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The high penetration level of power electronics interfaced Distributed Generation (DG) systems creates great ancillary services potential through the DG interfacing converters (IFCs) such as the grid unbalanced voltage compensation. However, the unbalanced voltage compensation may cause adverse effects on the IFCs' operation such as output active power oscillation and DC link voltage variations. Moreover,...
Synchronous rectifier (SR) is widely used in flyback converter to reduce the output side conduction loss in order to meet the system conversion efficiency requirement. The conventional SR driving methods are not suitable for high frequency (>500kHz) application. This paper proposes a novel SR driving method for MHz flyback converter operating at critical conduction mode (CRM). A RC network is in...
In this paper, it found that the low frequency oscillation phenomenon causing large inductor current and output voltage variations exists in the constant-on-time (COT) controlled boost converter, while the time constant of the output capacitor is below a critical value. The critical value is deduced, which is related to the main circuit parameters such as input voltage, inductance and load current...
In the basic zero-voltage-switching (ZVS) full-bridge (FB) converter, the output rectifier diodes suffer from hard-switching, results in severe voltage spike and oscillation across the output rectifier diodes. In this paper, a fundamental approach is proposed to tackle this issue, indicating that clamping the voltage across the winding of the power transformer could eliminate the voltage oscillation...
To achieve higher output PWM frequency with limited switching frequency of devices, a topology named parallel frequency-multiplication is employed in this paper, which, however, leads to more serious current spike and oscillation in the turn-on transient because of the parallel of devices. Aiming at this issue, the theoretical analysis of transient process is presented to explain how the current spike...
In this paper sub-synchronous control interactions (SSCI) in doubly-fed induction generator (DFIG) based wind farms are studied. The SSCI problem has come into prominence since the Electric Reliability Council of Texas (ERCOT) event of 2009, where a faulted line and subsequent outage in the network caused a large DFIG wind farm to become radially connected to the series compensation network, resulting...
The introduction of 1200 V Silicon Carbide (SiC) based technologies has enabled the use of high performance LLC converters for high input voltage (>500 VDC) applications such as datacenter power conversion. In this paper, we describe performance of the magnetics for a 2 kW-level LLC converter, operating at 100 kHz with SiC devices. We present magnetics designed for high converter efficiencies (>...
By utilizing next-gen wide band-gap (WBG) devices, such as GaN and SiC, at high switching frequency in a single-phase Quasi-Z-Source PV inverter (qZSI), the impedance network can be significantly reduced. Although, the reduced qZS impedance network will decrease cost and improved power density, it will also result in frequency resonance that will introduce oscillations in the capacitor voltage and...
Multilevel Cascaded H-Bridge (CHB) converters have attractive features for the implementation of large scale photovoltaic systems. They can be directly connected to high voltages and the multilevel voltage synthesis reduces the harmonic distortion introduced. In addition, they have individual DC links ideal for connecting photovoltaic arrays. Existing high performance voltage balancing techniques...
In this paper, the impact of dc-link voltage ripples on the machine-side spectrum is investigated. The analysis is targeted for a high-power converter using NPC H-bridge topology. Due to the high amplitude of 2nd harmonic and additional f0/2 sub-harmonic that is introduced by a special modulation scheme, their impacts on the machine are at question. In this work, these questions are addressed via...
The multi-terminal DC grid can be integrated to the existing meshed AC grid system to provide back-up in case of transmission line failure and enhance power transmission capacity and flexibility in existing ac grids. In addition to that, Power oscillations can also be damped effectively through modulation of both active and reactive power of a voltage source converter (VSC) based multi-terminal DC...
In order to integrate renewable energy into the utility grid with high penetration, AC/DC hybrid microgrids have obtained much attentions in recent years since they feature both advantages of AC microgrids and DC microgrids. In an AC/DC hybrid microgrid, the parallel-operated AC/DC bi-directional interfacing converters (IFCs) are key elements to connect AC bus and DC bus. When unbalanced grid faults...
An output filter design is presented for high bandwidth high power inverter in this paper. Various filter topologies are compared to eliminate the switching frequency components effectively while generating various output voltage waveforms up to 10 kHz without distortion. This ultimate design consists of an R-C series branch connected in parallel with the C of conventional L-C filter resulting in...
Harvesting renewable energy sources is the key to solving the global energy crisis. The grid-connected voltage source inverter (VSI) is an essential part of the two-stage power conditioning system used to extract power from renewable energy systems and deliver it to the utility grid. Conventionally, an L-filter has been used to filter switching harmonics produced by the VSI. The LCL-filter, however,...
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