Research On Control Technique For Voltage Source Combined Inverter And Current Source Inverter Based On Sliding-Mode Control Theory

With a fast development of power electronics and the advancement of required power quality, inverters have been applied to more and more fields. And the control performance of inverters becomes much higher. Sliding mode control (SMC) strategy was introduced initially for variable structure systems (VSS) which is well-known for its several advantages such as wide stability range, robustness for disturbance of system, and good dynamic response. Characterized by switching, inverters are inherently variable structured. Therefore, it is appropriate to apply SMC to inverters.Based on the overview of the existing control techniques, this dissertation mainly focuses on the SMC for inverters and has presented several novel continuous- and discrete-time SMC strategies, which are applied to Buck inverter and current-source inverter (CSI) respectively. The CSI is one of the most important circuit in the relay protection testing equipment. This testing equipment is used for the performance testing of the relay protection equipment. It is a very important guarantee for the safe operation of power network.Firstly, a novel third-order continuous-time SMC strategy for Buck inverter is proposed in this dissertation. Based on traditional second-order SMC, integral action is introduced into the sliding surface to eliminate the steady state error and maintain the dynamic performance of Buck inverter. The proposed control strategy is discussed detailedly based on the Lie derivative method. The geometry associated with the sliding mode control is easy to understand and could be particularly exploited in circuits which are designed to exhibit a time scale separation property. To simplify the analysis, three-dimensional trajectory transforms into the two-dimensional one through mapping method. The sliding motion is described by phase trajectory vividly. And the selection of the sliding surface coefficient is presented. Experimental results of these two continuous-time SMC strategies are included to validate the analysis.Then, three common discrete-time SMC strategies based on reaching law are discussed in this dissertation. A discrete-time SMC strategies based on variable rate reaching law is designed and applied to the CSI system. The proposed control strategy provides excellent robustness with regard to external disturbances and great dynamic response, and ensures that the system converges to original point asymptotically. Base on the model of the CSI system, the design process of the sliding mode controller is presented. The sliding domain and sliding surface coefficient are designed in detail. To illustrate the properties of the proposed control strategy, a numerical example is studied here using Matlab/Simulink. A prototype of the DSP-based CSI system has been built in the laboratory to verify the proposed control scheme experimentally.In order to figure out the conflict between the dynamic response and the chatting of the variable rate reaching law, a novel discrete-time SMC is presented which is called the attenuating variable rate reaching law. It not only has the advantage of reaching the original point asymptotically, but also can force the state vectors into the sliding domain quickly and reduce the chattering of the system greatly. It is applied to the CSI system. The sliding domain and the sliding surface coefficient are analyzed to ensure that the system converges to original point asymptotically. Simulation and experiment results would be shown that the proposed controller could offer good dynamic response and insensitivity to disturbances and parameter variations.Furthermore, the state predictive observer is introduced into the discrete-time SMC based on the controllability and observability of system. The proposed control strategy can predict the system variables one beat advanced and solve the delay problem of digital control primely, which greatly improves the dynamic performance and stability of system. Base on the dynamic model of the CSI system, the state predictive observer matrix is designed detailedly using the pole placement theory of state feedback. Final experimental results show that the system has good steady and dynamic characteristics.Last, this dissertation presents a novel discrete-time passivity-based sliding-mode control (PB-SMC) strategy based on the nonlinear control theory. It reduces the chatting greatly of the discrete-time sliding mode controlled system using the advantages of the passivity-based control (PBC). The Euler-Lagrange model of the CSI system is analysed and designed. Based on the dynamic model, the proposed control strategy has been designed detailedly. The stability property is simultaneity accomplished using the Lyaponov theorem. Comparing SMC with PBC, a doable selection of the damping assignment is presented. Final experimental results are demonstrated to validate the theoretical discussion.