Motor Control Domestic Appliance Applications DSP-based motor con

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Motor Control Domestic Appliance Applications DSP-based motor con

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Motor Control Domestic Appliance Applications
DSP-based motor control systems offer control bandwidth required make possible development advanced motor drive systems domestic appliance applications
Aengus Murray, Analog Devices, Inc.
lectric motors major components electric appliances such refrigerators, washing machines. energy consumed electric motor very significant portion total energy consumed machine. Controlling speed appliance motor both directly indirectly reduce total energy consumption appliance. many major appliances advanced three phase variable speed drive systems provide performance improvements needed meet energy consumption targets. based motor control systems offer control bandwidth required make possible development advanced motor drive systems domestic appliance applications.
Motor Control Domestic Refrigeration Applications
System Requirements: Energy efficient compressors require motor speed controlled range from 1200 4000 rpm. fractional horsepower applica-
tions, motor choice with highest efficiency electronically controlled three phase permanent magnet motor. Motor Control Strategy: order permanent magnet motor efficiently, important synchronize frequency applied voltage position permanent magnet rotor. very effective control scheme motor six-step commutation mode with only windings active time. this case, back unconnected winding direct indication rotor position. rotor position estimated matching back waveform samples correct segment stored waveform profile. This technique averages data from large number samples giving high degree noise immunity. control system, outlined below, inner position control loop which adjusts angles applied stator field keep rotor synchronization. Integrator input tracks motor velocity when rotor position error forced zero. outer velocity loop adjusts applied
stator voltage magnitude maintain required velocity. controller capable accelerating compressor target speed within seconds regulate speed within percent target. Motor Control Hardware: essential hardware variable speed drive system consists input rectifier, three-phase power inverter motor control circuits. motor control processor calculates required motor winding voltage magnitude frequency operate motor desired speed. pulse width modulation circuit controls duty cycle power inverter switches vary magnitude motor voltages. analog digital converter allows processor sample motor feedback signals such inverter voltage current. this sensorless control application, motor winding back signals sampled order calculate drive motor most efficient point operation. voltage signal conditioning consists resistive attenuators passive filters. precision amplifier used capture motor winding current sensing current. controller uses this information limit motor starting current shut down compressor overload conditions. based motor heart system. power program performs initialization diagnostic functions before starting motor.
motor started open loop until back reaches minimum level, before switching running mode. Then, every cycle, uses converter sample motor back emf, motor current voltage. internal multiplexer selects appropriate back signals converted. control calculates rotor position estimate calculates duty cycle required applying required voltage motor. particular values estimated rotor position angle, algorithm selects active motor windings writing segment selection register. algorithm also performs diagnostic functions, monitoring voltage, motor current speed. case overload conditions, drive will shut down attempt restart after short time delay.
Motor Control Washing Machine Applications
System Requirements: drum horizontal axis washing machine driven speeds between 1200 rpm. motor, however, must speeds range 15,000 rpm. Three phase induction motors provide advantages over universal motors through elimination brushes wider speed range. properly control three-phase induction motor over wide speed range both motor current motor speed information required. speed ripple
position estimator
back
rotor position loop
integrator
Sine generation winding selection
Inverter
PMSM
rotor angle point speed point
Velocity loop
Velocity
Figure Sensorless Control System
load torque washing machine motor also provides valuable information about washing load. washing drive described here 500W induction motor with speed range from 15,000 rpm. Induction Motor Control Strategy: control induction motor (ACIM) potentially much simpler than that required permanent magnet motor. ACIM driven open loop three-phase inverter giving adequate speed control performance many simple pump applications. However, when wide speed range high dynamic performance required, then field oriented control scheme necessary. this case flux torque currents independently controlled give performance similar that obtainable from permanent magnet synchronous motor. speed range operation, flux kept constant torque directly proportional torque current. highspeed range, when motor voltages limited voltage, flux reduced allow operation higher speeds direct stator field oriented control algorithm described Figure motor variables flux torque producing components motor currents. choice reference frame element that distinguishes various vector control approaches from another. this scheme, reference frame synchronized rotating stator flux selected because avail-
ability stator current voltage information. number other field oriented schemes require position information, stator flux measurements suitable this application where controlled operation close zero speed required. Park Clark reference frame transformation functions calculate effect stator currents voltages reference frame synchronized rotating stator field. This transforms stator winding currents into quasi currents representing torque producing (Iqs) flux producing (Ids) components stator current. stator flux angle essential input reference frame transformations. stator flux calculated fixed reference frame integrating stator winding voltages. this system, stator voltage demands inverter known, applied stator voltages calculated from voltage demands voltage measurement. flux estimation block uses stator current compensate winding resistance drop. outputs this block stator flux magnitude stator flux angle. There four control loops closed this application. There inner current loops which calculate direct quadrature stator voltages required force desired torque flux currents. Park Clark functions transform these voltages three stator voltage demands fixed reference frame. outer loops speed flux control loops. flux demand rated flux below
Dash
Gate Drives
phase inverter
PMSM
Serial Ports
Flash
resistive divider fiter line
DC_DC
Figure PMSM Control Drive
Iqs*
Ids*
Timers
(Vdc_xs Rs*Ixs)dt (Vdc_ys Rs*Iys)dt (xs2 ys2) flux estimation
Vdc_xs Vxs*(VDC/VDCmax) Vdc_ys Vys*(VDC/VDCmax)
Figure Direct Stator Field Oriented Control Scheme
base speed operation reduced inversely with speed above base speed operation `field weakening mode'. Finally, torque loop same classical motion control system. Induction Motor Control Hardware based induction motor system similar hardware permanent magnet drive described previously. this case, motor rated over IGBTs power devices most suited. feedback signals include motor currents, voltage pulse train from digital tachometer. motor winding currents derived from sensing resistors power inverter circuit. Induction Motor Control Software: challenge development control software four simultaneous control loops where variables have very wide dynamic range. solution,
which very much improved performance, floating point variables control loops. This extended processing time somewhat found significant burden when using MIPS core. processor easily handle multiple interrupt sources from converter, digital block, communications ports timer. number useful device features device such auto-buffered serial port single context switch made task possible without significant overhead pushing popping stack. Finally, code development somewhat simplified availability motor control library functions internal ROM. Aengus Murray Director Systems Engineering team within Analog Devices Embedded Control Systems Group. reached Woburn St., Wilmington, 02161; (781) 935-5565; aengus.murray@analog.com.
Reprinted from May, 2000 2000 CAHNERS BUSINESS INFORMATION
Technology Tel: 4700, 5643, U.S.A. only) Fax: 8703 www.analog.com\motorcontrol DSP-MC-DOM-APPLI

Motor Control Domestic Appliance Applications DSP-based motor con

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