Active and Reactive Power Controller for Single-Phase Grid- Connected Photovoltaic Systems

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1 Active and Reactive Power Controller for Single-Phae Grid- Connected Photovoltaic Sytem Tran Cong Binh, Mai Tuan Dat, Ngo Manh Dung, Phan Quang An, Pham Dinh Truc and Nguyen Huu Phuc Department of lectrical- lectronic ngineering- HoChiMinh City niverity of Technology. Vietnam National niverity in HoChiMinh, Vietnam. Abtract- Thi paper at firt preent a control algorithm for a ingle-phae grid-connected photovoltaic ytem in which an inverter deigned for grid-connected photovoltaic array can ynchronize a inuoidal current output with a voltage grid. The active and reactive power are equentially controlled by load angle and by inverter output voltage magnitude beide a maximum power point tracker (MPPT) alway find optimal power of the PV array in ue. The controller feed maximum active power into grid at unity power factor, wherea it alo allow the adjutment of reactive power injected into the grid. Simulation and experimental reult how that the control ytem ha good performance. The econd part of thi paper preent briefly the Green Power Laboratory (Department of lectrical and lectronic ngineering in HoChiMinh City niverity of Technology), where the experimental et-up are carried out. Thi lab ha been developed and ettled up in order to focu aiming of the converter deign and variou control of the renewable energy ytem like iolated or grid-connected photovoltaic ytem, fuel-cell and wind power. Thi paper decribe laboratory hardware a well a the context of which they are ued in the undergraduate and graduate teaching, and epecially in reearch activitie. ndex Term grid connected, photovoltaic ytem, active power, reactive power, DSP TMS32F2812. NTRODCTON N PHOTOVOLTAC SYSTMS, a grid connected inverter convert the DC output voltage of the olar module into the AC ytem. The grid-connected photovoltaic (PV) ytem extract maximum power from the PV array. The maximum power point tracking (MPPT) technique i uually aociated with a DC-DC converter. The DC-AC inject the inuoidal current to the grid and control the power factor. An important apect related to the photovoltaic ytem connected to the electric grid i that it can operate the double function of active power generator and reactive power compenator. The proper power factor i elected according to active power and reactive power that the grid demand. At the ame time, it can upply reactive power to the electrical grid when there i little or no olar radiation. That i important for compening the reactive power at peak hour, when the main grid need a amount of reactive power higher than average conumtion. Although the photovoltaic ytem doe not generate active power in uch period of time, it can upply reactive power up to it maximum. Thi inverter control trategy i not only capable to control the active power, but alo dynamically reconfigured to change the magnitude of the reactive power injected into the grid. Some olution are propoed [1-6], [1], to obtain a high reliability inverter. The baic idea of the propoe control i to obtain a low cot and imple controller. n thi method, the active power i controlled by load angle and the reactive power i controlled by inverter output voltage magnitude. The controller feed maximum active power into grid at unity power factor, wherea it alo allow the adjutment of reactive power fed into the grid. L 1 PV array D 1 Fig. 1: Single-phae inverter topology. The current of the inverter connected to the grid mut be got from a PV panel. The analyi i baed on inductor coupling and applied for other type of output filter configuration, uch a L, LC, LCL, etc [1,4,9]. The equivalent electrical circuit i hown in Fig.2. inverter C 1 S S 2 S 4 S 1 S 3 L Fig. 2: quivalent electric cirrcuit n order to explain the circuit characteritic, the Fig. 3 repreent the phae diagram of the fundamental component, including the inverter output voltage (), the inverter output current (), the drop voltage on the inductance L (jx =jωl), and the fundamental component of the grid voltage (). [1]. grid L grid. OPRATONAL PRNCPLS The power tage of the ingle phae inverter connected to the grid in the Fig.1 explain the inverter output current.

2 PV array φ δ Fig. 3: Phae diagram with grid voltage () and load angle (δ). jx P r Q r P g P P δ Δ Pg θ u m θ u in(θu+δ) dc e DC/AC nverter LCL ug u g θu V Fig. 4: Control tructure for a ingle phae gridconnected PV ytem. m timator DC/DC MPPT i g GRD min(θu) φ i repreented a the power angle between the grid voltage and the inverter output current. And, δ i repreented a the load angle between the grid voltage and the inverter output voltage. The phae diagram i hown in Fig. 3. The following relation can be repreented: & = & + jx (1) & ( δ ) X. co( ϕ ) in = (2) The active power (P) provided by the converter to the grid can be expreed a: P = co( ϕ ) = in( δ ) (3) X And the reactive power (Q) provided by the converter to the grid, can be expreed a: 2 Q = co( δ ) = ( co( δ ) ) (4) X X X According to figure 3, equation (3) and (4), the power flow adjutment of the inverter i parallel connected to the main grid, can be performed by controlling the inverter ouput voltage magnitude () and load angle (δ). On the other hand, to inject power to the grid, the value of the DC voltage mut be high enough o that the output voltage can get a value which i equal or greater than the grid peak voltage. From equation (3) and (4), the active and reactive power depend on both the inverter output voltage magnitude and the load angle δ [6]. So, the active power injected into the grid can be controlled by the phae difference between grid voltage and inverter output voltage δ. At the ame time, the reactive power can be controlled by the inverter output voltage magnitude.. PROPOSD CONTROL MPLMNTATON The propoed control tructure for a ingle-phae inverter connected to the grid i hown in Fig.4. The photovoltaic ytem conit of photovoltaic generator (PV array), DC/DC converter with maximum power point tracking (MPPT), a ingle phae inverter and an active and reactive power controller. The control circuit ha two part: the firt one control the active power injected into the grid by the load angle δ, and the econd one control the reactive power through the inverter output voltage magnitude. A how in figure 4, the controller compene the reactive power injected into the grid ( ) and compare it with it reference (Q r ), originating an reactive power error. Thi error pae through an P controller and it i added to grid voltage amplitude ( m cont), reulting the inverter output voltage amplitude ( m ). On the other hand, the controller produce the active power generated by the inverter (P g ) and compare it with a reference ignal (P r ), generating an active power error. Thi error pae through another P controller, originating reference load angle (δ). The load angle i added to grid voltage phae angle (θ u ), generating inverter output voltage phae angle (δ+θ u ). The inverter output voltage amplitude ( m ) i multiplied by in(δ+θ u ), reulting the intantaneou value of the inverter output voltage (e) the DC/AC inverter reference ignal. The grid voltage: u = m in(ωt) = m in(θ u ) (5) and δ ~ P and Δ ~ Q (6) nverter output voltage: e = m in( θ u + δ ) (7) where: = + Δ (8) The main advantage of thi control trategy i it implicity related to the computational requirement of the control circuit and hardware implementation. By another way, it allow controlling not only an active power need to be injected but alo a reactive component. When the reactive power reference i zero, the power factor will approach to the unity. V. SMLATON RSLTS MATLAB/Simulink oftware were ued in all imulation accomplihed here which how the reult obtained for voltage and current waveform, active, reactive and apparent power on the AC ide upplied to the grid. The rate value of grid voltage (=22Vrm) and the inverter i connected to the grid through a coupling inductance L=1mH. Simulation at low-power cale (1 kva) i implemented in predicting the behaviour of the ytem for the experiment to be performed on the laboratory tet bench. m m

P [W] Q [VAr] 1 8 6 4 2 1 8 6 4 2.5 1 1.5 2 2.5 3 3.5 4.5 1 1.5 2 2.5 3 3.5 4 time () Fig. 5: Active and Reactive Power upplied by the inverter with 1%-5%-1% of photovoltaic ytem power.

The active power and reactive power injected into the grid for four generation condition: [P,Q]=[%, %], [1%, %], [5%, %], [5%, 87%]. [V] delta [degree] 5 4 3 2 1 Load angle -1.5 1 1.5 2 2.5 3 3.

The load angle (δ) i proportional to the active power and the inverter output voltage () i proportional to the reactive power. [V] [V] 4 2-2 -4.5 1 1.5 2 2.5 3 3.

3 P [W] Q [VAr] time () Fig. 5: Active and Reactive Power upplied by the inverter with 1%-5%-1% of photovoltaic ytem power. The imulation reult obtained for teady-tate operation are hown in Fig. 5. Active and reactive power repone ha good performance. The active power and reactive power injected into the grid for four generation condition: [P,Q]=[%, %], [1%, %], [5%, %], [5%, 87%]. [V] delta [degree] Load angle time () P ref P g Q ref nverter output voltage Fig. 6: Load angle δ [degree] and nverter output voltage [Vrm]. The load angle (δ) i proportional to the active power and the inverter output voltage () i proportional to the reactive power. [V] [V] P [W] Q [VAr] S [VA] 1 P 5 ref P g time () Fig. 8: Active, Reactive and Apparent power injected into the grid with four generation condition: [P,Q]=[%, %], [1%, %], [5%, %], [5%, 87%]. A oberved in figure 5 to 8, when the active power i reduced, the control i adjuted to increae the reactive power upplied capacity. Hence, the value of inverter current and the apparent power injected into the grid can get the rate value wherea the olar radiation i low. [6]. The active power upplied by the photovoltaic ytem to the grid preented a agreeable performance, due to a reonable ytem repone. When there i untroke variation, the ytem adjut to a new reference of active power with a good performance. Moreover, it wa oberved an interaction between the active and reactive power delivered to the grid. So, the ytem take advantage of the moment of little active power generation to accomplih the compenation of reactive power. V. XPRMNTAL RSLTS AND RMARKS OF TSTNG A prototype of a ingle phae inverter (Fig.9), ha been built to validate the performance of the digital control previouly decribed and teted. A voltage ource inverter ha been developed in a DSP platform (DSP TMS32F2812) reconfigurating eaily and imply the ytem [3]. t i poible to configure the inverter output voltage and the load angle hifting to the grid voltage reference. Two digital P control-algorithm are implemented in DSP TMS32F2812 to optimize the performance of the control ytem. The propoed inverter i teted with a PV array of 8W. Q ref S g 4 [A] time () Fig. 7: Grid voltage [V], nverter output voltage [V], and nverter output current [Arm]. Fig. 9: Single-phae inverter prototype.

A firt, the inverter output voltage and it phae mut be ynchronized to the grid voltage ignal before the power output of the inverter i connected

1: nverter output voltage generated in phae with the grid voltage in open loop. Grid voltage Fig.

1ec Fig. 11 & 12: > and δ >. Second, the gid-connected algorithm i executed to control the power flow delivered into the grid.

Code compoer tudio ofware of Texa ntrument DSP allow drawing real-time meaurement value. Fig. 13 and Fig.

The graph of figure 15 how the active power injected into the grid, which ha good performance.

And the control i applied to regulate the active and reactive power of low power PV ytem.

W Active Power repone = 2.26W Fig. 15: Active power repone.

4 A firt, the inverter output voltage and it phae mut be ynchronized to the grid voltage ignal before the power output of the inverter i connected to the grid (Fig. 1). Fig. 13: nverter output current in phae with the grid voltage emulator by Ocillocope nverter output curent Fig. 1: nverter output voltage generated in phae with the grid voltage in open loop. Grid voltage Fig. 14: nverter output current in phae with the grid voltage emulator by Code compoer tool. Active Power reference Active Power repone jx φ δ x.1ec Fig. 11 & 12: > and δ >. Second, the gid-connected algorithm i executed to control the power flow delivered into the grid. The controller varie magnitude and phae of the inverter output voltage (Fig. 11). Code compoer tudio ofware of Texa ntrument DSP allow drawing real-time meaurement value. Fig. 13 and Fig.14 how the experimental reult of inverter output current compared to the grid voltage emulator. The graph of figure 15 how the active power injected into the grid, which ha good performance. The experimental reult how the feaibility of the propoe control. And the control i applied to regulate the active and reactive power of low power PV ytem. The propoe implementation i very imple and not required a high peed hardware and computational reource. Active Power reference = 2.W Active Power repone = 2.26W Fig. 15: Active power repone. RMARKS OF TSTNG n thi part, the imulation and experiment reult prove that the propoe ytem ha the ability of changing inverter output voltage amplitude a well a load angle. Conequently, the ytem i controllable for the active and reactive power injected into the grid with a good performance. Thu, it become poible to operate independently the photovoltaic ytem in any condition of the untroke level and upplie both the active and reactive power according to the availability of olar radiation. Thi photovoltaic ytem i neither complex to implement nor expenive to realie. t i a better cot-benefit ratio in the implementation for the other alterative energie.

5 V. NTRODCTON TO GRN POWR LAB All of the reearch activity, uch a the firt part of thi paper, concerning the renewable energy are focued on the development of the Green Power Laboratory (GPL). GPL now belong to Faculty of lectrical- lectronic ngineering- HoChiMinh City niverity of Technology- i a fruitful collaboration between HCMT and PFV- NSHT in the framework of the project NTDD (Nouvelle Technologie t Développement Durable = New Technologie and Sutainable Development) from 27 in etting up a lab on Renewable, aiming at undergraduate and graduate teaching and reearch of new electricalelectronic technologie applied in green energy. The objective of thi lab are to focu on renewable energy technologie (wind power, olar power, fuel cell) a well a on the deign and control of the power electronic converter ued in ingle-phae and three-phae renewable energy ytem like photovoltaic, wind, fuel cell and water turbine connected to the utility grid or to a microgrid. The laboratory comprie variou equipment for tudent ue and other reearch activitie in the field of renewable energy. DSP technology, either Texa ntrument TMS32F2812 DSP from Texa ntrument, or dspac DS114 card are widely ued in order to provide higher flexibility. Fig. 1 how a photo of the Green Power Laboratory. The coure Renewable nergy Sytem given to undergraduate and graduate tudent i going in parallel with Green Power Lab include (3 hou lecture per week): 1. ntroduction to Renewable nergy Sytem Need for more energy Renewable nergy Source (olar, wind, hydro, tidal, wave) Fuel-cell introduction Cot and environmental impact Renewable energy in a utainable future 2. Stand alone and gird-connected Photovoltaic Sytem Solar cell technology (crytalline, amorphou, thin film) lectrical characteritic of ilicon PV cell/module Tracking maximum power point Grid-connected and off-grid PV ytem (reidential, farm, etc) Converter topologie for PV ytem Control of dc-dc boot converter Control of ingle-phae and three-phae dc-ac inverter Compliance with power quality and afety ytem 3. Wind nergy Sytem Power and energy from wind turbine Wind turbine ytem configuration Converter topologie for variable-peed wind turbine Modeling and imulation of DFG ued in wind power 4. Fuel Cell technology Variou technologie of Fule Cell Characteritic of Fuel Cell Fuel Cell Application a an energy vector Matlab and Bondgraph (2SM) oftware are extenively ued by tudent to carry out modeling, imulation and tudy of renewable energy equipment performance and it behaviour when connected to power grid. The laboratory exercie include: 1. Solar cell and panel Matlab imulation of olar cell and panel electrical characteritic (-V, P-V, MPPT temperature dependence, irradiation-dependence, hadowing etc). 2. Grid-connected PV ytem Sytem imulation 3. MPPT controller experimental tet 4. Control of ingle-phae grid converter ued for PV reidential application experimental tet 5. Control of three-phae Wind Turbine ytem experimental tet PROJCT XAMPLS GPL offer a variety of project to undergrad or grad tudent in their program. Operation and imulation of tand alone PV ytem (of 3 W, BondGraph or Matlab, comparion of reult obtained from experiment meaurement and thoe from imulation) Operation and imulation of grid-connected PV ytem (of 96 W, BondGraph or Matlab, comparion of reult obtained from experiment meaurement and thoe from imulation) Operation and imulation of off- grid wind power ytem (of 4 W, BondGraph or Matlab, comparion of reult obtained from experiment meaurement and thoe from imulation) Operation and imulation of Fuel cell (principle of electrolyi, application) Off- grid wind power ytem (of 4 W, BondGraph or Matlab, comparion of reult obtained from experiment meaurement and thoe from imulation) Some pecific theme are alo offered a final project for enior cla tudent. Some of topic are a follow: Digital imulation of Three phae Grid-Connected PV ytem with improved performance: The concept of the intantaneou p-q (real-imaginary) power theory i preented in the control algorithm to deign the ytem with feature of eparate control of active and reactive power, which reult in the maximal tranfer of the dc energy from PV array and improve the power factor of the electrical ytem. The whole ytem of PV array, dcdc converter, MPPT, dc-ac PWM converter along with hyterei current controller i deigned and imulated in Matlab- Simulink environment. The reult obtained from digital imulation will how dynamic ytem performance in term of changing irradiance, power factor correction, a well a eay tracking of inverter current fed into grid. Digital imulation and xperimental tet of One-phae Grid-Connected PV ytem with improved performance. Thi topic preent a control algorithm for a ingle-phae grid-connected photovoltaic ytem. An inverter deigned for grid-connected photovoltaic array can ynchronize a inuoidal current output with a voltage

grid. Thi method control active power by load angle and control reactive power by electromotive force. A maximum power point tracker (MPPT) alway find optimal power of the PV array in ue.

Simulation and experimental reult how that the control ytem ha good performance.

6 grid. Thi method control active power by load angle and control reactive power by electromotive force. A maximum power point tracker (MPPT) alway find optimal power of the PV array in ue. The controller feed maximum active power into grid at unity power factor, wherea it alo allow the adjutment of reactive power fed into the grid. Simulation and experimental reult how that the control ytem ha good performance. Modeling and imulation of wind power DFG connected to power ytem Variou eminar, workhop are held in GPL offering baic knowledge and expertie in the field given by profeor coming from NPT- NSHT, niverity of Dreden, NS Cachan (Fig 2) on topic: Alternative nergy: technologie, impact on utainable development. Fuel Cell technology and Application in the future a an energy vector. Wind power Generato and Simulation. Small hydro power and exploitation operation. PV technology tand alone and grid connected operation and characteritic. Power converter in Green Power technology. Wind power: Operation and ite election etimation of wind potential economic ide conideration. Power LD and efficient ue of electric power. Power LD technology. BondGraph oftware application in hybrid ytem reearch. V. CONCLSON GPL how it effectivene and attraction when it draw a real interet of tudent majoring in Power. ngineering. Student are really intereted in new concept, new technologie introduced into the curriculum. n addition, the introduction of micro electronic and DSP technique into the renewable energy field really make the ubject tate-ofthe art and more interdiciplinary. Power electronic, electrical machine, dp, microelectronic, control technique, all integrated in the dicipline give even more attractivene to tudent. Fig. 15: Green Power Laboratory. Fig. 16: Three-phae inverter prototype. Fig. 17: Single-phae inverter prototype. RFRNCS [1] Haaine, L.; Olia,.; Quintero, J.; Barrado, A., Digital control baed on the hifting phae for grid connected photovoltaic inverter, Applied Power lectronic Conference and xpoition, 28. APC 28. Twenty-Third Annual, pp , Feb. 28. [2] Byunggyu Yu; Youngeok Jung; Junghun So; Hyemi Hwang; Gwonjong Yu, A Robut Anti-ilanding Method for Grid-Connected Photovoltaic nverter, Photovoltaic nergy Converion, the 26 4th World Conference, vol. 2, pp , May. 26. [3] Jeyraj Selvaraj and Narudin A. Rahim, Multilevel nverter For Grid-Connected PV Sytem mploying Digital P Controller, TRANSACTONS ON NDSTRAL LCTRONCS, vol.56, no.1, pp , Jan. 29. [4] Matromauro, R.A.; Lierre, M.; Dellapo;Aquila, A., "Single-Phae Grid-Connected Photovoltaic Sytem With Power Quality Conditioner Functionality", Power lectronic and Application, 27 uropean Conference, pp.1-11, Sep. 27. [5] Sung-Hun Ko; Seong-Ryong Lee; Dehbonei, H.; Nayar, C.V., A Grid-Connected Photovoltaic Sytem with Direct Coupled Power Quality Control, ndutrial lectronic, CON 26-32nd Annual Conference, pp , Nov. 26. [6] Albuquerque, F.L.; Morae, A.J.; Guimarae, G.C.; Sanhueza, S.M.R.; Vaz, A.R., Optimization of a photovoltaic ytem connected to electric power grid, Tranmiion and Ditribution Conference and xpoition: Latin America, 24 /PS, pp , Nov. 24. [7] Huili Sun; Lope, L.A.C.; Zhixiang Luo, Analyi and comparion of ilanding detection method uing a new load parameter pace, ndutrial lectronic Society, CON 24. 3th Annual Conference of, vol.2, pp , Nov. 24. [8] Phan Quoc Dzung; Le Minh Phuong; Pham Quang Vinh; Nguyen Minh Hoang; Tran Cong Binh, New Space Vector Control Approach for Four Switch Three Phae nverter (FSTP), Power lectronic and Drive Sytem, 27. PDS7. 7th nternational Conference, pp.12-18, Nov. 27. [9] Myrzik, J.M.A.; Calai, M., String and module integrated inverter for ingle-phae grid connected photovoltaic ytem - a review, Power Tech Conference Proceeding, 23 Bologna, vol.2, June 23. [1] Phan Quang An, "tude par imulation d un ytème photovoltaïque hybridé", Mater thei, ntitut National Polytechnique de Touloue (NSHT), 27.

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