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Frequently Asked Question

Topic: How to calculate AC Choke for Mains Supply and DC Choke for DC Bus

Author Yaskawa

Product: All Date 31-Aug-2010

Keywords: Choke, Reactor, DC bus voltage, harmonics Pages 1 of 2 Distribu-tion: Internal Use only Customer

I. Generally An AC reactor and also a DC reactor reduce the harmonics on the current drawn from the Mains Power Supply. An AC reactor has to be connected between mains and input rectifier of the inverter. In

addition to the reduction of harmonics it does help to protect against nuisance tripping due to voltage spikes, but it causes a voltage drop which reduces available propulsion power.

A DC reactor has to be connected between input rectifier and DC Bus capacitors. The voltage drop is much less than with an AC reactor, but inductance shall be twice as much to get the same effect to harmonics.

II. Calculation of the Inductance

Generally, a DC reactor has less performance than an AC reactor with same inductance. Therefore, a DC reactor has to have a bigger inductance than an AC reactor (per phase) to accomplish the same performance. This does not mean that the total voltage drop in the cir-cuit is higher with DC choke, in fact it is much less, because the DC reactor is incorporated into the DC Bus circuit, which provides mainly a DC current to the capacitors, but the DC re-actor operates only on the overlaid harmonics. To calculate a choke inductance for given percentage short circuit voltage (vsc%), the follow-ing formulas can be used:

InputInverterMains

MainsscChokeMains If

UvL = 23%

MainsaverageDC UU = 35.1 UDC average average value of DC bus voltage

IDC average average value of DC bus current PM maximum motor power M motor efficiency inv inverter efficiency vsc% percentage short circuit voltage (E.g.: Use 0.03 for 3% short circuit voltage)

invMaverageDC

MaverageDC U

PI =

averageDCMains

averageDCscChokeDC If

UvL = 2%

H o w t o c a l c u l a t e A C C h o k e f o r M a i n s S u p p l y a n d D C C h o k e f o r D C B u s . d o c

Se i te 2 von 2 07 .09 .2010

Example (HD) Motor data: PM = 55kW / UM = 400V / IM = 98.5A / M = 0.935 / cos M = 0.86 Inverter data: CIMR-AC4A0139: IInverter Output = 112A(HD) / UMains = 400V

inv = 0.96 / Motor Power = 55kW(HD) / IInverter Input = 105A(HD) / Percentage Short Circuit Voltage (Vsc%): 3%

mHAHz

VL ChokeMains 21.0105502340003.0 ==

The inductance of the 3 phase mains reactor is 0.21 mH with a current rating of 105 A.

AV

WI averageDC 11896.09.040035,155000 ==

mHAHz

VL ChokeDC 437.011850235.140003.0 =

= The inductance of the DC reactor is 0.44 mH.

III. Calculation of the Rated Current for the DC Choke The (distortion) power factor for a B6 rectifier bridge is 0.955. The rated current of the DC choke shall consider this value.

AAI rmsChokeDC 124955.0118 ==

The rated current of the DC choke is 124 Amps.

H o w t o c a l c u l a t e A C C h o k e f o r M a i n s S u p p l y a n d D C C h o k e f o r D C B u s . d o c

How to calculate AC Choke for Mains Supply and DC Choke for DC Bus