Modular Multilevel Inverter with New Modulation Method and Its Application to Photovoltaic Grid-Connected Generator
TL;DR: In this article, an improved phase disposition pulse width modulation (PDPWM) was proposed for a modular multilevel inverter which is used for Photovoltaic grid connection.
Abstract: This paper proposed an improved phase disposition pulse width modulation (PDPWM) for a modular multilevel inverter which is used for Photovoltaic grid connection. This new modulation method is based on selective virtual loop mapping, to achieve dynamic capacitor voltage balance without the help of an extra compensation signal. The concept of virtual submodule (VSM) is first established, and by changing the loop mapping relationships between the VSMs and the real submodules, the voltages of the upper/lower arm's capacitors can be well balanced. This method does not requiring sorting voltages from highest to lowest, and just identifies the MIN and MAX capacitor voltage's index which makes it suitable for a modular multilevel converter with a large number of submodules in one arm. Compared to carrier phase-shifted PWM (CPSPWM), this method is more easily to be realized in field-programmable gate array and has much stronger dynamic regulation ability, and is conducive to the control of circulating current. Its feasibility and validity have been verified by simulations and experiments.
Citations
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TL;DR: A general overview of the basics of operation of the MMC along with its control challenges are discussed, and a review of state-of-the-art control strategies and trends is presented as mentioned in this paper.
Abstract: The modular multilevel converter (MMC) has been a subject of increasing importance for medium/high-power energy conversion systems. Over the past few years, significant research has been done to address the technical challenges associated with the operation and control of the MMC. In this paper, a general overview of the basics of operation of the MMC along with its control challenges are discussed, and a review of state-of-the-art control strategies and trends is presented. Finally, the applications of the MMC and their challenges are highlighted.
1,765 citations
TL;DR: A review of the latest achievements of modular multilevel converters regarding the mentioned research topics, new applications, and future trends is presented in this article, where the authors present several attractive features such as a modular structure, the capability of transformer-less operation, easy scalability in terms of voltage and current, low expense for redundancy and fault tolerant operation, high availability, utilization of standard components, and excellent quality of the output waveforms.
Abstract: Modular multilevel converters have several attractive features such as a modular structure, the capability of transformer-less operation, easy scalability in terms of voltage and current, low expense for redundancy and fault tolerant operation, high availability, utilization of standard components, and excellent quality of the output waveforms. These features have increased the interest of industry and research in this topology, resulting in the development of new circuit configurations, converter models, control schemes, and modulation strategies. This paper presents a review of the latest achievements of modular multilevel converters regarding the mentioned research topics, new applications, and future trends.
1,123 citations
Cites background from "Modular Multilevel Inverter with Ne..."
...direct connection of the PV plant to medium voltage or high voltage ac or dc grids [124]....
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TL;DR: The development of MMC circuit topologies and their mathematical models over the years are presented and the evolution and technical challenges of the classical and model predictive control methods are discussed.
Abstract: Modular multilevel converter (MMC) is one of the most promising topologies for medium to high-voltage high-power applications. The main features of MMC are modularity, voltage and power scalability, fault tolerant and transformer-less operation, and high-quality output waveforms. Over the past few years, several research studies are conducted to address the technical challenges associated with the operation and control of the MMC. This paper presents the development of MMC circuit topologies and their mathematical models over the years. Also, the evolution and technical challenges of the classical and model predictive control methods are discussed. Finally, the MMC applications and their future trends are presented.
404 citations
Cites background or methods from "Modular Multilevel Inverter with Ne..."
...The centralized control approach can be implemented with the PSC-PWM, LSC-PWM, NLM, SHE, SAM, and SVM schemes [62], [108], [110], [111], [127]–[129]....
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...When the arm current is positive, the SMs with the lowest voltage is chosen to be inserted to let them charge and avoid any overcharging of those capacitors with the highest voltages and vice-versa [110], [111], [127], [128]....
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TL;DR: A new method is introduced, which is able to reduce the capacitor voltage ripples compared to the other methods, and a closed-loop control is also proposed which are able to track the circulating current references.
Abstract: This paper studies different circulating current references for the modular multilevel converter. The circulating current references are obtained from the instantaneous values of the output current and modulation signal of the phase leg. Therefore, the determination of the amplitude and phase of the output current is not needed, which is a significant improvement compared to other methods such as those based on injecting specific harmonics in the circulating currents. Among the different methods studied in this paper, a new method is introduced, which is able to reduce the capacitor voltage ripples compared to the other methods. A closed-loop control is also proposed which is able to track the circulating current references. With the discussed methods, the average values of the capacitor voltages are maintained at their reference while the voltage ripples are kept low. Experimental results are presented to demonstrate the effectiveness of the proposed and discussed methods.
333 citations
Cites background from "Modular Multilevel Inverter with Ne..."
...2336608 which make it a potential candidate for various applications, including high-voltage-direct-current transmission systems [7]–[9], flexible-alternating-current-transmission-system controllers [10], photovoltaic generation [11], wind turbine applications [12], and motor drives [13]–[15]....
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TL;DR: This paper presents a new E-type module for asymmetrical multilevel inverters (MLIs) with reduced components that makes some preferable features with a better quality than similar modules such as the low number of semiconductors and dc sources and low switching frequency.
Abstract: This paper presents a new E-type module for asymmetrical multilevel inverters (MLIs) with reduced components. Each module produces 13 levels with four unequal dc sources and 10 switches. The design of the proposed module makes some preferable features with a better quality than similar modules such as the low number of semiconductors and dc sources and low switching frequency. Also, this module is able to create a negative level without any additional circuit such as an H-bridge, which causes reduction of voltage stress on switches. Cascade connection of the proposed structure leads to a modular topology with more levels and higher voltages. Selective harmonics elimination pulse width modulation (SHE-PWM) scheme is used to achieve high-quality output voltage with lower harmonics. MATLAB simulations and practical results are presented to validate the proposed module good performance. Module output voltage satisfies harmonics standard (IEEE519) without any filter in output.
268 citations
References
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TL;DR: In this article, two types of pulsewidth-modulated modular multilevel converters (PWM-MMCs) with focus on their circuit configurations and voltage balancing control are investigated.
Abstract: A modular multilevel converter (MMC) is one of the next-generation multilevel converters intended for high- or medium-voltage power conversion without transformers. The MMC is based on cascade connection of multiple bidirectional chopper-cells per leg, thus requiring voltage-balancing control of the multiple floating DC capacitors. However, no paper has made an explicit discussion on voltage-balancing control with theoretical and experimental verifications. This paper deals with two types of pulsewidth-modulated modular multilevel converters (PWM- MMCs) with focus on their circuit configurations and voltage-balancing control. Combination of averaging and balancing controls enables the PWM-MMCs to achieve voltage balancing without any external circuit. The viability of the PWM-MMCs, as well as the effectiveness of the voltage-balancing control, is confirmed by simulation and experiment.
1,506 citations
"Modular Multilevel Inverter with Ne..." refers background in this paper
...The reasons of this situation are as follows: 1) MMCrelated research is mostly in theoretical research stage [12], [13]; 2) the characteristic of the photovoltaic power generation is that PV panels are intermittent sources, and their output voltages continuously vary; the dc link’s voltage has to be regulated to keep them working in maximum power point tracking (MPPT) status; 3) the dynamic voltage balance has to be considered in multilevel PWM, while the system stability would be damaged by adding improper signals to the reference voltage [14]; and 4) the unique circulating current of the MMC will increase the system losses and is not conducive for improving the efficiency of the inverter output [15], [16], and the most important point is that the uncontrolled circulating current threatens the stability of the MMC....
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TL;DR: In this paper, a modified phase-shifted carrier-based pulsewidth-modulation (PSC-PWM) scheme for modular multilevel converters (MMC) is presented.
Abstract: This paper describes a modified phase-shifted carrier-based pulsewidth-modulation (PSC-PWM) scheme for modular multilevel converters (MMC). In order to reduce the average device switching frequency, a reduced switching-frequency (RSF) voltage balancing algorithm is developed. This paper also proposes a circulating current suppressing controller (CCSC) to minimize the inner circulating current in an MMC. Based on the double line-frequency, negative-sequence rotational frame, the three-phase alternative circulating currents are decomposed into two dc components and are minimized by a pair of proportional integral controllers. Simulation results based on a detailed PSCAD/EMTDC model prove the effectiveness of the modified PSC-PWM method and the RSF voltage-balancing algorithm. The proposed CCSC not only eliminates the inner circulating current but also improves the quality of the converter ac output voltage. A simple loss evaluation demonstrates that the RSF voltage-balancing algorithm and the CCSC reduce the converter power losses.
1,183 citations
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
"Modular Multilevel Inverter with Ne..." refers background in this paper
...To achieve the SVLM, it needs to sort the capacitor voltage as [29], [30] described, but frequent sorting is very time consuming, and requires more hardware resources, which would be a large burden especially for high-voltage applications needing more submodules....
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TL;DR: In this paper, the modular multilevel cascade converter (MMCC) family based on cascade connection of multiple bidirectional chopper cells or single-phase full-bridge cells is classified from circuit configuration.
Abstract: This paper discusses the modular multilevel cascade converter (MMCC) family based on cascade connection of multiple bidirectional chopper cells or single-phase full-bridge cells. The MMCC family is classified from circuit configuration as follows: the single-star bridge cells (SSBC); the single-delta bridge cells (SDBC); the double-star chopper cells (DSCC); and the double-star bridge cells (DSBC). The term MMCC corresponds to a family name in a person while, for example, the term SSBC corresponds to a given name. Therefore, the term “MMCC-SSBC” can identify the circuit configuration without any confusion. Among the four MMCC family members, the SSBC and DSCC are more practical in cost, performance, and market than the others although a distinct difference exists in application between the SSBC and DSCC. This paper presents application examples of the SSBC to a battery energy storage system (BESS), the SDBC to a static synchronous compensator (STATCOM) for negative-sequence reactive-power control, and the DSCC to a motor drive for fans and blowers, along with their experimental results.
1,018 citations
"Modular Multilevel Inverter with Ne..." refers background in this paper
...The reasons of this situation are as follows: 1) MMCrelated research is mostly in theoretical research stage [12], [13]; 2) the characteristic of the photovoltaic power generation is that PV panels are intermittent sources, and their output voltages continuously vary; the dc link’s voltage has to be regulated to keep them working in maximum power point tracking (MPPT) status; 3) the dynamic voltage balance has to be considered in multilevel PWM, while the system stability would be damaged by adding improper signals to the reference voltage [14]; and 4) the unique circulating current of the MMC will increase the system losses and is not conducive for improving the efficiency of the inverter output [15], [16], and the most important point is that the uncontrolled circulating current threatens the stability of the MMC....
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TL;DR: In this paper, the authors proposed an alternative topology of nonisolated per-panel dc-dc converters connected in series to create a high voltage string connected to a simplified dc-ac inverter.
Abstract: New residential scale photovoltaic (PV) arrays are commonly connected to the grid by a single dc-ac inverter connected to a series string of pv panels, or many small dc-ac inverters which connect one or two panels directly to the ac grid. This paper proposes an alternative topology of nonisolated per-panel dc-dc converters connected in series to create a high voltage string connected to a simplified dc-ac inverter. This offers the advantages of a "converter-per-panel" approach without the cost or efficiency penalties of individual dc-ac grid connected inverters. Buck, boost, buck-boost, and Cu/spl acute/k converters are considered as possible dc-dc converters that can be cascaded. Matlab simulations are used to compare the efficiency of each topology as well as evaluating the benefits of increasing cost and complexity. The buck and then boost converters are shown to be the most efficient topologies for a given cost, with the buck best suited for long strings and the boost for short strings. While flexible in voltage ranges, buck-boost, and Cu/spl acute/k converters are always at an efficiency or alternatively cost disadvantage.
989 citations