4. Simulation and experimental results

In this section, the simulation and experiment results are reported. By using Matlab/Simulink, a single-phase PV inverter is simulated. The switching model simulation provides the most detailed results including the switch information and all the potential harmonic distortions. By using the Simulink SimPowerSystems toolbox, the developed model includes both electronic components and control blocks. The schematic diagram is shown in Figure 7. It is a timeconsuming process. A 0.2-s simulation period takes about 10 min to run on a computer with average performance (Intel Core 2 Duo CPUs and 4 GB of 800 MHz DDR2 RAM).

The two-stage grid-connected PV system prototype is constructed in the laboratory to verify the abovementioned analysis. It includes a boost converter connected with the full-bridge inverter as the second stage. The operating voltage range of the system has been scaled down due to the limitation in the experimental setup. An AC source with 50 Vrms is used as the grid voltage. The full-bridge inverter DC-link voltage is 100 V. The capacitor size has been changed with different capacitance to create different voltage ripple across the DC link. The experimental setup with the prototype circuit is shown in Figure 8, which is the same as in Figure 9, and the main circuit parameters are shown in Table 1. A dSPACE controller set has been used to control these two stages.

Figure 8. Experimental setup.

Figure 9. Two-stage PV inverter with feedback control.

Table 1. Specification of the PV inverter.

Parameter Label Value Unit Switching frequency f sw 20 kHz Rated output frequency f 50 Hz Rated output voltage Vg 70 V DC-link capacitance CDC 770 μF DC-link voltage VDC 100 V Inverter-side inductor L<sup>1</sup> 2.56 mH Grid-side inductor L<sup>2</sup> 1.10 mH Output capacitor Cout 2.2 μF Damping resistor Rd 1 Ω

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An averaged model has also been built in Simulink. The parameters listed in Table 1 are substituted into the derived closed-form solution in order to calculate the harmonics. Different levels of DC-link voltage ripple in simulation and experiment have been created by using different sizes of capacitors. Only the third-order harmonics from the fast Fourier transform (FFT) analysis is considered in calculating the THD, in order to simplify the analysis process. In

Figure 7. Simulation schematic model.

Harmonic Distortion Caused by Single-Phase Grid-Connected PV Inverter http://dx.doi.org/10.5772/intechopen.73030 61

Figure 8. Experimental setup.

4. Simulation and experimental results

Figure 7. Simulation schematic model.

In this section, the simulation and experiment results are reported. By using Matlab/Simulink, a single-phase PV inverter is simulated. The switching model simulation provides the most detailed results including the switch information and all the potential harmonic distortions. By using the Simulink SimPowerSystems toolbox, the developed model includes both electronic components and control blocks. The schematic diagram is shown in Figure 7. It is a timeconsuming process. A 0.2-s simulation period takes about 10 min to run on a computer with

The two-stage grid-connected PV system prototype is constructed in the laboratory to verify the abovementioned analysis. It includes a boost converter connected with the full-bridge inverter as the second stage. The operating voltage range of the system has been scaled down due to the limitation in the experimental setup. An AC source with 50 Vrms is used as the grid voltage. The full-bridge inverter DC-link voltage is 100 V. The capacitor size has been changed with different capacitance to create different voltage ripple across the DC link. The experimental setup with the prototype circuit is shown in Figure 8, which is the same as in Figure 9, and the main circuit parameters are shown in

An averaged model has also been built in Simulink. The parameters listed in Table 1 are substituted into the derived closed-form solution in order to calculate the harmonics. Different levels of DC-link voltage ripple in simulation and experiment have been created by using different sizes of capacitors. Only the third-order harmonics from the fast Fourier transform (FFT) analysis is considered in calculating the THD, in order to simplify the analysis process. In

average performance (Intel Core 2 Duo CPUs and 4 GB of 800 MHz DDR2 RAM).

60 Power System Harmonics - Analysis, Effects and Mitigation Solutions for Power Quality Improvement

Table 1. A dSPACE controller set has been used to control these two stages.

Figure 9. Two-stage PV inverter with feedback control.


Table 1. Specification of the PV inverter.

Author details

\* and Dylan Dah-Chuan Lu2

2 University of Technology Sydney, Australia

\*Address all correspondence to: yang.du@xjtlu.edu.cn 1 Xi'an Jiaotong-Liverpool University, Suzhou, China

[1] Du Y, Lu DDC, Cornforth D, James G. A study on the harmonic issues at CSIRO microgrid. IEEE 9th International Conference on Power Electronics and Drive Systems

Harmonic Distortion Caused by Single-Phase Grid-Connected PV Inverter

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[2] Du Y, Lu DD-C. Battery-integrated boost converter utilizing distributed MPPT configu-

[3] Bennett T, Zilouchian A, Messenger R. Photovoltaic model and converter topology con-

[4] Lu DDC, Nguyen QN. A photovoltaic panel emulator using a buck-boost DC/DC con-

[5] Papaioannou IT, Alexiadis MC, Demoulias CS, Labridis DP, Dokopoulos PS. Modeling and measurement of small photovoltaic systems and penetration scenarios. Power Tech

[6] Jain SK, Singh SN. Harmonics estimation in emerging power system: Key issues and

[7] Chicco G, Schlabbach J, Spertino F. Experimental assessment of the waveform distortion in grid-connected photovoltaic installations. Solar Energy. 2009;83(7):1026-1039

[8] Infield DG, Onions P, Simmons AD, Smith GA. Power quality from multiple grid-connected single-phase inverters. IEEE Transactions on Power Delivery. 2004;19(4):1983-1989

[9] Wu TF, Sun KH, Kuo CL, Yu GR. Current distortion improvement and dc-link voltage regulation for bi-directional inverter in dc-microgrid applications. Applied Power Elec-

[10] Twining E, Holmes DG. Grid current regulation of a three-phase voltage source inverter with an LCL input filter. IEEE Transactions on Power Electronics. 2003;18(3):888-895 [11] Shimizu T, Wada K, Nakamura N. Flyback-type single-phase utility interactive inverter with power pulsation decoupling on the DC input for an AC photovoltaic module

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Yang Du1

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Figure 10. Simulation, calculation, and experimental results.

Figure 10, the switch model, averaged model, and calculation results agree with one another. It proves that the closed-form solution can fully represent the switch model for harmonic analysis. Higher-order harmonics also can be analyzed by using the same method.

The same parameters as the simulation have been used in the experiment, and the results are also plotted in Figure 10. The experimental results show the same trend as the analysis suggests that the harmonic distortion increases as the DC-link voltage increases.
