Analogue Drives are subdivided into three predominant categories – Velocity, Torque and Power Block as detailed below.
Analogue Velocity Drives
In an Analogue Velocity Drive system the Position Loop is enclosed in the controller and passes information about the motor speed to the drive and the drive controls the velocity and current loops along with the power to the motor.
A Velocity Drive system contains many wires, not only in shear number of wires required for feedback but also as these wires are required both by the controller and drive, effectively doubling the quantity. If the methods of controlling the position and velocity by the controller and drive are not the same, the system becomes complicated, especially when schemes such as feed-forward require implementing. Velocity drive systems suffer from noise and poor resolution.
Analogue Torque Drives
The controllers in Torque Drive systems take control of the Velocity loop. Consequently the drives functions are reduced to commutation, current loop and power stage. As with the Velocity drive system, both the drive and the controller must receive positional feedback.
Torque drives remove the noise and resolution problems of the Velocity drive systems as it is less sensitive to differences in the supply current. It does however share similar numbers of wires, doubling up to the controller and drive.
Analogue Power Block Drives
In a Power Block Drive system the drives functions are reduced again so that it is solely responsible for the power stage only. The controller sees to the position, velocity and current loops along with the commutation and sends the drive digital signals to control the transistors in the power stage. The feedback is in analogue and the drive need not know positional information which greatly reduces wiring and therefore limits noise issues.
While Power Block Drives are cheaper, the majority of functions are carried out in the controller resulting in an increased computational load and amount of wiring to the controller. The Power Block Drive system can be the hardest to set up as it is very susceptible to manufacturing inconsistencies and locating and isolating errors is made difficult by the close union of controller and drive.