The paper presents to develop a new control strategy of limiting the dc-link voltage fluctuation for back-to-back pulsewidth modulation converter in doubly fed induction generator (DFIG) wind turbine systems. reasons are analyzed. An improved with instantaneous rotor power feedback is proposed limit range voltage. experimental rig set up valid strategy, and dynamic performances DFIG compared traditional method under constant grid Furthermore, capabilities keeping stable also ride-through...

This paper presents an enhanced control method for a doubly fed induction generator (DFIG)-based wind-power generation system with series grid-side converter (SGSC) under unbalanced grid voltage conditions. The behaviors of the DFIG SGSC during network unbalance are described. By injecting generated from to balance stator voltage, adverse effects upon DFIG, such as and rotor current unbalances, electromagnetic torque, power pulsations, can be removed, then conventional vector strategy...

We report a highly sensitive refractive index (RI) sensor based on three cascaded single-mode fiber tapers, in which weak taper is sandwiched between the two tapers to improve sensitivity of sensor. Experimental results show that device 0.286 nm for 0.01 RI change, about four times higher than normal two-cascaded-taper-based Mach-Zehnder interferometer. In addition, could be enhanced by tapering longer and thinner middle taper. Such kinds low-cost fiber-optic sensors would find applications...

With the increasing penetration of wind power, stability issues weak AC grid-connected doubly fed induction generator (DFIG)-based turbines during low-voltage ride through (LVRT) cannot be neglected. In order to explore instability mechanism DFIG system grid fault, small signal state-space model is established in this paper. The results modal analysis show that dominant unstable poles are mainly impacted by phase-locked loop (PLL), rotor current control loop, and terminal voltage where PLL...

Large-scale wind farms are generally integrated by long-distance transmissions, but power grids cannot sufficiently support the access point voltage of these farms. The undergoes a stability problem under speed variations. However, reactive compensation device reconcile requirements response and capacity. Despite their fast decoupling control, capability doubly fed induction generators is restricted active output. To satisfy demand system variations, coordinating output farm key solution,...

In this paper, we propose an improved subsynchronous resonance (SSR) damping controller (SSRDC) and a related control strategy to mitigate the SSR in capacitive series-compensated double-fed induction generator based wind farms, on torque analysis. The proposed is utilized for enhancing system stability. Compared with traditional controller, SSRDC simultaneously embedded into d-axis q-axis channels inner current loop of rotor-side converter. On basis, combined eigenvalue analysis particle...

The dynamic behavior of converters with different synchronous control modes is significantly different. Therefore, the renewable energy grid-connected system cannot be equivalent as same type power electronics equipment. There are interactions among multiple time scale controllers each equipment, which may lead to small signal instability hybrid system. In this paper, a phase-locked loop (PLL) controlled doubly fed induction generator (DFIG) and virtual (VSG) converter studied. On basis...

The voltage-frequency coupled transient stability and risk assessment issues of weak grid-connected large-scale renewable energy plants (REPs) during low voltage ride through (LVRT) have received little attention to date. shape mechanism instability LVRT are investigated in detail by the voltage-vector-triangle graphic (VTG) method utilized this article, which avoids complex mathematical calculations. In addition, margin transmission line's angle (MTVA) is defined article then used...

In this article, the transient synchronization process of grid-connected voltage source converters (VSC) is studied detailly. Firstly, phase-locked loop (PLL)-synchronized VSC modeled according to rotor motion equation synchronous generator (SG). Furthermore, VSC's damping ratio derived, and effects control parameters operation status on equivalent power angle (EPA) investigated. Moreover, influence PLL's dips degree frequency behavior are analyzed. Analysis result reveals that decreases...

The virtual synchronous generator (VSG) control has been widely used in grid-connected inverter to effectively increase the equivalent inertia of power system. However, active oscillation similar electromechanical transient characteristics conventional (SG) is introduced grid, especially under condition multi-virtual synchronizer. In this paper, dynamic stability multiple voltage source converters (VSC) controlled by VSG studied. Firstly, system linearization model established analyze risk....

To enhance the frequency regulation capability of direct‐drive permanent magnet synchronous generator (PMSG)‐based wind‐power generation system, control strategy for system with flywheel energy storage unit (FESU) based on fuzzy proportional plus differential (PD) controller is proposed in this study. According to mathematical model PMSG‐based FESU, small‐signal whole deduced detail. In addition, eigenvalue loci are investigated obtain appropriate ranges FESU's PD parameters ensuring stable...

The commutation failure fault usually occurs in the line-commutated-converter-based high-voltage direct current transmission system. When occurs, voltage of sending alternate (ac) system changes rapidly, and connected doubly fed induction generator (DFIG)-based wind turbine may be tripped. Thus, ride through (FRT) control strategy DFIG should investigated for enhancing stability ac However, during is not changed rectangular shape, besides, presents "first reduce then rise" characteristic,...

In an offshore wind farm connected with a high-voltage direct current (HVDC) transmission system based on modular multilevel converter (MMC), symmetric fault the outgoing line at sending end (SFOLSE) exhibits complex controlled characteristics in current, which can undermine reliability of relay protection. Detailed analysis control interaction between and MMC station (MMCSS) is conducted to ascertain characteristics. Considering constraints imposed by existence stable operating point (SOP)...

This paper investigates a control strategy for wind farm with the direct-driven permanent-magnet synchronous generators (PMSG)-based turbines and fixed speed induction (FSIG)-based under unbalanced grid voltage condition. By controlling PMSG-based to inject negative-sequence current decreasing unbalance factor (VUF) at point of common coupling (PCC), double frequency oscillations in electromagnetic torque, active, reactive power output from FSIG-based can be suppressed. In this paper,...

The instability issues of grid-connected voltage source converters (VSC) may easily occur during low ride-through (LVRT), especially when connected to a weak ac grid. In this study, small-signal model the VSC system was developed deal with stability problems deep sags. Based on model, interaction between phase-locked loop (PLL) and current control has been illustrated. addition, eigenvalue modal analysis method employed investigate influencing factors stability, which include bandwidths PLL...

In this paper, the coupling mechanism of phase-locked loop (PLL)-synchronized multiparalleled wind farms under grid faults is analyzed in detail. First, effects currents and equivalent power angles (EPAs) among are identified by analyzing voltage characteristics during low ride-through (LVRT). Subsequently, a transient stability assessment method proposed for to evaluate effect output multiple on EPA distribution characteristics. This can be applied whether each farm system has equilibrium...

This paper mainly proposes a capacity configuration strategy for hybrid wind farm with fixed-speed induction generator (FSIG)-based and permanent magnet synchronous (PMSG)-based farms during grid faults. In this paper, FSIG-based realizes low voltage ride through (LVRT) the associated control of nearby PMSG systems as StatComs to provide required reactive power. By establishing mathematical model containing network parameters, operation characteristics faults are analyzed in detail. Based on...

As the share of wind power in system increases, grid exhibits characteristics a weak grid. The dynamic stability issues grid-connected doubly fed induction generator (DFIG)-based turbines caused by interaction between phase-looked loop (PLL) and rotor current controller (RCC) high impedance have become acute, especially during low-voltage ride-through. In this article, output model DFIG is derived, where dynamics PLL been first taken into account. addition, RCC analyzed. Furthermore, novel...