The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments wi...The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.展开更多
为了使光伏并网发电系统输出高质量的电能,在分析无差拍控制工作原理的基础上,推导了一种三相光伏并网逆变器电流无差拍控制PWM算法,提出了一种基于电流无差拍控制的两级式光伏并网逆变器的总体控制策略。该控制策略包括MPPT(Maximum Po...为了使光伏并网发电系统输出高质量的电能,在分析无差拍控制工作原理的基础上,推导了一种三相光伏并网逆变器电流无差拍控制PWM算法,提出了一种基于电流无差拍控制的两级式光伏并网逆变器的总体控制策略。该控制策略包括MPPT(Maximum Power Point Tracking)环、直流电压环和交流电流环。Matlab/Simulink仿真验证了电流无差拍控制的有效性。最后将提出的控制策略应用到10kW光伏并网逆变器中,实验结果验证了该并网控制策略的正确性和有效性,系统具有良好的动态特性和稳态特性。实验结果所得的三相并网电流总畸变率均在3%以内,优于国标规定值;并网功率因数为1。展开更多
基金supported by National High-tech Research and Development Program of China（863 Program）（2009AA04Z416） National Science Foundation of China（51021005） Scientific Innovation of Colleges and Universities（200704）
基金Project supported by National Basic Research Program of China(973 Program) (2011CB 209400)Program of State Key Laboratory of Power Systems for ±1 100 kV UHVDC Technology(SKLD10M09)
文摘The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.
基金supported by National High-tech Research and Development Program of China（863 Program）（2009AA04Z416） National Science Foundation of China（51021005） Scientific Innovation of Colleges and Universities（Project v-200704）
文摘为了使光伏并网发电系统输出高质量的电能,在分析无差拍控制工作原理的基础上,推导了一种三相光伏并网逆变器电流无差拍控制PWM算法,提出了一种基于电流无差拍控制的两级式光伏并网逆变器的总体控制策略。该控制策略包括MPPT(Maximum Power Point Tracking)环、直流电压环和交流电流环。Matlab/Simulink仿真验证了电流无差拍控制的有效性。最后将提出的控制策略应用到10kW光伏并网逆变器中,实验结果验证了该并网控制策略的正确性和有效性,系统具有良好的动态特性和稳态特性。实验结果所得的三相并网电流总畸变率均在3%以内,优于国标规定值;并网功率因数为1。
