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A control method of distributed generators in smart distribution system considering system loss and voltage. Pyeongik Hwang School of Electrical Engineering Seoul National University Korea. Hwang – Korea – RIF Session 4a – 0324. Introduction.

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slide1

A control method of distributed generators in smart distribution system considering system loss and voltage

Pyeongik Hwang

School of Electrical Engineering

Seoul National University

Korea

Hwang – Korea – RIF Session 4a – 0324

slide2

Introduction

  • Increased installation of distributed generations(DGs)
    • The characteristics of the distribution system is changed
      • Voltage profile, system loss, power flow, etc.
  • Introduction of the smart distribution system
    • The status of the distribution system can be measured and calculated more accurately
    • The power output of DGs can be controlled using the communication infrastructures.

 Chance to more effective operation using DGs

Hwang – Korea – RIF Session 4a – 0324

slide3

DG control problem formulation

  • The objectives of the proposed method
    • Minimize the system loss
    • Maintain the system voltage within its limit

- Minimize

- Subject to

Hwang – Korea – RIF Session 4a – 0324

slide4

Sequential Linear Programming

  • Relationship among loss, voltage, and output of DGs is highly non-linear
    • Formulated DG control problem is a non-linear optimization problem
  • Sequential Linear Programming(SLP) method is adopted
    • Optimal solution is calculated by solving series of linear programming (LP) problem linearized at the operation point
    • Operation point is determined at the previous iteration

Hwang – Korea – RIF Session 4a – 0324

slide5

SLP application to DG control

  • Sub-functions of SLP
    • LP formulation
    • Step size adjustment
    • Convergence test
  • Decision variable for LP

Hwang – Korea – RIF Session 4a – 0324

slide6

LP formulation

Loss sensitivity matrix

  • Linearized Optimization problem

-Minimize

-Subject to

Voltage sensitivity matrix

Injection power sensitivity matrix

Hwang – Korea – RIF Session 4a – 0324

slide7

LP formulation

  • Differences between distribution system and transmission system
    • Existence of mutual impedance in line parameter
    • Unbalanced connection of DGs
  • Bus admittance matrix with mutual line impedance
    • Used for calculation of loss and voltage sensitivity matrices

A : bus incidence matrix, [y] : primitive admittance matrix.

Hwang – Korea – RIF Session 4a – 0324

slide8

LP formulation

  • Differences between distribution system and transmission system
    • Existence of mutual impedance in line parameter
    • Unbalanced connection of DGs
  • Bus admittance matrix with mutual line impedance
    • Used for calculation of loss and voltage sensitivity matrices

A : bus incidence matrix, [y] : primitive admittance matrix.

Hwang – Korea – RIF Session 4a – 0324

slide9

LP formulation

  • Injection power sensitivity matrix calculation method

Hwang – Korea – RIF Session 4a – 0324

slide10

SLP application to DG control

  • Step size adjustment
    • Prevent oscillation in SLP
  • Convergence test

Hwang – Korea – RIF Session 4a – 0324

slide11

Proposed method

  • Flow chart of the proposed method

Hwang – Korea – RIF Session 4a – 0324

slide12

Case Study

  • IEEE 37 node test feeder system with three DGs

DG 1

A-B-C phase

DG 2

A-B phase

DG 3

B-C phase

Hwang – Korea – RIF Session 4a – 0324

slide13

Initial voltage vs. voltage limit

  • Under voltage violation is occurred in case 2 and case 3

Under Voltage

Hwang – Korea – RIF Session 4a – 0324

slide14

Performance of the proposed method

  • The proposed method is implemented as a Matlab code
    • Matlab provided function “linprog” is utilized as the LP solver
  • Comparing with results of the function “fmincon”
    • Maximum error is less than 0.1%
    • Proposed method is at least 90 times faster than fmincon

Hwang – Korea – RIF Session 4a – 0324

slide15

Case 1 ( Vmin = 0.97 p.u., Vmax = 1.03 p.u. )

  • The system loss is reduced about 19 %(97kW 78 kW)

 Operation cost can be reduced by minimizing the loss

Hwang – Korea – RIF Session 4a – 0324

slide16

Case 2 ( Vmin=0.98 p.u., Vmax=1.02 p.u.)

  • Without proposed method, tap position of OLTC must be changed to eliminate the voltage violation
    • Increasing operation cost
  • With proposed method, Under violation is eliminated without tap changing

 System operation cost can be reduced by preventing the tap changing of OLTC

 System stability can be improved by maintaining system voltage within its limit

Hwang – Korea – RIF Session 4a – 0324

slide17

Case 2 ( Vmin=0.98 p.u., Vmax=1.02 p.u.)

  • System voltage

Hwang – Korea – RIF Session 4a – 0324

slide18

Case 3 ( Vmin=0.985 p.u., Vmax=1.015 p.u.)

  • Tap changing to eliminate the under voltage violation

 New over voltage violation is occurred

Over voltage

Hwang – Korea – RIF Session 4a – 0324

slide19

Case 3 ( Vmin=0.985 p.u., Vmax=1.015 p.u.)

  • System voltage can be maintained within its limit

 Power quality can be enhanced by controlling the voltage more tightly

Hwang – Korea – RIF Session 4a – 0324

slide20

Conclusions

  • DGs control problem was formulated as a non-linear optimization problem.
  • Sequential Linear Programming (SLP) based DGs control method was proposed
  • Effects of the proposed method were identified
    • Operation cost reduction
    • System stability improvement
    • Power quality enhancement

Hwang – Korea – RIF Session 4a – 0324

slide21

Thank You !

(hpi@powerlab.snu.ac.kr)

Hwang – Korea – RIF Session 4a – 0324