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For high power three-level Neutral Point Clamped (NPC) converter widely used in medium voltage speed regulation system, which has the characteristics of low switching frequency and complex harmonic distribution of output current waveform, output filter is needed in order to protect AC-side device. Normally, LC filter is used for its good performance. However, the low switching frequency and complex...
For a Voltage Source Converter based High Voltage Direct Current Transmission(VSC-HVDC)system the most important part is the VSC part because it determines main performance of the whole system. This paper proposed a new topology of PWM AC/DC converter which is cascaded VIENNA rectifier. In addition, in this paper a current controller based on the working modes of three-phase VIENNA rectifier will...
A new Buck-Boost multilevel inverter is proposed. The proposed inverter is derived from Buck-Boost converter, which is with the ability to buck/boost the input voltage. This is much suitable for the application with wide range varied DC link voltage, such as renewable energy generation. The topology and operate principle of the Buck-Boost multilevel inverter is presented. And the current sharing with...
In this paper, an efficiency comparison of neutral-point-clamped (NPC) inverters and bipolar switch NPC (T-Type) inverters is studied and the result shows that the T-Type inverter is more efficient at lower switching frequencies. Nevertheless, its efficiency suffers when the switching frequency increases due to high switching loss of the equipped high voltage power switches. In order to reduce switching...
This article has proposed a control strategy for balancing the capacitors' voltage of cascaded H-bridge rectifier. The working principle of cascaded H-bridge rectifier has been described, as well as the balancing boundary condition of capacitors' voltage. Then, the dual modulation curves control strategy has been proposed for balancing the capacitors' voltage in dc side of the rectifier. Furthermore,...
The 1700V/400A hybrid module is consisted of Si-IGBTs and SiC-SBDs mounted in a general 2in1 package. Because the reverse recovery current of SiC-SBD is very small to be an unipolar device, reverse recovery and turn-on losses at 400A on the hybrid module are 83% and 38% lower than that of the conventional all Si module, respectively. Therefore there is a further advantage of hybrid module at high...
A stability or resonance analysis of a micro-grid consisting of multiple grid-connected-converters (GCC) with LCL filter is important but complicated, because it is influenced by many factors such as LCL filters of the GCC, the grid impedance and various (nonlinear or even time-variable) loads. It is necessary to construct a framework for revealing and analyzing the main unstable factors and then...
A new Fisher discriminant function based passive islanding detection approach is proposed for distributed generation system in this work. Through observing the harmonic components in the output instantaneous power of distributed generation system, six-dimensional features are obtained for islanding detection. Based on utilizing Fisher discriminant function, a model is constructed to convert the obtained...
Under unbalanced grid voltage conditions, negative-sequence will generate the double fundamental frequency in the dq synchronous rotating reference frame. In order to detect the positive-sequence component of the grid voltages fast, this paper proposes a new phase-locked loop method, called double fundamental frequency phase-locked loop (DFF-PLL). The operation principle is analyzed, giving the extract...
The use of LCL-filter for reducing current harmonics has been commonly used for converters connected to the power grid. However, under non-ideal power grid condition, a converter using an LCL-filter may interact with other converters connecting to the grid. In this paper, a three-phase voltage source converter using an LCL-filter is studied. Simulations show that resonant oscillation occurs in the...
The resonance problem in multi-paralleled grid-connected inverters in microgrid is more complex than single one. The Norton's equivalent circuit associated with grid-connected inverter with LCL filter is figured out in this paper. And in terms of different reasons of causing resonance, resonance problems associated with multi-paralleled grid-connected inverters are categorized into three types: individual...
In this paper, a current-feed resonant two-switch forward DC-DC Transformer (DCX) is proposed for high-efficiency and high-density unregulated bus converter applications. With a resonant capacitor in series with the leakage inductance of the transformer, ZCS turn-on and nearly ZCS turn-off can be achieved for the primary switches and there is no body diode and reverse recovery losses in the SR. Meanwhile,...
LLC resonant converter is an attractive topology to achieve high power density with high efficiency. However, the high switching frequency and circulating current result the poor efficiency of a LLC resonant converter under light load condition. To improve efficiency further, a modified burst-mode control is implemented in the proposed controller. The switching frequency decreases gradually during...
The interleaving technique is necessary for multiphase LLC resonant converters in high output current high power level applications. But the conventional frequency-controlled LLC converters will lose current sharing if all the phases are operating at the same switching frequency. In this paper, a two-phase interleaved LLC-Regulated DCX (LLC-RDCX) with parallel PWM output regulation is presented to...
Multi-MW wind power converters are widely applied in wind power field. Converters are paralleled to expand converter's capacity. Due to the wind power fluctuation, IGBT's power handling ability together with its drive power is fluctuating largely and rapidly, which will cause a large temperature variation, affecting the reliability and lifetime of power semiconductors. In this paper, the thermal smooth...
Offshore wind power converter is usually packed in a closed cabinet equipped with water cooling to meet the moisture and salt spray prevention requirements. When a sudden dip of wind speed happens, the generated power will reduce significantly, making power semiconductor device and cooling water's temperature reduced quickly. While the air temperature inside cabinet decreases slowly. Thus, the water-cooling...
The wind power has the characteristics of intermittent, randomness and uncertainty. In order to make better use of wind power, many scholars use historical data to study the power fluctuation characteristics of wind power generation system,but as for the preparation or built-in wind farms, there are abundant wind speed data but without power data. So how to infer the electric power fluctuations from...
This paper shows that the hybrid bridge resonant converter which is based on the traditional LLC resonant converter, use DSP to toggle between the full bridge mode and the half bridge mode. So the input voltage range is enlarged, and in the high voltage range, the working efficiency is increased by 3%. The switching process between the full bridge mode and the half bridge mode could be made a smooth...
This paper proposes a new integrated control method for modular multilevel converter (MMC). Common mode and differential mode of MMC system are established in this work. As the effect of voltage and current at different frequencies does not produce active power exchange, it is possible to use a set of orthogonal currents to achieve the balancing control of sub-module voltages based on the above modes...
This paper analyzes the active power in modular multilevel converters (MMCs), and presents a novel comprehensive control scheme of low frequency operation for the arm capacitor voltages and high frequency circulating current. The inner loop of this scheme employs the arm current direct control which can control the ac side currents, dc-link current and circulating currents simultaneously; an improved...
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