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An Overview of Activities in

C ONTROL AND P OWER

             Qing-Chang Zhong
             zhongqc@ieee.org


 Electric...
Outline

   Research activities in control
   Research activities in power
   Other research activities
   Practical exper...
Research activities in control
On the theoretical side, my research has been focus-
ing on robust control, time-delay syst...
Major publications

   IEEE Trans. Automatic Control: 7
   Automatica: 4
   Other IEEE Transactions: 3
   IET Control Theo...
Projections
For a given nonsingular matrix partitioned as M N , denote
the projection onto the subspace Im M along the sub...
J-spectral factorisation
J-spectral factorisation is defined as

                Λ(s) = W ∼ (s)JW (s),
where the J-spectral...
Triangular forms of Hp and Hz
Assume that a para-Hermitian matrix Λ as given in (1)
is minimal and has no poles or zeros o...
Factorisation with two matrices
Lemma Λ admits a Jp,q -spectral factorisation for some unique
Jp,q (where p is the number ...
Factorisation with one common matrix
In general,
                      ∆z = ∆p .
However, these two can be the same.

Theo...
The Delay-type Nehari problem

Given a minimal state-space realisation Gβ = −C B ,
                                       ...
The optimal value
The optimal value γopt is
                                                                              ...
The structure of K

z'    j'           u
               −sh '
                                                            ...
1
Example: Gβ (s) =                    − s−a                       (a > 0)
                                             1
...
∞
The standard H problem of
single-delay systems
Given a γ > 0, find a proper controller K such that the
closed-loop system...
Simplifying the problem
                     z'
                                              u
                          ...
Solution to the problem
Solvability ⇐⇒ :
      H0 ∈ dom(Ric) and X = Ric(H0 ) ≥ 0;
      J0 ∈ dom(Ric) and Y = Ric(J0 ) ≥ ...
Implementation of the controller
As seen above, the control laws associated with delay systems
normally include a distribu...
A trivial but significant result
  y(τ)                                                y(t)                                ...
Rational implementation
     xN            x N −1       x2          x1              ub
              Π             …      ...
Unified Smith predictor (USP)
A numerical problem with the modified Smith predictor (MSP) is
identified. See the simple but a...
Feedback stabilisation of delay systems
The feedback stabilizability of the state–input delay
system
 x(t) = A0 x(t) + A1 ...
Research activities in power
Focusing on power electronics & renewable energy

     Voltage control of DC-AC converters
  ...
DC-AC converters in the context
of distributed generation

                                DC
      Local        Diode    ...
Control problems involved
                                        voltage control:
                                       ...
Voltage control of DC-AC converters
The single-phase circuit:




The objective is to make sure that the output voltage
Vo...
Structure of voltage controller




Techniques used:
    H ∞ control
    Repetitive control, where a delay is introduced
 ...
Formulation of the H ∞ control problem




               Q.-C. Z HONG : A N OVERVIEW   OF   ACTIVITIES   IN   C ONTROL T ...
Nyquist plot of the system
                                 −L(jω)
        8

        6

        4

        2
  Im




   ...
Simulation results
               400                                                                400
                 ...
Experimental results
                                     20


                                     10




          Volta...
Neutral-point control:                          Existing schemes




 Split DC link




 Conventional
  neutral leg


    ...
Neutral-point control:                              Proposed scheme




Control objective: to force ic ≈ 0 so that the poi...
∞
H       control design




This is a double-integrator system.

                           Q.-C. Z HONG : A N OVERVIEW  ...
Experimental results


                                                                                                   ...
Grid-friendly inverters
Many strategies have been set to explore renewable en-
ergy sources, such as wind and solar power,...
Synchronous generators
                                                                                         di
       ...
The synchronverter
  +
                                                                                                  C...
Experimental setup




             Q.-C. Z HONG : A N OVERVIEW   OF   ACTIVITIES   IN   C ONTROL T HEORY & E NGINEERING –...
Experimental results: I
Frequency (Hz)




                                                    P (W) and Q (Var)
         ...
Experimental results: II
                                                                                                 ...
Regulation of induction generators
for wind power




              Q




               P




              Q.-C. Z HONG ...
Control of wind turbines




Patented by Nheolis, France, installed on the department’s rooftop
Experiments show that the ...
Buck       Boost
Converter   Converter




            Q.-C. Z HONG : A N OVERVIEW   OF   ACTIVITIES   IN   C ONTROL T HEO...
Energy recovery from landing aircraft


                   Aircraft
                                                    Ri...
Voltage and current (zoomed)
                                  6000
                                  4000




       Phas...
800
                                                                                 600
                                 ...
Damping control of inter-area oscilla-
tions in large-scale power systems




 TCSC: Thyristor Controlled Switched Capacit...
AC-DC converters: DC drives




             Q.-C. Z HONG : A N OVERVIEW   OF   ACTIVITIES   IN   C ONTROL T HEORY & E NGI...
AC-DC-AC converters: AC drives




                                                            Philips Semiconductors




...
Ward Leonard drive systems
             Prime                                                                      Load
  ...
Exp. results: high-speed, no load




          (a) speed                        (b) torque




         (c) current      ...
Exp. results: low-speed, no load




          (a) speed                        (b) torque




         (c) current       ...
Other research activities
   Rapid control prototyping
     dSPACE
     MICROGen
     Texas Instruments kits
   Embedded s...
Rapid control prototyping (RCP)
            There are two sets of
  dSPACE+Matlab/Simulink/SimPower in the lab.




   Sin...
MicroGen



A universal electronic control unit with MPC555
built-in
Software-configurable I/O and signal
conditioning
Usin...
Texas Instruments kits
TI has donated about 20 sets of different digital signal
controllers (including TMS320F28335) equip...
Embedded systems & control
Different development kits for embedded control:
    Wind River Workbench + Wind River Probe
  ...
Wind River
Support a wide range of processors
USB 2.0-compliant host connection
High-speed JTAG run control and
program do...
Freescale
MPC5567




   132 MHz PowerPC-based e200z6 core
   a dual-channel FlexRay controller (10 Mbit/sec)
   Fast Ethe...
Mathworks xPC target




   Provide a high-performance host-target environment
   Design a control system using Simulink® ...
EasyPIC4
   3 in 1: Development, USB 2.0 programmer, ICD
   Supports 8, 14, 18, 20, 28 and 40 pin PIC




                ...
dsPICPro2
   Supports dsPIC in 64 and 80 pins package.
   USB 2.0 programmer on board + A/D + D/A




                   Q...
Chemical process control (1992)




   16 reactors, controlled by 3 industrial computers
   Effective object code > 100 KB...
Integral processes with dead time
Integral process with dead-time (IPDT):     G(s) = Gp (s)e−τ s = k e−τ s
               ...
Robust stability region

                                                                                                 ...
Deadbeat response
Theorem The considered system rejects a step distur-
bance at t = T2 (T2 > T1 > 0) if Q(s) is chosen
as
...
Robustness indicator
                  2
                  i=0 |qi |
Point A J =          λ
                              ...
Robustness indicator (cont.)
Denote
                                                    λ         T2
                     ...
Simulation example
Consider a process with
                                                  Control parameters:
         ...
Practical experiences
   Software design
      Intel 8086 assembly language:
      > 100kB binary code
      C language: >...
New-ACE: www.newace.org.uk
Leading a nation-wide collaborative network: New-ACE, which
is funded by a £88k EPSRC grant.

 ...
Objectives of the New-ACE
   to provide a platform for the members to
   exchange ideas, experience and practise
   to dev...
Teaching
Philosophy:
    Teaching and research help each other.
    Quality teaching provides a constant flow of ex-
    ce...
Funding
Current projects:
    Royal Academy of Engineering, £41k
    EPSRC: EP/H004351/1, £112k
    EPSRC: EP/H004424/1, £...
Research team
   One part-time secretary
   Currently 5 PhD students, one postdoctoral research fellow
   and two Honorary...
Future research topics

                                          Renewable Energy:
                                      ...
Vision
Closely working with colleagues, to develop the team
into an international key player in research and teach-
ing in...
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Recent developments in control, power electronics and renewable energy by Dr Zhong

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Recent developments in control, power electronics and renewable energy by Dr Zhong

  1. 1. An Overview of Activities in C ONTROL AND P OWER Qing-Chang Zhong zhongqc@ieee.org Electrical Drives, Power and Control Group Dept. of Electrical Eng. & Electronics The University of Liverpool Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 1/77
  2. 2. Outline Research activities in control Research activities in power Other research activities Practical experiences New-ACE Teaching Funding Future research plan Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 2/77
  3. 3. Research activities in control On the theoretical side, my research has been focus- ing on robust control, time-delay systems, process control, and recently applying the theory of infinite- dimensional systems to time-delay systems. A series of problems have been solved: Projections J-spectral factorisation Delay-type Nehari problem Standard H ∞ problem of single-delay systems Realisation of distributed delays in controllers Feedback stabilizability of linear systems with state and input delays in Banach spaces Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 3/77
  4. 4. Major publications IEEE Trans. Automatic Control: 7 Automatica: 4 Other IEEE Transactions: 3 IET Control Theory & Applications: 4 One research monograph Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 4/77
  5. 5. Projections For a given nonsingular matrix partitioned as M N , denote the projection onto the subspace Im M along the subspace Im N by P . Then, the projection matrix P is −1 P = M 0 M N . Similarly, the projection Q onto the subspace Im N along the sub- space Im M is −1 −1 Q= 0 N M N = N 0 N M . If M T N = 0, then the projection matrices reduce to P = M (M T M )−1 M T and Q = N (N T N )−1 N T . Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 5/77
  6. 6. J-spectral factorisation J-spectral factorisation is defined as Λ(s) = W ∼ (s)JW (s), where the J-spectral factor W (s) is bistable and Λ(s) ∼ . T is a para-Hermitian matrix: Λ(s) = Λ (s) = Λ (−s). Assume that Λ, having no poles or zeros on the jω-axis including ∞, is realised as Hp BΛ Λ= = D + CΛ (sI − Hp )−1 BΛ (1) CΛ D and denote the A-matrix of Λ−1 as Hz , i.e., Hz = Hp − BΛ D−1 CΛ . Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 6/77
  7. 7. Triangular forms of Hp and Hz Assume that a para-Hermitian matrix Λ as given in (1) is minimal and has no poles or zeros on the jω-axis including ∞. There always exist nonsingular matrices ∆p and ∆z (e.g. via Schur decomposition) such that −1 ? 0 ∆p Hp ∆p = ? A+ and A− ? ∆−1 Hz ∆z z = , 0 ? where A+ is antistable and A− is stable (A+ and A− have the same dimension). Note: No structural information of Hp and Hz is needed. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 7/77
  8. 8. Factorisation with two matrices Lemma Λ admits a Jp,q -spectral factorisation for some unique Jp,q (where p is the number of the positive eigenvalues of D and q is the number of the negative eigenvalues of D) iff I 0 ∆= ∆z ∆p 0 I is nonsingular. If this condition is satisfied, then a J−spectral factor is formulated as     I  I 0 ∆−1 Hp ∆   I 0 ∆−1 BΛ     0  W =    ,  (2)  −∗ I   Jp,q DW CΛ ∆   DW  0 ∗ where DW is a nonsingular solution of DW Jp,q DW = D. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 8/77
  9. 9. Factorisation with one common matrix In general, ∆z = ∆p . However, these two can be the same. Theorem Λ admits a J-spectral factorisation if and only if there exists a nonsingular matrix ∆ such that Ap 0 z A− ? ∆−1 Hp ∆ = − p , ∆−1 Hz ∆ = ? A+ 0 Az + where Az and Ap are stable, and Az and A+ are an- − − + p tistable. When this condition is satisfied, a J-spectral factor W is given in (2). Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 9/77
  10. 10. The Delay-type Nehari problem Given a minimal state-space realisation Gβ = −C B , A 0 which is not necessarily stable, and h ≥ 0, characterise the optimal value γopt = inf{ Gβ (s) + e−sh K(s) L∞ : K(s) ∈ H ∞ } and for a given γ > γopt , parametrise the suboptimal set of proper K ∈ H ∞ such that Gβ (s) + e−sh K(s) L∞ < γ. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 10/77
  11. 11. The optimal value The optimal value γopt is   Lo γopt ˆ = max{γ : det Σ22 = 0}, ˆ Σ22 = −Lc I Σ , I where Lo and Lc are stabilising solutions, respectively, to    A γ −2 BB ∗ I −Lc I    = 0, 0 −A∗ Lc    A 0 Lo I −Lo    = 0. −C ∗ C −A∗ I     Σ11 Σ12 . A γ −2 BB ∗ Σ=  = Σ(h) = exp(  h) Σ21 Σ22 −C ∗ C −A∗ Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 11/77
  12. 12. The structure of K z' j' u −sh ' @ ' @ K e I T c Gβ Z W −1 Q T T - c E j E w y Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 12/77
  13. 13. 1 Example: Gβ (s) = − s−a (a > 0) 1 0.9 aγopt 0.8 0.7 0.6 aγ 0.5 0.4 ˆ Σ22 0.3 0.2 ah 0.1 0 0 1 2 3 4 5 6 7 8 9 10 aγ ah ˆ ˆ 22 with re- The contour Σ22 = 0 on the The surface Σ spect to ah and aγ ah-aγ plane 1 Since I −Lc Lo = 1−4a2 γ 2 , there is ΓGβ = 2a . As a result, the optimal value γopt satisfies 0.5 ≤ aγopt ≤ 1. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 13/77
  14. 14. ∞ The standard H problem of single-delay systems Given a γ > 0, find a proper controller K such that the closed-loop system is internally stable and Fl (P, Ke−sh) ∞ < γ. ' z ' w P u '1 y e−sh I ' u E K Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 14/77
  15. 15. Simplifying the problem z' u @' 1 @ ' u −sh e I Cr (P ) K T E w y z' @' 1 @ u @ 'z1 @ u @' 1 @ ' u −sh e I Cr (P ) Gα Cr (Gβ ) K T E E wE 1 w y y Delay-free problem 1-block delay problem Gα is the controller generator of the delay-free prob- . −1 lem. Gβ is defined such that Cr (Gβ ) = Gα . Gα and Cr (Gβ ) are all bistable. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 15/77
  16. 16. Solution to the problem Solvability ⇐⇒ : H0 ∈ dom(Ric) and X = Ric(H0 ) ≥ 0; J0 ∈ dom(Ric) and Y = Ric(J0 ) ≥ 0; ρ(XY ) < γ 2 ; γ > γh , where γh = max{γ : det Σ22 = 0}. u ' @' @   c A + B2 C1 B2 − Σ12 Σ−1 C1 Σ−∗ B1 22 ∗ 22 −1 Q V −1 = C1 I 0  Z V −γ −2 B1 Σ∗ − C2 Σ∗ ∗ 21 22 0 I T - E c h E y Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 16/77
  17. 17. Implementation of the controller As seen above, the control laws associated with delay systems normally include a distributed delay like ¢ h v(t) = eAζ Bu(t − ζ)dζ, 0 or in the s-domain, Z(s) = (I − e−(sI−A)h ) · (sI − A)−1 . The implementation of Z is not trivial because A 1 may be unstable. This problem had confused the 10 delay community for several years and was pro- 0 10 Approximation error posed as an open problem in Automatica in 2003. −1 N=1 It was reported that the quadrature implementation 10 might cause instability however accurate the imple- −2 N=5 10 mentation is. −3 10 N=20 My investigation shows that: −4 10 The quadrature approximation error converges to 0 −2 10 10 −1 10 0 10 1 10 2 10 3 in the sense of H ∞ -norm. Frequency (rad/sec) Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 17/77
  18. 18. A trivial but significant result y(τ) y(t) p(t) = ∗ 1 t−h/N t τ 0 t 0 h/N t ¢ h ¢ t N y(t − τ )dτ = y(τ )dτ = y(t) ∗ p(t). 0 h t− N N −1 ¢ (i+1) h ¡h N 0 eAζ Bu(t − ζ)dζ = eAζ Bu(t − ζ)dζ h iN i=0 N −1 ¢ h (i+1) N h ≈ eiA N B u(t − ζ)dζ h iN i=0 N −1 h h = eiA N Bu(t − i ) ∗ p(t) i=0 N Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 18/77
  19. 19. Rational implementation xN x N −1 x2 x1 ub Π … Π Π Φ −1 B u vr … Π = ( sI − A + Φ ) −1 Φ Π = (sI − A + Φ)−1 Φ, ¡ h Φ=( N 0 e−Aζ dζ)−1 . Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 19/77
  20. 20. Unified Smith predictor (USP) A numerical problem with the modified Smith predictor (MSP) is identified. See the simple but a little bit extreme example 1 1 P (s) = + . s + 1000 s − 1 The MSP is e1000h − e−sh e−h − e−sh ZMSP (s) = + . s + 1000 s−1 According to the IEEE Standard 754, e1000h is regarded to be +∞ (INF) for h ≥ 0.71sec. This is not acceptable in practice. A unified Smith predictor is proposed to fix this problem. An equivalent structure of systems incorporating USP is derived and then applied to solve various problems. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 20/77
  21. 21. Feedback stabilisation of delay systems The feedback stabilizability of the state–input delay system x(t) = A0 x(t) + A1 x(t − r) + P u(t) + P1 u(t − r) ˙ is equivalent to the condition Rank (P + e−rλi P1 )∗ · ϕi = di , i = 1, 2, · · · , l. where λi ∈ {λ1 , λ2 , · · · , λl } = {λ ∈ C : det ∆(λ) = 0 and Reλ ≥ 0} with ∆(λ) := λI − A0 − A1 e−rλ . The dimension of Ker∆(λi )∗ is di and the basis of Ker∆(λi )∗ is ϕi , ϕi , · · · , ϕi i for i = 1, 2, · · · , l . 1 2 d Appeared in IEEE Trans. Automatic Control as a reg- ular paper. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 21/77
  22. 22. Research activities in power Focusing on power electronics & renewable energy Voltage control of DC-AC converters Neutral point generation Grid-friendly inverters: Synchronverters Regulation of induction generators for wind power Control of wind turbines Energy recovery from landing aircraft Damping control of inter-area oscillations in power systems DC and AC drives AC Ward Leonard drive systems Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 22/77
  23. 23. DC-AC converters in the context of distributed generation DC Local Diode link DC-AC grid generator Rectifier Converter Micro- grid Fuel cells Photo-voltaic etc. Gas turbines Wind-mills etc. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 23/77
  24. 24. Control problems involved voltage control: e = Vref − Vc as small as possible neutral point control: to provide a non-drifting neutral point power control: to regulate the active/reactive power phase-locked loop (PLL): to synchronise the con- verter with the grid Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 24/77
  25. 25. Voltage control of DC-AC converters The single-phase circuit: The objective is to make sure that the output voltage Vout or Vc is a clean sinusoidal signal even when the load is nonlinear and/or the public grid is polluted with harmonics. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 25/77
  26. 26. Structure of voltage controller Techniques used: H ∞ control Repetitive control, where a delay is introduced into the controller Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 26/77
  27. 27. Formulation of the H ∞ control problem Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 27/77
  28. 28. Nyquist plot of the system −L(jω) 8 6 4 2 Im 0 −2 −4 −6 −8 −2 −1 0 1 2 3 4 5 6 Re Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 28/77
  29. 29. Simulation results 400 400 V (external) grid c e 300 300 200 200 micro−grid Voltage (V) 100 Voltage (v) 100 0 0 −100 −100 −200 −200 −300 −300 −400 −400 0 0.05 0.1 0.15 0.2 0.36 0.37 0.38 0.39 0.4 Time (sec) Time (sec) (a) Transient response (b) Steady-state response Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 29/77
  30. 30. Experimental results 20 10 Voltage [V] 0 #1:1 #1:2 -10 -20 0.00 0.01 0.02 0.03 0.04 0.05 Time [sec] (a) voltage and its reference 4 Voltage error [V] 2 #1:1 0 -2 -4 0.00 0.01 0.02 0.03 0.04 0.05 Time [sec] (b) tracking error Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 30/77
  31. 31. Neutral-point control: Existing schemes Split DC link Conventional neutral leg Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 31/77
  32. 32. Neutral-point control: Proposed scheme Control objective: to force ic ≈ 0 so that the point N will be the mid-point of DC supply. No need to re-design the converter; The controller is decoupled. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 32/77
  33. 33. ∞ H control design This is a double-integrator system. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 33/77
  34. 34. Experimental results 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) Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 34/77
  35. 35. Grid-friendly inverters Many strategies have been set to explore renewable en- ergy sources, such as wind and solar power, to lead to a low carbon economy. However, the increasing share of the electricity generated from these sources (which is often fed into the grid via inverters) could be a po- tential threat to the overall stability of the future power system when it reaches a certain level. Utility com- panies would expect to minimise the impact of a large number of grid-connected inverters on the power sys- tem. Moreover, how to share load among these invert- ers autonomously is also a problem. Our Solution: Synchronverters: Inverters that mimic synchronous generators Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 35/77
  36. 36. Synchronous generators di (θ = 0 ) v = −Rs i − Ls + e, dt Rotor field axis Rs , L ˙sinθ−Mf dif cosθ, e = Mf if θ Rotation dt M M N Te = pMf if i, sinθ , Field voltage Rs , L Rs , L ˙ Q = −θMf if i, cosθ , M ¨ ˙ J θ = Tm − Te − Dp θ. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 36/77
  37. 37. The synchronverter + Circuit Ls , R s va Lg , R g Breaker ia vga ea vb VDC ib vgb eb vc ec ic vgc C - (a) The power part Dp - Tm 1 θ& 1 θ Js s - Te Eqn. (7) Q Eqn. (8) Eqn. (9) e Mf if i (b) The Zelectronic part Q.-C. :A O A HONG N VERVIEW OF CTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 37/77
  38. 38. Experimental setup Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 38/77
  39. 39. Experimental results: I Frequency (Hz) P (W) and Q (Var) s d d P Q   ©   Time (Second) Time (Second) (a) synchronverter (b) real power P and frequency reactive power Q Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 39/77
  40. 40. Experimental results: II y ˆ ˆ Frequency (Hz) P (W) and Q (Var) P Q ©   Time (Second) Time (Second) (a) synchronverter (b) real power P and frequency reactive power Q Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 40/77
  41. 41. Regulation of induction generators for wind power Q P Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 41/77
  42. 42. Control of wind turbines Patented by Nheolis, France, installed on the department’s rooftop Experiments show that the new wind turbine is very efficient. The maximum mechanical power of a prototype with a 2m (diame- ter) rotor reached 12kW at a wind speed of 20m/s. The nominal power is 4.1kW at 14 m/s. A 1-meter 3-bladed prototype recorded 2.8kW mechanical power at 14 m/s. This is much more efficient than any commercial wind turbines available. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 42/77
  43. 43. Buck Boost Converter Converter Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 43/77
  44. 44. Energy recovery from landing aircraft Aircraft Risen slope to fall when energy recovery is activated Coils Runway Magnets with alternative poles (N, S, N, …) Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 44/77
  45. 45. Voltage and current (zoomed) 6000 4000 Phase A voltage 2000 0 -2000 -4000 -6000 0 0.1 0.2 0.3 0.4 0.5 5 x 10 1 Phase A current 0.5 0 -0.5 -1 0 0.1 0.2 0.3 0.4 0.5 Time Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 45/77
  46. 46. 800 600 d 400 200 0 6000 100 4000 Phase A voltage 2000 v 50 0 0 -2000 0 -4000 a -5 -6000 0 5 10 15 20 25 30 -10 7 x 10 2000 2 p 1 Phase A current 1000 0 7 0 x 10 10 -1000 E 5 -2000 0 5 10 15 20 25 30 0 0 5 10 15 20 25 30 Time Time (a) Phase current and (b) Distance, speed, the generated voltage deceleration, power and (phase) energy Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 46/77
  47. 47. Damping control of inter-area oscilla- tions in large-scale power systems TCSC: Thyristor Controlled Switched Capacitors Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 47/77
  48. 48. AC-DC converters: DC drives Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 48/77
  49. 49. AC-DC-AC converters: AC drives Philips Semiconductors VVVF speed control by: using the PWM circuit HEF4752V shown above using Intel 8051 microcomputer to generate space vector PWM signal Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 49/77
  50. 50. Ward Leonard drive systems Prime Load mover Constant Variable speed speed Controllable field Fixed field Conventional (DC) Ward Leonard drive systems Inverter Variable speed Prime Load VDC SG SM/IM mover Variable speed Fixed field AC Ward Leonard drive systems Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 50/77
  51. 51. Exp. results: high-speed, no load (a) speed (b) torque (c) current (d) voltage Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 51/77
  52. 52. Exp. results: low-speed, no load (a) speed (b) torque (c) current (d) voltage Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 52/77
  53. 53. Other research activities Rapid control prototyping dSPACE MICROGen Texas Instruments kits Embedded systems and control Process control Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 53/77
  54. 54. Rapid control prototyping (RCP) There are two sets of dSPACE+Matlab/Simulink/SimPower in the lab. Single-board PCI hardware for use in PCs powerful development system for RCP Real-Time Interface provides Simulink® blocks for graphical configuration of A/D, D/A, digital I/O lines, incremental encoder interface and PWM generation Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 54/77
  55. 55. MicroGen A universal electronic control unit with MPC555 built-in Software-configurable I/O and signal conditioning Using industry standard SimuLink® Enabling technology for RCP and HiL applica- tions Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 55/77
  56. 56. Texas Instruments kits TI has donated about 20 sets of different digital signal controllers (including TMS320F28335) equipped with the full version of latest Code Composer Studio 4.0. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 56/77
  57. 57. Embedded systems & control Different development kits for embedded control: Wind River Workbench + Wind River Probe Freescale MPC5567 Mathworks xPC target EasyPIC4 dsPICPro2 Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 57/77
  58. 58. Wind River Support a wide range of processors USB 2.0-compliant host connection High-speed JTAG run control and program download Hot-plug-capable interconnect system RTOS: VxWorks, Linux, and ThreadX Built-in hardware diagnostics Flash memory programming Wind River Probe Source-level debugging Support for Memory Management Units Open API integration Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 58/77
  59. 59. Freescale MPC5567 132 MHz PowerPC-based e200z6 core a dual-channel FlexRay controller (10 Mbit/sec) Fast Ethernet controller, 5 FlexCAN modules 40-channel dual analog-to-digital converter (ADC) 24-channel PWM 32-channel direct memory :access (DMA) controller E Q.-C. Z HONG A O N A C VERVIEW OFT & CTIVITIES IN ONTROL HEORY NGINEERING – p. 59/77
  60. 60. Mathworks xPC target Provide a high-performance host-target environment Design a control system using Simulink® and Stateflow® Generate code with Real-Time Workshop® and Stateflow Coder™ and download the code to a target PC running the xPC Target real-time kernel Execute the code in real time on low-cost PC-compatible hardware Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 60/77
  61. 61. EasyPIC4 3 in 1: Development, USB 2.0 programmer, ICD Supports 8, 14, 18, 20, 28 and 40 pin PIC Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 61/77
  62. 62. dsPICPro2 Supports dsPIC in 64 and 80 pins package. USB 2.0 programmer on board + A/D + D/A Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 62/77
  63. 63. Chemical process control (1992) 16 reactors, controlled by 3 industrial computers Effective object code > 100 KB (Intel 8086 assembler) Analogue control variables include pressure, temperature, level, flow and weight etc. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 63/77
  64. 64. Integral processes with dead time Integral process with dead-time (IPDT): G(s) = Gp (s)e−τ s = k e−τ s s Consider the disturbance observer-based control scheme (Zhong and Normey-Rico, 2001) d r Ef E Ef c u c Ef E y E d C(s) Gp (s)e−τ s T − T − r u c y ˆ E CGm E h E F (s) E h E Gp (s)e−τ s E d (1+CGm )F (s) Gm (1−Qe−τm s ) T ' c − n Gm (s) ' E e−τm s Ef' G−1 (s) m ' f − ' cn ' ' Q(s) h Q(s) F (s) Disturbance Observer (a) Disturbance observer-based control scheme (b) equivalent structure for implementation where k 1 (2λ + τm )s + 1 1 Gm (s) = , C(s) = , Q(s) = , F (s) = s kT (λs + 1)2 λs + 1 and λ is a free design parameter. 1 Setpoint response: Gyr (s) =T s+1 e−τm s Disturbance response: Gyd (s) = k 1 − Q(s)e−τm s s e−τm s Measurement noise response: Gyn (s) = Q(s)e−τm s Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 64/77
  65. 65. Robust stability region 1.5 2 3 0.6 1 3 5 2. 2 6 2.5 0.5 0.4 1.5 5 1.5 4 0.2 2 0.2 1 β 1 0.5 ∆k/k 3 0 2 0.2 2 0.5 1.5 1 −0.2 1.5 0 −0.4 1 −0.7 0.5 −0.5 1 −0.3 2 1 −0.1 1.5 1.5 0.1 1 −0.6 ∆K/K 0.5 2 0.3 0 ∆τ/τ 1.5 0.5 −0.5 0.7 −1 −1 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 1 τ /τ ∆ m Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 65/77
  66. 66. Deadbeat response Theorem The considered system rejects a step distur- bance at t = T2 (T2 > T1 > 0) if Q(s) is chosen as q0 + q1 e−T1s + q2 e−T2s Q(s) = λs + 1 with  eT2 /λ (λ+τm +T1 )−eT1 /λ (λ+τm +T2 )  q0 =    T2 −T1 +T1 eT2 /λ −T2 eT1 /λ    λ+τm +T2 −eT2 /λ (λ+τm ) q1 = T2 −T1 +T1 eT2 /λ −T2 eT1 /λ        q = − λ+τm +T1 −eT1 /λ (λ+τm ) 2 T −T +T eT2 /λ −T eT1 /λ 2 1 1 2 where λ > 0 is a free parameter. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 66/77
  67. 67. Robustness indicator 2 i=0 |qi | Point A J = λ can be interpreted as a robustness indicator: The lower the point A, the better the robustness. In order to obtain the largest robust region for given T2 and λ, minimise the robust indicator: 2 |qi | min J = min i=0 T1 T1 λ 1 where J can be re-written as 0.9 0.8 0.7 1 2(λ + τm )(eT2 /λ − 1) − 2T2 0.6 J= 1+ T1/T2 λ T2 − T1 + T1 eT2 /λ − T2 eT1 /λ 0.5 0.4 0.3 Since 2(λ + τm )(eT2 /λ − 1) − 2T2 > 0 and 0.2 T2 − T1 + T1 eT2 /λ − T2 eT1 /λ > 0 for T2 > 0.1 1 T1 > 0 and λ > 0, J is always larger than λ . 0 0 1 2 3 4 5 6 7 8 9 10 Differentiate J with respect to T1 and let it be 0, T2/λ then When T2 /λ → 0, T1 → 0.5T2 ; when −1 + eT2 /λ − T2 eT1 /λ = 0 λ T2 /λ → ∞, T1 → T2 . Thus, T1 is always Solve it, we have less than T2 , as expected. T1 T2 /λ T2 = λ T2 ln e T /λ −1 2 Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 67/77
  68. 68. Robustness indicator (cont.) Denote λ T2 α= and β = τm τm then the minimal cost is   1 1  2(1 + )(eβ/α − 1) − 2β/α α Jo = 1+  β/α −1 ατm β/α + (eβ/α − 1) ln e β/α − 1 150 100 Τm Jo 50 0 1 1 2 2 3 3 T2 Τm 4 4 5 Λ Τm Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 68/77
  69. 69. Simulation example Consider a process with Control parameters: 1 T2 = 2τm = 10sec Gm (s) = , τm = 5 sec, s λ = 0.5τm = 2.5sec T1 = 6.5sec assume that the worst multiplicative uncer- 1 q0 = 2.36, q1 = −1.75, q2 = 0.39 tainty is ∆(s) = 0.1s+1 e−0.5s − 1. (a) Nominal case (b) The worst case Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 69/77
  70. 70. Practical experiences Software design Intel 8086 assembly language: > 100kB binary code C language: > 10,000 lines Database/Javascript Hardware design Micro-computers: Intel 8051, Zilog Z80, Motorola ... DC, AC drives etc Lift control systems System design experience Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 70/77
  71. 71. New-ACE: www.newace.org.uk Leading a nation-wide collaborative network: New-ACE, which is funded by a £88k EPSRC grant. Partners: Imperial, Sheffield, Loughborough and Queen’s Belfast. Advisory members: D.J.N. Limebeer (Imperial), D.H. Owens (Sheffield), R.M. Goodall (Loughborough), G. Irwin (Queen’s Belfast), Q.H. Wu (Liverpool). Main activities and outcomes: to organise six workshops in subject areas including renewable energy and control in power electronics to submit 6~12 joint proposals in the coming three years. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 71/77
  72. 72. Objectives of the New-ACE to provide a platform for the members to exchange ideas, experience and practise to develop and strengthen long-term collaboration activities, including joint applications and collaborations with industry to support potential future leaders in control engineering and related areas to develop and sustain a strong future for control engineering in the UK Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 72/77
  73. 73. Teaching Philosophy: Teaching and research help each other. Quality teaching provides a constant flow of ex- cellent students for research. The best student of 2007, whose FYP was directed by me, has been attracted to study for a PhD degree under my supervision. He won both the principal Faculty undergraduate award and the IET Prize. Modules taught this year: Power electronics and electromechanics Energy conversion and power systems Digital control Discrete-time signals and systems Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 73/77
  74. 74. Funding Current projects: Royal Academy of Engineering, £41k EPSRC: EP/H004351/1, £112k EPSRC: EP/H004424/1, £68k EPSRC: EP/E055877/1, £88k EPSRC: one DTA studentship EPSRC and Add2: DHPA Award, £90k ESPRC and Nheolis: DHPA Award, £90k Completed projects: EPSRC: EP/C005953/1, £126k Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 74/77
  75. 75. Research team One part-time secretary Currently 5 PhD students, one postdoctoral research fellow and two Honorary Researchers Another postdoc researcher and one PhD student to join soon (funding already secured) A former postdoctoral research fellow is still in active collaboration. Also closely working/worked with researchers from Brazil, China, France, Italy, Israel, Netherlands, Singapore and USA, in addition to those from the home department, the Dept of Engineering and other UK universities and industry. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 75/77
  76. 76. Future research topics Renewable Energy: • Wind power • Solar power • Other energy sources Control Theory Power Electronics: & Engineering • Grid-connected inverters • Inverter-dominated power systems • DC drives and AC drives • Applications in power systems etc Enabling Control Theory: • Robust H∝ control • Time-delay systems • Grid monitoring, control and stability Industrial collaboration to consolidate research Theoretical research to deepen the depth of research Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 76/77
  77. 77. Vision Closely working with colleagues, to develop the team into an international key player in research and teach- ing in control, power electronics and renewable en- ergy, with long-term collaborations with industrial partners and world-leading research groups. Breadth of research: focusing on control theory, power electronics and renewable energy; developing activities in automotive electronics and process control. Depth of research: Looking for fundamental prob- lems; providing significant/simple solutions. Q.-C. Z HONG : A N OVERVIEW OF ACTIVITIES IN C ONTROL T HEORY & E NGINEERING – p. 77/77

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