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Steady-state mathematical model of active and reactive circulation in parallel system of modular UPS power supply

The structure of parallel operation system composed of modular UPS power modules is complex, and there is a strong coupling relationship between them. In order to simplify the system, the steady-state analysis of the two-unit parallel system of modular UPS power supply is made. Through the analysis, it can be concluded that:

First, the phase difference between the output voltage of each modular UPS power supply mainly results in the difference of active power. The direction of active circulating current is from the phase-advanced unit to the phase-lagged unit, i.e., the phase-advanced positive active circulating current is emitted, and the phase-lagged active circulating current is emitted by the phase-lagged unit (the active circulating current is absorbed).

Secondly, the difference of the amplitude between the output voltage of each modular UPS power supply mainly results in the difference of reactive power. The direction of reactive power circulation is from the unit with larger amplitude to the unit with smaller amplitude, that is, the unit with larger amplitude emits positive and reactive current, and the unit with smaller amplitude emits negative reactive power circulation (absorbs reactive current).