ZVT-PWM phase-shift soft switching communication basis - design of power module

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ZVT-PWM phase-shift soft switching communication basis - design of power module [Copy link]

As power electronic devices have evolved from thyristors (SCRs) to high-power transistors (GTRs), and then to VMOSFETs and IGBTs, power conversion technology has also experienced a development process from load resonant conversion to hard-switching PWM, and then to double-zero switching and double-zero conversion. Double-zero conversion technology includes zero voltage conversion (ZVT) and zero current conversion (ZCT). Their basic working principle is to use auxiliary switch tubes and resonant circuits to work with the main switch tube to achieve zero voltage switching (ZVS) or zero current switching (ZCS) respectively. It is a true fixed-frequency soft-switching PWM conversion, which has the common advantages of fixed-frequency PWM conversion and soft-switching conversion. Therefore, double-zero conversion technology is one of the development trends of power conversion technology.

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Phase-shifted full-bridge ZVT soft switching conversion technology Among the double zero conversion technologies, ZVT conversion technology is widely used, mainly for high-frequency active PFC and DC/DC conversion circuits. The basic working principle of ZVT conversion is that the auxiliary switch tube works together with the resonant circuit to enable the main switch tube to achieve zero voltage switching. The main advantages of ZVT conversion technology are: (1) Fixed frequency PWM conversion. Compared with the ZVS conversion that works in the form of frequency modulation, the design of the transformer and filter reactor is easier and the utilization rate is higher; (2) In the process of turning on and off the main switch tube, partial resonance technology is used to achieve soft switching conversion, which greatly reduces the switching loss and improves the working efficiency; (3) The current flowing through the main switch tube when it is turned on and the voltage it bears when it is turned off are similar to hard switching PWM conversion, which is lower in cost and higher in reliability than double zero switching conversion; (4) Soft switching conversion, low electromagnetic interference (EMI). Figure 1 Phase-shifted full-bridge conversion circuit The typical application of ZVT conversion technology is the full-bridge conversion circuit of phase-shift control, and its basic circuit is shown in Figure 1. VDA, VDB, VDC, and VDD are the equivalent anti-parallel body diodes of the switch tubes VA, VB, VC, and VD (IGBT is used as an example here); CA, CB, CC, and CD are the equivalent output capacitances (junction capacitances) of VA, VB, VC, and VD respectively; L1 is the sum of the primary circuit lead inductance LX, the transformer primary winding leakage inductance LL, and the external inductance L, that is, Figure 2 Phase-shift PWM control waveform L1 = LX + LL + L (1) The switch tube adopts a phase-shift PWM control method, and the control waveform is shown in Figure 2. It can be seen that the four switch tubes of the phase-shift full-bridge conversion circuit are both the main switch tubes and the auxiliary switch tubes of each other, which does not increase the number of switch tubes, and absorbs the distributed parameters as the resonant circuit parameters to achieve zero voltage conversion [1]. 3 Application design in ZVT soft switching conversion circuit The phase-shift full-bridge ZVT soft switching conversion circuit can be used to design many types of switching power conversion devices, and the design methods and processes are similar. Since the main circuit is determined to be a full-bridge inverter circuit, the integrated control chip is generally selected as UCX875~79 or ML4148, so the most important design content is summarized into two points: one is to optimize the design of ZVT soft switch conversion resonance parameters based on heat dissipation balance, and the other is the loop design of the control system.