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Small signal stability of inverter based droop controlled microgrid is a major problem from past decade. In this work, an optimal state feedback controller is designed to improve the stability of the two inverter based test microgrid. The detailed full order small signal model of the test microgrid is developed in state space considering network and load dynamics. Eigen value and sensitivity analysis...
In single-phase inverters, the proportional control is paralleled with the repetitive control to improve the dynamic performances. Meanwhile, in order to guarantee the stability of system, the static error cannot be eliminated in this control. This paper proposed an advanced scheme for the repetitive control to achieve zero error tracking. Taking the advantage of comb filtering by using Fourier transform...
In three-phase grid-tied inverter, grid voltage feedforward is helpful to improve grid-tied power quality for strong grid condition. This paper found that the voltage feedforward had different effect on power quality under weak grid condition compared with that in ideal grid condition. And recent reported studies show that grid voltage feedforward has negative effect for grid-inverter system stability...
In cascaded-type microgrid, the synchronization and power sharing of distributed generators (DGs) become two new issues that needs to be addressed urgently. In this paper, a unified droop control is proposed and its stability is analyzed in the islanded mode. The proposed scheme can ensure the system stability and accurate power sharing without communication in four-quadrant operations. Finally, simulation...
In this paper, a dual parallel connected brushless direct current (BLDC) motors drive system fed by a single inverter is presented and the control method for stable operation in electric vehicles (EVs) application is proposed. To obtain the stability of such a system, both motors should always be respect the synchronism even if they have different load torque. The proposed control method is based...
The accurate and fast detection of the grid voltage attributes (e.g. frequency and amplitude) are gaining more attention in microgrids due to the new stringent amendments to the microgrid standards. In this paper, two novel observer based techniques are introduced; one for estimating the frequency and another for the amplitude of the grid voltage. The proposed observer techniques offer superior performance...
In this paper, a wireless modular control strategy for input-series output-parallel (ISOP) inverter system is proposed to ensure equal sharing of input voltage and output current among the constituent inverters. Compared with existing control strategies for the ISOP inverter system, such as centralized control which restricts the modularity of the system and distributed control which realizes voltage...
A hybrid impedance model of Islanded MicroGrid with Paralleled Inverters Controlled by Droop and PQ Strategies (IMG-PICDPS) is derived, in which the PQ-controlled Inverters (PQ-Invs) are equivalent to Norton's circuits, while the DRoop-controlled Inverters (DR-Inv) to Thevenin's circuits in this paper. An impedance-based stability analysis method is further proposed according to the Nyquist criterion...
Full Feed-forward (FF) approach has been proved to be an effective method to suppress the output current distortion of the LCL type grid-connected inverter (GCI) due to grid voltage harmonics. Since most of the existing FF approachs are realized by digital control, a futher study of the digital control based (DCB) FF approach has been carried out in this paper firstly. It is shown that, there are...
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...
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...
Flux-Weakening (F-W) based on feedback voltage regulation is commonly adopted in Interior Permanent Magnet Synchronous Motor (IPMSM) drive systems. Voltage vector magnitude is controlled in closed-loop by modifying the current reference space vector, following a reference value related to the inverter limitations. Stable and fast voltage control allows to operate with lower voltage margin, which leads...
This paper deals with a newly conceived control topology based on the Repetitive action in 4-leg VSI for stand-alone Ground Power Unit (GPU) applications. In such mode of operation, a dedicated controller has to regulate the inverter output voltages, which are measured at the output of the power filter. The proposed Repetitive Control can provide the required harmonic compensation capabilities that...
This work presents a new Finite Control Set Model Predictive Control (FCS-MPC) strategy based on an input reference tracking. The control structure admits a closed-loop representation featuring a linear dynamic and a perturbation term. Thus, the stability and the design process can be carried out by means of standard control methods. Besides, it reduces the computational burden because the minimization...
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...
The resonance problems may arise among multi-connected LCL-filtered inverters and make the system instable. The recently proposed GSPWM can reduce the filter order without reducing other performance in large-scale application, which has potential to avoid the resonance. But GSPWM will introduce specific phase delay to PWM sequences and it may influence the response character in different grid conditions...
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...
The high R/X ratio of distributed lines in low voltage microgrid causes the coupling between the active and reactive power control. Forcing the output impedance to achieve the decoupling through additional virtual inductor impedance loop heavily causes the voltage amplitude drop at the point of common coupling. Such voltage drop deteriorates the microgrid voltage stability. To avoid the problem of...
High voltage direct current (HVDC) technology has been widely used for its advantages of interconnection of non-synchronous networks and off-shore wind farm to the main power system. In Peru, the perspective of the energy trade between Perú and Chile by a traditional line-commutated converter HVDC (LCC-HVDC) link is being evaluated by Comité de Operación del Sistema Interconectado Nacional (COES)...
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