Journal of Science & Technology 101 (2014) 071-077 A Three-Phase Grid-Connected Photovoltaic System with Power Factor Regulation Le Minh Phuong*, Nguyen Minh Huy Ho Chi Minh City University of Technology No 268 Ly Thuong Kiet Dist 10 Ho Chi Mmh City Received: August 22, 2012; accepted: April 22, 2014 Tfiis paper presents the control model of three phase gnd connected photovoltaic generation system with a new approach for power factor regulation The model contains a detailed representation of the mam components of the system that are the solar panels, DC/DC converter, DC-link, a grid side three phase voltage source inverter (VSI) and output filters to reduce harmonic distortion of tine current In this paper, a complex control scheme including two PI controllers cooperated with MPPT is proposed to stabilize DC voltage A three phase grid connected voltage source inverter synchronizes to the grid by a robust phaselocked loop (PLL) The new approach of power factor control scheme is proposed, simulated by Matiab Simulink Toolbox and implemented using DSP Tf\AS320F2612 Simulation and experimental results show the high stability and high efficiency of this three-phase grid-connected PV system It also proves the excellent performance control units as improving a flexible regulation of power factor (PF) for the interval (0.5-1) Keywords: Three phase Grid-connected inverter, Maximum power point tracking (MPPT); Photovoltaic (PV); solar energy Introduction Nowadays fossil fuel is the main energy ipplier of the worldwide economy, but the cognition of it as being a major cause of ivironmental problems makes the mankind to look r alternative resources in power generation [1] The control strategies applied to distributed 'Stems become of high interest And how to iprove the performance of gnd inverter, increase e switching frequency and power density to meet )wer quality requirements has become a research rtspot in recent years [2] The main circuit block diagram of the PV grid connected system is shown in Fig 1, including: (1) DC-DC unit: DC boost converter is used to boost the PV array voltage and track the maximum solar power (2) DC-AC unit: The three phase inverter with bridge topology converts DC to sinusoidal AC and provides to load (3) Filter circuit: AC-side filter is composed of R-L-C, used to filter AC side current harmonics to ensure the quality of grid current Many researches have focused on resolving iportant problems of the distributed system and its mtrol In this paper, the authors focus on two main •oblems, as a control of dc-link voltage and a mtrol of load power factor This paper also oposes an improved MPPT control algorithm for lotovoltaic under rapidly changing solar radiation, le simulation results on Matlal>^Simulink show that Section MPPT quickly in conditions of changes in diation and temperature The simulation and periment results show good response, high stability id high efficiency of this three-phase grid-connected / system ability when the grid voltage and load langes :orTesponding Author' Tel: (-f-84) 988.572.177 mail: Imphuong@hcmut.edu.vn Fig General diagram photovoltaic system of grid connected Journal of Science & Technology 101 (2014) 071-077 Fig Proposed control structure of three phase grid-connected PV system mi Vp„ Ip ^ ( J ^ - | p i j — Compar — Fig Block diagram of PV DC-DC converter control part 2.1 The control scheme for DC/DC unit The PI controller keeps PV at V^j, which provides by MPP tracking algorithm The coefficients of PI arc defined based on the DC/DC converter switching frequency 20kHz The DC/DC converter is a push pull step up converter The pulse transformer has primary hinis Np, secondary turns Ns, input voltage Vin and output voltage Vi The LC filter is output voltage filter whicli model is shovra in Fig Differential equations are established thanks It Kirchhoff s law by equations (I)-(4) v,^ =2x~^xDxV Fig DC/DC model Proposed cootrol structure for grid converter dt The proposed control structure of three-phase gnd-connected PV system consists of PV panels is presented in Fig can be divided into parts: MPPT control and Grid tie control, (1) R+R L V L V L dv^ ~dt^ i^ i^ 'C~'C R L ' J^ — ^ c \ •'"*' ~ ^ e * D MPPT algorithm samples Ipv and Vpv from solar panels to keep them working at Maximum Power Point while output voltage of DC/DC converter lets floating DC Link controller provides reference cun^ent ij which relate to power from solar panels to keep DC Link at fix DC voltage Gnd connected controller is a current controller using SVPWM algorithm in synchronous dq frame The gnd tie power factor can adjust by setting iq = when cos(