VisSim for Dynamic
Simulation and Control
Design
Visual Solutions, Inc.
487 Groton Road, Westford MA 01886 USA
(800) VISSIM-1
www.vissim.com
Agenda
• Morning
–
–
–
–
–
–
VisSim product line review
VisSim basics
Dynamic systems with feedback
Building hierarchical systems
Data import/export
System tuning with auto restart
• Afternoon
–
–
–
–
Optimization
PID Tuning
3D plotting & animation
UML State Charts
VisSim Overview
• Visual block diagram software for dynamic
system simulation and embedded system
development.
– Automatic production of high quality fixed point code
– Exceptional dynamic and DSP-in-loop simulation
capabilities
– Automatic programming of on-chip DSP peripherals
Product Line
• VisSim Core Visual Simulation Tool - build,
simulate and debug dynamic systems
–
–
–
–
–
–
Simulink Translator
State Transition block
Over 100 built-in blocks
Built-in C interpreter
Matlab interface
Royalty free redistributable Viewer
VisSim Viewer
• Free redistributable run-time version of VisSim
• Download from
www.vissim.com/downloads/demos.html
• Allows free distribution of models to anyone
• Easy way to share ideas, models and
simulations
• Supply proof-of-concept simulations to
potential customers
VisSim Add-ons
• Real-Time - Allows up to 30 kHz closed loop
sampling from VisSim on PC
• C-Code - Generates ANSI C from diagram
• Analyze - Frequency domain analysis of
linearized non-linear subsystem
• Fixed-point - Block set of bit true scaled
integer operations for simulation and code
generation
VisSim Add-ons (cont.)
• Comm - Physical layer data communication
• Optimize Pro - Generalized Reduced Gradient
method of parameter optimization
• Neural nets - Neural network construction and
training package
• DSP Targets - F243,LF2407, F2812,
C30,C40,C67
VisSim/Real-Time
• Supports National Instruments and Measurement
Computing
• Analog (12-16 bit), digital, thermocouple, counter,
PWM, encoder
• Devices can be PCI, PCMCIA, USB, ISA
• 30 kHz closed loop sampling straight from
Windows/NT,XP – (Jitter ~1-5ms)
• Just place block and select “Run in Real-Time” from
Simulations Properties dialog.
VisSim/CAN
• VisSim driver for USB device that connects to
Controller Area Network (CAN) bus
• Can read and write CAN packets up to 1 kHz rate.
• Packets configurable as to:
– data length
– number and types of data elements in the packet
– Byte sex (bigendian vs little endian)
• Enable pin on write, data ready pin on read
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
VisSim/OPC
• OLE for Process Control
• VisSim OPC block set has server connection
block, OPC read and OPC write block
• Connects to any server (Kepware, Matrikon
etc.) Supports all major DCS, PLC vendors
(Honeywell, Allen Bradley, Foxboro, GE
Fanuc, Siemens, etc)
VisSim Plays Well with Others
• OLE interface- allows inclusion of any OLE
compliant software
– VisSim - Mathcad OLE interface allows graphics
plus data exchange
• VisSim - Matlab Integration allows matrix data
exchange and Matlab expression evaluation
• Simulink Translator brings Simulink diagrams
into VisSim workspace.
VisSim Custom Block API
• MSVC Wizard creates project for
custom block. Just drop in code.
• API allows:
– Menu positioning
– Block & connector naming and data typing
– Code generation
– Simulation info on integration method,
integration step, time step, current time
etc.
VisSim Co-simulation API
• VisSim co-simulation API allows fast, efficient
interprocess communication for co-simulation
interfacing.
• Based on NT shared memory and Events
• In use by iLogix Statemate
• General purpose API
Large Model Support
• Load 300,000 block model in under 2 minutes
• Embed blocks insert separate component
model files as subsystems
• Path aliases allow macro expansion to remove
file system dependencies
• Tags allow quick navigation in large system
Diagram Construction
• Insert block by clicking toolbar icon or Block
menu
• Change parameter by double or right mouse
click on block
• Connect by mouse-down on connector, drag,
mouse up on or near target connector
• Must have consumer to execute (Plot, display,
export etc.)
Exercise: Plot sin





Insert sin and plot blocks
Connect sin to plot and run
Right click sin, change to 1 Hz, and run
Double click plot title bar to enlarge
Double click again to restore
Block manipulation
•
•
•
•
Select blocks by left-mouse+drag background
Right click to operate on selected blocks
Edit menu also operates on selected blocks
Left-mouse+drag on any selected block moves
group
• Left click background to remove selection
Exercise: Add triangle wave




Insert triangle wave to existing sin plot
Connect triangle to plot and run
Select sin and triangle blocks
Right click one, select “align outputs”

Try and keep wires short and straight if possible
System Properties
•
•
•
•
System/System Properties…
Sets start time/stop time for simulation
Sets step interval for both simulation and code gen
Auto-restart puts sim in continuous mode for Monte
Carlo or parametric investigation
• “Retain states”: states not initialized on restart
• “Run in real-time” for real-time response
• “RT Scale Factor” to run at some multiple faster or
slower than real-time
Exercise: Change Time Range



Select System Properties…
Enable run in real time
Run diagram again. Now it takes 10 real secs.



Useful for monitoring embedded target
> 1 kHz Data acquisition and control
Change End Time to 1 sec, rerun
Simulation Debug
•
•
•
•
•
•
Single step button (click single “shoe”)
Right click on connector to see value
Stop block allows user controlled stop point
Error block allows user controlled error alert
Interactive plots
Display blocks
Exercise: Basic 2nd order system
• Create new diagram
• Insert and connect const “1” to two 1/S
integrators and a plot.
• Input is acceleration, output is position,
intermediate pin is velocity.
• Run (what is expected output?)
Exercise: More 2nd order system
• Put summing junction between const and 1/S
• Output of 1st 1/S is velocity, 2nd is position
• Put feedback gain from “position” to summer
• Change sign on sum feedback (ctrl+right+click)
• Run (what is expected output?)
• x” = 1 + -kx
VisSim Variables
• VisSim variables allow data exchange by
name instead of by wire
– Create variables “u” and “y” to represent input and
output to filter and wire to diagram. Use variable
“find” operation. Note “Find definition only” option
• Variable Scoping
– “:” prefixed variables are scoped to current level
– “::” prefixed variables are scoped to definition level
and down
Usage of Variables
• Built-in variables: pi, $timeStart, $timeStep,
$timeEnd, $runCount, $firstPass, $lastPass,
$randomSeed
• Variable block
• Can use in many blocks as parameters: 1/S,
gain, transferFunction, const etc.
• Expression block
• Constants
• Scoping (:prefix local, ::definition scope)
Exercise: More 2nd order system
• Change feedback gain to “k”
• Insert Annotation >Variable block
• Right+click and name “K”
• Insert Signal Producer > slider block, cx to var
• Right+click and change bounds to 0 to 10
• Run
Finding Blocks or Variables
• Edit/Find… dialog lets you search for variables
or blocks
• Can look only for definitions
• Case sensitivity
• Partial match
• Match on block type
Plot Options
• Right click to configure ->
• Most options obvious
• Plot averaging filters data
points over multiple runs
• Marker count of -1 marks all points
• Multiple XY traces uses pairs of inputs for each trace
• Line type controls paint style of data points
• Max plotted points limits total # of points in sim range
(0 plots all points)
Plot Options(cont)
• “External Trigger” places
enable pin on plot and only
plots when pin is 1
• “Read Coordinates” enables
interactive coordinate readout
• “Snap to Data” restrict readout
to actual data points
• “Over Plot” retains data run to run
• “Save Data to File” saves current plot data to a file
Exercise: Add damping term to 2nd
order system
• Add pin to sum input (Edit > Add Connector, then
click next to existing connector when grey bar
appears) and ctrl+right+click to toggle sign
• Add new gain called kDamp
• Copy/paste slider and “k” var
• rename var to “kDamp” and reconnect
Numerical Integration
• Change time step for 2nd order system
• Notice instability at large step relative to
system frequency
• Euler is simplest fastest, least accurate
• Adaptive step are most accurate
• Stiff good for solving “stiff” sets of equations (hi
freq component that has small amplitude)
Exercise: Change integration step
and method for 2nd order system
• Change time step to .5
• Run, and see divergence due to numerical instability
• Change integration method to adaptive step and see
that system is now stable
– Adaptive step tries smaller steps to see if it improves
results
– Gives good answer but is slow
Limited and Reset Integral
• Limited Integrator lets you specify upper and
lower limits for the internal state. Avoids
“windup” of limit block and plain integrator
– Wire slider->limited integrator->plot
– Connect const 50 to u, and 0 to l of limited integ
– Set to “run in real-time”, click 'go' and play with slider
– Add 1/s in parallel and plot both outputs. Notice “windup”
• Reset Integrator allows you to reset internal
state on the fly. (See bounce.vsm)
Plot Axis Settings
• Bounds set here for
“fixed bounds” option
• Scaling is applied to x axis
• Sub Plot Count gives multiple y-axis windows
• Axis divisions fixes tick count manually
• Retrace options restricts plot to given interval
and sets x-axis interval (used for eye-diagrams)
View Options
• Presentation Mode: Prettier diagrams
• Display Mode: for front panels and animation
• Data Types: colors connectors based on data type.
Green=integer, yellow=scaled integer, red=floating
point, purple=matrix
– Fat wires=Matrix, thin wire=scalar
• Block labels appear under block
• Connector labels appear on compound block or user
function block
Hierarchy
• Edit/Create Compound… creates container for selection
• Edit/Add Connector.. gets “Add” cursor. Click cursor on block
to add connectors. Click left side to add on left edge, right side
to add right.
• Edit/Remove Connector… gets “Remove” cursor. Click cursor
on block to remove connectors. Click left side to remove on
left edge, right side to remove from right.
• Ctrl+Right-Mouse on Compound to edit subsystem properties
• Click Right-Mouse on Compound to enter compound
• Click Right-Mouse on background to leave compound
• Double-Left click on connector to add label
Subsystem Properties
• Local Time – allows running at slower rate than main
sim. Must be multiple of base clock for DSP targeting.
• External Trigger – Use external logic to control
execution of subsystem.
• Name – Applies name to face of block
• Bitmap- Applies bitmap image to face of block
• Password protection – Use password to control
access to compound contents
• Create dialog box from contained dialog constants
User Dialog Box
• Insert “Dialog Constant” blocks into compound
contents for each dialog item.
• Dialog constants can be numeric, integer list,
or boolean.
• Check “Create dialog box from contained
dialog constants” option in compound block.
• User selections are saved to .vsm file.
• Nice way to encapsulate complexity.
Exercise: Create compound from
2nd order system
• Select 2nd order system, right click on a selected
block and create compound
• Insert dialog constants for feedback gains
• Ks (spring const) Kd (damping factor)
• Label input and output pins
• Enable “create dialog from contained dialog
constants” in compound properties
• Right click compound to see user dialog
• Run
Labeling
• Use label block to insert label anywhere in
diagram
• Label can be hyperlink to doc or URL
• Doc can link to .vsm label
• Double left click Compound connector to give
a label
• Use Comment block to put large body of
scrollable rich text into diagram
System Setup: Preferences
•
Checkpoint state: saves integrator, delay states and plot contents to file
– Useful for restarting from known state
•
•
•
•
•
•
•
•
•
Notify Sim End: gives message box on sim end
Warn nonintegral clock: gives warning at sim start if requested time step for
periodic signal like pulseTrain, squareWave etc. is not integral multiple of
sim timeStep.
Warn nonintegral delay: warn if continuous delay is given time delay that is
not integral multiple of timeStep
Checkpoint during sim: saves checkpointed diagram to file with name
suffixed with current time at specified checkpoint intervals.
Check Connections: warns of unconnected inputs at sim start.
Warn numeric overflow: warn if conversion causes numeric truncation
Startup Script file: Specify .m or .c file to run before starting sim
Random Seed: specify starting random seed for random variables.
Frequency Units: specify units for filter design wizards in transfer function
Conditionals (“if-then”)
• Relational expressions can be used anywhere
• Merge and case use a selector input to
produce an output from several possible inputs
– Create new diagram with button, merge, 2 consts
and display
Dialog Table
• Inserts parametric data from an external data
set or spread sheet.
• User selects item from 1st column via
dropdown combo.
• See Diagrams > examples > blocks >
signalProducer > dialogTable.vsm
Exercise: Build IIR Filter 1
•
•
•
•
Place step, xfer, and plot blocks in workspace
Connect & run
Change sim rate to .001, end time to .1
Design 2nd order 100Hz Butterworth lowpass
filter
• run
Build filter 2
• Ctrl-Rt quick dup xfer, convert copy from S->Z
domain
• run
• enable fixed point precision
• run
• change to 2 bits magnitude
• run - zoom plot
FIR filter
• Rt-click xfer, check “discrete”, click FIR Filter button
• For each band, enter start, end freq, weight & gain
• Be sure to leave room between end of one band and
start of next
• Click “Calc Filter”
• FIR requires large state count (>10) for good
operation
Discrete systems
•
•
•
•
1/Z sampled delay - clock input
Discrete transfer function
Sample hold
Other blocks work with both continuous and
discrete systems
• Compound block can be enabled, or run at
different sampling rate
• Work with scaled fixed-point data
Data Import/Export/Lookup Table
• Import block
– Can import text data, .mat, .wav
– Optional header supplies time start/stop/step info
• Export block
– Can export text, .mat, .wav
– Can control data flush interval, inclusion of import header
• Map block
– 1D, 2D, 3D lookup tables
Import Export Usage
• How to use...
– Place sin block and export in work space, configure export
for file name “test.dat”, wire sin to export and run. Note
possibility for decimation, data flush interval, and
suppression of header information.
– Place import block in diagram, configure for “test.dat”,
connect to plot, and run. Note possibility for interpolation
and extrapolation.
Import/Export features
• Import block
– Option for ‘,’ as decimal point
– Allows text data column. Treats as null.
– Accepts hh:mm:ss.ff time notation as data element
• Export block
– Option for ‘,’ as decimal point
– Can make data export background task
Matrix Operations
• All arithmetics (add,mul,div,gain etc)
• Const block takes matrix syntax ([1:n],eye(n)
etc.
• Unit delay, merge, plot, display all take matrix
operations
• Matrix mul, buffer, dot product, vector sum,
diag, PSD, fft,ifft,transpose,reshape,index
Q&A - Lunch
• 1 hour
Put .vsm files on VisSim menu
• Save to directory structure that you want
mirrored in VisSim menu
• Edit > Preferences… > Menu Directories
– Double click “…”
– Add directory path to be put on menu and menu
name to be stored under
– Next time you restart VisSim, all .vsm files in
directory tree will appear on VisSim menu
Optimization
• Built-in optimizer can find optimal system
parameters
– Open diagram
\vissim80\examples\SystemID\2ndOrder6DOF.vsm
– Note that cost function can be anything, but a good one is
integral of square error between test function and data set
Issues when optimizing
• OptimizePro addon will restrict parameter search to bounds in
parameterUnknown blocks. Built-in solver will not.
• Do not simply sum multiple error terms for cost function, as
terms may cancel. Terms must be squared or abs() before
sum.
• Try to minimize # of unknowns as optimization can bog down
with too many unknowns
• If using real-world plant, allow settling time between runs
• Cost function is typically integration of sum of square error
PID Tuning
•
•
•
•
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
--
++
+
--
Degrade
↑ KI
-
++
++
---
Degrade
↑ KD
-
--
--
~
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
I
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
3D Plotting
• 3D plot block takes time sequence of 3
element vectors for xyz position
• Use mouse to rotate and zoom plot even while
simulation running
• See Diagrams > Examples > New in 7.0 >
3D Animation
•
•
•
•
Manipulate individual meshes
Manipulate objects in 3D VRML (.wrl) file
Manipulate scene elements with mouse
Control “camera” (view angle, position)
programatically
• See Diagrams > Examples > New in 7.0 >
Lunar Lander Game
Event Logging
• Event log quietly tracks time-stamped events
• Signal Consumer > EventLog takes event
string and boolean enable pin to send text to
log
• Signal Consumer > EventDisplay gives display
of all events in run
• VisSim/RT and VisSim/OPC have quiet
eventLog mode
VisSim/OPC Client
• OPC server block select server connection
and connection mode (continous connection
vs sim run connection)
• OPC read/write blocks select tags to read and
write.
• Works with any OPC server
Scaled Fixed-Point Operations
• Arithmetics (add,mul,div,gain etc)
• Limit, unit delay, merge, map, PI regulator
• Hands-on
•
•
•
•
•
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 F243, LF2407, F2812 on-chip
peripherals: Analog in, PWM, CAN, encoder,
event capture, serial, SPI, I/O ports, watch dog
DSP Target Support
• Texas Instruments:
TMS320F243, LF2407, F2812,F2808,C31,
C32, C44, C54xx,C67xx
• Card Vendors:
Innovative Integrations, California
Spectrum Digital, Houston, Texas
Softbaugh, Atlanta, GA
Debug, Test, and Validate
•
Minimize time spent in debug and test
•
Use high-level, predebugged blocks
•
Support simulation of
controller at block level on
PC
•
Allow mouse probe of every
input and output to display
values at any instant
•
Debug block-level simulation
on PC
Debug and Validation
•
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
•
Inject plant failure modes to test controller response
•
High/Low watermark on fixed-point blocks gives numerical “headroom” safety factor
•
Interactive DSP utilization gives continuous CPU load factor
•
Interactively Change DSP controller gains from VisSim and plot DSP response.
Debug and Validate
•
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:
•
Virtual plant
•
Interactive gains
•
Plots of DSP response
•
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
•
Test, debug, and validate the complete control system executing on DSP using an interface block
•
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
7
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
–
–
–
–
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