Transformerless photovoltaic inverter for photovoltaic power generation in Perlis to run high AC load

Abstract

This thesis presents the transformerless photovoltaic (PV) inverter for PV power generation in Perlis to run high AC load. This study involves the data collection of solar radiation and temperature. The data of solar radiation and temperature were measured at the Centre of Excellence for Renewable Energy (CERE) Station, Universiti Malaysia Perlis in Kangar, Perlis, Northern Malaysia. These analyzed data were discussed in order to know the potential for PV power generation. The result shows that the average monthly solar radiation was 4862.4 Wh/m2. It is greater than 3 kWh/m2 and indicates that the sky in Perlis was clear and the solar radiation intensity was very high. It indicates that the solar radiation in Perlis gives big potential for PV power generation. In this study the solar radiation was also estimated. The estimation is important to be done if these data are absent, incomplete or inaccessible in an area due to financial, maintenance, calibration requirement of the measuring equipment or institutional limitations. To estimate these data, Hargreaves method, linear regression and a proposed method were used. The proposed method is a combination of Hargreaves method and linear regression, the advantage of the proposed method compared to the linear regression is that the linear regression needs the measured solar radiation and the daily temperature difference, but the proposed method needs the daily temperature difference only. The measured and estimated solar radiations were analyzed using statistical analysis. The results show that the value of coefficient of residual mass (CRM) is closer to zero, it indicates that the methods have high accuracy. The value of root mean squared error (RMSE) is low value, it indicates that the methods have minimal value. The value of percentage error (e) indicates that the proposed method is acceptable and applicable. The solar radiation affects the performance of a PV module. Power of the PV module is influenced by the solar radiation incidents on the surface of PV module. To obtain maximum solar radiation on surface of the PV module, tilt angle of PV module should be determined. It is important to find an optimum tilt angle in order to obtain the optimum performance of PV module (voltage, current and power of PV module). The recommended optimum tilt angle of the PV module from the horizontal surface for Perlis (has latitude 6.290 N) is 6.840. The best performance of PV module was reached when the tilt angle is 6.840. Potential of solar radiation as PV power generation is applied to PV inverters. Normally, the low frequency (50 Hz) inverter uses a transformer that it is bigger in size, heavy, and expensive and also has problem to run a high alternating current (AC) load. The simplest technique to invert direct current (DC) power into AC power is to generate a square wave. However, the harmonic content of the square wave is relatively high, also the efficiency of this waveform is relatively low. For reducing the manufacturing size, weight, and cost, a three-level single phase transformerless PV inverter was designed, which manage to reduce harmonic and improve efficiency. It has successfully run high AC load (30 W resistive lamp, R7S 500 W halogen lamp, 20 W water pump, 66 W refrigerator, 480 W jig saw, 50 W standing fan, 80 W air cooler and personal computer), since its design had a high switching current mode. This new topology was found to reduce current total harmonic distortion (CTHD) of the three-level single phase transformerless PV inverter. In order to optimize the CTHD on AC three-level waveform transformerless PV inverter, it was developed by using a microcontroller PIC16F627A-I/P. This technique could change maximum voltage angle of the AC three-level waveform from 200 to 1800. An AC load applied to the transformerless PV inverter shows that the lowest CTHD was obtained when the maximum voltage angle was 1340. This proposed topology is considered as novel and inventive, since it has obtained a certificate of filing from Intellectual Property Corporation of Malaysia with application number PI 2012700152. A comparative study of CTHD between measurement and simulation has been conducted and validated using statistical analysis. The result shows that the measurement and simulation was valid. A comparative study of CTHD between the proposed three-level single phase transformerless PV inverter and the market three-level inverters (1000 W power inverter Model DY 8111 SUVPR Series, 1000 W Charger 10A SUVPR Series DY 1000C, 2000 W charger power inverter SUVPR Series DY 2000C and Power inverter 200 W) has been also conducted. The result shows that the CTHD of proposed three-level single phase transformerless PV inverter was lower than the CTHD of the market three-level inverters.