In the dead of winter (around 04 Jan), we're 3 million miles closer to the sun than we are in the height of summer.
I refer you to Wikipedia's
list of common misconceptions. In fact, we're closest to the sun in the northern hemisphere's winter. I'd also point out that since winter/summer don't co-incide in the hemispheres it should be obvious that the Earth's orbit can't be the primary driving factor.
Edited by Mr Jack, : Addendum and clarification.