Enhanced Control and Operation of Doubly-Fed Induction Generator Based Wind Farm during Network Unbalance

本课题旨在研究在电网电压不平衡时，基于双馈感应发电机（DFIG）的风电场的系统控制和运行，DFIG与输电系统连接或嵌入配电系统。不平衡电压既可以是由非对称交流故障引起的大的暂态不平衡，也可以是小的稳态不平衡。该项目将首先开发一个数学模型，其中包括一个DFIG和两个背靠背连接的转换器在不平衡供应下。不平衡网络电压对DFIG和相关变流器运行的影响将被检查。本项目将进一步探索在电网电压不平衡情况下，DFIG可以采用的策略，以提供增强的运行，如改善系统运行和非对称故障期间和之后的恢复，保持平衡的定子电流，最小化DFIG的电转矩脉动或对网络电压的再平衡做出贡献。在网络电压不平衡期间，通过提供定子/转子电流的精确控制，以及如果需要，不对称的有功和无功输出，控制DFIG系统的方法将被研究。将进行实验测试以验证所提出的控制策略。

This proposal intends to study the system control and the operation of wind farms based on Doubly-Fed Induction Generators (DFIG), connected to either a transmission system or embedded within a distribution system, when the network voltage is unbalanced. The unbalanced voltage can either be a large transient unbalance caused by asymmetric AC faults or a small steady-state unbalance. The project will first develop a mathematical model which includes a DFIG and two back-to-back connected converters under unbalanced supply. The impact of unbalanced network voltage on the operation of the DFIG and the associated converters will be examined. This project will further explore strategies that can be employed by the DFIG under unbalanced network voltage for providing enhanced operation such as improving the system operation and recovery during and after asymmetric fault, maintaining a balanced stator current, minimising DFIG electric torque pulsation or making a contribution to the rebalancing of the network voltage. Methods for controlling DFIG systems during network voltage unbalance, by providing precise control of the stator/rotor current and if required, the asymmetric active and reactive power outputs, will then be investigated. Experimental tests will be carried out to validate the proposed control strategy.