Empc 8-110329 a[1]

Electric Machines and the Power ConversionsElectric Machines and the Power Conversions for Renewable Systems

Dc Grid Connections

Jung-Ik HaAssistant ProfessorSchool of Electrical EngineeringSchool of Electrical EngineeringSeoul National University

Background

Renewable Energy System and Grid Connections

– Considerations

• Energy Flow

– (Negative) Unidirectional

– Bidirectional

• Safety: Grounding

Non Isolation– Non-Isolation

– Isolation

• Regulation: Filteringegu at o : te g

– EMI

Page 2ENERGYCONVERSION___________

Grid Connected Buck Converter

Page 3

Buck Converter

Basic Form

– Uni-Directional DC LOAD

– Bi-directional

• Synchronous Rectification

Operation StatesOperation States

– On: Charging

– Off: Fly-wheelingy g


Power Delivery Grid Connection

– Power Delivery

Power Control

– Voltage Control Mode

V (Vflt ) Vd• Vo ↔ (Vflt ↔) Vdc

• Voltage Source ↔ Voltage Source

– No Current LimitNo Current Limit

. Converter : Cout

. Filter : Cflt, Lfltflt flt

. Line : Rline, Cline, Lline1, Lline2

– Disturbance

Power Circulation


Power Delivery Grid Connection

– Object: Power Delivery

In Renewable System

– Power Control

C t C t l• Current Control

– Transmission Line

– Additional FilteringAdditional Filtering

– RES Model Considerations


Power Control Current Based Power Control

ogav VPI /** I

g

dtdILVV L

oi DCRESrViV oV

– Averaged Assumption in T

DT

1 ir vsfv i

DT

ir DVdtvT

V 01

di Rdi 1dtdiLRiVV or or VV

Li

LR

dtdi

1

A or VVBAxx



– Closed LoopI

• Assumptions

: ∆Vo= ∆Vi=0 @t=0~T

Output Feedforward• Output Feedforward

: Vff=Vo

or VVBAxx

iRdi 1 iG 1

rvL

iLdt

RLsvG

rp

• PI Control

sKKG i

pc s

KsKG ip

c



– Closed Loop

• PI Control

– Pole-Zero Cancellation

K RK p RLsLsK

G pc

K

LK p

i

LsK

G po

LKLsKi

c

c

p

p

p

p

sLKsLK

LsKLsK

ii

1*

swc *5/1 : Decoupling of Discrete System

Ttvv 0@01


Ttvv oi ..0@0,1

Power Control Vin Consideration

– Anti-windup

• Integration Problem

: Vo* Saturated Fast Recovery

VPI /** dcVPI /**

LIIe *

ino DVVu *


Power Control Vin Consideration Li i d I Vin Consideration

– Anti-windup• Limited Integrator

• Limited Integrator

– High Feedback Gain

– Uin = Limit + Kp*eg

– Hard Limit Imposed

• Tracking Anti-windup • Tracking Anti-windup

– with unrestricted control signal

– Recursive Problem


Power Control Vin Consideration

– Anti-windup

• Tracking Anti-windup

– Back Calculation

One Step Delay– One-Step Delay

Ks = 1/Kp

(multiplied by 1/3~3)(multiplied by 1/3 3)


Transmission Line Line Consideration

: Ideal Voltage Source Case

– Model

– Original

– Exact Model ILine +ΔILine

• Check Point: ΔILine

• On State

• Off State


Transmission Line Line Consideration

– Approximated Model

1 lineI designedVo :

ttriVV rpo

Line DropsLR

Vi o

LjR

Vi o

Line Drop

– Delivered Power Offset, Losses

• Approximated Modelpp

– R Loss: Pr = R*I^2

– G Loss: Pg = G*V^2

• Line Loss Compensation Required

P = P1 + Pr + Pg


Current Harmonics Control Conducted EMI

– AC Case

• 2~40th Order Harmonics Limits: Differential Mode

– IEC61000-3-2,12, IEEE519

150kHz(450kHz) 30MHz: Differential and Common Modes• 150kHz(450kHz)~30MHz: Differential and Common Modes

– CISPR 22(FCC)

– DC CaseDC Case

• No Regulation Currently.

• Standards for Vehicles, Ships, and Others in the Restricted Grids


Current Harmonics Control Countermeasure: Reduction of Conducted EMI

– Lower Voltage Ripples

• C: Higher Co, Lower ESR

• L: Higher Lc, Lower R

Higher Switching Frequency• Higher Switching Frequency

– Additional Filter(s)


RES Model Renewable Energy System Model

– Voltage Source

• Same

– Power Source

Control ObjectVDCVoVinIs

Vr

• Control Object

– Vin Vi*

.Ex) Dual Stage Cascade Control.Ex) Dual Stage Cascade Control

– Exact Models


RES Model Dual Stage Cascade Control

– Inner Loop: Current Control

• Model

Feedforward

dtdiLRiVV or

• Feedforward

off VV uffr VVV dtdiLRiVu

sLRVi

u

1

iiGcVu * iisLR

Gci

*

GcsLR

Gc

ii *

Gci*

• Pole-Zero Cancellation

sLR sLR

Gci

1 GcsLRi *

KK

sLRsLK

Gc p K

s

LK

KsLK

ii

p

p

p

p

1* L

K pc


Ls

sL1


– Outer Loop: Voltage Control

dVC 2• Model

Feedforward: Pin

oininin PP

dtdVC

2

2ff PP • Feedforward: Pin

• IP Control

inff PP

o

ininin

iinp V

PVVs

KVKi

**

o

inin

iinpo

inin VVs

KVKVdt

dVC *2

2 oininin

iinpo ViPVV

sKVKV **

• Bias Point Details

– Taylor 1st: 020

2 2 inininin VVVV

inin

iinpoinin VV

sKVKVsVC *



– Outer Loop: Voltage Control

• Transfer Function

20ii

io

i VCKV

V

• Gains

22

00

2

0* 2 nn

n

inin

io

inin

po

inin

in

in

ssVCKVs

VCKV

s

VCVV

Gains

o

ininnp V

VCK*

2o

ininni V

VCK*

2

• Bandwidths

21

24421 242 BW 24421 242 nBW


EMI Measurement LISN: Line Impedance Stabilization Network

– Configuration

– ExampleExample


EMI Measurement LISN: Line Impedance Stabilization Network

– Measurement Gain

Common and Differential Modes– Common and Differential Modes


HW5 Grid Buck Converter Design : Due to 4/7 Consider the Converter Designed in HW4

You can change parameters in order to improve the performance.

1) Using Power Source Model Design Controller1) Using Power Source Model, Design Controller. Line Inductance=50uH, Cap=0, R=0, G=inf,

2) Discuss about the Step Response: Vin* = 100V, Pin=90 step(t1) +10 W, Compare the results with/without the Feed forward Control.

3) Discuss about the Steady-State performance: Vin* = 100V, Pin=100W4) Vin* = 100V, Pin=100W) ,

A. FFT of Current Ripples @150k~30MHz?B. Adjust Co to reduce the peak harmonic component to 1/2.C D i d I t Filt ith t Adj ti C t d th kC. Design and Insert Filter without Adjusting Co to reduce the peak

harmonic component to 1/2. (option)5) FFT of the Differential Mode Current in the LISN @150k~30MHz, Vin*

= 100V, Pin=100W? Neglect Line Impedance.



Education

Empc 8-110329 a[1]