Symmetrical rule sampling of UPS uninterruptible power supply with dead zone

Since the switches used in UPS uninterruptible power supplies are not ideal switches, their turn-on and turn-off have a fixed turn-on time and turn-off time. Due to the inherent storage time of the switch, the same arm in the UPS uninterruptible power supply. When the two switch tubes are turned on, the other one may not be turned off, which is very easy to produce the through-short circuit of the two switch tubes. In order to avoid such a fault to ensure the safe operation of the UPS uninterruptible power supply, a dead zone must be set in the control of the SPWM. Usually the position of the dead zone is at the leading edge of the trigger pulse and the trailing edge of the pulse remains unchanged. The existence of this dead time will have a certain impact on the output voltage waveform of the UPS uninterruptible power supply, and it has its special effect on the output characteristics of the digitally controlled UPS uninterruptible power supply under the regular sampling mode.

It can be seen from the simulation results:

1. Symmetrical rule sampling with UPS The UPS uninterruptible power supply SPWM control mode still has the similar modulation ratio control characteristics as the symmetric regular sampling spwm wave, but with the same carrier ratio, with dead zone control The modulation of the mode is slightly better than the control characteristics.

2. After adding the dead zone, the fundamental wave voltage of the SPWM wave of the UPS uninterruptible power supply is slightly lower than the fundamental voltage of the ideal SPWM wave. When the modulation ratio is constant, the higher the carrier ratio, the more obvious the influence of the dead zone, that is, the voltage difference. The larger the value, and the difference is substantially inversely proportional to the carrier ratio.

In summary, it can be seen that under the existing all-digital UPS uninterruptible power supply SPWM control mode, the control characteristics of the modulation ratio and the influence of the dead zone have an adverse effect on the parallel operation characteristics of the UPS uninterruptible power supply, and a voltage closed loop is formed. The output voltage is unstable during control and a certain reactive current flow and harmonics between the inverters are first-class. However, when the load ratio is relatively large, the load ratio is substantially linear with the fundamental of the output voltage, and the small change of the modulation ratio does not form a large fundamental voltage change, thus the current sharing characteristic of the UPS uninterruptible power supply. The impact will not be too great.