Research On Current-Sharing Technology Of Three-level DC-DC Converter

The power electronics technology is used more and more widely in all kinds of electrical equipment, however, the power electronic device will produce a large number of harmonics which causes serious of pollution to the power grid and affects the power quality. The traditional bridge rectifier circuit is one of the main harmonic sources, power factor correction system has been widely developing and applicating to over the phenomenon. However, the DC side voltage of PFC is much higher than that of the traditional bridge rectifier circuit because that PFC is essentially a boost circuit. So, the switch of the DC-DC converter after the PFC will tube greater voltage stress. In addition, high power supply which can output high current is required in the electric vehicle,communication and many other fields. If all the power is supplied by a single centralized power supply, the reliability of the system will be greatly reduced because of switch tubing greater current stress.In order to solve the problem that the reliability of the system is reduced because of the switch tubing greater voltage stress and current stress, in this paper, a single power supply module consists of three-level DC-DC converter which reduce the voltage stress because of every switch tubing half of the input voltage, and the whole system consists of some paralleling three-level DC-DC converter module, which reduce the current stress because of every module sharing part of the current.In this paper, firstly, the development history of the three-level DC-DC converter, the principle of the phase-shift control ZVS three-level DC-DC converter, and the topology with clamping diodes to overcome the parasitic oscillation are introduced, and an improved topology with clamping diodes which is proposed by author is used as the final power supply module, also do the simulation. Secondly, the principles and the respective advantages and disadvantages of some current-sharing schemes are introduced, and the maximum-current automatic current-sharing method is used as the final scheme. Finally, current feedback loop is joined to improve the dynamic performance of the system. The whole control system adopts three loop strategy which consists of voltage loop, current-sharing loop and the current loop. The mathematical models of the system without current loop and with current loop are respectively established, and the bode diagrams of them are drawn out. The reason why three loop control strategy can improve the dynamic performance is analyzed theoretically by comparing the bode diagrams, and the simulation of the whole system is done.