Implementation of DVR With PV Cells to Reduce Voltage Sag for Industrial Application

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International Journal of Electrical, Electronics and Computer Systems (IJEECS)

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ISSN (Online): 2347-2820, Volume -3, Issue-5 2015 19

Implementation of DVR With PV Cells to Reduce Voltage Sag for Industrial Application

1D.Kavitha, ²K.M.Kavitha, ³B.Kantharaj, ⁴T.R Narasimhegowda

1,2,3,4Department of Electrical and Electronics Engineering, Adichunchanagiri Institute of Technology, Chikkamagaluru.

Email: ¹[email protected], ²[email protected], ³[email protected]

4[email protected]

Abstract- The DVR is a power electronic based device that provides three-phase controllable voltage source, whose voltage vector (magnitude and angle) adds to the source voltage during sag event, to restore the load voltage to pre- sag conditions. The DVR can restore the load voltage within few milliseconds. This paper presents different voltage injection schemes for dynamic voltage restorers (DVRs) are analyzed and with particular focus on In-phase compensation method used to minimize the rating of DVR.

The synchronous reference frame theory is used for the conversion of voltages from rotating vectors to the stationary frame. The compensation of the voltage sag is demonstrated. The results of the simulation studies performed in the MATLAB software.

Index Terms-Dynamic Voltage Restorer(DVR),power quality, voltage sag, SRF theory.

I. INTRODUCTION

The fulfillments of the industrial goals were possible only because the modern industries were able to find innovative technologies that have successfully become technological developments. Cessation to provide the required quality power output may sometimes cause complete shutdown of the industries which will make a significant financial loss to the industry concern. Some aberrant electrical conditions that can disrupt a process caused both at the utility and the customer end are Voltage Sags, Phase Outages, Voltage Interruptions, Transients due to Lighting loads, capacitor switching, non linear loads, Harmonics etc.

The solutions for above mentioned anomalies are FACTS devices (Flexible AC Transmission Systems) and Custom power devices that are based on solid state power electronic components. The custom power devices are developed and installed at consumer point to meet the power quality standards such as IEEE-519. When the fast variations in the source voltage cannot be ignored, these can affect the performance of critical loads such as semiconductor fabrication, plants paper mills, food processing plants and automotive assembly plants. Voltage sags are the common reasons for interruption in production plants and for end-user equipment malfunctions in general. In particular, tripping of equipment in a production line can cause production interruption and significant costs due

to loss of production. One solution to this problem is Dynamic Voltage Restorer (DVR).Its primary application is to compensate for voltage sags and swells.

Also, a DVR is expected to respond fast (less than 1/4 cycle) and thus employs PWM converters and IGBT.[1]

An energy-optimized control of DVR is discussed in [2].

The design of a capacitor-supported DVR that protects sag, swell, distortion, or unbalance in the supply voltages is discussed in[3]. The performance of a DVR with the high- frequency-link transformer is discussed in [4]. In this paper, the control and performance of a DVR are demonstrated with a reduced-rating voltage source converter (VSC). The synchronous reference frame (SRF) theory is used for the control of the DVR.

II. COMPONENTS OF DVR

Dynamic Voltage Restorer is one of custom power device specially used to inject a (fundamental frequency) voltage in each phase of required magnitude and phase to maintain the load voltage constant in the distribution system. Fundamental of DVR is shown in fig1.a.The power circuit of DVR shown in fig 1.b.

Fig 1.a. Fundamental of DVR.

Fig:1.b. The power circuit of DVR

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The DVR consists of boost/series injection transformer, voltage source converter, passive filters, energy storage device and control circuit. Three single phase transformers are connected in series with the distribution feeder to couple the VSC (at the lower voltage level) to the higher distribution voltage level. In DVR voltage source converter is used to either completely replace the supply voltage or to inject the missing voltage. The missing voltage is the differeerence between the nominal voltage and the actual one.

Switching device used is Insulated Gate Bipolar Transistors(IGBT). The passive filters placed at the high voltage side of the DVR to filter the harmonics.

Energy storage is required to provide active power to the load during deep voltage sags. Lead-acid batteries, flywheel or SMES can be used for energy storage.

Control circuit continuously monitors the supply voltage. The function of control system is to detect the disturbance in the supply voltage, compare it with the set reference value and then generate the switching pulses to the VSC to generate the DVR output voltages which will compensate the voltage sag.

III. DVR COMPENSATION TECHNIQUES.

Compensation by DVR depends upon limiting factors such as power rating, load conditions, and voltage-sag type. Different methods of compensation are Pre-sag/Dip compensation method(PDC): This method is recommended for the non linear loads which needs both voltage magnitude as well as phase angle to be compensated. Drawback of this method is that it requires higher capacity energy storage device as well as large voltage injection transformer.

Fig.2. Vector diagram of PDC method

In-phase compensation method: In this method only voltage magnitude is compensated. It is recommended for linear loads.

Fig.3. Vector diagram of In-Phase compensation method Energy optimised compensation (or) In-phase advanced compensation(IPAC) In this method the real

power spent by DVR is minimised by decreasing the power angle between the sag voltage and the load current.

Voltage tolerance method with minimum energy injectiom: Generally the voltage magnitude between 90%- 110% of the nominal voltage and phase angle variations between 5-10% of the nominal state will not disturb the operation characteristics of loads. This method can maintain the load voltage in the tolerance area with small change of voltage magnitude.

Fig.4. Voltage tolerance method with minimum energy

injection.

IV. MODELING OF DVR WITH SOLAR PANEL FOR VOLTAGE SAG

Fig. shows a MATLAB model of the DVR in which the SRF theory is used for reference signal estimation. The voltages at the PCC vS and at the load terminal vL are sensed for deriving the IGBTs’ gate signals. The reference load voltage V*L is extracted using the derived unit vector [5]. Load voltages (VLa, VLb, VLc) are converted to the rotating reference frame using abc−dqo conversion using Park’s transformation with unit vectors (sin, θ, cos, θ) derived using a phase-locked loop as

Similarly, reference load voltages (V*La, V*Lb , V*Lc) and voltages at the PCC vS are also converted to the rotating reference frame. Then, the DVR voltages are obtained in the rotating reference frame as

vDd = vSd – vLd (2) vDq =vSq – vLq (3)

The reference DVR voltages are obtained in the rotating reference frame as

v*Dd =v*Sd – vLd (4) v*Dq =v*Sq − vLq (5)

The error between the reference and actual DVR voltages in the rotating reference frame is regulated using proportional–integral-derivative (PID) controllers.

Reference DVR voltages in the abc frame are obtained from a reverse Park’s transformation taking V*Dd from (4), V* V*D0 as zero as from (5),

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Dq

Reference DVR voltages (v^∗_dvra, v^∗_dvrb, v^∗_dvrc) and actual DVR voltages (v_dvra, v_dvrb, v_dvrc) are used in a pulsewidth modulated (PWM) controller to generate gating pulses to a VSC of the DVR. The PWM controller is operated with a switching frequency of 10 kHz.

Fig.5. MATLAB based model of the Solar Panel supported DVR connected system.

V. SIMULATION RESULTS

A. System Analysis without DVR

The simulation results for system with-out DVR are given below. The voltage sag during overloading condition at the interval 0.2-0.4secs are shown in Fig 6

Fig.6. Simulation of the system without DVR.

B. System Analysis with DVR

The simulation results for system with DVR are given below. The Load voltage is regulated to constant amplitude under sag during overloading condition at the interval 0.2-0.4secs are shown in Fig.7.

Fig.7. Simulation of the system with DVR

VI. CONCLUSION

Dynamic Voltage Restorer (DVR) with Solar Panels is an effective device for power quality enhancement due to its quick response and high reliability. The SRF theory has been used for estimating the reference DVR voltages. The conclusion is that it is an effective apparatus to reduce the Voltage Sag during disturbances. The lod voltage is maintained sinusoidal by voltage injection in-phase with pcc voltage.

REFERENCES

[1]. K. R. Padiyar, FACTS Controllers in Transmission and Distribution. New Delhi, India:

New Age Int., 2007.

[2] M. Vilathgamuwa, R. Perera, S. Choi, and K.

Tseng, “Control of energy optimized dynamic voltage restorer,” in Proc. IEEE IECON, 1999, vol. 2, pp. 873–878.

[3] A. Ghosh and G. Ledwich, “Compensation of distribution system voltage using DVR,” IEEE Trans. Power Del., vol. 17, no. 4, pp. 1030–1036, Oct. 2002.

[4] A. Y. Goharrizi, S. H. Hosseini, M. Sabahi, and G. B. Gharehpetian, “Three-phase HFL-DVR with independently controlled phases,” IEEE Trans. Power Electron., vol. 27, no. 4, pp. 1706–

1718, Apr. 2012.

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