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The MMC is an emerging and highly attractive multilevel converter topology for medium and high voltage applications. Various modulation strategies are being used to control the MMC system. Balancing the cascaded submodule voltages and eliminating the second order circulating current in the leg of the MMC system are the main concerns of many researchers in the area of MMC system. Mostly, for circulating...
This paper presents a high-power-density high-power-factor GaN-based two-stage electrolytic-free offline LED driver. The LED driver achieves high power density through the use of a hybrid film-ceramic stacked switched capacitor (SSC) energy buffer, and a comprehensive optimization methodology that evaluates various converter topologies and designs, and minimizes overall system volume while maintaining...
This paper proposes a concept of two-terminal active capacitor implemented by power semiconductor switches and passive elements. The active capacitor has the same level of convenience as a passive one with two power terminals only. A control strategy that does not require any external feedback signal is proposed and a self-power scheme for gate drivers and the controller is applied to achieve the...
Input current of a Current Fed Switched Inverter (CFSI) contains the switching frequency component (75 kHz) and a second harmonic component of line frequency (100 Hz) apart from the DC part. In prior designs, the second harmonic component was suppressed by increasing the size of passive components (inductor or capacitor), which makes the inverter implementation bulky. This paper presents a control...
Further growth in renewable energy integration would be dependent on reliability and cost-effectiveness. These two factors can be achieved through power converter topologies that enable transformer-less connection of renewable energy based technology to the grid. This paper presents a three phase five level dual tapped inductor quasi impedance source (qZS)-nested neutral point clamped (NNPC) topology...
A capacitor-isolated structure with brightness and color controlling for multicolor LED strings is proposed. Such structure mainly plays the role of current-balancing and color mixing. Moreover, in order to decrease the color shift, the current amplitude of LED strings is controlled constant. The luminous flux and chromaticity coordinates are regulated through controlling the sum and ratio of duty...
In this digest, a coupling coefficient estimation method for wireless charging system is proposed based on its transmitter and receiver current and voltage harmonics analysis. One of the main challenges of wireless charging in vehicular application is the significant variation of magnetic coupling coefficient between transmitter (Tx) and receiver (Rx) coils due to large air-gap and lateral misalignment...
A capacitor voltage-balancing control strategy based on switching state redundancies is proposed for the hybrid stacked five-level converter. In order to obtain the balancing properties for flying capacitors, a hybrid model in state-space representation is established by considering the continuous and discrete variables. The proposed balancing strategy can control the flying capacitor voltages to...
This paper proposes a new high-voltage Pulse Generator (PG), fed from low voltage dc supply Vs. This input supply voltage is utilized to charge two arms of N series-connected modular multilevel converter sub-module capacitors sequentially through a resistive-inductive branch, such that each arm is charged to NVS. With a step-up nano-crystalline transformer of n turns ratio, the proposed PG is able...
Modular multilevel converters (MMC) have many advantages owing to their power-stage modularity. However, this modularity does not extend directly to the control. Particularly, the balancing control usually requires central coordination and increases in complexity with the system size. This paper presents a balancing control method for a more general modular multilevel converter with series and parallel...
In this paper, a cost-effective and reliable equivalent series resistance (ESR) estimation method for aluminium electrolytic capacitors used as DC-link capacitors in front-end rectifier fed inverters is proposed. The proposed method is based on the extraction of switching frequency components of DC-link voltage and current using band-pass filters. A limiting value of switching frequency is identified,...
Transformer-less single-phase grid-tied inverter is attractive due to low cost, high efficiency, and small size. However, leakage current and second-order ripple power have to be well dealt with. Because the leakage current is a potential threat for body safety and the ripple power will decrease overall efficiency and system reliability. Both issues become obstacles for practical applications. This...
This paper presents a novel control method that enables operation of Modular Multilevel Converters under non-sinusoidal AC supply conditions based on frequency domain decomposition of supply voltages. The proposed control method enables to inject or draw near sinusoidal grid currents even during the presence of harmonic distortions in the supply voltages without the use of additional hardware filters...
The modular multilevel converter (MMC), is widely adopted in high voltage applications because of its simplicity and modularity. However, the current and power flow is very complicated. As a result, methods proposed for capacitor reduction, which is required to stored line frequency related circulating energy, all went through complicated mathematical derivation. C. Li proposed a state plane analysis...
This paper proposes two hybrid asymmetric cascaded multilevel inverters. Both inverters consist of the series connection of a three-level (3L) H-bridge cell and a nine-level (9L) H-bridge cell with an unequal dc voltage ratio of 1:8. The topologies of the 9L H-bridge cell are based on modular multilevel cascade converter (MMCC) with double-star chopper cells (DSCC). Both the proposed inverters can...
To improve the reliability of modular multilevel converter (MMC), the fault submodules must be isolated rapidly. In this paper, a new fast fault diagnosis method is proposed containing two steps: fault detecting and fault locating. Fault detection step finds failures by improved predictive model which detects the fault by comparing the difference between the predictive value and the measured one of...
The modular multilevel converter (MMC) has become the most promising converter technology for high power applications. However, to get more number of levels in the output voltage, a conventional MMC requires large number of submodules. The main technical challenges of an MMC, with a large number of submodules, are the requirement of large number of semiconductor switches, submodule capacitors and...
DC grid technology is regarded as a promising solution for future electric networks integrating a great amount of renewable energies. It calls for high-efficiency bidirectional dc-dc converters with a high step-up ratio to interconnect mediumvoltage dc (MVDC) distribution grids and high-voltage dc (HVDC) transmission grids. This paper focuses on dynamic performance and fault-tolerant capability of...
In this paper, an asymmetric mixed MMC topology of multilevel converter for bipolar HVDC transmission systems is introduced. Among the existing MMC topologies for the bipolar HVDC systems, the asymmetric mixed MMC topology provides the benefits of: a lower number of submodule cells, fewer switching devices and lower conduction losses. Furthermore, the HVDC based on asymmetric mixed MMC can be flexibly...
For Smart Transformers (ST), reliability is one of the major problems when compared to the traditional low-frequency transformers. Modular ST with advanced control algorithms could increase the reliability compared to the non-modular solutions. This could be achieved by distributing differently the power among the cells depending on their aging. This unequal power transfer is a challenge for Cascaded...
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