Post on 09-Jun-2018
ELECTROMECHANICAL DRIVE SYSTEMSDr. Bartłomiej Ufnalski | B.Ufnalski@isep.pw.edu.pl | Electric(al) Drive Division
Science is always wrong. It never solves a problem without creating ten more.
We need science to help us solve all the problems we wouldn’t have if there
were no science.
George Bernard Shaw
The lecture and the laboratory are passed based on two mini-projects and on the bonus points
from exercises (i.e. activity during laboratory+lecture meetings). The final grade is a weighted
average of these marks. Lectures will be combined with hands-on training in a dedicated teaching
laboratory equipped with a Matlab/Simulink/PLECS simulational environment. This means that
lectures are interactive and you can get bonus points during all our meetings for being active.
The typical meeting will include 30 mins of solving problems during lecture-like part, just to create
ten times more problems during 60 mins laboratory-like part. And don’t worry – I’ll be at your
service to help you create these problems.
HANDBOOKS & OTHER (RE)SOURCES OF
INFORMATION/KNOWLEDGE
• Google.com – good for warm-ups
and brain storms – be aware that
most documents indexed by popular
search providers are not reviewed,
thus it is common that highly biased
opinions are published, incl.
statements that solution X is better
than Y without providing any info
on quality indicator taken into
account.
• More advanced filtering is
implemented in Scholar.Google.com
– most indexed documents are of
scientific and of popular scientific
type. Try these keywords: DC drives,
modern AC drives, PID control(lers),
etc.
• E-libraries available at our Main Library: http://www.bg.pw.edu.pl/ezrodla.html
• For the case of this lecture, I can recommend e.g.: IEEExplore www.ieeexplore.ieee.org and ENGnetBASE www.crcnetbase.com.
• Examples of handbooks:
Bose B. K.: „Modern Power Electronics and AC Drives”, Prentice Hall PTR, 2002
[in Polish] Orłowska-Kowalska T.: „Bezczujnikoweukłady napędowe z silnikami indukcyjnymi”, seria„Postępy Napędu Elektrycznego i Energoelektroniki”, -tom 48, Oficyna Wydawnicza Politechniki Wrocławskiej, 2003
[in Polish] Krzemiński Z.: „Cyfrowe sterowaniemaszynami asynchronicznymi” seria „Postępy NapęduElektrycznego i Energoelektroniki” - tom 45,
Wydawnictwo Politechniki Gdańskiej, 2001 (available on-line)
Mohan N.: „Electric Drives: An Integrative Approach”, Mnpere 2003, „Advanced Electric Drives: Analysis, Control and Modeling Using Simulink”, Mnpere 2001, „First Course on Power Electronics”, MNPERE 2009
Syed A. Nasar, Ion Boldea: „Electric Drives”, 2nd edition, 2005
[in Polish] Sieklucki G.: ‚Automatyka napędu”, 2009
ELECTROMECHANICAL DRIVE SYSTEM:
THE DEFINITION
• Electromechanical drive system is a set of devices that
enables to control electromagnetic torque [force] or speed
(velocity) or position [angular or linear] by shaping
electromagnetic torque [force] produced in the rotary
[linear].
• Electromechanical drive system consist of:✓ electric machine (motor, generator)✓ power electronic converter✓ control system (microcontroller)
Tips and tricks:
• The instantaneous speed is the magnitude of the velocity vector. In an electromechanical drive system we control velocity rather than speed because the direction (clockwise or counterclockwise) is usually important. However, it is common to use term „speed” even if it’s not totally consistent with the definition, e.g. speed cannot be negative (according to the definition). Nevertheless, we use negative and positive values to indicate the direction.
CONTROL TASKS: SHAPING MECHANICAL QUANTITIES
(TORQUE [FORCE], SPEED (ANGULAR OR LINEAR), POSITION
(ANGULAR OR LINEAR) AND JERK
• Torque [force] (acceleration is proportional to the resultant torque [force]) – the need for controlling this quantity is present in vast variety of drives. This controller can work as a slave for speed/position controller or can work as a master controller (e.g. screwing with a desired torque on automated assembly line).
• Speed [angular or linear] – the need for controlling this quantity is present in vast variety of variable-speed drives.
• Position – the need for controlling this quantity is present in vast variety of servo-drives, e.g. robotic arms, CNC milling machine.
• Jerk (the derivative of acceleration with respect to time) – its value can be „controlled” by shaping the reference signal (e.g. reference speed signal). This means that usually there is no additional jerk feedback controller present in the system. Jerk can be controlled by feed-forward controller (signal proportional to the change in acceleration is introduced in control scheme). Too high jerk in transportation makes people uncomfortable. Too high jerk is harmful for mechanical power transmission systems (e.g. gears).
• Jerk is the derivative of acceleration with respect to time.
• Acceleration is the derivative of velocity with respect to time.
• Velocity is the derivative of position with respect to time.
• Position is the derivative of… The integral of position control deviation (error) can constitute reference speed – what about units???
Tips and tricks:
• Speed is the first derivative of distance with respect to time (scalar quantity) . Velocity is the first derivative of displacement (or position) with respect to time (vector quantity).
• The derivative of jerk is called jounce or snap (http://sprott.physics.wisc.edu/pubs/paper229.pdf) and was considered in development of e.g. the Hubble Space Telescope's pointing control system.
REFERENCE SIGNAL SHAPING (LIMITING THE JERK)
spe
ed
acc
ele
rati
on
acc
ele
rati
on
spe
ed
jerk
jerk
MATHEMATICAL MODEL OF „THE SIMPLEST” ELECTRIC MOTOR
(MENTIONED SIMPLICITY DOES NOT REFER TO ITS
CONSTRUCTION)
How one can control/change speed of this motor? Topology of control system as a result of
dependencies between state variables and inputs – it’s time for brain storm on whiteboard.
disturbance
input output
output
Tips and tricks:
• State variables of a dynamical system --> search for derivatives (a rule of thumb).
• Outputs --> it depends on what you are willing to control.
• Inputs and disturbances --> external actions (e.g. force acting on an object, voltage imposed to the terminals). In control systems we usually distinguish between the two by a very simple rule: input signal comes from control system (its value can be changed intentionally), whereas disturbance signal comes from source that is unknown/unpredictable to us.
SIMPLIFIED MODEL OF VOLTAGE-SOURCE
CONVERTER
First order inertia as an approximation of converter dynamics.
Tips and tricks:
• Take two first terms of the e^x Taylor (Maclaurin) series.
• Average delay and switching frequency: if the bus pulls out every 30min but you don’t know when this happens then you will have to wait statistically half of this time (15sec).
H-BRIDGE CONVERTER TOPOLOGY
Bi-directional (in terms of energy flow and rotation) converter for brushed DC motor
SEMICONDUCTOR SWITCH IGBT+D. WHY „+D”?
The inductance of output circuit (load circuit) makes diodes indispensable in this
topology. Notice that any current loop has non-zero L (you’ve got at least one turn of
wire).Tips and tricks:
• Observe what happens when you switch off the light using a rocker switch
circuit breaker. See electric spark? It comes from energy stored in magnetic
field of the circuit - you’ve got at least one turn of wire.
FRONT-END CONVERTER TOPOLOGY AND ENERGY
RECOVERY WITH FEEDBACK TO THE GRID
Diode rectifier enables energy flow only from grid. You cannot return energy to the grid! You will
need a break chopper to control DC-link voltage (to dissipate energy in generating mode of the drive),
e.g. during speed reduction (kinetic energy is converted to electric one), elevator going down
(potential energy is converted to electric one).
FRONT-END CONVERTER TOPOLOGY AND ENERGY
RECOVERY WITH FEEDBACK TO THE GRID
Bi-directional (in terms of energy flow) transistor rectifier (fully-controlled rectifier, force-
commuted PWM voltage-source rectifier). Optional break chopper can support the system
during grid failures in generating mode.
ENERGY RECOVERY = MONEY SAVINGS?
Case study 1. WHEEL BALANCER
1kWh=3600kJ=3.6MJ --> 50gr; wheel 1kg*m*m (rough approx.) revolving
at 140rad/s stores ca. 10kJ of kinetic energy
This gives approx. 0.2gr/wheel.
40 cars every day (very optimistic assumption), 300 days per year (incl.
Saturdays) will give savings at the level of 100 PLN/year.
AFE @0.4kW will cost you ca. 400 PLN gross.
Case study 2. TOWING CARRIAGE FOR TOWING TANK IN SHIP MODEL BASIN
50000kg (50t), 12m/s, 1m/s/s --> 3.6MJ=1kWh
Energy trade price: 25gr/kWh (2010)
Let us assume: 15 years of operation, 20 runs a day, 200 days per year
This gives: 15000 PLN
Peak power: 600kW
AFE will cost you ca. 30000 PLN.
Diode rectifier as front-end converter? What about an impact on the grid?
PULSE WIDTH MODULATION (PWM)
• Why power converters (e.g. drive converters) are not designed to work the same way as class A or B audio amplifiers?
• Switching and conduction losses in real semiconductor device.
• Is it impossible or just impractical to build e.g. 10kW drive with a linear (non-PWM) amplifier? Losses and junction cooling discussion.
• Class D amplifiers – switching amplifiers (PWM method also implemented in audio amplifiers)
• Class D amplifiers have efficiency usually higher than 90%.
• Typical drive converters have efficiency at the level of 96%-98% (efficiency depends on the working point).
• PWM concept should be familiar to you from previous lectures (prerequisites). If it happened that you missed them, please visit pages listed on the next slide.
PWM CONCEPT – LET’S PLAY IN VIRTUAL
LABS OR ATTEND WEBMINARS
• Interactive Power Electronics Seminar (iPES) http://www.ipes.ethz.ch/, http://www.ipes.ethz.ch/ipes/PWMsimpel/e_pwmsimpel.html,http://www.ipes.ethz.ch/ipes/Inverter/e_H_Bruecke.html
• Virtual Laboratory of Power Electronics http://www.isep.pw.edu.pl/icg/vlab/index.html
• Wolfram Demonstrations Project http://demonstrations.wolfram.com/PulseWidthModulationPrinciple/
• Motion System Design http://motionsystemdesign.com/engineering-basics/pulse-width-modulation-1000/index.htm
Some videos may also inspire you:
http://www.youtube.com/watch?v=YmPziPfaByw
http://www.youtube.com/watch?v=Lf7JJAAZxEU
PROPORTIONAL-INTEGRAL CONTROLLER (PI
CONTROLLER)
It is assumed that you are familiar with PID control basics (prerequisites), but… let’s discuss some basics:
• continuous-time and discrete-time realizations
• actor as an element with natural constraints (limited/saturated action), e.g. angular position of a vertical steering fin can be limited to 35 degrees port to 35 degrees starboard
• anti-windup (conditional integration)
• derivative action is often deactivated in PWM-based converter systems – why?
• PID controller tuning
DISCRETE-TIME PI CONTROLLER (WITH
ANTI-WINDUP ALGORITHM)
PID (PI, P) CONTROLLER TUNING
PROCEDURES (SELECTED METHODS)
Please see the attached PDFs for more information.
PID (PI, P) CONTROLLER TUNING
PROCEDURES (SELECTED METHODS)
Please see the attached PDFs for more information.
DC MOTOR DRIVE WITH H-BRIDGE
CONVERTER
Now we are ready to „experiment” with simulational model of a DC drive. It is assumed that the group is familiar with Matlab/Simulink environment. Nevertheless, short introduction to Simulink+PLECS tools will take place along with presentation of the attached simulation model of the drive. To make this meeting more smooth, please install on your notebooks Matlab/Simulink (you can connect to license.ee.pw.edu.pl via VPN, more info at www.ee.pw.edu.pl in IT section) and PLECS from Plexim (license server is also started on license.ee.pw.edu.pl).
THANK YOU FOR YOUR ATTENTIONdr. Bartłomiej Ufnalski | B.Ufnalski@isep.pw.edu.pl | Electrical Drive Division
Warsaw University of Technology
Faculty of Electrical Engineering
Institute of Control and Industrial Electronics