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This paper proposes two hybrid asymmetric cascaded multilevel inverters for driving medium-voltage open-end winding motors. Each phase of the proposed systems consist of a three-level (3L) H-bridge cell and a nine-level (9L) H-bridge cell connected in series. An unequal dc-voltage ratio of 1:8 between cells is used, providing 19 phase voltage levels. The topologies of the 9L H-bridge cell are based on modular multilevel cascade converter (MMCC) with double-star chopper cells, while the 3L H-bridge cell is fed by a floating capacitor. Compared to conventional MMCC for open-end stator winding motor drives, the proposed inverters can produce more phase voltage levels. In addition, they require a smaller number of power semiconductor switches, drivers and capacitors. Simulations and experimental results are presented in order to demonstrate the performance and feasibility of the proposed topologies. [ABSTRACT FROM AUTHOR]

This paper presents a method for generating a multilevel dodecagonal voltage space vector structure using a single dc source for induction motor drives. Multilevel dodecagonal structure combines the advantages of both multilevel and dodecagonal structures, and hence, generates low dv/dt phase voltage along with the elimination of fifth- and seventh-order harmonics over the entire modulation range. This eliminates low-order harmonic currents and prevents the generation of sixth-order torque ripple in the motor. The topology used requires only one dc source making four-quadrant operation of the drive system simpler compared to previously proposed multilevel topologies generating dodecagonal space vector structures. The topology used consists of a three-level flying capacitor (FC) inverter cascaded with a capacitor fed H-bridge. The FC inverter operates at a lower switching frequency and the low-order harmonics are eliminated by the switching action of the cascaded H-bridge inverter. The capacitors in the cascaded H-bridge modules are maintained at a substantially smaller voltage compared to the dc-link voltage and are inherently balanced during the pulsewidth modulation operation. This results in low switching loss, in the FC inverter as well as in the cascaded H-bridge inverter. Experimental results are included to validate the operation of the topology and modulation scheme presented in this paper. [ABSTRACT FROM AUTHOR]

Impedance-source networks are an increasingly popular solution in power converter applications, especially in single-stage buck–boost power conversion to avoid additional front-end dc–dc power converters. In the survey papers published, no analytical comparisons of different topologies have been described, which makes it difficult to choose the best option. Thus, the aim of this paper is to present a comprehensive analytical comparison of the impedance-source-based buck–boost inverters in terms of passive component count and semiconductor stress. Based on the waveform of the input current, i.e., with or without a transformer, and with or without inductor coupling, the impedance-source converters are classified. The main criterion in our comprehensive comparison is the energy stored in the passive elements, which is considered both under constant and predefined high frequency current ripple in the inductors and the voltage ripple across the capacitors. Two-level and multilevel solutions are described. The conclusions provide a “one-stop” information source and a selection guide of impedance-source-based buck–boost inverters for different applications. [ABSTRACT FROM PUBLISHER]

Due to a substantial shortage of conventional energy sources, the utilization of renewable energy is gaining attention. Power converters form interfaces to provide power from renewable energy sources to end user systems. Impedance-source inverters (ZSIs) have become a research hotspot and are widely used to overcome the drawbacks of conventional voltage-source inverters and current-source inverters such as two-stage power conversion and less immunity to electromagnetic interference noises. This paper presents various transformer-based ZSIs mainly classified as trans-ZSIs, improved trans-ZSIs, inductor-capacitor-capacitor transformer ZSI, TZSIs, and their comparisons with a new family of ZSIs called Γ-Z-source inverters (ΓZSI). Full operational analysis of an improved ΓZSI with the clamping diode D2 and its benefits over the conventional ΓZSI are also discussed. The improved ΓZSI utilizes a higher modulation index and consequently a lower duty cycle to achieve same gain, thus reducing the switch voltage stress and providing better output quality. Additionally, an extra diode provides voltage clamping to the dc-link voltage to limit voltage overshoots. The comparative evaluations of all the above mentioned ZSIs are presented in the literature and to validate the advantages of the improved ΓZSI, simulations, and experimental comparisons are also performed. [ABSTRACT FROM AUTHOR]

Multilevel inverters are receiving more attentions nowadays as one of preferred solutions for medium- and high-power applications. As one of the most popular hybrid multilevel inverter topologies, the five-level active-neutral-point-clamped inverter (5L-ANPC) combines the features of the conventional flying-capacitor type and neutral-point-clamped (NPC) type inverter and was commercially used for industrial applications. In order to further decrease the number of active switches, this paper proposes a seven-switch 5L-ANPC (7S-5L-ANPC) topology, which employs only seven active switches and two discrete diodes. The analysis has shown a lower current rating can be selected for the seventh switch under high power factor condition, which is verified by simulation results. The modulation strategy for 7S-5L-ANPC inverter is discussed. A 1 kVA single-phase experimental prototype is built to verify the validity and flexibility of the proposed topology and modulation method. [ABSTRACT FROM AUTHOR]

The reduced capability of multilevel converters with more than one intermediate node to balance the dc-link capacitors voltage, as well as the lack of standard modulation methods to improve their balancing performance, makes these converter topologies unattractive for real power applications. This is especially true when the load demands active power. One of these topologies is the five-level multipoint clamped (5L-MPC) converter. The back-to-back (B2B) configuration of two 5L-MPC converters and the use of a space vector modulation (SVM) that exploits the voltage balancing capability of the redundant switching vectors extend the operation conditions range in which a proper voltage balance can be achieved. However, if practical modulation restrictions are considered (limitation of voltage steps, dead times, switching losses, etc.), the voltage balance cannot be achieved for all operation conditions. In this paper, an SVM which takes into account practical restrictions is proposed. In order to guarantee the voltage balance at any operation condition, the grid-side rectifier exchanges reactive power with the grid-side LCL filter. Thus, the voltage balance of the dc-link is guaranteed while a unity grid-side power factor is achieved. The proposed modulation scheme and the voltage balancing strategy are experimentally validated in a 6.6 kV 1.5 MW 5L-MPC B2B converter. [ABSTRACT FROM AUTHOR]

In this paper, a novel cascaded seven-level inverter topology with a single input source integrating switched-capacitor techniques is presented. Compared with the traditional cascade multilevel inverter, the proposed topology replaces all the separate dc sources with capacitors, leaving only one H-bridge cell with a real dc voltage source and only adds two charging switches. The capacitor charging circuit contains only power switches, so that the capacitor charging time is independent of the load. The capacitor voltage can be controlled at a desired level without complex voltage control algorithm and only use the most common carrier phase-shifted sinusoidal pulse width modulation strategy. The operation principle and the charging–discharging characteristic analysis are discussed in detail. A 1-kW experimental prototype is built and tested to verify the feasibility and effectiveness of the proposed topology. [ABSTRACT FROM AUTHOR]

Multilevel converters have become an interesting alternative for medium- and high-voltage drives over the last decade. Among the existing alternatives, multicell structures offer advantages due to their modularity and scalability. This paper presents experimental results of a recently introduced multilevel topology. The converter is based on the mixture of the two most popular multicell topologies, namely, flying capacitor and cascaded multicell inverter. The new cell provides a high number of output levels, a low number of components, high modularity, and low losses. The results presented in this paper confirm that this new medium-voltage inverter topology is able to reach high-quality output voltages, allowing further advances in modulation techniques and other issues. [ABSTRACT FROM AUTHOR]

Featuring modularity and high efficiency, a modular multilevel converter (MMC) has become a promising topology in high-voltage direct-current transmission systems. However, its distributed capacitors lead to a more complicated startup process than that of a two-level converter. To fully understand this issue, the charging loops of an MMC rectifier and an MMC inverter during an uncontrolled precharge period are analyzed in this paper, with special focus on the necessity of additional capacitor charging schemes. Moreover, a small-signal model of a capacitor charging loop is first derived according to the internal dynamics of the MMC inverter. Based on this model, a novel startup strategy incorporating an averaging capacitor voltage loop and a feedforward control is proposed, which is capable of an enhanced dynamic response and system stability without sacrificing voltage control precision. The design considerations of the control strategy are also given in detail. Simulation results from a back-to-back MMC system supplying passive loads and experimental results from a scaled-down MMC prototype are provided to support the theoretical analysis and the proposed control scheme. [ABSTRACT FROM PUBLISHER]

In this paper, a sensorless method for low- and zero-speed operations is proposed for a high-power medium-voltage pulsewidth-modulated current-source-converter-fed interior-permanent-magnet motor drive system. The proposed method is based on the injection of a high frequency (HF) pulsating sinusoidal signal in the estimated synchronous reference frame of the drive's field-oriented control (FOC) scheme. The conventional FOC control scheme, low switching frequency, dc-link inductor, and the inverter output three-phase filter capacitor of the medium-voltage high-power current-source drive present some challenges in the generation and design of the HF-injection signal. To overcome these challenges, the FOC scheme is modified by introducing a modulation index control with suitable dc-link current compensation to enhance the dynamic response of the injected signal and prevent any clamp in the injected signal. In addition, a multisampling-space-vector-modulation method is proposed to prevent the distortion in the HF signal due to a low switching frequency to injected signal ratio. A detailed study and analysis regarding the influence of low switching frequency, output filter capacitor, and magnetic saturation in the injection method is carried out to determine the visible HF range of the injected signal. It is found that, by using the proposed FOC scheme and multisampling modulation scheme and by the proper design of the HF signal, an accurate rotor flux angle can be estimated for sensorless zero-/low-speed operations. Experimental results are provided to verify the proposed control method. [ABSTRACT FROM PUBLISHER]

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

A novel H-bridge multilevel pulsewidth modulation converter topology based on a series connection of a high-voltage diode-clamped inverter and a low-voltage conventional inverter is proposed in this paper. A dc link voltage arrangement for the new hybrid and asymmetric solution is presented to have a maximum number of output voltage levels by preserving the adjacent switching vectors between voltage levels. Hence, a 15-level hybrid converter can be attained with a minimum number of power components. A comparative study has been carried out to present high performance of the proposed configuration to approach a very low total harmonic distortion of voltage and current, which leads to the possible elimination of the output filter. Regarding the proposed configuration, a new cascade inverter is verified by cascading an asymmetrical diode-clamped inverter, in which 19 levels can be synthesized in output voltage with the same number of components. To balance the dc link capacitor voltages for the maximum output voltage resolution as well as synthesize asymmetrical dc link combination, a new multi-output boost converter is utilized at the dc link voltage of a seven-level H-bridge diode-clamped inverter. Simulation and hardware results based on different modulations are presented to confirm the validity of the proposed approach to achieve a high-quality output voltage. [ABSTRACT FROM PUBLISHER]

The Z-source inverter has gained popularity as a single-stage buck–boost inverter topology among many researchers. However, its boosting capability could be limited, and therefore, it may not be suitable for some applications requiring very high boost demand of cascading other dc–dc boost converters. This could lose the efficiency and demand more sensing for controlling the added new stages. This paper is proposing a new family of extended-boost quasi Z-source inverter (ZSI) to fill the research gap left in the development of ZSI. These new topologies can be operated with same modulation methods that were developed for original ZSI. Also, they have the same number of active switches as original ZSI preserving the single-stage nature of ZSI. Proposed topologies are analyzed in the steady state and their performances are validated using simulated results obtained in MATLAB/Simulink. Furthermore, they are experimentally validated with results obtained from a prototype developed in the laboratory. [ABSTRACT FROM PUBLISHER]

The output voltage quality of some of the single-phase multilevel inverters can be improved when their dc-link voltages are regulated asymmetrically. Symmetrical and asymmetrical multilevel diode-clamped inverters have the problem of dc-link capacitor voltage balancing, especially when power factor of the load is close to unity. In this paper, a new single-inductor multi-output dc/dc converter is proposed that can control the dc-link voltages of a single-phase diode-clamped inverter asymmetrically to achieve voltage quality enhancement. The circuit of the presented converter is explained and the main equations are developed. A control strategy is proposed and explained in details. To validate the versatility of the proposed combination of the suggested dc–dc converter and the asymmetrical four-level diode-clamped inverter (ADCI), simulations and experiments have been directed. It is concluded that the proposed combination of introduced multioutput dc–dc converter and single-phase ADCI is a good candidate for power conversion in residential photovoltaic (PV) utilization. [ABSTRACT FROM PUBLISHER]