  We have studied the short-cadence Kepler public light curves of SU UMa stars,
V344 Lyr and V1504 Cyg extending over a period of more than two years by using
power spectral analysis. We determined the orbital period of V344 Lyr to be
Porb=0.087903(1) d. We also reanalyzed the frequency variation of the negative
superhump in a complete supercycle of V1504 Cyg with additional data of the O-C
diagram, confirming that its characteristic variation is in accordance with the
thermal-tidal instability model. We present a new two-dimensional period
analysis based on a new method of a least absolute shrinkage and selection
operator (Lasso). The new method gives very sharp peaks in the power spectra,
and it is very useful for studying of the frequency variation in cataclysmic
variable stars. We also analyzed simultaneous frequency variations of the
positive and negative superhumps. If they are appropriately converted, it is
found that they vary in unison, indicating that they represent a disk-radius
variation. We have also studied the frequency (or period) variations of
positive superhumps during superoutbursts. These variations can be understood
in a qualitative way by combining of the disk radius variation and the
variation of pressure effects during a superoutburst. A sudden excitation of
oscillation with a frequency range near to the negative superhump (which we
call "impulsive negative superhump") was observed in the descending branch of
several outbursts of V344 Lyr. These events seem to have occurred just prior to
the next superoutburst, and to act as a "lead" of the impending superoutburst.
