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Development of a Plug-in Type Synchronous Inverterfor Grid Stability Enhancement

Yutaka Sasaki, Shinya Sekizaki, and Naoto Yorino（Hiroshima university)Best Western Plus Hotel, May 14-17, 2017 in Wiesloch, Germany

Presenter: Yutaka Sasaki and Shinya Sekizaki

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Outline

Background

Synchronous inverter (SI)

Experimental example

Application for west Japan model

Summary

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Background

Difficulties in system operations due to rapidincrease in renewable energy sources such as PV

Implementation of virtual inertia into an inverter such as PV‐PCS improves the system damping.

In West Japan interconnected system, the grid operation is limited by transient stability, which is an important subject to be studied from the point of view of grid operation.

[1] N. Yorino, Y, Sasaki, “Power System Reliability Monitoring and Control for Transient Stability”, The 14th International Workshop on EPCC , Wiesloch, Germany, May 14‐17, 2017

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Outline

Background

Synchronous inverter (SI)

Experimental example

Application for west Japan model

Summary

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Purpose

Synchronous machine

Synchronization

Transmission line

Introduction of renewable energy sources

Renewable energy sources

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Purpose

Synchronous machine

Transmission line

Introduction of renewable energy sources

Renewable energy sources

Disconnection

Introduction

Synchronization

Phase detection

Phase detection

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Weak damping by RESs

Strong dampingTime

FaultFault

Synchronization

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Weak damping by RESs

Inverter

Reactance

DC/DC converter

Phase detection

TrackingPower

Strong dampingTime

Time

Weak damping

Fault

FaultReplace

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Synchronous inverter (SI)Inverter

Reactance

DC/DC converter

Inverter

Storage device

DC/DC converter

Phase detection

TrackingPower

Power

Power

Like synchronous machine

Synchronous inverter

Normal inverter

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Single-phase synchronous inverter

X

invinvinv Vv sin2

A single-phase winding

Rotorθinv

Single-phase inverter iinv

iinv

Damping coefficient

Energy balanceem

invinv PPdtdD

dtdM

2

2

Inertiacoefficient

Internal dynamic rotating mass model

Δθ

vgrid

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Transmission line

Damping enhancement by SIs

Time

Multiple SIs

Synchronization by synchronizing power

Damping

Desired behavior like SM

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Single-phase micro grid by SIs

Single-phase SIs

Fault

DisasterLoads

single-phase micro grid

Steady-state

IslandedoperationFault

Time

Resiliency

Volta

ge

Fault

Stable operation

Freq

uenc

yStrong damping

Weak damping

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Disturbance by multiple loops

Voltage controller

Current controller

+

－

+

Current

Reference current

－

Voltage

Reference voltage

Internal dynamic rotating mass model

+Automatic Voltage Regulator (AVR)

sLR 1

mP

eP

DMss 1 inv

sC*inv

invinv *

Multiple feedback loops

Multiple loops with bad parameters disturb the desired behavior

tracking tracking

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Direct implementation

Current

Gate signalInternal dynamic rotating mass model

+Automatic Voltage Regulator (AVR)

PWM

Protection controller

sLR 1Voltage

Inverter

Direct implementation

mP

eP

DMss 1 invinv *

The desired behavior is directly implemented in steady state contribution to the strong damping

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Plug-in operation

Time

vgrid vinv

vgrid vgrid

vinv vinvAutomatic synchronization

& connectionPlug-in Synchronization

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Outline Background

Synchronous inverter (SI)

Experimental example

Application for west Japan system model

Summary

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Experimental Example

[V] [A] [Hz]

BatteryDC48[V]

Inv.

DC/DC DC/DC DC/DC DC/DC DC/DC

SI ControllerMyway PE‐Expert 4

To Utility

• Construction the laboratory experiments to performed the examination of SI.

• Demonstration an independent micro‐gird operation using five inverters and storage batteries.

• Low voltage distribution   line of 100 [V] (Japanese typical V std.) is used with real load, a single‐phase short fault circuit.

Measurements

Outlets

BatteryDC48[V]

BatteryDC48[V]

BatteryDC48[V]

BatteryDC48[V]

Inv. Inv. Inv. Inv.

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Synchronous Inverter (SI) UnitCharacteristics:The proposed SI can connect/disconnect  easily and flexibility to single‐phase outlets (Japanese Std. AC100V)

The application of SI are PV‐PCSs, Home Batteries, and EVs.

Single‐phaseInverter 1kVA(Myway Plus)

SiC DC/DCConverter 3kVA(Myway Plus)

Lead‐acid Battery48V (12Vx4)(GS YUASA)

To single‐phaseAC100V

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Single-phase MG using Five SI

5‐inverter (SI) units with storage batteries

Digital Controller for SI

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Outline Background

Synchronous inverter (SI)

Experimental example

Application for west Japan model

Summary

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Xdʼ generator swing modelDynamics of the Xd’ generator model in the SI.The system damping of West Japan system assuming that a large amount of the proposed inverter is introduced.

Power Swing Equation:2

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inv invinv inv inv iuv inv inv gridm m

m m gov ed dM D K P P Pdt dt

1

invgovinv

gov ref invinvgov

KP

T s

Stability Evaluation by using Eigenvalue

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West Japan system model (case1)

Contingency3LG‐Fault

Improvement  of the systemdampingby using SI.

West Japan system model: 30‐machines

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Stability analysis using Eigenvalue○: Conventional Gen. only○: Conventional Gen. + SI (the capacity of 10% G1)○: Conventional Gen. + SI (the capacity of 20% G1)

Real

Imag.

The effect ofstabilizationBy using SI

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West Japan system model (Case2)

Contingency3LG‐Fault

Improvement  of the systemdampingby using SI.

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Stability analysis using Eigenvalue○: Conventional Gen.○: Conventional Gen. + SI(ALL 10%)○: Conventional Gen. + SI(ALL 20%)

Improvement ofthe stability of west Japan system 

Real

Imag

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Outline Background

Synchronous inverter (SI)

Experimental example

Application for west Japan model

Summary

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Summary

The proposed synchronizing inverter (SI)has the characteristics of virtual inertiaand more effective function to improve the system damping.

(1) Proposed SI and its controller(2) Experimental study is going on.(3) The effect of proposed SI for West Japan system