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This paper presents the DC analysis of the Negative Output Elementary Luo Converter (NOELC), which includes the continuous-conduction mode (CCM) voltage gain and the boundary condition between the CCM and the discontinuous-conduction mode (DCM). The main features of the NOELC are the high gain with small ripple and the reverse output. Additionally, we address the parameters design of the NOELC and...
This paper proposes a transformer-less modular multilevel DC/DC converter. The proposed converter can be used to interconnect two HVDC systems with different dc voltage levels and realize bidirectional power flow. Based on the arm energy balance condition, the optimal design arming at minimum inner circulating current is presented. A power close-loop control method is adopted to regulate the converter...
Vector control is the most commonly used control strategy for modular multilevel converter (MMC) based HVDC system. However, due to the complicated structure of MMC, there is no precise mathematical model for the outer DC voltage loop. The conventional model ignores the capacitor voltage dynamics, and the AC voltage boosted operation scenario is not considered. This paper proposes a small signal model...
In this paper, the energy conservation law in physics is introduced into the control prototype of boost converters. Firstly, the input and output energy and the energy changes in the reactive components in each switching cycle are analysed. Then an energy balance control (EBC) method is designed based on the energy conservation law, which is independent of converter work modes, continuous conduction...
This paper proposes a transient modeling and analysis method for the fractional-order DC-DC converters in continuous conduction mode (CCM), in which a fractional-order Buck converter is taken as an example. By extending the usage of equivalent small parameter method (ESP), the converter is modeled by a general state vector differential equation. Then by adopting the principle of harmonic balance,...
A novel load current sharing method is proposed for multi-module LLC resonant converters in high power application in this paper. The paralleled system is controlled by the maximum current sharing method to achieve load sharing automatically. Moreover, a series inductor is connected to each LLC output side to restrain the current ripple of double switching frequency. The maximum current sharing method...
Transformerless inverters are being widely used in low power grid-connected photovoltaic (PV) generation systems. Transformer elimination has many advantages; it reduces cost, size, weight and also increases the whole system efficiency. However, once the transformer is removed, there is no galvanic isolation between grid and PV array and, as a consequence, a leakage current may appears due to the...
Grid-connected inverter is an important part of the grid-connected system. Compared with the traditional L or LC filter, LCL filter has a better high-frequency harmonic attenuation performance. However, LCL filter has resonant peak, which has a great influence on the stability of the system. This paper first analyzes the effect of passive damping method on the resonance peak; then a double closed-loop...
Series compensated transmission lines challenge legacy protection schemes. In this paper, a dynamic state estimation based protection (EBP) method is proposed to address these challenges. The method requires GPS synchronized measurements at both ends of the line and a high-fidelity model of the protection zone. The paper presents the dynamic model of the protection zone and its impact on the performance...
This paper presents the application of a robust nonlinear optimal controller for regulating the active and reactive power in a grid-connected three-phase inverter, which includes an LCL filter to mitigate the total harmonic distortion. The optimal control law is derived from the Hamilton-Jacobi-Bellman equation for state-dependent coefficient factorized nonlinear systems. An integral control term...
This paper presents a voltage control strategy for a DC load powered by a three phase inverter connected to a Permanent Magnet Synchronous Generator (PMSG). The DC load consists of a DC capacitor in parallel with the inverter and the unknown current load. The control strategy is designed based on Simple Adaptive Control (SAC) technique. The structure is a cascade controller designed in rotor reference...
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...
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...
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...
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) 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...
Since the capacitor equivalent series resistance (ESR) above 1kHz almost stays constant, dc-link current root-mean-square (RMS) closed form equation is an easy way to evaluate the capacitor losses from the switching harmonic currents (SHCs). But when the ac current contains multiple low order harmonics (LOHs), their impacts on the dc-link has not been systematically studied. In this paper, a straightforward...
This paper proposes possibilities of Y-connected three-leg topologies, that are built from combinations of two-level and three-level legs (hybrid structures). Therefore, four topologies are studied and compared in aspects such as harmonic distortion of output voltages and rating of power switches. Additionally, semiconductor losses comparisons in different scenarios of load (either high current or...
This paper presents an indirect model predictive control to develop a direct power regulator for a modular multilevel converter connected to a high voltage direct current bus line, where the main task is to bidirectionally transfer active power to the grid and simultaneously compensate reactive power. The main advantage, of the proposed dynamic matrix control methodology, is to capture the system...
This paper proposes a high efficient soft-switching multiple-input positive buck-boost converter. Multiple-input converters (MIC) use usually forward-conducting-bidirectional-blocking (FCBB) switches to control their input voltages and currents. However, these FCBB switches may decrease the overall system efficiency because of their switching losses. This paper applied a soft-switching method into...
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