Modeling on converter of direct-driven WECS and its characteristic during voltage sags

Abstract

The output power of direct-driven wind energy conversion system (WECS) will be limited during grid voltage sag, but the operation of wind turbine will not be influenced by adding damp load in DC-side, then the capability of low voltage ride through (LVRT) may be enhanced. Full power back-to-back PWM converter is adopted in direct-driven variable-speed constant frequency WECS using permanent magnet synchronous generator (PMSG), which can effectively improve system efficiency; the principles of generator-side, grid-side converters and damp load are analyzed in detail, and the whole system modeling of converters is realized. Then the simulation model of converters is built based on Matlab7.3/simulink6.5, and the characteristic during grid voltage sag is simulated; the validity of the model and analysis is verified by simulation, and the results show that direct-driven WECS have good fault ride through capability. Index Terms-direct-driven, wind energy conversion system (WECS), permanent magnet synchronous generator (PMSG), voltage sags, low voltage ride through (LVRT), damp load

Low Voltage Ride through Characteristics Analysis of Direct-Driven Wind Power System

“…In this paper, the given reactive power was zero, system running on under unit power factor. Grid fault occurred at time of 1 sec, continued 0.5 sec with the voltage sag depth 50% [3,9] , simulation waveforms were showed in fig.5. When grid voltage dropped the grid current increased rapidly in order to ensure the power output to the grid.…”

“…However, the directdriven wind power system with the advantages of high efficiency, low noise, low cost of maintenance has been increasingly concerned in the field of wind power generation. There are already some studies about the modeling and simulation of direct-driven wind power system, but most of them made some simplified [3][4][5][6] . Some of them concerned about the output characteristics of grid side converter neglecting the generator side; in contrast, some of them concerned about the pitch angle and the speed control strategy of the generator neglecting the grid side converter.…”

Study on low voltage ride through characteristic of full power converter direct-drive wind power system

“…When the voltage drop lasts longer, it will result in generating too much heat to effectively release. At this time we must adopt other control strategies, such as pitch-control to limit the input power to the wind turbine [6]. Fig.1 Control strategy schematic of grid converter STATCOM model during voltage sag…”

“…At the same time as the conventional thermal power system, wind power system is required to easily control the output power factor and safely operate within a certain range of power factor, and also be able to quickly provide reactive power to the grid in order to regulate the voltage of the system in the case of failure such as voltage drop and so on [6][7]. Hence we should analyze and research the capability of low voltage ride through and the capacity of reactive power compensation of the direct-drive permanent magnet synchronous generator.…”

Grid-integrated permanent magnet synchronous generator based wind energy conversion systems: A technology review

“…A unified dc-link current control scheme has been proposed in [29] so as to assist the CSC based WECS for faultride-through. Compliant with the grid codes, additional measure such as the braking chopper is applied to support the system operation during grid disturbances [213,[215][216][217]. In the event of grid fault, the dc chopper dissipates the unbalanced power between the generator and the grid with no more control effort.…”