VLT2881PT4B20STR0DBF00A00 summary：

　　Units with the built-in load sharing option contain terminals (+) 89 DC and (–) 88 DC. Within the frequency converter, these terminals connect to the DC bus in front of the DC link reactor and bus capacitors.

　　The use of the load sharing terminals can take on 2 different configurations.

　　In one method, the terminals are used to tie the DC-bus circuits of multiple frequency converters together. This allows one unit that is in a regenerative mode to share its excess bus voltage with another unit that is running a motor. Load sharing in this manner can reduce the need for external dynamic brake resistors while also saving energy. In theory, the number of units that can be connected in this way is infinite, however, each unit must be the same voltage rating. In addition, depending on the size and number of units, it may be necessary to install DC reactors and DC fuses in the DC link connections and AC reactors on the mains. Attempting such a configuration requires specific considerations and should not be attempted without first consulting Danfoss application engineering.

　　In the second method, the frequency converter is powered exclusively from a DC source. This is a bit more complicated. First, a DC source is required. Second, a means to soft charge the DC bus at power up is also required. Last, a voltage source is required to power the fans within the unit. Again such a configuration should not be attempted with out first consulting Danfoss application engineering.