Topology Simplification Method based on Switch ... - Power on · 9/23/2015 · Topology...

Renewable Energy and Vehicular Technology Lab

Topology Simplification Method based on Switch Multiplexing Technique to Deliver DC-DC-AC Converters for Microgrids

Wen Cai, Shanxu Duan, Fan Yi & Babak Fahimi

HUST & UTDallas

September , 2015

Some pictures are from www.google.com

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Introduction

List of contents

Topology simplification with switch multiplexing

Conclusion

Experimental results

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1. Inclusion

In microgrid, various sources and loads with different electrical characteristics are connected together,

like solar panels, wind generators, batteries, fuel cells, utility grid and AC motors. Conventionally, several

converters are used with the common DC bus.

Background

Common DC bus

Fuel cell

Wind turbine

Battery

Solar panel

DC/DC

DC/DC

DC/DC

DC/DC

DC/AC

DC/AC

AC motor

Utility grid

For energy generating devices, like fuel cell and solar panel, unidirectional DC-DC converters are necessary;

For utility grid and AC motor, bi-directional DC-AC converters are required;

For energy storage devices, like battery and super-capacitor, one needs bi-directional DC-DCconverters.

……

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1. Inclusion

In order to integrate all the sources and loads and achieve high power conversion efficiency for microgrid

application, a compact multiport power converter with fewer components can be used to replace all the

converters with centralized control scheme which is easy to implement and protect.

Research objective

Common DC bus

Fuel cell

Wind turbine

Battery

Solar panel

DC/DC

DC/DC

DC/DC

DC/DC

DC/AC

DC/AC

AC motor

Utility grid

Fuel cell

Wind turbine

Battery

Solar panel

AC motor

Utility grid

Multiport

power

converter

Centralized contol

fewer components

2015/11/12 5

Introduction

List of contents


Conclusion


2015/11/12 6

2. Topology simplification with switch multiplexing

Basic units for bi-directional power transfer

Basic unit for DC-DC power conversion

Basic unit for AC-DC power conversion

Fuel Cell

DC bus

Load DC bus

Solar panel

DC bus

Basic unit Buck Boost Bi-directional

DC busSource

DC busAC load DC bus

Grid

Basic unit Rectifier Inverter Bi-directional

In order to analyze multiport converter, two-port converter are investigated firstly. Then it is desired to

derive from two-port system to multi-port system. Here, non-isolated topologies are considered mainly.

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Topology derivation based on switch multiplexing

AC-DC-ACDC-AC-DC

DC-DC-DC DC-DC-AC

1V 3V2V DC

DC

DC

DC

1V 3V2V DC

AC

DC

DC

1V 3V2V DC

AC

AC

DC

1V 3V2V AC

DC

AC

DC

Basic idea: constitute three-port converter by combining two basic units.

There are four cases as follows:

DC-DC Basic unit AC-DC Basic unit

AC-DC-ACDC-AC-DC

DC-DC-AC

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Case 1: DC-DC-AC topologies

DC-DC Unit

DC/AC Unit

oL1V

2V

3V

1V 3V2V DC

AC

DC

DC

DC-DC-AC

oL

1L

1V 2V3V

Published

2V

1V

1 2<VV

1 2V Amp V

Note：The Voltage drop of

L is ignored

1 2 1 3,V V V Amp V 2 1 3V V Amp V

2015/11/12 9



DC-DC Unit DC-AC Unit

1V 3V2V DC

AC

DC

DC

DC-DC-AC

3V

2V

1V

Equivalent mode

1L

2L

1L 2L

1L

2L

1L 2L

1L

2L

2L1LG1

G2

T

G1

G2

G3

TExamples

L L

2 3V Amp V

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1V 3V2V DC

AC

DC

DC

DC-DC-AC

Examples

1L

1V

2V

3V

Verified

Equivalent mode

1L

1L 2L

1Li2Li

2L

1L

1L 2L

1Li2Li

2L

1L

1L 2L

1Li2Li

2L

1L

2L

1 3V Amp V

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2V

1V

3V1V 3V2V DC

AC

DC

DC

DC-DC-AC

DC-DC-AC three-port converter can be constituted with 4-6 switches.

Published

Equivalent mode

2L1L1L 2L

1Li2Li 1Li

2Li

2L1L1L 2L

1Li2Li 1Li

2Li

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Case 2: DC-AC-AC topologies

DC-AC Unit

2)Switch multiplex

AC-DC-AC

1V 3V2V DC

AC

AC

DC

DC-AC Unit

1V

3V2V

1V

2V

3V

Examples

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Case 2: DC-AC-AC topologies

DC-AC Unit

4) Bridge multiplex3) Dual switchmultiplex

AC-DC-AC

1V 3V2V DC

AC

AC

DC

DC-AC Unit

Examples

1V 2V

3V

1V 2V

3V

DC-AC-AC converter can beconstituted with 6-8 switches.

Published

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Case 3: isolated topology derivation

Basic structure

Examples

1V 1L

2V 2L

3V3L

1V

2V

3V

DC

AC

DC

AC

DC

AC

Published

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Previous topology

Multi-level units

Less harmonic

Low switch frequency

More switches

Resonant units

High efficiency

High power density

Frequency modulation

Multiport units

Flexible power flow

Low switch power loss

Complicated control

• NPC

• Flying cap

• MMC/CMC

• LLC-type

• LCC-type

Ls

Lm

C

Ls

C2

C1

C

1V

C1V

2V

outV

C

1V

2V

outV

• Isolated

• Non-isolated2V

1V

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Extension

Combination of multi-level technique and switch multiplexing technique

Multi-level technique

Switch multiplexing

Less harmonic


More switches

Flexible power flow


Complicated control

Topology

Optimization

New topology

2V

1V

2V

1V

1L2L

3V

To be analyzed

2V

1V

3V

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Extension

Combination of resonant technique and switch multiplexing technique

Switch multiplexing

High efficiency

High power density

Frequency modulation

Less switches

High efficiency

High voltage/current stress

New topology

2V

1V

1L2L

3V

Ls

Lm

C

sL1L

1C

2C

oC

inV

outV

sC

To be analyzed

Resonant technique

Topology

Optimization

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Extension

Combination of multi-level unit and resonant unit with switch multiplexing technique

High efficiency

High power density

Frequency modulationNew topology

Resonant technique

Topology

OptimizationMulti-level technique

Less harmonic


More switches

Switch multiplexing

sL

1C

2C

oC

outV

sC

sL

1C

2C

oC

outV

sC

3V

1L

To be analyzed

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Introduction

List of contents


Conclusion


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3. Experimental results

Prototype pictures

5-switch DC-DC-AC (1kW)

6-switch DC-AC-AC (5kW) 8-switch DC-AC-AC (2kW)

4-switch DC-DC-AC (500W)

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4-switch converter

Microgrid can achieve higher efficiency with modified topology;

2V

1V

1L2L

3V

6-switch converter 4-switch converter

C

1V

2L

3V1L

2 switches are omitted which leads to efficiency improvement and power integration;

Voltage rating of DC link capacitors is decreased with better reliability;

Power decoupling can be achieved with small capacitance;

Power flow control is more complicated;

PI

PWM

distribution

-+iL2_ref

vg

K

iL2

g1

g2

g3

g4

K

-+

ibat

ibat_refPI

d1-d3

++

d1

PIvcap_ref

-+vcap

PLL

Sin(Ө)

Control strategy

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4-switch converter

Experimental results demonstrate the feasibility of the 4-switch three-port DC-DC-AC converter

and 2.0% power efficiency improvement in comparison with conventional topology.

85.0%

87.0%

89.0%

91.0%

93.0%

95.0%

100 200 300 400 500

Efficiency comparison

4-switch 6-switch

W

CH1:2A/div CH2:200V/div CH3:200V/div Time:20ms/divCH4:5A/div

Grid voltage

Grid current

Battery current(I1)

Battery voltage(V1)

Experimental waveform

Efficiency comparison


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5-switch converter

Reliability is improved with lower voltage requirement for battery;

6-switch converter5-switch converter

C

1V

2L

3V1L

One switch is omitted which leads to high power density;

Voltage range for battery is expanded with better reliability;

Power decoupling can be achieved with small capacitance;

Modulation method is complicated.

CH1:2V/div CH2:2V/div CH3:5V/div Time:40µs/div

1L

1V

2V

3V

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5-switch converter

Experimental results demonstrate the feasibility of the derived 5-switch three-port DC-DC-AC

converter with capability to low-voltage batteries or super-capacitors.

Experimental waveform

CH1:2A/div CH2:200V/div CH3:5A/div Time:20ms/divCH4:200V/div

Grid voltage

Grid current

Battery current(I2)

Output voltage(V1)

70.0%

74.0%

78.0%

82.0%

86.0%

90.0%

50 100 150 200 250

Efficiency

W

Experimental efficiency


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Introduction

List of contents


Conclusion


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4. Conclusion

What has been done

1. Proposed topology derivation method based on switch multiplexing;

2. Derived a series of three-port DC-DC-AC topologies and DC-AC-AC topologies;

3. Verified the feasibility of the derived topologies and their superiority.

Future work

1. To discuss topology selection method based on application requirements;

2. To optimize the derived topologies with multi-level technique and resonant technique;

3. To approach modular multi-level converter modeling and discuss its stability.

2015/11/12 27

Wen Cai

PhD candidate & Research assistant

University of Texas at Dallas

Email: [email protected] / [email protected]

Phone: (469) 412-0040

Topology Simplification Method based on Switch ... - Power on · 9/23/2015 · Topology...

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