Analytical calculation of resonant inductance for zero voltage switching in phase‐shifted full‐bridge converters

Abstract

The phase shift full bridge (PSFB) converter allows high efficiency power conversion at high frequencies through zero voltage switching (ZVS); the parasitic drain-to-source capacitance of the MOSFET is discharged by a resonant inductance before the switch is gated resulting in near zero turn-on switching losses. Typically, an extra inductance is added to the leakage inductance of a transformer to form the resonant inductance necessary to charge and discharge the parasitic capacitances of the PSFB converter. However, many PSFB models do not consider the effects of the magnetizing inductance or dead-time in selecting the resonant inductance required to achieve ZVS. The choice of resonant inductance is crucial to the ZVS operation of the PSFB converter. Incorrectly sized resonant inductance will not achieve ZVS or will limit the load regulation ability of the converter. This paper presents a unique and accurate equation for calculating the resonant inductance required to achieve ZVS over a wide load range incorporating the effects of the magnetizing inductance and dead-time. The derived equations are validated against PSPICE simulations of a PSFB converter and extensive hardware experimentations.

The Impact of Parasitic Elements on Spurious Turn-On in Phase-Shifted Full-Bridge Converters

“…Meanwhile, according to (25) and (26), the power loss equivalent resistor R eq also has an impact on the damping ratio and natural frequency, where the power loss equivalent resistor R eq can be expressed as: loss eq 2 out P R I  (27) P loss is the power loss in a PSFB converter. Meanwhile, the selection of the transformer turns ratio has a significant influence on the overall efficiency of the PSFB converter [27], [28]. Specifically, a smaller turns ratio means a wider output voltage range.…”

An Enhanced Model for Small-Signal Analysis of the Phase-Shifted Full-Bridge Converter

“…In order to achieve soft switching in a PSFB converter, the leakage inductance alone may not be sufficient. Often an additional external inductor is added to the primary current path [22] to achieve the desired resonant inductance. However, a resonant inductance that is too large would result in longer transition times, higher value of lost duty and reduced dynamic range of the converter.…”

“…Thus, a lot of innovative research has been produced on topology variations and control techniques [18] [19] for the PSFB, overcoming some intrinsic limitations of the converter, including the possibility of hard switching and high voltage stresses on the secondary side [20]. Several literature references have shown how circulating currents during normal operation can be reduced at the converter primary or secondary side [20] [21] and poor light-load efficiency, occurring when ZVS is lost, can be avoided given a correctly sized resonant inductance [22]. Nevertheless, only a few published works (discussed in detail in Section II) deal with the dynamic modeling of the PSFB converter and, more importantly, at the time of writing no references can be found in literature regarding the impact of the parasitics on the small-signal analysis of the converter.…”

Dead-Time for Zero-Voltage-Switching in Battery Chargers with the Phase-Shifted Full-Bridge Topology: Comprehensive Theoretical Analysis and Experimental Verification

“…The main influencing factors of dead-time are studied. In [15] and [16], the relationship between resonant inductance and dead-time is analyzed. Equations for calculating the resonant inductance required to achieve ZVS are presented while incorporating the effect of magnetizing current and dead-time.…”