LEGO-MIMO Architecture:

A Universal Multi-Input Multi-Output (MIMO) Power Converter

with Linear Extendable Group Operated (LEGO) Power Bricks

Yenan Chen, Ping Wang, Youssef Elasser, and Minjie Chen

Princeton University

MIMO Applications

2

• Large number of modular cells

• MPPT, power balancing, SOC monitoring

• Multiple energy sources/loads

• Energy routing

MIMO Architectures

3

DC-Coupled MIMO☺ Decoupled controlMultiple conversion stages Low efficiency

AC-Coupled MIMO☺ Single-core multi-winding transformer☺ Fewer conversion stages☺ High efficiency Coupled power flow

Energy Router

AC-Coupled MIMO: Previous Work

4

+

-

• 50V-5V 10-Port converter for data center[2]

• 400V-48V-15V-5V 4-Port converter for DC power distribution in smart home[1]

• 12-Port converter for submodule capacitor balancing in 3-Phase MMC inverter[3]

❑Large number of ports with single magnetic core

❑Cover wide voltage & current range

LEGO-MIMO Concept

Linear

Extendable

Group

Operated

5

LEGO Power Brick (Active-Bridge)

LEGO-MIMO Converter

❑ Identical active-bridge unit: LEGO toy bricks

❑ Series/parallel connecting for wide voltage/current range

❑Modular design, reconfiguration

Power Rating of LEGO Bricks

6

Device selection area

• Traditional converterPmax = Vmax Imax >> Po

• 2 LEGO bricks• Vmax - 0.5Imax

• 0.5Vmax - Imax

Pmax = 2 0.5Vmax 0.5Imax

• N LEGO bricks• Pmax Po

Group Operated Control

7

Group Control Strategy

❑ LEGO bricks in the same group (port): same gate driver

❑ Plug-and-play, simpler controller, fewer sensors

LEGO Power Brick (Active-Bridge)Linear

Extendable

Group

Operated

Reduced Order Control Model

8

𝑉𝑊1

⋮𝑉𝑊𝑛

= 𝑗𝜔𝑴𝑾𝟐𝑾

𝐼𝑊1

⋮𝐼𝑊𝑛

Series Parallel

N bricks and M ports: N M

𝑉𝑃1⋮

𝑉𝑃𝑚

=𝑄𝑉11 ⋯ 𝑄𝑉1𝑛⋮ ⋱ ⋮

𝑄𝑉𝑚1 ⋯ 𝑄𝑉𝑚𝑛 𝑚×𝑛

𝑉𝑊1

⋮𝑉𝑊𝑛

𝐼𝑊1

⋮𝐼𝑊𝑛

=𝑄𝐶11 ⋯ 𝑄𝐶1𝑛⋮ ⋱ ⋮

𝑄𝐶𝑛1 ⋯ 𝑄𝐶𝑛𝑚 𝑛×𝑚

𝐼𝑃1⋮𝐼𝑃𝑚

𝑉𝑃1⋮

𝑉𝑃𝑚

= 𝑗𝜔𝑸𝑽𝑴𝑾𝟐𝑾𝑸𝑪

𝐼𝑃1⋮𝐼𝑃𝑚

Impedance matrix simplification

Voltage conversion

Current conversion

𝐼𝑃𝑋 = 𝐼𝑊ℎ = 𝐼𝑊𝑖 = 𝐼𝑊𝑗

𝑉𝑃𝑋 = 𝑉𝑊ℎ + 𝑉𝑊𝑖 + 𝑉𝑊𝑗

𝐼𝑃𝑌 = 𝐼𝑊𝑘 + 𝐼𝑊𝑙 + 𝐼𝑊𝑚

𝑉𝑃𝑌 = 𝑉𝑊𝑘 = 𝑉𝑊𝑙 = 𝑉𝑊𝑚

ො𝑣𝑃1ො𝑣𝑃2⋮

ො𝑣𝑃𝑚

= 𝑮𝑷𝒊

Ƹ𝑖𝑃1Ƹ𝑖𝑃2⋮Ƹ𝑖𝑃𝑚

+ 𝑮𝑷𝝓

𝜙𝑃1𝜙𝑃2⋮𝜙𝑃𝑚

• M × M transfer matrix

• For port P/V regulation

𝑃𝑖 =𝑁𝑖𝑉𝑖2𝜋2𝑓𝑠

𝑗≠𝑖

𝑁𝑗𝑉𝑗 Φ𝑖 −Φ𝑗 𝜋 − Φ𝑖 −Φ𝑗

𝑁𝑖2𝑁𝑗

2𝐿𝑖𝑗 + 𝑁𝑗2𝐿𝑖 + 𝑁𝑖

2𝐿𝑗Brick power:

DC

AC

DC

AC

AC

DC

AC

DC

DC

AC

DC

AC

AC

DC

AC

DC

DC

AC

DC

AC

AC

DC

AC

DC

Control Methods

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• Phase-shift • Time-sharing • HybridΦ1

Φ2

Φ3

Φ4

𝐷1

𝐷2

𝐷3

𝐷4 Φ𝑖 𝑎𝑛𝑑 𝐷𝑖

IL1

IL2

IL3

IL4

IL1

IL2

IL3

IL4

IL1

IL2

IL3

IL4

LEGO-MIMO Design Example

10

❑ 1 magnetic core❑ Air-cooling ❑ No heatsink

• HV PCB (1 HV brick)• VH = 72V, NH = 8• Pmax = 200W, fs = 200kHz• GaN GS1004B/100V

• LV PCB (2 LV bricks)• VL = 9V, NL = 1• Pmax = 2100W, fs = 200kHz• DrMOS SIC632/24V

Multi-Winding Transformer Design

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• HV windings as primary side, LV windings as secondary side• Current excitation: Ip = 4A, Is = 16A

PCB copper current density Magnetic field strength and core flux density

• Thermal measurement: HV input, LV output• P = 80W, Ta = 20C, no air-cooling

Interleaved structure:• Lower B and H• Smaller ac resistance (56% of non-interleaved

structure)

Port Configuration

12

• System maximum power: 500W

Input operation range Output operation range

• Experiment Setup

Power Distribution

13

Measured power of the 9V, 18V and 36V ports with same Φ

Interleaved structure:

• Balanced power distribution

• Able to be linearly extended

• P9V ≠ P18V

• P9V + P18V ≠ P36V

• P9V P18V

• P9V + P18V P36V

Input Output

Efficiency with Different Winding Structures

14

Winding currents in the HV bricks, Po = 300W

Input Output

Interleaved structure:

• Lower current peak

• Higher efficiency

Efficiency with Different Port Structures

15

Winding currents in the LV bricks with interleaved structure, Po = 300W

• 96.7% @ 288V - 9V /300W

• Voltage slightly unbalanced among

series bricks

• Tradeoff: cost vs. efficiency

Thermal Measurement

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• LV Group 1: 9V-18V-36V output• P = 500W, Ta = 23C • Airflow = 21.9 CFM

❑ Hottest components: HV inductors and LV DrMOS❑ Natural distribution of heat❑ No heatsink

Design Guideline

For equal power distribution

• Interleaving the input bricks (windings)

and output bricks (windings)

• Using bricks with similar linkage

inductance Lij for the same port

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input output

Summary

• LEGO-MIMO: Linear Extendable Group Operated Multi-Input Multi-Output

• Applicable to wide operation range multiport dc-dc applications

– Battery balancer, energy router, PV MPPT

• Design example: 500W 12-Brick MIMO dc-dc converter

• Wide operation range: 72V/8A-288V/2A input, 9V/56A-72V/7A output

• Multi-winding single-core transformer design

• 96.7% peak efficiency @ 288V-9V/250W

• Natural heat distribution

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References

1. Y. Chen, P. Wang, H. Li and M. Chen, "Power Flow Control in Multi-Active-Bridge Converters: Theories and Applications," 2019 IEEE Applied Power Electronics Conference and Exposition (APEC), Anaheim, CA, USA, 2019, pp. 1500-1507.

2. P. Wang, Y. Chen, Y. Elasser and M. Chen, "Small Signal Model for Very-Large-Scale Multi-Active-Bridge Differential Power Processing (MAB-DPP) Architecture," 2019 20th Workshop on Control and Modeling for Power Electronics (COMPEL), Toronto, ON, Canada, 2019, pp. 1-8.

3. Y. Chen, Y. Elasser, P. Wang, J. Baek and M. Chen, "Turbo-MMC: Minimizing the Submodule Capacitor Size in Modular Multilevel Converters with a Matrix Charge Balancer," 2019 20th Workshop on Control and Modeling for Power Electronics (COMPEL), Toronto, ON, Canada, 2019, pp. 1-8.

4. R. W. Erickson and D. Maksimovic, “A multiple-winding magnetics model having directly measurable parameters," PESC 98 Record. 29th Annual IEEE Power Electronics Specialists Conference (Cat. No.98CH36196), Fukuoka, 1998, pp. 1472-1478 vol.2.

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Control Model for Multi-Active-Bridge

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• N-Brick multi-active-bridge converter • Cantilever model for an N-winding transformer[4]

𝑃𝑖 =𝑁𝑖𝑉𝑖2𝜋2𝑓𝑠

𝑗≠𝑖

𝑁𝑗𝑉𝑗 Φ𝑖 −Φ𝑗 𝜋 − Φ𝑖 −Φ𝑗

𝑁𝑖2𝑁𝑗

2𝐿𝑖𝑗 + 𝑁𝑗2𝐿𝑖 + 𝑁𝑖

2𝐿𝑗Average power of Brick i:

Small signal model[1][2]: ො𝑣1ො𝑣2⋮

ො𝑣𝑛

= 𝑮𝒊

Ƹ𝑖1Ƹ𝑖2⋮Ƹ𝑖𝑛

+ 𝑮𝝓

𝜙1𝜙2⋮𝜙𝑛

• Gi and G: n × n transfer matrix

• For independent P/V regulation

Prototype Parameters

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• System maximum power: 500W