The Research On Torque Elevation Control Strategy For LCI Fed Synchronous Motor

In high-power electrical transmission applications like pumped storage power stations,the electrical excitation synchronous motor has outstanding advantages such as high load carrying capacity,weak magnetic speed control and large stand-alone capacity compared with other motors.At present,the electric excitation synchronous motor generally uses the frequency conversion starting method to reduce the impact on the power grid when the motor is directly started.The Load Commutated Inverter(LCI)is characterized by high cost performance and large power capacity due to the using the thyristor as switching devices,which is suitable for high power AC drive control system.The six-pulse LCI topology is the most common used structure.Under this topology,the LCI drive device contains rich harmonic components and the motor torque ripple is also large.The use of a multi-pulse LCI topology can effectively improve the above problems.In addition,in many transmission applications,the motor needs to be started with a load,and the motor must have a certain load carrying capacity.So it is of great significance and value to study the elevation of the torque during starting the motor.Firstly,this paper analyzes the principle of the electromagnetic torque generated when the LCI drives the motor,and gives the motor torque's characteristics under different LCI topology to make a comparative analysis.Models of different topological LCI-driven electric excitation synchronous motors are established with the help of Matlab/Simulink,and the characteristics of torque and harmonics are compared.The correctness of the theoretical analysis is fully proved.It is concluded that the adoption of multi-pulse LCI topology can improve the average electromagnetic torque of the motor and reduce the torque ripple and harmonic content.Secondly,the control strategy for improving the motor torque's characteristics is studied from the level of the commutation control of LCI's inverter bridge.The commutation principle of the load commutated inverter is analyzed.A constant commutation residual angle control method is proposed based on the derivation of mathematical models of the commutation overlap angle and the motor power angle.Theoretical analysis of the torque's characteristics of the motor under this control method was conducted and compared with the constant commutation lead angle control method.In order to analyze and verify the feasibility of this control strategy,a corresponding simulation model was built in Matlab/Simulink.Under the constant commutation residual angle control strategy,the commutation reliability of the LCIinverter bridge is ensured,and the torque's characteristics of the motor are improved.Finally a 15 KW electric excitation synchronous motor driving device platform with a variety of topological structures is built,and the experimental related hardware circuit design is carried out,including a DC bus current detection circuit and a back electromotive force depth filter circuit etc.The relevant software control algorithm was designed based on DSP(TMS320F2812)control platform.On this basis,the proposed LCI commutation control strategy was tested under different load conditions under the 12+6 LCI topology.The experimental results verify the feasibility and effectiveness of the proposed control strategy,which improves the motor torque's characteristics.