Automatic Resonant Frequency Tracking in Parallel LLC Boost DC–DC Converter

Abstract

This paper proposes an automatic resonant frequency tracking scheme for resonant converters. A plant modeling approach is presented based on realistic ramp variation of resonant frequency due to slowly varying environmental conditions. The drift in resonant frequency is detected by observing the phase relationship of an electrical variable pair. A rigorous analysis is carried out to select the most suitable variable pair for phase comparison. The effects of circuit nonidealities on the proposed phase detection technique have been detailed. The proposed control technique has been implemented using low cost analog circuitry and is applied to a parallel LLC tank-based resonant boost dc-dc converter. Experimental results are presented on a 160-W prototype to validate the analytical predictions.

Gain-Relationship-Based Automatic Resonant Frequency Tracking in Parallel <inline-formula> <tex-math notation="LaTeX">$LLC$</tex-math></inline-formula> Converter

“…Content may change prior to final publication. where, R is the reflected load resistance in transformer primary [30]. The designed values are listed in Table III.…”

“…where, A k and ϕ k , k = 1, 2, 3 are functions of tank excitation frequency, f s , detailed in [30]. Assuming accurate online measurement of the amplitude ratio (gain)…”

“…Many variants of phase locked loop (PLL) based ARFT strategy have been reported for different RC topologies viz. series (SRC) [4], PT based RCs [28]- [29] and parallel LLC [30]. But PLL based schemes inevitably suffer from gate driver and sensor delays, precise prediction of which is extremely difficult in practical circuits.…”

“…These variables are passed through second order generalized integrators (SOGIs) which completely remove any high frequency noise. The provision for noise-free peak detection is an advantage of this technique over PLL based [4], [28]- [30] and SS schemes [17]- [20]. Moreover, switching time-lag due to gate driver and sensor delays does not appear in the feedback loop.…”

“…Moreover, switching time-lag due to gate driver and sensor delays does not appear in the feedback loop. Thus the proposed technique remains unaffected from these circuit delays, inevitable in PLL based schemes [4], [28]- [30]. Being an active solution, gain based ARFT scheme does not require any additional startup circuit [17]- [20].…”