Tham khảo tài liệu 'wind power 2011 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Analysis and Investigation of the Inverter for Energy Transfer from Small Wind Power Plant to Common Grid 197 where I2m is the value of current before switching-off the transistors. The amplitude of output current of the converter is taken in the formula in order to obtain the maximum voltage increase. The energy flows to the capacitor. The increase Aw of capacitor voltage U1 is bounded with the energy according to the equation Ju1-Au 2 uỉ Á A2u I AE Cv 1 _ - C-22 CI u Au I. 19 2 2 12 J Comparison of 18 and 19 gives the equation r c A2iI . . A2uI Ln I I Ai - I CI u Au - I. 20 2 I 2m 2 I I 1 2 I The increase of capacitor voltage calculated from 20 is r L A2i I . . Au u 2 2- 2-I h Ai- -- I -u . 21 1 C I 2m 2 1 At the and of the transistor off state the filter transistor source and receiver voltage is L A2i I u u. Au u2 223-I I2 Ai- -A I. 22 m 1 V 1 2 I m 2 v For the initial value of u1 El the overvoltage written like 10 is r t 1 2- 2- I2m Ai- I. 23 E1 E2C 2m 2 J In formulas 18 and 19 the terms A2i 2 and A2u 2 can be neglected. In this case instead of 20 is L2I2m Ai Cu1 Au 24 and instead of 21 is Au LI2m Ai. 25 Filter containing capacitor without serial resistance is a good solution from point of view of softening switching phenomena. In this case the voltage jump Au during diode conducting is small. For R 0 and for the basic data of remaining parameters the jump according to 21 is Au 1 38V only and according to 25 is Au 1 5V. Unfortunately the operation without filter resistance can be inadmissible. Decrease of the resistance results in decrease of the overvoltage according to the formula 10 and of the power loss. The decreased voltage drop on filter resistance is visible in in comparison with . But the resistance can not be too small due to resonance phenomenon. The resonance arises in the circuit containing filter capacitance C and source inductance L1. It produces oscillations of voltage supplying the converter. Hysteresis shaping of the current 198 .
