Research On Adaptive Sliding Mode Control Strategy Of PMSG Grid Inverter System

With the continuous development of human society, energy and environmental issues of the world become more critical. Wind energy is an abundant clean energy. In the aspect of improving the environment and solving the energy shortage, wind energy has very important significance. Grid converter, as an important part of the wind turbine, directly determines the output of the wind power energy system. Based on the analysis and control of the operation of grid-connected inverter grid voltage state of balance and unbalance condition, this article focuses on grid inverter adaptive sliding mode control algorithm.The main objective of the grid inverter is to achieve system of three-phase AC side current output and to be synchronized with the grid voltage, and further to achieve the interconnection of wind power generation system. This article first studies grid inverter’s mathematical model in the three-phase grid voltage equilibrium conditions, uses voltage and current double closed loop feed forward decoupling to control algorithm to achieve grid side active and reactive power decoupling control and independence.When grid voltage is imbalanced, and in order to implement smoothly grid-connection system, this article, based on grid side converter on a mathematical model, mainly focuses the asymmetric component of the grid voltage decomposition strategy, uses a complex coefficients notch filter phase-locked loop decoupling the control methods to achieve network-side voltage positive sequence component and negative sequence component extraction. And it uses dual synchronous reference frame PLL(DDSRF-PLL) decoupling method to achieve line phase detection and control under the conditions of unbalanced grid voltage,enabling the smooth interconnection of system.This article proposes the use of adaptive sliding mode control algorithm for PMSG(permanent magnet synchronous wind turbines) grid inverter. Using the dq axis of the grid current negative sequence component constructs sliding mode control algorithm switching surface and analyzes variable structure sliding mode control law. Using smooth function to improve the control law to achieve theelimination of chattering and combining with adaptive control, it designs adaptive sliding mode controller to improve system stability and reliability. Adaptive sliding mode control algorithm enables the grid Converters when the grid voltage is balanced and unbalanced, to achieve voltage and current double-loop control and Dual synchronous reference coordinate system decoupled phase-locked loop algorithm switching to ensure system and network run.Theory of the previous section control algorithm simulation results show that the voltage and current double closed loop control strategy can achieve grid voltage inverter under equilibrium conditions and achieve the smooth implementation system interconnection. Dual synchronous reference coordinate system decoupled phase-locked loop can achieve grid inverter’s phase detector and grid control under unbalanced conditions. Adaptive sliding mode control algorithm can realize grid inverter in the power grid voltage balance and unbalance control algorithm under the condition of switching, to achieve a good dynamic performance of the system. It verifies the validity and rationality of the mentioned policies in the text.