The formula for current harmonics

Current harmonics are a burden for the power grid and the budget. Instead of going to great lengths to reduce then, it is best to avoid them alto­gether.

Bern­hard Siedler, Team Leader Air Condi­tioning, ebm-papst Mulfingen (Foto: ebm-papst)

The need for data centers is growing world­wide, just like the quan­ti­ties of data to be processed and the power density of the indi­vidual compo­nents. In spite of this trend, the average annual power consump­tion for air condi­tioning in data centers fell by eleven percentage points in the past ten years,
mainly due to the increased use of adjustable and effi­cient EC tech­nology in fans.

Current wave­form with passive PFC
ebm-papst series product:
Power factor (λ) = 0.94; THDI 33.5%

Modern motors are oper­ated with vari­able frequency drives to exactly adjust their speed to require­ments, which results in nonlinear currents. A non-sinu­soidal current curve arises, which can be repre­sented as a sum of sinu­soidal curves with frequen­cies that are an exact multiple h of the funda­mental frequency. This is total harmonic distor­tion (THDI), which is given in percent. A THDI of 33 percent means that in addi­tion
to the 100 percent total active current, a 33 percent distor­tion reac­tive current is lost. The current harmonics also result in a heavy load on the supply network, distur­bances, and high main­te­nance and replace­ment costs. So the aim is to mini­mize THDI. That is usually done with external passive or active filters that are barely able to reach a single-digit THDI value even with very high devel­op­ment and vali­da­tion costs. They also involve other disad­van­tages such as space require­ments, high system complexity, or high procure­ment costs. The best approach is to prevent harmonics from arising in the first place.

Current wave­form with active PFC
New ebm-papst product:
Power factor (λ) = 0.99; THDI ≤ 5%

To do so, we devel­oped the inte­grated 3-phase active PFC solu­tion. “Active recti­fi­ca­tion” causes the input current to be sinu­soidal instead of pulsed, with the current curve shifted so that the current level and voltage are in phase. The power factor  is an impor­tant para­meter, describing the ratio between effec­tive power and apparent power. A value of  = 1 is consid­ered optimum. By filtering the harmonics, the 3-phase elec­tronics with active PFC in the RadiCal and RadiPac series of EC centrifugal fans reach  = 0.99 and a THDI value of less than five percent. Compared with the industry stan­dard, active PFC tech­nology reduces the costs for the required energy supply compo­nents by about 38 percent. 

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