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Voltage source converter-based high-voltage direct current transmission system (VSC-HVDC) technology has been widely used. However, traditional half-bridge sub module (HBSM)-based module multilevel converter (MMC) cannot block a DC fault current. This paper proposes that a full-bridge director switches based multi-level converter can offer features...
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... summarize, the number of IGBTs of the FA-MMC is less than that of the AAMC, and the DC voltage and number of sub-modules of the FA-MMC is nearly half those of the AAMC, leading to smaller size, less need for insulation, and lower cost. And the comparison results of the number of IGBTs and sub-module capacitors between FA-MMC, AAMC and various MMC topologies mentioned in the introduction is shown in Table 4. ...
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Citations
... MMC configurations are primarily categorised into two main types: half-bridge (HB) or full-bridge (FB) [1]. FB-MMCs experience higher power losses and require a larger number of semiconductor devices [27,28]. As a result, the more common topology is the HB-MMC, which offers several advantages discussed in ref. [1]. ...
Multiterminal high‐voltage direct current (MTDC) systems are anticipated to enable the massive integration of renewable energies into modern grids. However, the protection of MTDC systems is a major challenge for their application in connection with offshore wind farms (OWF). This is due to the extremely high short circuit currents, present for very short timeframes, and characterised by the absence of zero‐crossing currents. Additionally, economic and technological issues further challenge widespread implementation of MTDC systems. The main constraints of MTDC protection coordination systems are generally associated with fault detection, DC reactor (DCR), DC circuit breaker (DCCB) operation time, and converter blocking time. This paper presents strategies for achieving full‐selectivity (F‐S) and partial‐selectivity (P‐S) in the protection of voltage source converter (VSC)‐MTDC systems. A case study is setup to design both the F‐S and P‐S protection schemes. Initially, suitable DCRs are calculated for the case study, followed by selecting DCCB operation times with offshore converter blocking for both cases. Finally, an inverse time‐current curve is proposed for different scenarios, considering sensitivity to DCR ratings to enhance converter blocking performance. The case study is conducted in PSCAD/EMTDC software and the simulation results demonstrate the impact of the different scenarios on the MTDC systems.
... This configuration produces more voltage levels, which contributes to a more pronounced reduction in harmonic content within the output voltage. Full-bridge MMCs are commonly used in high and ultrahigh voltage HVDC applications [22]. The modular multi-level converter layout is shown in Figure 6 where SM represents a sub-module of the half-bridge topology [23] . ...
This extensive review article provides a comprehensive analysis of control strategies for power sharing in Multi-Terminal High Voltage Direct Current (MT-HVDC) systems utilizing voltage source converters (VSC) and multi-level modular converters (MMC). MT-HVDC systems have become essential components of modern power infrastructures due to their ability to efficiently transmit energy over long distances, connect renewable energy sources, and enhance grid stability. Effective power sharing control is of uttermost importance in these systems for ensuring equitable energy distribution between terminals and grid reliability. The paper begins with a thorough explanation of the fundamental concepts underlying MT-HVDC systems, emphasizing their significance, and examining the various configurations of such systems. The discussion then examines the functions of VSCs and MMCs in these systems, highlighting their distinct advantages and applications. The review analyses in depth the complex power sharing control strategies within VSC-based and MMC-based multi-terminal HVDC systems, as well as a number of control methods, algorithms, and optimization techniques. In addition, the article discusses difficulties and solutions associated with power sharing control in MT-HVDC systems, such as communication and synchronization issues.
... In this work, RC absorber, a group of inverse-series IGBTs and diodes are added to the sub-module. Ref. Zhu et al. (2019) proposes the full bridge director switch based MMC topology, which has the features of DC side fault blocking capability and is more compact. Also, it provides a more effective predictive control strategy in order to reduce the error of sub-module capacitor voltage and output AC current. ...
The voltage source converter (VSC) based HVDC (high voltage direct current system) offers the possibility to integrate other renewable energy sources (RES) into the electrical grid, and allows power flow reversal capability. These appealing features of VSC technology led to the further development of multi-terminal direct current (MTDC) systems. MTDC grids provide the possibility of interconnection between conventional power systems and other large-scale offshore sources like wind and solar systems. The modular multilevel converter (MMC) has become a popular technology in the development of the VSC-MTDC system due to its salient features such as modularity and scalability. Although, the employment of MMC converter in the MTDC system improves the overall system performance. However, there are some technical challenges related to its operation, control, modeling and protection that need to be addressed. This paper mainly provides a comprehensive review and investigation of the control and protection of the MMC-based MTDC system. In addition, the issues and challenges associated with the development of the MMC-MTDC system have been discussed in this paper. It majorly covers the control schemes that provide the AC system support and state-of-the-art relaying algorithm/ dc fault detection and location algorithms. Different types of dc fault detection and location algorithms presented in the literature have been reviewed, such as local measurement-based, communication-based, traveling wave-based and artificial intelligence-based. Characteristics of the protection techniques are compared and analyzed in terms of various scenarios such as implementation in CBs, system configuration, selectivity, and robustness. Finally, future challenges and issues regarding the development of the MTDC system have been discussed in detail.
... As a result of the above limitation, several fault tolerant MMC SMs such as the Full-Bridge (FB), Clamp Double (CD), Alternate Arm (AA) types and all the hybrid designs were proposed to offer primary protection to the grid, although, at the expense of costs and losses. Alternatively, the Half-Bridge (HB) SM could be used as a primary protective device because of its commercial viability but it must be supported by a secondary protection since it has reduced fault blocking voltage capability [11][12] [13]. ...
Half-bridge Modular Multilevel Converters (HB-MMCs) enable the transmission of renewable energy from remote places to load centres with high levels of efficiency. Further, and relative to other MMC topologies, the HB-MMC is low in cost to implement. However, in cases where the severity of the fault increases beyond a given threshold, HB-MMCs could become blocked, which may lead to a grid collapse before the fault can be isolated. Therefore, an intelligent system is proposed to locate and isolate the exact fault path using Quadratic Support Vector Machine (QSVM) and Squared Exponential Gaussian Process Regression (seGPR) algorithms. This allows for timely fault clearance and, for meshed systems, identification of alternative power flow paths to achieve fault ride-through. Thus, the continuous operation of the grid under a fault condition can be assured. Converter simulation, data analysis and fault estimation are presented using MATLAB/Simulink to show the effectiveness of the proposed system.
... An addition of a directional switch and two diodes to existing HB sub module has been provided to quickly block DC fault current without changing original control strategy. Reference [76] has proposed a full bridge director switch based MMC that effectively blocks DC side faults in a more compact way. A suitable control strategy is also proposed in order to minimize the error of sub module voltages and AC current. ...
For decades high voltage alternating current (HVAC) was considered as most economical solution to transmit and deliver electric power. With the recent developments in power electronic devices, high voltage direct current (HVDC) system becomes most prominent technology. Multi-terminal direct current (MTDC) based system as a promising technology for future power system is the major focus area for researchers and industries these days. A number of MTDC systems have been implemented physically. The major motivation to construct such MTDC systems is the integration of large-scale offshore power sources such as wind turbines and solar systems. This article discusses the most critical challenges and issues related to operation, control and protection schemes for integration of modular multi-level converter (MMC) based MTDC systems. At first detailed literature survey has been presented to show the challenges for MMC based MTDC systems, then an analysis related to those challenges for operation, control and protection schemes for existing MMC based MTDC systems has been provided. Finally, a road map to tackle such challenges has been suggested.
... Compared with the above topological structure, the modular multi-level converter (MMC) proposed by Siemens company performs well in modularity, output harmonic content, reliability and other aspects, and is suitable for back-to-back structure. There are many literatures to study its application and control strategy in various fields such as DC transmission, harmonic and reactive power compensation [6][7][8][9][10][11][12][13][14][15][16]. ...
The current popular modular multilevel converter topology (MMC) needs a large number of cascaded sub modules and switches, a high voltage level of DC bus and a large loss. Based on these problems, a new multilevel converter topology with H-bridge alternate arm is proposed. This topology combines two structures of H-bridge sub module cascade and H-bridge switch series arm. In high-voltage and high-power applications, on the premise of outputting the same AC voltage level, this topology reduces the DC bus voltage level, system loss and cost, and the number of components, simplifies the control method, and improves the system reliability compared with the MMC structure. In this paper, the working mechanism of the topology is described in detail. On this basis, the control strategy of sub module capacitor voltage balancing is proposed. Finally, the PSIM simulation of the topology is carried out, and a single-phase prototype is made in the laboratory. The simulation and experimental waveforms are obtained, which verify the correctness and feasibility of the topology structure.
... However, the availability of DC CBs are restricted due to their high cost and imperfections [18,19]. The other approach is to use sub-modules with DC fault handling capabilities [19][20][21]. For example, by replacing the half-bridge sub-module (HBSM) with the full-bridge submodule (FBSM) in the NA-MMC, a reverse voltage can be generated by the FBSM capacitors to block the short-circuit current subsequent to the DC-side fault. ...
... One is to employ a DC circuit breaker (CB) with relatively high let-through current to isolate the DC fault current in a short time after the DC side fault occurs. However, the availability of DC CBs are restricted due to their high cost and imperfections [18,19]. The other approach is to use sub-modules with DC fault handling capabilities [19][20][21]. ...
... However, the availability of DC CBs are restricted due to their high cost and imperfections [18,19]. The other approach is to use sub-modules with DC fault handling capabilities [19][20][21]. For example, by replacing the half-bridge sub-module (HBSM) with the full-bridge sub-module (FBSM) in the NA-MMC, a reverse voltage can be generated by the FBSM capacitors to block the short-circuit current subsequent to the DC-side fault. ...
The nine-arm inverter integrates two modular multilevel converters (MMCs) into one compact inverter to diminish the number of power semiconductor devices. It can be used for dual-motor driving or connecting two AC power sources in a multi-terminal high voltage direct current (HVDC) system, etc. Although the half-bridge based modular multilevel converter has the fewest components, it is generally not resistant to the DC-side faults. In order to achieve a DC fault blocking capability with high efficiency and low cost, this paper proposes a hybrid nine-arm high-voltage inverter, which is consists of a full-bridge sub-module (FBSM) and a half-bridge sub-module (HBSM). Firstly, the topology, operation modes, and modulation strategy of the proposed hybrid inverter are presented. Then, by analyzing the potential short-circuit current paths between different ports, the ability of the proposed hybrid inverter to block the DC faults is described and the appropriate ratio of HBSM and FBSM is determined to further reduce the number of devices and the losses of the proposed hybrid inverter. Finally, simulation results based on MATLAB/Simulink are provided to demonstrate the effectiveness and feasibility of the proposed hybrid nine-arm high-voltage inverter under normal operation and DC fault condition.
... The cascaded module structure contains two different type: The cascaded chopper/half-bridge (CC) structure that can be used in a H-MMC topology and the H-bridge/full-bridge (CHB) structure that can be used in a CHB rectifier (CHBR), CHB-STATCOM, or alternate-arm converter (AAC) topology [22][23][24]. A new method based on PD-PWM for achieving the effect of dynamic regulation ability used in CC structures has been proposed in [20,21], but this modulation strategy cannot be used directly in a CHB structure control strategies because there are fundamental differences between the configurations of two structures. ...
CHB is a suitable type of topology for synchronous rectifier application which has two or more independent DC loads. Focusing on the individual DC-link capacitor voltage balancing problems caused by asymmetric parameters of independent DC loads, this paper developed a new dual modulation signals based phase disposition pulse width modulation (PD-PWM) strategy using dynamic carrier bias allocation method. Its main idea is to allocate the bias of the carrier wave dynamically according to the balance situation of the system. Compared with the traditional modulation strategies, this method is more easily to be realized and has much stronger dynamic regulation ability. This modulation strategy is widely applicable to various types of CHB structures. A detailed analysis of the DC-link capacitor charge-discharge profile is performed, and an operation condition based dynamic bias allocation method is described using the cascaded H-bridge rectifier (CHBR) structure of five sub-modules as an example. A simulation model and an experiment platform are developed, and the feasibility and effectiveness of the modulation strategy are verified by simulation and experiment results.
