Research On Sliding Mode Inverse System Control Of H-type Chain Static Var Generator

In recent years,with the widespread use of various power electronic devices,the pollution of power quality of the power grid has become more serious.Static Var Generation is an important device that can comprehensively improve power quality.It is attracting more and more researchers' attention with its advantages of easy expansion,low output harmonics and high device utilization.With the development of ultra-high voltage and extra-high voltage power grids,the scale of power systems is expanding.In order to meet the needs of power systems better,the capacity and compensation efficiency of SVG should also be improved.but the design of SVG is relatively complicated.However,the design of SVG is relatively complicated.there are still many problems to be solved in the main circuit design method,linear decoupling control,DC side capacitor voltage balance control and asymmetric three-phase system signal detection.In this paper,the control strategy of static var generator is taken as the research object.First,the harm caused by lack of reactive power and the development of reactive power compensation technology are summarized.Then the principle and design of inverse system control and sliding mode control are introduced in detail.Then the H-bridge module modulation method and the dynamic model and working principle of chain SVG are analyzed.In view of the strong coupling characteristics of input and output nonlinearity of SVG,a decoupling control strategy based on inverse system is proposed.On this basis,according to the strong robustness of sliding mode control,combined with sliding mode control and inverse system control,the control strategy of chain SVG based on sliding mode inverse system is explored.Secondly,the causes and influencing factors of unbalanced capacitor voltage on DC side are analyzed.The three-stage balancing control strategy is designed to maintain voltage balance from three aspects:whole,inter-phase and intra-phase.The method of signal detection is discussed.The influence of traditional ip-iq on the detection accuracy of reactive current signal in three-phase unbalanced grid voltage is studied carefully.An improved method of ip-iq reactive current signal detection is proposed.Finally,the correctness and validity of AC control strategy,DC control strategy and signal detection of SVG are verified by simulation experiments,and control system hardware and software of chain SVG are analyzed and discussed.In view of the precise and efficient reactive power compensation characteristics of chain SVG,the sliding mode inverse system control strategy proposed in this paper can decouple the strongly coupled nonlinear SVG into a linearized system,and can still maintain the stability,response speed and accuracy of the system under the condition of parameter perturbation.The proposed capacitor voltage balance control method realizes that the capacitor voltage is maintained in a stable range with small fluctuation.The improved reactive current signal detection method proposed in this paper realizes the accurate acquisition of the reactive component in the load current,even when the grid voltage is unbalanced.The simulation results provide experimental basis for the above methods and prove the correctness of these methods.