8 PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 88 NR 7a/2012 Zamre Abdul GHANI, Mohammad Abdul HANNAN, Azah MOHAMED Dept. of Electrical, Electronic & Systems Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia Investigation of Three-Phase Grid-Connected Inverter for Photovoltaic Application Abstract. This paper describes the investigation of the grid-connected three-phase inverter for photovoltaic (PV) application. The inverter control system modeling is carried out in MATLAB/SIMULINK environment. With the aids of the proportional-integral controllers, sinusoidal pulse-width modulation (SPWM) control technique and Park transformation, the inverter control system managed to convert PV power to ac power, stabilize the output voltage and current, and feeds the excess power to the utility grid. The control system generates the PWM signals for power devices, the insulated gate bipolar transistors in order to regulate the output voltage and current. In addition, the system is simulated with the PV simulator in order to facilitate the real PV power that to be fed to the input of the inverter. The control system produced 2.48% and 4.64% of output voltage and current total harmonic distortion, respectively. The simulation results such as the ac output voltages and currents, inverter system power flow, and grid disturbances detection signals, proved the effectiveness of the developed control algorithm. For the validation, this model is to be linked to the inverter prototype by utilizing the dSPACE controller. Streszczenie. W artykule badano trójfazowy przekształtnik w zastosowaniu do urządzeń fotowoltaicznych podłączonych do sieci. Układ składa się ze sterownik PI, układu modulacji SPWM i transformacji Parka i umożliwia konwersję napięcia z systemu fotowoltaicznego do sieci ac, stabilizację napięcia i prądu. (Badania nad trójfazowym przekształtnikiem podłączonym do sieci w zastosowaniu do urządzeń fotowoltaicznych) Keywords: Photovoltaic; three-phase inverter; grid; PI; SPWM Słowa kluczowe: systemy fotowoltaiczne, przekształtnik, sieć zasilająca Introduction Having realized the importance of finding alternative energy resources for the future energy sustainability, photovoltaic (PV) energy has becomes one of the important renewable energy sources [1]. With the aid of electronics power converters mainly the dc (direct current) boost converters and inverters, this kind of energy can be utilized and transported to the electric utility [2]-[4]. However, the inverter efficiency need to be improved further on in order to mitigate the effects of the self-consumption losses, unbalanced load on inverter output voltage, nonlinearity, PV low efficiency and output fluctuation [5], electromagnetic interference and high level of harmonics content [6]-[13]. In addition, it is important that the inverter system acquires the capability to operate with high speed and frequency in generating the pulse-width modulation (PWM) signals [14]. Hence, the inverter controller which plays an important role in the improvement of the abovementioned issues, needs to be enhanced further to uplift the inverter performance in renewable energy applications, especially in PV. Analogue circuit controllers, microcomputers, digital circuit controllers, field programmable gate arrays (FPGAs) and digital signal processors (DSP), e.g. dSPACE, are among the controllers used in the inverter control system [15]-[25]. In this investigation work, the inverter control system algorithm, strategies and modeling are developed and simulated in MATLAB/SIMULINK. Indeed, the results presented in this paper are based on the simulation environment. However, the successfulness of this modelling is very essential in order to convert it to the prototype later on for the result validation. This simulation creates a potential and justification for hardware realization. For this purpose, the dSPACE controller is utilized for the process of inverter prototype linking. It serves as handy process to develop the control algorithm for the inverter development. The main objective of the inverter control system is to generate and stabilized the 50 Hz sinusoidal-shape ac (alternating current) output voltage and frequency. Having achieved that, together with the grid synchronization algorithm, the interconnecting of the inverter to the utility grid is achievable. Detail explanations of the inverter control system algorithm and its strategy have been discussed. Grid-Connected Inverter System Description Fig. 1 illustrates the block diagram of the three-phase grid-connected voltage-source inverter (VSI) PV system for the investigation. As illustrated, this transformer-less PV system consists of the control system, inverter which interfaces the PV and the grid, harmonic filter, and PV power simulator featuring the maximum power point tracking (MPPT) function. Fig.1. Block diagram of the grid-connected inverter PV system Firstly the control system consists of several subsystems which include voltage and current control functions, grid synchronization function, PWM generator, abnormal voltage and frequency detection units, e.g. over and under voltage and frequency. For the control algorithm, generating the correct and precise PWM signals for the power devices is the key factor to the generating and regulating the inverter ac output waveforms. By means of the output voltage and current parameters sampling, the system controller is able to transfer the available maximum PV power to the load and simultaneously stabilize the output voltage to a desired level. Secondly, the PV power simulator with a built-in dc to dc boost converter and maximum power extracting feature, generates and simulates the PV dc power that required for the inverter input stage. With the MPPT algorithm, the system ensures that the maximum power output from the PV is achieved. Basically, different solar irradiations and ambient temperatures exhibit different maximum power output level. For simplification of the analysis, the investigation and simulation are executed only at a fixed solar irradiation of 1000 watt/m 2 and 25º Celsius.