ABSTRACT• This work deals with low-voltage ride-through operation of solar photovoltaic (PV) array along

with power quality (PQ) improvement features in the distribution grid such as grid currentsbalancing, improve solar power penetration into the distributed network, power factor correctionfeatures.

• Under balanced/unbalanced grid voltage faults, the proposed strategy controls DC-DC converterin such a way that voltage source converter (VSC) currents are achieved within its permissiblelimits along with improving stability of the grid. (it is mandatory to follows since 2014 as perIEEE-1547-2014 and E.ON standards)

• The effectiveness of the GI algorithm is illustrated with frequency domain analysis andLissajous plot to extract fundamental load component (FLC).

• Test results show satisfactory performance for a proposed system under steady state anddynamic conditions such as load currents unbalancing, variable solar insolation, distributionstatic compensator mode and line to ground fault.

FUNCTIONALITIES OF THE CONTROL STRATEGY• Ride-through operation under symmetrical and unsymmetrical faults in the grid.

• Inverter is protected by accommodating its rating into control strategy.

• Balanced grid currents are achieved even under imbalanced load currents.

• Improve dynamics of the grid currents by including solar PV feed-forward term.

• Reduce losses in VSC: Adaptive DC link approach is adopted for reference DC link voltages.

• System performance is not affected even under presence of DC offset (for continuous/short

time) in the load current.

• Capable to operate even under distorted grid voltages.

• Grid currents are balanced even under balanced and unbalanced faults and its total harmonics

distortions are maintained according to IEEE-519 standard.

REFERENCE

• Y. Yang, F. Blaabjerg and H. Wang, "Low-Voltage Ride-Through of Single-Phase Transformerless Photovoltaic Inverters," in IEEETransactions on Industry Applications, vol. 50, no. 3, pp. 1942-1952, May-June 2014.

LIST OF PUBLICATIONS AND PATENTS

1. P. Shah, I. Hussain and B. Singh, "Fuzzy logic based FOGI-FLL algorithm for optimal operation of single-stage three-phase gridinterfaced multifunctional SECS," IEEE Transactions Industrial Informatics, vol. 14, no. 8, pp. 3334-3346, Aug. 2018.

2. P. Shah, I. Hussain and B. Singh, "A novel fourth-order generalized integrator based control scheme for multifunctional SECS in thedistribution system," IEEE Transactions Energy Conversion, vol. 33, no. 3, pp. 949-958, Sept. 2018.

3. P. Shah, I. Hussain and B. Singh, "Single stage SECS interfaced with grid using ISOGI-FLL based control algorithm," IEEETransactions Industry Applications, Early Access.

4. P. Shah, I. Hussain, B. Singh, A. Chandra and K. Al Haddad, "GI based control scheme for single stage grid interfaced SECS forpower quality improvement," IEEE Transactions Industry Applications, Early Access.

5. B. Singh, P. Shah and I. Hussain, "ISOGI-Q based control algorithm for a single stage grid tied SPV system," IEEE TransactionsIndustry Applications, vol. 54, no. 2, pp. 1136-1145, March-April 2018.

6. P. Shah, I. Hussain and B. Singh, "Multi-resonant FLL-based control algorithm for grid interfaced multi-functional solar energyconversion system," IET Science, Measurement & Technology, vol. 12, no. 1, pp. 49-62, 1 2018.

7. P. Shah, I. Hussain and B. Singh, "Real-time implementation of optimal operation of single-stage grid interfaced PV system underweak grid conditions," IET Generation, Transmission & Distribution, vol. 12, no. 7, pp. 1631-1643, 10 4 2018.

8. B. Singh, S. Mishra, V. L. Srinivas and P. Shah, “A self-synchronizing microgrid system and method thereof,” Pending Indian PatentNo. 201811041032 Filed on: October 30, 2018.

9. B. Singh. S. Mishra, V. L. Srinivas and P. Shah, “Ride-through Operation of two-stage grid interfaced solar PV system under grid-sideabnormalities,” Indian Patent No. 201911025465, Filed on June 26, 2019.

CONCLUSIONS• The performance and behaviour of the system are found robust and reliable using generalised

integrator based adaptive control strategy under dynamic and steady-state conditions.• The proposed control effectively provides reactive power control, frequency regulation, and

dynamic grid support.• The performance of the control strategy is found satisfactory, which is validated through

simulations results and through a developed setup in the laboratory for different operatingconditions.

• The proposed GI based algorithm is effectively extracted the fundamental component of loadcurrent under any operating scenarios.

• The total harmonic distortions (THDs) of grid currents are found within limits of IEEE-1547.4.and IEEE-519 standards.D

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INDUSTRIAL SIGNIFICANCE• The proposed control strategy provides better system performance under weak grid scenario,

which is major issues in under-developed and developing countries.• It follows IEEE-1547.4 standard and grid code of country (as per designed in control structure).• The feed forward term provides better dynamic response under variation of solar insolation and

voltages at point of common coupling.• The stability of distribution grid is improved as reactive power is supplied to the distribution

grid based on revised grid code.• It is able to suffice various functionalities, 1) Reactive power control, 2) Frequency control

through active power control, 3) Dynamic grid support capability.

Low-Voltage Ride-Through Operation of Grid Interfaced Solar PV System with Harmonic Compensation Capability

Priyank Shah (2015EEZ2507) Supervisor: Prof. Bhim Singh

SIMULATION RESULTS

Clean Energy for Sustainable Economy and Environment

PRESENTED TOPOLGY AND CONTROL STRATEGY

Three Phase Grid

SPVA

VSC

Common

Coupling Point

vsa

vsb

vsc

VDC

Cdc

S1

S4

S3

S6

S5

S2

Interfacing

Inductors

Ipv

Vpv

Lf

isa

isb

isc

Rs

Rs

Rs

Ls

Ls

Ls ila

ilc

ilb

Ripple filter

Nonlinear

Loads

ivsc-a

ivsc-b

ivsc-c

Rf Cf

PWM Pulses

Lb

Sb

Boost converter

PWM Pulse

Extraction of phase ‘a’ Ipa components

Currrent

Error

Extraction

Generation

of Gating

Pulses

To

VSC

Iap

Ibp

Icp

iap*

iaq*

Ibp*

icp*

icq*

ibq*

isa*

isb*

isc*

1/3 LPF

2/3Ppv

Vt÷

VDC

LPFVDCref

Iload

iLa

uap

iLb

ubp

iLc

ucp

PI

isaisbisc

Estimation of active reference current

for phase ‘c’ using proposed GI

Estimation of active reference current

forphase ‘b’ using proposed GI

Vt

Inet

Inet

Inet

Ipvff

Iloss

Inet

uaq

ubq

ucq

Estimation of active reference current

for phase ‘a’ using proposed GI

Generation of

reactive reference

currents

Q

Adaptive

DC link

approach

Vpu<0.9

Fault

signal=1

Pmax<Pvsc

Comparator

signal=1

Enable

signal=1Non-MPPT

Evaluation

of NNP, Pmax

Enable

signal=0

MPPT

Vpu PvscPmax

SenseStart

Pmax

Frequency (rad/s)10

-210

010

210

4-180

-135

-90

-45

0

45-150

-100

-50

0

50 Proposed GI

GI [4]

Mag

nit

ud

e (d

B)

Ph

ase

(d

egre

e)

-1 0

-1 0 1

1

-1

0

1

-1

0

1

ilq

i ld

GI [4]

Proposed

GI

Polluted output

Clean output

i ld

ilq

Better DC offset

rejection

Proposed control has

better harmonics

rejection capability

ω

ω

ω

2ξ

2ξ

Sample &

hold logic

Triggering

pulse

ω

ω

ω

2ξ

2ξ

iL iLd

iLq

Ip

Fig. Double stage grid interfaced SECSFig. Operating point of SECS

Fig. Generalized integrator (GI)

Fig. Effectiveness of generalized integrator

Fig. Switching strategy of VSC

-700

0

700

0

200

400

0

20

40

0

20

40

0.5 0.6 0.7 0.8 0.9 1-10

-5

0

5

400

500

600

0

20

40

-50

0

50

v sa

bc(

V)

v pn(V

)N

NP

Pm

ax(k

W)

Vp

v(V

)P

pv(

kW

)i s

ab

c(A

)Q

s(k

VA

r)

Time(s)

L-G fault L-L-G fault

Normal

condition

Normal

condition

Fig. Performance of the system under L-G and L-L-G fault

(a) (b) (c)

(a) (b) (c)

Case-I Grid Currents Balancing Features

EXPERIMENTAL RESULTS

vsab= 500V/div

isa= 20A/div

ivsca= 25A/div

iLa= 10A/div

Load current imbalancing

to balancing

Grid current is sustained

balanced

vsbc= 500V/div

isb= 20A/div

ivscb= 25A/div

iLb= 10A/div

Dynamics of phase ‘b’

VDC= 500V/div

Vpv= 500V/div

IPV= 15A/div

PPV= 1.5kW/div

Solar power generation

remains unaffected

vsab= 500V/div

isa= 20A/div

ivsca= 25A/div

iLa= 10A/div

Compensating

current

Power in the grid is

reversed

30° phase

shifted210

° phase

shifted

VDC= 500 V/div

Vpv= 500 V/div

IPV= 15 A/div

isa= 20A/div

Solar power generation is reduced

to zero under absence of

insolations

Iloss= 1A/div

Ipvff= 1A/div

Iload= 1A/div

Inet= 1A/div

Feed-forward unit is

reached to zero

Loss term is altered the

direction as system transits

to DSTATCOM mode

Amplitude of

reference currents is

varies

vsa= 50V/div vsb= 50V/div vsc= 50V/div

Steady-state imbalanced voltages

Case-II DSTATCOM Feature

Fig. (a) grid voltage, grid current, VSC current, load current for phase ‘a’ (b) grid voltage, grid

current, VSC current and load current for phase ‘b’ (c) DC link voltage, PV array voltage-current-

power

Case-III Ride-through Feature

Ipv= 15 A/div

Vpv= 300 A/div

SPVA system transits from

MPOP to non-MPOP

operation

(a) (b)

Fig. (a) grid voltage, grid current, VSC current, load current for phase ‘a’ (b) DC link voltage, PV

array voltage-current-power (c) intermediate control signals

Fig. (a) grid voltage (b) solar PV array current

VI Sensing Opto-Couplers VI Sensing

73 8

ADC’s DIO’s ADC’s

Control Algorithm loaded on FPGA

dSPACE

DS-1202

PC

MATLAB

Interface

PWM

RC Filter

Load

Three

Phase

Grid

Ipv

Vpv VDC

CDC

VSI

ivsc

iL

is

SPV

Array

Vpv VDCIpv is iL vsPWM7

Sb

Lb

Fig. Equivalent circuit of

experimental prototype

✉Email Contact: priyankshah1504@gmail.com