updated overview of research in control, power electronics, renewable energy and smart grid...
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An Overview of Research Activities in
CONTROL AND SMART GRID I NTEGRATION
Qing-Chang ZhongQ.Zhong@Sheffield.ac.uk
Chair in Control and Systems Engineering
Dept. of Automatic Control and Systems Engineering
The University of Sheffield
United Kingdom
Outline of the talk
A little bit about myself
Activities in process control
Activities in control theory
Activities in power and energy systems
Some sample platform technologies
Applications in wind power, HEV and high-speed trains
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 2/44
A little bit about myself1990, started working in the area of control after receivingthe first degree
1997, MSc in Control Theory & Eng. from Hunan University
2000, PhD in Control Theory & Eng. from Shanghai Jiaotong University
2004, PhD in Control & Power from Imperial College, awarded the Best Thesis Prize
2006, first research monographRobust Control of Time-delay Systems published by
Springer-Verlag London.
2007, Director of EPSRC-funded Network for New Academics inControl Engineering,
currently more than 170 members, joined UKACC in Oct 2010 as aGroup Member with
support from UKACC.
2009, Senior Research Fellow of Royal Academy of Engineering /Leverhulme Trust
2010, Fellow of IET
2010, Professor in Control Engineering, Loughborough University
2010, research monographControl of Integral Processes with Dead Time by
Springer-Verlag
2012, Chair in Control and Systems Engineering, The University of Sheffield
2012, research monographControl of Power Inverters in Renewable Energy and Smart
Grid Integration to be published by Wiley-IEEE PressQ.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 3/44
Evolution of my research activities
1998 2004 2001
Process Control
Robust Control Theory & Time-Delay Systems
Power & Energy Systems
Year 2007 2010
Res
earc
h ac
tiviti
es
2013
Wide spectrum of expertise
From hardware to software
From applied to theoretical
From control to power
Cover many application areas
Research philosophy
Focused and thorough research
Holistic approach: Down to details but keep
the big picture in mind
Looking for solutions and problems as well
Looking for hidden linksQ.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 4/44
Activities in process controlControl of integral processes with dead-time: A research monograph,Control of Integral
Processes with Dead Time, jointly with Antonio Visioli from Italy, appeared in 2010.
Disturbance observer-based control strategy
Dead-beat response
Stability region on the control parameter space
Achievable specifications etc
Practical experience with a production line
16 reactors, controlled by 3 industrial computers
Effective object code > 100 KB (Intel 8086 assembler)
Analogue control variables and measurements etc.
Continuous Stirred Tank Reactor (CSTR) System
Antonio VisioliQing-Chang Zhong
Control of Integral Processeswith Dead Time
Advances in Industrial Control
1
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 5/44
Activities in control theoryRobust control of time-delay systems (frequency-domain approaches): Solved a series of
fundamental problems in this area:
Projections
J-spectral factorisation
Delay-type Nehari problem
StandardH∞ problem of single-delay systems
Unified Smith predictor
Realisation of distributed delays in controllers
Infinite-dimensional systems: applied the generic theory
of infinite-dimensional systems to time-delay systems
and solved problems about feedback stabilizability,
approximate controllability, passivity etc
Uncertainty and disturbance estimator (UDE)-based
robust control: can be applied to linear or nonlinear,
time-varying or time-invariant systems with or
without delays; attracted several Indian groups.
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 6/44
Algebraic Riccati EquationsThe well-known algebraic Riccati equation (ARE)
A∗X + XA + XRX + E = 0
can be represented as
H XX
+ -
U
V
W
Y
U1
V1=0
W1
Y1 (=0)
H =
A R
−E −A∗
.
Assume thatU1 is nonsingular andV1 = 0. The solution is obtained
whenY1 = 0 while changingX. The transfer matrix fromU1 to W1 is
AX =[
I 0]
H
I
X
.
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 7/44
J-spectral factorisationJ-spectral factorisation is defined as
Λ(s) = W∼(s)JW (s),
where theJ-spectral factorW (s) is bistable andΛ(s)
is a para-Hermitian matrix:Λ(s) = Λ∼(s).= ΛT (−s).
Assume thatΛ, having no poles or zeros on thejω-axisincluding∞, is realised as
Λ =
[
Hp BΛ
CΛ D
]
= D + CΛ(sI − Hp)−1BΛ (1)
and denote theA-matrix ofΛ−1asHz, i.e.,
Hz = Hp − BΛD−1CΛ.Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 8/44
Theorem Λ admits aJ-spectral factorisation if andonly if there exists a nonsingular matrix∆ such that
∆−1Hp∆ =
[
Ap− 0
? Ap+
]
, ∆−1Hz∆ =
[
Az− ?
0 Az+
]
whereAz− andA
p− are stable, andAz
+ andAp+ are anti-
stable. If this condition is satisfied, then aJ−spectralfactor is formulated as
W =
[
I 0]
∆−1Hp∆
I
0
[
I 0]
∆−1BΛ
Jp,qD−∗
WCΛ∆
I
0
DW
,
whereDW is a nonsingular solution ofD∗WJp,qDW = D.
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 9/44
The standard H∞ problem ofsingle-delay systemsGiven aγ > 0, find a proper controllerK such that theclosed-loop system is internally stable and
∥
∥Fl(P, Ke−sh)∥
∥
∞< γ.
P
e−shI
K
y
z
u
w
u1
-
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 10/44
Simplifying the problem
Cr(P )
@@ e−shI
K
-
w
z u
y
u1
6
Cr(P )
@@
Gα
@@
Cr(Gβ)
@@ e−shI
K
Delay-free problem 1-block delay problem
-
-
-
w
z u
y
u1
6w1
z1
y
u1
Gα is the controller generator of the delay-free pro-blem. Gβ is defined such thatCr(Gβ)
.= G−1
α . Gα andCr(Gβ) are all bistable.
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 11/44
Solution to the problemSolvability⇐⇒ :
H0 ∈ dom(Ric) andX = Ric(H0) ≥ 0;
J0 ∈ dom(Ric) andY = Ric(J0) ≥ 0;
ρ(XY ) < γ2;
γ > γh, whereγh = maxγ : det Σ22 = 0.
Z V −1
h
Q
@@
--
u
y-
6
?
?
V −1 =
A + B2C1 B2 − Σ12Σ−122 C∗
1 Σ−∗22 B1
C1 I 0
−γ−2B∗1Σ
∗21 − C2Σ
∗22 0 I
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 12/44
Implementation of the controllerAs seen above, the control laws associated with delay systems
normally include a distributed delay like
v(t) =
h
0
eAζBu(t − ζ)dζ,
or in thes-domain, Z(s) = (I − e−(sI−A)h) · (sI − A)−1.The implementation ofZ is not trivial becauseA
may be unstable. This problem had confused the
delay community for several years and was pro-
posed as an open problem inAutomatica in 2003.
It was reported that the quadrature implementation
might cause instability however accurate the imple-
mentation is.
My investigation shows that:
The quadrature approximation error converges to0
in the sense ofH∞-norm.10
−210
−110
010
110
210
310
−4
10−3
10−2
10−1
100
101
Frequency (rad/sec)
N=1
N=5
N=20 A
ppro
xim
atio
n er
ror
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 13/44
Rational implementation
1x2xΠ
Nx 1−Nx
B1−Φbu
u
rv
…
ΦΦ+−=Π −1)( AsI
Π Π
…
Π = (sI − A + Φ)−1Φ,
Φ = (
hN
0 e−Aζdζ)−1.
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 14/44
Feedback stabilisation of delay systemsThe feedback stabilizability of the state–input delaysystem
x(t) = A0x(t) + A1x(t − r) + Pu(t) + P1u(t − r)
is equivalent to the condition
Rank[
(P + e−rλiP1)∗ · ϕi
]
= di, i = 1, 2, · · · , l.
whereλi ∈ λ1, λ2, · · · , λl = λ ∈ C : det ∆(λ) =
0 andReλ ≥ 0 with ∆(λ) := λI − A0 − A1e−rλ.
The dimension ofKer∆(λi)∗ is di and the basis of
Ker∆(λi)∗ is ϕi
1, ϕi2, · · · , ϕi
difor i = 1, 2, · · · , l .
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 15/44
UDE-based Robust ControlThe Uncertainty and Disturbance Estimator (UDE) is a strategy to estimate the
uncertainties and disturbances in a system. The controlleris designed so that
the state of the system tracks the state of the reference model chosen, with all
the uncertainties and disturbances estimated with an estimator, called UDE. It
can be applied to linear or nonlinear, time-invariant or time-varying systems
with or without state delays.
The resulting control law for a nonlinear system
u(t) = b+ (−(g1(t) + ε(g2(t) + g3(t))) + Amxm(t) + Bmc(t))
+b+ 1
T
(
(I − (Am + K)T ) e(t) − (Am + K)
t
0
e(t)dt
)
The simplified nonlinear control law consists of three terms. The first term
cancels all the known system dynamics, while the second termintroduces the
desired dynamics given by the reference model and the last term performs a PI
control action.
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 16/44
The two-degree-of-freedom natureIf the system is linear without delay, then
X(s) = Hm(s)C(s) + Hd(s)Ud(s)
withHm(s) = (sI − Am)−1
Bm, Hd(s) = (sI − (Am + K))−1·(1 − Gf (s)) .
)( ωjH f
)( ωjHki
)( ωjHdi
dB0
kiω fωω
δlog20
kiωlog20−
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 17/44
Application to Continuous Stirred Tank Reactors
(CSTR)
x1(t) = −
1
λx1(t) + Da(1 − x1(t)) × exp
x2(t)
1 +x2(t)
γ0
+
(
1
λ− 1
)
x1(t − τ),
x2(t) = −
(
1
λ+ β
)
x2(t)+HDa(1−x1(t))×exp
x2(t)
1 +x2(t)
γ0
+
(
1
λ− 1
)
x2(t−τ)+βu(t),
wherex1(t) is the reactor conversion rate andx2(t) is the dimensionless temperature.
-2 -1.5 -1 -0.5 0 0.5 1 1.5 20
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Steady-state input: u
Ste
ady-
stat
e st
ates
: x1 a
nd x
2/10
x1
x2/10
0 5 10 15 200
0.5
Con
vers
ion
Rat
e
0 5 10 15 200
5
Tem
pera
ture
0 5 10 15 20
0204060
Time [sec]
Con
trol
Effo
rt
SetpointState
SetpointState
Steady-state operating points Change of operating points
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 18/44
Activities in power and energy systemsSample platform technologies
Provision of a neutral line
Power quality improvement
Synchronverters: Grid-friendly inverters
Parallel operation of inverters
C-inverters
Active capacitors
Harmonic droop controller
Sinusoid-locked loops
AC Ward Leonard drive systems
Applications
Wind power
Hybrid electric vehicles
High-speed trains
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 19/44
Neutral line provision
Vave
0.2V/div
iN
50A/div
iL
50A/div
ic
20A/div
0.17 0.18 0.19 0.20 0.21 0.22 0.23 0.24 0.25 0.26 0.27
Time (sec)
Proposed a topology and control algorithms to provide a stable balanced
neutral line for inverters.
This decouples its control from that of the inverter;
It enables independent phase control for inverters;
Can be used for multi-level inverters as well.
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 20/44
Power quality improvementPower quality is a very important problem for renewable energy and
distributed generation.
Phase-lead low-pass
filter
DC power source
Inverter bridge
LC filter
Transformer
PWM modulation
Internal model M and stabilizing compensator C
Id* Iq*
iref e
abc
dq θ
Current controller
PLL
ugb uga ugc
u
+ +
+ +
+ +
u’gb u’ga
u’gc
u’
u’gb u’ga
u’gc
ia ib ic
- +
- +
- +
-3
-2
-1
0
1
2
3
Cu
rren
t [A
]
0.00 0.01 0.02 0.03 0.04 0.05
Time [sec]
#1:1
#1:2
The recorded current THD
was0.99%, while the grid
voltage THD was2.21%.
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 21/44
Synchronverters:Grid-friendly inverters
Synchronverters are inverters that are mathematically
equivalent to the conventional synchronous generators and
thus are grid-friendly.
Can be used for STATCOMs, HVDC, grid connection of
renewable energy, distributed generation and electric
vehicles etc.
Can automatically change the energy flow between the AC
bus and the DC bus.
Time (Second)
P(W
)an
dQ
(Var
)
PXXy
Q
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 22/44
The basic idea
M
M M
Rs , L Rs , L
Rs , L
Rotor field axis
( 0=θ )
Field voltage
Rotation
N
Te Eqn. (7) Eqn. (8) Eqn. (9)
s
1
Dp
Tm
-
θ θ&
i
e
Mf if
Q
Js
1
-
The basic idea is to adopt the mathematical model of a synchronous generator
as the core of the controller. What’s left is for the inverterto reproducee
at its terminals. Control strategies developed for conventional synchronous
generators can be used for inverters.Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 23/44
Js
1
Te Eqn. (7) Eqn. (8) Eqn. (9)
s
1
Dp
Tm
-
θ θ&
i
e
rθ&-
Dq
rv
Qset -
-
Mf if
Ks
1
Q
n
p
θ& Pset
PWM generation
Fro
m\to
the
pow
er
part
fbv
Reset gθ
Amplitude detection
cθ
mv
Four control parameters
No conventional PI controlNo dq transformation etc
Frequency control, voltage control, real power control andreactive
power control are packed in one controllerQ.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 24/44
Parallel operation of inverters 222 jQPS +=
~ 11 δ∠E
1oR
111 jQPS +=
~ 22 δ∠E
2oR
Z
o0∠oV
Conventional droop controller
Ei = E∗− niPi,
ωi = ω∗ + miQi,
ni
-
vr
E*
s
1 mi
ω
*
vo
i
Ei
ω it+δ i
Pi
Qi
Limitations:
Ei should be the same
The per-unit output impedance should be the same
Fundamental trade-off between the power sharing accuracy and the voltage drop
=⇒Not robust at all !
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 25/44
Robust droop controller (Patent pending)
-
vri
s
1
ω
*
vo
i
Ei
ω it+δ i
Pi
Qi
ni
mi
eK -
E*
RMS
s
1
Accurate sharing of both real power and reactive power
Excellent voltage regulation
Low THD
Fast responseQ.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 26/44
Experimental results
0 1 2 3 4 5 6 7 8 9 10 11 12−4
048
1216202428
Time [s]
Rea
l Pow
er [W
]
P1
P2
0 1 2 3 4 5 6 7 8 9 10 11 12−12−10−8−6−4−2
02
Time [s]
Rea
ctiv
e P
ower
[Var
]
Q1
Q2
0 1 2 3 4 5 6 7 8 9 10 11 12048
1216202428
Time [s]
Vol
tage
[V]
E1
E2
7 7.01 7.02 7.03 7.04 7.05 7.06−24−16−8
08
1624
Time [s]
Out
put V
olta
ge [V
]
vo
7 7.01 7.02 7.03 7.04 7.05 7.06−4
−2
0
2
4
Time [s]
Cur
rent
[A]
i1
i2
0 1 2 3 4 5 6 7 8 9 10 11 120123456789
10
TH
D o
f vo [%
]
Time [s]
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 27/44
C-invertersThe output impedance of an inverter is normally inductive and can be
made resistive. Is it possible to make it capacitive? Yes, and it turns out
to be better than the other ones. Such inverters are called C-inverters.
This has filled up a gap in the theory.
Implementation
Optimal design to minimise the voltage THD
Parallel operation
Optimal capacitance to eliminate the
h-th harmonic voltage:
Co = 1(hω∗)2L
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7−14−12−10−8−6−4−2
0246
ω/ω*
The
gai
n fa
ctor
Original inductor
3rd and 5th
3rd only
5th only
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 28/44
C-inverters R-inverters
0 1 2 3 4 5 6 7 8 9 10 11 12048
1216202428
Time [s]
P [W
]
P1
P2
0 1 2 3 4 5 6 7 8 9 10 11 12048
1216202428
Time [s]
P [W
]
P1
P2
0 1 2 3 4 5 6 7 8 9 10 11 12−8−6−4−2
024
Time [s]
Q [V
ar]
Q1
Q2
0 1 2 3 4 5 6 7 8 9 10 11 12−8−6−4−2
024
Time [s]
Q [V
ar]
Q1
Q2
0 1 2 3 4 5 6 7 8 9 10 11 1205
1015202530
TH
D o
f vo (
%)
Time [s]0 1 2 3 4 5 6 7 8 9 10 11 12
05
1015202530
TH
D o
f vo (
%)
Time [s]
7 7.01 7.02 7.03 7.04 7.05 7.06−20−10
01020
v o [V]
Time [s]7 7.01 7.02 7.03 7.04 7.05 7.06
−20−10
01020
v o [V]
Time [s]Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 29/44
Active capacitorsCapacitors are fundamental building blocks for electronicand electrical cir-
cuits. A capacitor can be built via putting two conducting plates together,
separated with an electric insulator. A control strategy has been proposed to
implement capacitors with inverters.
More accurate
More stable, e.g. w.r.t temperature
Controllable frequency characteristics
Changing the way how active power
filters (APF) are controlled
−60
−40
−20
0
20
40
60
Mag
nitu
de (
dB)
10−1
100
101
102
103
104
−90
−45
0
45
90
Pha
se (
deg)
Frequency (rad/sec)
Ro=0.0Ω, no K
R
Ro=0.0Ω, with K
R
Ro=0.2Ω, with K
R
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 30/44
0 0.01 0.02 0.03 0.04−6−4−2
0246
Time [s]
i, v
i v
0 0.01 0.02 0.03 0.04−10−8−6−4−2
02468
10
Time [s]
i, v
i v
0 0.01 0.02 0.03 0.04−10−8−6−4−2
02468
10
Time [s]
i, v
i v
0 0.01 0.02 0.03 0.04−16−12−8−4
048
1216
Time [s]
i, v
i v
0 0.01 0.02 0.03 0.04−20−16−12−8−4
048
121620
Time [s]
i, v
i v
0 0.01 0.02 0.03 0.04−20−16−12−8−4
048
121620
Time [s]
i, v
i v
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 31/44
Harmonic droop controller
…
~
oZ
rv ov
i
~
↓~
… ↓… …
1ov
ohv
1i hi
Load/grid
(a) One circuit including all harmonics
~
)( *ωjhZo
hhh QPS +=
rhv~ ↓ ohv hi
hi
(b) The circuit at theh-th harmonic
frequency
voh = 0 if vrh is the same asthe voltage dropped on theoutput impedanceZo bythe harmonic current com-ponentih.
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 32/44
Without With 3rd and 5th harmonics droop controller
7 7.01 7.02 7.03 7.04 7.05 7.06−4−2
0246
Time [s]
Cur
rent
[A]
i1
i2
7 7.01 7.02 7.03 7.04 7.05 7.06−4−2
0246
Time [s]
Cur
rent
[A]
i1
i2
(a) Currents
7 7.01 7.02 7.03 7.04 7.05 7.06−20−10
01020
v o [V]
Time [s]7 7.01 7.02 7.03 7.04 7.05 7.06
−20−10
01020
v o [V]
Time [s](b) Output voltage
1 3 5 7 9 11 13 15 17 19048
121620
Harmonic order
Mag
(%
)
THD=15.92%
1 3 5 7 9 11 13 15 17 19048
121620
Harmonic order
Mag
(%
)
THD=8.57%
(c) Harmonic voltage componentsQ.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 33/44
Sinusoid-locked loops
~
sX
~
vmvv θsin= θsinEe =i
SSM model
When there is no power exchanged with the grid, the voltagee is the same as the terminal voltage
v. That is, they have
the same frequency
the same phase
the same amplitude
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 34/44
Tracking the grid voltage
0 0.04 0.08 0.12 0.16 0.20
10
20
30
40
50
60
70
f [H
z]
Time [s]
0 0.04 0.08 0.12 0.16 0.20
10
20
30
40
50
60
70
f [H
z]
Time [s]
0 0.04 0.08 0.12 0.16 0.20
10
20
30
40
50
60
70
f [H
z]
Time [s]
(b) Frequency tracking
0 0.04 0.08 0.12 0.16 0.20
5
10
15
20
25
30
E [
V]
Time [s]
0 0.04 0.08 0.12 0.16 0.20
5
10
15
20
25
30
E [
V]
Time [s]
0 0.04 0.08 0.12 0.16 0.20
5
10
15
20
25
30
E [
V]
Time [s]
(c) Detection of the voltage amplitude
0 0.04 0.08 0.12 0.16 0.2−30
−15
0
15
30
e [V
]
Time [s]
0 0.04 0.08 0.12 0.16 0.2−30
−15
0
15
30
e [V
]
Time [s]
0 0.04 0.08 0.12 0.16 0.2−30
−15
0
15
30
e [V
]
Time [s]
(d) Voltage tracking
0.1 0.12 0.14 0.16 0.18 0.20
2
4
6
8
10
TH
D [
%]
Time [s]
0.1 0.12 0.14 0.16 0.18 0.20
2
4
6
8
10
TH
D [
%]
Time [s]
0.1 0.12 0.14 0.16 0.18 0.20
2
4
6
8
10
TH
D [
%]
Time [s]
(e) THD of e
0 0.04 0.08 0.12 0.16 0.20
2
4
6
8
θ [
rad
]
Time [s]
0 0.04 0.08 0.12 0.16 0.20
2
4
6
8
θ [
rad
]
Time [s]
0 0.04 0.08 0.12 0.16 0.20
2
4
6
8
θ [
rad
]
Time [s]
(e) Phase tracking
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 35/44
Tracking a voltage with avarying frequency
With the proposed SLL With the SOGI-based PLL With the STA
0 2 4 6 8 1030
40
50
60
70
Fre
quen
cy [
Hz]
Time [s]
f fv
0 2 4 6 8 1030
40
50
60
70
Fre
quen
cy [
Hz]
Time [s]
f fv
0 2 4 6 8 1030
40
50
60
70
Fre
quen
cy [
Hz]
Time [s]
f fv
(a) Frequency tracking
0 2 4 6 8 1015
25
35
45
Am
pli
tude
[V]
Time [s]
E vm
0 2 4 6 8 1015
25
35
45
Am
pli
tude
[V]
Time [s]
E vm
0 2 4 6 8 1015
25
35
45
Am
pli
tude
[V]
Time [s]
E vm
(b) Amplitude tracking
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 36/44
Tracking a square waveWith the proposed SLL With the SOGI-based PLL With the STA
0.1 0.12 0.14 0.16 0.18 0.2−40
−20
0
20
40
v [
V]
Time [s]
0.1 0.12 0.14 0.16 0.18 0.2−40
−20
0
20
40
v [
V]
Time [s]
0.1 0.12 0.14 0.16 0.18 0.2−40
−20
0
20
40
v [
V]
Time [s]
(a) Input signal
0.1 0.12 0.14 0.16 0.18 0.20
20
40
60
80
100
Fre
quen
cy [
Hz]
Time [s]
f fv
0.1 0.12 0.14 0.16 0.18 0.20
20
40
60
80
100
Fre
quen
cy [
Hz]
Time [s]
f fv
0.1 0.12 0.14 0.16 0.18 0.20
20
40
60
80
100
Fre
quen
cy [
Hz]
Time [s]
f fv
(b) Frequency tracking
0.1 0.12 0.14 0.16 0.18 0.230
35
40
45
50
Am
pli
tud
e [V
]
Time [s]
E vm
0.1 0.12 0.14 0.16 0.18 0.230
35
40
45
50
Am
pli
tud
e [V
]
Time [s]
E vm
0.1 0.12 0.14 0.16 0.18 0.230
35
40
45
50
Am
pli
tud
e [V
]
Time [s]
E vm
(c) Amplitude tracking
0.1 0.12 0.14 0.16 0.18 0.2−60
−30
0
30
60
e [V
]
Time [s]
0.1 0.12 0.14 0.16 0.18 0.2−60
−30
0
30
60
e [V
]
Time [s]
0.1 0.12 0.14 0.16 0.18 0.2−60
−30
0
30
60
e [V
]
Time [s]
(d) Recovered voltage e
0.1 0.12 0.14 0.16 0.18 0.20
5
10
15
TH
D [
%]
Time [s]
0.1 0.12 0.14 0.16 0.18 0.20
5
10
15
TH
D [
%]
Time [s]
0.1 0.12 0.14 0.16 0.18 0.20
5
10
15
TH
D [
%]
Time [s]
(e) THD of e
0.1 0.12 0.14 0.16 0.18 0.20
2
4
6
8
θ [
rad
]
Time [s]
θe v
0.1 0.12 0.14 0.16 0.18 0.20
2
4
6
8
θ [
rad
]
Time [s]
θe v
0.1 0.12 0.14 0.16 0.18 0.20
2
4
6
8θ
[ra
d]
Time [s]
θe v
(f) Phase tracking
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 37/44
AC Ward Leonard drive systemsExtended the concept of Ward Leonard drive systems to AC machines.
Constant speed
Variable speed
Controllable field Fixed field
Prime mover
Load
Variable speed
Variable speed
Fixed field
SM/IM Load
SG Prime mover VDC
Inverter
(a) Conventional (DC) Ward Leonard drive systems (b) AC WardLeonard drive systems
Potential application areas:
High-speed train drive systems
Ship drive systemsQ.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 38/44
Wind turbine control
Aerodynamics (Rotor blades)
Drive-train Generator Rotor-side Converter
Grid-side Converter
Energy Storage System
Wind v
Tr Tg us UDC
is ωg ωr IDC
u
i
Grid
Pitch/yaw/stall/brake Control
Control ? Control Control
Control
Power Processing Unit
The wind turbine, patented and donated by Nheolis, France, was installed on the EEE building at Liverpool.Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 39/44
HEV driver modelJoint work with Dr Shen et al at Ricardo UK.
Regenerative braking is an important feature of HEVs. According to the EU regulations, if the
travel of brake pedal is used to derive the regenerative braking torque then more stringent brake
safety requirements need to be met. The use of the engine or vehicle speed inevitably introduces
a discontinuous powertrain torque when the acceleration pedal is released or when the brake pedal
is applied, which causes oscillations in the torque. A rule-based driver model with look-ahead
information is proposed and tested in an HIL system consisting of an HCU and a vehicle model.
0 200 400 600 800 1000 12000
50
100
150
Veh
icle
Spe
ed(k
m/h
)
0 200 400 600 800 1000 1200−0.5
0
0.5
1
Ped
al p
ositi
onga
s>0,
bra
ke<
0
0 200 400 600 800 1000 1200−100
0
100
200
Tor
que
(Nm
)B
lue−
engi
ne, R
ed−
ISG
0 200 400 600 800 1000 12000
2000
4000
Eng
ine
Spe
ed
(rpm
)
0 200 400 600 800 1000 12000.6
0.62
0.64
0.66
Sta
te o
f Cha
rge
Time (sec)
ECE ECE ECE ECE
EUDC
Restart engine
ISG torque ro restart engine
Engine idle stopShift to 2nd
to 3rd
to 4th
to 5th
Driver
HC
U
Pedals
VehicleVehicle
Reference Speeds
Vehicle Speeds
Clu
tch
Clu
tch
Tra
nsm
issi
on
Tra
nsm
issi
on
Fin
al D
rive
Fin
al D
riveISGISG
ICEICE
BatteryBattery
MCU
EMS
TCU
BMS
Control flow Information flow Power flowVehicle SystemsModel in dSPACE
HCU strategyIn control Unit
Performancemonitor
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 40/44
HEV powertrain
EPSRC grant with the total funding of £3.5M (to be started early next year)
WP2.1: Power electronics and energy management (£571K)Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 41/44
Traction power systems forhigh-speed trains
Compensation of negative-sequence currents
Compensation of reactive power
Reducing harmonic currents
Capacity reduction of the traction transformer
ib
iL
A
B
C
iA iB iC
B
ia C
iL
a b
Section insulator
c
A
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2−20
−16
−12
−8
−4
0
4
8
12
16
20
Time/s
i [A
]
iA
iB
iC
(simulation results)Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 42/44
Power electronics lab
Converter A
Grid Local AC Bus
Converter B
Converter C
DC Bus • Converters can be connected to either the local AC
bus or the grid • Load can be connected to either the local AC bus or
the grid as well • For LV batteries, a DC/DC converter is needed
(being built)
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 43/44
Current funding: ~£1.5MEPSRC: £180Kto foster long-term “best-with-best” international collaboration with top
researchers in the US.EPSRC: £571K, HEV, two postdocs (not started yet)EPSRC KTA: £126K, EV charging systems, one postdocEPSRC KTA: £120K, synchronverter, one postdocEPSRC, TSB and Power Systems Warehouse (KTP): £181K, one RAEPSRC: EP/H004424/1, £68K, airport operations, one PhD studentEPSRC and Add2: DHPA Award, £90K, wind power, one PhD studentEPSRC and Nheolis: DHPA Award, £90K, HIL, one PhD student
Q.-C. ZHONG: AN OVERVIEW OF RESEARCHACTIVITIES IN CONTROL AND SMART GRID INTEGRATION – p. 44/44
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