The Affect Of The Dead-time And Improvement Of The Output Of The Inverter

In some practical applications such as military applications, the low-speed control system with good static and dynamic performances are often required. However, the dead time of power devices, inherent characteristic of switches and other nonlinear characteristics affect the output current and voltage waveforms of the inverter. Especially when a high switching frequency or low output voltage amplitude, low frequency are needed. the presence of the dead-time will make large harmonic to the output voltage and current, even cause the motor's low-frequency oscillations. Therefore, in order to make the speed control system have a good dynamic and static performance not only in the high-speed but also in low speed, the performances of the inverter output should be improved. So dead-time and the inherent characteristics compensation are necessarily needed.In this article, firstly, the inverter control mode was selected, the inverter can use a lot of control modes, such as PFW(pulse frequency modulation), PAM(pulse amplitude modulation)control, PWM(pulse width modulation)control, and so on. In these control ways, the output of the inverter controlling by PWM is better. Because of its harmonic components in the less torque ripple and improving the situation, eliminating transmission in the low speed cogging time, reducing the loss of the motor, improving the efficiency of the motor. Then, as to the voltage source SPWM converter topology used in this paper, its working principle and the dead-time effect were analyzed, and a detailed analysis about the effect of the dead-time to the output voltage was made. The dead-time effect made the output fundamental voltage dropping, phase changing, increasing of the low-order harmonics. Especially in the case that the output voltage was very low, the effect would become more serious. So, dead-time compensation was necessary.In view of the effects on the output voltage of the inverter from the dead-time and the switch's inherent characteristics, its compensation was very necessary. Several common dead-time compensation methods were described in this paper, based on that, the current feedback compensation and invalid device based on DSP dead-time compensation were simulated specifically. The simulation results showed the validity, feasibility and superiority.Based on what were done above, the second dead-time compensation was used to the inverter. Through the simulation comparison of the inverter in different output frequencies and output voltages, stable inverter output waveforms in the wide range can be got after the compensation.Finally, the experimental platform of SPWM inverter which took TMS320F2812 as its center control chip was constructed. Some experiments of the constructed SPWM inverter platform were carried out. And related experiment waveforms were listed and analyzed at the end of this paper.