Research Of Predictive Control On Permanent Synchronous Magnet Generator And Fault-tolerant Capability Of Tidal Current Energy System

With the declining of land resources,more attention began to be devoted to the development of marine resources.Tidal current energy system through tidal-driven turbines to obtain mechanical energy,driving the motor rotate to produce electricity,then electricity will be transferred to the grid through converters,which is the same with wind power for capturing fluid kinetic energy.Despite the difference in operation circumstances and structure,the current research on tidal current energy technology is based on the experiences of wind power system operation,and the it's environmental specificity makes it important to maintain system operation stability and reduce maintenance.So the direct drive permanent synchronous magnet generator system which can save the gear device and slipping ring is preferable for the tidal current system.On the one hand,in order to optimize the operation of tidal current system,this paper analyzes the current response under the control of PI,dead-beat predictive and model based predictive,and selects the dead-beat control who has the best performance to do the further research.Considering the problems of pulse width modulation duty cycle delay and dead zone introduced by the inherent quantization and retention characteristics of digital control system impacts on the transient response and steady-state accuracy of controlled variables.Firstly,analyze the root cause of delay and dead-band.Secondly,using the known quantity to calculate the unknown quantity of the next cycle to eliminate the influence of delay on the transient oscillation.Then,considering the effect of the dead time which is set by turn-off non-linearity of the converter on the voltage during a sampling period,calculate the distorted voltage and compensate it to the voltage vector value,finally achieve the goal of eliminating the transient oscillation and improving the steady-state accuracy.On the other hand,to reduce the possibility of unexpected outage of tidal current energy system,based on operational failure data in wind power generation system,propose corresponding fault-tolerant measures to solve the most frequent occurrence of motor-side converter' single-phase open circuit failure which keeps the tidal current energy system still operating in degrade mode after the fault has occurred.This paper analyzes and compares these fault-tolerant topology including three phase four switches type,adding redundant arm,changing the control strategies,multi-phase motor system and parallel converter system,advantages and disadvantages in aspects of switching element investments,method simplicity and fault-tolerant capability,selects only changing the control strategies,adding redundant arm leg and paralleling converter these three fault-tolerant topology to do simulation analyzing.The simulation results prove that for single converter system,changing the control strategies can make the system still under control but has the bad fault-tolerant effects,while adding redundant converter arm could improve the fault-tolerant capability;for parallel converter systems,the torque compensator designed by this paper can ensure the output of torque and power under fault-tolerant operation is quite the same as normal operation.