Study On Parallel Technique Of Single Phase On-line UPS

UPS (Uninterruptible Power Supply) parallel operation is a good method of achieving high-reliability and large-capacity for power supply system, because the output of UPS is the sinusoidal AC voltage, its parallel operation needs to consider the factors of amplitude, frenquency and phase, therefore, more complicated than the DC power supply. Meanwhile, the study on UPS parallel technology has become a difficulty in the field of power electronics. Multiple UPS parallel operation to achieve high power capacity has become one of important directions for power conversion technology.In this paper, a kind of method with interconnection lines and no master-slave is used. Every paralleled UPS is equivalent in the parallel system, and doesn't need additional control module when it constitutes a parallel system, only by a small amount of signal lines between modules to achieve synchronization and load current sharing. Theoretically, the system can operates with any number of modules in parallel and also only one module. Through modeling and analysising a single UPS inverter, then this paper build the mathematical model of two parallel UPS inverters, and discuss the relationship of the amplitude difference, phase difference and the active and reactive power generated by the parallel system. Based on the analysis and referrence the existing inverter parallel methods, this paper employs the control strategy of PQ regulation based on current inner loop and voltage outer. This paper propose a parallel control plan based on TMS320LF2806A, adopt two step phase-locked method to achieve the paralleled UPS's phase synchronization, and present a method to directly calculate the instantaneous active and reactive power. By calculating active and reactive power difference to adjust the UPS output voltage amplitude and phase, then achieve a comparatively high precise synchronization and current sharing of parallel systems. This paper make use of the simulation tool—saber to simulate two UPS parallel system with pure resistor load, the results show that this method can control circulation current well and realize the purpose of load-sharing. Design A/D sampling, IGBT drive and Electricity shaping circuit, write the primary part program of UPS parallel operation, including starting sub-program, timer interruption sub-program, SPWM generating sub-program and so on. At last, two 6kVA single phase on-line UPSs are manufactured for the parallel system experiments, the results support the feasibility of the scheme, verify the method based on the double closed-loop control feasible and the re-modulation method can effectively improve the precision of phase-locked and sharing current.