An Optimal Integrated Control Scheme for Permanent Magnet Synchronous Generator-Based Wind Turbines under Asymmetrical Grid Fault Conditions

Dan Wang,Chongru Liu,Gengyin Li

doi:10.3390/en9040307

Abstract

In recent years, the increasing penetration level of wind energy into power systems has brought new issues and challenges. One of the main concerns is the issue of dynamic response capability during outer disturbance conditions, especially the fault-tolerance capability during asymmetrical faults. In order to improve the fault-tolerance and dynamic response capability under asymmetrical grid fault conditions, an optimal integrated control scheme for the grid-side voltage-source converter (VSC) of direct-driven permanent magnet synchronous generator (PMSG)-based wind turbine systems is proposed in this paper. The optimal control strategy includes a main controller and an additional controller. In the main controller, a double-loop controller based on differential flatness-based theory is designed for grid-side VSC. Two parts are involved in the design process of the flatness-based controller: the reference trajectories generation of flatness output and the implementation of the controller. In the additional control aspect, an auxiliary second harmonic compensation control loop based on an improved calculation method for grid-side instantaneous transmission power is designed by the quasi proportional resonant (Quasi-PR) control principle, which is able to simultaneously restrain the second harmonic components in active power and reactive power injected into the grid without the respective calculation for current control references. Moreover, to reduce the DC-link overvoltage during grid faults, the mathematical model of DC-link voltage is analyzed and a feedforward modified control factor is added to the traditional DC voltage control loop in grid-side VSC. The effectiveness of the optimal control scheme is verified in PSCAD/EMTDC simulation software.

Highlights

With the tremendously increasing total installed wind power capacity in power systems, large scale wind power integration brings new challenges to the secure and stable operation of these power systems [1,2]
During asymmetrical faults in a grid, on the one hand, grid-side active power injected into the grid is sharply reduced and generator-side active power delivered by the permanent magnet synchronous generator (PMSG) basically remains unchanged, which would cause the DC voltage to swell seriously; on the other hand, the unbalanced three-phase voltages during asymmetrical faults would result in the continuous oscillation of transmission power and DC voltage
Asymmetrical grid fault, paper the differential flatness-based theorytheory to design the main during asymmetrical gridthis fault, this adopts paper adopts the differential flatness-based to design the controller for grid-side

Summary

Introduction

With the tremendously increasing total installed wind power capacity in power systems, large scale wind power integration brings new challenges to the secure and stable operation of these power systems [1,2]. For PMSG-WTs, fault-tolerance capability in wind power transmission and power converters becomes more and more important in order to increase their reliability and availability [6], especially when asymmetrical faults happen. The dynamic response capability of wind power generation systems is a critical factor during disturbances, especially for the PMSG-based wind power systems that transmit the captured power via full size power converter systems. Based on the above statements, PMSG-based wind power system requires robust dynamic response ability and the grid-side controller should be able to reduce the fluctuation of DC voltage and transmission power during grid asymmetrical faults. The control strategy based on differential flatness-based theory shows robust dynamic performance during perturbations and disturbances [21,22]. According to DFB theory, a system is considered to be differentially flat if a set of variables (flat output components) can be found such that all state variable and input components can be determined from these output components and its finite order differentiation without any integration [23]

Methods

Results

Conclusion