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In this paper, the stability study of a multiple offshore parallel long-cable-connected inverters (MOPLI) systemhs has been presented. It is shown that, since this MOPLI system is consisted of a large number of different inverters and long cables, its stability assessment actually faces big challengs. In addition, though there are lots of existing impedance-based stability criteria about prallel inverters,...
This paper proposes spread spectrum methods to reduce radiation noise caused by an inductive power transfer (IPT) system. A noise reduction method with spread spectrum techniques has been proposed. The proposed noise reduction method randomly changes the output frequency of an inverter within a range of 79-to-90 kHz. Changing the output frequency, the radiation noise is spread in a frequency domain...
In this paper, a three loop control strategy (TLCS) based on decoupled zero voltage switching angle (ZVSA) loop is proposed for a series-series (SS) compensated wireless power transmission (WPT) system. To realize constant current charging for EVs and ZVS operation of primary inverter, variable frequency and phase shift control strategy (VF-PSC) is adopted. However, the control variables that are...
Current-controlled LCL-filtered inverters are usually paralleled together for interconnecting the renewable energy resources into the grid. When the inverter output impedance is not well designed, the harmonic circulating currents out of the control bandwidth may be easily aroused. To reveal this resonant phenomenon and to enhance the stability of the parallel system, this paper builds the parallel...
The increasing use of grid-connected inverters to connect renewable energy sources to a power grid will have globally important effect on grid performance. A mismatch between the grid and inverter impedance may cause harmonic resonances, which can lead to instability of the grid and disruption of inverter operation. The grid dynamics vary over time, so the inverter should adapt to the varying conditions...
The proportional power sharing has been identified as an important issue to guarantee reliability on the operation of low voltage AC-Microgrids. However, inaccurate reactive power sharing in scenarios with line impedance mismatches, and slow transient response remain important limitations of most of the conventional power sharing controllers. In this context, an improved method for power sharing control...
Ultra sparse matrix converter(USMC) is a derived form of Indirect matrix converter(IMC) having less no of switches. Though it has unidirectional power flow capability it is very useful for specific applications such as wind energy systems, electrohydrostatic actuator, variable speed drives etc. However its main limitation is lower gain for which various control strategies and topological changes had...
Applying RF circuit design techniques to dc-dc power conversion has pushed the switching frequency of power converters using discrete components beyond 100 MHz. This paper proposes a simple solution to implement synchronous rectification for resonant dc-dc power converters operating in the Very-High-Frequency (VHF) range, by using a symmetric bandpass matching network between the inverter and rectifier...
This paper introduces a single-stage isolated 48V-to-1.8V point-of-load converter based on the impedance control network (ICN) resonant converter architecture. This point-of-load ICN converter achieves large step-down while maintaining high efficiency across a wide range of input voltage and output power. Large step-down is achieved through a combination of stacked inverters, a transformer and a resonant...
There has recently been a significant interest directed towards residential battery storage systems mainly motivated by high penetration of renewables, the low cost and high efficiency of power electronic devices, and the advancements in the safety and energy density of the batteries, especially Lithium-Ion (Li-Ion) batteries. Furthermore, the possibility for the end user to become a utility-independent...
Capacitor-current-feedback active damping method is commonly used in LCL-filtered grid-connected inverters, which attenuates the resonance peak by emulating a virtual resistor in parallel with the filter capacitor. Taking the digital control delay into account, the emulation component becomes frequency-dependent, and it will turn negative when the filter resonance frequency becomes higher than one-sixth...
Because of the differences in line impedances, parallel inverters with conventional droop control will have huge circulating current, which does not flow through the loads. To mitigate the circulating current, the research in this paper finds out that parallel-operated inverters should have the impedance in inverse proportion to their capacities, which is difficult to realize in practice. To meet...
To avoid the stability problem of grid connected inverter caused by the conventional phase locked loop (PLL), the direct power control of voltage source inverter in virtual synchronous reference frame without PLL is investigated considering grid voltage disturbance in the paper. Based on the small signal analysis methods, comparison between conventional PLL and no PLL is made. It can be found that...
Instabilities due to mutual interactions among inverters in a grid system are sometimes observed. This paper proposes a stabilization method which adds feed-forward (FF) loop characteristics to improve output frequency impedance characteristics which satisfy the Nyquist stability criterion. The principle is that the output impedance is compulsively made passive with the FF loop characteristics and...
There is an increasing need to model large networks of inverter-based distributed generation due to the limits of existing simulation tools. A deliberate enforcement of intra-feeder coherency between adjacent droop-controlled inverters is a worthwhile objective, as phase angle coherency will allow for a deliberate partitioning of fast and slow dynamics within the network. This partitioning, in turn,...
As a basic building block, the phase-locked loop (PLL) has been widely used in the grid-connected voltage source inverter (VSI). But it has been shown recently that PLL has adverse impact on stability of grid-inverter system. In a weak grid, the PLL may cause unexpected harmonic, or even instability. In order to overcome this problem, this paper proposes a q-axis voltage feedforward control method...
Harmonic resonances around the intersection frequency is triggered with the stability margin decreasing to zero and the system will be unstable with the stability margin reducing to be negative. For suppressing harmonics, the phase difference between the inverter admittance and grid admittance should be lower than 120° at their intersection. Based on this principle, a phase-reshaping strategy aiming...
Fault current limiters (FCLs) are one class of solutions to cope with the upcoming challenges in microgrid protection. Considering high penetration of distributed generations (DGs) in microgrids, the necessity of designing cheap and effective FCL is getting higher. This paper attempts to fill this gap by proposing an embedded FCL operating based on modifying the secondary control of DGs. As this method...
In this paper, magnetically-coupled impedance source (MCIS) three-phase four-switch inverters are introduced for renewable energy applications. This inverter utilizes two single-phase MCIS inverters to obtain a three-phase output, where less component-count is achieved in order to reduce the inverter volume. On the other hand, as a result of the reduced number of switches, the proposed inverter suffers...
The grid-connected inverter with a LCL filter has the ability of attenuating the high-frequency current harmonics. The current distortion caused by harmonics in the grid voltage is difficult to be eliminated. Applying proportion feedforward of the grid voltage can suppress the effect of grid voltage harmonics. However, weak grid is commonly seemed as a voltage source which contains a grid impedance...
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