Rockwell Automation Publication 750-RM100A-EN-P - August 2019 25
Chapter 3
Precharge Sequence
This section defines the precharge sequence of the PowerFlex® 750-Series
products with TotalFORCE® control.
Overview
PowerFlex 755T products use a precharge sequence to control powerup. The
precharge sequence starts as soon as the drive detects incoming three-phase
power on the input terminals. The sequence ends when the main control board is
able to communicate with all necessary peripherals. The following frame-specific
sections guide you through the precharge sequence and define what occurs at
each step.
Frames 5 and 6
1. Three-phase power is applied.
2. Incoming three-phase power is stepped down and the main control board
is powered.
3. The main control board performs a check before it initiates the precharge
sequence.
4. A precharge resistor bank is connected between the AC line and the input
of the converter. This resistor bank limits the voltage that is available while
the DC bus and LCL filter capacitors begin charging.
5. When the DC bus is 85% of the nominal voltage rating, the AC precharge
circuit bypasses the precharge resistor bank. Full line voltage is applied to
the input of the converter to complete the precharge sequence.
6. Main control board checks for an ‘Ok’ status to verify that the precharge
sequence was completed successfully and that the drive is ready.
Frames 7…15
1. Three-phase power is applied.
2. The operator closes the main fuse disconnect (FD1).
3. A step-down transformer limits incoming three-phase power to 240V.
Power is applied to the AC precharge board and to the 24V DC network.
4. 24V DC is applied to the control pod and main control board. Fiber-optic
communication is established between the main control board and the AC
precharge board.
5. The main control board performs a check and sends an ‘Ok’ status to the
AC precharge board to proceed with the precharge sequence.
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