Updated overview of research in control, power electronics, renewable energy and smart grid integration

An Overview of Research Activities in

CONTROL AND SMART GRID I NTEGRATION

Qing-Chang [email protected]

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


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.


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

.


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.


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

-


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.


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


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


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.


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 .


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.


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−


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


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


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.


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%.


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


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 !


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]


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


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


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


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.


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


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


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


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


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


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)


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


Updated overview of research in control, power electronics, renewable energy and smart grid integration

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