Inverter Control Scheme in Modular UPS Power Switching
Considering the factors affecting circulation and the actual parallel connection of modular UPS power supply, the following control schemes are proposed for switching:
First, in the switching process, modular UPS inverters are controlled as voltage sources, but the inverters are not controlled by closed-loop voltage, which increases the equivalent output impedance of the inverters and reduces the shunt circulating current; the output amplitude of modular UPS inverters always follows the running through the bypass until the bypass channel is closed, regardless of the length of the shunt cycle or the short period. Reduce the difference between output voltages. In order to prevent bus voltage pumping caused by active power output from bypass power supply to inverters, the output amplitude of modular UPS power supply inverters can even be controlled to output power to bypass at a higher price than that of bypass power supply. When the bypass thyristor is completely switched off, it is delayed for a period of time, then closed-loop voltage control is carried out to restore the amplitude to 220V.
Secondly, in the switching process, the inverter is controlled as a current source. Before the relay closes, the output voltage amplitude of the inverter tracks the bypass voltage. When the modular UPS power supply inverter relay is completely closed, the current is given according to the phase amplitude information and estimated load power. The inverter is controlled to be converted to the current mode, and a certain power is output during the parallel connection process, so that the modular UPS can be realized in the parallel connection process. Load power is transferred from bypass to inverter or fed to power grid, and the output voltage depends on the power grid voltage. When the bypass thyristor closes the life of hemiplegia, the modular UPS inverter control is switched to the voltage mode at the same time, and the output voltage of the thyristor is controlled until the thyristor is completely turned off, gradually reaching the given value.