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Journal ArticleDOI

A Generalized Switching Strategy and Capacitor Sizing Algorithm for Granular Multilevel Converters

TL;DR: A generalized switching strategy to control the output voltage as well as capacitor voltages of H-bridge submodules for a GMC with an arbitrary number of submodules and a systematic analysis for optimal sizing of the submodule capacitors to minimize the required total energy of the installed capacitors are proposed.
Abstract: The granular multilevel converter (GMC) is a multilevel converter built by hybridizing a conventional two-level converter with an asymmetrical cascaded H-bridge converter. Addition of each additional H-bridge submodule doubles the number of the GMC output voltage steps. Thus, with a small number of power electronic switches and associated gate drive signals and circuits, a GMC can offer a high-quality ac voltage to meet the stringent requirements of high-performance drives and grid-tied converters in low and medium voltages. This paper proposes: 1) a generalized switching strategy to control the output voltage as well as capacitor voltages of H-bridge submodules for a GMC with an arbitrary number of submodules $n$ (this proposed strategy is scalable, which allows for easy modification of the voltage rating or the number of the voltage steps of the GMC) and 2) a systematic analysis for optimal sizing of the submodule capacitors to minimize the required total energy of the installed capacitors. Simulation and experimental case studies evaluate the performance of the proposed switching and capacitor sizing algorithms.
Citations
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Journal ArticleDOI
TL;DR: A new family of multilevel inverter topology that is able to generate seven voltage levels by utilizing one or two floating capacitors and 10 power switches is proposed, and a single dc source is sufficient in both its single-phase and three-phase topologies.
Abstract: This paper proposes a new family of multilevel inverter topology that is able to generate seven voltage levels by utilizing one or two floating capacitors and 10 power switches. This novel boost switched-capacitor seven-level inverter possesses voltage boosting capability with an achievable maximum voltage level 1.5 times the input direct current (dc) voltage. The generation of higher output voltage does not incur high-voltage stress on any power switch in this topology, as the peak inverse voltages of all power switches do not exceed the input source voltage. In addition, capacitor voltage balancing is not essential since the floating capacitors are effectively balanced during the charging and discharging processes. Furthermore, the proposed topology eliminates the need for multiple isolated dc sources, and a single dc source is sufficient in both its single-phase and three-phase topologies. The operating principle and steady-state analysis of the proposed topology are elaborated. Experimental results from a single-phase prototype are then presented to verify the validity of the proposed topology.

110 citations


Cites methods from "A Generalized Switching Strategy an..."

  • ...Similar configurations with a T-type inverter [14] or half-bridge [15], [16] in place of the three-level ANPC inverter, have been proposed...

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Journal Article
TL;DR: A multilevel inverter for generating 17 voltage levels using a three-level flying capacitor inverter and cascaded H-bridge modules with floating capacitors has been proposed in this article.
Abstract: A multilevel inverter for generating 17 voltage levels using a three-level flying capacitor inverter and cascaded H-bridge modules with floating capacitors has been proposed. Various as- pects of the proposed inverter like capacitor voltage balancing have been presented in the present paper. Experimental results are presented to study the performance of the proposed converter. The stability of the capacitor balancing algorithm has been verified both during transients and steady-state operation. All the capac- itors in this circuit can be balanced instantaneously by using one of the pole voltage combinations. Another advantage of this topol- ogy is its ability to generate all the voltages from a single dc-link power supply which enables back-to-back operation of converter. Also, the proposed inverter can be operated at all load power fac- tors and modulation indices. Additional advantage is, if one of the H-bridges fail, the inverter can still be operated at full load with reduced number of levels. This configuration has very low dv/dt and common-mode voltage variation.

58 citations

Journal ArticleDOI
TL;DR: An improved topology, namely the one-switched-capacitor integrated MLI (1SCI-MLI) is proposed in this paper, which resolves the high voltage stress problem in the existing counterparts.
Abstract: The integration of switched-capacitor techniques into multilevel inverters (MLIs) with a dc source string contributes to the boosting of voltage gain, renders it particularly attractive in reducing the number of input dc sources in the series string. However, the recent two-stage MLI topologies suffer from high voltage stress across the backend H-bridge. Addressing this concern, an improved topology, namely the one-switched-capacitor integrated MLI (1SCI-MLI) is proposed in this paper. An extended topology of 1SC-MLI is also established by appropriate incorporation of another switched-capacitor circuit. The two proposed topologies are endowed with voltage boosting capability. They also feature low switch count and low number of dc sources. More importantly, they resolve the high voltage stress problem in the existing counterparts. Their corresponding operational analysis and comparisons with recent MLI topologies are discussed. Simulation and experimental results from a laboratory prototype are presented to validate the effectiveness of the proposed topologies.

54 citations

Journal ArticleDOI
TL;DR: This article proposes a self-balanced cascaded H-bridge multilevel inverter with a binary asymmetric ratio that is validated by MATLAB simulations and experimentation on the hardware prototype and results match well with simulation results.
Abstract: This article proposes a self-balanced cascaded H-bridge multilevel inverter with a binary asymmetric ratio. The inverter uses only one dc source per phase that will feed the H-bridge with the highest dc-link voltage (called main bridge). The dc links of all other H-bridges (called auxiliary bridges) are formed by floating capacitors. Floating capacitors converge to the corresponding steady-state voltages by the principle of a level-doubling network without using any closed-loop control technique. In a steady state, the dc-link voltage of each auxiliary bridge will be equal to half of the dc-link voltage of its preceding H-bridge. This will result in an inherent binary asymmetric ratio among all the dc-link voltages. Operation of the proposed topology is validated by MATLAB simulations and experimentation on the hardware prototype. Experimental results match well with simulation results.

40 citations


Cites methods from "A Generalized Switching Strategy an..."

  • ...A granular MLI with a binary asymmetric ratio presented in [17] also uses the advantage of switching redundan-...

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Journal ArticleDOI
TL;DR: The uniqueness of 1:7 ratio of asymmetry (between the TMs) to maximize the number of levels without having any loss in the intermittent voltage levels for the line-to-line voltage in a three-phase system is shown.
Abstract: Asymmetrical cascaded topology can produce more number of levels. This can be further boosted by using level doubling networks (LDNs). An LDN is a floating capacitor fed two-switch topology that almost doubles the number of levels without necessitating any closed-loop control for the voltage balancing of the floating capacitors. Topological modules (TMs) are formed by using LDN. This paper shows the uniqueness of 1:7 ratio of asymmetry (between the TMs) to maximize the number of levels without having any loss in the intermittent voltage levels for the line-to-line voltage in a three-phase system. A new control technique to select the right space vector without generating any dc component in the output phase voltage is reported. Step-by-step description of the controller is presented in this paper. Extensive simulations using MATLAB/Simulink and supporting experimental results using a laboratory prototype have confirmed the usefulness of the proposed controller.

31 citations

References
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Journal ArticleDOI
TL;DR: A survey of different topologies, control strategies and modulation techniques used by cascaded multilevel inverters in the medium-voltage inverter market is presented.
Abstract: Cascaded multilevel inverters synthesize a medium-voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic allows one to achieve high-quality output voltages and input currents and also outstanding availability due to their intrinsic component redundancy. Due to these features, the cascaded multilevel inverter has been recognized as an important alternative in the medium-voltage inverter market. This paper presents a survey of different topologies, control strategies and modulation techniques used by these inverters. Regenerative and advanced topologies are also discussed. Applications where the mentioned features play a key role are shown. Finally, future developments are addressed.

2,111 citations


"A Generalized Switching Strategy an..." refers background or methods in this paper

  • ...Several recent A-CHB converters use one dc voltage source per phase to supply the submodule with the largest voltage level and use capacitors (instead of dc voltage sources) for other submodules [22], [23]....

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  • ..., n = 1, where n is the number of submodules per phase); [24] and [25] modify the topology of [22] for motor control; [26] introduces a GMC with n = 3; and [27] introduces a GMC with n = 3 and a three-level FC converter as its dc/ac converter....

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  • ...Based on the previous case studies, unlike [22] and [24]–[27], the proposed switching strategy employs an online algorithm and does not need to derive and implement a large switching table....

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  • ...All references [22], [24]–[27] use a switching table, which makes it difficult to develop GMCs with a large number of Hbridge submodules (i....

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  • ...References [22] and [24]–[27] study the topology and control of a GMC with up to three submodules per phase (n ≤ 3): [22] introduces a GMC with one H-bridge submodule per phase (i....

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Journal ArticleDOI
TL;DR: In this paper, the authors proposed a phase-disposition (PD) sinusoidal pulsewidth modulation (SPWM) switching strategy for the operation of an MMC-HVDC system.
Abstract: The modular multilevel converter (MMC) is a newly introduced switch-mode converter topology with the potential for high-voltage direct current (HVDC) transmission applications. This paper focuses on the dynamic performance of an MMC-based, back-to-back HVDC system. A phase-disposition (PD) sinusoidal pulsewidth modulation (SPWM) strategy, including a voltage balancing method, for the operation of an MMC is presented in this paper. Based on the proposed PD-SPWM switching strategy, a mathematical model for the MMC-HVDC system, under both balanced and unbalanced grid operation modes, is developed. Dynamic performance of the MMC-based back-to-back HVDC converter system, based on time-domain simulation studies in the PSCAD/EMTDC environment, is then evaluated. The reported time-domain simulation results show that based on the adopted PD-SPWM switching strategy, the MMC-HVDC station can respond satisfactorily to the system dynamics and control commands under balanced and unbalanced conditions while maintaining voltage balance of the dc capacitors.

1,104 citations


Additional excerpts

  • ...Therefore, these converters are used mostly in high-voltage applications such as HVDC systems [12], static synchronous compensators [13], and grid integration of large photovoltaic systems [14]....

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Journal ArticleDOI
TL;DR: In this paper, a switched-capacitor (SC) dc-dc converter's steady-state performance was evaluated through evaluation of its output impedance. But the performance of SC converters was not compared with conventional magnetic-based dc-DC converter circuits, in the context of various application settings.
Abstract: Analysis methods are developed that fully determine a switched-capacitor (SC) dc-dc converter's steady-state performance through evaluation of its output impedance. This analysis method has been verified through simulation and experimentation. The simple formulation developed permits optimization of the capacitor sizes to meet a constraint such as a total capacitance or total energy storage limit, and also permits optimization of the switch sizes subject to constraints on total switch conductances or total switch volt-ampere (V-A) products. These optimizations then permit comparison among several switched-capacitor topologies, and comparisons of SC converters with conventional magnetic-based dc-dc converter circuits, in the context of various application settings. Significantly, the performance (based on conduction loss) of a ladder-type converter is found to be superior to that of a conventional magnetic-based converter for medium to high conversion ratios.

743 citations


"A Generalized Switching Strategy an..." refers background in this paper

  • ...The total energy stored in the capacitor bank is commonly used as a measure of its weight and cost [28]....

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  • ...straint on this total energy, the individual capacitors should be sized so that the output voltage satisfies the specified voltage quality metrics [28], [29]....

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Journal ArticleDOI
TL;DR: A new multilevel converter topology that has many steps with fewer power electronic switches results in reduction of the number of switches, losses, installation area, and converter cost.
Abstract: This paper introduces a new multilevel converter topology that has many steps with fewer power electronic switches. The proposed circuit consists of series-connected submultilevel converters blocks. The optimal structures of this topology are investigated for various objectives, such as minimum number of switches and capacitors, and minimum standing voltage on switches for producing maximum output voltage steps. A new algorithm for determination of dc voltage sourcespsila magnitudes has also been presented. The proposed topology results in reduction of the number of switches, losses, installation area, and converter cost. The operation and performance of the proposed multilevel converter has been verified by the simulation and experimental results of a single-phase 53-level multilevel converter.

645 citations


"A Generalized Switching Strategy an..." refers background in this paper

  • ...This ability increases the converter efficiency and reliability and results in a small number of required gate drive signals and their associated electronic circuits, fewer measurement and protection devices, and lower size and cost of the converter [6]....

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  • ...Thus, synthesizing a high-resolution ac voltage requires a large number of components for energy conversion, control, and protection [6]....

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  • ...Based on the idea of an A-CHB converter, several multilevel converters with high voltage quality have been proposed [1], [6],...

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  • ...2772200 quality and electromagnetic compatibility [6]....

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Journal ArticleDOI
TL;DR: A new topology for cascaded multilevel converter based on submultileVEL converter units and full-bridge converters is proposed, optimized for various objectives, such as the minimization of the number of switches, gate driver circuits and capacitors, and blocking voltage on switches.
Abstract: In this paper, a new topology for cascaded multilevel converter based on submultilevel converter units and full-bridge converters is proposed. The proposed topology significantly reduces the number of dc voltage sources, switches, IGBTs, and power diodes as the number of output voltage levels increases. Also, an algorithm to determine dc voltage sources magnitudes is proposed. To synthesize maximum levels at the output voltage, the proposed topology is optimized for various objectives, such as the minimization of the number of switches, gate driver circuits and capacitors, and blocking voltage on switches. The analytical analyses of the power losses of the proposed converter are also presented. The operation and performance of the proposed multilevel converter have been evaluated with the experimental results of a single-phase 125-level prototype converter.

471 citations


"A Generalized Switching Strategy an..." refers background or methods in this paper

  • ...[21], but all need multiple dc voltage sources....

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  • ...Reference [21] creates these sources using one dc voltage source and multiple dc/dc converters....

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