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#EEwebinar
#EEwebinar
This webinar will be available afterwards at www.eeworldonline.com & email
Q&A at the end of the presentation
Hashtag for this webinar: #EEwebinar
Before We Start
#EEwebinar
Meet your Speakers
MODERATOR FEATURED SPEAKERDal Y. OhmPresidentDrivetech, Inc.
Aimee KalnoskasModeratorEE World
#EEwebinar 4
FOC (Field oriented Control) for AC motors• Synchronously rotating reference frame
o Analogy: Geo-centric vs Helio-centric view• AC motor current can be divided into two components
o Torque producing current componento Field flux current component
• PM motor – Zero normally, Nonzero for IPM• Induction motor – Magnetization Current
• Independent control of two current components• Operation is very similar to separately excited DC motors
#EEwebinar 5
Frame Transform (1) - Clarke• 3 Phase to 2 Phase Transform
S 1 cos120 cos120 Sa S =1.5 0 -sin120 sin120 Sb So 0.5 0.5 0.5 Sc
• All polyphase currents produceso Rotating mag flux!
• Equivalent 2-Phase Machine• Identical magnitude, Reversible• Not invariant power
Sa,S
S
Sb
Sc
#EEwebinar 6
Frame Transform (2) - Park• Coordinate attached to the rotor
(rotating)o D-axis on rotor N poleo Q-axis on N-S mid point
Id cos sin Ix Iq = - sin cos Iy
Ix cos - sin Id Iy = sin cos Iq
x
+yd
q
#EEwebinar 7
Dynamic Equations of Brushless Motors• Voltage Model in Synchronous Frame
Vq = (Rs + Ls p) Iq + Ls Id + mVd = (Rs + Ls p) Id - Ls Iq
• Correspondent to DC Motor equation• Can be extended to Induction Motors
m
+
Rs Ls
+-
VqIq +
Ls Id
Rs Ls
+-
VdId
Ls Iq
#EEwebinar 8
Synchronous Current Regulator (SR)
o Zero steady-state phase error with PI control“Internal Model Principle”
o Id* is nonzero for phase angle advanceo Easy to add back emf & cross-coupling compensation
PWM (SVM)
VaVbVc
IaIbIc
eCross-
Coupling Compensation
Inverse Park
RegulatorPI
RegulatorPI
Iq* + -
Id* + -
Iq
Id
Vd
Vq
e
Vector Saturatio
nAlgorith
m
Inverse
Clarke
V
V
ClarkePark
I
Ie
#EEwebinar 9
Characteristics of FOC Drives• Inherent “zero steady-state tracking error”• Simple to add “disturbance feed-forward”
o Back emf and cross-coupling• Results
o Accurate commutation at any speed!!o Maximum torque per ampere
• With nonzero Id* for IPMo Improved Dynamicso Induction motor flux weakening by changing Id*
#EEwebinar 10
Disturbance Feedforward Techniques
• Compensates for Back emf and cross-coupling terms
• Quick integrator response – Improved performance
Transform
abc -> dq
PI
PI
Transform
dq -> abc
IaIbIc
Va*Vb*Vc*
-+
-+
Iq*
Iq
Id*
Vq*
Id
Vd*
e - Lq Iq
Ld Id + m
#EEwebinar 11
Analytic Tuning of Velocity PI (1)• Used for initial gain before fine tuning• Based on simple 1st order plant model• (1) Cancellation Tuning for bw of v
Kp( s + i)s
KtJm s + Bm
+-
c
Gc(s) = 1/{Jm / (Kp Kt) s + 1} v = (Kp Kt / Jm)
Kp = v (Jm / Kt), i = Bm / Jm
#EEwebinar 12
Analytic Tuning of Velocity PI (2)(2) Pole placement Tuning
o Based on critically damped poleso No control of closed-loop zeros
Kt ( Kp s + i) Jm s2 + (Kt Kp + Bm) s + Kt iGc(s) =
Kp = 2 v (Jm / Kt), i = (1/2) v
#EEwebinar 13
Gains for Per Unit Systems• Conversion of S.I. Gains to Per Unit Systems• Kp, i, max, Imax are in SI units• Kp’, max’, Imax’ are in per unit units• i’ = i, Kp’ from two identical block equations• Note: id = i Ts (digital controller gain)
Kp( s + i)s
i*
Kp’( s + i’)s
i* max’max
ImaxImax’
#EEwebinar 14
Tuning of Current Loop
• Cancellation tuningKp = c Lq, i = (Rs/Lq)
• Pole-placement tuningKp = 2 c Lq, i = c
2 Lq• Gain translation for Per-unit systems
– similar to Velocity-loop
Kp( s + i)s
(1/Rs)(Lq/Rs) s + 1
+-
IqIq* Vq
#EEwebinar 15
Low-cost Sensors & Sensorless Control• Hall sensors (with linear interpolation)• Magnetic Rotary Hall Position Sensors (AMS, Avago) • Sensoless - Estimation of Flux Angle & Velocity
o Popular technologiesVemf detection (6-step)Model-based Observer (Estimator)Carrier injection (IPM, Audible noise)
o PerformanceBW limited, limited accuracyChallenges at startup and near-zero speed, high torque
applicationModel of nonlinearities (Extra voltage drops)Algorithm selection and tuning – key to success
#EEwebinar 16
Carrier Injection Method (IPM)
Current Regulator
PWMVoltageInverter
LPF
BPF
HeterodyningCalculation
LuenbergerObserver
FrameTransform
InverseTransform
Carrier VoltageInjection (0.5 – 2
kHz)
+ -
θr^
θr^
Iqds
θr^
VqdsIqd*
Iqde
motor
(Sensored Block)
#EEwebinar 17
Observers (Linear or Sliding mode)
• Applied to 2-ph stationary quantities (I, I, E, E, etc.)o 2-ph Synchronous variables can also be used.
• Luenberger: Select K so that observer bw is >>10X motor model
• Sliding mode: Sliding gain L > max(E, E), K = o Chattering, heavy LPF
• Atan() or Phase Locked-Loop
MotorModel
KIs~ +
Is-V
s Es s
(Optional outer loop)
(Saturate to +/-L)
LPFATAN(
)
#EEwebinar
Sensorless Start-up Strategies• Open-loop forced start
o Kt Iqs = J d/dt + TL o Startup current Iqs and acceleration rate should beo Slightly higher than worst case J and TL
• Inductance-based angle detection for motors with high ΔLo V – IR = L di/dto Voltage injection with Current rise-time measurment
• Carrier Injection Startup for motors with high ΔL
#EEwebinar 19
Power Factor Correction (PFC)
(Pavg)p.f. = ---------------------------
(Vrms) (Irms)• A figure of merit that measures how effectively energy is
transmitted• p.f = (Is1/Is) cos
o Distortion factor (Is1/Is) o Displacement factor cos
• IEEE 519 recommends <5%• Dedicated PFC Converter IC or Processor Controlled (1
Phase)
#EEwebinar 20.
Conclusion• High motor reduces size and total operating
cost• Sensorless or Low-cost feedback reduces cost • Proper control algorithm & optimally tuned
driveallows precise commutation to improve
efficiency, maximum torque, and dynamics• Selection of uC, Gate drives and Power
switches for low-cost and compact design
#EEwebinar
Questions?
MODERATOR FEATURED SPEAKERDal Y. OhmPresidentDrivetech, [email protected]
Aimee KalnoskasModeratorEE [email protected]
@DW_Aimee
#EEwebinar
This webinar will be available at eeworldonline.com & email
Tweet with hashtag #EEwebinar
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Continue the discussion on our forums
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#EEwebinar