Transcript VisSim/Embedded Controls Developer for TI C2000

VisSim for Electric Motor
Control
Visual Solutions, Inc.
487 Groton Road, Westford MA 01886 USA
(800) VISSIM-1
www.vissim.com
VisSim Supported Motors
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AC Induction
BLDC
Brush
PMSM
Stepper
Switched Reluctance
TI-Based Motor Control Blocks
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Sensored AC Induction Control Blocks
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V/Hz Profile Generator
Sensorless AC Induction Control Blocks
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AC Motor: Simulated ACI Motor
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ACI Speed Estimator: Speed estimation from phase currents
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ACI Flux Estimator
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Current Model
PMSM Sensorless Control Blocks
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Phase Voltage Calc
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SMO Position Estimator
General Transforms
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Clarke & Inverse Clarke Transform
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For balanced three-phase circuits, the Clarke transform is the projection of three-phase AC signals (phase
currents) to two stationary orthogonal signals
Park & Inverse Park Transform
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For balanced three-phase circuits, the Park transform is the projection of stationary 3-phase AC signals two
axes rotation with the same frequency as the original signal. This results in two DC quantities easier to use for
control before performing the inverse transform back to AC values for the PWM.
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PID Regulator
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PWM Wave Form Generator
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Space Vector Generator (Quadrature Control)
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Space Vector Generator (Magnitude/Frequency)
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2nd harmonic wave form generator w/D+ Q inputs
2nd harmonic wave form generator w/ Mag+Freq inputs
Space Vector PWM: Used for 2812 PWM modulation
Rotational Sensors
• QEP Speed
– Takes normalized unit sawtooth and produces fraction of max speed
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To normalize, apply gain of 1/<max counts> to EQEP output
• Resolver Decoder
– Resolver is like rotating transformer. Base carrier frequency is picked
up by sensing coils at 90 deg. Carrier freq is filtered out, and atan2 of 2
coil intensities gives rotor angle.
• Speed Calculator
– Takes event capture count as input, produces fraction of max count as
result
– Enter max count (interval between edge event) as block parameter
Stepper Motors
• Multiple "toothed" electromagnet stators
around gear-shaped magnet or
iron core rotor (switched reluctance)
• Each stator coil is slightly offset from the next
• By energizing each winding in turn, you move the rotor a bit
• Order of energizing gives rotational direction
• Used with open-loop positioning since it can be assumed that the rotor
turns a discrete amount with each pole activation
• A unipolar stepper motor has two windings per phase, one pole per winding
• Bipolar motors have single winding per phase, 2 poles per winding. Must
use H-bridge to reverse polarity
Stepper motor wave forms
• To output waveform from
DSP, write sequence of
bit patterns to GPIO port.
• Wave Drive – one coil
energized at a time
• Full Step – two coils
– Less smooth, more
power, more torque
• Half Step – alternates
one and two coils
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Hybrid, 2x steps
VisSim for Stepper Motor Control
• Use case block to select hex constant for
GPIO pattern sequence
• Use counter to drive case block
• Output of case connects to GPIO write
Stepper Control Issues
• Rate of pole switching controls rotational speed
• Rate is limited by rated torque and load – If you switch too
fast, you will not rotate
• maximum start frequency rating at no load
• maximum start-stop torque is the pull-in torque
• pull-out torque is max torque without losing steps
• step rate is ramped up during start
• Use variable frequency ramp block for stepper
speed control
VisSim/Motion
• Extensive block set for simulation of electric
motor systems
• Supports AC induction, brush and brushless
DC motors
• Stepper motors
• Low level PWM switching simulation level
• Selection of Sensors, Loads, Controllers,
Transforms
Brush DC Motors
• Commutation done mechanically
– Simple to control, but brushes wear over time
• Low cost
• Rotor has multiple coils, stator can be
permanent magnet or coils.
– Magnets lose strength over time
BDC motor types
• Shunt-Wound – stator coils in parallel to rotor coils
– Current in stator and rotor are independent. Good for speed
control
• Series-Wound – stator coils in series with rotor coils
– Good for high torque since current in stator and rotor
increases at same rate
• Wound stators does not suffer torque degradation like
permanent magnet stator
BDC directional control
• Requires H-bridge to reverse polarity of supply
• Ifwd = forward motion, Irvs = reverse, Ibrk = braking
• Need grounding R’s to avoid shorts on startup
BDC Speed Control
• BDC motor speed is proportional to voltage
• Motor coils act as low-pass filter for PWM so voltage
is proportional to PWM duty cycle
• Frequency of PWM an issue
– Too low a frequency results in audible noise at low speed
and sluggish response
– Too high a frequency loses efficiency due to switching
losses
– 4 to 20 kHz is typically used
Feedback control
• For speed control, use speed sensor with PID
feedback control
• QEP speed block needs “normalized” QEP
input. (QEP / encoder tick count) for fraction of
complete revolution
• Use enabled blocks for forward and reverse
PWM configuration
Motion Trajectory
• Trapezoidal - spec max vel, max accel
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Diagrams>Examples>Applications>Motion>TrapezoidalProfile.vsm
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Linear acceleration from stop to max vel, hold max vel to stop zone,
constant deceleration to stop
• S-Curve - spec max vel, max accel, max jerk
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Diagrams>Examples>Applications>Motion>S-curveProfile.vsm
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Linearly increase acceleration from stop to max accel, hold max accel,
then decel to max vel, hold max vel to stop zone, linearly increase
deceleration to max decel hold max decel, then decrease decel to stop
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Smoother, more computation
PID Tuning
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ParameterUnknown blocks for PID terms
Use overshoot penalty to find stable solution
Use sliders with simple plant in auto-restart mode to examine the PID response space
Good paper “PID Control System Analysis & Design” Feb 2006, IEEE Control Systems
Magazine
Effects of independent P, I, and D tuning on closed-loop response.
Rise Time
Overshoot
Settling Time
Steady-State
Error
Stability
↑ KP
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Degrade
↑ KI
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Degrade
↑ KD
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~
Improve
- derivative term can degrade stability if plant has transport delay
- 80% of PID controllers in use have the derivative part switched off
PID structures
• Simple 3 term: y = e(x)(Kp + Ki/s + Kds)
– Implement s (d/dx) via zero/pole, zero gives derivative,
pole is tuned for low pass filter.
• If Ti ≥ 4TD can do series PD-PI:
y =e(x)(α + TDs) KP(1 +1/αTis)
Where α =(1 ± √(1 − 4TD/ Ti ) )/2 > 0
• Examine response w/autorestart, sample plant, and
sliders for gains.
• Can be helpful to fix d/dt coef by hand and opt P and
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State Transition Block
• Allows creation of any number of states
• Each state has any number of transition conditions to
change to another state
• Conditions are written in C code and may reference
VisSim variables (must be syntactic C – no space or
punctuation in name)
• Block output is current state, and rule that last fired to
enter this state
• VisSim lets you use state names anywhere you can
use expressions, like const and expression blocks
Scaled Fixed-Point Operations
• Arithmetics (add,mul,div,gain etc)
• Limit, unit delay, merge, map, PI regulator
• Hands-on
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Make sample diagram of sin->FixPt gain->plot
run - observe high/low values in block.
Change scaling to 13.16. Run. Observe plot
Change sin amplitude to 4, scaling to 1.16
Run. Enable Tools/FixedPoint Configure… Autoscale.
Rerun.
VisSim/Embedded Controls
Developer
• Bundle of VisSim, C-Code, C2000 target, TI
DMC block-set , fixed-point block set, TI Code
Composer Studio plug-in
• Supports F280x, F28 MSP430, F2812 on-chip
peripherals: Analog in, PWM, CAN, encoder,
event capture, serial, SPI, I/O ports, watch dog
Debug, Test, and Validate
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Minimize time spent in debug and test
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Use high-level, predebugged blocks
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Support simulation of
controller at block level on
PC
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Allow mouse probe of every
input and output to display
values at any instant
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Debug block-level simulation
on PC
Debug and Validation
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Pure simulation plus DSP-in-loop simulation and block level monitoring gives rapid
feedback of controller response
VisSim on PC
C2000TM
DSP
External
Hardware
Peripheral
Input Blocks
Peripheral
Output Blocks
(I/O
Only)
VisSim block diagram
User
Blocks
DMC
Blocks
Fixed-Point
Blocks
Standard
Blocks
Test DSP based controller against virtual plant on PC using JTAG HotLink
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Inject plant failure modes to test controller response
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High/Low watermark on fixed-point blocks gives numerical “headroom” safety factor
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Interactive DSP utilization gives continuous CPU load factor
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Interactively Change DSP controller gains from VisSim and plot DSP response.
Debug and Validate
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Rapid diagram edit-compile-download-debug cycle (under 10 secs)
* Code automatically generated, compiled, linked, and
downloaded
VisSim on PC
Plant
Under
Control
C2000
Peripherals
Control
Application
Code*
C2000
DSP
JTAG
VisSim Interface block
downloads and monitors
code running on DSP
VisSim blocks for:
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Virtual plant
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Interactive gains
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Plots of DSP response
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DSP-in-loop simulation of controller at code level on DSP through automatic code generation, compile, link,
and download, and using JTAG in Real-Time Monitor mode
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Test, debug, and validate the complete control system executing on DSP using an interface block
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Provide test input vectors and observe DSP results in VisSim on PC
Build AC - induction DSP in loop
• Open AC induction motor speed control system
– C:\visSim50\Embed_Controls_Developer\c2407(281
2)eZdsp\QuickStart\acim_spd_control_qs.vsm
• Run and observe pure simulation results
• Select controller, click Tools/Codgen…, click
“Include VisSim Comm Interface”
• Push “Codegen” button
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Insert DSP component
• Delete simulated controller
• Insert
VisSim/DSP|C2407(F28xx)|DSPinterface block
• Wire up in diagram same as simulated
controller
• Save diagram as <filename>-d.vsm
Add blinking LED to controller
• Add blink logic to sim model
– Hint LED connected to C0 (2407) or F14 (F2812)
• Re-codegen
• Re-rerun DSP based version
• Compare F2812 waveforms to LF2407
– Difference is due to increased JTAG delays in
2407 part
Burn FLASH
• Create FLASHable blink program and burn to
flash.
Note that 2812 must use Spectrum Digital
FLASH utility.
Break
• 15 min
Basic pressure-flow system
• Pressure differential causes flow
• Integral of flow into a volume gives current
mass occupying the volume
• Pvolume = nRT/V
Review of User Diagram
Look at specific customer diagram
On-chip peripherals
• All on-board DSP peripherals supported including:
analog inputs (outputs on EVM)
digital inputs and outputs
simple PWMs and full compare PWMs
quadrature encoder
event capture, watch dog, interrupt, CAN bus
serial port
SPI
I/O ports
TI Digital Motor Control (DMC)
Library
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written by TI in C-callable assembler
hand-written, tested and optimized by TI
available in VisSim/ECD in easy-to-use block set
supports simulation mode (pure PC based
simulation with 16-bit truncation effects)
– supports code generation mode
Custom Block Creation
• VisSim DLL Wizard for MSVC
• Automatically creates project with code for creating
block, naming block, pin count and pin names, data
types, dialog for parameters
• VisSim exported function vissimRequest() allows
query of VisSim properties: current time, time step,
current block handle, block properties.
– DLL exported function:
<my block>Event(eventCode, p1, p2)
is called by VisSim on interesting events like sim start,
end, step, code gen, mouse click