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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...
Grid-connected Voltage Source Inverters (VSIs) equipped with LCL filters are attractive in utility applications for their better power quality features, while the inherent LCL resonance may limit the current control loop bandwidth or even threaten system stability. Simple but effective single-loop current control strategies have been studied for obtaining a stable system, where either the inverter-side...
The resonant stability problems of LCL filter have become big challenges for grid-connected inverter in weak grid. This paper takes the effect of non-minimum phase time delay on the ratio between resonance frequency and sampling frequency into account and use it to design the LCL filter. Both LCL resonance frequency and inverter-side inductor and filter capacitor related L1C resonance frequency are...
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...
The virtual synchronous generator (VSG) is the interface between distribute generator and power grid, which has the inertia and damping characteristics of the synchronous generator. This strategy can effectively control influence of inverters on power grid. In order to reduce the circulating current and power oscillation, this paper proposed a pre-synchronization control strategy which adds the pre-synchronization...
In this paper, a simplified robust control is proposed to improve the performance of three phase current controlled voltage source converter connected to the grid with an inductance-capacitor-inductance (LCL) filter. The presence of the LCL filter resonance complicates the control system dynamics and limits its overall performance, particularly when disturbances and parametric uncertainty are considered...
A large amount of distributed generation is connected to the grid, reducing rotational inertia of the power system. Based on the Static Synchronous Generator Model, inertia controller is introduced on outer voltage loop in this paper to enhance grid inertia. The developed inertia controller can generate inertial current superposed in conventional current reference. The inertial current can be adjusted...
The recently proposed concept virtual synchronous generator (VSG) has been intensively researched. Its core idea is to add a segment in traditional inverter control to simulate synchronous generator's rotor motion characteristic so that the distributed energy resources (DER) can have virtual inertia. VSG control usually contains output current amplitude limiting part to avoid too large current from...
A supplementary control method based on the internal model principle (IMP) is proposed to control damped oscillations. As a case study, low frequency oscillations threaten the stability and the performance of power systems. The challenge, however, is how to acquire the frequency and the damping of oscillations on-line since the parameters of oscillations are unknown in a power system. To design an...
This paper presents a new approach that provides scaling the LCL-filter inductances based on the harmonic analysis of the filter output current. The approach considers the filter design together with the inverter control, both together, improving the system stability and the dynamic response. The model and general guidelines for selecting the filter parameters, taking into account the variation of...
The inverter based on LCL-type filter is a main technical approach used to improve the technical index of grid-connected current, but it is likely to trigger a problem of system stability due to the existence of resonance peak. In terms of the grid-connected inverter with LCL filter, a double closed-loop control strategy based on the combination state feedback is proposed in this paper. This double...
This research work proposes an application of conjugate gradient algorithm for optimization of adaptive Feedback Linearization Control (FBLC) strategy for damping power system oscillations through HVDC link. The nonlinear supplementary control scheme is based on real-time optimized NeuroFuzzy identification of the power system dynamics. A self-tuned (FBLC) is employed to derive appropriate control...
LCL-filter is commonly used as an output-side filter in a grid-connected converter due to its good attenuation capability at the switching harmonic frequencies. LCL-filter creates several resonances in the converter dynamics which shall be damped for ensuring robust performance of the converter. The resonant behavior introduced by the LCL-filter can be attenuated with active damping (AD) instead of...
For the grid-connected voltage source inverters, the feedforward scheme of grid voltage is commonly adopted to mitigate the current distortion caused by grid background voltages harmonics. This paper investigates the grid-voltage-feedforward active damping for grid connected inverter with LCL filter. It reveals that proportional feedforward control can not only fulfill the mitigation of grid disturbance,...
Dynamic frequency regulation and effect of penetration of static and inertial sources on system stability are important issues for islanded microgrid power quality and reliability. This work presents a novel strategy of utilizing an inverter based source as a voltage source inverter (VSI) or virtual synchronous generator (VSG). Electro-mechanical and power modes are critical for small signal stability...
LCL-type filters are widely used in grid-connected voltage source inverters, since it provides switching ripples reduction with lower cost and weight than the L-type counterpart. However, the inclusion of LCL-filters in voltage source inverters complicates the current control design regarding system stability issues; because an inherent resonance peak appears due to zero impedance at that resonance...
Supplementary control of active power through the HVDC converter station to improve the damping of power oscillations in the GB network is demonstrated. Measurement-based system identification approach is applied to accurately estimate linear state-space models of the GB system. The linearized models are used to design controllers to improve the dynamic stability of the system using both local and...
Stability in the nowadays distribution power system is endangered by interaction problems that may arise from newly added power-electronics based power devices. Recently, a new concept to deal with this higher frequency instability, the active damper, has been proposed. The active damper is a power electronics based power device, which provides an adjustable damping capability to the power system...
This work presents a virtual synchronous generator (VSG) strategy for a single-phase current-source inverter. The proposed strategy uses PI controllers with reference tracking capability to control the inverter in either voltage or current mode. For each mode of operation a particular VSG model is developed. From the simulated cases it was observed that the control was capable of controlling the inverter...
This paper demonstrates a novel approach for the design of Unified power flow controller (UPFC) based damping controller. A damping controller is universally adopted to reduce the low frequency of oscillation in a power system. Finding the controller parameters is considered to be an optimization problem. The estimation of optimum values for a damping controller requires strong and efficient optimization...
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