MMC-HVDC改进模型预测控制策略研究

Research of Improved Model Predictive Control Strategy for MMC-HVDC

控制策略对保证基于模块化多电平换流器的高压直流输电系统(modular multilevel converter-high voltage direct current transmission,MMC-HVDC)正常工作起着至关重要的作用。经典双闭环矢量控制具有控制精度高、响应速度快等特点,但需要控制器设计和控制参数调节;模型预测控制具有建模直观、无需控制器优点,但预测指令的求解过程稍显复杂。该文在两相静止坐标系下,综合2种控制策略的优点,基于功能等效思想,将双闭环矢量控制等效划分为2个模型预测环节,构成改进模型预测控制。研究2种不同的控制指令获取方法,避免传统预测控制运算量大、权重因子调节复杂等问题。通过对模块化多电平换流器技术(modular multi-level converter,MMC)数学模型离散化,建立MMC阀侧电压控制指令输出预测模型,实现内环控制器等同功能。分别针对电网电压平衡和不平衡工况,从功率跟踪、负序电流抑制及功率波动抑制等方面验证所设计控制策略的有效性。

The control strategy plays an important role in ensuring the normal operation of MMC-HVDC.Classical double closed-loop vector control has the characteristics of high control accuracy and fast response speed,but it needs to design the controllers and adjust the parameter.Model predictive control has the advantages of intuitive modeling and no need of controllers,but the solving process of predictive instruction is complex.In this paper,based on the idea of functional equivalence,the double closed-loop vector control was equivalently divided into two predictive links by synthesizing the advantages of the two control strategies in two-phase stationary coordinates and the improved model predictive control was formed.Two different control command acquisition methods are studied to avoid the problems of large computational load and complex adjustment of weight factor in traditional predictive control.At the same time,through the discrimination of MMC mathematical model,MMC valve-side voltage control command output prediction model is established to realize the same function of inner loop controller and centralize control function of inner loop to one controller.In order to verify the effectiveness of the proposed control strategy,this paper simulated and verified the performance of power tracking,negative sequence current suppression and power fluctuation suppression under voltage balance and unbalanced conditions respectively.