不平衡电网电压下T型三电平光伏并网逆变器的有限集模型预测控制

FINITE CONTROL SET-MODEL PREDICTIVE CONTROL FOR T-TYPE THREE-LEVEL PHOTOVOLTAIC GRID-CONNECTED INVERTER UNDER UNBALANCED GRID

为实现电网电压不平衡时对T型三电平光伏并网系统输出功率和电流质量的控制,以达到入网功率平稳或电流正弦为控制目标,结合光伏阵列输出功率前馈,在两相静止坐标系下提出一种直流母线电压外环PI控制、并网电流内环有限集模型预测控制的控制策略,并在电压外环中引入2倍频陷波器以获得平滑的入网功率参考值。仿真结果表明:当电网电压不对称时,采用所提控制策略能够实现对入网有功、无功功率2倍频脉动及负序电流的分别抑制或协调控制,且并网电流谐波畸变小、入网电能质量高,同时实现T型三电平逆变器的中点电位平衡。

Aiming to realize the control of the output power and current quality of T-type three-level PV grid-connected system when the grid voltage is unbalanced,a control strategy whose DC bus voltage out loop based on PI controller combined with the PV power feed forward and current inner loop based on model predictive controller is proposed in two-phase stationary coordinate system in the paper to achieve the stable output active/reactive power or sinusoidal output current,and a double frequency notch filter is introduced in the voltage outer loop to obtain smooth grid-connected power reference. The simulation results show that the proposed control strategy can be used to separately control or coordinate the double frequency pulsation of active/reactive power and negative sequence current,and the harmonic distortion of the grid current is small and the grid-connected power quality is high when the power grid voltage is asymmetrical,and the T-type three-level inverter neutral point voltage is balanced.