Private equity group 3i saw a 15% return on its portfolio in the year to March 31 as the companies it invests in participated in the strong rally that followed the economic collapse of the previous year.The group's net asset value (NAV) climbed totalled 321p at the end of the period, up from 279p a year previously.Debt was also sharply lower, falling to £258m from £1,912m.Outgoing chairman Baroness Hogg said that economic conditions remain difficult following the economic crisis.'The after-shocks from the credit crunch continue to destabilise financial markets, as they wait with decreasing patience for governments to repair their fiscal deficits,' chairman Baroness Hogg said. 'But 3i has a great ability to adapt, a brand built on its reputation as an investment partner, committed and engaged shareholders, and is strongly placed to deploy these advantages in fast-changing markets.'Hogg's replacement by Sir Adrian Montague, former chairman of the pensions group Friends Provident, was announced on Monday.