Study of Diode-Clamped Three-Level Inverter(2)

into Buck transform mode and Boost mode transformation. The working condition of the two change models should be complement. When Uc1 Uc2, Buck conversion circuit (T1,D1,L1,C1) begin work. At the same time, Boost conversion circuit stop working. In Buck transform mode, it can restrain

[3]

二极管钳位三电平逆变器研究Study of Diode-Clamped Three-Level Inverter

the shift of the midpoint potential by adjusting the voltage of C2. When T1 turns on, the one hand, the current flows through T1、L1and C2 under the action of the Udc, the other hand, the voltage Uc1of the capacitor

C1 through T1 and L1 constitute the circuit, which can make L1 charge ;

When T1turns off, the energy of L1convert toC2though the loop circuit

consist of C2、And C2is charged, the charging voltage increase D1and L1.

until the voltage balance of C1and C2. When Uc2 Uc1, Buck converter is

no longer work and Boost conversion circuit begin to work. Because Uc2 Uc1, the energy of C2will be transferred to C1 indirectly. When T2 turns on, the one hand, the voltage Uc2of C2discharge by L2and T2, the energy store in L2; the other hand, Udcdistribute voltage by C1 and C2. When T2 turns off, the diode D2 conducts, the energy of L2 can be transferred to C1 through D2. In this way, Boost transform mode, it can

restrain the shift of the midpoint potential by adjusting the voltage of C1, until Uc2 Uc1.

2.2 The balance of the midpoint potential on the decline of

DC side voltage Udc When Udc reduce to below the voltage protection setting value, T3 turn off in Fig.2. The fig.4 shows the equivalent circuit. Boost converter and Buck converter work simultaneously. The voltage of C1and C2 not only counterbalance, but also the sum equal to the setting value of Udc. Buck converter adjust the voltage of the capacitor C2. When T1 turns on, the current flows from Udc to T1、 L1and C2,so that L1is charged; when T1 turns off, the energy of L1 should be transferred to C2. At the same time, Boost converter convert energy from C2to C1, and it can adjust the voltage of C1. Its work process and the above-mentioned Boost transform mode is identical congruent. [2]

二极管钳位三电平逆变器研究Study of Diode-Clamped Three-Level Inverter

3. Conclusion

This paper analyses the midpoint balance problem of the three-level inverter, and proposes a design of the hardware circuit. This method provides a good reference for the evenly distributed capacitor voltage, and could be considered for the performance improvement of the low-voltage system, and provides a theoretical and experimental basis for the application of the three-level inverter at the high-voltage power occasions.

REFERENCES

[1] TAO Sheng-gui, GONG Xi-guo, YUAN Deng-ke. Design and Simulation of

Novel Circuit for Neutral-Point Voltage Balance in Three-Level Inverter. JOURNAL OF TONGJI UNIVERSITY (NATURAL SCIENCE), 2005

[2] LI Song, LIU Zhi-hong. Simulation Study of Diode Clamping Three-Level

Inverter. Journal of Nanchang Institute of Technology, 2006

[3] LIN Lei, ZOU Yun-ping, ZHONG He-qing, ZOU Xu-dong, DING Kai. STUDY

OF CONTROL SYSTEM OF DIODE-CLAMPED THREE-LEVEL INVERTER. Proceedings of the CSEE, 2005

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