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ABSTRACT The unidirectional multilevel rectifier has immense potential in high‐power medium‐voltage industrial applications. This paper proposes a multiobjective control method based on the combination of optimal‐vector‐pair modulated model predictive control (OVP‐M2PC) and a phase‐shifted modulation strategy for a unidirectional five‐level rectifier. This strategy takes both of the inductor current tracking and capacitor voltage balancing as the control objectives. First, an optimal vector pair is determined based on the AC‐side current variation rate, and then, through combining the calculated action duration of OVP with carrier phase‐shifted modulation, inductor current tracking is achieved. Second, capacitor voltage balancing control is carried out by compensating for the duty cycles which also decouples the input current tracking and output capacitor voltage balance control. Compared with traditional FCS‐MPC, under the proposed control strategy, complex cost function calculation and weighting factor tuning are not required, which much reduced computational burden. Multiobjective control is achieved with better performance in both steady‐state and dynamic conditions. The superiority of the proposed strategy over traditional FCS‐MPC are validated through simulations and hardware experiments. [ABSTRACT FROM AUTHOR]

Incorporating AC-type flying capacitors (FC) between series-connected devices is an effective way to enhance the rated voltage for high-power applications based on current source converters (CSCs). Through appropriate modulation and FC voltage control, it is possible to achieve improved DC bus voltage quality with reduced common-mode voltage (CMV) and low dv/dt. On the other hand, the parallel CSC is a popular choice for increasing the system's rated current to accommodate higher power applications. The use of interleaved modulation techniques can improve the harmonic performance of parallel converters while reducing the need for passive filters. The modular flying capacitor clamped (FCC)-CSC structure can combine these advantages, achieving higher rated power along with improved power quality on both the DC and AC sides. Moreover, the enhanced AC quality contributes to the regulation of FC voltage and further improves the DC-side voltage quality. This paper analyzes the operation principle of the parallel FCC-CSC structure and proposes an interleaved space vector modulation (SVM) method to enhance the harmonic performance of the AC output. Additionally, an optimized zero-state replacement (ZSR) based FC voltage control and a DC-link current balance strategy built on this control are introduced. Simulation and experimental results validate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

A modular multilevel converter (MMC) is reflected to be an emerging multilevel topology for medium- to high-power induction motor drives due to its highly reliable structure, modularity and scalability. However, large circulating current produced in the phase arm of MMC during low-speed operation of induction motor drive is a major drawback of MMC, which leads to affect the size of a sub-module capacitor, inductor and switch rating. To mitigate the circulating current and improve the performance of MMC-fed induction motor drive, this paper proposed a new circulating current error compensator (CCEC) technique with reduced arm current peak. By proper control of instantaneous voltage between arms and DC link current, second-order fundamental frequency current harmonic from circulating current is eliminated which leads to a significant reduction in circulating current. A comparative evaluation between conventional control scheme and the proposed CCEC control scheme is presented. The performance and effectiveness of the proposed CCEC technique are validated using a MATLAB-based simulation. Scale-down laboratory experimental setup is also developed to check the effectiveness of the proposed CCEC control technique. Reduction in circulating current for entire speed range with improved DC link current profile is observed as compared to conventional circulating current suppression control. [ABSTRACT FROM AUTHOR]

The low-harmonic (LOH) voltage of the DC link of three-phase voltage source converter (VSC) requires a large aluminum electrolytic capacitor for suppression under nonlinear AC current. Consequently, this work proposes an active decoupling control method combining DC-link LOH voltage closed loop and LOH current feedforward based on a DC–DC converter. This methodology effectively transfers the DC-link LOH voltage to the smaller-sized decoupling capacitor in the DC–DC converter, thereby reducing the number of capacitors required to stabilize of the VSC DC-link voltage. This work first investigates the relationship between the DC-link LOH voltage and the VSC nonlinear current. Second, a mathematical model for the decoupling capacitor voltage is derived, indicating that its voltage form is complex under nonlinear AC current, making direct voltage control arduous. Subsequently, the principle and design process of the proposed active decoupling control strategy are analyzed in detail. A dedicated fast-response filter structure is also utilized to extract the feedback LOH voltage and feedforward LOH current in the DC link. Meanwhile, a simple control strategy for the DC component of the decoupling capacitor voltage is proposed to improve the utilization of the decoupling capacitor. Finally, the effectiveness and correctness of the method are experimentally verified. [ABSTRACT FROM AUTHOR]

This paper proposes a smooth mode-switching method based on state trajectory control to suppress overshoot and to shorten switching time during the mode switching of LLC-C resonant converters. First, the resonant tank trajectories of the LLC and LCCL are analyzed. Second, through a transformation of the resonant tank trajectory, the optimal trajectory of the resonant tank switching is drawn. Then the switching optimization cycle time is calculated by a diagram of the optimal trajectory. Thus, the PWM conversion to the optimization cycle is controlled directly when the switching signal comes. By this control method, a smooth transition of the resonant tank voltage and current between the two modes is achieved. At last, a prototype with a rated power of 500 W is built to check the feasibility and effectiveness of the proposed switching method. Experiment results show that the current surge of the resonant tank is reduced from 12.3 to 8.6 A when the state trajectory control is applied. The voltage surge of the second resonant capacitor in parallel is reduced from 906 to 712 V. Meanwhile, the switching time is shortened by 0.21 ms, which speeds up the switching process. [ABSTRACT FROM AUTHOR]

A wide band trans-impedance amplifier (WBTIA) with tunable bandwidth for near infra-red spectroscopy (NIRS) bio-medical applications is presented in this research article. The first stage of the proposed WBTIA is implemented by a modified inverter-cascode (InvCas) trans-impedance amplifier (TIA) with series and shunt inductive peaking for the bandwidth extension and a common-source amplifier as a second stage for gain boosting. Bandwidth tuning is achieved by a novel tuning mechanism with a fixed capacitor and tunable metal-oxide-semiconductor (MOS) capacitor with a control voltage. The fixed capacitor provides a coarse-grain bandwidth tuning whereas the tunable MOS capacitors are used for finegrain bandwidth tuning. The WBTIA is designed in 45 nm technology and it achieved a maximum trans-impedance gain (TIG) of 84.91 dBO and 354.81 MHz bandwidth. The proposed WBTIA consumes 41.24 µW power from 1 V supply voltage. The input referred current noise at 100 MHz is 169 fA/sqrt (Hz) and the output noise voltage is 69.8 pV/sqrt (Hz). [ABSTRACT FROM AUTHOR]

This paper presents a novel generalized step‐up switched‐capacitor multilevel inverter (SCMLI) appropriate for low/medium voltage input applications. To reduce the overall number of power switches, the suggested topology makes use of reduction switch count (SC) technology. The complementary working mechanism of each pair of switches simplifies the modulation method. The complete inductive‐load capability is taken into account in the proposed inverter. Furthermore, because capacitor voltages are automatically balanced, complex voltage control circuitry is not necessary. Due to a reduction in current spikes on the devices, the topology also has the ability to soft‐charge the capacitors in a quasi‐resonant manner. Performance is also enhanced by extending the lifetime and dependability of the inverters. The construction, operation, modulation method, values of the capacitors, and circuit losses are explained to demonstrate how the suggested topology should function. One of the inverter's primary differentiators from the others is its double‐boosting capability based on reduced components. Based on loss calculations, a thorough analysis of the suggested topology's efficiency of 98.31% is presented. Next, the benefits of the suggested inverter are compared to those of other inverters that have been recently suggested. The steady‐state and dynamic performance of the suggested topology is then confirmed by modeling the system on the Simulink platform and performing experiments using a DSP‐based prototype experimental setup. [ABSTRACT FROM AUTHOR]

This letter derives and discusses the superiority of a simple dc-link capacitor voltage control configuration for multilevel neutral-point-clamped converters with any number of levels. The control involves n − 2 control loops regulating the difference between the voltage of neighbor capacitors. These control loops are inherently decoupled, i.e., they are independent and the control action of one loop does not affect the others. This method is proven to be equivalent to previously published approaches, with the added advantages of increased simplicity and scalability to a higher number of levels, all while imposing a lower computational burden. The good performance of such control is confirmed through simulations and experiments. [ABSTRACT FROM AUTHOR]

The issue of sub-module (SM) capacitor voltage unbalance is a hot topic in the current research into the modular multilevel converter (MMC). An excellent strategy comprises mitigating the SM capacitor voltage imbalance by adjusting the SM on time. The traditional capacitor voltage balancing control regulates the speed to maintain accuracy. A unique SM capacitor voltage balancing control strategy is presented in this paper and is based on conventional capacitor voltage balance management and neural network prediction. Firstly, the SM capacitor voltage and arm current are speculated by operating the time series forecasting technique in real time, considering the dynamic changes in the SM capacitor voltage and arm current. Secondly, the SM capacitor voltage distinction between the actual and theoretical value is determined, and a deviation's mixed Gaussian distribution is established to estimate its compensation voltage. Thirdly, the SM triggering sequence is anticipated by using the neural network along with the pilot values of the SM capacitor voltage, arm current, and the offset compensation value, and the control is executed. Finally, a three-phase, six-leg, eight-module, nine-level MMC model is built to verify the feasibility of the suggested approach. [ABSTRACT FROM AUTHOR]

In this article, a generalized control scheme is proposed to extend the operating range of three-phase hybrid cascaded H-bridge (HCHB) inverters into various voltage levels without necessitating alterations to the core structure or the integration of additional H-bridge submodules. This study addresses a critical challenge related to capacitor voltage drift at various modulation indices and power factors, which is a serious impediment to various applications. To overcome this challenge, a novel balancing control scheme has been developed based on the injection of two independent offset voltages to simultaneously control the DC-link and flying capacitors. A distinctive aspect of the proposed technique involves adjusting the common reference voltage to attain the nearest level in the same cluster, thereby mitigating the insufficiency of redundant switching states. The effectiveness of the proposed technique to regulate the capacitor voltages at various operating conditions has been verified through simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents the performance analysis of a five-level T-type multilevel inverter (MLI) based six-phase induction motor drive (SPIMD) for high-power industrial applications. In the adopted T-type MLI, the sensorless self-capacitor voltage balancing control is designed, which controls the voltage across the capacitor at half the magnitude of the direct current (DC) source value, creating a symmetrical five-level output voltage waveform. Moreover, self-capacitor voltage balancing control reduces complexity and improves system performance. The SPIMD with distributed neutral is taken as the load, and the whole system is simulated using MATLAB/Simulink software. The system's performance is determined by considering the power loss and efficiency. This paper also presents a comparative performance analysis of the adopted T-type, cascaded h-bridge (CHB) and Flying Capacitor (FC) MLI-based SPIMD. Finally, a prototype is developed as a proof of concept and tested experimentally to validate the analytical development of the adopted system. [ABSTRACT FROM AUTHOR]

This paper introduces a cost-effective control method to enhance the low voltage ride-through (LVRT) capability and smooth the output power of a three-phase multilevel flying capacitor inverter (FCI) in wind turbine-based permanent magnet synchronous generator (PMSG). The proposed approach utilizes the energy storage capability of flying capacitors to mitigate wind power fluctuations and address short-duration outages and deep voltage sags. Additionally, a nonlinear controller based Lyapunov theory is developed to regulate capacitor voltages, improve power factors, and balance DC-link voltage. Numerical simulations are conducted in MATLAB/SimPower systems environment to validate the effectiveness of this comprehensive control strategy across different grid operation scenarios. [ABSTRACT FROM AUTHOR]

The problem of submodule switching frequency reduction in half‐bridge modular multilevel converters (HB‐MMCs) with capacitor voltage self‐balancing control is considered and explored in this paper. A selection principle of submodule switching state vectors is proposed based on the voltage self‐balancing switching state matrix, aiming to lower submodule switching frequency and device losses. The relationship between system stability and submodule switching signals is revealed according to the capacitor voltage self‐balancing characteristics, and the full‐rank constraints on the voltage self‐balancing switching state matrix are proposed. Considering the tradeoff between switching loss and capacitor voltage fluctuation, the evaluation indexes of voltage self‐balancing control effect are determined. The selection principle of submodule switching state vectors and the optimized construction method of switching state matrix are presented. Voltage self‐balancing HB‐MMC models are built in MATLAB/Simulink, and it is verified that the submodule switching state vector selection principle proposed in this study can effectively reduce switching frequency while meeting the evaluation requirements of practical engineering projects, so as to achieve the balance between switching loss and steady‐state capacitor voltage fluctuation. [ABSTRACT FROM AUTHOR]

This paper proposes a discrete space vector modulation and optimized switching sequence model predictive controller for three-level neutral-point-clamped inverters in grid-connected applications. The proposed strategy is based on cascaded model predictive control (MPC) for controlling the grid current while maintaining the capacitor voltage balanced without weighting factor. To enhance the closed-loop performance, the external MPC evaluates 19 basic and 138 virtual vectors (VV) of the proposed space vector method. The optimal control voltage is then selected using an extended deadbeat method to reduce the execution time of the proposed control algorithm. By using the discrete space vector modulation principle, the VV are synthesized based on switching sequence (SS) and are divided into negative and positive SSs considering their impact on the neutral point (NP) potential. The inner MPC evaluates both types of SSs and selects the one that keeps the capacitor voltage balanced. Various controllers are evaluated and compared against the proposed control strategy. The results show that the proposed strategy improves performance without weighting factor, while maintaining a total harmonic distortion of current to be less than 2%. Compared to the modulated MPC which provides the same fixed switching frequency, the proposed controller reduces the computational burden by over 50% while also providing better NP voltage balance accuracy. [ABSTRACT FROM AUTHOR]

Summary: Nowadays, Z‐source inverter (ZSI) has received several attentions compared to other power converters owing to their simplicity and reliability. In this paper, a refine control methodology of capacitor voltage control is presented based on third‐order small signal analysis. The proposed control is applied to the improved switched inductor ZSI (ISL‐ZSI). Proportional, integral, and derivative controller (PID) is adopted due to their capability to operate with large operation levels, reliable operation, and cheaper implementation. In addition, the function of this control can be achieved even with incomplete system data or parameters variations. ISL‐ZSI has been presented because of its advantages such as the high gain of direct current voltage, low voltage stress for both the Z‐network and the inverter bridge switches, and ensuring good soft starting. In addition, the inrush current has been removed based on its configuration. The proposed control is validated by both experimental and simulation results under input voltage change, load change, and steady‐state operations using DSP F28335 and MATLAB SIMULINK Real‐Time Workspace. [ABSTRACT FROM AUTHOR]

This paper deals with the stability analysis and enhancement in the AC‐microgrid system comprising parallel‐operated voltage‐source inverters (VSIs) supplying an active‐load. The active‐load behaves such as a constant power load from the AC‐side. In the paper, two models for the active‐load modeling in the AC microgrid are considered: (i) simple model in which the active‐load is modeled as an ideal current source, (ii) detailed model in which all dynamics of the active‐load converter and related controllers are taken into account. The main findings and contribution of this paper are as follows. (a) All linearized state equations of the study system are extracted and transferred into a unified common dq‐reference frame, and then, small‐signal stability of the study system is carried out in the common reference frame by using the simple and detailed models of the active‐load. (b) It is shown that the simple model of the active‐load, as a current source, leads to more pessimistic results in comparison to the active‐load detailed model. (c) Impacts of the active‐load power and bandwidth of the active‐load voltage control loop on the system stability are examined. (d) Control of the generation‐side VSIs is modified and a stabilizing approach, called generation‐side virtual capacitor, is proposed for stabilizing the system under high active‐load penetration. Next, modal analysis and time‐domain simulations are used to investigate the study system responses with and without the proposed stabilizing approach. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper proposes a novel voltage balancing control approach for the flying capacitors in a five-level Active-Neutral-Point-Clamped inverter (ANPC). The projected method is based on the control signal of the flying capacitor (FC) voltage. A Staircase reference voltagebased Phase-Shifted PWM (PS-PWM) technique is used to generate the different levels and simple logic-equations. The proposed control can regulate the voltage of the FC at the requested reference value and generate the required five-level output voltage with fast dynamics. It requires fewer and simpler calculations and it has a fast execution time. The Simulations are performed using MATLAB and Simulink. The obtained results demonstrate the good performance of the FC voltage control and the high quality of the output voltages and current spectrum. [ABSTRACT FROM AUTHOR]

This paper explores some efforts to suppress the voltage surge appearing during the operation of a SiC-MOSFET-based half-bridge circuit in an inverter topology. The study is important to carry out, as the voltage surge problem does not come up when a Si-IGBT is used as the switching component in the half-bridge; however, some applications demand certain properties like what is found in a SiC-MOSFET. Compared to Si-IGBT with rise-time/fall-time larger than 100 ns in general, the use of SiC-MOSFET is preferable due to its much shorter switching time, less than 50 ns, which brings about a much lower switching loss and lower operating temperature. However, the choice of the usual electrolytic capacitor in the dc-link would produce an undesired voltage surge during the half-bridge operation. The origin of the surge is sometimes assigned to the inductance parasitic effect of the SiC-MOSFET high frequency. This research proves the benefit of a film capacitor to suppress the surge due to its lower equivalent series resistance (ESR) than that of the electrolytic capacitor. The results contribute to the consideration to take during the circuit realization in various applications, as there are not many papers yet found discussing the use of film capacitor in the dc-link of a SiC-MOSFET half-bridge inverter. This study also reveals the importance of the film capacitor placement during the design stage of SiC-MOSFET applications; moreover, motor controllers being equipped with an inverter such as described in this study have not been found yet in the market. The efforts investigated in this work would help to control the undesirable voltage spikes that frequently occur when applying a SiC-MOSFET to a half-bridge inverter design. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Synchronized switch damping on negative capacitance (SSDNC), as one of the nonlinear synchronized switch damping (SSD) techniques, has been received much attention in recent years. The damping effect depends on the effective voltage on the piezoelectric actuator in SSDNC control. The applicable bipolar voltage of a piezoelectric element is unsymmetrical. However, the voltage on the piezoelectric actuator is applied symmetrically in SSDNC, which greatly wastes the driving capability. An unsymmetrical SSDNC (un-SSDNC) is proposed in this paper to further boost the voltage on the PZT actuator and make full use of the driving ability to improve the control performance. A bypass capacitor, two diodes and switches are attached to the SSDNC circuit to realize unsymmetrical bipolar voltage. The control logic of the switches is introduced and the switched voltage is derived as well as the control performance. Experiments and simulations were carried out to verify the designed circuit and the theoretical results of the switched voltage. The influence of the bypass capacitor on the switched voltage and the stability of the un-SSDNC system were investigated. The voltage ratio and control performance increase with increasing bypass capacitor, but too large of bypass capacitor will cause the problem of system stability. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) tends to cause resonance instability in interconnected systems. Current studies on the stability of MMC mainly focus on high-voltage and large-capacity power systems, while the impedance modeling process of MMC ignores the harmonics of the submodule (SM) capacitor voltages and the influence of voltage feedforward control. The applicability of the MMC impedance model with fewer submodules is doubtful. According to the circuit structure and control mode, the AC-side sequence impedance model of the MMC is established, which takes into account the capacitor voltage balance control of submodules and voltage feedforward control. Based on the RT-Lab control hardware-in-loop (CHIL) test platform, the MMC impedance frequency scanning was carried out to verify the accuracy of the impedance modeling method. The influence of control parameters in different frequency bands on the impedance characteristics of MMC was studied. The AC terminal voltage feedforward causes phase lag in the mid-/high-frequency range and increases the risk of resonance. In the low-frequency range, the dynamics and control of capacitor voltages reduce the impedance magnitude of MMC. Using the resonance phenomenon of an MMC connected to a weak grid as an example, the high-frequency resonance mechanism caused by control parameters is analyzed from the perspective of the negative damping effect. The simulation results show that the detailed wideband impedance model can improve the accuracy of the stability analysis results. [ABSTRACT FROM AUTHOR]

Single-loop current sensorless control allows for abolishing of the instantaneous current measurement in the control system using only a single control loop with voltage feedback to stabilise the DC-bus voltage. This approach eliminates current sensors in the control circuit, benefiting from saving space on the printed circuit board and minimising power dissipation in the current measurement circuitry. This paper focuses on the single-loop current sensorless control applied to bidirectional three-phase four-wire three-level NPC MLC by simulation analysis and demonstrates the performance of the proposed current control algorithm in the rectifier and inverter modes and the step response with power direction change and grid-voltage change. In capacitor voltage balancing, an additional controller is applied, which is capable of compensating for the voltage asymmetry caused by adding a 2.5 kOhm resistor in parallel to one of the DC-bus capacitors. Our results demonstrate good performance of the proposed control method both in the inverter and rectifier modes, showing stable current shape in the low power and full power modes with acceptable harmonics content, meeting the requirements of the IEC 61000-3-2 standard for Class A devices. The analysis showed that the proposed control approach is suitable for industrial application. [ABSTRACT FROM AUTHOR]

Summary: Since the output voltage accuracy of the off‐grid inverter is low with the proportional‐integral (PI) control and a two‐stage inverter is often used in the low input voltage application, a single‐stage buck‐boost off‐grid inverter with feedforward control is proposed. The proposed inverter consists of a buck‐boost converter and a full‐bridge inverter. The buck‐boost converter operates at high frequency, while the full‐bridge inverter operates at line frequency. Therefore, the intermediate bus voltage is controlled as the unipolar half‐cycle sinusoidal voltage wave to reduce the voltage stress of semiconductors, and film capacitors can be used as intermediate bus capacitors for high reliability and high power density. The operating principle is illustrated. Design guidelines and example are given. The stability analysis and external characteristic analysis are given. A 500‐W proposed inverter is constructed to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

Flexible direct current (DC) grids face a serious challenge in terms of rapidly isolating DC faults. A DC circuit breaker is an effective solution for DC fault isolation. To improve the fault-isolation and reclosing capability of flexible DC systems, a new high voltage direct current (HVDC) circuit breaker topology with adaptive reclosing capability is proposed in this paper. The topology of the circuit breaker is a T-shaped structure, which has the ability to break the current in both directions and effectively reduce the cost of components. Meanwhile, after the fault is cleared, the circuit breaker is controlled to inject a voltage signal into the line. Based on this, to prevent the circuit breaker reclosing in the event of a permanent fault from having an impact on the system, a method for fault identification based on Euclidean distance that uses the voltage signal to identify the fault properties is proposed. Finally, the performance of the circuit breaker is simulated and verified by PSCAD/EMTDC simulation software, and compared with the typical existing circuit breakers to verify the effectiveness of the circuit breaker and reclosing scheme. [ABSTRACT FROM AUTHOR]

Single-phase rectifiers are one of the most practical instruments with various applications. Among them, active front-end (AFE) rectifiers are introduced with bidirectional power transfer capability for power factor correction and the elimination of current harmonics. This paper proposes an adaptive model predictive control (MPC) for a single-phase AFE rectifier. The AFE topology used in this paper is a half-bridge boost converter. This topology has higher efficiency than other single-phase AFEs due to the fewer number of active semiconductor devices. Considering the presence of one leg of capacitors in this topology, balancing the voltages of these capacitors is a challenge, along with other control objectives. Also, this paper benefits from an MPC approach by which the switching signal for every switching state is chosen such that the defined cost function is minimized in the operation state to achieve all control goals based on the predefined model of the rectifier. Furthermore, an adaptive algorithm for the inductor current estimation is presented to robustify the control system against any unwanted disturbance in the control system. As a demonstration of the superior performance of the proposed method, a 1kW rectifier setup with 700Vdc output voltage fed from a 230Vrms/50Hz grid is built in the laboratory. The applicability of the MPC controller is verified and all operation waveforms of the test setup are presented. The proposed method offers a high-quality input current with total harmonic distortion (THD) below 5% and a high-power factor (PF) close to one. Also, the efficiency is comparable with the available commercialized rectifiers. [ABSTRACT FROM AUTHOR]

When the input inductor operates in discontinuous current mode (DCM), the Cuk converter can automatically achieve power factor correction (PFC) function with only a simple voltage mode control loop. However, the conventional Cuk PFC converter suffers from high intermediate capacitor voltage because of the lack of feedback of the intermediate capacitor voltage and relatively low power factor (PF). In this paper, a Cuk PFC converter using variable inductor which varies with the transient rectified input voltage is proposed to enhance the PF and reduce the intermediate capacitor voltage by injecting a controlled DC bias current into the auxiliary winding of the variable input inductor. The operating principles of the proposed Cuk PFC converter based on variable inductor are analyzed in detail, and the analysis of PF, the voltage of intermediate capacitor, and design considerations are provided. To verify the feasibility of the proposed scheme and compare the characteristics of both the traditional and proposed Cuk PFC converter, a 108W experimental prototype of the proposed converter is built and tested. The experimental results show that the proposed Cuk PFC converter can significantly enhance the PF, decrease the intermediate capacitor voltage, and increase efficiency compared with the traditional Cuk PFC converter. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to improve the performance of the transformerless modular multilevel converters (MMC) under AC and DC grid fault conditions, this paper proposes an improved four‐layer capacitor voltage control strategy combined with arm current control. The proposed control strategy consists of overall submodule capacitor voltage averaging control, leg‐balancing control with flexible weight factor W, arm‐balancing control with zero‐sequence suppression, and inner‐arm individual balancing control. The new concept of weight factor W for leg‐balancing control is also originated, considering negative‐sequence current and DC circulating current jointly from power point of view. The proposed approach effectively realizes the capacitor voltage balance, ac‐side current tracking, and unwanted circulating current elimination. The practical implementation of the proposed control strategy and the experimental results from a downscale three‐phase transformerless MMC prototype are presented to validate the performance of the proposed four‐layer capacitor voltage control strategy under grid faults. [ABSTRACT FROM AUTHOR]

The open-winding permanent magnet synchronous motor (OWPMSM) system is a novel high-cost system that uses dual-inverters to control both sides of the stator to improve the performance of the motor. To save the system cost, the three-phase four-switch open-winding permanent magnet synchronous motor (TPFS-OWPMSM) system is proposed to replace the general three-phase six-switch OWPMSM system, but it brings the problem of bridge arm capacitor voltage offset. To solve the instability problem caused by capacitance, this paper carries out the state analysis and offset source analysis of the inverter capacitor voltage, and proposes a dual-inverters capacitor voltage balance control strategy. The capacitor balance control converts unstable capacitor offset voltage into current and injects the currents into the stator current loop through closed-loop correction. And this strategy includes the optimal control of different capacitors under dual-inverters with the goal of system stability. The effectiveness of the balancing strategy is verified by the simulation of various motor working conditions. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMC) are frequently used in industrial applications thanks to their modular structure and quality output waveform. Nearest level modulation (NLM) method is preferred in MMC applications. Selection of the sampling frequency value for the NLM method is important in terms of the MMC output performance parameters. In addition, a capacitor voltage balancing scheme is necessary to control the capacitor voltages of the MMC submodules. In this article, a generalized capacitor voltage balancing scheme using NLM method is proposed and effect of the sampling frequency on the output parameters of the MMC is analyzed. The proposed method can be adapted to all possible cases by generalizing according to the use of different number of submodules. Thanks to the proposed method, the capacitor voltage balancing process is accelerated and a positive effect is made to the MMC performance by using all submodules as equally as possible. The proposed method is applied to the upper and lower arms of the MMC and arm voltages are controlled. Also, effect of the sampling frequency on balancing quality of submodule capacitor voltages as well as the total harmonic distortion and fundamental frequency component magnitude values of the output waveforms are analyzed. Changes on the output parameters and capacitor voltages of the MMC are investigated at 0.5 kHz, 5 kHz and 20 kHz sampling frequency values in the designed MMC model. The applicability of the proposed method and sampling frequency analysis are tested and demonstrated in the simulation environment with the help of different case studies. [ABSTRACT FROM AUTHOR]

Capacitor voltage balancing is a critical issue for neutral-point-clamped-based converters, including the two/three-level dual-active-bridge dc–dc converters. The unbalanced capacitor voltage will increase the voltage stress on power devices and negatively affect the reliability of the converters. Two typical problems during the capacitor voltage balancing process should be solved, i.e., power fluctuation minimization and determination of the transformer current polarity. Accordingly, this article proposes a balancing control scheme based on the complementary switching-state (CSS) method. In the CSS method, the switching states, which are identified to be adverse for balancing, will be replaced by their corresponding CSSs to control the neutral-point current while keeping the voltage and current waveforms unchanged. By doing so, the power fluctuation and current overshoot during the balancing process can be significantly reduced. Moreover, since the dynamic voltage and current waveforms are identical to the steady-state waveforms, the transformer current polarity during the balancing process can be identified based on the steady-state power and current models. Therefore, the determination of the transformer current polarity can be simplified compared to the traditional balancing control scheme. Finally, experimental results are carried out to verify the performance of the proposed balancing control scheme. [ABSTRACT FROM AUTHOR]

Wireless power transfer system has played an important role in rail transit, industrial production, and daily life. This article proposes a wireless power transfer permanent-magnet synchronous motor (WPT-PMSM) drive system based on the matrix converter (MC). The direct conversion of low-frequency ac and high-frequency ac is realized without dc link by using MC. The dual LCC compensation network is designed for better performance. In addition, a new control method has been proposed for the proposed WPT-PMSM drive to operate stably. In particular, the bidirectional power flow is achieved with the proposed WTP-PMSM drive and related control scheme. Through the mathematical modeling, the coordinated control of power converters on both sides of the coupling coil is achieved and the reactive power of the LCC compensation network is eliminated. The experiments on a 1 kW and 85 kHz laboratory prototype of the WPT-PMSM drive are presented to verify the feasibility and effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

Low-speed drive is one of the challenges for modular multilevel converters (MMCs) due to large capacitor voltage fluctuation. In this article, a cascaded MMC and cycloconverter (CCV) based machine drive system is proposed to ensure stable operation of medium-voltage and low-speed machine. The MMC provides medium-frequency ac voltage for the CCV, and the CCV converts the medium-frequency ac input to low-frequency ac output required by the machine. Detailed analysis about MMC's operation frequency, device current stress, and submodule (SM) capacitance are given in this article. Proposed drive system can operate at zero/low frequency under rated load torque, while the SM capacitance is much smaller than that in existing methods. Simulation and experimental studies are conducted, and the results verify the effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

Multilevel inverters (MLIs) featuring reactive power ability and common ground (CG) have become much popular in transformerless grid-tied photovoltaic applications. A switched-capacitor (SC) based five-level transformerless inverter configuration is thus proposed in this article, which requires only six switches, one diode, three capacitors, and one input dc voltage supply. Notably, only four power switches are operated in high frequency, thus, the switching losses are reduced. Moreover, the presented topology can effectively tackle the leakage current problem using a CG architecture. A multicarrier phase disposition pulsewidth modulation strategy is employed to achieve reactive power regulation and SC voltage self-balancing. To achieve the neutral point voltage balance of the presented five-level inverter, a simple closed-loop voltage-balancing control method is proposed. The operation principles with modulation strategy and voltage self-balancing of SC are discussed in depth. Comparisons between the proposed and the state-of-the-art MLIs are presented in detail. Finally, experimental tests on a single-phase 1.1-kW prototype validate the appropriate performance of the proposed inverter. [ABSTRACT FROM AUTHOR]

An improved voltage balancing control (VBC) method is proposed in this paper to optimize control performance of single‐phase cascaded H‐bridge rectifier (CHBR). Firstly, the steady‐state error of the VBC method based on capacitor energy estimation is analyzed. An error compensation method is therefore presented to eliminate the steady‐state error. The proposed method delivers fast dynamic performance without steady‐state error. In addition, it requires less parameter tuning than traditional proportional‐integral‐based (PI‐based) VBC methods, and coupling effect between the upper‐ and the lower layer control system is also eliminated in both dynamic and steady state. Moreover, a mixed second‐ and third‐order generalized integrator (MSTOGI) method is applied to suppress the dc offset of grid voltage, which may occur in the process of sampling or conversion. Finally, a physical experiment platform is developed and a series of comparisons are given to verify the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) have become one of the most popular power converters for medium/high power applications, from transmission systems to motor drives. However, to operate the MMC, typical control schemes use a voltage measurement per submodule (SM), which increases dramatically the number of sensors required to build an MMC, adding complexity in terms of communications and increasing costs, hence limiting its applicability. As an effort to overcome these issues, this article presents a technique based on Kalman filtering for estimating the capacitor voltage at each SM and the converter current. The proposed approach operates both in open and closed-loop, during transients and steady-state, enabling the use of estimator-based state feedback control without the need of a voltage sensor per SM, and filtering the electromagnetic interference from voltage and current sensors. Experiments conducted in a three-phase MMC with 24 SMs confirm the effectiveness of the proposed approach during transients and steady-state operation. [ABSTRACT FROM AUTHOR]

The switched-capacitor of boost seven-level active neutral-point-clamped inverter has the large voltage ripple due to its inherent long discharging interval. Aiming at reducing the switched-capacitor voltage ripple and subsequently the capacitance, this article proposes a flexible third harmonic voltage modulation method. In specific, the long discharging interval can be divided into short intervals or even avoided by flexibly regulating the amplitude and phase-angle of third harmonic voltage based on various modulation indexes and power factors. An offline particle swarm optimization algorithm is employed to find the corresponding optimal amplitude and phase-angle of third harmonic voltage, which will further be put into the online look-up table to simplify the real time implementation. Experimental results verified the performance of the proposed modulation method. [ABSTRACT FROM AUTHOR]

In switched-capacitor (SC) based multilevel inverters (MLIs), capacitors are usually replenished by a dc voltage source or other capacitors, inrush charging current are found at switching instants. In order to solve this issue, this article presents a new type of step-up MLIs, which is implemented by using a front-side quasi-Z-source unit to feed SC-based multilevel circuits. As a result, the charging current variation of capacitors is effectively limited by the quasi-Z-source impedance. Moreover, the charging voltage can be regulated by controlling the duty ratio of shoot-through states of the quasi-Z-source unit, and the total voltage gain of the new MLI is enhanced as both SC and quasi-Z-source units have boost capability. Structurally, the two units share a common switch network so that the new MLI has simple structure. Topologies for single- and three-phase configurations, operation, and modulation, as well as the parameter design are analyzed in detail. Finally, the feasibility of the new MLI is verified experimentally by a downscale three-phase prototype. [ABSTRACT FROM AUTHOR]

This article develops the constant power control technology of LCC resonant capacitor charging power supply (CCPS) to accelerate the charging speed and use the full capacity of the device at the same time. For the constant power control of the CCPS, variable frequency modulation works in a wide frequency range with large reactive power, and phase-shift modulation (PSM) cannot work with a wide gain range. Therefore, a variable frequency (VF)-PSM constant power control strategy is proposed in this article, which achieves high utilization of transformer and high efficiency of power supply system. Based on state plane analysis, the analytical expressions in different operating modes are derived for the ZVS boundary and the multidimensional relationship between power, output voltage, frequency, and phase-shift angle. Accordingly, a control trajectory of the phase-shift angle and frequency in gain-power plane is calculated. Thus, the problems caused by using the current with large harmonic components to calculate the output power in real time are avoided and the control is simple and accurate. Finally, a 500 W, 1 kV charging experiment was conducted to verify the effectiveness of the VF-PSM constant power control strategy and the feasibility of phase-shift angle and frequency trajectory control in gain-power plane. [ABSTRACT FROM AUTHOR]

Gate driver circuits to ensure proper turn-on and turn-off for power switches are essential parts of a power converter design. They become significantly challenging for multilevel converters, where multiple switches are operated at active voltage domains. The recent favorable use of gallium nitride devices for power switches makes gate driving even more difficult as the switch performance and reliability are very sensitive to the variations of the gate driving signals and power rails compared with traditional power MOSFETs. This article discusses gate driving methods using a multilevel multi-inductor hybrid (MIH) converter as the demonstration prototype to address two key challenges in designing gate drivers: 1) providing level-shifted pulsewidth modulation signals to active voltage domains and 2) powering schemes for gate driver circuits. To solve the first challenge, an optimal use of available half-bridge drivers is proposed to eliminate the need for separate signal isolator chips. This method was implemented and verified in an MIH converter prototype for 48-V point-of-load applications using three different powering schemes for gate drivers, including isolated power modules, regulated supplies from switch blocking voltages, and cascaded bootstrap power rails with regulations. The gate driver techniques and powering schemes are compared experimentally in terms of performance to illustrate their benefits and tradeoffs. [ABSTRACT FROM AUTHOR]

Unbalanced ac voltages drastically deteriorate the performance of five-level flying capacitor (FC) rectifiers. Without introducing an extra buffering circuit to absorb the second-order oscillating power, it is an incompatible contradiction for realizing both negative-sequence current reduction and second-order voltage ripple suppression. In this article, based on the idea of using FCs in the rectifier to absorb the oscillating power, a second-order voltage ripple suppression strategy for unbalanced ac voltage conditions is proposed. Reducing the negative-sequence currents and suppressing the dc voltage ripples can be simultaneously realized. Simulations and experimental results verified the effectiveness and performance of the proposed scheme well. [ABSTRACT FROM AUTHOR]

The multiport dc/dc converter with input independent output series structure is simple and efficient for photovoltaic (PV) applications. Through the cascade of sub-modules (SM), the converter has a high step-up ratio to connect MVdc bus. However, it has many ports which increase the risk of short-circuit faults. Therefore, this article proposes a fault ride-through (FRT) topology for multiport converter. When low-voltage ports are short-circuited, they can be isolated by blocking the switches of their own. The FRT topology can support the output voltage of faulty SMs to avoid the disconnection from MVdc bus. Other healthy ports can still generate power to MVdc bus. When the medium-voltage port is short-circuited, the FRT topology can quickly clear the fault current to prevent devices from being damaged. Due to the zero voltage switching, the proposed topology has higher efficiency. For medium-voltage fault, the FRT topology has faster fault clearing speed because more capacitors are reused. Finally, the proposed topology is verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

Three-level boost dc–dc converters present several advantages in comparison with conventional boost converters, such as reduced switching losses, lower voltage ratings for the diodes and switches, and smaller size of reactive components. The topology requires three voltage levels at the output, therefore, replacing the output capacitor of the traditional boost converter with two capacitors and a midpoint. However, due to component tolerances and/or current flowing through the midpoint, output capacitors voltages become unbalanced, leading to converter malfunctioning or destruction. To overcome this issue, an exact feedback linearization control strategy is proposed, for which an implementation with minimum sensors is obtained. Analyses of its performance at different input voltages and of its robustness against component variations are included. Simulation results are provided, showing a comparison of the proposal with a conventional control strategy and its steady-state performance with nonlinear loads. The proposed control strategy was implemented in a low-cost microcontroller unit and, experimental verification is included. [ABSTRACT FROM AUTHOR]

Fault-tolerant methods have been recognized for improving the reliability of multiphase bidirectional dc–dc converters, including current-fed and voltage-fed dual active bridge converters. Fault-tolerant research for voltage-fed dual active bridge converters has caught much attention recently. In this article, a new fault-tolerant method for current-fed dual active bridge (CF-DAB) converters with blocking capacitors is proposed. The operation of the CF-DAB converter when an open-circuit fault occurs is comprehensively presented and analyzed. A frozen-phase fault-tolerant method with additional blocking capacitors on both sides of the transformer is proposed. The aim of the use of blocking capacitors is to block the dc current component of the high-frequency transformer, which could avoid the core saturation of the transformer. Also, the dc blocking capacitors help isolate the faulty phase when a frozen-phase fault-tolerant method is applied. The proposed method is shown to be a practical, simple, low loss, and effective solution for not only open-circuit fault isolation but also for shedding capability of the multiphase converter. The proposed concept could be applied for general multiphase current-fed converters. The experiment of a 6-kW prototype is implemented to confirm the proposed concept. [ABSTRACT FROM AUTHOR]

In this article, a single-switch continuous input current (CIC) buck–boost converter with noninverted output voltage is proposed. The proposed converter utilizes capacitor and inductor along with three diodes in conjunction with a quadratic boost converter to adopt its CIC feature. The features of high voltage gain, single active power switch, less ripple CIC, and noninverted output voltage make the proposed converter suitable for renewable and industrial applications. In addition, it provides a wide operating voltage gain with optimum component count, which is higher than the conventional buck–boost converter. Furthermore, it has low voltage stress across the power switch with comparable converters. To elevate the importance of the proposed converter, a detailed comparison analysis has been carried out considering voltage stress, voltage gain, effectiveness index, and component count. The operating principle and steady-state analysis in continuous conduction mode and discontinuous conduction mode of the proposed converter are discussed in detail. To validate the theoretical analysis and performance of the proposed converter, a prototype has been developed and tested in laboratory. [ABSTRACT FROM AUTHOR]

Hybrid ac/dc off-grid topologies offer the combined advantage of higher energy efficient dc loads, and existing low-cost ac loads. Such budding topologies tender a promising solution for rural electrification when supplied from solar power along with battery backup. The desirable features of such a scheme for catering household appliances are: low semiconductor count, continuous current ports for PV, battery and dc load, low-voltage levels for PV and battery, dc and ac load voltage regulation, maximum power point tracking, battery overcharge and deep-discharge protection, high-voltage boosting sans low-frequency transformer, and reduced power converter stages. The schemes reported in the literature lack one or more of these features. To address this concern, a hybrid ac/dc scheme is proffered. The first stage is formed by a novel three-switch four-port converter, which facilitates most of the aforesaid features required in a hybrid system. The remaining features are obtained using a conventional dc–ac converter, which forms the second stage of the proposed solution. The overall solution is substantiated through comprehensive analysis and experimental demonstrations using a 400 W experimental prototype. [ABSTRACT FROM AUTHOR]

Medium voltage dc system has fast rise rate in the event of a short-circuit fault. To avoid high-peak fault current, it is necessary to configure dc circuit breaker with fast operation. Solid-state dc circuit breaker has short breaking time and high reliability, which is suitable for Dc system. In this letter, a novel oscillating-commutation solid-state dc circuit breaker based on compound integrated gate-commutated thyristors (IGCTs) is proposed. By combining IGCTs with different advantages, such as high current breaking and high withstand-voltage capability, the proposed dc breaker has the advantages at less breaking time, high performance, low cost, and small volume. The working principle of the proposed scheme is described in detail, and an 8 kV prototype with 7 kA current breaking ability is built to verify its feasibility. [ABSTRACT FROM AUTHOR]

DC–DC converters with a wide input voltage range have earned numerous daily applications in the industry. An example is power systems for electric vehicles, where $LLC$ converters with remarkable features have also been deployed to provide isolation. It is, therefore, common to find a front buck converter cascaded to a back $LLC$ converter, where their intermediate bus voltage is set low to accommodate the lowest input voltage to the buck converter. Unfortunately, this causes efficiency to drop at a high input voltage. To avoid the drop, a reconfiguring strategy has been proposed to convert the front buck converter from full bridge to half bridge, as its input voltage rises above a specified threshold. Furthermore, to ensure a smooth and fast reconfiguration, a dynamic control method has been proposed to direct the intermediate bus voltage to track a reference trajectory with a lower current surge. Besides, the method employs pulse-shift modulation to keep a stable output voltage and proper control initialization to prevent oscillation during the transition. These favorable features and an overall higher efficiency have subsequently been verified through experimental testing with a wide input voltage range. [ABSTRACT FROM AUTHOR]