Research On Control Strategy For Multi-Pulse Boost Type Load Commutated Inverter

Load Commutated Inverter(LCI)has the advantages of high power factor,large capacity,especially suitable for pumped storage power station,synchronous camera,large air compressor,high power pump fan and other megawatt-class electrical transmission occasions.In these electrical transmission occasions,the use of multipulse structure can effectively reduce the network side and the motor side of the harmonic content,improve the network side power factor.The high-low-high voltage structure driver system can reduce the device withstand voltage and improve the device reliability.In addition,the LCI device has the energy feedback function can effectively improve the system efficiency.It is of great theoretical and practical value to study the control strategy of multi-pulse boost LCI drive.This paper first deduces the basic equations of multi-pulse LCI drive.Aiming at the LCI driving device in the case of 12 pulsation,this paper analyzes the working state of the driving signal,and proposed a 4-pulse triggering method to improve the reliability of the device operation.Comparison and analysis are carried out for the common multi-pulse LCI drive device,from the harmonic,power factor,torque ripple situation.It is concluded that the multi-phase LCI device has a lower harmonic content and a smaller torque ripple.Secondly,for the high-low-high voltage structure LCI drive device,the output step-up transformer is operated at different frequencies Therefore,the basic equation of the low-frequency operation of the transformer is established,and its operation at low frequency is analyzed.Analysis is carried on the output capacity,loss and so on.As the actual use,the transformer is usually bypassed at very low frequency,so the mathematical model of the LCI drive and the causes of the current shock at the time of switching are analyzed.A feed-forward control strategy is proposed to solve the impact of the current in the drive system at the switch time of transformer access in and the time of intermittent commutation switch to the load commutation.Thirdly,the energy feedback control strategy of LCI drive is studied.The working condition of the device running in the energy feedback state is analyzed,and the control method of the of LCI drive device switch from the electric operation to the energy feedback state is given.A control strategy is proposed to control the braking current.this method controls the excitation current to adjust motor voltage to change the current of the energy feedback.and a mathematical model is established for the proposed control strategy.The feasibility of the control strategy is verified by simulation analysis.Finally,a 15 kW multi-pulse LCI driven synchronous motor experiment platform was built,and the corresponding hardware circuit design was carried out,including multi-pulse trigger signal circuit.The multi-pulse LCI control system based on TMS320F2812 is designed,and the proposed multi-pulse LCI driving control strategy and low-frequency transformer crossing control strategy are experimentally verified.The experimental results verify the feasibility of multi-pulse LCI control strategy and transformer switching control.