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Advanced Applications

corresponds to a percentage of the full load current in the motor. In practice it is not possible to calculate the braking torque this will produce. Continuous use of the DC braking will cause overheating in the motor and suitable protection systems must be considered. The braking can also be activated by an external switch.

Compound Braking

If DC braking and regenerative braking are combined, braking with minimal regeneration but with controlled motor speed is possible. This consists of a reducing frequency with DC component added to it. This braking system, developed by Siemens for the MICROMASTER, is known as Compound braking. Compound braking can prove very effective, combining the best of DC braking and Regenerative braking. As with DC braking, the load energy is dissipated in the motor, and therefore excessive, frequent braking can lead to overheating. Parameter P1236 sets the level of compound braking.

The above braking methods are summarized in the Figure 8-4.

Frequency Ramp down

DC Braking

Compound Braking

Figure 8-4 Braking Methods

8.3Using the Serial Interface

All Siemens Drives include a serial interface as standard. The serial interface uses a RS485 two wire connection which is designed for industrial applications.

Up to 31drives may be connected on a single RS485 link, and drives addressed individually or with a broadcast message. A separate master controller is required, and the drives act as slaves.

A communications protocol known as the USS protocol has been developed by Siemens and is common to all Siemens drive products. Each inverter can be set up using parameters to receive and respond to USS protocol telegrams.

Using a serial interface has several advantages:

·Wiring can be greatly reduced.

·Control functions can be changed without re-wiring.

MICROMASTER Applications Handbook

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