Effect of digital control on phase-shifted full-bridge system stability and dynamic performance

Digital control has become the mainstream of DC/DC converter control technique. However, conventional analog control is less effective compared with analog control. In this paper, taking phase-shifted full-bridge ZVZCS (Zero-Voltage-Zero-Current-Switching) converter as an example,we analyze in detail the effect of the digital control on system stability and dynamics in the sampling process, zero-order-hold, and the control of one-step-delay. It shows that the introduction of all aspects of digital control makes the open-loop zero, pole points with the sampling frequency change a lot. It not only affects the closed-loop characteristic equation coefficients and order, reduces the ranges of critical and stable gain greatly, but also changes the dynamic performance of a system. Furthermore, through experiments, we validate that the theoretical analysis is correct.