High-efficiency on-line double-conversion UPS

Everyone today is aware of the need to conserve energy. It is one of most hotly debated topics, especially in the field of power protection. Here, there are several innovations that can provide a valuable contribution; in terms of higher operating efficiency and significant energy savings. One of the most important of these is the neutral point clamped inverter. This report compares the three-level, neutral point clamped (NPC) type inverter with the more traditional 2-level version. The objective of this comparison is to demonstrate (in cost and benefit terms) that whilst a UPS with an NPC type inverter has a higher initial purchase outlay (due to its greater complexity and component count), this can be quickly recovered as a result of the far higher energy savings typically achieved. The analysis starts by comparing the two different approaches, illustrating the advantages and disadvantages of one compared to the other, in terms of their technical features and performance. Next the inverter cost differences are quantified (in percentage terms) individually and as part of a complete UPS. This markup is expressed as a percentage of the selling price, based on the average market price of a 40 kVA model. The sizeable efficiency gap between the two different UPS types, (92% to 96.5% under nominal conditions), means that the lower running costs and power losses of an NPC inverter-based UPS typically results in a faster purchase capital recovery period.