Constant Slip Speed Control of 3-Phase ACIM Kartik Liao 1 © 2014 Spansion Inc. Background Application − Lathes, mills, drilling machines − Conveyers, lifts, cranes − Compressors, pumps, fans ACIM Features − High reliability − Less maintenance − Low cost Control Schemes − V/f control − Constant slip voltage(V/f, current)control − FOC − DTC 2 © 2014 Spansion Inc. Elements of AC Induction Motor (From Article Library) Schematic of Slip Speed Control Solution AC ~ 𝑉𝑞∗ = 0 𝜔𝑟∗ + 𝜔𝑟 𝑉𝑑∗ PI Rectifier Inv. Park DC PWM - 𝜔𝑠𝑠𝑒𝑡 𝜔𝑠∗ 𝜃𝑒 + + 1 𝑠 IPM PI Speed sensor 𝑀𝑎𝑥 𝑉𝑑∗ DC bus voltage sample Field weakening Software 3 © 2014 Spansion Inc. ACIM 𝜔𝑟 Speed signal capture Hardware Slip Speed Solution Features High efficiency Fast dynamics Low cost Simple control structure Easy tuning Features 4 V/f Control Slip Control DTC FOC Dynamics Low Moderate High High Efficiency Low High High High Cost Low Moderate High High Complexity Low Low Moderate High Tuning Easy Easy Moderate Difficult © 2014 Spansion Inc. Control Theory Phasor Model of ACIM at Steady State − 𝑉𝑠 = 𝑅𝑠 𝐼𝑠 + 𝑗𝜔𝑒 𝐿𝑠 𝐼𝑠 + 𝐿𝑀 𝐼𝑟 − 𝑉𝑟 = 𝑅𝑟 𝐼𝑟 + 𝑗𝜔𝑠 (𝐿𝑀 𝐼𝑠 + 𝐿𝑟 𝐼𝑟 ) = 0 Torque Generation − 𝑇𝑒 = = 3𝑃 𝐿2𝑀 𝑅𝑟 𝜔𝑠 ∙ 2 𝜔𝑠 2 𝐿2 −𝐿𝑠 𝐿𝑟 2 +𝑅𝑟2 𝐿2𝑠 𝑀 3𝑃 2 ∙ 𝑽𝒔 2 𝝎𝒆 𝐿2𝑀 𝑅𝑟 𝜔𝑠 𝑅𝑠 𝑅𝑟 +𝜔𝑠 𝜔𝑒 𝐿2𝑀 −𝐿𝑠 𝐿𝑟 2 + 𝑅𝑟 𝜔𝑒 𝐿𝑠 +𝑅𝑠 𝜔𝑠 𝐿𝑟 Control Target 2 𝑽𝒔 2 𝑗𝜔𝑒 𝐿𝑙𝑠 𝐼𝑠 𝑗𝜔𝑒 𝐿𝑙𝑟 𝐼𝑟 − Slip Speed 𝑅𝑠 − Stator voltage (or V/f, stator current) 𝐼𝑀 𝑉𝑠 Phasor model of AC Induction Motor 5 © 2014 Spansion Inc. 1 𝑅 𝑠 𝑟 𝑉𝑟 𝑠 Motor Efficiency and Slip Speed MTPA minimizes stator current for a certain load level, which requires the slip speed to satisfy below equation − 𝜔𝑠 = 𝑅𝑟 𝐿𝑟 Maximum efficiency control minimizes copper loss and core loss, which is realized by setting slip speed as − 𝜔𝑠 = 1 𝑅𝑟 √2 𝐿𝑟 Switching loss [𝑷𝒔𝒘𝒊𝒕𝒍 ] 𝑉𝑑𝑐 3-phase Inverter Copper loss [𝑷𝒄𝒖𝒍 ] Mechanical loss [𝑷𝒎𝒆𝒄𝒉𝒍] Input Power [𝑃𝑖𝑛 ] Output Power [𝑃𝑜𝑢𝑡 ] AC Induction Motor Core loss [𝑷𝒄𝒐𝒓𝒆𝒍 ] 6 © 2014 Spansion Inc. Field Weakening and Slip Speed High speed operation requires weakening flux level to suppress backEMF under a certain level If the load torque is 𝑇𝑒∗ , the stator flux linkage is determined by slip speed − 𝜆𝑠 = 2𝑇𝑒∗ 3𝑃 2 ∙ 𝐿𝑠 𝑅𝑟2 +𝜔𝑠2 𝐿𝑠 𝐿2𝑟 −𝐿𝑟 𝐿2𝑀 + 𝜔𝑠 𝑅𝑟 𝐿2𝑀 𝐿2𝑀 𝑅𝑟 𝜔𝑠 𝑅𝑟2 + 𝐿𝑟 𝜔𝑠 2 2 Flux level decreases with the increase of slip speed Magnitude of stator flux linkage 1.000 Te= 0.5 0.900 0.800 Te= 1.5 0.700 0.600 0.500 0.400 0.300 0.200 0.100 0.000 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96 Slip speed Slip speed v.s. flux linkage 7 © 2014 Spansion Inc. Related Resources Documents − S6E1A1_AN710-00001-E 3-Phase ACIM Scalar Control − AN710-00009-1v0-E-3-Phase_ACIM_Scalar_Control_User_Manual Find more http://www.spansion.com/Pages/Default.aspx 8 © 2014 Spansion Inc. www.spansion.com Spansion®, the Spansion logo, MirrorBit®, MirrorBit® Eclipse™ and combinations thereof are trademarks and registered trademarks of Spansion LLC in the United States and other countries. Other names used are for informational purposes only and may be trademarks of their respective owners. This document is for informational purposes only and subject to change without notice. Spansion does not represent that it is complete, accurate or up-to-date; it is provided “AS IS.” To the maximum extent permitted by law, Spansion disclaims any liability for loss or damages arising from use of or reliance on this document. 9 © 2014 Spansion Inc.