MicroMaster 6SE92 - ECT Sales & Service

MICROMASTERMICROMASTER VectorMIDIMASTER VectorPrinciples of Operation2. TECHNICAL DESCRIPTIONThe MICROMASTER, MICROMASTER Vector andMIDIMASTER Vector form a family of inverters that havebeen designed to connect directly to the mains utility powersupply. They are self-contained units housing all thecomponents required for their operation.Depending on the supply voltage, power output and level offunctionality requirement, the series consists of threevariants; MICROMASTER, MICROMASTER Vector andMIDIMASTER Vector. The MICROMASTER should beconsidered as the low cost option for simple applications.It comprises of three frame sizes offering IP20 protection. TheMICROMASTER Vector is form and fit identical to theMICROMASTER, however its functionality and dynamicperformance is much superior with the addition of SensorlessVector Control, additional I/O and larger intelligent powermodules to cope with the additional overload requirements.The MIDIMASTER Vector has identical features to theMICROMASTER Vector whilst extending its power range to75kW (90kW variable torque). In standard form the protectionrating is IP21, however it is also available in IP56 (NEMA 4).2.1 Power SectionAll inverters contain fully integrated power modules mountedon high efficiency heatsinks, cooled by software-controlledfans. Heat dissipation is such that no thermal derating isrequired for ambient temperatures up to 50°C (40°C forMIDIMASTER Vector).All of the units are fitted with an uncontrolled input rectifier, acapacitor-buffered DC voltage link and a PWM inverter withIGBT output device.When the unit is connected to the line supply, the DC link ispre-charged via resistors and pre-charging relays, thuslimiting the level of inrush current.The DC link voltage is then converted into a pulsed variablefrequency and voltage system, using latest generation lowloss IGBTs combined with fully optimised PWM (PulsedWidth Modulation) waveforms, offering the followingadvantages:• Lower inverter and motor losses.• Motor voltage frequency range: 0 to 650 Hz.• Motor voltage range: 0 V to the line supply voltage.• Almost sinusoidal motor currents.• High motor utilisation.• Silent motor operation using high switching frequenciesup to 16 kHz.• Inverter protected against short-circuits and earth faults.MICROMASTERs (MM12/2 to MM300/2) specified for usewith three phase 230V AC supplies may also be used forsingle phase 230V AC inputs. All single phase and threephase 230V MICROMASTERs may be operated from anominal 2ph 208V AC supply.Caution:Connection of a 400V 3ph supply to a 1ph or 3ph 230Vinverter will destroy the inverter.2.1.1 Thermal Protection and AutomaticDe-ratingLosses within the power module rise with increasing switchingfrequencies, leading to higher heatsink temperatures.Operation of the inverter outside its recommended ambientoperating temperature would normally trip the inverter with anover-temperature fault code. To avoid such nuisance tripping,the MICRO/MIDIMASTER Vector automatically reduces itsswitching frequency ( e.g. from 16kHz to 8kHz), thus reducingthe temperature of the heatsink, enabling the application tocontinue running - trip free. Should the load or ambienttemperature then reduce, the inverter will first check to see ifit is safe to increase the switching frequency again and thendo so.2.1.2 Fast Current LimitFast Current Limit (FCL) is a cycle by cycle hardware currentlimit built into the inverter. Its threshold is set slightly belowthe software over-current trip threshold (F002) and reactsmuch quicker, thus preventing spurious and unwanted tripswhen sudden loads are applied or fast accelerationsrequested.2.1.3 Operation from Unearthed SuppliesThe MICROMASTER/MICROMASTER Vector range can beconnected directly to an unearthed line supply. Whilstoperating from such a supply, if one of the input phases isconnected directly to earth the inverter will continue to runwithout consequential damage.The MICROMASTER/MICROMASTER Vector will trip with anover-current alarm if one of the motor output phases isshorted to earth.The MIDIMASTER Vector (at 2kHz) will continue to operate ifone of the motor output phases is shorted to earth. Operationabove 40Hz or at near full load current may result in an overcurrenttrip.Two or more phases shorted to earth will always result in anover-current trip.An OFF command will not isolate the inverter from the mains.An additional main switch or contactor should be provided toelectrically isolate the unit from the line supply.Slow-acting line fuses can also be used for protectionAll MICROMASTER and MICROMASTER Vector units mayalso be connected directly to a suitably rated clean DC supplyusing the DC link connections provided.Siemens DA 64 – 1998/99 (04/99) 2/1