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9.3Braking Modules and Braking Resistors
During regeneration (see section 8.2.2) it may be necessary to dissipate the energy that is returned to the inverter. MICROMASTER MM420 units do not have the capability to dissipate regenerated energy.
Some Siemens inverters have a built in ‘braking chopper’ and require only an external resistor to allow controlled dissipation. The resistors can be supplied as optional parts to the inverters, and fit alongside the inverters. They are specially designed to operate with the high voltages present in the DC link, and are of metalclad, IP54 design. Braking resistors for operation with earlier MICROMASTERs were designed to mount underneath the inverters. Other resistors can also be used, but care must be taken to ensure they are of adequate voltage and power rating.
9.4EMC Filters
MICROMASTER inverters are designed to minimize conducted and radiated interference. However, they are power electronic products and generate significant levels of interference over a wide electromagnetic spectrum.
In many applications it is possible to operate without filters or with the built in filter. However, in order to achieve higher levels of attenuation an external filter may be required. In particular, an external filter will be needed in order to meet residential, commercial and light industrial levels.
The purpose of EMC filters is to reduce the conducted levels of interference from the inverter to the supply. It is not intended to reduce radiated interference or attenuate interference into the inverter. It should be fitted to the input supply to the inverter and will be damaged if installed in the inverter output.
The filters are designed to mount underneath the MICROMASTER to minimize space requirements. Full installation instructions and information concerning the appropriate filters are given in the Reference Manual.
9.5PROFIBUS Module
Siemens Standard Drives incorporate an RS485 serial interface as standard. In order to operate on a PROFIBUS system a separate conversion module is required. The PROFIBUS module and the PROFIBUS system is described in section 8.4.2.
9.6Input and Output Chokes
Chokes can be fitted to the input of the inverter to reduce harmonic distortion and to reduce the effect of supply disturbance on the inverter. Chokes are also recommended where supply impedance is less than 1%.
Chokes are fitted to the output of the inverter to allow operation with long cables. The choke compensates for the stray capacitance of the cables. Recommended chokes for different cable lengths and inverters are available.
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