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Cai F.,Fuzhou University | Cai F.,Nanjing University of Aeronautics and Astronautics | Cai F.,Zhangzhou Kehua Technology Co. | Zheng B.,Fuzhou University | And 3 more authors.
Diangong Jishu Xuebao/Transactions of China Electrotechnical Society | Year: 2012

Anti-islanding protection is a mandatory feature for grid-connected photovoltaic system. A new method for islanding detection is proposed, that is the adaptive PWM period disturbance(APD) which combined with PLL (phase locked loop) of grid-connected current. This method is a uniform algorithm with PLL which is equivalent to adaptive frequency drift and adaptive phase shift simultaneously. Simulation programs for the control schemes are run in PSIM software initially to see the effect of control method. Afterwards, control board is designed to control a 6kW inverter. Simulation and experimental results are also provided to show that the proposed method has advantages such as fast response, no NDZ and slight impact on power quality.

Cai F.,Fuzhou University | Cai F.,Zhangzhou Kehua Technology Co. | Lin Q.,Fuzhou University | Lin Q.,Zhangzhou Kehua Technology Co. | And 2 more authors.
Dianli Zidonghua Shebei/Electric Power Automation Equipment | Year: 2014

The harmonic currents induced by the traditional AFD (Active Frequency Drift) method for island detection are analyzed by fast Fourier transform and the formulas of its third-, fifth-and seventh-order harmonic currents are obtained. Therefore, the currents with inverse phase can be applied to compensate the harmonic currents caused by the AFD method. The way to implement the AFD method with harmonic compensation in digital control system is introduced. Simulative and experimental results show that, the proposed method effectively reduces the harmonic currents without influencing the island detection.

Cai F.-H.,Fuzhou University | Cai F.-H.,Zhangzhou Kehua Technology Co. | Wang W.,Fuzhou University | Wang W.,Zhangzhou Kehua Technology Co. | And 2 more authors.
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2013

To improve the efficiency of island detection and the quality of current waveform, a new current disturbance strategy is proposed based on the traditional AFD. As to the traditional AFD, the rising of chopping fraction (cf) leads to more current distortion and the smaller cf resulted in low efficiency of island detection. Therefore, it's difficult to achieve good balance between the efficiency of island detection and current distortion in anti-islanding detection. Now the proposed current perturbation method can effectively improve the THD of stable current by applying variable step disturbance on grid current. And the new method also improves the rate of detection by strengthening disturbance in negative half wave. Theoretical analysis and simulation experiment prove the validity and reliability of the strategy.

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