Pre-Charge - WEG CFW11W G2 Series User Manual

Installation and Connection

3.2.1.3 Pre-Charge

The resistors of the pre-charge circuit must be sized according to the following criteria:
Maximum voltage.
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Maximum energy.
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Power overload capacity of the resistors during the pre-charge period (energy dissipation capacity).
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3
Where R is the ohmic value of the resistor used on each phase and N the number of power units.
E.g.:
In a drive composed of three power units, whose line voltage on the rectifier input is 690 Vrms (UP11W-01 G2),
the obtained values would be:
Energy stored in the capacitor bank: 3x0,007x6902 = 9998.1 J.
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Using three 10 Ω resistors (one per phase), each resistor must withstand 3332.7 J.
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The manufacturer of the resistor can inform the energy the component withstands.
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The peak current during the pre-charge would be 56.6 A and the pre-charge duration would be 0.51 s.
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3-14 | CFW-11W G2
Table 3.8: Sizing of the pre-charge
Peak Current During the Pre-charge (A)
Energy Stored in the Capacitor Bank (J)
Pre-charge Duration
0.82 x (V /R)
line
N x 0.007. V
2
line
0.017 x N x R