Figure 18 - Harmonic Content With And Without Line Inductance; Figure 19 - Harmonic Content Varying According To The Percentage Of Non-Linear Loads - Daikin EWYD-BZ Series Installation, Maintenance & Operation Manual

In a VFD without remedial devices, harmonic distortion can reach values of more than 100% (i.e. the harmonic
components can, all together, reach more than the fundamental component).
To reduce the harmonic content of the current (and so the THD), the units illustrated in this manual are equipped with
line inductance. Since the harmonic content depends on the ratio of the current required by the VFD to the short-circuit
current in the wiring point, for a given plant, the THD varies according to the machine absorption. For example, fig. 14
illustrates the value of the THD with or without a filter inductance, for different values of the ratio of VFD current to the
short-circuit current in the wiring point.

Figure 18 - Harmonic content with and without line inductance

It must however be mentioned that the harmonic distortion drops in value if other utilities are connected at the connection
point (PCC): the greater the weight of these utilities, the smaller the current distortion will be. Fig. 16 illustrates the total
harmonic distortion in the point where the unit is wired to the grid, according to the ratio between the short circuit current
in the connection point (I ) and the current drawn by the unit (I ) and the percentage power absorbed by the unit
SC L
compared to the total power supplied by the grid at the connection point.
Notice how the harmonic distortion at the connection point can feature very low values (below 5%) when the short circuit
current is less than 20 times the unit current and this makes up a percentage of no more than 20% of the total load of the
grid.
In any case, the harmonic distortion introduced by the unit must be evaluated in relation to the specific application,
subject to a detailed analysis of the entire grid and of the loads powered.

Figure 19 - Harmonic content varying according to the percentage of non-linear loads

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