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An Overview of Research Activities inC ONTROL AND S MART G RID I NTEGRATION                     Qing-Chang Zhong          ...
Outline of the talk   A little bit about myself   Activities in process control   Activities in control theory   Activitie...
A little bit about myself    1990, started working in the area of control after receiving the first degree    1997, MSc in ...
Evolution of my research activities             Research activities                                                       ...
Activities in process control   Control of integral processes with dead-time: A research monograph, Control of Integral   ...
Activities in control theory   Robust control of time-delay systems (frequency-domain approaches): Solved a series of   fu...
Algebraic Riccati EquationsThe well-known algebraic Riccati equation (ARE)                          A∗ X + XA + XRX + E = ...
J-spectral factorisationJ-spectral factorisation is defined as                Λ(s) = W ∼ (s)JW (s),where the J-spectral fac...
Theorem Λ admits a J-spectral factorisation if andonly if there exists a nonsingular matrix ∆ such that                Ap ...
∞The standard H problem ofsingle-delay systemsGiven a γ > 0, find a proper controller K such that theclosed-loop system is ...
Simplifying the problem                     z                                              u                              ...
Solution to the problemSolvability ⇐⇒ :      H0 ∈ dom(Ric) and X = Ric(H0 ) ≥ 0;      J0 ∈ dom(Ric) and Y = Ric(J0 ) ≥ 0; ...
Implementation of the controllerAs seen above, the control laws associated with delay systemsnormally include a distribute...
Rational implementation     xN            x N −1          x2              x1                   ub              Π          ...
Feedback stabilisation of delay systemsThe feedback stabilizability of the state–input delaysystem x(t) = A0 x(t) + A1 x(t...
UDE-based Robust ControlThe Uncertainty and Disturbance Estimator (UDE) is a strategy to estimate theuncertainties and dis...
The two-degree-of-freedom natureIf the system is linear without delay, then                            X(s) = Hm (s)C(s) +...
Application to Continuous Stirred Tank Reactors(CSTR)                                                                     ...
Activities in power and energy systems   Sample platform technologies        Provision of a neutral line        Power qual...
Neutral line provision                                                                                                    ...
Power quality improvementPower quality is a very important problem for renewable energy anddistributed generation.        ...
Synchronverters:Grid-friendly inverters   Synchronverters are inverters that are mathematically   equivalent to the conven...
The basic idea                                    (θ = 0 ) Rotor field axis                                               ...
Dp                                     θr                                                                                 ...
Parallel operation of inverters                                   S1 = P1 + jQ1              S 2 = P2 + jQ2               ...
Robust droop controller (Patent pending)                                                                          E*      ...
Experimental results                                                                                                      ...
C-invertersThe output impedance of an inverter is normally inductive and can bemade resistive. Is it possible to make it c...
C-inverters                                                            R-inverters                 28                     ...
Active capacitorsCapacitors are fundamental building blocks for electronic and electrical cir-cuits. A capacitor can be bu...
6                                                                 10                                        i             ...
Harmonic droop controller                                               Zo                                                ...
Without                       With 3rd and 5th harmonics droop controller                6                                ...
Sinusoid-locked loops                     v = vm sin θ v               i            Xs        e = E sin θ                 ...
Tracking the grid voltage                     70                                                                 70       ...
Tracking a voltage with avarying frequency                              With the proposed SLL                             ...
Tracking a square wave             40                                                   With the proposed SLL             ...
AC Ward Leonard drive systemsExtended the concept of Ward Leonard drive systems to AC machines.                           ...
Wind turbine control                                                                                                      ...
Updated overview of research in control, power electronics, renewable energy and smart grid integration
Updated overview of research in control, power electronics, renewable energy and smart grid integration
Updated overview of research in control, power electronics, renewable energy and smart grid integration
Updated overview of research in control, power electronics, renewable energy and smart grid integration
Updated overview of research in control, power electronics, renewable energy and smart grid integration
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Updated overview of research in control, power electronics, renewable energy and smart grid integration

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April 2012

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

  1. 1. An Overview of Research Activities inC ONTROL AND S MART G RID I NTEGRATION Qing-Chang Zhong Q.Zhong@Sheffield.ac.uk Chair in Control and Systems Engineering Dept. of Automatic Control and Systems Engineering The University of Sheffield United Kingdom
  2. 2. 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. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 2/44
  3. 3. A little bit about myself 1990, started working in the area of control after receiving the 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 monograph Robust Control of Time-delay Systems published by Springer-Verlag London. 2007, Director of EPSRC-funded Network for New Academics in Control Engineering, currently more than 170 members, joined UKACC in Oct 2010 as a Group 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 monograph Control of Integral Processes with Dead Time by Springer-Verlag 2012, Chair in Control and Systems Engineering, The University of Sheffield 2012, research monograph Control of Power Inverters in Renewable Energy and Smart Grid Integration to be published by Wiley-IEEE Press Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 3/44
  4. 4. Evolution of my research activities Research activities Power & Energy Systems Robust Control Theory & Time-Delay Systems Process Control 1998 2001 2004 2007 2010 2013 YearWide spectrum of expertise Research philosophy From hardware to software Focused and thorough research From applied to theoretical Holistic approach: Down to details but keep the big picture in mind From control to power Looking for solutions and problems as well Cover many application areas Looking for hidden links Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 4/44
  5. 5. Activities in process control Control 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. Advances in Industrial Control Disturbance observer-based control strategy Dead-beat response Stability region on the control parameter space Antonio Visioli Qing-Chang Zhong Achievable specifications etc Practical experience with a production line 1 Control of Integral Processes 16 reactors, controlled by 3 industrial computers with Dead Time Effective object code > 100 KB (Intel 8086 assembler) Analogue control variables and measurements etc. Continuous Stirred Tank Reactor (CSTR) System Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 5/44
  6. 6. Activities in control theory Robust 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 Standard H ∞ 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. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 6/44
  7. 7. Algebraic Riccati EquationsThe well-known algebraic Riccati equation (ARE) A∗ X + XA + XRX + E = 0can be represented as W1 W U U1   A R X H X H= . - + −E −A∗ Y1 (=0) Y V V1=0Assume that U1 is nonsingular and V1 = 0. The solution is obtainedwhen Y1 = 0 while changing X. The transfer matrix from U1 to W1 is  IAX = I 0 H . X Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 7/44
  8. 8. J-spectral factorisationJ-spectral factorisation is defined as Λ(s) = W ∼ (s)JW (s),where the J-spectral factor W (s) is bistable and Λ(s) ∼ . Tis a para-Hermitian matrix: Λ(s) = Λ (s) = Λ (−s).Assume that Λ, having no poles or zeros on the jω-axisincluding ∞, is realised as Hp BΛ Λ= = D + CΛ (sI − Hp )−1 BΛ (1) CΛ Dand 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 R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 8/44
  9. 9. Theorem Λ admits a J-spectral factorisation if andonly if there exists a nonsingular matrix ∆ such that Ap 0 Az ?∆−1 Hp ∆ = − p , ∆−1 Hz ∆ = − ? A+ 0 Az + p pwhere Az − and A− are stable, and and are anti- Az + A+stable. If this condition is satisfied, then a J−spectralfactor is formulated as     I  I 0 ∆−1 Hp ∆   I 0 ∆−1 BΛ  0     W =    ,   −∗ 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 R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 9/44
  10. 10. ∞The standard H problem ofsingle-delay systemsGiven a γ > 0, find a proper controller K such that theclosed-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 R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 10/44
  11. 11. 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 problemGα is the controller generator of the delay-free pro- . −1blem. Gβ is defined such that Cr (Gβ ) = Gα . Gα andCr (Gβ ) are all bistable. Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 11/44
  12. 12. Solution to the problemSolvability ⇐⇒ : 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 @ @ B2 − Σ12 Σ−1 C1 Σ−∗ B1 ∗   c A + B2 C1 22 22 Q V −1 = C1 I 0  Z V −1 −γ −2 B1 Σ∗ − C2 Σ∗ ∗ 21 22 0 I T - E c h E y Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 12/44
  13. 13. Implementation of the controllerAs seen above, the control laws associated with delay systemsnormally include a distributed delay like ¢ h v(t) = eAζ Bu(t − ζ)dζ, 0or in the s-domain, Z(s) = (I − e−(sI−A)h ) · (sI − A)−1 .The implementation of Z is not trivial because A 1may be unstable. This problem had confused the 10delay community for several years and was pro- 0 10 Approximation errorposed as an open problem in Automatica in 2003. −1 N=1It was reported that the quadrature implementation 10might cause instability however accurate the imple- −2 N=5 10mentation is. −3 10 N=20My investigation shows that: −4 10The quadrature approximation error converges to 0 −2 10 10 −1 10 0 10 1 10 2 10 3 Frequency (rad/sec)in the sense of H ∞ -norm. Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 13/44
  14. 14. Rational implementation xN x N −1 x2 x1 ub Π … Π Π Φ −1 B uvr … Π = ( sI − A + Φ ) −1 ΦΠ = (sI − A + Φ)−1 Φ, ¡ hΦ=( N 0 e−Aζ dζ)−1 . Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 14/44
  15. 15. Feedback stabilisation of delay systemsThe feedback stabilizability of the state–input delaysystem x(t) = A0 x(t) + A1 x(t − r) + P u(t) + P1 u(t − r) ˙is equivalent to the conditionRank (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 ofKer∆(λi )∗ is ϕi , ϕi , · · · , ϕi i for i = 1, 2, · · · , l . 1 2 d Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 15/44
  16. 16. UDE-based Robust ControlThe Uncertainty and Disturbance Estimator (UDE) is a strategy to estimate theuncertainties and disturbances in a system. The controller is designed so thatthe state of the system tracks the state of the reference model chosen, with allthe uncertainties and disturbances estimated with an estimator, called UDE. Itcan be applied to linear or nonlinear, time-invariant or time-varying systemswith or without state delays.The resulting control law for a nonlinear system u(t) = b+ (−(g1 (t) + ε(g2 (t) + g3 (t))) + Am xm (t) + Bm c(t)) ¢ t + 1 +b (I − (Am + K)T ) e(t) − (Am + K) e(t)dt T 0The simplified nonlinear control law consists of three terms. The first termcancels all the known system dynamics, while the second term introduces thedesired dynamics given by the reference model and the last term performs a PIcontrol action. Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 16/44
  17. 17. 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)) . 0dB H f ( jω ) H ki ( jω ) − 20 log ω ki 20 log δ H di ( jω ) ω ki ω ωf Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 17/44
  18. 18. Application to Continuous Stirred Tank Reactors(CSTR)   1 x2 (t)  1 x1 (t) = − x1 (t) + Da (1 − x1 (t)) × exp  ˙ x2 (t) + − 1 x1 (t − τ ), λ 1+ λ γ0   1 x2 (t)  + 1 − 1 x2 (t−τ )+βu(t), x2 (t) = − ˙ +β x2 (t)+HDa (1−x1 (t))×exp  x (t) λ 1+ 2 λ γ 0 where x1 (t) is the reactor conversion rate and x2 (t) is the dimensionless temperature. Conversion 0.9 Rate 0.5 Steady-state states: x1 and x2/10 0.8 Setpoint x1 State 0.7 x2/10 0 0 5 10 15 20 0.6 Temperature 5 0.5 Setpoint 0.4 State 0 0.3 0 5 10 15 20 60 0.2 Control 40 Effort 0.1 20 0 0 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 0 5 10 15 20 Steady-state input: u Time [sec] Steady-state operating points Change of operating points Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 18/44
  19. 19. Activities in power and energy systems Sample 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. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 19/44
  20. 20. 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 balancedneutral 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. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 20/44
  21. 21. Power quality improvementPower quality is a very important problem for renewable energy anddistributed generation. Transformer DC power Inverter LC source bridge filter ia ib ic uga ugb ugc u’ga Phase-lead u’gb low-pass PWM u’gc filter modulation u’ u’ga + PLL + + u’gb + + u’gc u + θ - e + iref Internal model M - dq Id* and stabilizing + - Iq* compensator C + abc Current controller 3 #1:1 2 #1:2 Current [A] 1 0 The recorded current THD -1 was 0.99%, while the grid -2 voltage THD was 2.21%. -3 0.00 0.01 0.02 0.03 0.04 0.05 Time Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 21/44 Q.-C. [sec]
  22. 22. 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. y ˆ ˆ P (W) and Q (Var) P Q ©   Time (Second) Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 22/44
  23. 23. The basic idea (θ = 0 ) Rotor field axis Dp Rs , L Rotation - Tm 1 θ& 1 θ Js s M - M Te N Eqn. (7) Field voltage Q Eqn. (8) Rs , L Rs , L Eqn. (9) e Mf if i MThe basic idea is to adopt the mathematical model of a synchronous generatoras the core of the controller. What’s left is for the inverter to reproduce eat its terminals. Control strategies developed for conventional synchronousgenerators can be used for inverters. Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 23/44
  24. 24. Dp θr & - Reset θgPset p Tm 1 θ& 1 θ θ& n Js s - θc Fromto the power part Te Eqn. (7) Q Eqn. (8) PWM Eqn. (9) e generation - Mf ifQset 1 i Ks Dq - Amplitude v fb vm detection vr Four control parameters No conventional PI control No dq transformation etc Frequency control, voltage control, real power control and reactive power control are packed in one controller Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 24/44
  25. 25. Parallel operation of inverters S1 = P1 + jQ1 S 2 = P2 + jQ2 Vo ∠0 o Ro1 Ro 2 ~ E ∠δ 1 1 Z E 2 ∠δ 2 ~ E*Conventional droop controller Ei - Pi vo ni vr Ei = E ∗ − ni Pi , 1 Qi i ωi = ω ∗ + mi Qi , mi s ω it+δ i ω*Limitations: Ei should be the same The per-unit output impedance should be the same } =⇒ Not robust at all ! Fundamental trade-off between the power sharing accuracy and the voltage drop Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 25/44
  26. 26. Robust droop controller (Patent pending) E* Ke - RMS Ei 1 - ni Pi s vo vri 1 Qi i mi s ω it+δ i ω* Accurate sharing of both real power and reactive power Excellent voltage regulation Low THD Fast response Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 26/44
  27. 27. Experimental results Reactive Power [Var] 28 2 24 P1 P2 0 Q1 Q2 Real Power [W] 20 −2 16 −4 12 8 −6 4 −8 0 −10 −4 −12 0 1 2 3 4 5 6 7 8 9 10 11 12 0 1 2 3 4 5 6 7 8 9 10 11 12 Time [s] Time [s] 28 24 Output Voltage [V] 24 E1 E2 16 vo Voltage [V] 20 8 16 0 12 8 −8 4 −16 0 −24 0 1 2 3 4 5 6 7 8 9 10 11 12 7 7.01 7.02 7.03 7.04 7.05 7.06 Time [s] Time [s] 4 10 i1 i2 9 THD of vo [%] 2 8 Current [A] 7 6 0 5 4 −2 3 2 1 −4 0 7 7.01 7.02 7.03 7.04 7.05 7.06 0 1 2 3 4 5 6 7 8 9 10 11 12 Time [s] Time [s] Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 27/44
  28. 28. C-invertersThe output impedance of an inverter is normally inductive and can bemade resistive. Is it possible to make it capacitive? Yes, and it turns outto 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 6 4 2 The gain factor 0Optimal capacitance to eliminate the −2 Original inductor −4h-th harmonic voltage: −6 3rd only 1 −8 Co = (hω ∗ )2 L −10 3rd and 5th −12 5th only −14 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 ω/ω* Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 28/44
  29. 29. C-inverters R-inverters 28 28 24 P1 P2 24 P1 P2 20 20 P [W] P [W] 16 16 12 12 8 8 4 4 0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 0 1 2 3 4 5 6 7 8 9 10 11 12 Time [s] Time [s] 4 4 2 Q1 Q2 2 Q1 Q2 Q [Var] Q [Var] 0 0 −2 −2 −4 −4 −6 −6 −8 −8 0 1 2 3 4 5 6 7 8 9 10 11 12 0 1 2 3 4 5 6 7 8 9 10 11 12 Time [s] Time [s] THD of vo (%) THD of vo (%) 30 30 25 25 20 20 15 15 10 10 5 5 0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 0 1 2 3 4 5 6 7 8 9 10 11 12 Time [s] Time [s] 20 20 10 10vo [V] vo [V] 0 0 −10 −10 −20 −20 7 7.01 7.02 7.03 7.04 7.05 7.06 7 7.01 7.02 7.03 7.04 7.05 7.06 Time [s] Time [s] Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 29/44
  30. 30. Active capacitorsCapacitors are fundamental building blocks for electronic and 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 toimplement capacitors with inverters. 60 More accurate 40 Magnitude (dB) 20 More stable, e.g. w.r.t temperature 0 Ro=0.0Ω, no KR −20 Ro=0.0Ω, with KR Controllable frequency characteristics −40 Ro=0.2Ω, with KR Changing the way how active power −60 90 filters (APF) are controlled 45 Phase (deg) 0 −45 −90 −1 0 1 2 3 4 10 10 10 10 10 10 Frequency (rad/sec) Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 30/44
  31. 31. 6 10 i v i v 8 4 6 2 4 2i, v i, v 0 0 −2 −2 −4 −4 −6 −8 −6 −10 0 0.01 0.02 0.03 0.04 0 0.01 0.02 0.03 0.04 Time [s] Time [s] 10 16 8 i v 12 i v 6 8 4 2 4i, v i, v 0 0 −2 −4 −4 −8 −6 −8 −12 −10 −16 0 0.01 0.02 0.03 0.04 0 0.01 0.02 0.03 0.04 Time [s] Time [s] 20 i v 20 i v 16 16 12 12 8 8 4 4i, v i, v 0 0 −4 −4 −8 −8 −12 −12 −16 −16 −20 −20 0 0.01 0.02 0.03 0.04 0 0.01 0.02 0.03 0.04 Time [s] Time [s] Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 31/44
  32. 32. Harmonic droop controller Zo Load/grid i ~ v o1 i1 ih … ~ vr vo ↓ … ↓ … ~ voh … (a) One circuit including all harmonics S h = Ph + Qh ih voh = 0 if vrh is the same as Z o ( jhω * ) the voltage dropped on the ~ ~ ↓ output impedance Zo by v rh voh ih the harmonic current com-(b) The circuit at the h-th harmonic ponent ih .frequency Q.-C. Z :A O HONG N VERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 32/44
  33. 33. Without With 3rd and 5th harmonics droop controller 6 6 i1 i2 i1 i2 Current [A] Current [A] 4 4 2 2 0 0 −2 −2 −4 −4 7 7.01 7.02 7.03 7.04 7.05 7.06 7 7.01 7.02 7.03 7.04 7.05 7.06 Time [s] Time [s] (a) Currents 20 20 10 10 vo [V] vo [V] 0 0 −10 −10 −20 −20 7 7.01 7.02 7.03 7.04 7.05 7.06 7 7.01 7.02 7.03 7.04 7.05 7.06 Time [s] Time [s] (b) Output voltage 20 20 16 16Mag (%) THD=15.92% Mag (%) THD=8.57% 12 12 8 8 4 4 0 0 1 3 5 7 9 11 13 15 17 19 1 3 5 7 9 11 13 15 17 19 Harmonic order Harmonic order (c) Harmonic voltage components Q.-C. Z HONG : A N OVERVIEW R A COF ESEARCH CTIVITIES IN ONTROL AND S MART G RID I NTEGRATION – p. 33/44
  34. 34. Sinusoid-locked loops v = vm sin θ v i Xs e = E sin θ ~ SSM model ~When there is no power exchanged with the grid, the voltage e is the same as the terminal voltagev. That is, they have the same frequency the same phase the same amplitude Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 34/44
  35. 35. Tracking the grid voltage 70 70 70 60 60 60 50 50 50 f [Hz] f [Hz] f [Hz] 40 40 40 30 30 30 20 20 20 10 10 10 0 0 0 0 0.04 0.08 0.12 0.16 0.2 0 0.04 0.08 0.12 0.16 0.2 0 0.04 0.08 0.12 0.16 0.2 Time [s] Time [s] Time [s] (b) Frequency tracking 30 30 30 25 25 25 20 20 20 E [V] E [V] E [V] 15 15 15 10 10 10 5 5 5 0 0 0 0 0.04 0.08 0.12 0.16 0.2 0 0.04 0.08 0.12 0.16 0.2 0 0.04 0.08 0.12 0.16 0.2 Time [s] Time [s] Time [s] (c) Detection of the voltage amplitude 30 30 30 15 15 15 e [V] e [V] e [V] 0 0 0 −15 −15 −15 −30 −30 −30 0 0.04 0.08 0.12 0.16 0.2 0 0.04 0.08 0.12 0.16 0.2 0 0.04 0.08 0.12 0.16 0.2 Time [s] Time [s] Time [s] (d) Voltage tracking 10 10 10 8 8 8 THD [%] THD [%] THD [%] 6 6 6 4 4 4 2 2 2 0 0 0 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 Time [s] Time [s] Time [s] (e) THD of e 8 8 8 6 6 6 θ [rad] θ [rad] θ [rad] 4 4 4 2 2 2 0 0 0 0 0.04 0.08 0.12 0.16 0.2 0 0.04 0.08 0.12 0.16 0.2 0 0.04 0.08 0.12 0.16 0.2 Time [s] Time [s] Time [s] (e) Phase tracking Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 35/44
  36. 36. Tracking a voltage with avarying frequency With the proposed SLL With the SOGI-based PLL With the STA 70 70 70 f fv f fv f fvFrequency [Hz] Frequency [Hz] Frequency [Hz] 60 60 60 50 50 50 40 40 40 30 30 30 0 2 4 6 8 10 0 2 4 6 8 10 0 2 4 6 8 10 Time [s] Time [s] Time [s] (a) Frequency tracking 45 45 45 E vm E vm E vmAmplitude [V] Amplitude [V] Amplitude [V] 35 35 35 25 25 25 15 15 15 0 2 4 6 8 10 0 2 4 6 8 10 0 2 4 6 8 10 Time [s] Time [s] Time [s] (b) Amplitude tracking Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 36/44
  37. 37. Tracking a square wave 40 With the proposed SLL 40 With the SOGI-based PLL 40 With the STA 20 20 20 v [V] v [V] v [V] 0 0 0 −20 −20 −20 −40 −40 −40 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 Time [s] Time [s] Time [s] (a) Input signal 100 100 100 f fv f fv f fv Frequency [Hz] Frequency [Hz] Frequency [Hz] 80 80 80 60 60 60 40 40 40 20 20 20 0 0 0 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 Time [s] Time [s] Time [s] (b) Frequency tracking 50 50 50 E vm E vm E vm Amplitude [V] Amplitude [V] Amplitude [V] 45 45 45 40 40 40 35 35 35 30 30 30 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 Time [s] Time [s] Time [s] (c) Amplitude tracking 60 60 60 30 30 30 e [V] e [V] e [V] 0 0 0 −30 −30 −30 −60 −60 −60 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 Time [s] Time [s] Time [s] (d) Recovered voltage e 15 15 15 THD [%] THD [%] THD [%] 10 10 10 5 5 5 0 0 0 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 Time [s] Time [s] Time [s] (e) THD of e 8 8 8 θe v θe v θe v 6 6 6 θ [rad] θ [rad] θ [rad] 4 4 4 2 2 2 0 0 0 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.12 0.14 0.16 0.18 0.2 Time [s] Time [s] Time [s] (f) Phase tracking Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 37/44
  38. 38. AC Ward Leonard drive systemsExtended the concept of Ward Leonard drive systems to AC machines. Inverter Load Variable Prime speed mover Load Prime VDC SG SM/IM Constant Variable mover speed speed Variable speed Fixed field Controllable field Fixed field (a) Conventional (DC) Ward Leonard drive systems (b) AC Ward Leonard drive systemsPotential application areas: High-speed train drive systems Ship drive systems Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 38/44
  39. 39. Wind turbine control Power Processing Unit Tr Tg us UDC u Wind Aerodynamics Drive-train Generator Rotor-side Grid-side v (Rotor blades) Converter Converter Grid ωr ωg is IDC i Pitch/yaw/stall/brake Control ? Control Energy Control Control Storage System ControlThe wind turbine, patented and donated by Nheolis, France, was installed on the EEE building at Liverpool. Q.-C. Z HONG : A N OVERVIEW OF R ESEARCH ACTIVITIES IN C ONTROL AND S MART G RID I NTEGRATION – p. 39/44

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