Selectmen voted unanimously Tuesday to support a 15-year tax break on more than $30 million in renovations at Invensys, and urged Town Meeting voters on May 13 to do the same. The software manufacturer formerly known as the Foxboro Co. has two local campuses and a 100-year history of employing residents. Officials there have said upgrades are needed, or the company may have to relocate. Tax increment financing, or TIF, is designed to promote job creation by allowing communities to reduce the real estate tax on a new project for up to 20 years. In this case, Invensys would save $1.8 million in taxes over the span of the pact, but continue to pay $376,000 annually on the existing property. After four years of no taxes on the additions, a discounted program would kick in. If the tax break is granted, it will be forwarded to the state Economic Assistance Coordinating Council for approval.