A phase-shifted full-bridge conversion circuit and control method

Abstract

The invention discloses a phase-shifting full-bridge conversion circuit, which includes a transformer; the leading bridge arm is composed of a MOS tube 1 and a MOS tube 2 connected in series, and the connection point of the two MOS tubes is connected to the primary side of the transformer through a capacitor and a resonant inductance in sequence. The capacitor and the resonant inductor are connected in series; the lagging bridge arm is composed of three MOS tubes and four MOS tubes connected in series, the connection point of these two MOS tubes is connected to the other end of the primary side of the transformer, and the input DC voltage is added between the connection point of MOS tube one and MOS tube three and the connection point of MOS tube two and MOS tube four; the output circuit is composed of four rectifier diodes and an output capacitor; the two ends of the output capacitor are output the DC voltage. The invention also discloses a control method for the phase-shifting full-bridge conversion circuit. The invention realizes the full-bridge soft switch of the phase-shifting full-bridge conversion circuit, reduces switching loss and improves the efficiency of the whole machine.

Description

technical field [0001] The invention relates to the technical field of phase-shifting full-bridge conversion, in particular to a medium and high-power phase-shifting full-bridge conversion circuit and a control method. Background technique [0002] The phase-shifted full-bridge conversion topology is currently one of the most widely used topologies in high-power DC / DC converters, and it is also a circuit structure that has been studied more. It uses the charge-discharge resonance mode between the inductor and the capacitor to enable the full-bridge MOS tube to realize soft switching when it is turned on to reduce switching loss, thereby improving the switching frequency and overall efficiency without increasing switching loss. However, there are many defects in the traditional phase-shifted full-bridge circuit. figure 1 The circuit shown, the main problems are: [0003] 1) At light load, the energy stored in the resonant inductor L1 is not enough to drain the drain-source ...

AI Technical Summary

Problems solved by technology

[0003] 1) At light load, the energy stored in the resonant inductor L1 is not enough to drain the drain-source capacitance charge of the rear axle MOS tubes (Q3, Q4), so that the rear axle works in a hard switching state at this time, resulting in increased switching loss and severe heat generation

[0004] 2) The reverse recovery of the rectifier diode on the secondary side of the transformer is serious, resulting in low efficiency of the whole machine. When the traditional phase-shifted full bridge works, the rear bridge works in the ZVS state, causing the secondary rectifier diode to be hard-off, so the diode has reverse recovery loss. and increases with output power

[0005] 3) During the period when the primary current of the traditional phase-shifting full-bridge transformer is from positive downshoot to negative or from negative upshoot to positive, the current of the output filter inductor L2 cannot change abruptly, so the primary side of the transformer is "short-circuited" due to the freewheeling current of the output diode. ", so the power supply voltage is added to the resonant inductor at this time, and the voltage applied to the transformer is 0V, resulting in a loss of duty cycle

[0006] 4) There is a contradictory relationship between the loss of duty cycle and the design of the ZVS load range of the rear axle, which reduces the efficiency of the whole machine

At the same time, the EMI caused by the sudden change of the main circuit current and the loss of duty cycle also have a contradictory relationship, which further reduces the efficiency of the whole machine

Because the greater the slope of the current change, the more serious the EMI of the power supply. If you want to reduce the EMI, you need to reduce the slope of the current change. From the perspective of the current change on the primary side of the main circuit, you must increase the inductance of the resonant inductor. From the previous description, you can see out doing so after increasing the duty cycle of the power supply is lost

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