Research On The Vector Control Methods Of Cascaded H-Bridge Converter

The cascaded H-bridge converter is widely employed in high-voltage and high-power industrial applications,due to its advantages such as mature topology,easy to modularize and expand,high power factor,small harmonic output,as well as achieving high-voltage output using low-voltage modules.On such occasions,the use of variable-frequency regulating speed technology,not only can achieve energy conservation and emission reduction,but also significantly improves the motor performance,so that it has a broad application prospect.However,under the situation where high speed control performance is required,VVVF control technology cannot yet meet the requirement of production process.Therefore it is of significance to study the vector control method of the cascaded H-bridge converter.To achieve high-voltage motor vector control,motor speed signal is a must,but the installation of rotational speed sensor influences the excellent features of asynchronous motor including simple,reliable,and low cost.Hence,speed sensorless vector control technology based on cascaded H-bridge converter,becomes an important research direction of high-voltage high-power AC drive system.In this paper,cascaded H-bridge converter is studied,including its circuit topology,working principle,modulation algorithm and vector control method.Its speed sensorless vector control method is deeply studied.First,after introducing topological structure and working principle of cascaded H-bridge converter,the carrier phase shift SPWM modulation method highly suitable for the topology is introduced,whose output performance is also studied by MATLAB simulation;through the analysis of carrier phase shift modulation method,a carrier phase-shift modulation algorithm is proposed based on the DSP-FPGA + CPLD control board;aiming at the disadvantageous effect of the dead-zone in the modulation method,a dead-zone compensation algorithm is studied,and simulation analysis is carried on,and the simulation results prove the effectiveness of the dead-zone compensation algorithm.Secondly,the dynamic mathematical model of induction motor and the basic principle of vector control based on rotor magnetic field orientation are introduced in this paper;magnetic flux observation method based on voltage model and current model is studied,and by using voltage model as the reference model,current model as the adjustable model,flux angle as the error parameter,the MRAS speed sensorless vector control system is constituted.Then,the open-loop speed estimation method based on rotor back electromotive force is introduced,and stability analysis of the speed estimation method is carried out.Simulation of speed sensorless vector control system based on rotor back EMF speed estimation is conducted.MRAS speed estimation method and speed estimation method based on rotor back EMF are compared and analyzed,and application conditions of the two methods are given.In order to improve the reliability of the system,a method of on-line switching from speed sensor vector control system to speed sensorless vector control system is proposed and tested by simulation.Finally,a hardware experimental platform is set up.The carrier phase shift SPWM modulation algorithm,the sensorless vector control algorithm and the switching algorithm are testified by experiments.The feasibility and correctness of the above algorithm are verified by the experimental results.