The Design And Implementation Of Three-level Inverter Based On SHEPWM For PMSM

Three-level inverters have been widely applied in power drive field of high-voltage large-capacity AC drive technology. Due to the limitation of switching loss and heat dissipation of the switching device, the maximum switching frequency of inverters can just be kept at a low value of only a few hundred Hertz, and bring rich harmonic content in the wave of PWM.Meanwhile, throughout the speed range in traction drive system of high-speed trains, carrier ratio range is very large, using just one modulation is unable to meet the requirements of speed control. To solve this problem, The high efficiency and energy saving three-level inverters permanent magnet synchronous machines(PMSMs) are employed as traction motors, and the selective harmonic elimination PWM and vector control(SHEPWM+VC) is proposed in this paper, include the following:First of all, The mathematical model of SHEPWM aimed at two-level and three-level inverter is built respectively. And based on the model, the computational method and choice of initial value of selective harmonic eliminated nonlinear equations are developed. The SHEPWM of PMSMs based on two-level topology and three-level topology are respectively studied and simulated by MATLAB/Simulink. Compared with the two-level inverter,the output current harmonic components of three-level inverter is lower, and proves the validity of eliminating harmonics based on SHEPWM.The FFT analysis of stator currents verify that having N switching angles per quarter cycle, up to N-1 harmonics can be eliminated.Furthermore, a multi-mode modulation strategy based on SHEPWM, has been adopted to realize smooth operation of the traction motor during its whole speed range. The realization and implementation of SHEPWM strategy,the smooth transition between SPWM and SHEPWM, and the smooth transition between SHEPWM with different pulse number N are presented inthis paper.The inverter system based on multi-mode modulation strategy was established in the MATLAB/Simulink environment, after the simulation, the SHEPWM algorithm was well verified, the smooth transition was also realized.At last, in order to carry out studies about permanent magnet synchronous motor control system based on three-level inverter, a three-level variable flow cabinet and general hardware platform based on DSP+CPLD are designed, the flowchart of control software in DSP was completed. And experiments in the former platform were carried out and other major design were proved to be effective during the experiments. The results showed that some functions can be implemented and the preliminary conditions of the multi-mode PWM modulation algorithm of permanent magnet synchronous motor based on three level inverter were possessed.