Multi-Mode Operation of Different

PV/BESS Architectures in a Microgrid:

Grid-connected and Islanded

Thursday, April 17, 2014

Manohar Chamana, Iman Mazhari,

Badrul H. Chowdhury and Babak Parkhideh

1

Table of Contents

2

2

3

1 Photovoltaic/Battery Architectures

Different Modes in a Reconfigurable Solar Converter (RSC)

Comparison between two PV/BESS inverter control

5 Results and Comparison

6 Conclusion

4 Comparison between two BESS converters control

(a) Direct Integration I (b) Indirect Integration (TSC) (c) Direct Integration II (RSC)

(a) Direct Integration I: o Simplest option

o Low efficiency operation of the overall conversion system

o Not considered for utility-scale PV/battery applications

o No option to charge battery from PV

(b) Indirect Integration: (Two Stage Converter) o Most Common configuration (two stage converter)

o PV and battery are connected indirectly using two stage power conversion.

(c) Direct Integration II: (Reconfigurable Solar Converter) o Divided in two different sections which would be

• DC/AC for delivering power to the grid

• DC/DC for delivering the power from the PV to the battery.

4

PV/BESS Architectures

a

m

𝐵𝑎𝑡𝑡𝑒𝑟𝑖𝑒𝑠 𝑎𝑟𝑒 𝑢𝑠𝑒𝑑 𝑓𝑜𝑟 𝑝𝑒𝑎𝑘 𝑠ℎ𝑖𝑓𝑡𝑖𝑛𝑔, 𝑠𝑚𝑜𝑜𝑡ℎ𝑖𝑛𝑔, 𝑎𝑛𝑑 𝑝𝑜𝑤𝑒𝑟 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛𝑖𝑛𝑔 𝑖𝑛

𝑃𝑉 𝑠𝑦𝑠𝑡𝑒𝑚𝑠.

3-5% conversion efficiency gain compared to existing solutions.

30-40% cost reduction on PV/battery power electronics

If not exceed, no compromise on battery charging techniques

Retrofit and expandable Platform for existing and future PV power plants

PV to Grid (Mode 1) Battery to Grid (Mode 4)

PV+Battery to Grid (Mode 3) PV to Battery (Mode 2)

RSC Benefits

4 5

Operation Modes of RSC

o PV Array operated

at MPPT.

o Battery is

connected to the

DC link directly.

Synchronous-

reference frame

current-mode control

𝑃𝑟𝑒𝑓 𝑎𝑛𝑑 𝑄𝑟𝑒𝑓 are the reference

power values

o In grid connected mode the reference phase angle is measured using a phase

locked loop that utilizes the system frequency 𝜔0 = 60 𝐻𝑧.

o In Mode 3, 4 and 5 the 𝑃𝑟𝑒𝑓 𝑎𝑛𝑑 𝑄𝑟𝑒𝑓 are activated

o In Mode 1 𝑉𝑚𝑝𝑝𝑡/ and 𝑄𝑟𝑒𝑓 are activated.

8

Inverter side control system comparison for

Reconfigurable Solar and Two Stage Converter

is the

reference DC link

Voltage.

𝑉𝑚𝑝𝑝𝑡 is the

MPPT Voltage.

ref

DCV

ref

DCV

o PV Array operated

at MPPT utilizing a

Boost converter.

o Battery connect to

the DC link though

a Synchronous

Buck for

discharging and

charging process.

o Discharging

DC link voltage

is regulated at

its nominal

value.

o Charging

DC link voltage is

regulated at its nominal

value.

Synchronous buck

converter

Also Connects the PV

to the grid

7

Battery side control system:

Two-Stage Architecture

o Charging

PV voltage is regulated

at the maximum power

point voltage.

o Charging

DC link voltage is

constant at battery

Voltage.

Boost

converter

9

Battery side control system:

RSC Architecture

• Microgrid test-bed implemented

in PSCAD /EMTDC environment

Grid connected

Islanded mode

• Two PV/BESS systems at

different locations with different

architectures.

• Diesel generator

connected near the point

of common coupling for

regulating and meeting

deficiency in islanded

mode.

• During the simulation period loads

and PV output are assumed to be

constant.

Single Line Diagram of the Microgrid

PV + Battery

System (RSC)

G

Bus 0

Bus 1

Bus 2

Bus 3

Bus 4

Bus 5 Bus 11

Bus 10

Bus 9Bus 6

Bus 7

Bus 8

L

L

L

L L

L

L L

L

L

L

2

8

7

6

an

1

3

4

5bn

9

1.2 km

1.0 km

0.6 km

0.6 km 0.5 km

0.3 km

0.8 km0.3 km 1.7 km

0.2 km

1.3 kmL

L

11

10

PCC

12.47/0.48 kV

2 MVA, x = 2 %

PV + Battery

System (TS)

DG

10

Microgrid Testbed

o During Simulations PV constant and load changes at time t = 3 sec and t = 6 sec in the

microgrid.

Active Power Outputs Reactive Power Outputs

Time Microgrid State PV/BESS

mode

Diesel Generator

State

1-4 seconds Grid connected Mode 1 Disconnected

4-8 seconds Islanded Mode 3 Connected

8-12 seconds Islanded Mode 4 Connected

12-16 seconds Grid Connected Mode 2 Connected

a) Grid

b) Diesel

Generator

c) RSC

d) TS

PV systems

maintain a

constant

reactive

power of 0.3

p.u.

12

Power Outputs at Source Terminals

a) PV power at the DC link b) Battery Power

o Transients are higher in case of the

RSC during discharging mode.

o Transients are higher in case of the

TSC during charging mode.

o Reason – Inductance

RSC

o Battery voltage is applied in parallel

with the PV.

o Forces the PV to move away from

the MPPT point.

13

PV/BESS Internal Power Outputs

All Voltages are within band of

0.95<Vrms<1.05 p.u.

• Frequency is maintained constant at 60

Hz.

• Some distortion in the island mode due

to harmonic injection by PV/BESS

systems.

(a) Voltage at PCC, (b) Voltage at DG (b) Voltage at RSC (c) Voltage at

two-stage converter

System frequency

14

Voltages and frequency within Microgrid

• Simulations were performed on a microgrid test-bed.

Internally connected loads

Two different PV/BESS architectures.

• Distributed Generators

A single stage converter (RSC)

A two stages converter (TSC)

Diesel Generator Islanded mode – regulate voltage and frequency

Grid connected mode –meet deficiency

• Both architectures show satisfactory results with

many similarities and few dissimilarities

If economics of conversion stage is important,

RSC offers higher benefits.

15

Conclusions

Thank You

Questions ?

16