AC Line Reactors vs. DC Link Chokes Introduction This application note is designed to provide an overview of why impedance on the line side of a drive is beneficial in adjustable frequency drives and compares the expected performance of line reactors and DC link chokes. In addition, performance testing is presented to provide a harmonic comparison between the two filtering devices using an VTdrive V5-H-4T15G drive with the 3% line reactor and an VTdrive E5-H4T15G drive with a 5% DC link choke. Harmonics All drives naturally create harmonics on a system given the nature of the AC to DC rectifier of a drive. These harmonics are created because the drive only draws current when the magnitude of the AC, line to line voltage is higher than the voltage of the DC bus. In Figure 1 below, the current is blue and the time where the AC, line to line input voltage exceeds the DC voltage is designated as Id. Current is drawn during the crossover point of the phase voltages and results in a humped waveform. This double hump waveform is typical of most drives. Figure 1: Current draw by drive [1] 2 Harmonics need to be removed because they can increase the I R losses of the system and they can disrupt the proper functioning of other loads on the system as well as potentially damage them. Additionally, utilities often require customers to adhere to IEEE 519 standards of total harmonic distortion (THD). This specifies the amount of harmonics that can be injected back onto the grid. Harmonics that are generated within in a facility, if not properly filtered, will be seen by the utility. For very small drives, this sinusoidal current draw is not a problem for the utility because the drive is not a significant load on the system. However, for larger horsepower drives additional impedance is normally necessary to remove the impact of these periodic pulses of current. In this regard, the two most common options to choose from are an AC line reactors and a DC link choke. What is a choke and how does it affect harmonics? A choke (or line reactor) is a coil of wire around a magnetic core that creates a magnetic field when current flows through it. This magnetic field increases the impedance of the line and reduces the total harmonic content injected from the drive onto the facilities electrical system. To analyze harmonics, we

can examine the harmonic content by breaking down a non-sinusoidal waveform into components. The th th lower harmonics, like the 5 and 7 ,have a larger current magnitude and thus have a larger effect on the total harmonic distortion. This is because the current magnitude is inversely proportional to the harmonic number. What is an AC line reactor? AC line reactors are added to the input of the drive and placed in series with the incoming line. They help to mitigate harmonics and because they are between the line and the drive, they are able to act as a buffer for surges and other transients....

V5-H-4T15G vs. E5-H-4T15G Drive Performance VTdrive V5-H-4T15G drive offers a standard 3% AC line reactor while the new E5-H-4T15G drive comes standard with a two coil 5% DC choke and MOV surge protection on the line side of the drive. There are two critical aspects to consider when comparing these two solutions: the amount of harmonic reduction and the physical size and layout of the drive. Harmonic Analysis Full load tests were run to examine the amount of harmonic content for both a V5-H-4T15G and E5-H4T15G drive at 380V 15kw. As a point of order, the phase to ground voltage is displayed in...

Figure 6: Percent Total Harmonic Distortion at Various Harmonics for V5-H-4T15G The harmonic analysis indicates that the E5-H-4T15G with the DC choke exhibits lower %THD at the 3rd, 51 7th harmonics which are the most detrimental to meeting IEEE 519. The E5-H-4T15G does allow slightly %THD the higher order harmonics which, as was stated before, are more of a concern for EMI sensitive areas. While the E5-H-4T15G does provide better %THD than the V5-H-4T15G, the DC choke is certainly not a cure all for meeting harmonic requirements for a system. Harmonic systems studies are the best option for...