MODELING AND SIMULAT

ION OF A

DYNAMIC VOLTA

GE

RESTORER

(DVR)

D E P A R T M E N T O F E L E C T R I C A L E N G I N E E R I N G

S U B M I T T E D B Y - P U N I T K U M A R V I N A Y M A L I

INTRODUCTION:  Among the power quality problems (sags, swells, harmonics…) voltage

sags are the most severe disturbances. In order to overcome these problems the concept of custom power devices is

introduced recently. One of those devices is the Dynamic Voltage Restorer (DVR), which is the most efficient and effective modern custom power device used in power distribution networks.

DVR is a recently proposed series connected solid state device and is normally installed in a distribution system between the supply and the critical load feeder at the point of common coupling (PCC). It employs a series of voltage boost technology using solid (static) state switches of 3-PHASE VSC that injects voltage into the system; to restore the load side voltage for compensating voltage sags/swells.

Other than voltage sags and swells compensation, DVR can also added other features like: line voltage harmonics compensation, reduction of transients in voltage and fault current limitations

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40kV /13 .2kV 40kV /13.2kV

NONC

40kV Bus

Industria l Substation

40kV Bus

Custom PowerDevice

Input Waveform

Output To Customer• A voltage sag/swell in the utility

waveform is seen by the customer without a Custom Power Device in the substation

• Sags and swells can have severe affects on the Customer Load

• Implementing the Customer Power Devices into the substations will correct the waveform

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Filter

Charger

Q1 Q2

Q3

T1 TL

Control

VG

VB VL

Dis

tribu

tion

Bus Lo

adB

us

DVR

IB= IG

• Power electronic converter injects appropriate voltage

• Acts as a buffer, used for injecting or absorbing

• Can Compensate a 50% three phase voltage dip for up to 50 cycles

• Cover a power range from 3MVA up to 50 MVA

DynamicVoltage Restorer

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FEATURES OF DVR: Lower cost, smaller size, and its fast dynamic

response to the disturbance. Ability to control active power flow. Higher energy capacity and lower costs

compared to the SMES device. Less maintenance required. UPS is costly, it also

requires a high level of maintenance because batteries leak and have to be replaced as often as every five years.

Fig. Location of DVR

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When a fault occurs on the line feeding Load 1, its voltage collapses to zero. Load 2 experiences sag equals to the voltage at the PCC and the voltage of sensitive load protected by the DVR is restored to its pre-fault value.

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Fig. Basic structure of DVR

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Basic Configuration of DVR: The general configuration of the DVR consists of: i. An Injection/ Booster transformerii. A Harmonic filteriii. Storage Devicesiv. A Voltage Source Converter (VSC)v. DC charging circuitvi. A Control and Protection system

Fig. Schematic diagram of DVR

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INJECTION/BOOSTER TRANSFORMER: The Injection / Booster transformer is a specially designed transformer that attempts to limit the coupling of noise and transient energy from the primary side to the secondary side. Its main tasks are:connects the DVR to the distribution network via the HV-windings and transforms and couples the injected compensating voltages generated by the voltage source converters to the incoming supply voltage.serves the purpose of isolating the load from the system (VSC and control mechanism).HARMONIC FILTER:This can cause voltage drop and phase shift in the fundamental component of the inverter output and has to be accounted for in the compensation voltage.

VOLTAGE SOURCE CONVERTER: -consists of a storage device and switching devices-generate a sinusoidal voltage at any required frequency, magnitude, and phase angle. -In the DVR application, the VSC is used to temporarily replace the supply voltage or to generate the part of the supply voltage which is missing.DC Charging Circuit:The dc charging circuit has two main tasks:- The first task is to charge the energy source after a sag compensation event.- The second task is to maintain dc link voltage at the nominal dc link voltage

CONTROL AND PROTECTION:The control mechanism of the general configuration typically consists of hardware with programmable logic. All protective functions of the DVR should be implemented in the software. Differential current protection of the transformer, or short circuit current on the customer load side are only two examples of many protection functions possibility.

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OPERATING MODES OF DVR:

1. PROTECTION MODE:

If the over current on the load side exceeds a permissible limit due to short ccircuit on the load or large inrush current, the DVR will be isolated from the systems by using the bypass switches (S2 and S3 will open) and supplying another path for current (S1 will be closed)

2. STANDBY MODE: (VDVR= 0)

-In the standby mode the booster transformer’s low voltage winding is shorted through the converter. -No switching of semiconductors occurs in this mode of operation and the full load -Current will pass through primary

3.INJECTION/BOOST MODE: (VDVR>0)the DVR is injecting a compensating voltage through the booster transformer due to the detection of a disturbance in the supply voltage

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TEST SYSTEM OF DVRThe test system for DVR is composed by a 13 kV, 50 Hz Generation system, feeding transmission line through a 2- winding transformer connected in Y/ Δ,13/115KV. Such transmission line feed distribution network through step down transformer connected in Δ/Y, 115/11 kV. To verify the working of DVR for voltage compensation a fault is applied at point X at resistance 0.66 U for time duration of 200 ms. The DVR is simulated to be in operation only for the duration of the fault.

Simulink model of DVR controller

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Sr. no.

System quantities Standards

1. Three phase source 13KV, 50Hz.2. Step-up transformer Y-Δ , 13/115KV3. Transmission line parameter R=0.001 ohms,L=0.005 H4. Step-down transformer Δ-Y, 115/11KV5. Load 1 &2 10KW, 400VAR6. Inverter IGBT based,3 arms ,

6 Pulse,Carrier Frequency =1080 Hz,Sample Time= 5 μs

7. PI controller Kp=0.5Ki=50Sample time=50 μs

8. DC battery 6.5 KV9. C2 750 μF10. Linear/Isolation transformer 1:1 turns ratio, 11/11KV

SYSEM PARAMETERS

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SIMULATION AND RESULT

D E E PA K G U P TA 13System without DVR & with fault

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Phase –phase, three-phase and p.u. voltages at load point for a-b-c fault

sag

15System with DVR & fault

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Phase –phase and three-phase voltages at load point for a-b-c fault

p.u voltages at load point for a-b-c fault