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Ramon Costa CastellóAdvanced Control of Energy Systems (ACES)
Instituto de Organización y Control (IOC)Universitat Politècnica de Catalunya (UPC)
Barcelona, Spain
Repetitive control : Power Electronics
Applications
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Contents• Repetitive Control Basics
– Introduction– Periodic Signals – Performance– Discrete Time– The Odd-Harmonic case– Control Scheme
• Cascade Approach• Plug-in Approach
• The active filter application– Introduction– Basic Concept– Architecture– Control Problem– Experimental Setup– Experimental Results
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Introduction• A key topic in classical control theory is the
Internal Model Principle (IMP). – B. Francis and W. Wonham, “Internal Model Principle
in control theory,” Automatica, vol. 12, pp. 457–465, 1976.
• This principle states that if a certain signal must be tracked or rejected without steady-state error, the generator must be inside the control loop, in the controller, or in the plant itself.
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Introduction : Type Concept
• Standard classical control subjects include the IMP concept implicitly when they introduce the system-type concept.
• The type concept can only be applied to polynomial signals (step, ramp, and parabola) whose generator has the form in the Laplace domain.
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Introduction : Type Concept (II)
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Introduction : Systems with periodical disturbances or
references• In practice, many real systems have to
handle tracking and rejecting periodic signals.
Magnet power supply for a proton synchrotron (Nakano and others)
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Introduction : Systems with periodical disturbances or
references (II)
Demonstration of the Internal Model Principle by Digital Repetitive Control of an Educational Laboratory Plant. Ramon Costa-Castelló and Jordi Nebot and Robert Griñó.IEEE Transactions on Education. Vol. 48, No.1, Pages 73- 80 (February 2005). ISSN : 0018-9359.
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Introduction : Power Electronics
• Inverter : Generating a 50/60 Hz signal from dc one (Tracking a reference signal)
• Active filter : Compensation of harmonic signals (Rejecting periodic signals)
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Periodical Signals
• Any periodical signal can be written as:
• The control loop should include:
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Periodical Signals : Generator
Yamamoto, Y. (1993). Learning control and related problems in infinite-dimensional systems. In: Proceedings of the 1993 European Control Conference. pp. 191-222.
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Periodical Signals : Generator I
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Periodical Signals : Generator II
+pT
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Periodical Signals : Generator III
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Performance
C(s) P(s)
Open Loop Transfer Function
Sensitivity Function
Complementary Sensitivity Function
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Digital Case
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Digital Case II
Nz
+
p sT N T
1
1NR z
z
2 2j iN
i ip
z e iN T
pT
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Odd-Harmonic Case
Digital repetitive plug-in controller for odd-harmonic periodic references and disturbances Robert Griñó and Ramon Costa-Castelló. Automatica. Volume 41, Issue 1,Pages 153-157(January 2005)
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Odd-Harmonic Case II
Pole-Zero Map
Real Axis
Imag
inar
y A
xis
-1 -0.5 0 0.5 1-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
N=3 odd harmonic
N=3 traditional
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Control Scheme
• Cascade form
• Plug-in Form
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Control Scheme : Cascade form
P(z)
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Control Scheme : Plug-in Approach
pG z cG z
xG z F zNz
Repetitive Controller
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Control Scheme : Plug-in Approach II
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Control Scheme : Plug-in Approach III
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Jornadas de Ingeniería de Control Zaragoza Mayo 2005
Plug-in Approach : Stability Conditions
1. First stability Condition : The System without the Repetitive Controller must be stable.
2. Second stability Condition
3. Third stability Condition :
cG z
1F z
xG z
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Plug-in Approach : Filter• F(z) should fulfill the second stability condition.• Usually, a low-pass null-phase FIR filter is used.
• To assure unitary gain a DC frequency the parameters must fulfill :
• No causality problems exist because that the filter is in cascade with a N periods delay.
• The filter reduces the open-loop gain at those frequencies at which uncertainty exists (robustness). Unfortunately it slightly moves the open-loop pole positions in z-plane (precision loose).
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Plug-in Approach : Gx(z)
• A common approach to design Gx(z) is
• Unfortunately, this approach cannot be applied to non-minimum-phase plants. Another approach is to cancel minimum-phase zeros and compensate the phase for the non minimum-phase ones:
• kr is fixed by a trade-off between robustness and transient response.
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Jornadas de Ingeniería de Control Zaragoza Mayo 2005
Contents• Repetitive Control Basics √
– Introduction– Periodic Signals – Performance– Discrete Time– The Odd-Harmonic case– Control Scheme
• Cascade Approach• Plug-in Approach
• The active filter application– Introduction– Basic Concept– Architecture– Control Problem– Experimental Setup– Experimental Results
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Introduction
• Proliferation of nonlinear loads ->This fact has deteriorated the power quality of electrical power systems.
• More stringent requirements proposals IEC-61000-3-{2,4} and IEEE-519.
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Basic Concepts
sv
si Linear Load
Nonlinear Load
Active Filter
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Architecture : Complete Picture
Full BridgeBoost Converter
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Control Problem: Control Goals
• Current in phase with the voltage waveform:
• Constant average value of the voltage at the DC bus capacitor:
*
2 0 dx V
* sins d ri I t
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Architecture : Boost Converter
1 2 1
2 1
1 sL x x r x vu
C x x
1 2 1
2 1
1 sL x x r x vu
C x x
r L
CsV 2x
1x
r L
CsV 2x
1x
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Architecture : Boost Converter II
1 2 1
2 1
1 sL x x r x vu
C x x
1 2 1
2 1
1 sL x x r x vu
C x x
1 2 1
2 1
sL x ux r x v
C x ux
1 2 1
2 1
sL x u x r x v
C x u x
[ 1,1]u
The averaged model
1,1u
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Control Problem: Current Control loop
1 2 1 sL x u x r x v
2 dx V
1 1d sL x u V r x V
1
1
d
p
Vx s r G s
Lu s sr
1 ( )( ) 1 pp
G sG z z Z
s
ZOH, T
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Control Problem: Voltage Loop
2 1C x u x 1 2C y u x x
22
2
xy
11
sin cos sind r l r l rl
Iload
x t I t a l t b l t
Current loop in steady state
21 2 21 12
k T k kd l l dkT
l
E TC y r I b a b I b
1
12k T k
dkT
E TC y I b
r=0
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Control Problem: Voltage Loop
21
E T
z
1b
PI
2
2dV
y
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Control Problem: Proposed Scheme
• Two control loops :– Current loop : Digital Repetitive Control– Voltage loop : Classical PI Control
sin r t
Boost Converter
Repetitive Controller
PI Controller2x
dVdI
1x lI
*sI
Odd-Harmonic Digital Repetitive Control of a Single-Phase Current Active Filter . Ramon Costa-Castelló, Robert Griñó & Enric Fossas IEEE Transactions on Power Electronics. Volume: 19, Issue: 4, Year: July 2004. E.Page(s):1060- 1068.
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Experimental Setup• Active filter parameters:
– Capacitor: 6600 uF, 450 V DC – Inductor: 0.8 mH– parasitic resistance: 0.04 Ohm– IGBT: 1200 V, 100 A
• Feedback paths (sensors):– Network voltage: voltage
transformer (220V/15V) – Network current: Hall-effect
sensor (TECSA-HA-050053) (50A)
– DC bus voltage: AD-215BY isolation amplifier
• Control hardware:– ADSP-21161 floating-point
DSP – ADMC-200 coprocessor:
A/D channels and PWM generation
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Experimental Setup : General view
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Experimental setup : IGBT drivers
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Experimental setup : Control hardware
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Experimental Results: Nonlinear Load
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Experimental Results: No-Load
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Experimental Results: Full NL load
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Experimental Results: Full NL load
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Experimental Results: Full load to No-load
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Experimental Results: No-load to full load