AC voltage

Current of V1(I1)

CH1:150V/div CH2:2A/div t:10ms/div

A Power Decoupling Method based on Four-Switch Three-Port DC/DC/AC Converter in DC Microgrid

Wen Cai, Ling Jiang, Bangyin Liu and Shanxu Duan Huazhong University of Science and Technology (caiwen600@gmail.com)

Abstract—This paper presents a power decoupling method based on a novel four-switch three-port DC/DC/AC converter in DC microgrid, which can restrain the low-

frequency ripple power caused by the single-phase inverter. The proposed topology is compact and cost effective in consideration of that no extra switches or devices

are required compared with. With the model of the proposed DC/DC/AC converter, the power decoupling control method is analyzed and the parameters are designed

as well. Experimental results on the laboratory prototype verified the feasibility of the proposed power decoupling method and the availability of parameters design.

By choosing the arguments (D1-D2) and D2

as variables, the two inductors’ current can

be controlled independently. In addition,

the controllers are able be designed

without consideration of interaction as well.

According to the experimental data and

index, this method based on four-switch

three-port DC/DC/AC converter can

reduce 92% of 100-Hz low-frequency

ripple current caused by the 50-Hz AC grid.

I Four-switch three-port DC/DC/AC converter for power decoupling with small capacitor

Experimental results

1. Modeling

The proposed DC/DC/AC topology and the power decoupling control

method are verified by a 400-W laboratory prototype

Four-switch three-port

DC/DC/AC converter

Conclusion: A power decoupling method based on four-switch three-

port DC/DC/AC converter is presented and analyzed in this paper.

Both the validity of the four-switch DC-DC-AC converter and the

performance of the corresponding power decoupling control method

are verified by the theoretical analysis and the experiment results.

VL2

Vc

VaD1-

+2 2

1

L s R

IL2K

VL1

Vg

D2

-1 1

1

L s R

IL1K

+-+

Va-Vb

Ripple Ripple

Inverter

Power decoupling:

How to control the low-frequency (100/120 Hz)

power ripple transmission with small capacitor

PV modules Grid

The corresponding power decoupling control method

PI

PWM

distribution

-

+Ig_ref

Vg

Ig

g1

g2

g3

g4

PIVcap_ref

Calculation

IL_ref

-+

K

Vcap

Ig_ref

Irip_ref -+

IL2

IL2_refPI

D1-D2+

+

K

D2

The equivalent system block diagram of

the proposed converter

Power decoupling control diagram based on

the proposed converter

Current of L2(IL2)

CH1:150V/div CH2:5A/div t:10ms/div

AC voltage

0

0.5

1

1.5

2

2.5

0 50 100 150 200

Frequency Domain

Ibus

2.1

0.06 0.03 0.02 0.03

Parameters Value

DC source(V1 & V2) 200V

Grid voltage(V3) 110V

Switching Frequency(fs) 18-kHz

Inductors(L1 & L2) 6mH, 0.2Ω

C1

L2

V1

L1

Grid

CV1

L1

Grid

S1

S3

S2

S4

a

b

Full-bridge inverter Small capacitor

Large capacitor

2. Control method

There are three control loops in this control scheme:

Grid-connected current control loop;

The control loop of the inductor current IL2;

The capacitor voltage control loop;

The PWM distribution unit is employed to get the

PWM signal as introduced in the modeling section.

L2

V1 L1

Grid

V2

iL2

iL1

L2

V1 L1

Grid

V2

iL2

iL1

L2

V1 L1

Grid

V2

iL2

iL1

Mode 1 Mode 3 Mode 2 Mode 4

C

L2

V1 L1

Grid

S1

S3

S2

S4

a

b

Frequency-domain distribution

of the DC source current V3 & I1 V3 & IL2