Now, in the theory and practice of the control systems, the fundamental role played the feedbacks. For modern excitation systems of synchronous machines, the feedbacks realised thru automatic voltage regulators (AVRs), and power system stabilizers (PSSs). That different feedbacks need for control of electromagnetic (terminal voltage), and electromechnical (rotor angle or speed) states of a synchronous machine. The use of multiple feedback loops creates difficulties in the design, commissioning and operation of the excitation control systems. In book the new structures of the excitation control systems is considered. The key features of offered excitation control system structures is optimization of input signals and used the parameters of magnetic field in the gap for rotor motion stabilization. Also considered the excitation control system structure with complex feedback by terminal voltage phasor, that considerably reduces influence of noises and disturbances, simplifies its design and operation.