A unified model for the ZVS DC-DC converters with active clamp

Abstract

Active clamp dcdc converters are recently intro'duced family of two switch pulse width modulated converters featuring zerovoltage switching. The topological structure of these converters in relation to their hard-switched PWM converters is highlighted. With proper designation of the circuit variables (throw voltage V and the pole current I), all these convertem are seen to be governed hy an identical set oiequations. In this framework, these circuits exhibit 6 sub-periods per cycle with identical current waveform in the resonant inductor. With idealized switches, the steady-state performance is obtainable in an analytical form. This set of equations may be solved through a simple spreadsheet programme. The steady-state performance provides a design constraint on the normalized current. The conversion ratio of the converter is also readily available. A generalized equivalent circuit emerges for all these converters from this steady-state conversion ratio. It is interesting to note that this equivalent circuit provides a dynamic model as well. The circuit model proposed in this paper enables one to use the familiar state space averaged results of the standard PWM de-to-de convertem (both steadystate and dynamic) for their ZVS active clamp counterparts

Effect of the Output Impedance in Multiphase Active Clamp Buck Converters

“…Nevertheless, to ensure the ZVS operation, the energy stored in L r when S 2 is turned off must be greater than the energy required to discharge C r from (V in + V C 1 ) to 0. Considering that the output filter current ripple could be neglected, the ZVS condition can be expressed as (17). Here, the steady-state clamp capacitor voltage expressed in (18) can be derived from (6) assuming that…”

“…In [17], it was proved that the active clamp buck converter has high output impedance, but that model did not include clamp capacitor and soft-switching effects in the converter input. In Section II, a complete model is presented, following the method shown in [18].…”

Implementation of a ZVT based power factor correction converter

“…Active clamp topology has been introduced in [6], [12]. But, soft switching in this topology is dependent on load condition and the VA rating of the switches is greater than the load voltage & the load current [7], [13].…”

Small signal analysis of current mode active-clamp ZVS dc-dc converters

“…A reduced order averaged modeling of active clamp converters is subsequently presented in [4]. A unified steady-state analysis for the whole family of Md constant frequency active clamp dc-dc converters has been reported in [5]. It has been established that, the output voltage of active clamp converters exhibit a load dependent droop.…”

“…The load dependent droop is function of resonant inductor and switching frequency . In other words active clamp converters exhibit lossless damping in the system and this leads to better dynamic performance of duty cycle controlled converters [5]. The current programmed control is one of the popular schemes used in high power dc-dc converters due to its advantages over duty cycle control like parallel operation without load sharing problem, simpler dynamics, robust output voltage control, and prevention of transistor failure against excessive current etc.…”