Supply harmonics of converters in fully controlled, three-phase bridge connections B6C annd (B6)A(B6)C

SIMOREG DC MASTER applications comply with the EMC product standard EN 61 800-3 for electrical drives provided that the rules for electromagnetically compatible installation of the converters in the plant are observed.

However, the EMC legislation requires that the entire installation be electromagnetically compatible with the environment. If the system is to comply with the “A1” degree of radio interference suppression according to EN 55011, RI suppression filters must be installed in addition to commutating reactors. In conjunction with the commutating reactors, the RI suppression filters reduce the radio interference voltages that arise due to the converters. RI suppression filters can only be installed in grounded-neutral systems. The RI suppression filters generate discharge currents.

In accordance with DIN VDE 0160, a PE connection with a cross-sectional area of 10 mm² is necessary. To ensure the best possible action of the filter it must be mounted with the converter on a common metal plate.

For converters with a three-phase system, the minimum rated current of the filter is equal to the output DC current multiplied by 0.82. For units with a two-phase system (field supply and electronics power supply), only two phases are connected to the three-phase RI suppression filter. The line current is equal to the field DC current (plus 1 A for the electronics power supply).

a) О± = 20 °
Fundamental factor g = 0.962

b) О± = 60 °
Fundamental factor g = 0.953

The fundamental current I1 as the reference quantity is calculated with the following formula:

I₁ = g x 0.817 x I_d

where I_d = DC of the examined operating point

and g = fundamental factor (see above)

The harmonic currents calculated from the above tables apply only to

a) Short-circuit power S_K at the connection point of the converter:

S_K = U²_VO (VA) / X_N (VA)

where

X_{N =} X_K – X_D = 0.03536 x = U²_VO / I_d (VA) – 2 ПЂ f _N x L_D (ОЏ) and

U_V0 No-load voltage at the connection point of the converter in V

I_d DC current for the examined op

f_N Line frequency in Hz

L_D Inductance of commutating choke in H.

b) Armature inductance L_a:

L_a = 0.0488 x U_VO / f_N x I _d (H)

If the actual values of short-circuit power S _K and/or die armature inductance L _a differ from the values calculated, a separate calculation is necessary.

Example:

The given drive has the following data:

U_vo = 400 V

I_d = 150 A

F_rated = 50 Hz

L_D = 0.169 mH (4EU2421-7AA10 with ILN = 125 A)

where

X_rated = 0.03536 x 400/150 – 2 ПЂ x 0.169 x 10^–3 = 0.0412 WО©

resulting in the following required short-circuit power of the system at the connection point of the converter:

S_K = 400²/0.0412 = 3.88 MVA

and the following required armature inductance of the motor:

L_a = 0.0488 x 400/50 x 150 = 2.0 mH

The harmonic currents listed in the tables I_ОЅ

(where I₁ = g x 0.817 x I_d for delay angle О± = 20° and О± = 60°)

apply only to the values S_K and L_a. If the values differ, a separate calculation is necessary.

When designing filters and reactor compensations, the harmonic values thus calculated can only serve as a basis if the calculated values for SK and La coincide with the actual values of the drive. In all other cases a separate calculation must be made (especially when compensated machines are used because of the very low armature inductance).