Consensus-based Control for Microgrids

4TH IEEE SOUTHERN POWER ELECTRONICS CONFERENCE(SPEC 2018) Enhanced Consensus-based Distributed Control for Accurate Reactive Power Sharing of Islanded Microgrids Without LBC lines

Author: Aiting Jiang, Yang Han, Ping Yang, Congling Wang, Jingqi Xiong Presenter: Aiting Jiang, Master Student

School of Mechanical and Electrical Engineering University of Electronic Science and Technology of China, Chengdu, P. R. China December 11, 2018

Content

Background and Significance Hierarchical Control for Microgrid

Proposed Control Scheme Simulation Results Conclusion

1. Background and Significance ◼ Distributed generation (DG)

wind energy biomass energy

Distributed energy

natural gas

Decentralized

solar energy ocean energy

Other energies

Centralized

Advantages： Taking a full use of the clean energy and renewable energy resource(RES). Disadvantages: High randomness and volatility, uncontrolled system, applying in the low-voltage network.

(microgrid)

1. Background and Significance Microgrid main grid

Transformer

central controller

local controller

Wind turbine

Communication network

Battery Nonlinear loads

PV DC Bus

Features of MGs： • •

Two model (grid-connected or islanded); Schedulability.

Fig. 1. A typical MG structure in IEEE P1547.1 • •

Various distributed generators； smooth transition between islanded and grid-connected modes；

2. Hierarchical Control for Microgrid DGi Loi

Lii

Vdc,i

Load

+

−

Cfi

ilabc

ioabc

vabc

• the primary control

Virtual Impedance Control

Voltage & Current Inner Loop Control Droop Control

Primary Control

P Q

Power Calculator

keep the desired voltage and frequency values and active/ reactive power sharing.

Low Band-Width Communication

MG

+

k pf +

kif sec s

Esec

k k pe + ie s

−

* EMG

+

* MG −

• the secondary control

EMG

Secondary Control

Fig. 2. An islanded Microgrid with the typical hierarchical control method

eliminate the error of the output voltage and frequency caused by the droop control.

3. Proposed Control Scheme for Islanded Microgrid System Question ： ✓ How to achieve accurate active and reactive power sharing? ✓ How to maintain the frequency of the output voltage of each DG at the rated value without communication delay? ✓ How to maintain the voltage amplitude of the output voltage of each DG at the rated value without communication delay? Droop Control for Microgrids To achieve the accurate power sharing among multiple DG units, and ensure the stability of voltage and frequency :

 =  * − k pd ( P − P* )

E = E * − kqd ( Q − Q* )

(1)

where ω* and E* denote the rated angular frequency and the rated amplitude, respectively. kpd and kqd are the control parameters of the droop controller. P and Q are the DG unit active power and reactive power, respectively. P* and Q* are defined as the rated active power and reactive power, respectively, which are usually set as 0.

3. Proposed Control Scheme for Islanded Microgrid System BPF based Control for Microgrids Secondary control

 = − *

Frequency restoration

c  k pf + 1 s + c k pd



s+

Droop control

s kif

p

(2)

k pf + 1

band − pass

E = E* − Amplitude restoration Droop control

Fig. 3. The detailed secondary control structure for the frequency and voltage restoration.

c  k pe + 1 s + c kqd



s  q (3) kie s+ k pe + 1

band − pass

where kpf and kif are the parameters of the PI controller in the secondary frequency control and kpe and kie are the parameters of the PI controller in the secondary amplitude control.

From (2) and (3), it can be concluded that the secondary control strategy with the LBC delay consideration can be recognized as an enhanced droop control method with the band-pass filter (BPF) and it is intrinsically an ideal secondary control without communication delay, which helps to solve the problem of the time delay existed in the secondary control.

3. Proposed Control Scheme for Islanded Microgrid System Consensus-based Control for Microgrids uQi = −cQ   ij ( kqd i Qi − kqd j Q j )

(4)

j N i

where cQ is the coupling gain. The Overall Control Strategy

DGi

Power System

Ei(sinωit)

ωi Dq0->abc ->αβ Ei

Voltage PI Controller

BPF Regulator

Ei + ωi +

p

* j

-

Ei

s s + h

c s + c

kpdi

s s + h

s + c

ωi *

pi*

c  jNi

P

ij

++

1 s

( P − Pi ) *

Reactive Power Sharing Regulator

q*j

 cQ ij (niQi − n jQ j )

uQi

jNi

x1

kQ_L Di(s)

DG/Node

x2

Inverter i Voltage & Current Measurement

c

Active Power Sharing Regulator * j

SPWM

kqdi *

-

Current PI Controller

kQ_R

pi*

Active Power Calculator

Reactive Power Calculator

LPF

LPF

vQdq

LV,i RV,i

N

j∈Ni Cyber Layer

Power Grid

Primary Control

Pi, kpdi xn

x3

1

i

 ( n −1) n

xi

x4

Graph Model

2

Qi, kqdi

Fig. 4. The proposed BPF+consensus-based enhanced distributed reactive power sharing control strategy.

DG1

Li

Li

Zline1

Lo

STS1 Load1

Zline2

TABLE I

PARAMETERS OF THE SYSTEM

Symbol

Values

DC Link Voltage (Vdc) Sampling and switching period(Ts) Fundamental frequency (ω0) Parameters of the LCL Filter (L)

LDG1&RDG1 LDG2&RDG2 LDG3&RDG3 LDG4&RDG4

650V 100μs 100π rad/s Li= Lo=1.8 mH,Cf=25 μF kpd 1= kpd 2=0.001 rad/s/W, kpd 3= kpd 4=0.002 rad/s/W kqd1= kqd2=0.001 V/Var, kqd3= kqd4=0.002 V/Var Lline1=1.5mH rline1=0.25Ω Lline2=2.26mH rline2=0.2Ω Lline2=1.8mH rline2=0.15Ω Lline2=1.1mH rline2=0.1Ω

Load1

Lload1=0.182H rload1=200Ω.

Load2

Lload2=0.138H rload2=120Ω.

Load3

Lload3=0.207H rload3=85Ω.

kpd1，kpd2，kpd3，kpd4

Cf

DG2 DG3

Li

Lo

kqd1，kqd 2，kqd 3，kqd 4

Zline3

STS2 Load2

Cf Li

DC Source

DC Source

Lo Cf

DC Source

DC Source

4. Simulation Results

Lo

Zline4 STS3 Load3

DG4

Cf

STS4

Fig. 5. Structure of the paralleled-connected DG units in an islanded MG.

Parameters of

the BPF

Communication delay

4π, 10π Td=7.2ms

To evaluate the effectiveness of the proposed power sharing control strategy, an islanded MG is established, which consists of four parallel DG units. As shown in Fig.4, the MG system operates on the unequal feeder impedance and resistive-inductive load conditions. The different load and feeder impedance conditions are controlled by the switch (SW) 1, 2, 3 and 4. Each DG unit is connected to an LCL filter and the parameters of the system is shown in TABLE I.

4. Simulation Results Case-1: Load Disturbance Condition

f1 f2 f3 f4

Load 1 cutoff

Load 1&2 cutoff

f1 f2 f3 f4

Active Power (W)

P3

(a)

P2 P4

P1

P2

P3

P4

(b)

Q4

Q3

Q1

Q2 (c)

Reactive Power (W)

Reactive Power (W)

Active Power (W)

(a) P1

Q1 Q3

Loads connection

Loads connection

Frequency (Hz)

Loads connection

(b) Q2 Q4

(c)

Active Power (W)

Loads connection

Reactive Power (W)

Frequency (Hz)

Load 1&2 cutoff

Frequency (Hz)

Load 1 cutoff

Loads connection

Load 1 cutoff

Load 1&2 cutoff

Loads connection

f2 f3

f1

f4

(a) P1

P2

P3

P4

(b) Q1 Q3

Q2 Q4

(c)

Fig. 6. Performance of the islanded microgrid Fig. 7. Performance of the islanded microgrid Fig. 8. Performance of the islanded microgrid with with the conventional droop control. with the consensus-based control scheme. the proposed control scheme.

• frequency has errors； • the reactive power is failed to be shared proportionally； • remarkable ripples due to the communication delay.

• frequency has errors； • remarkable ripples due to the communication delay.

• accurate active and reactive power sharing； • rated frequency and voltage amplitude; • smooth and stable.

4. Simulation Results Case-2: Feeder Disturbance Condition

Reactive Power (W)

Active Power (W)

(a)

P1 P2 P3

P4 (b) Q3

Q1

Q2

Q4 (c)

f2

f3

(a)

P1 P2 P3

P4

Frequency (Hz)

f1

Active Power (W)

f3

f4

(b) Q3

DG 4 Cutoff

DG 1, 2, 3 and 4 connection

f1

f2

f4

f3

(a)

P1 P2 P3

P4 (b)

Q1

Q2

Q4 (c)

Reactive Power (W)

Frequency (Hz)

f2

Active Power (W)

f1

Reactive Power (W)

Frequency (Hz)

f4

DG 4 Cutoff

DG 1, 2, 3 and 4 connection

DG 4 Cutoff

DG 1, 2, 3 and 4 connection

Q3

Q1

Q2

Q4 (c)

Fig. 9. Performance of the islanded microgrid Fig. 10. Performance of the islanded microgrid Fig. 11. Performance of the islanded microgrid with the conventional droop control. with the consensus-based control scheme. with the proposed control scheme.

• frequency has errors； • the reactive power is failed to be shared proportionally； • remarkable ripples due to the communication delay.

• frequency has errors； • remarkable ripples due to the communication delay.

• accurate active and reactive power sharing； • rated frequency and voltage amplitude; • smooth and stable.

5. Conclusion ➢ Conclusion ✓ This paper proposes a new enhanced consensus-based distributed control scheme to

ensure the reactive power sharing in the islanded microgrid, which combing the consensus-based control and the BPF controller. In this paper, the consensus concept is introduced to achieve the accurate reactive power sharing and the BPF controller is applied to solve the problem of the communication delay caused by the LBC.

✓ In addition, it has been proven that the BPF can be considered an ideal secondary control without the time delay. Compared to the conventional droop control and the consensus-based control strategy, the proposed control strategy can not only ensure the accurate power sharing under the disturbance situation, but also adjust the frequency of the microgrid to the rated value. Moreover, it offers a fast dynamic response and a strong robustness during the transient time.

✓ Finally, the simulation results are presented to validate the effectiveness of the proposed control strategy.

7. References [1] Yang Han*, Hong Li, Pan Shen, Ernane A. A. Coelho, Josep M. Guerrero, Review of active and reactive power sharing strategies in hierarchical controlled microgrids, IEEE Transactions on Power Electronics, vol.32, no.3, pp.2427-2451, March 2017. [2] Yang Han*, Pan Shen, Xin Zhao, Josep M. Guerrero, Control strategies for islanded microgrid using enhanced hierarchical control structure with multiple current-loop damping schemes, IEEE Transactions on Smart Grid, vol.8, no.3, pp.1139-1153, May 2017. [3] Yang Han*, Mingyu Luo, Xin Zhao, Josep M. Guerrero, Lin Xu, Comparative performance evaluation of orthogonal-signal-generators based single-phase PLL algorithms – A survey, IEEE Transactions on Power Electronics, vol.31, no.5, pp.3932-3944, May 2016. [4] Yang Han*, Ke Zhang, Hong Li, Ernane A.A. Coelho, Josep M. Guerrero, MAS-based distributed coordinated control and optimization in microgrid and microgrid clusters: A comprehensive overview, IEEE Transactions on Power Electronics, vol.33, no.8, pp.6488-6508, August, 2018. (Highlighted paper)

[5] Yang Han, Xu Fang, Ping Yang, Congling Wang, Lin Xu, Josep M. Guerrero*, Stability analysis of digital controlled single-phase inverter with synchronous reference frame voltage control, IEEE Transactions on Power Electronics, vol.33, no.7, pp.6333-6350, July 2018. [6] Yang Han*, Hong Li, Lin Xu, Xin Zhao, Josep M. Guerrero, Analysis of washout filter-based power sharing strategy—an equivalent secondary controller for islanded microgrid without LBC lines, IEEE Transactions on Smart Grid, vol.9, no.5, pp.4061-4076, September 2018. 13

7. References [7] Yang Han*, Lin Xu, M. M. Khan, Chen Chen, Gang Yao, Li-Dan Zhou, Robust deadbeat control scheme for a hybrid APF with resetting filter and ADALINE-based harmonic estimation algorithm, IEEE Transactions on Industrial Electronics, vol.58, no.9, pp.3893-3904, September 2011. [8] Yang Han*, Aiting Jiang, Ernane A.A. Coelho, Josep M. Guerrero, Optimal performance design guideline of hybrid reference frame-based dual loop control strategy for standalone single-phase inverters, IEEE Transactions on Energy Conversion, vol.33, no.2, pp.730-740, June 2018. [9] Yang Han*, Zipeng Li, Ping Yang, Congling Wang, Lin Xu, Josep M. Guerrero, Analysis and design of improved weighted average current control strategy for LCL-type grid-connected inverters, IEEE Transactions on Energy Conversion, vol.32, no.3, pp.941-952, September 2017. [10] Yang Han*, Pan Shen, Xin Zhao, Josep M. Guerrero, An enhanced power sharing scheme for voltage unbalance and harmonics compensation in an islanded AC microgrid, IEEE Transactions on Energy Conversion, vol.31, no.3, pp.1037-1050, September 2016.

For detailed description, please refer to the following link: http://faculty.uestc.edu.cn/hanyang/en/index.htm 14

4TH IEEE SOUTHERN POWER ELECTRONICS CONFERENCE(SPEC 2018)

Thank you!

Author: Aiting Jiang, Yang Han, Ping Yang, Congling Wang, Jingqi Xiong Presenter: Aiting Jiang, Master Student

School of Mechanical and Electrical Engineering University of Electronic Science and Technology of China, Chengdu, P. R. China December 11, 2018