Research On Long Cable Drive Technology Of Permanent Magnet Synchronous Motor Based On Current Source Inverter

Electric system has advantages of fast dynamic response,high control accuracy,and strong instantaneous overload capability,thus shows good prospects in long-distance oil and gas extraction.Furthermore,direct-drive permanent magnet synchronous motors(PMSM)can be used to replace induction motors and gearboxes,which can improve transmission efficiency and system stability.For motor drive,the voltage source inverter(VSI)is widely used.However,researches and applications of current source inverter(CSI)are less.The capacitor at CSI output terminal,together with circuit inductance,forms a second-order low-pass LC filter,which can effectively weaken the high-frequency harmonics and suppress the overvoltage caused by the cable.Therefore,the research on long cable drive technology of permanent magnet synchronous motor based on current source inverter,has high theoretical significance and practical value in engineering.Drive schemes,that topology structure and control strategy are switched under certain conditions,based on CSI for PMSM with a step-up transformer are proposed and studied in this thesis.At low-speed stage of the motor,I/f control is applied,and the transformer is bypassed in parallel.While in high-speed stage,vector control is used,and the transformer is switched to work in the main circuit.Then the system is structured as a low-high-voltage topology.This thesis combines the system mathematical model to carry out the system design research about the switching of control strategy and topological structure,and the calculation of related parameters.Firstly,mathematical models of the system are established in three-phase frame and models of the capacitor,step-up transformer,cable and PMSM on AC side in dq frame are obtained according to the control needs.The leakage inductance,winding resistance,iron loss resistance of the transformer are discussed and conditions are set for simplifying the model.Then the transfer functions are founded to describe the changes of system voltages and currents in both low-speed stage and high-speed.Secondly,the motor model in reference frame is established,and a closed-loop I/f control scheme for real-time adjustment of reference angular frequency and reference current amplitude is designed.Aiming at weakening the impact of the coupling term and feedback term of current and voltage,the feedforward compensation calculation methods are proposed.Rectifier angle controller and multi-closed-loop control structure are designed based on PI regulator.The system parameter design is completed according to the system model and the needs of its performance.Third,by calculating the applied time of each current vector,the sector allocation,and the logical correspondence between the modulation signal and the switching device,the carrierwave-based CSI-SVPWM modulation is completed.And based on the existing VSI-SVPWM modulation scheme,binary-ternary-conversion-based CSI-SVPWM modulation is completed.In addition,to prevent the overvoltage during commutation,overlap-time inserting method for the carrier-wave-based CSI-SVPWM modulation is designed.Finally,parameters are calculated according to needs of system performance,and through simulation on Matlab/Simulink for CSI-SVPWM modulation,conclusion is drawed that the smaller the modulation ratio,the higher current harmonics the inverter output.Furthermore,DC current reference values of low-speed,high-speed and on-load stages are designed respectively.The simulations are completed by establishing the whole system simulation model.It is verified that good control performance is achieved by the system and control strategy designed in this thesis.