Adding renewable generation to the power grid requires appropriate control and grid extensions. The control is realized on different time scales to cope with short-term fluctuations and long-term power imbalance alike. Many studies investigated the effect of the fast primary control on frequency quality and power grid stability. However, secondary control is rarely considered. Furthermore, not all grid extensions are beneficial but some added lines cause the grid to lose its synchronous state (Braess' paradox). In this work, we propose a simple implementation of secondary control and demonstrate its effectiveness in stabilizing the power grid. We compute stability boundaries and show how secondary control prevents Braess' paradox when all nodes of the grid, generators, and consumers, are controlled.