POWER QUALITY IMPROVEMENT USING UPQC IN DISTRIBUTION … · 2019-04-22 · POWER QUALITY IMPROVEMENT USING UPQC IN DISTRIBUTION SYSTEM WITH HYBRID RENEWABLE RESOURCES CONSIDERING

VOL. 14, NO. 7, APRIL 2019 ISSN 1819-6608

ARPN Journal of Engineering and Applied Sciences ©2006-2019 Asian Research Publishing Network (ARPN). All rights reserved.

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POWER QUALITY IMPROVEMENT USING UPQC IN DISTRIBUTION

SYSTEM WITH HYBRID RENEWABLE RESOURCES

CONSIDERING DYNAMICS

J. P. Sridhar Department of Electrical and Electronics Engineering, SJB Institute of Technology, Bangalore, India

E-Mai: [email protected]

ABSTRACT

The DG placement algorithms perform the optimal placement and sizing in distribution system. But it only

considers the real and reactive power loss minimization. The analysis is static. The DGs are generally dynamic in nature as

they are renewable resources. But the loads connected in the DGs are not only linear loads. Many loads at the feeder are

non-linear. In this paper the unified power quality conditioner (UPQC) is interfaced with PV (Photo Voltaic) and wind

generators. The current reference generation technique is used for series converter and shunt converter by using this hybrid

combination. This takes care of all types of voltage sags and swells. The real and reactive power both is controlled from

PV and wind to grid. The system is considered as a standard distribution feeder system. The 230V feeder system is

considered here for testing these dynamics.

Keywords: unified power quality conditioner, photo voltaic, squirrel cage induction generator

INTRODUCTION

There are many papers published on this problem.

Some literatures study different impact of wind farms on

power system under symmetrical and asymmetrical grid

faults [2-5]. Some methods to compensate voltage sag

have been investigated in [6-7]. Flexible AC Transmission

System (FACTS) devices such as Static Var Compensator

(SVC) [8], STATic synchronous COMpensator

(STATCOM) [9], Dynamic Voltage Restorer (DVR) [10-

11] are effective solution for voltage sag compensation.

These devices absorb or inject reactive and active power to

the grid to overcome the fault problems. In the other hand,

FACTS devices can control the power between SCIG and

grid to avoid disconnection of wind turbine from grid [4-

5].

Unified power quality conditioner (UPQC) is one

of the versatile FACTS devices that consists of two parts

which are connected in series (SERC) and shunt (SHUC)

Voltage Source Inverters (VSI) [12-13]. Depending on the

type of control system, the UPQC represents a practical

solution to protect sensitive loads in the presence of grid

disturbances, such as voltage sags, swell, harmonics and

etc. Some methods have published to control of UPQC

such as UPQC-P [12-14], UPQC-Q [14]. UPQC-P can

compensate only the magnitude of voltage but it could not

compensate the phase jump recovery. This control scheme

can compensate the voltage sag by a minimum injection

voltage. UPQC-Q need a large voltage magnitude and this

can be increase the rating of UPQC. However, UPQC-Q

inject a minimum energy to the grid [14].

In this paper the hybrid PV and Wind dynamics

are added to the standard distribution system and the

performances are analyzed with UPQC and without

UPQC. By using the MATLAB 2017b/Simulink for

testing the proposed solution method.

METHODOLOGY

Block diagram

mailto:[email protected]

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Figure-1. Block diagram of proposed system.

Problem definition

The UPQC previously is analyzed only with the grid

connected system

The Renewable energy resources are having problem

of harmonics, sag and swell due to dynamics.

The real and reactive power control is not properly

done in renewable energy resources

Problem solution

The UPQC is analyzed with wind and grid

synchronization

The PV is used for supplying real and reactive power

at DC link, which make stability in the system

Here disturbances like Harmonics, Sag and swell can

be mitigated by using PV and wind-based grid

integrated with UPQC.

The current reference generation technique is used

here for doing all the above.

RESULTS AND DISCUSSIONS

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Figure-2. Simulation diagram of UPQC with PV and wind (SCIG).

The project is designed on the basis of working of

Unified Power Quality Conditioner (UPQC)

connected between the Grid and a Squirrel cage

Induction generator (SCIG) to eliminate the voltage

sag occurred during fault condition.

One side of system is connected with a three-phase

programmable voltage source which is considered as

source to the distribution system adjacent to it.

The other end is provided with a Squirrel cage

Induction generator to which it will operate as

generator when the Mechanical torque is negative.

The UPQC circuit is connected between the

distribution system and SCIG to compensate the

voltage sag, swell and harmonics during fault

condition. It also provided with a Photo voltaic

system as hybrid to wind generation.

UPQC (Unified power quality conditioning):

Unified power quality conditioning is the matter of

conditioning the components of the power i.e. Supply

voltage and Load current.

The conditions to satisfy the conditioning are as

follows:

a) If there is any fluctuations or harmonics occurs in the

supply voltage, which should not be affected to the

load. So, we need to take care of the voltage to be

sinusoidal and controlled at desired value.

b) If there is a non-linear load is working at the load

side, then it consumes non-linear current which leads

to non-linearity in the grid part and that affects to

other loads also. So, we need to take care of the

current to be sinusoidal and to make it like there

should have minimum amount of THD value.

c) And we need to take care of the reactive power to be

maintained at zero level at Grid point.

The UPQC part includes 3 points:

Voltage compensation (Series APF)

Current compensation (Shunt APF)

DC capacitor voltage controller

A. Voltage compensation (Series APF):

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Figure-3. Voltage Compensation block.

Voltage compensation will decide how much

voltage error is there in the grid and how much voltage has

to induce in the grid to make the voltage sinusoidal with

desired voltage magnitude and frequency.

Figure-4. Series converter controller block.

The supply voltage have to be subtracted by

Reference voltage (Vabc*), it calculates the error in

voltage which is then compared with error voltage

produced in 3 lines and then proceeded to Hysteresis

control to produce the pulses to minimize that error

produced by difference in calculated error voltage and

produced error voltage.

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Figure-5. PWM and reference voltage generation.

B. Current compensation (Shunt APF):

Current compensation will decide how much

current error is there in the grid and how much current

have to induce in the grid to make the current non-linearity

sinusoidal with desired current magnitude and frequency.

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Figure-6. Shunt converter active power filter block

The load current has to be subtracted by

Reference currents (Iabc*) which will be sinusoidal which

Id and Iq currents are purified by collecting load currents,

it calculates the error in current which is then compared

with error current produced in 3 lines and then proceeded

to Hysteresis control to produce the pulses to minimize

that error produced by difference in calculated error

current and produced error current.

Figure-7. Shunt controller of active power filter.

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Figure-8. Reference current generation blocks.

Figure-9. DC link capacitor voltage control:

The DC capacitor voltage has to be maintained at

some desired value. For that the controlling part has to be

designed. The reference value has to be subtracted by

measured DC voltage and the Error has to be minimized to

zero by a transfer function and the control signal have to

be added to Id current.

PI

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Figure-10. Photo voltaic system with boost converter for MPPT:

When PV works, the DC voltage may oscillate.

Boost converter also provided to boost up the voltage

from 500V from PV to 800V DC across capacitor

with MPPT capability.

RESULTS AND DISCUSSIONS

The entire system is built for 230 V, 50 Hz

system. There are four disturbances created in this system

as given in tabular column. Grid has the change in its

amplitude to 230 to 184 V at 0.1 secs, then 184 to 230V at

0.2 secs and 230V to 276 V at 0.5 secs. Then the UPQC is

turned on at 0.06 secs. Solar changes from 1000 w/m2 to

500 w/m2 at 0.75 secs. Wind speed is changed from 10 m/s

to 1m/s. Figure-11 shows the voltage without UPQC

during fault. Figure-12 shows the Injected Voltage and

current by UPFC, Figure-13 shows the Grid side voltage

and current. Figure-14 shows Grid side current before

compensation THD. Figure-15 shows the Grid current

after compensation. Figure-15 shows the DC capacitor

voltage. Figure-16 shows before and after compensation in

RMS voltage. So, from these figures the voltage sag and

swell are compensated very well even with solar and wind.

The THD is 28.68% without any compensation. After

compensation 1.97% of THD.

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Figure-11. Voltage and current without UPQC during fault.

Figure-12. Injected Voltage and current by UPFC.

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Figure-13. Grid side voltage and current after compensation by using UPQC.

Table-1. Dynamics applied to the simulation.

grid dynamics

Voltage in pu [1 0.8 1 1.2 1.2]

Time in secs [0 0.1 0.2 0.5 1]

UPQC dynamics

relay [off on on]

Time in secs [0 0.06 1]

solar dynamics

Irradiance (W/m2) [1000 500 500]

Time in secs [0 0.75 1]

Wind dynamics

wind speed 10

Time in secs 1

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Figure-14. Grid side current before compensation THD.

Figure-15. Grid current after compensation.

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Figure-16. DC capacitor voltage:

Figure-17. Before and after compensation in RMS.

CONCLUSIONS

The UPQC device is constructed for series and

shunt compensation. The grid produces sags and swell in

the system which can be overcome with using controller

gives better performance in transient switching conditions

is explained and the results shows the same performance is

achieved including PV and wind. The UPQC controller is

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performing better to rectify the problem of harmonics,

voltage sag and swell in distribution system.

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POWER QUALITY IMPROVEMENT USING UPQC IN DISTRIBUTION … · 2019-04-22 · POWER QUALITY IMPROVEMENT USING UPQC IN DISTRIBUTION SYSTEM WITH HYBRID RENEWABLE RESOURCES CONSIDERING