How to design a PLL locked at 60 Hz

[Gagan_SJSU]

Hi Friends

As an intern, I am designing a PLL which has to lock on to a grid reference signal coming at 60 Hz and has to feed some fets on a solar inverter . The design has a multiplier, a LPF and a VCO. I have searched hundreds of papers but I have not seen any frequencies like this. The maximum phase error allowed is 2 degrees and lose of grid should result in VCO to drift back to its center frequency at around 60 Hz. The VCO center frequecy if between 45 Hz equivalent to 50Hz and 60 Hz equivalent to 55Hz. the lock rande is 45Hz to 65Hz. So both the input and output frequencies are same. I am really confused about how to design that filter. What are the constraints and equations that need to be used? Plz help me. I am new to this topic and I have learned how to design with charge pump and divide by N as I can easily find a lot of papers and the equations. But this one can not be found any where.

please provide me any kind of details
Thanks

 

[FvM]

Regarding basic PLL properties, there's no difference between a 60 Hz and a 60 MHz (or 60 GHz) PLL. At 60 Hz, PLLs are often realized as DSP design with an "analog" mutiplier and a sine reference voltage, but the operation is basically easy, because you don't have to fear abrupt phase or frequency changes. Simply start with a first order (PI) loop filter.

 

[betwixt]

At such low frequencies it may be feasible to simply use a zero crossing detector and microprocessor to both measure and produce the frequencies. It could also incorporate a loss of grid signal detector quite easily without having to wait for the PLL to go out of lock to sense a power failure.

Brian.

 

[Gagan_SJSU]

Thank you Friends

The things that both of you said are totally right. This PLL will be implemented using a code later on. Can you suggest me a way to start designing the filter because I believe I have to use control theory in it so where should I start from. I have to decide upon a damping factor. What would be my loop natural frequency. i have read somewhere that for PLL's working for signals less than 5KHz, the cutoff frequency is between 1/4 of Fref - 1/6 of Fref and then Natural Freq is around 1/2.