  Black hole X-ray binaries routinely exhibit Quasi Periodic Oscillations
(QPOs) in their Power density spectrum. Studies of QPOs have demonstrated
immense ability to understand these dynamical systems although their
unambiguous origin still remains a challenge. We investigate the
energy-dependent properties of the Type-C QPOs detected for H 1743-322 as
observed with AstroSat in its two X-ray outbursts of 2016 and 2017. The
combined broadband LAXPC and SXT spectrum is well modelled with a soft thermal
and a hard Comptonization component. The QPO exhibits soft/negative lags i.e.
variation in soft band lags the variation in hard band, although the upper
harmonic shows opposite behaviour i.e. hard/positive lags. Here, we model
energy-dependent properties (fractional root mean square and time-lag variation
with energy) of the QPO and its upper harmonic individually with a general
scheme that fits these properties by utilizing the spectral information and
consequently allows to identify the radiative component responsible for
producing the variability. Considering the truncated disk picture of accretion
flow, a simple model with variation in inner disk temperature, heating rate and
fractional scattering with time delays is able to describe the fractional RMS
and time-lag spectra. In this work, we show that this technique can
successfully describe the energy-dependent features and identify the spectral
parameters generating the variability.
