The Philadelphia Orchestra is renewing its commitment to performing free summer concerts in underserved areas of its home community. The performances, which were briefly suspended last summer due to lack of funds, draw thousands of people to unconventional venues to hear one of the world’s top orchestras, and music director Christoph Eschenbach has been said to be a key proponent of the idea. But it apparently took the financial security of a $50 million pledge from the Annenberg Foundation to make the orchestra, which has struggled with debt over the past several seasons, confident enough to move ahead with the three free concerts, which will cost the organization $375,000 in total.