ELECTRIC DRIVES INTRODUCTION TO ELECTRIC DRIVES. Electrical Drives Drives are systems employed for motion control Require prime movers Drives that employ

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  • ELECTRIC DRIVESINTRODUCTION TO ELECTRIC DRIVES

  • Electrical DrivesDrives are systems employed for motion control Require prime moversDrives that employ electric motors as prime movers are known as Electrical Drives

  • Electrical DrivesAbout 50% of electrical energy used for drivesCan be either used for fixed speed or variable speed75% - constant speed, 25% variable speed (expanding)

  • CONTENTPower electronic system Modern electric drives

    Power electronic converter in electric drives

  • Modern electric drives (With power electronic converters)SmallEfficientFlexible

  • Components in electric drivesMotorsDC motors - permanent magnet wound fieldAC motors induction, synchronous (IPMSM, SMPSM), brushless DCApplications, cost, environment Natural speed-torque characteristic is not compatible with load requirements Power sourcesDC batteries, fuel cell, photovoltaic - unregulatedAC Single- three- phase utility, wind generator - unregulatedPower processorTo provide a regulated power supplyCombination of power electronic convertersMore efficient Flexible Compact AC-DC DC-DC DC-AC AC-AC

  • Components in electric drivesControl unitComplexity depends on performance requirementanalog- noisy, inflexible, ideally has infinite bandwidth.digital immune to noise, configurable, bandwidth is smaller than the analog controllers DSP/microprocessor flexible, lower bandwidth - DSPs perform faster operation than microprocessors (multiplication in single cycle), can perform complex estimationsElectrical isolation between control circuit and power circuit is needed:Malfuction in power circuit may damage control circuitSafety for the operatorAvoid conduction of harmonic to control circuit

  • Components in electric drivesSensorsSensors (voltage, current, speed or torque) is normally required for closed-loop operation or protectionElectrical isolation between sensors and control circuit is needed for the reasons previously explainedThe term sensorless drives is normally referred to the drive system where the speed is estimated rather than measured.

  • Overview of AC and DC drivesDC motors: Regular maintenance, heavy, expensive, speed limitEasy control, decouple control of torque and fluxAC motors: Less maintenance, light, less expensive, high speedCoupling between torque and flux variable spatial angle between rotor and stator flux

  • Torque-speed quadrant of operation1234T +ve +vePm +veT -ve +vePm -veT -ve -vePm +veT +ve -vePm -veQuadrant of operation is defined by the speed and torque of the motorMost rotating electrical machines can operate in 4 quadrantsNot all converters can operate in 4 quadrants

  • Torque-speed quadrant of operationQuadrant of operation is defined by the speed and torque of the motorMost rotating electrical machines can operate in 4 quadrantsNot all converters can operate in 4 quadrants

    Quadrant 1Forward motoringQuadrant 2Forward brakingQuadrant 3Reverse motoringQuadrant 4Reverse braking

  • Load steady state torque-speed characteristicHoist drive

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