PV Power Injection with improved Power Quality by DSTATCOM using Variable DC Link Voltage Control from RSC-MLC

G CHANDRA SEKHAR1, S.MADDILETY2, G.BALA SUBBARAYUDU3

Assistant Professor, Dept of EEE, SVR Engineering College, Nandyal, Andhra Pradesh, India1,2,3

chandras.211@gmail.com 1 , maddiletysuddula@gmail.com 2 , rayuduzink@gmail.com 3

Abstract

Proposed work describes the study of

improvement of dc-link voltage for

DSTATCOM (Distribution static

compensator) which is based on PV(Photo-

Voltaic) system combined with RSC-

MLC(Reduced Switch Count Multi-level

converter).For power quality improvement ,

implementation can be capable of reactive

power compensation , capable of handling

distribution side non-linear loads as well as

three phase demands for harmonics. It

avoids source over-loading by providing

support of real power. The switching loss is

avoided or minimizes for inverter and also

voltage stress is reduced in switches of

inverter by dropping r value to certain level

during off-peak loads. Variation in DC-link

voltage supply gets by using RSC-MLC

which also requires DC voltage. Proposed

work uses DC voltage supply by using solar

cells which is renewable resource of energy.

Voltage of PV panel is boosted using RSC-

MLC and HGBC (High gain boost

converter).Perturb and Observe (P and O)

gives us the details of PV panel MPPT

(Maximum power point tracking).Finally the

proposed results obtained by given

algorithm and Matlab simulation.

Key points: DSTATCOM, PV Power

Injection, Switching Losses, Variable DC

Link Voltage, Power Quality, RSC-MLC.

I. Introduction

There are three main parts in

DSTATCOM like controller, pair of

coupling reactors and main is voltage source

converter. Main working principle of

DSTATCOM is generating controlled ac

voltage source with the help of VSI(Voltage

source inverter) connected with DC

capacitors(storage sources).Voltage

difference at reactance can be created with

the help of active and reactive power

transfer in-between DSTATCOM and power

system. PV system has basic features such

as current, voltages and total inputs to it.

Many researchers are working on it to get

the characteristics of multi input PV system

and to get its efficiency. Many research

algorithms proves that higher

MPPT(maximum power point tracking) is

obtained for multi-input systems only

compared to single input system. DC-link

voltage selected by many three phase

inverters is 600V to avoid increase in output

current ripple. Inverter switching methods

can produce different current patterns which

causes grid current ripple which is related to

grid angle.

There are certain power quality issue

we faced because of unbalanced and

inductive loads in the distribution system

[1].This is because of many sensitive types

of equipment such as television, refrigerator

as well as inverters we used in banks,

industries, domestics and in commercial

places. Power electronics converters

demands for regular and controlled power

supply. As generators used by us produces

sinusoidal voltage and the current collected

from it may produce the loads with

distortions and unbalanced. It affects many

PV systems for connecting different loads

but the CPDs (Custom Power Devices)

overcomes the problem produced [2],

[3].There are many power quality problems

based on current generated which can also

shows issues like increased neutral current,

poor power factor and unbalanced currents.

DSTATCOM structure was changed

in literature design as per the requirement of

existing methods such as split capacitor

DSTATCOM and 4-leg DSTATCOM [4],

[5].4-leg DSTATCOM has one more leg to

provide the path for neutral current. As there

is use one more switch so there may be

chances of getting extra switching losses.

Because of two capacitors at dc-link there is

capacitive voltage problems in split

capacitor DSTATCOM. To overcome this

problem we used 3 leg VIS (Voltage source

inverter) with capacitor as neutral state

which overcomes the existing problems

[6].As it has only single capacitor at

available dc link so there is no chances of

getting capacitor voltage unbalance. Also in

existing they proved that there is no need of

any extra leg with more switches because

the reason is neutral capacitor can

compensate neutral current compensation.

Many topologies for rated load conditions dc

voltage should be kept constant [7].This can

produce the unnecessary switching losses

for given loads. Without affecting

compensation dc-link voltage reduces the

loads to get less switching losses for VSI

(Voltage source Inverter).

In reference paper [8], By using PI

controller adaptive DC voltage variations

are produced. It causes very low transit

response because of produced behavior of

the PI controller and dc voltage can make it

unreliable for given loads. Hysterisis is used

for controlling the gate pulses using RSC-

MLC. It is very faster as well as simple

phenomenon [9].Instantaneous symmetrical

component theory produces gate pulses for

getting reference harmonic current depends

on load demands by the client

[10].Reference dc link voltages can be

obtained by using harmonic current. To get

required DC link voltage we use RSC-MLC

with PWM (Pulse Width Modulation).Main

advantage of use of RSC-MLC is it reduces

the voltage stress at any given conditions of

switches which also reduces the switching

losses produced.

Next sections includes literature survey

which shows existing methods and detailed

information about them, after that the

proposed work is designed which indicates

our contribution to the work, result analysis

will include simulation results produced in

Matlab software by design of proposed

system. Conclusion section shows the final

decision of designing proposed work.

II.Literature Survey

The reduction of distortions

produced in current and voltage waveforms

to above the acceptable level is the major

problem in power system design. The recent

trends are focusing on using PV systems and

waveform sensitive devices. Utilization of

power is mostly depends on frequency and

voltage control while generation and

transmission based on constant supply of

power. Thereare certain power quality issue

we faced because of unbalanced and

inductive loads in the distribution system

[1].

Most of the power quality improvement in

electricity distribution uses custom devices

such as series compensating DVR, shunt

DSTATCOM also shunt with UPQC.Many

other devices also used like solid state

transfer switches and fault current limiters

with basic modifications. Application of

these is exactly related weak connection at

rural networks. There are many

requirements got cover such as voltage

balancing, voltage support and harmonic

suppression. This is because of many

sensitive types of equipment such as

television, refrigerator as well as inverters

we used in banks, industries, domestics and

in commercial places. Power electronics

converters demands for regular and

controlled power supply. As generators used

by us produces sinusoidal voltage and the

current collected from it may produce the

loads with distortions and unbalanced. It

affects many PV systems for connecting

different loads but the CPDs (Custom Power

Devices) overcomes the problem produced

[2],[3]. Power quality is one of the major

concerns last decades; also many analytic

systems are designed to overcome this

drawback using system interactions. In this

mathematical models are designed and

applied to get the solution for produced

disturbances. There are many power quality

problems based on current generated which

can also shows issues like increased neutral

current, poor power factor and unbalanced

currents.

The 4-leg DSTATCOM with

adaptive algorithms for control system as

neural network using linear as well as non-

linear source is presented in the paper. To

get the reference supply from current this

technique uses adaptive neural network with

its fundamental active and reactive power

components of the power. Under different

load conditions like linear and nonlinear we

observed DSTSTCOM performance which

found very satisfactory. DSTATCOM

structure was changed in literature design as

per the requirement of existing methods

such as split capacitor DSTATCOM and 4-

leg DSTATCOM[4],[5].In this

DSTATCOM performance is analyzed using

split capacitor under state space model. In

this inverter topology is utilized using zero

sequence coefficients also harmonic

compensation with load balancing. The

voltage get unbalanced that is the major

problem faced in capacitor topology.

III.PROPOSED WORK

Fig. 1: RSC-MLC based on DSTATCOM to

improve power qualitywith real power from

PV system.

Fig.1 shows the schematic of PV

improvement in DSTATCOM also power

injection in RSC-MLC on dc side of

VSI.Many existing techniques maintain

constant dc-link voltage under many load

conditions (double the peak of Vpcc)

[7].There is low requirement of dc-link

voltage when it is under off peak conditions.

To avoid unwanted switching losses while

reduced load time there is use of constant

rated dc-link voltage is preferred to use.

While going through the compensation dc-

link voltage may get reduced for off peaks.

This avoids the switching losses and stress

in switches.

Fig.2 Flowchart for calculation of dc-link

voltage

DC-link voltage of the DSTATCOM

can be regulated using proposed RSC-MLC.

At low loads conditions it makes reduction

in dc-link voltage which gives the

advantages of reducing switching losses. As

per the requirement of loads we will select

the dc-link voltage and operation of RSC-

MLC. The real power source can be

obtained by using PV panels for RSC-MLC.

The real power may be obtained by using

dependability of sunlight as well as load

requirements.DC-link voltage can be

proposed as per the flowchart mentioned in

fig.2.Icmax indicates the max.compasation

of current produced by DSTSTCOM with

given rated load conditions.

Fig. 3: Producing the pulses for modulated

and carrier signal

A. Designing Parameters for RSC-MLC

There is much necessary concentration on

designing dc-link inductor which is very

important to get voltage in smooth manner

and also to eliminate current ripples. Buck

converter with better features is nothing but

operated by RSC-MLC.

B. DSTATCOM Gate Pulses Generation

Gate pulses generated by control algorithm

for DSTATCOM is shown in below figure,

with the help of ISCT we generated

compensating current. Reference and actual

currents are compared and the error from it

is passed through hysteresis controller. Here

in algorithm it is shown that gate pulses are

generated as per load requirement while

operating with DSTATCOM.

Fig.4.DSTATCOM gate pulses generation

using control algorithm

With the help of proposed work it is possible

to compensate both reactive and harmonic

power requirements for load and it also

gives real power got from PV system. There

is improvement in power factor as the

current is totally free from producing

harmonics and also supplies real power.

C. PV panels- MPPT and real power

injection

Some of the real power generated is

compensated using PV panels combined

with DSTATCOM.Due to compatible

environment renewable sources are best

sources for many applications. This

proposed work uses solar energy which is

obtained from PV panels as DC supply to

give it to RSC-MLC. With the help of

HDBC(High gain boost converter) as well as

BC(boost converter) PV voltage gets

boosted as per requirement.One of the

famous algorithm named as P and O

algorithm is used to get maximum power

from PV panels.

IV.RESULT ANALYSIS

The proposed work is successfully designed

and analyzed by using MATLAB 2016a

version.

The parameters we used for

simulations of proposed work are mentioned

in below table, with the interval of gap 0.2

sec there is use of seven unbalanced and

non-linear loads.

Table 1: Simulation Parameters for Proposed Method

Fig: 5. Simulink Diagram in MATLAB

Above simulink model is designed for

proposed work in MATLAB.

4.PV-DSTATCOM Operations

Modes

The proposed model with PV panel

using RSC-MLC can be obtained in given

different modes of operation depending on

availability of load irradiation. Below it is

mentioned in details,

4.1Operation Mode I

This mode is mostly during night

hours and also in cloudy environment

because of inefficient real power to get the

load requirement generated by PV panels. In

this batteries maintain sufficient power

requirement for dc link voltage by collecting

small part of real power. Because of that

there is maintenance of harmonic mitigation,

load balancing and also reactive power

compensation in this mode I. The flow of

reactive power during DSTATCOM is given

below; it’s shown that in fig. reactive power

to load is generated by DSTATCOM.

Fig.6. Reactive powers flow in mode-1: Ql

is load reactive power, Qs is source reactive

power and Qc is reactive power

compensated by DSTATCOM.

4.2 OperationMode II

As PV panels can generate the

improved output when there is sufficient

irradiation (mostly in day time).So

DSTATCOM provides the real power

required for load and also there is

improvement in power quality required for a

system. This mode is explained in constant

and variation irradiation cases.

Fig.7 MPPT power (Ppv) (a) constant

irradiation: G=1000 W/m2, (b) variable

irradiation: G=0 W/m2 (0 s to 0.6 s), G=500

W/m2 (0.6 s to 1 s) and G=1000 W/m2 (1 s

to 1.4 s).

Constant Irradiation:

Fig. 7 shows there is MPPT power in

case of constant irradiation. This case

mostly takes place at day time where

constant irradiations are produced.PV panel

generates constant and real power which is

required for loads.

Variable Irradiation:

This case produced mostly at such

time when there are sudden changes in sun-

light. It may be produced at cloudy

environment and sun transition time. In this

case there is variation in irradiation of PV

panels because of that maximum real power

output changes w.r.t. time.

TABLE 2: %THD of source current also source power

factor indicating before as well as after compensation for

different load conditions.

Simulation parameters used in

proposed work are shown in table 2.

Simulation is performed on nonlinear loads

with interval of 0.2 s.

Fig. 8: Simulation waveforms for t = 0.1 s to 0.7 s:

(a) PCC voltage (vpcc), (b) load current (il), (c) and

(d) source current (is) and compensating current (ic)

without real power injection and with real power

injection, respectively.

Fig. 9.: Simulation waveforms for t = 0.7 s to 1.3 s:

(a) PCC voltage (vpcc), (b) load current (il), (c) and

(d) source current (is) and compensating current (ic)

without real power injection and with real power

injection, respectively.

The above waveform indicates the

power quality improvement in real power

injection.Fig.8 indicates t=0.1sec to 0.7 sec

and fig.9 from the t=0.7 to 1.3 sec. Its

observed from fig.8 and fig.9 when real

power injected from PV system there is

reduction in source current which indicates

that there is prevention of load-shedding and

over-loading.

The output waveforms from the fig.8

and fig.9 shows source current for

conditions at both cases. One is showing that

only condition at DSTATCOM mode while

another condition is at variable real power

which is injected through PV system. When

there is injection of real power then the

demand in real power taken through sources

got reduced. This shows that prevention of

overloading of load shedding and sources by

reduction in source current.

V.CONCLUSION

We designed proposed method

successfully using Matlab for regulating the

dc-link voltage with the help of RSC-MLC

without variations in the performance of

DSTATCOM.PV panels which is dc voltage

source are obtained by using renewable

energy resource. With the help of this PV

cells we can deliver the real power as well

as load compensation for day time load and

also it work for power quality improvement

at night as DSTATCOM. With the help of

simulations obtained by using Matlab

software we can show that there is

compensation in reactive power with

effective achievement of harmonics. The

advantage of proposed work is there is

balance in the source current, it is sinusoidal

also it’s a distortion free with improvement

in the power factor. After compensation

there is significant reduction in % TDH.And

because of reduced dc link voltage for given

lesser loads , there is very low voltage stress

at for switches also the switching losses are

reduced to great extent in which its

advantage we get is DSTATCOM efficiency

and life time is increased. With the help of

proposed work we can deliver the real

power to the loads and improved power

quality improvement.

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