Photovoltaic Based Dynamic Voltage Restorer with Outage Handling Capability Using PI Controller

Transcription

1 Available online at Energy Proedia 12 (2011) ICSGCE 2011: September 2011, Chengdu, China Photovoltai Based Dynami Voltage Restorer with Outage Handling Capability Using PI Controller M. Ramasamy a*, S. Thangavel b a K. S. R. College of Engineering, Tiruhengode, Namakkal, , India b Department of Eletrial and Eletronis Engineering, K.S.Rangasamy College of Tehnology, Tiruhengode, Namakkal, India Abstrat In this paper, Photovoltai (PV) based Dynami Voltage Restorer (DVR) is proposed to handle deep voltage sags, swells and outages on a low voltage residential distribution system. The PV based DVR an reover sags up to 10%, swells up to 190% of its nominal value. Otherwise, it will operate as an Uninterruptable Power Supply (UPS) when the utility grid fails to supply. PV based DVR system is omprised of PV System with low and high power DC-DC boost onverter, PWM voltage soure inverter, series injetion transformer and semiondutor swithes. Simulation results proved the apability of the proposed DVR in mitigating the voltage sag, swell and outage in a low voltage distribution system Published by Elsevier Ltd. Open aess under CC BY-NC-ND liense. Seletion and/or peer-review under responsibility of University of Eletroni Siene and Tehnology of China (UESTC) Keywords: Dynami Voltage Restorer (DVR), Photovoltai, Voltage sag, Voltage Swell, Outage, DC DC Boost Converter 1. Introdution Dynami Voltage Restorer (DVR) an provide the most ost effetive solution to mitigate voltage sags, swells and outages by establishing the proper voltage quality level that is required by sensitive loads. Problems faing industries and residential regarding the power qualities are mainly due to voltage sag, voltage swells and power interruptions. This may our in developing ountries, where the generated eletrial power is less then the demand. The above-mentioned power quality problems may disturb the proess of prodution in industries and residenes, resulting in equipment damage and loss of revenue. Voltage sag is a sudden redution of utility supply voltage whih may vary from 90% to 10% of its nominal value. On the other hand, voltage swell is a sudden rise of supply voltage whih may vary from 110% to 180% of its nominal value. Aording to the IEEE and IEEE standards, a * Corresponding author. Tel.: address: ramasamyksre@gmail.om Published by Elsevier Ltd. Seletion and/or peer-review under responsibility of University of Eletroni Siene and Tehnology of China (UESTC). Open aess under CC BY-NC-ND liense. doi: /j.egypro

2 M. Ramasamy and S. Thangavel / Energy Proedia 12 (2011) typial duration of voltage sag and swell is 10 ms to 1 minute [1]. The outage refers to an interruption of power for long duration. Many researh works have been arried out fousing in the design and ontrol of DVR [2] [5]. The voltage sags and swells often aused by starting of large indution motors, energizing a large apaitor bank and faults suh as single line to ground fault, three phase to ground fault, double line to ground fault on the power distribution system. Voltage sag and swell in power systems produe an important effet on the behavior of sensitive loads. In general, the voltage injetion from DVR ompensates the voltage sag, swell and outage. However, it needs a high apaity DC storage system. In the proposed DVR design, a PV system with low and high power DC-DC boost onverters are inorporated to funtion as a high apaity DC voltage soure. This Paper presents a simulation model of a PV based dynami voltage restorer apable of handling 10% voltage sags, 190% of voltage swells and outages on a low voltage distribution system. In the daytime, DVR will at as online UPS to feed the generated power in PV system to battery and load [6]. 2. Proposed DVR The blok diagram of the proposed PV based DVR is shown in Fig.1. The proposed system mainly onsists of a photovoltai array, low and high power DC/DC boost onverters, battery, PWM inverter, series injetion transformer, and semiondutor swithes S 1, S 2, S 3, R 1 and R 2. Fig.1. Blok Diagram of the proposed PV based DVR. Fig. 2 In-phase ompensation An injeting transformer is onneted in series with the load for restoring sag and swell, and is reonfigured into parallel onnetion using swithes S 1, S 2 and S 3 when handling outage [7]. A DVR an ompensate voltage drop aross a load by injeting a voltage through a series injetion transformer [8]. The injeted voltage is in phase with supply voltage, as shown in Fig. 2. In normal ondition, the supply voltage is equal to the load voltage with zero angle. During sag, the supply voltage dereases to a value less than its nominal value. The DVR reats to the sag event and injets a ompensating voltage V inj in phase with the supply voltage to restore the voltage at nominal

3 562 M. Ramasamy and S. Thangavel / Energy Proedia 12 (2011) value. This method is very simple to implement, very fast espeially in alulating the DVR ompensating voltage. The injeted voltage of a DVR (V DVR ) an be expressed as (1) The inverter is a ore omponent of the DVR. Its ontrol will diretly affet the dynami performane of the DVR. A sinusoidal PWM (SPWM) sheme is used. The arrier waveform is a triangular wave with higher frequeny (1080 Hz). The modulation index varies aording to the input error signal from the PI ontroller. The basi idea of SPWM is to ompare a sinusoidal ontrol signal of normal frequeny 50 Hz with a triangular arrier signal. When the ontrol signal is greater than the arrier signal, the swithes turned on and their ounter swithes are turned off. The output voltage of the inverter mitigates the sag, swell and outage. The DC voltage might be used from PV array if available. Otherwise, the line voltage is retified and the DC energy is stored in batteries. 3. Photovoltai Array Modeling PV array is a system whih uses two or more solar panels to onvert sunlight into eletriity. Photovoltai array is a linked olletion of solar ells. The use of new effiient photovoltai solar ells has emerged as an alternative soure of renewable green energy onversion. In the proposed DVR, PV array provides a DC soure for the DVR. The eletrial system powered by solar array requires DC/DC onverter due to varying nature of the generated solar power resulting from sudden hanges in weather onditions whih hange the solar irradiation level as well as ell operating temperature. Solar arrays are built up with ombined parallel/series ombination of solar ells. The PV array is designed and modelled with a low step up boost onverter to harge the batteries. The PV model is developed using basi equations of photovoltai ells inluding the effets of temperature hanges and solar irradiation [9]-[11]. The PV ell output voltage is a funtion of the photo urrent that mainly determined by load urrent depending on the solar irradiation level during the operation. The solar ell output voltage is shown in equation (2). (2) where, e - Eletron harge ( V Cell output voltage in volts. I ph - Photo urrent (10 A). I Reverse saturation urrent of diode ( A). 0 k Boltzmann onstant (1.38 / 0 k). I Cell output urrent in A. R s Solar ell internal resistane (0.001 ). T - Operating temperature of the referene ell (40 0 ).

4 M. Ramasamy and S. Thangavel / Energy Proedia 12 (2011) When the irradiation and ambient temperature hange, the solar ell operating temperature also hanges, resulting in a new output voltage and a new photo urrent. The solar ell operating temperature varies as a funtion of solar irradiation level and ambient temperature. The effet of temperature variations are represented in the model by the temperature oeffiients C TV and C TI. (3) (4) where, = and = for the ell used and T a =40 0 is the referene ambient temperature. Tx is atmospheri ambient temperature. The hange in the photourrent and operating temperature due to variation in the solar level an be expressed as follows. (5) (6) where, S - referene solar irradiation level (100 W/m 3 ). S new level of solar irradiation. x The new value of ell output voltage and photo urrent an be expressed as follows. V CX = C TV C SV V C (7) I phx = C TI C SI I ph (8) The temperature hange, T, ours due to the hange in solar irradiation level. T = A funtional blok diagram of photovoltai (PV) array is shown in Fig.3

5 564 M. Ramasamy and S. Thangavel / Energy Proedia 12 (2011) DC/DC Converter Fig.3. Funtional blok diagram of photovoltai array. A DC-DC onverter is an eletroni iruit to onvert a soure of DC voltage from one level to another level. Additionally, the battery voltage delines as its stored power is drained. Swithed DC to DC onverters offer a method to inrease voltage from a partially lowered battery voltage thereby saving spae instead of using multiple batteries to aomplish the same thing and it regulates the DC voltage Low Power DC-DC Boost Converter. In the boost onverter, the output voltage is greater than the input voltage [12]. A low step up DC-DC onverter is shown in Fig.4. Its main funtion is to regulate the output voltage of the PV array. Fig.4. Ciruit diagram of low step up DC-DC onverter Fig.5 High step up DC-DC onverter The iruit operation an be divided into two modes. When the swith S is on, the diode D m is reverse biased by swith and V, thus isolating the output stage. The input urrent (i s ), whih raises, flows through indutor L and swith S. The input supplies energy to the indutor during on period (T on ). The voltage aross the indutor (L) in mode 1 is shown in equation (9).

6 M. Ramasamy and S. Thangavel / Energy Proedia 12 (2011) (9) When the swith S is off, the indutor urrent is fored to flow through the diode D m and load for a period T off. As the urrent tends to derease, polarity of the emf indued in indutor L is reversed and it is onneted in series with voltage soure V s and load through diode D m. The output voltage V o in mode 2 is expressed in equation (10). (10) The average output voltage of the onverter is depited in equation (11). (11) where, D Duty Cyle, T on On time, T off Off time High Power DC-DC Boost Converter. The output voltage level of the low power DC-DC onverter and batteries are low. Hene, it is not suffiient to injet the required amount of voltage to load to mitigate voltage sags, swells and outages. For that a high step up DC-DC onverter is used to step up the low power d to high power d. It is onneted in between batteries and PWM voltage soure inverter. Fig. 5 shows the iruit diagram of high step up DC-DC onverter [13]-[16]. The main operating priniple of this onverter is that when the swith S is turned on, the oupled indutor indues voltage on the seondary side and magneti indutor L m is harged by V in. The indued voltage in the seondary makes V in, V 1, V 2 and V 3 to release energy to the load in series. When the swith S is turned off, the energy stored in the magneti indutor L m is released via seondary side of oupled indutor to harge the apaitors C 2 and C 3 in parallel. The proposed onverter operation an be divided into five mode of operation [13]. The output equation of high step up DC-DC onverter is shown in equation (12). (12) where, V 1 Voltage aross the apaitor C1 in voltage. V 2 Voltage aross the apaitor C2 in voltage. V 3 Voltage aross the apaitor C3 in voltage.

7 566 M. Ramasamy and S. Thangavel / Energy Proedia 12 (2011) Voltage aross the seondary of the oupled indutor (N s ) in mode II. (13) (14) (15) where, k - Coupling oeffiient (k = ). n - Coupled indutor turns ratio ( ). D Duty Cyle ( ). or (16) (17) 5. Simulation Results and Disussions A 3 KVA, 230/230V transformer is used for onneting the DVR to the network. The proposed DVR model is simulated by MATLAB simulink to ompensate voltage sag, voltage swell and outages at the soure side. The total simulation period is 1 se. Using the failities available in MATLAB the DVR is simulated to be in operation only when the supply voltage differs from its nominal value. Otherwise, the DVR will at as online ups when the PV array output is greater than 6V. It redues the energy onsumption from the utility grid. During the night times the output voltage of the PV array is too low. At that time, the batteries get the harge from the retifier. A programmable three phase voltage soure is used to provide the single phase variable voltage at the soure end. The first simulation ontains no DVR, a redued voltage (184 V) is applied, during the period 0.1 se to 0.2 se, a raised voltage (276 V) is applied, during the period 0.7 se to 0.8 se and zero voltage (0V) is applied, during the period 0.3 se to 0.6 se, as presented in Fig. 6 (a). The voltage sag and swell at the soure point is 30% and 20% with respet to the referene voltage. The injeted voltage, load voltage and load urrent of the DVR are shown in Fig. 6 (b), Fig. 6 () and Fig 6 (d).

8 M. Ramasamy and S. Thangavel / Energy Proedia 12 (2011) (a) Supply Voltage (b) Injeted Voltage ()Load Voltage (d)load Current Fig. 6 Supply voltage, Injeted voltage, Load voltage and Load Current The PV array onsists of 9 PV ells, all onneted in series to have a desired voltage output. Depending on the load power required, the number of parallel branhes an be inreased to 9 or more [17]. PV array with boost onverter an give greater output voltage. Fig.7 (a) and Fig 7 (b) show PV array voltage without and with boost onverter, respetively. (a) PV array output voltage without low power boost onverter (b) PV array output voltage with low power boost onverter Fig. 7 PV array output voltage without and with boost onverter Two lead aid batteries with 12 V, 88 Ah are onneted in series to obtain 24 V. Fig.8 (a) and Fig. 8 (b) shows the disharge harateristi of the battery. (a)nominal Current Disharge Charateristis (b)disharge Charateristis for various output urrent Fig. 8 Battery Charateristis The high power boost onverter speifiations are: [1] Input DC voltage V in = 24 V. [2] Output DC voltage V o = 230 V. [3] Maximum output power = 4 KW. [4] Swithing frequeny = 25 khz. [5] L m = 48 µh, L k = 0.25 µh. [6] C 1 = µf / 100V, C 2 = C 3 =1.062 µf / 200 V and C 0 = 500 µf /450V. Fig. 9 shows the output voltage of the high power boost onverter. The onverter is operated in

9 568 M. Ramasamy and S. Thangavel / Energy Proedia 12 (2011) ontinuous ondution mode (CCM). Under the full load operating ondition V in =24V, V 0 =230V and P o =2.3KW. A ontrol iruit is inorporated with the proposed onverter to regulate the output voltage at 230V. Fig. 9 Output voltage of the high step up DC-DC onverter 6. Conlusion The design of a Dynami Voltage Restorer (DVR) whih inorporates a PV array module with low and high power boost onverters as a DC voltage soure to mitigate voltage sags, swells and outages in low voltage single phase distribution systems has been presented. The modeling and simulation of the proposed PV based DVR using MATLAB simulink has been presented. The PI ontroller utilizes the error signal from the omparator to trigger the swithes of an inverter using a sinusoidal PWM sheme. The proposed DVR utilizes the energy drawn from the PV array and the utility soure during normal operation and stored in batteries and whih is onverted to an adjustable single phase a voltage for mitigation of voltage sag, swell and outage. The simulation result shows that the PV based DVR performane is satisfatory in mitigating the voltage variations. Aknowledgment Authors wish to thank Er.S.Zahir Hussain, A.E., MRT, Er.G.Sakthivel, A.E., MRT, and Er.N.Ravihandran, A.E.E., MRT, Mettur Thermal Power Station (MTPS) for provides tehnial information about generation, transmission and distribution of eletrial power in southern grid, India. Referenes [1] H.Ezoji, A.Sheikholeslami, M.Tabasi, and M.M.Saeednia, Simulation of dynami voltage restorer using hysteresis voltage ontrol, European journal of sientifi researh, vol. 27, pp , Feb [2] F.A.L.Jowder, Modeling and simulation of different system topologies for dynami voltage restorer using simulink, in pro. EPECS 09, 2009, p [3] R.Strzeleki, and G.Benysek, Control strategies and omparison of the dynami voltage restorer, in pro. PQ 08, 2008, p [4] P.Boonhiam, and N.Mithulananthan, Understanding of dynami voltage restorers through MATLAB simulation, Thammasat Int. J. S. Teh., Vol. 11, No.3, pp. 1-6, Sep [5] K.C.Bayinder, A.Teke, and M.Tumay, A Robust ontrol of dynami voltage restorer using fuzzy logi, in pro. ACEMP 07, 2007, p.55. [6] S.Jayasimha, and T.PKumar, Photovoltai UPS, in pro. TENCON 03, Vol.4, p , Ot [7] M.Ashari, T.Hiyama, M.Pujiantara, H.Suryoatmojo, and M.Hery Purnomo, A Novel dynami voltage restorer with outage handling apability using fuzzy logi ontroller, in pro. ICICIC 07, p.51, Sep 2007.

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