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I understand that you have at least access to grid input voltage. Post #7 comment about rectified waveform is describing to your present circuit implementation, but no not a principle constraint.

I must confess that I'm designing only digital PFC control since about 20 years, some suggestions like PLL (usually an "all-digital" PLL processing ADC input signal) are unsuitable. Bandpass can be implemented in pure analog design, also with automatic switching or continuous tuning of center frequency. There also analog PLL implementations, but probably involving too much effort.