There are three factors leading to the efficiency of low frequency UPS lower than high frequency UPS. Firstly, the low frequency UPS rectifier for buck topology, the device operating current is large, whether the internal line of linear loss or square loss are higher than the online high frequency UPS; Secondly, due to the reasons for the need to boost the output, the low frequency UPS use the built-in multi output transformer, while the high frequency UPS not, resulting in the efficiency of low frequency UPS decreased by 2%-3%; Thirdly, in the practical application, in order to improve the input power factor to more than 0.95, and decrease the injection of harmonic pollution, the external low frequency UPS a 5 or 11 harmonic filter, the efficiency will drop again 2%-3%. According to a British operator and a Spanish operator network operation statistics, the efficiency of low frequency UPS in general about 85%, while the high efficiency UPS of 92% and modular UPS of 96%, compared to a lot of energy loss. To 400kW load, for example, the power consumption of low frequency UPS will be more than 410 thousand degrees per year, 580 thousand degrees higher than the high frequency UPS. In addition, the low frequency UPS also has the problem of high harmonic, low power factor and so on.
Because the low frequency UPS uses the low frequency device and the output transformer, causes the UPS volume and weight increase greatly. To compare 120 kva UPS with high frequency double conversion online UPS, low frequency UPS is 2.2 times the weight of the high frequency UPS, and the volume is 1.5 times of high frequency UPS, maybe the problem is the room door or aisle elevator load is not enough, the lack of floor bearing in actual transportation, even in some cases need to use the crane loading and unloading, greatly increased transport time and cost.
