A good reference for variable frequency ramp generation is the “Half-Bridge LLC Converter with Analysis Tools” demo model. Refer to the “VCO w/ programmable clock duty cycle” subsystem which implements the carrier generation. It uses a resettable integrator to generate a sawtooth waveform. The sawtooth waveform is then mapped into a triangular waveform.
I attached a model of that subsystem here as well.
VoltageControlledOscillator.plecs (26.1 KB)