase currents would be clipped by the harmonic currents to prevent the inverter current limit, where a new non-linear harmonic current controller is designed to precisely control the harmonic currents. Finally, the DBCC and modified SVPWM technology are utilized to generate the duty cycle. The proposed improved flux weakening control strategy is successfully implemented in an interior five-phase PMSM, and the performance demonstrate the effectiveness of this strategy. [ABSTRACT FROM AUTHOR]

Dual-three-phase permanent magnet synchronous machines (DTP-PMSMs) are famous for their fault-tolerant capability. However, the complex modeling, high copper loss, and torque ripple under postfault operation limit their further application. In this article, a fault-tolerant control (FTC) strategy is developed for DTP-PMSMs under the open-phase fault (OPF) with straightforward modeling and smooth output torque. The virtual healthy DTP-PMSM model, where the coordinate transformation, the modulation strategy, and the controller structure remain unchanged under OPF, is adopted in the proposed FTC scheme. And the current references are derived in sinusoidal waves with minimum copper loss. The inaccurate transmission of control signals under OPF is also focused on. Comprehensive theoretical analysis shows the relationship between the controller output voltage and the actual stator voltage should be considered in the proposed FTC strategy; otherwise, distortion in torque and current will be introduced. The voltage compensation is utilized to compensate for the voltage difference and ensure the smooth torque output. Besides, a quasi proportional resonance controller is designed to further suppress the residual torque ripple. The proposed strategy will not induce complex implementation and heavy computation burden. The simulation and experimental results prove the analysis and the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Parallel dc–dc converters are commonplace in applications such as computing power supplies, point of load systems, and dc microgrids. The presence of multiple converters in such systems allows for switch interleaving and ripple cancellation. One class of existing ripple reduction methods depends on central controllers that require communication among the converters. These approaches compromise system scalability and reliability. When it comes to decentralized methods, the state-of-the-art is limited to uniform conditions and cannot handle mismatches in physical parameters and operating points among converters. In this article, we address these shortcomings with fully decentralized controller that robustly drives the pulsewidth modulation carriers of a collection of heterogeneous converters to the phase-shifts that give minimized ripple. More precisely, the proposed controller eliminates the dominant fundamental switching harmonic from the output current and voltage using only local voltage feedback. After outlining a comprehensive analytical model, we experimentally validate our approach on a system of five parallel-connected buck converters under a variety of parametric and operational mismatches. Measurements show ripple reduction of more than $4\times$ in the output voltage and the fundamental switching frequency harmonic is attenuated by more than 30 dB compared to conventional symmetric interleaving. [ABSTRACT FROM AUTHOR]

The interphase reactor (IPR) is one of the most important components of the passive harmonic reduction circuit (HRC), and the optimum turns ratio design of the IPR is of great significance to ensure the effect of the passive HRC. In combination with the pulse number multiplication methods, the configuration of the multipulse rectifiers (MPRs) with single/dual/triple-passive HRCs are constructed, respectively. The general optimum turns ratio design method for the IPRs is proposed, which contains most of the realizable combinations of the HRCs. The relationship between the turns ratio of the IPR and the phase number of the bridge rectifier in the main circuit is established, the influence of the turns ratio selection on the power quality of the MPRs is presented. In addition, this article takes N equal to five as an example to verify the effectiveness of the proposed general optimum turns ratio design method of IPR. The power quality of the MPRs with different HRCs or phase number are compared. All the research can provide a useful guideline and theoretical foundation for the MPR selection and the HRC design under the specific occasions. [ABSTRACT FROM AUTHOR]

The overmodulation strategy plays an important role in the field weakening control for high-speed permanent magnet synchronous motor (PMSM) drives. However, the voltage jumps between the output voltage vectors (OVVs) in high overmodulation regions result in the deterioration of both current performance and loading capability. In order to solve this problem, a novel overmodulation strategy based on the voltage vector space division is proposed. The overmodulation regions are divided by the amplitude and the phase of reference voltage vectors to guarantee the continuity of OVVs. When the overmodulation region changes, the voltage jump can be efficiently suppressed, which contributes to eliminating current ripples. In addition, the proposed parallel projection replaces the traditional center projection to increase the modulation index, which can also improve the fundamental voltage amplitude, and make a reduction of the field weakening current and its current overshoot. By improving the utilization of the dc bus voltage, the higher capability of the output torque can be achieved in the field weakening region. Finally, the effectiveness of the proposed strategy is verified on a high-speed surface-mounted PMSM platform by the experimental results. [ABSTRACT FROM AUTHOR]

Sharp LC resonance peak may enlarge inherent harmonics, dominant harmonics of the supply voltage generated by a three-phase diode rectifier, around the resonance frequency, which will intensify fluctuations of the dc-link voltage, and grid currents in motor drives with small dc-link capacitor. In this article, a novel resonance suppression strategy based on inherent harmonics impedance shaping is proposed specially for three-phase input permanent magnet synchronous motor (PMSM) drives with small dc-link capacitor. Instead of increasing the damping of the whole system for resonance suppression, the motor side power disturbance can be reduced by designing the impedance for inherent harmonics around LC resonance frequency based on the new model with the consideration of motor side characteristic. For damping current generation, the angle of the virtual admittance is modified to eliminate the influence of the dc-link voltage sampling delay. Experimental results show the effectiveness of the method on a prototype of electrolytic capacitorless PMSM drive. [ABSTRACT FROM AUTHOR]

This article proposes a control and modulation strategy for medium-voltage (MV) drives that exhibits excellent steady-state and transient behavior. Specifically, optimized pulse patterns (OPPs) and direct model predictive control are employed so that the associated advantages of both, such as minimum stator current total demand distortion (TDD) and fast transients, respectively, are fully exploited. To do so, the current reference trajectory tracking and modulation problems are addressed in a coordinated manner in the form of a constrained optimization problem that utilizes the knowledge of the stator current evolution—as described by its gradient—within the prediction horizon. Solving this problem yields the optimal real-time modification of the offline-computed OPP, which guarantees that very low—and close to its theoretical minimum value—stator current TDD is produced at steady state, and very short settling times during transients. To highlight the effectiveness of the proposed strategy, a variable speed drive system consisting of a three-level neutral point clamped inverter and an MV induction machine serves as a case study. [ABSTRACT FROM AUTHOR]

In aviation aircraft, autotransformer rectifier units (ATRUs) have been widely used as front-end rectifiers. The comprehensive analysis of its operating characteristics under the fault is beneficial to assessing the hazards of the faults and developing a fault diagnosis scheme. This article investigates two types of open-circuit (OC) faults in delta-polygon 18-pulse ATRU, namely, diode OC fault and input OC fault. First, the effects of the diode OC fault on five aspects are quantitatively analyzed: diode conduction angle, output voltage ripple, winding current, input current harmonics, and diode and transformer winding losses. Next, the operating characteristics of ATRU are investigated under input OC fault, and the quantitative effects of the five aspects above are also calculated. Then, based on the affected intervals of dc output voltage, a fault diagnosis idea dealing with two types of OC faults is discussed. Meanwhile, the predictive maintenance objects after the fault location are also summarized. Finally, the simulation and experimental results validate the theoretical analysis and discussion. This work is very significant for guiding the fault detection, fault location, and predictive maintenance of ATRUs. [ABSTRACT FROM AUTHOR]

This article proposes a novel 5-D switching-table-based direct torque control (5D-DTC) strategy for asymmetrical six-phase induction machines (6PIMs). As is well-known, classical DTC of 6PIM is penalized by significant stator current harmonics, which are mapped into the nonenergy subspace ($x-y$ subspace). The concept of virtual voltage vectors (VVs) has been frequently perceived as able to tackle the problem of $x-y$ currents. Such a concept maintains zero average volt-second in the $x-y$ subspace, which in turn suppresses current harmonics due to discrete pulsewidth modulation implementation to a great extent compared to the classical DTC. However, it still cannot effectively compensate for $x-y$ currents, mainly arising from dead band effect and machine/converter asymmetry, due to lack of dedicated regulators for $x-y$ currents. Indeed, the $x-y$ currents can be fully suppressed only in the presence of active control over them. This article incorporates additional hysteresis regulators of $x-y$ currents into the direct torque control strategy. In the proposed 5D-DTC scheme, there are in total five indexes for optimal selection of VVs as torque, stator flux, $x-y$ currents, and stator flux position indexes. In this way, a clustering method is developed for synthesizing VVs to cover all possible cases of the switching table. A beneficial feature in comparison with 3-D switching-table-based DTC is effective suppression of $x-y$ currents with a rather simple structure, without increasing the switching frequency, and without decreasing dc-link utilization. Experimental results confirm the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

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

It is important to improve the accuracy of rotor position estimation for the high-performance operation of position sensorless permanent magnet synchronous motor (PMSM) drives. To mitigate the position harmonic error caused by the nonideal factors in high-frequency signal injection based methods, an adaptive quasi-proportional-resonant rotor position observer (AQPRO) for sensorless PMSM drives is proposed in this article. The AQPRO can track the estimation error and generate the compensation value, which can realize online suppression for position error. By analyzing the stability and the influence of parameters of the proposed position observer on the suppression performance, a proportional-resonant gain self-tuning strategy is investigated to improve the suppression effect of the position harmonic error for different loads and speeds. The influence of self-tuning regulator parameters is modeled and analyzed in detail. The proposed method does not require offline detection and has a strong suppression ability for different harmonic error components. The effectiveness is verified by experiments on a 2.2-kW PMSM drive platform. [ABSTRACT FROM AUTHOR]

Accurate synchronization and harmonics control are keys to achieve a distortionless zero-cross of currents in active unity power factor rectifiers. This article proposes a method to achieve optimal operation: 1) by settling a synchronization path that feeds the phase-locked loop with the output voltage reference that sets the theoretical unity power factor operation, and 2) low-order harmonics control with zero-cross driven antiwindup to reduce distortion further. Controller design is detailed and supported by theoretical analysis; the key performances are proved by experimental verification. [ABSTRACT FROM AUTHOR]

The elimination of periodic torque disturbance in permanent magnet synchronous machine (PMSM) drives is a multifrequency control task, and adding resonant parts to the controller has an impact on the robustness of the system. This article aims to address the torque-ripple reduction in PMSM drives for smooth speed control, where an extended harmonic state observer (EHSO) is designed for estimation and attenuation of the selective periodic disturbance. The defects of applying the conventional bandwidth-parameterization method to the harmonic disturbance observer are explored. To improve the disturbance-rejection capability and the relative stability, a pole-placement strategy is proposed and analyzed through sensitivity function, which can preserve the comparable dynamic performance as the conventional extended state observer at the low-frequency range. The proposed EHSO also features easy parameter tuning and a modular structure for multiple harmonic disturbance rejection. Finally, the proposed method is evaluated on a laboratory PMSM platform. [ABSTRACT FROM AUTHOR]

Modularity in hardware improves the manufacturability of power electronics systems and reduces maintenance costs. By paralleling modular ac–dc converters, the current capacity of SiC-based power conversion systems can be easily expanded. However, it is questionable which filter topology can be chosen for an arbitrary number of the converters ($N$). Considering interleaving, filters without any coupling may result in an overdesign. Meanwhile, filters that magnetically couple the paralleled converters may suffer from complexity in mechanical structure and $N-1$ redundancy. Based on these observations, this article proposes a filter structure that can be easily scaled to any number of converters. The proposed structure is comprised of a coupled inductor (CI) forming a loop of secondary windings, a single boost inductor on that loop, and a normally on normally closed (NONC) contactor per converter. Circulating currents are attenuated by the CI for any $N$. A single inductor rated for each channel realizes a boost inductor for a whole $N$ -converters, which can bring a significant benefit on power density and cost. When one of the converter faults, the faulty converter can be easily isolated from the system by the NONC contactor, thus achieving $N-1$ redundancy. The proposed filter topology is experimentally verified with a 20-kW full-SiC modular ac–dc converter. [ABSTRACT FROM AUTHOR]

This article presents the analysis and realization of a modular interconnected filter building block (FBB) operating under a single and multichannel (parallel three-phase converter blocks) configuration without loss of attenuation to any harmonic components. Emphasis is on the design of coupled inductor (CI) and boost inductor. In order to achieve a modular scheme with interleaved operation, indirect coupling between converters is realized using the secondary loop (SL)-based interconnection with inserted impedance. Here the “SL” serves as an additional pass for average grid side currents for N channels. A building block type configuration has been proposed using this topology, inspired by the power electronics building block (PEBB) nature. The purpose of the loop is to interconnect the parallel converters in series using an arrangement of CIs. In addition, a boost inductor has been introduced in the SL to realize a power factor correction rectifier operation. The CI serves as the circulating current filter while reflecting channel currents toward the SL. To meet conducted electromagnetic interference (EMI) limits, a two-stage LCLC filter has been integrated with the FBB by introducing the point of common coupling (PCC) connection between two stages for filter size reduction. A design procedure is presented to meet power quality, circulating current, and EMI limits as per industry standards (EN-55011 and IEEE-519/1594). The proposed FBB has been characterized using 3L-NPC converters enabled with 1.2 kV Silicon Carbide based modules with comprehensive performance validation up to three channels in parallel with 15-kW power rating per channel. [ABSTRACT FROM AUTHOR]

The existing simultaneous wireless power (SWP) and information transfer can only achieve serial signal transmission and it is hard to decouple the power and signal transmission without the additional circuits. To solve these problems, a SWP and multibit signals transfer technology is proposed in this article. Based on the working principle of the hybrid modulation waves pulsewidth modulation control technology, the power and multibit signals are modulated into the system through the modulation waves with different frequencies. Therefore, the signal transmission no longer depends on the power transmission, and the signal transmission rate is multiplied through the realization of parallel signals transmission. Subsequently, the parameter selection criterion of the signal channel is given by analyzing the signal transmission rate and the interference between the power and signal transmission. Finally, the proposed technology is verified with experimental results. The experimental results demonstrate that the power and two-bit signals can be transmitted stably. Compared to the serial transmission, the band signal transmission rate is increased by two times. [ABSTRACT FROM AUTHOR]

In order to increase the power density and the lifespan of light-emitting diodes (LED) drivers, several studies have proposed active ripple compensation (ARC) techniques for minimizing the converter bulk capacitance. However, a common side effect of the ARC method is the increase in the total harmonic distortion (THD) of the converter input current. In this context, a frequency-based ARC technique is proposed as an alternative to the conventional ARC methodology, in which the duty cycle is modulated. The analyses presented in this article show that the frequency-based ARC approach applied to resonant converters has a better performance than the one used in hard-switching converters, since it allows for a huge capacitance reduction with a small THD increase. Furthermore, this article presents a generalized analysis of ARC techniques applied to integrated offline LED drivers, which reduce the number of components and the overall LED driver cost. The input current harmonic content and the output ripple reduction have been theoretically predicted for several converters. Experimental results gathered from a 96-W laboratory prototype supplied from a 127-V 60-Hz grid attested the superior performance of the frequency-based active ripple compensation, since a capacitance reduction of 66.6% has been obtained with an increase of only 0.9% in the THD. [ABSTRACT FROM AUTHOR]

The permanent magnet synchronous motor is the most commonly used motor in servo systems. Torque ripple caused by the variation of the airgap magnetic field limits the steady-state performance of the servo system. In this article, a novel torque ripple model is established based on the general airgap field modulation theory. A compound control algorithm based on the current feedforward algorithm is proposed to suppress the torque ripple caused by the field modulation behavior. Finite element analysis simulation is conducted to verify the effectiveness of the proposed torque ripple model. Experimental results on a prototype machine show that the proposed torque ripple model is valid and the proposed control algorithm can effectively reduce the torque ripple and improve the steady-state performance of the servo system at medium or high speed. [ABSTRACT FROM AUTHOR]

Three-phase four-leg voltage-source inverter has been extensively investigated in recent years for its compactness, small size, and high efficiency, and it has been proved to be the best solution for providing transformer-less neutral connection to three-phase asymmetric loads. The main purpose of this article is to apply 3-D unbalanced coordinate transformation to the four-leg inverter, which supplies stand-alone asymmetric loads, to maintain the balance of the output capacitor voltages, and obtain simpler control structure and better control performance. First, a double closed-loop PI control structure can be designed based on the Clarke and Park transformations. Second, the phases and amplitudes of the capacitor voltages are locked based on the 3-D unbalanced coordinate transformation. Furthermore, the Clarke transformation oriented on the inductor currents is replaced by a 3-D unbalanced coordinate transformation, and the corresponding unbalance indices are continuously adjusted according to the unbalance indices of the capacitor voltages, so as to recover the capacitor voltages to the balanced condition. The simulation and experimental results of the whole control system for the four-leg inverter are provided in the end, so as to verify the feasibility and effectiveness of the 3-D unbalanced coordinate transformation for application to the power electronic systems. [ABSTRACT FROM AUTHOR]

Active electromagnetic interferences (EMI) cancellation is a promising solution to reduce the size of passive filters. Power electronic systems may generate periodic disturbances if they are controlled by periodic signals in steady-state operation. Periodic disturbances can be represented by a set of sine waves, according to the Fourier theory, and can be suppressed by an appropriate set of cancelling sine waves injected into the system. Since bothersome effects, like delay times or complex transfer functions, can be compensated by individually selecting the appropriate amplitude and phase for each cancelling sine wave, high EMI reductions can be achieved in a wide frequency range. In this contribution, this cancellation method is applied to the common-mode EMI of a three-phase motor inverter in stationary operation with periodic control signals in the frequency range from 150 kHz to 30 MHz. Approximately 2.4 million harmonics are suppressed. The characteristics of the overall system are discussed and the challenges for the cancellation system are elaborated. A method for the synthesis of the cancellation signal is introduced. The design of the cancellation system is described, and its signal processing is presented. The outstanding performance is proven by reference measurements in a laboratory setup. Extensions for practical applications are discussed. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) has been widely applied in various applications such as electric vehicles and consumer electronics. In this article, a voltage controller base on an improved pulse density modulator (IPDM) for H-bridge active rectifier in IPT is proposed. To reduce the power loss caused by the pulse sequence of the traditional pulse density modulation (PDM) controller, a general optimization method of the pulse sequence is given and proved in detail. More importantly, an analytical model, which illustrates the relation between interharmonics and power losses of the system, has been derived. Compared with traditional PDM, the stress on switching devices is reduced under various load resistance, and the overall system efficiency can be improved. The experiment results based on a 1-kW laboratory prototype demonstrate the proposed IPDM design method. Under different load conditions, ranging from 22.6–102 Ω, the overall system efficiency could reach up to 96%. Compared with phase-shift modulation and PDM, the efficiency is at most improved by 3.508%. [ABSTRACT FROM AUTHOR]

Grid-forming (GFM) inverters are dc–ac converters that regulate their ac terminal voltage and frequency in response to real-time measurements. Recent developments on GFM controls have focused on a particular dispatchable virtual oscillator control whose implementation features a nonlinear Andronov–Hopf oscillator at its core. In this article, we systematically model and study this controller, its synchronization dynamics, as well as its stability. We show that system voltages and frequency are regulated in a decentralized and autonomous manner while exhibiting nonlinear droop-like behavior. Small-signal models are formulated for an individual inverter connected to an infinite voltage bus in addition to systems of interconnected GFM inverters. These models allow us to characterize dynamical stability and synchronization. Robustness is shown after sweeping key system parameters under the aforementioned models that capture system performance. Numerical simulations and experimental results validate the analytical developments. [ABSTRACT FROM AUTHOR]

This article proposes a new duty-ratio-based direct torque control (DR-DTC) with enhanced harmonic current suppression for a dual-three-phase permanent magnet (DTP-PM) motor. First, a new virtual voltage vector construction method based on the carrier-based modulation technique is proposed. Twelve virtual voltage vectors with null average voltage values in two harmonic subspaces are constructed. The sequences of the constructed virtual voltages can be calculated directly in the natural coordinate system. In addition, the whole sequences are standard symmetrical, which can be easily generated by a digital controller. After that, an online harmonic current compensation method is investigated. Additional controllers compensate for the harmonic currents induced by the back electromotive force and nonlinear factors. Since the virtual voltage vectors have null average voltage values in two harmonic subspaces and the online harmonic current compensation method is designed, the proposed DR-DTC can be introduced to the DTP-PM motor with a single neutral point and two neural points. With the proposed strategy, the capability of harmonic current suppression can be significantly improved, and the processes of virtual voltage construction can be simplified. In addition, the advantages of the conventional DR-DTC can be inherited. Finally, experiments are carried out to validate the feasibility of the proposed strategy. [ABSTRACT FROM AUTHOR]

Bidirectional wireless power transfer greatly improves the reliability of power supply. However, wireless communication between the primary and pickup controllers is usually required to transmit load information, which has time delay and is easily interfered by electromagnetic fields. Existing solutions to avoid the use of communication can be divided into three categories: additional dc/dc circuit, primary side bridge control, and secondary side bridge control. Compared with the other two methods, the secondary side bridge control has low loss and good robustness. But, it usually requires phase-locked loop (PLL) to eliminate the frequency error between primary and secondary side bridges, which increases the complexity. In this article, a constant current control strategy without communication is proposed. It is based on the secondary side bridge control and the switching sequence of the secondary side bridge is periodically synchronized according to the phase of the resonant current. It works robustly without the need for additional hardware such as PLL or Multiplier. The harmonic sensitivity analysis, parameter optimization design and stability analysis are carried out to improve the control efficiency. Experimental results based on a 1 kW prototype with dual LCC resonant network are presented to verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This article proposes a novel remedial direct torque control (RDTC) for the postfault operation of the dual three-phase permanent-magnet (DTP-PM) motor. The DTP-PM motor is configured as a two-neutral points model and fed by an eight-leg voltage source inverter. Also, the harmonic torque induced by the third harmonic back electromotive force and zero-sequence currents is considered at the postfault operation. First, the switching tables for different fault conditions are pre-established. The proposed strategy can be applied to different postfault operations with one phase open by replacing the switching table simply. At the normal operation, the redundant auxiliary legs are disabled. So, the proposed eight-leg voltage inverter is the same as the conventional six-leg one. At the postfault operation, the auxiliary leg in the faulty three-phase windings provides an additional control degree of freedom. Hence, the fault-tolerant capability of the DTP-PM motor with two neutral points can be enhanced. Also, the proposed strategy compensates for the harmonic torque by modifying the reference torque. Based on the proposed RDTC, the postfault operational performance can be significantly improved. Finally, the simulations and experiments are conducted to validate the feasibility of the proposed strategy. [ABSTRACT FROM AUTHOR]

In the standalone power generation system based on brushle doubly fed induction generator (BDFIG), the special loads such as unbalanced loads and nonlinear loads will cause negative sequence, fifth and seventh harmonic components in power winding (PW) and the corresponding harmonic components in control winding, which will cause some torque ripple so as to make the machine unable to output stable active power, increase the vibration and noise, and so on. This article will first analyze the harmonic components of the torque in details, and then propose an optimized torque ripple suppression method. Through the low frequency harmonic control method of the line side converter without additional sensors, the negative sequence, and fifth harmonic components of PW voltage are controlled to achieve the suppression of the second and sixth harmonic components of the torque. Compared with traditional active filtration method, the proposed method in this article needs to satisfy fewer constraints and tune fewer parameters, and can be utilized more flexibly. Comprehensive experimental results based on a 5-kVA BDFIG demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Series arc fault is one of the main causes of electrical fire. In a three-phase motor with inverter circuit, it is difficult to accurately identify series arc fault occurred in the lines at the back of the inverter, especially when the power supply contains complicated harmonics. To solve this problem, a new feature extraction method of the series arc fault based on the current signal measured at the front of the inverter (CSMFI) was proposed. The series arc fault experiments under different harmonic power supply conditions were carried out in the three-phase motor with inverter circuit. Five-layer decomposition was performed on the CSMFI by using empirical wavelet transform. The attractor track matrix (ATM) of each decomposed signal was established. The fault features of the series arc fault were obtained by calculating and selecting the singular values of the ATM. The series arc fault was identified by using an optimized support vector machine. The effectiveness of the method and its applicability under different experimental conditions were tested. The method can simultaneously identify the series arc fault occurred in the lines at the front or back of the inverter by analyzing the CSMFI. It also has strong anti-interference ability. [ABSTRACT FROM AUTHOR]

This article is devoted to developing a unique series-winding drive (SWD) topology, analyzing and implementing its control schemes for asymmetrical multiphase permanent magnet synchronous motor (PMSM). Proposed SWDs have higher voltage utilization than ordinary wye or delta connection, but vary with the number of inverter legs and connection sequence. Also, they have a simpler topology, fewer inverter legs, and power modules than the open-end winding drives. The article selects the typical asymmetrical six-phase (ASP) PMSM as the target. The complex space vector mapping is screened and simplified by unified hexadecimal coding for both eight-leg and seven-leg drives. Given the multiple suspaces in ASP-PMSM, a multistage decoupling space vector modulation scheme is proposed and improved for SWDs. It incorporates the processes of vector synthetization, cost function minimization, and zero-sequence compensation. Prototype fabrication and control experiments are carried out. Results show that the proposed MSD SVM is applicable to all connection sequences. It can suppress the harmonic current to a quite low level, in both steady-state and dynamic states. Also, this article discusses the current burden of the inverter and provides suggestions. [ABSTRACT FROM AUTHOR]

This article proposes a new fault-tolerant control for five-phase fault-tolerant permanent-magnet motors under single-phase short-circuit fault. In the proposed method, the effect on torque performance caused by a short-circuit fault is attributed into two parts: the loss of the short-circuited phase, which is equivalent to a phase open-circuit fault, and the resultant short-circuit current. The remedial action for loss of a phase is realized in the fundamental space, while the torque ripple caused by the short-circuit current is compensated by the harmonic currents in the third space. To decouple the control of the fundamental and third space, the reduced-order Clarke and Park transformation matrixes for the two spaces are obtained separately under single-phase short-circuit fault. Afterward, the fundamental currents with minimum joule losses or equal joule losses for loss of a phase, and the harmonic currents in the third space for torque ripple reduction are derived. Hence, the proposed method can realize torque ripple-free operation under single-phase short-circuit fault. Finally, the effectiveness of the proposed method is verified by experimental results under various operational conditions. [ABSTRACT FROM AUTHOR]

Virtual oscillator control (VOC) is a time-domain strategy that leverages the dynamics of nonlinear oscillator circuits for synchronizing and regulating grid-forming inverters. In this article, we examine a class of second-order circuits composed of a harmonic oscillator and nonlinear state-dependent damping that has found extensive interest in the context of VOC. We center our analysis on the Van der Pol, Dead-zone, and Andronov-Hopf oscillators; these are characterized by several distinguishing attributes but they all share the common structure noted above. Analytical methods based on averaging and perturbation theory are outlined to derive several performance metrics related to harmonic and dynamic properties of these oscillators under a unified framework. Our results reveal that the Andronov-Hopf oscillator is well suited for grid-forming inverter applications since it can yield harmonics-free waveforms without compromising dynamic performance. Analytical results are validated with numerical simulations and experiments, and a multiinverter hardware setup is used to illustrate a practical use case. [ABSTRACT FROM AUTHOR]

In this article, a simple series-connected 24-pulse rectifier with a passive auxiliary current injection circuit (ACIC) is proposed. The proposed rectifier consists of a 12-pulse rectifier and an ACIC. The ACIC includes a circulation current forming circuit, an auxiliary single-phase transformer (AST), and an auxiliary single-phase full-bridge rectifier (ASFR). The ASFR extracts alternating square-wave current from the dc side and injects it into the outputs of three-phase rectifier bridges to increase the output state of these bridges. The operating mode of the proposed rectifier is analyzed, and the functional relationship between the input current and turns ratio of AST is established. The AST turns ratio that minimizes the input line current total harmonic distortion (THD) is derived. The voltage and current rating of AST are calculated, and the design method of capacitors C1 and C2 in ACIC is given. Under the optimal turns ratio, the ACIC extends the 12- to a 24-pulse rectifier. The resulting 24-pulse rectifier draws near-sinusoidal input currents with less than 5% THD. The AST in ACIC has a very low kilovolt-ampere rating (1.96% Pd), and the current ratings of ASFR are small. The theoretical analyzes are provided and experimentally verified using a 1.7 kW experimental prototype. [ABSTRACT FROM AUTHOR]

This article presents approaches for efficient modeling and systematic design of enhanced phase-locked loop (ePLL) structures. While different ePLL structures have found a wide acceptance for various applications, their modeling and design aspects have not been fully and systematically reported in the existing literature. This article fills this gap by presenting an effective modeling approach for both the single- and three-phase ePLLs. The models are derived with a view to minimize the number of parameters to be adjusted to simplify the design. The models are then used to develop systematic design algorithms for their parameters. As an example, application of the ePLL in a grid-connected inverter is formulated and studied through simulation and experimental results. The design and simulation files are made available. [ABSTRACT FROM AUTHOR]

This article presents a novel modulated model-predictive control (MMPC) scheme for modular multilevel cascaded converter-based static synchronous compensator (STATCOMs) (MMCC-STATCOMs) to compensate unbalanced load current and regulate reactive power flow. By adding a common-mode voltage (CMV) to the phase-voltages of the star-connected MMCC current model, the method allows natural injection of a nonsinusoidal voltage to the neutral point of the converter, hence achieving interphase cluster voltage balance. Moreover, the imposed CMV is shown to extend the operating ranges of MMCC-STATCOMs when used for negative sequence current compensation. The proposed MMPC method incorporates a modified branch and bound algorithm to optimize the per-phase switch duty ratios. It is shown to be computationally more efficient compared to model-predictive control schemes using the optimal voltage level method combined with voltage sorting schemes. Experimental results with different weighting factors confirm the effectiveness of this control scheme and compared favorably with the conventional scheme of injecting only a sinusoidal zero-sequence voltage. [ABSTRACT FROM AUTHOR]

The heavy computational burden and the complexity in pulse generation based on multivector synthesis represent serious challenges for applying finite control set model-predictive control (FCS-MPC) in multiphase open-end winding (OW) drive systems. In this article, a low-complexity model-predictive control with dead-time compensation is proposed for the nine-phase OW permanent magnet synchronous machine drive system. First, to simultaneously eliminate voltage vectors on the third, fifth, and seventh harmonic planes, three vectors in the same direction are selected to synthesize the virtual vector (VV). In addition, a multivector synthesis algorithm is designed to generate a symmetrical pulse sequence. Then, in order to suppress the harmonic voltage vector caused by the dead time, an additional voltage vector was added to the VV. Finally, the deadbeat principle was introduced to calculate the reference voltage vector, and the optimal voltage vector is determined according to the position of the reference voltage vector, which reduces the computational burden successfully. The proposed method is studied and compared with traditional FCS-MPC schemes. Simulation and experimental results have verified the effectiveness of the proposed method, which reduces the computational burden and complexity and enables the use of FCS-MPC for multiphase OW drive systems. [ABSTRACT FROM AUTHOR]

Many industrial applications are recently utilizing the advantages of a common dc-bus-based multiple-drive (multidrive) system, such as low installation cost, space savings as well as improved reliability, and flexibility. One of the main drawbacks of such systems is the requirement for a bulky dc capacitor due to the presence of large dc-link current ripples from the harmonic interaction between these multidrive and pulsewidth modulation (PWM) switching. This problem not only increases the cost and volume of the dc-link capacitors but also decreases its lifetime, which must be considered in the design from the industrial aspect. This article proposes a new dc-bus capacitor design method for a multidrive system, focused on the capacitor sizing, cost reduction, and lifetime improvements. First, an analytical model to obtain the dc-link capacitor current in a multidrive system is proposed, which would aid the designers to configure the dc-capacitor current in systems having numerous multiple drives. Next, using the developed analytical model, the dc-link current harmonics are reduced through optimal interleaving of the fundamental output currents in addition to the phase shifting of the carrier waves of the parallel connected inverters. Finally, new capacitor sizing/design is proposed considering the lifetime, power loss, cost, and volume of the dc-link capacitor bank. The proposed approach reduces the volume and cost of dc-cap bank by 50%, and increases the lifetime by four years ($\sim$ 35 000 h), considering the worst-case scenarios. Experimental and analytical results are given for validation of the proposed method. The results could serve as a guideline for designing the dc-link capacitor in multidrive applications in a low-cost manner. [ABSTRACT FROM AUTHOR]

Variable switching frequency PWM (VSFPWM) modulation can be advantageously implemented in industrial applications, such as renewable energy, motor drives, and uninterrupted power supply (UPS) systems, to reduce the injected current harmonic amplitudes, to suppress audible noise, and to improve semiconductor power efficiency. In this article, the usage of periodic VSFPWM methods in a voltage source converter (VSC) is proposed, analyzed, and benchmarked in terms of harmonic spectrum spreading, following the IEEE-519 current harmonic standard for the connection to the distribution grid. Particular attention is paid to the influence of VSFPWM on the ac filter design. First, the analytical model of the voltage harmonic spectrum generated by a three-phase three-wire two-level VSC implementing several periodic VSFPWM methods is derived. Subsequently, a design guideline for the commonly used LCL filter in the grid-tied VSC application is proposed, which minimizes the size requirement of the necessary components. The voltage spectrum models of the proposed VSFPWM method and the optimal switching profiles are verified by MATLAB/Simulink simulations and a 5-kW three-phase two-level VSC hardware demonstrator. The study shows that the ac filter power density for the studied VSFPWM methods can be greatly increased when compared with the conventional and widely employed constant switching frequency continuous PWM strategies. [ABSTRACT FROM AUTHOR]

Fault-tolerant control (FTC) strategies have been proposed to improve the reliability of power electronic systems. However, the FTC of the three-level T-type converter based shunt active power filter (SAPF) remains limited by redundant devices. To address this problem, an FTC strategy called sequential model predictive tolerant control (SMPTC) is combined with a nonintegral lexicographic optimization (LO) algorithm for solving multiobjective optimization problems. First, the power circuit, space voltage vector diagram, harmonic extraction, and prediction models of the SAPF system are introduced. Second, based on power-switch fault analysis, an adaptive dc bus voltage regulation method is proposed, which ensures that the candidate voltage vectors are fully utilized in the fault state. Third, an LO-SMPTC strategy is proposed by designing a sequential predictive controller that considers the neutral point (NP) voltage and the tracking of the SAPF output current. Compared with the traditional model predictive control, the proposed method not only achieves NP voltage balance and excellent harmonic compensation but also eliminates the selection of weighting factors, thereby improving the control flexibility and time efficiency. Finally, the effectiveness of the LO-SMPTC on the dc bus voltage, NP voltage oscillations, grid current power quality, and pole voltage under different scenarios is demonstrated through experiments. [ABSTRACT FROM AUTHOR]

This article proposes a high-level engineering guide to develop an integrated system model for power quality analysis in electrical submersible pump (ESP) applications with variable frequency drives (VFDs). Such analyses are troublesome in the industry due to the complexity of these systems. In this article, simple steps to perform system integration analyses of such arrangements, including torsional analysis, are developed. A simplified VFD-ESP model suitable for coupled electrical and mechanical analysis in steady state is proposed in all their configurations of practical interest. Such a model can be easily implemented in common simulation software, significantly reducing engineering efforts for implementation and analysis. The focus of the proposed model is the prediction of ESP failures that might result from a poor power quality caused by VFDs. Analytical expressions of different types of harmonics in these systems, as well as their accurate locations in the frequency domain, including their interharmonics and common-mode harmonics, are derived for this purpose. The effectiveness of the proposed model is verified through offline and real-time hybrid simulation results. Finally, a comparison between simulation results obtained using the proposed model and measurements collected on a down-scale laboratory prototype is carried out to demonstrate the accuracy of the suggested modeling approach. [ABSTRACT FROM AUTHOR]

The fast short-circuit fault ride-through capability of the inverter is an important indicator for the reliability of an independent power supply system. Fast short-circuit fault ride-through requires the inverter to output the short-circuit fault current quickly and reliably, which is conducive to shortening the duration of short-circuit faults and realizing fast short-circuit protection. In addition, when the single-phase inverter outputs a short-circuit fault current, the third harmonic in the short-circuit current may cause malfunction of the protection circuit. To effectively achieve the fast short-circuit current limiting and third harmonic suppression of the single-phase inverter, this article proposes a short-circuit fault diagnosis strategy and a current-limiting control strategy, respectively. The former is a short-circuit fault diagnosis strategy, and the latter is a fast current limiting control strategy based on adaptive reference feedforward and third harmonic elimination. The proposed strategies can enable the single-phase inverter to reach a current-limiting steady state within a fundamental period, which can greatly improve the response speed of single-phase inverters and achieve fast short-circuit protection. They can also be applied to three-phase inverters. A 35-kVA/50-Hz high-power single-phase inverter prototype is built to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In high-power applications, different multilevel voltage source converter (VSC) topologies are usually applied. The hybrid parallel multiconverters, which is a combination of multiactive and hybrid VSCs connecting in parallel, can be a promising solution in a high-power grid. In this article, the fusion VSC topology concept is proposed in which fusion VSC takes the advantages of both active (inductive coupling) VSC and hybrid (capacitive coupling) VSC. It corresponds to overcoming the insufficient-capacity problems when active VSCs are employed alone and vice versa. This article proposes fusion active power filter topology by combing active and hybrid power VSC through their equivalent model for power quality compensation. With the proposed VSC's equivalent model, it can reduce the converter rating by 17%–80% compared with the conventional approaches. Additionally, the corresponding control algorithm is proposed for the FAPF for power quality compensation. Finally, the simulation and real-time digital simulator hardware-in-the-loop experimental results of the proposed FAPF topology are given to demonstrate the validity and effectiveness for reducing its capacity and power loss compared with the conventional multi-VSC in power quality compensation. [ABSTRACT FROM AUTHOR]

In this article, a simple 18-pulse star rectifier using two new passive auxiliary circuits at dc link is proposed for reducing the harmonics content in ac line current. The proposed rectifier combines a double-star rectifier and four-tapped interphase reactor (FTIPR) with four diodes. Passive auxiliary circuits increase the state of the output voltage and current of the double-star rectifier, thereby increasing the pulse number of the load voltage and step number of the input line current. When FTIPR is optimally designed, passive auxiliary circuits convert double-star rectifier to 18-pulse star rectifier. Tap ratios of the FTIPR are determined based on minimum total harmonic distortion (THD) of the input line current and minimum ripple of the output voltage. The proposed rectifier simultaneously reduces ripple of the output voltage and THD of the input line current. A prototype is developed to verify the theoretical analysis through experimental results. Theoretical THD of the input line current is about 10.1%, whereas experimental THD is about 5.44%. [ABSTRACT FROM AUTHOR]

Aiming at the difficulties in modeling the active power filter (APF) system and the susceptibility to parameter perturbation and external disturbance, this article proposes a new adaptive sliding mode controller with using a nonlinear extended state observer (NESO) based on an interval type-2 fuzzy neural network (IT2FNN) structure. The IT2FNN is designed to estimate the unknown control coefficient, so that the NESO can estimate the state of the system and the total disturbance including the unmodeled dynamics and external disturbances, and then perform feedforward compensation to achieve active disturbance rejection. Simulation and experimental results show that the proposed control strategy is effective in the harmonic suppression of the APF system and has better steady-state and dynamic performance compared with the existing methods. [ABSTRACT FROM AUTHOR]

We present a hybrid analog/digital computing circuit to solve a selective harmonic minimization problem. The approach leverages favorable attributes of digital and analog controllers to yield a fast and scalable optimization solver. A digital microcontroller programs the cost function and other user-defined inputs to the optimization problem. Voltages in the circuit represent switching angles. In steady state, the voltages converge to Karush–Kuhn–Tucker (KKT) points of the problem. We present a specific realization of the computing circuit that solves for eight independent switching angles for a quarter-wave symmetric pulsewidth modulation (PWM) driven two-level single-phase inverter. Seven undesired harmonics are minimized while retaining control over the modulation index. The proposed computing circuit is verified with simulations and a hardware implementation. The experimental results demonstrate that the proposed circuit can converge to the optimal solution in less than 5.0 ms, which is substantially faster than the existing methods and facilitates real-time implementation. Moreover, the steady-state power consumption of the hardware implementation is approximately 750 mW, which is also significantly lower than the published methods for comparable applications. The computing circuit is utilized to generate the PWM for a 2-kW single-phase inverter, which validates its feasibility in practical applications. [ABSTRACT FROM AUTHOR]

Variable switching frequency sinusoidal pulsewidth modulation (VSFSPWM) method does well in many aspects such as lower harmonic peak and losses compared with constant switching frequency sinusoidal pulsewidth modulation (CSFSPWM) for DCAC converters. This article presents a passive VSFSPWM (PVSFSPWM) method for spectrum improvement, filter inductor reduction, and losses reduction, obtaining similar output current quality as that of the CSFSPWM method. Because the PVSFSPWM method does not need any feedback information compared with the model-predictive-based method, it is an open-loop method and is called the passive method. In order to obtain the law of harmonic distribution, the mathematical expression of harmonic spectrum distribution is derived. The required filter inductor under the same current ripple and the losses between CSFSPWM and PVSFSPWM methods have been compared. Simulation and experimental results show that the PVSFSPWM method achieves excellent performance in EMI suppression, inductance, and losses reduction without impairing the output quality. [ABSTRACT FROM AUTHOR]

Series-connected multipulse rectifiers (MPRs) are used to provide high-quality electric power for high-voltage and high-power occasions. Due to conventional MPRs have limited harmonic reduction ability that cannot fulfill the related harmonic standard, some effective dc side harmonic reduction methods have been proposed to further improve power quality of the MPRs. This article gives a comprehensive review on dc link harmonic reduction methods of series-connected MPRs. Passive and active harmonic reduction mechanisms are respectively analyzed based on two typical topologies, which are theoretical foundations for understanding and constructing novel harmonic reduction circuits (HRCs). Some useful dc side HRCs are presented and compared from aspects of their performances, complexity of the overall structure, magnetic device capacity and power losses, etc. The necessary simulation results are given to verify and compare the effectiveness of some involved harmonic reduction methods. Based on these topologies, the advantages, drawbacks and future trends of the passive or active methods are concluded; besides, the hybrid harmonic reduction methods are also considered. This article aims to provide useful guidance for the researches of harmonic elimination and multipulse rectification technology. [ABSTRACT FROM AUTHOR]

Simultaneous wireless power and data transfer (SWPDT) is widely investigated because of the increasing requirement for real-time communication between the primary and secondary sides in wireless power transfer systems. This article classifies SWPDT systems into four categories according to the type and number of data channels and data carrier generation method. They are power carrier-based SWPDT system, high-frequency data carrier-based SWPDT system, multiple inductive channels SWPDT system, and inductive–capacitive hybrid channels SWPDT system, respectively. Four key issues, including cross-talk minimization, improvement of signal-to-noise ratio, modulation method for high data rate and low bit error rate, and special design to achieve full-duplex communication and improve misalignment tolerance, are discussed. The advantages, disadvantages, and applications of the four types of SWPDT systems are summarized. Finally, conclusions and outlook of the SWPDT system are given. [ABSTRACT FROM AUTHOR]

Power electronic converter can produce massive voltage stresses on the connected transformer, with great effects on electrical ageing of the insulation. Such effects can be diverse upon different insulation components under different harmonic voltages, which have not been well clarified. This article aims at enhancing online monitoring of converter transformers from two aspects. First, electrical ageing evaluation models are developed for different types of transformer insulation. It is the first time to clarify the effects related to the component location and the ageing severity under differential-mode and common-mode (CM) voltages. Interlayer (IL) insulation faces a serious ageing threat and the line-lead component is aged with the severest degree. Second, CM voltages are used to build transfer function (TF) measurement for IL insulation monitoring. The key is to identify the optimal monitoring frequency with the highest sensitivity. Based on the analytical case introducing typical parameters, the TF performance is analyzed in different ageing conditions. Online experiments validate that the proposed method is effective and has good application prospect. The contributions lie in that the diverse ageing effects of converter harmonic voltages on different insulation components can be distinguished and online monitoring of IL insulation can be achieved effectively. [ABSTRACT FROM AUTHOR]

For the conventional resistive active power filter based on impedance matching idea in transmission line theory, which aims to damp out background harmonic propagation on the distribution feeders. The so-called damping refers to the suppression of the existing harmonic propagation, but there is no ability to attenuate the source harmonic voltages along the feeder under all cases theoretically. This article focuses on how to attenuate the source harmonic voltages along the feeder to achieve better performance. Not being based on the impedance matching idea, the proposed standing wave phase shifting active power filter moves the phase of the harmonic voltage standing wave so that the antinode of standing wave closes to or exactly located at the beginning of the feeder to achieve harmonic attenuation. According to the relationship between the wavelength of the harmonics and the feeder length, the application range and the control parameters of standing wave shifting to the left and to the right strategy are discussed, respectively. Finally, the correctness of the theoretical analysis and the effectiveness of the proposed scheme is verified by the simulations and experiments. [ABSTRACT FROM AUTHOR]

In an autonomous ac microgrid system, a peer-to-peer decentralized solution would be a preferred choice for the coordinative control of distributed generation units. However, due to the dispersed sources and loads, and mismatched line impedances, it is hard to achieve satisfactory power sharing performance and power quality without communication links. Therefore, a comprehensive decentralized solution based on dual-frequency-droop is proposed in this article. With only local information, appropriate virtual impedances could be obtained to compensate the mismatched complex line impedances in the required frequency range, and hence active, reactive, unbalanced, and harmonic powers could be shared accurately among parallel inverters under various load conditions. Then, the frequency deviation caused by the droop control is effectively attenuated without affecting power sharing through a dynamic droop-slope regulator. Moreover, the causes of steady-state ripples on virtual impedance waveforms are carefully analyzed, and the design criterions to eliminate these ripples are provided. Finally, case studies are provided in simulations and experiments to validate the effectiveness of this method. [ABSTRACT FROM AUTHOR]

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