Key Technologies Research In Large Capacity Power Electronics Distributed Control System

With power electronic device technology, information technology and control technology progressing increasingly, a significant trend of modern power converting techniques has appeared towards developing the power electronic devices which are characterized by intelligence, modularization, midium-high voltage, large capacity, high power density, high maintainability and high reliability. For our future aircraft carriers and large ships, their electric propulsion system, high-capacity regional distribution system and high-energy weapons sysem will mostly contain power electronics converter devices of large capacity or super large capacity (MW to hundreds of MW level). As there are lots of power switch devices, control variables and feedback variables, the use of the traditional centralized control architecture and control mode will bring non-modualarization, poor electromagnetic compatibility and flexibility to the system and cause the control system to be difficult to reconfigure. Besides, a large number of point-to-point communication and inner connection lines will directly affect the reliability and maintainability of the system and make the control system and communications architecture so complex that it is difficult to improve the modularization, reliability, maintainability and intelligent degree of the power electronic converter system. Therefore, there are some critical technical problems needed to be solved in this aspect. With the24MVA level fifteen-phase converter as an object of study, this paper has made a deep study of a distributed converter system based on a high-speed fiber optic ring network communication, especially an investigation of the related key technologies of the fifteen-phase propulsion converter didtributed control system.According to the space distribution characteristics of the fifteen-phase propulsion converter, the power level and control level of the converter is determined by modular division, and a distributed control system of the fifteen-phase propulsion converter is established based on the conventional high-speed fiber optic ring network communication. The function of the hardware controller for ring network communication is also analyzed and designed in detail. For the operation features of the fifteen-phase propulsion converter, the paper develops a communication protocol suitable to the high-speed fiber optic ring network communication.As for an inherent network delay in the conventional high-speed fiber optic ring network, a detailed analysis is made of the influence of single bridge arm and serial bridge arm network delay on the output voltage harmonics. The simulation results verify the correctness of the theoretical derivation and provides a theoretical basis for the synchronization in the distribution topology architecture of ring network communication. According to the characteristics of the conventional high-speed fiber optic ring network communication, the paper has proposed a method for the automatic measurement and compensation of system synchronization delay. The method can be used to automatically calculate the processing delay of the system data and command passing through each node according to differnet lengths of the fiber-optic lines between the nodes. Because of its high flexibility and contribution to simplifying the communication protocol and soft programming, this method is proved to be correct and feasible through experiments.Aiming at the problems such as a large network delay, the retransmission of network data through every slave node and the accumulation of synchronization delays and errors in the conventional high-speed fiber optic ring network, the paper has presented a novel switchable high-speed fiber optic network communication topology architecture, analyzed the operation mode and synchronization delay model of the topology and offered a high-performance synchronization method for the proposed network topology. The method can be used to achieve the synchronization accuracy within8ns, and there is no accumulation of synchronization errors.Considering that the existing narrow pulse compensation techology used in SPWM (Sine Pulse Width Modulation) inverter will influence the starting and low-speed performance and increase the torque ripple of the motor, the paper has proposed a three-level narrow pulse compensation technology for the distributed control system in a SPWM modulation mode by zero sequence bias injection. It can improve the low-speed performance and decrease the torque ripple of the motor, In addition, it is found from the experimental study that the dead time injection causes the turn-on and turn-off time of the IGBT to be longer in a cetain operating state. The mechanism of generating this phenomenon is theoretically analyzed and experimentally verified in detail in this paper. The results can provide certain reference for power electronics engineering researchers and also a certain theoretical basis for developing the active gate drive technology.Finally, the application of the related technologies mentioned in the paper to the fifteen-phase propulsion converter distributed control system aims at testing and verifying the data communication and the basic functions of the distributed control system based on the conventional high-speed fiber optic ring network communication. The results show that the distributed control system is correct and that the related technologies researched in the paper are effective and feasible.