The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

Multilevel inverters (MLIs) have gained increasing interest for advanced energy-conversion systems due to their features of high-quality produced waveforms, modularity, transformerless operation, voltage, and current scalability, and fault-tolerant operation. However, these merits usually come with the cost of a high number of components. Over the past few years, proposing new MLIs with a lower component count has been one of the most active topics in power electronics. The first aim of this article is to update and summarize the recently developed multilevel topologies with a reduced component count, based on their advantages, disadvantages, construction, and specific applications. Within the framework, both single-phase and three-phase topologies with symmetrical and asymmetrical operations are taken into consideration via a detailed comparison in terms of the used component count and type. The second objective is to propose a comparative method with novel factors to take component ratings into account. The effectiveness of the proposed method is verified by a comparative study.

Voltage Source Multilevel Inverters With Reduced Device Count: Topological Review and Novel Comparative Factors

Model predictive control (MPC) has emerged as a promising approach to control a modular multilevel converter (MMC). With the help of a cost function, the control objectives of an MMC are achieved easily by using an MPC approach. However, the MPC has several technical challenges and issues including the need of accurate system models, computational complexity, and variable switching frequency operation and weighting factor selection, when it comes to the control of an MMC. In the past few years, several research studies are conducted to address some of the challenges and issues in an MPC and developed several model predictive algorithms for an MMC. In this paper, the importance of each challenge and its impact on the system performance is discussed. Also, the MMC mathematical models used in the implementation of MPC are presented. Furthermore, some of the popular MPC algorithms are discussed briefly, and their features and performance are highlighted through case studies. Finally, summary and future trends of MPC for an MMC are presented.

Model Predictive Control of High-Power Modular Multilevel Converters—An Overview

The modular multilevel converter (MMC) is currently one of the power converter topologies which has attracted more research and development worldwide. Its features, such as high quality of voltages and currents, high modularity and high voltage rating, have made the MMC a very good option for several applications including high-voltage dc (HVdc) transmission, static compensators (STATCOMs), and motor drives. However, its unique features such as the large number of submodules, floating capacitor voltages, and circulating currents require a dedicated control system able to manage the terminal variables, as well as the internal variables with high dynamical performance. In this paper, a review of the research and development achieved during the last years on MMCs is shown, focusing on the challenges and proposed solutions for this power converter still faces in terms of modeling, control, reliability, power topologies, and new applications.

Modular Multilevel Converters: Recent Achievements and Challenges

High-voltage direct current (HVdc) transmission systems based on modular multilevel converters (MMCs) are a promising solution for efficient bulk power transmission over long distances. As in grid-connected converters, the occurrence of grid-side faults is rather common, leading to imbalances and distortions of the ac-side voltages. Therefore, operation and control of MMC-HVdc systems under grid imbalances become of great significance in order to satisfy grid codes and reliability requirements of the system. The aim of this paper is to provide a comprehensive review of operation and control methods applied to MMC-HVdc systems with a specific focus on unbalanced ac-grid conditions. The methods are classified based on their main control targets that include ac-side power control, control of the circulating current, and dc-side power ripple suppression control. Special attention is given to the comparison of the different control methods and specific requirements under certain operating conditions that include grid, load, or internal imbalances.

Operation and Control Methods of Modular Multilevel Converters in Unbalanced AC Grids: A Review

A new static synchronous compensator (STATCOM) based on the diode-clamped modular multilevel converter (DCM2 C) is proposed in this paper. In this converter topology, the capacitor voltage is clamped by using a low power rating diode in each submodule. The quantity of voltage sensors is significantly reduced and is free from the number of voltage levels. Furthermore, the voltage balancing control method becomes very simple and the capacitor voltage balance speed is fast. Based on the structure of modular multilevel converter, the DCM2C-STATCOM has the capability of Var compensation and negative-sequence current compensation. The topology characteristics and compensation control method of DCM2C-STATCOM are investigated in this paper. Experimental results obtained from a laboratory prototype validate that the capacitor voltage of the proposed DCM2C-STATCOM can be well balanced and the Var and negative-sequence current compensations are effective.

A Novel STATCOM Based on Diode-Clamped Modular Multilevel Converters

The modular multilevel converter (MMC or M2C) is an emerging attractive multilevel topology for medium-voltage high-power applications. The capacitor voltage balancing control and the improvement of output current rating are two challenging issues of MMC. This paper proposed a new parallel-connected diode-clamped M2C (DCM2C), in which each arm consists of two parallel-connected clusters. In this topology, the capacitor voltages can be balanced automatically without any balancing control algorithms. Theoretically, no voltage sensors are needed to measure the capacitor voltages theoretically. Thus, the control of the converter can be simplified greatly. With a simple current-sharing control, an equal current distribution can be achieved between the two clusters. Furthermore, an extended parallel-DCM2C is proposed for larger current applications, and the corresponding current-sharing control method is developed. Experimental results validated the voltage self-balancing capability of parallel-DCM2C and the effectiveness of the proposed current-sharing control.

A New Parallel-Connected Diode-Clamped Modular Multilevel Converter With Voltage Self-Balancing

Multilevel converters have become very attractive for high-voltage-level power conversion in renewable power generation applications. The converter topology is an important issue in the studies of multilevel converter. Many multilevel topologies have been developed, but few of them are qualified with capacitor voltage self-balancing capability. This paper proposes a novel diode-clamped modular multilevel converter with simplified capacitor voltage-balancing control. In this topology, low-power rating diodes are used to clamp the capacitor voltages of the converter. Only the top submodule in each arm of the converter requires capacitor voltage control. Consequently, very few voltage sensors are needed for voltage control and the control computation burden is reduced greatly when the quantity of the submodules is high. A simple voltage-balancing control method with carrier phase-shifted modulation strategy is developed for this topology. Experiments based on a laboratory prototype were carried out and the results validated the capacitor-balancing performance of the proposed topology.

/pdf/a-novel-diode-clamped-modular-multilevel-converter-with-4oh2p1s619.pdf

A Novel Diode-Clamped Modular Multilevel Converter With Simplified Capacitor Voltage-Balancing Control

Neutral-point-clamped (NPC) multilevel-converter (MLC) is very popular in high voltage converters with multilevel topology. However, the dc-link capacitor voltage unbalance of this topology is a key issue in the NPC applications, and which will cause distortion and asymmetry of the output voltages, and also increase the voltage stress of power switches. In this paper, the three-level (3L) NPC with unbalance capacitor voltages is analyzed. A capacitor voltage balancing control strategy based on fuzzy logic controller (FLC) for the 3L-NPC-MLC is studied and presented. A fuzzy membership function is ratiocinated and determined, and based of which a capacitor voltage control strategy to suppress the capacitor voltage imbalance is proposed. Finally, simulation results show that both the balancing strategy and the FLC are effective.

Jingliang Lv

Papers

A Novel STATCOM Based on Diode-Clamped Modular Multilevel Converters

A New Parallel-Connected Diode-Clamped Modular Multilevel Converter With Voltage Self-Balancing

A Novel Diode-Clamped Modular Multilevel Converter With Simplified Capacitor Voltage-Balancing Control

A voltage balancing controller with fuzzy logic strategy for neutral point clamped multilevel converter

Triboelectric sensor for planetary gear fault diagnosis using data enhancement and CNN