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The LLCL-filter is emerging into grid-connected converters due to a smaller size compared to the conventional the LCL-filter. Similar to LCL-filter, the high order resonance introduces potential instability to the overall system which should be properly damped either passively or actively. In this paper, different feedback coefficients like the proportional, derivative, integral, high pass and low...
The LLCL-filter has recently emerged into gridconnected converters due to the improved filtering capability which ensuring a smaller physical size. An LLCL -based gridconnected converter has almost the same frequency-response characteristic as that with the traditional LCL-filter within half of the switching frequency range. The resonance frequencies of the LLCL-filters based grid-connected converters...
The series ac capacitor has recently been used with the transformerless grid-connected converters in the distribution power grids. The capacitive characteristic of the resulting series LC filter restricts the use of conventional synchronous integral or stationary resonant current controllers. Thus this paper proposes a fourth-order resonant controller in the stationary frame, which guarantees a zero...
This paper investigates the harmonic stability of small-scale inverter-based power systems. A holistic procedure to assess the contribution of each inverter to the system stability is proposed by means of using the impedance-based stability criterion. Multiple unstable modes can be identified step-by-step coming from the interactions among inverters and passive networks. Compared to the conventional...
This paper proposes an active damper with a series LC-filter for suppressing resonances in an ac power electronics based power system. The added filter capacitor helps to lower the voltage stress of the converter to be used for implementing the damper. Unlike active filters for the compensation of low-order harmonics, the proposed active damper deals with the resonances caused by the interactions...
This paper presents a simple design procedure for LC filters used in wide band gap device based adjustable speed drives. Wide band gap devices offer fast turn-on and turn-off times, thus producing high dV/dt into the motor terminals. The high dV/dt can be harmful for the motor windings and bearings and must therefore be reduced. This may be accomplished by a sine LC filter with DC link feedback, which...
This paper investigates the dynamic interactions of current controllers for multi-paralleled, grid-connected inverters. The consequent harmonics instability phenomena, which features with oscillations above the fundamental frequency, are evaluated by the impedance-based stability criterion. The frequency range of effective impedance-based stability analysis is first identified. The effect of each...
This paper addresses the harmonic compensation error problem existing with parallel connected inverter in the same grid interface conditions by means of impedance-based analysis and modeling. Unlike the single grid connected inverter, it is found that multiple parallel connected inverters and grid impedance can make influence to each other if they each have a harmonic compensation function. The analysis...
Resonant interactions of grid-connected converters with each other and with cable capacitance are challenging the stability and power quality of renewable energy sources based power plants. This paper addresses the instability of current control of converters with the multiple resonance frequencies consisting in LCL filters and cables. Both grid and converter current controls are analyzed. The frequency...
Body diode of SiC MOSFETs has a relatively high forward voltage drop and still experiences reverse recovery phenomenon. Half bridge with split output aims to decouple both the body diode and junction capacitance of SiC MOSFETs, therefore achieving a reduced switching loss in a bridge configuration. This paper makes the current commutation mechanism and efficiency analysis of half bridge with split...
This paper investigates the active damping of LCL-filter resonance within single-loop grid current control of grid-connected voltage source converters. First, the basic analysis in the continuous s-domain reveals that the grid-current-feedback active damping forms a virtual impedance across the grid-side inductor, and the use of a high-pass filter with a negative sign shapes the virtual impedance...
LLCL-filter is recently emerging into grid-connected inverters due to its high attenuation of high-frequency harmonics with a smaller size. Active damping methods have been proposed to reduce the resonance peak caused by the LLCL-filter to stabilize the whole system without extra losses. The active damping method with an extra feedback provides a high rejection of the resonance so that the dynamic...
A straightforward method is proposed in this paper to optimally design the damping sections of the LCL or LCL plus trap filters. The proposed method simplifies the iterative design procedure of the overall filter while ensuring minimum resonance peaking and smaller capacitor than otherwise would be the case. The choice of the traps parameters in case of adopting multi-tuned traps is systematically...
IL-10 signalling blockade by intra-peritoneal injection of anti-IL-10 receptor antibodies at the time of immunization enhances vaccine induced CD8+ T cell responses and promotes bacteria, parasitic and viral control. We now show that blockade of IL-10 signalling at the time of immunization enhances vaccine induced antigen specific CD8+ T cell responses to both dominant and subdominant CTL epitopes...
This paper investigates the effect of grid impedance variation on harmonic resonant current controllers for grid-connected voltage source converters by means of impedance-based analysis. It reveals that the negative harmonic resistances tend to be derived from harmonic resonant controllers in the closed-loop output admittance of converter. Such negative resistances may interact with the grid impedance...
This paper addresses the interaction between harmonic resonant controllers and active damping of LCL resonance in voltage source converters. A virtual series R-C damper in parallel with the filter capacitor is proposed with the capacitor current feedback loop. The phase lag resulting from the digital computation and modulation delays is thus compensated by the virtual capacitor. The frequency region...
In this paper a comprehensive analysis of three passive damping methods is done under parallel operation of multiple current controlled voltage source converters. One could argue that a well damped LCL filter with no peaking in the output impedance and stable designed controllers will turn into stable status under the parallel operation with other converters that share similar configuration. However,...
This paper analyses the stability of paralleled voltage source converters in AC distributed power systems. An impedance-based stability analysis method is presented based on the Nyquist criterion for multiloop system. Instead of deriving the impedance ratio as usual, the system stability is assessed based on a series of Nyquist diagrams drawn for the terminal impedance of each converter. Thus, the...
This paper presents a communication-less distributed voltage control strategy for a multi-bus AC islanded microgrid. First, a Kalman Filter-based network voltage estimator is proposed to obtain voltage responses without communication links in the presence of load disturbances. Then, a voltage optimal controller using MPC (Model Predictive Control) are developed to implement voltage optimal control...
In this paper two promising LCL based filter topologies are evaluated against the well-known LCL with a damping resistor. The filters are designed for high power applications where the frequency modulation index is relatively low. The first topology is the selective resonant LCL filter which aim is to minimize the damping losses by bypassing the resistor at the fundamental and switching frequencies...
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