Phase-locked loop (PLL) and grid impedance easily negatively affect the stability of grid-connected inverter system even cause oscillation. To suppress this oscillation, a enhancing voltage feed-forward control method is proposed to reduce effects PLL impedance. Then, considering frequency coupling characteristic, admittance model with established, characteristic inverters traditional are compared analyzed. Analysis results indicate that improves in different short-circuit ratio (SCR)...

It tends to cause system oscillation when the inverter with a phase-locked loop based on proportional integral controller (PI-PLL) is connected weak grid. To improve suppression ability of grid-connected inverter, linear active disturbance rejection applied PLL (LADRC-PLL). Considering influence extended state observer, voltage outer-loop, current inner-loop, and frequency coupling, admittance model LADRC-PLL established. Based established generalized Nyquist criterion, stabilities inverters...

Source-side virtual synchronous machines (VSGs) and load-side VSMs (LVSM) are gradually utilized together in the microgrid to provide inertia damping. However, instability occurs islanded system due interaction dynamics between VSG LVSM, which has been investigated this article. At first, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -frame impedance models of LVSM established compared. It is revealed that d-d channel behaves...

Microgrid cluster as an interconnected system of multiple AC subgrids and DC subgrids, its complex structure increases the difficulty power coordination control for it. To address this issue, a microgrid autonomous strategy are proposed in paper. The is composed exchange unit (PEU) energy pool (EP). aim PEU mainly to coordinate between EP. Meanwhile, coordinated method design controller PEU, which can realize mutual support among each sub-grid reduce bus voltage deviation subgrid. Besides,...

Small-signal stability problems often occur when the inverter for renewable energy generation is connected to weak grid. A small-signal transfer function integrated model reflecting interaction of grid impedance, phase locked-loop (PLL), and current control loop established in this paper. Based on model, oscillation mechanism grid-connected system revealed: inductance flowing through impedance can produce a voltage disturbance, which will eventually affect PLL loop. Therefore, composed...

The stability of grid-connected wind power system (GCWPS) is prone to deteriorate due the impedance interaction between turbines and weak grid. For purpose finding out cause oscillation effectively improving GCWPS under grid, firstly all, a frequency coupling model (FCIM) for established. Through analyzing characteristic GCWPS, significant effect grid in middle-low region observed, which easy oscillation. restraining this paper proposes an suppression strategy based on composite feedforward...

Direct power control (DPC) is widely used in grid-connected inverters. First, considering the effects of phase-locked loop (PLL), voltage outer loop, inner delay, and frequency coupling, a broadband admittance model inverter with DPC established. The characteristics inverters closed-loop current (CCC) are compared analyzed. Due to different objects, components produced by calculation Park's transformation CCC cause differences between CCC. Then, grid impedance, output power, parameters on...

The load-side virtual synchronous machine (LVSM) enables the load to actively participate in grid regulation, but it might still induce oscillations a weak grid. Considering dc-link voltage controller, power loops, ac and current control delay, sampling filters, wideband dq-frame impedance model of LVSM is first established, found that Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dd</sub> exhibits negative resistor within 10 Hz. In...

Impedance-based approachis generally studied for stability analysis of the power electronic converter-based system. Considering multiple-frequency coupling effects, in this article, we establish harmonic transfer function (HTF) based <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">αβ</i> -frame impedance models droop inverters islanded microgrid with unbalanced loads. Therein, HTF-based -impedance modeling methods loads, as well parallel, are...

This paper intends to comparatively study the stabilities of grid-connected inverters with three closely related controllers: quasi-proportional resonance (quasi-PR), proportional integral (PI), and (PR) under weak grid. Firstly, considering influence frequency coupling characteristic, a admittance model quasi-PR controlled inverter is established. Then, characteristics quasi-PR, PI PR are compared. Admittance similar while quite different: amplitude larger than that phase difference between...

Due to the dynamic interaction between inverter and grid, may have power oscillation problems under a weak grid. In this article, considering frequency coupling, more precise broadband sequence admittance model of current-controlled virtual synchronous generator (CVSG) is established, characteristics CVSG traditional grid-connected (TGCI) are compared analyzed. The amplitude generally larger than that TGCI in low-frequency region, entire sweep range, coupling TGCI. has great impact on...

Transient angle instability and fault overcurrent are two serious problems affecting the safe operation of virtual synchronous generator during grid faults. However, aspects mostly treated as independent in existing studies. In this article, taking both transient into consideration, a two-stage control collaboratively utilizing impedance (VI) switching PI is put forward. stage one, VI switched to boundary value determined by iteration algorithm avoid overcurrent. two, proportional loop or...

Admittance identification is an effective tool to solve the issue of black-box admittance modeling in wind farms. However, due large operating range farms, it difficult accurately identify model farms under all conditions, which limits research on wideband oscillation caused by interaction between and power grid. This paper analyses characteristics frequency-coupling for It found that power-sharing ratio turbine generators (WTGs) affects characteristic farm, leads a huge number points farm....

Self-synchronizing voltage source inverter (SSVSI) can effectively improve grid frequency stability. However, the synchronous resonance (SFR) inevitably exists in SSVSI. In this paper, a small-signal model considering power coupling is established to analyze system characteristics. It found that control parameter adjustment and virtual resistance method suppress SFR. will change dynamic steady-state characteristics of system, exacerbate system. For reason, based on idea eliminating peaks,...

The impedance or admittance characteristics of the grid-connected inverter play an important role in its stability analysis. traditional sequence-admittance measurement methods mostly rely on special equipment adjacent inverters for disturbance injection. Because high hardware cost inconvenience, abovementioned are not suitable price-conscious testers to some extent. To address issues, this article proposes a method with control system disturbance. First, model measured when...

In the grid-connected inverter based on deadbeat current control, filter inductance variation and single update PWM affect distortion of grid current, stability, dynamic system. For this, a double method for controller in three-phase system is proposed, which not only effectively decreases control delay, but also improves stability response speed due to reducing characteristic root equation order closed-loop transfer function. The influence deviation coefficient performance analyzed. As...

The island inverter under dual-sequence control method controls the negative sequence voltage by introducing a branch to ensure symmetry of output voltage. In this paper, small-signal wide-band impedance model is established harmonic linearization method. Then, frequency-sweeping simulation carried out in MATLAB. sweep result consistent with model, which proves correctness impedance. analysis shows: fundamental cause double-sequence can suppress that greatly reduces at frequency (50Hz),...

The control structure and parameters of the grid-connected inverter in actual projects are usually unknown, which results "black-box" phenomenon. traditional impedance modeling method is not suitable for black-box. In this paper, a black-box identification admittance inverters under all operating conditions considering frequency-coupling proposed. Firstly, accurate discrete data acquired by measurement. Then, vector fitting (VF) applied to identify single condition. models identified VF...

In the series-compensated grid-connected system (SCGCS), there is an impedance interaction between inverter and grid that prone to cause resonance in SCGCS. this paper, firstly, considering effects of phase-locked loop (PLL), current-loop, frequency coupling, broadband model SCGCS established. The stability analyzed by impedance-based Nyquist criterion. It found from analysis leading resonance. An reshaping based suppression method proposed suppress phase characteristics equivalent output...

When the control parameters and operating conditions remain unchanged, it is usually believed that admittance characteristic of grid-connected inverter time-invariant. However, considering effect frequency-coupling, an abnormal phenomenon observed in measurement inverter: phase off-diagonal elements <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> <sub xmlns:xlink="http://www.w3.org/1999/xlink">12</sub>...