What is a servo system? Also known as servo system, servo system is a basic link of automation system, is composed of a number of components and parts have power amplification effect of a kind of automatic control system. According to form the physical properties of the system components are divided into electrical servo system, electric hydraulic servo system and electrical pneumatic servo system. Electrical servo system is divided into a dc servo system and ac servo system, and is widely used in the 1970 s dc servo, dc motor, wide speed range and start to stop convenient, large torque, small energy consumption system, and widely applied to the control in the servo system performance requirements are higher. What is the excitation control? Dc servo system is suitable for power range is very wide, including from dozens of tile to tens of kilowatts of controlled object. Usually, from the view of improving system efficiency consideration, dc servo system is more applied to the control object in more than 100 watts of power. The output of the dc motor torque to add to the armature current and magnetic flux produced by exciting current. Flux is fixed, the greater the armature current, the bigger the motor torque. When the armature current is fixed, increase magnetic flux can increase the torque. Therefore, by changing the excitation current and armature current, can be to control dc motor torque. To control the armature current said armature control when the control voltage in the armature. If to control excitation current, then add the control voltage on the field winding, known as the excitation control. Armature control, the armature inductance usually small, therefore the armature control can get a good response. Defect is load power provided by the control power supply of the armature, so need larger control power, increased the complexity of the power amplifier unit. That control power of the larger systems, for example, must adopt - electric generator controller unit, motor controller enlarger and thyristor power amplifier components. Excitation control requirements on the armature and constant current power supply, make the torque of the motor excitation current control. Constant current characteristic through access to a large resistance in the armature loop (10 times the armature resistance)To get it. For high power control objects, the series resistance of power consumption will be very big, very not economic. So the excitation control in low power use only. Armature after power supply with constant current source, on the mechanical properties of the slope is equal to zero, cause the electromechanical time constant increase of motor controller, combined with the excitation winding inductance of the larger, these all make the dynamic behavior of the excitation control is poorer, response is slow.
