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Principles of OperationMICROMASTERMICROMASTER VectorMIDIMASTER Vector2.1.4 Vector Control PrinciplesWhat is vector control?This is easiest explained through comparison with a DCmachine.In a DC Machine, the field is a separatewinding and therefore the armature current(Torque) and field current (Flux) can becontrolled independently.Independent control of the Flux andTorque producing currents permitsoptimum performance, i.e. Torque at zerospeed, rapid response to load changes etc..SupplyAC InverterEncoderPosition FeedbackTh e ,In an AC Machine, the stator windingcurrents set the Flux and the Torque;therefore it is difficult to control theTorque and Flux separately.Control of the magnitude of the current,will not allow independent control.Therefore the magnitude and phase -“the Vector” - of the current must becontrolled.AC MotorIn order to control the Torque and Flux in the AC motor, the stator current must becontrolled in magnitude and phase, i.e. the Vector quantity.To control the phase with reference to the rotor, the rotor position must be known.Hence for full vector control, an encoder must be used to tell the inverter the rotorposition.2.1.5 Sensorless Vector ControlMany applications do not need and cannot justify theadditional expense of an encoder.For an inverter to simulate the attributes of an encoder, thesoftware algorithm has to accurately calculate the rotorposition and speed by mathematically modelling thefundamental properties of the motor.To do this the inverter must:• Monitor the output voltage and current very accurately.• Calculate motor parameters (Rotor, Stator resistance,leakage inductance etc.).• Accurately model the motor thermal characteristics.• Adapt motor parameters in the light of motor operatingconditions.• Have the ability to perform very rapid mathematicalcalculations. This was made possible using an in-housedesigned custom ASIC;loadperformance criteria. As a result, torque production increasesto 150% or more at 0.5Hz and to over 200% at 2.5Hz andthrough the use of a motor thermal adaptation model, theperformance is maintained over the complete temperaturerange.The entire MICRO/MIDIMASTER Vector series offer anoverload capability of 200% for 3 seconds, making theinverters particularly suitable for arduous applications such ashoists and lifts.Calculation of motor constants is not necessary, this is doneautomatically, leaving the user only entering motorparameters and vector tuning parameters to fine tune theinverter.2.1.6 Flash Floating Point ProcessorSensorless Vector Control is a highly demanding real timecontrol process which is typically achieved using DSPprocessors, RISC processors or multiple microprocessors.The Siemens solution relieves the microprocessor of timeconsuming repetitive tasks and provides floating pointmathematics capability in a custom ASIC. The floating pointcapability means that control equations are implementedverbatim without continuous re-scaling steps. Through theuse of such a system, arithmetic overflows do not happenand full accuracy is always available. The overall result is areliable product with repeatable dynamic performance.The floating point processor is implemented using entirelycombinatorial logic, hence the term ‘Flash Floating PointProcessor’ with performance levels approaching 3 Mflops.The algorithm adopted by the MICRO/MIDIMASTER Vector isvirtually identical to that used in the widely acceptedMASTERDRIVE range.2.1.7 Benefits of Sensorless Vector Control• Excellent speed control with inherent slip compensation.• High Torque at low speed without excessive boost.• Lower losses, higher efficiency.• Higher dynamic performance - better response to steploads.• Stable operation with large motors.• Better performance at current limit with improved slipcontrol.• The Flash Floating Point Processor (F²P²).Siemens, pioneers in this technology, has brought within astandard product, almost closed loop vector performancewithout the need for an encoder.This has been achieved through the use of a bespoke FlashFloating Point Processor, performing the millions ofcalculations per second required to achieve the stringent2/2 Siemens DA 64 – 1998/99 (04/99)
MICROMASTERMICROMASTER VectorMIDIMASTER VectorPrinciples of Operation2.1.8 Vector Operating Rangeinformation and the accuracy of the inverter’s currentmonitoring.2.55Frequency (Hz)Constant current regionConstant current + searching orientation regionFully orientated Vector controlOperation in Sensorless Vector Control (SVC) requires the ratingplate data of the connected induction motor to be accuratelyentered (parameters P080 to P085). These parameters arefactory set with the data of Siemens 4-pole 1LA5 motors, andmust be adapted if other motors are used. Once SVC mode isinvoked (P077=3), the next time the inverter is run, CAL willappear on the display for several seconds, during which time theinverter fully optimises itself and calculates motor modelcharacteristics such as stator resistance, leakage inductance,rotor and stator thermal time constants etc.The ‘Calibration’ routine must be performed on a cold motorsince the inverter automatically compensates itself forchanges in motor temperature.SVC can be used only for induction motors and for singlemotor drives or multi-motor drives with a mechanicallycoupled load.SVC cannot be used for:• Synchronous or reluctance motors.The above diagram illustrates the sensorless vector operatingregions for the MICRO/MIDIMASTER Vector.Constant current regionIn this region the inverter acts like a current source andindependent of load will output the value of currentprogrammed into parameter P083.E.g. for a 750W motor, P083 may be set to 3.4A, therefore,regardless of the motor load (full load or no load), the motorcurrent will remain at 3.4A.Continuous Boost (P078) and Starting Boost (P079) areactive in this region and offer up to 250% boost capability.This region is active below approximately 5Hz (whilst the outputfrequency is ramping up from zero) and below 2.5Hz (whilst theoutput frequency is ramping down from a frequency above 5Hz).The 2.5Hz hysterisis bandwidth is present to prevent oscillationbetween the two operating modes. The 2.5Hz and 5Hz valuesshown are approximately 5% and 10% of the value programmedin P081 - the nominal rating plate frequency for motor.Constant current and searching orientation regionWhilst operating in this region and the output frequency isramping up, the back emf from the motor begins to build up. Withthis information the system will search and lock onto the rotorspeed - once locked, it will stay locked until the output frequencyis requested to go below 2.5Hz. Slip compensation is also activein this region.Fully oriented Vector controlIn this region, the inverter knows the orientation of the motorand will maintain the frequency setpoint within the operationalboundaries of the inverter. Variations in ambient temperature,stator resistance, motor slip etc., are fully compensated forover the complete load operating region.Sensorless Vector Control is a true closed loop system anddepends very much on the integrity of the motor rating plate• Multi-motor drives, group drives (several motorsconnected in parallel at the drive converter output).• Motors with power ratings less than half of the inverterrating.• Motors with current requirements greater than those theinverter can supply. i.e. I motor > P083 max.In the above cases, a V/f characteristic must beparameterised:• P077=0 for applications with linear torquecharacteristics• P077=2 for applications with pump or fancharacteristics (square-law torque characteristics,variable torque, VT)The ‘flying start’ feature in both MICROMASTER Vector andMIDIMASTER Vector depend on the vector algorithm andtherefore must follow the same rules which govern SVCoperation.The above restrictions also apply to inverters configured tooperate in Flux Current Control mode (FCC, P077=1). Thisfeature has been retained within the vector range to maintainbackward compatibility with previous generation MICRO andMIDIMASTERs.For MIDIMASTER, when a square-law torque characteristic isused, it permits a significantly higher motor current, wherebyin almost all cases, the rated output is achieved using thenext largest motor (the motor current can be increased viaparameter P083).For a specific output, fan and pump drives can have a smallerdrive converter.Siemens DA 64 – 1998/99 (04/99) 2/3
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AppendixMICROMASTERMICROMASTER Vect
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MicroMaster 6SE92 - ECT Sales & Service

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