The paper reviews modeling of thyristor-controlled series capacitors (TCSC) which are highly nonlinear systems with continuous and discontinuous states, and proposes three nonlinear controllers for them: (1) a Lyapunov-based controller; (2) an interconnection and damping assignment (IDA) controller; and (3) a dynamical flatness-based feedback linearizing (FLC) controller. The stability of all three controllers is analyzed and detailed (switched) time-domain simulations are used to verify the control performance achieved by the three controllers.