Connection method of braking resistor for Siemens MM440 frequency converter:
1. Four internal terminals:
DC/R+;B+/DC+;B-;DC-, where DC/R+ and B+/DC+ are shorted at the factory.
2. Internal wiring of the four terminals:
DC/R+ is the positive terminal of the DC bus generated by the three-phase bridge.
When B+/DC+ and DC/R+ are shorted together, they also become the positive terminals of the DC bus.
B- is connected to the negative terminal of the DC bus via a switching transistor;
DC- is directly connected to the negative terminal of the DC bus.
3. How to connect the braking unit and the braking resistor:
For devices with a power rating of 75KW or less, there is no need to connect a braking unit; simply connect a braking resistor between B+/DC+ and B-. When there is an overvoltage on the DC bus, the switching transistor will conduct, and the electrical energy will be converted into heat energy and dissipated through the resistor.
For loads above 75KW, a braking unit and a braking resistor are required. The braking unit is connected to B+/DC+ and DC-, and the braking resistor is connected to the terminals of the braking unit. When the braking unit connected to both ends of the DC bus detects an overvoltage, the internal switching transistor of the braking unit is turned on, and the electrical energy is converted into heat energy and dissipated through the resistor.
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