Four cascaded quasi-impedance source inverter (qZSI) modules are required for achieving nine-level output voltage waveform. In case of one module failure, number of levels in output voltage are reduced to seven. This ...
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Four cascaded quasi-impedance source inverter (qZSI) modules are required for achieving nine-level output voltage waveform. In case of one module failure, number of levels in output voltage are reduced to seven. This leads to decrease in the output voltage magnitude and increased THD (higher than conventional seven-level qZSI). This is due to the dominance of unwanted harmonic component introduced in the harmonic spectrum. To restore voltage magnitude and optimize THD performance, novel voltage balancing algorithm is proposed. To validate the control algorithm for off-grid and grid connected system, simulation results of the multilevel qZSI are discussed in two categories: (i) DC voltage source powered multilevel qZSI for RL load subjected to module failure and (ii) solar powered multilevel qZSI connected to utility grid subjected to module failure and variable solar irradiation. Pre-fault and post-fault performance of the system with the proposed control algorithm is discussed for both categories, which validates the effectiveness of the algorithm. Hardware results for proof-of-concept are discussed for DC voltage source fed cascaded qZSI connected to RL load during pre-fault and post-fault conditions. FPGA Virtex-5 is used for hardware implementation of the control algorithm. The results validate the improvement in output voltage both quantitatively and qualitatively.
This study introduces a new single phase nine-level inverter using two capacitors and a single DC source. voltage imbalances in the capacitors are eliminated using two control algorithms namely charging algorithm and ...
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This study introduces a new single phase nine-level inverter using two capacitors and a single DC source. voltage imbalances in the capacitors are eliminated using two control algorithms namely charging algorithm and discharging algorithm. The charging algorithm is used to change the inverter switching states when the measured voltage across the capacitors is less than the prescribed value. Alternatively, if the voltage across the capacitors is greater than the set value, the discharging algorithm determines the switching pattern of the inverter switches. The proposed voltage balancing algorithm is very simple to implement and makes the proposed inverter attractive for industrial applications. An extensive comparison of the proposed inverter is made against other topologies proposed in the literature in terms of the components used. The proposed inverter is tested in both standalone and grid connected modes. The proposed inverter is simulated and implemented as a prototype in the laboratory. Experimental results obtained from the prototype confirm the high-quality transient performance of the proposed inverter in terms of its dc capacitor voltagebalancing capability.
Dead time is necessary for the coupled power switches to prevent shoot-through,especially in the modular multilevel converters(MMCs)with a large number of power *** paper proposes a dead-time effect suppression strate...
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Dead time is necessary for the coupled power switches to prevent shoot-through,especially in the modular multilevel converters(MMCs)with a large number of power *** paper proposes a dead-time effect suppression strategy for MMCs with nearest level *** operational principles of MMCs are first *** to the operational features of MMCs,the method that removes a switching signal from the coupled switches and the reduced switching frequency voltage balancing algorithms(RSFVBAs)are mixed in the proposed *** the intervals that are furthest away from the zerocrossing points(ZCP)of arm currents,the single switching signal method can completely eliminate the dead-time effect(DTE).Alternatively,the DTE is suppressed by the RSFVBA in intervals that are close to the *** the combination of the two methods,the dependence of the DTE suppression method on currents is reduced and the influences of ZCP are also released without degrading the normal operation performance of ***,the output performance of MMCs is improved and the voltage stress on the arm inductor dramatically ***,the validation of the method is verified by the simulation results with the professional tool Matlab/Simulink.
The capacitor condition monitoring is an important issue for the reliable operation of modular multilevel converters (MMCs) in high-voltage applications. The numerous capacitors make the monitoring for the capacitor c...
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The capacitor condition monitoring is an important issue for the reliable operation of modular multilevel converters (MMCs) in high-voltage applications. The numerous capacitors make the monitoring for the capacitor condition complex and computation-consuming. This paper proposes a hierarchic capacitor condition monitoring strategy to assure the reliability of high-voltage MMCs. In the strategy, the switching times of the switching signals are counted to detect the condition of the capacitor in each submodule (SM). Then, the subsequent capacitance calculation method is only conducted to the abnormal capacitors indicated by the above condition detection algorithm. Meanwhile, the variations of the measured and reference capacitor voltages are employed to calculate the capacitance in the proposed method. The condition detection algorithm shrinks the scope where the abnormal capacitors locate, which avoids calculating the total capacitances in MMCs. In the proposed capacitance calculation method, the complex operations are further saved. Both the two measures reduce the computation burden effectively. The implementation of the whole monitoring strategy is simple and fit for high-voltage MMCs. Moreover, the strategy has no adverse influence on the normal operation of MMCs. The effectiveness of the proposed strategy is verified by the simulation studies with the professional tool Matlab/Simulink.
Vital traits of a Modular Multilevel Converter (MMC), including size and total cost, are mostly proportional to the circulating current and voltagebalancing capabilities. Hence, this article proposes a novel Input-Ou...
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ISBN:
(纸本)9798350336641
Vital traits of a Modular Multilevel Converter (MMC), including size and total cost, are mostly proportional to the circulating current and voltagebalancing capabilities. Hence, this article proposes a novel Input-Output Feedback Linearization (IOFL) based control approach strategy incorporated by several virtual compensators. To this end, the detailed mathematical model of the utilized MMC, including both circulating currents and the output ones, is employed to shape the IOFL along with a simple SMs capacitor balancing method. Besides, the dynamic of DC-link voltage along with the SMs capacitor voltage errors is exerted to reach the zero component of the proposed control strategy. The ability of the proposed control mechanism in the presence of load variation and fault condition is verified by simulation results obtained from MATLAB/Simulink environment.
Modular multilevel converters (MMC) are potential candidates for high power and high voltage applications as suggested in [1]. balancing capacitor's voltage, controlling circulating current, switching frequency an...
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ISBN:
(纸本)9781728158495
Modular multilevel converters (MMC) are potential candidates for high power and high voltage applications as suggested in [1]. balancing capacitor's voltage, controlling circulating current, switching frequency and, high capacitive energy storage are the important matters in this topology. This paper presents a new modulation scheme to tackle three of the mentioned problems by considering capacitance reduction. An adequate amount of negative voltage in full-bridge sub-modules (FBSMs) at normal operation has been used to reduce the capacitor ripple through the proposed scheme. The modification has been made in the existing voltage-balancingalgorithm in the literature [2] and [3] to select and insert modules negatively according to the signal modulation, which improves the performance of the MMC. The resulting reduction in capacitor voltage fluctuations eventuate in reduction of capacitance of sub-modules which is a space-saving and capacitance optimization solution in MMC topology. Feasibility of MMC in practical applications, like any other converter, is highly depends on its size. Capacitors' voltage fluctuation in MMC structure can both reduce voltage rating of capacitors and capacitance value of each SM in the overall MMC structure. The proposed method capability has confirmed in MATLAB SIMULINK software. The outcomes in terms of capacitors voltage ripple is compared with the conventional and the employed method in [2]. These results suggest 43% ripple reduction respect to the conventional method as well as 43% increase in transmitted power.
Modular multilevel converters (MMC) have proven to be a viable candidate for high-voltage direct current transmission systems. Here, asymmetric modular multilevel converters (A-MMC) are introduced wherein each series ...
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Modular multilevel converters (MMC) have proven to be a viable candidate for high-voltage direct current transmission systems. Here, asymmetric modular multilevel converters (A-MMC) are introduced wherein each series connected module has two half-bridge (HB) submodules, with asymmetric voltage rating. Compared to conventional symmetric MMCs, such systems offer the following benefits: (i) generation of four distinct voltage levels using one module;(ii) 33% lesser semiconductor and gate drive requirement;(iii) higher system efficiency;(iv) reduction in overall cost and size. A hybrid pulse-width modulation technique generates optimised switching pulses of the A-MMC. A novel voltage balancing algorithm is proposed to stabilise each asymmetric HB submodule at the rated voltage. Circulating current control is implemented to suppress the dominant second harmonic in the arm currents of the A-MMC. Detailed simulations in MATLAB/Simulink are performed to validate the operation and control. A quantitative and qualitative comparison with conventional MMCs is also presented in terms of the converter losses, output voltage/current total harmonic distortion, capacitor ripple voltages, circulating currents etc.
There is a need to transmit the power generated from windfarm in remote locations to the residential and industrial load. One of the suitable and economic solution for such long distance transmission of power is the H...
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ISBN:
(纸本)9784886864055
There is a need to transmit the power generated from windfarm in remote locations to the residential and industrial load. One of the suitable and economic solution for such long distance transmission of power is the High voltage DC (HVDC) transmission. The Modular Multilevel Converter (MMC) based HVDC transmission is a proven technology with very high power quality. A multi-objective control is used to control the MMC, one of the objectives is to deliver the power from windfarm to grid, the other objective of the control is to achieve stable operation of the MMC. In order to achieve a stable operation, the capacitors in the MMC should be balanced and the currents circulating within the phases of the MMC need to be controlled. Many control strategies have been proposed to suppress such Circulating Current (CC). However, there is no clear comparison between these control strategies. In this paper control strategies for the MMC are reviewed specifically the circulating current suppressor. The cascaded control based on PI-controller and the Model Predictive Control (MPC) for outer current control are compared. Results show that traditional method has better steady state performance, while MPC based method has much faster dynamic response and has the advantage of involving less control loops in controlling systems with multiple control aspects. The control methods for capacitor voltagebalancing and the circulating current suppression are simulated and compared.
There is a need to transmit the power generated from windfarm in remote locations to the residential and industrial load. One of the suitable and economic solution for such long distance transmission of power is the H...
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There is a need to transmit the power generated from windfarm in remote locations to the residential and industrial load. One of the suitable and economic solution for such long distance transmission of power is the High voltage DC (HVDC) transmission. The Modular Multilevel Converter (MMC) based HVDC transmission is a proven technology with very high power quality. A multi-objective control is used to control the MMC, one of the objectives is to deliver the power from windfarm to grid, the other objective of the control is to achieve stable operation of the MMC. In order to achieve a stable operation, the capacitors in the MMC should be balanced and the currents circulating within the phases of the MMC need to be controlled. Many control strategies have been proposed to suppress such Circulating Current (CC). However, there is no clear comparison between these control strategies. In this paper control strategies for the MMC are reviewed specifically the circulating current suppressor. The cascaded control based on PI-controller and the Model Predictive Control (MPC) for outer current control are compared. Results show that traditional method has better steady state performance, while MPC based method has much faster dynamic response and has the advantage of involving less control loops in controlling systems with multiple control aspects. The control methods for capacitor voltagebalancing and the circulating current suppression are simulated and compared.
In the application of lead-acid series batteries, the voltage imbalance of each battery should be considered. Therefore, additional balancer circuits must be integrated into the battery. An active battery balancing ci...
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ISBN:
(纸本)9781538605103
In the application of lead-acid series batteries, the voltage imbalance of each battery should be considered. Therefore, additional balancer circuits must be integrated into the battery. An active battery balancing circuit with an auxiliary storage can employ a sequential battery imbalance detection algorithm by comparing the voltage of a battery and auxiliary storage. The system is being in balance if the battery voltage imbalance is less than 10mV/cell. In this paper, a new algorithm is proposed so that the battery voltagebalancing time can be improved. The battery balancing system is based on the LTC3305 working principle. The simulation verifies that the proposed algorithm can achieve permitted battery voltage imbalance faster than that of the previous algorithm.
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