Research On Networked Control Technique And Correlated Issues Based On Inverter Parallel Operation System

How to use the communication technique fully in power electronics has been a more and more important research field. After the summary of current application and research in power electronics communication, the concept and idea of networked control is furthered in this dissertation. Network channel can be not only the medium of power electronic data transmission, but also the key participation of power electronic control system. Networked control for power electronic system is to make network cooperate with control loop in operation, allocate the power electronic data flow rationally by means of network scheduling and enhance the performance of power electronic system.Based on the research on inverter parallel with power droop control and networked control for power electronic system, inverter parallel technique with networked control and power droop control is proposed in this dissertation. Moreover, the main factors influencing power electronic system features are introduced. Among them, the influence of the network time-delay and data dropout in power electronic system with networked control are analyzed in detail. The design method and problem-solving strategy of networked control for power electronic system is proposed.Firstly, to enhace the stable and dynamic performance, modified power droop control algorithms towards inverter parallel system without control interconnection are proposed in this dissertation. Because the current-sharing feature of inverter parallel system with power droop algorithm depends upon the output and link impedance of inverter, the parameter adjustment is added in traditional power droop equation. By changing droop parameter varied with output power, the difference of output power in steady-state can be decreased and the ideal current equation degree can be achieved finally. Experiment demonstrates that the ideal performance can be attained even in unbalance of inverter output and link impedance. Moreover a novel attenuator to decrease DC current circulating is presented in this dissertation. By controlling DC component of output voltage to zero through close-loop, the DC circulating restriction is realized. A novel power droop method for improving dynamic performance of parallel system is presented. Integration and differential is added in antecedent parameter adjustment equation. The simulation and experiment shows that dynamic performance can be enhanced if droop, integration and differential coefficient are in proper design.Then, networked control of power electronics system is furthered in this dissertation. By adopting networked control in inverter parallel system, inverter parallel technique based on networked control and power droop control is proposed in order to improve the system performance. The concept, application foreground and design method of networked control in power electronics system are introduced, as well as some networked control design methods. Networked control is employed in inverter parallel system in this dissertation. The individual power information of inverter modules can be achieved by each other through network transmission. The novel networked control strategy is proposed based on power droop control in this dissertation. After the analysis of control data type and network environment of this system, the dynamic access mode of Try-Once-Discarded, one-time abandonment MAC for real-time data is employed. In experimental analysis, the comparison between novel method and traditional method is carried on. It proves that degree of current equation error of parallel output current of inverter is even less and performance is optimized after using new control strategy.Furthermore, based on the main influence factors of networked control for power electronics, the effect of time-delay and data drop-out over networked control system of inverters is emphasized. Stablility analysis and related design techniques is presented. One analysis method based on network combined allocating is proposed. The mathematical model with variable of time-delay for networked control based on average power droop method is constructed. As the predictive estimation of network time-delay. Maximum Allowable Transfer Interval based on TOD dynamic access algorithm can be calculated with linear control theory. The experiment results verify the validity of estimation by watching output current in dynamic state with different time-delay. Moreover, one analysis method of system stability with time-delay within one control period is presented in this dissertation. Then each discrete-time system model with variable of different time-delay is built by each strategy. The judgment of system stability depends on time-delay symbolic matrix whether is Schur stable, and the experiment results is in accord with theoretical results approximately. Following, one analysis method of constant occurrence rate for data dropout is proposed in this dissertation. On the basic of the construction of two non-linear functions using linear control system theory, the calculation method of stable data dropout rata to guarantee system stable is presented. The effect of data misfit over system control is analyzed and described by experiment.Finally, to guarantee system stable under the influenece of time-delay and data dropout, two problem-solving strategies are proposed in this dissertation: On the one hand, new data dispatching mode is given from the point of view of networked control algorithm, which ideal dynamic and static performance can be achieved in normal communication condition and reliable operation will maintain even in abnormal network condition. On the other hand, new feedback control design is presented based on network condition with random time-delay. The validity of these two strategies is verified by experiment in the way of parallel output current-sharing error and output comparison with the same time-delay condition.