Pendulum Potential energy equation

hello every one
i have this pendulum:

i need to stabilize the pendulum in the inverted position , i need to know the potential energy for the pendulum , i read several articles in each one i have a different equation :
[itex]V=mgl_{p}cos\alpha[/itex]
[itex]V=-mgl_{p}cos\alpha[/itex]
[itex]V=mgl_{p}(1-cos\alpha)[/itex]
[itex]V=mgl_{p}(cos\alpha-1)[/itex]
Now i'am really confused which equation is the correct one?
Please help me