Ward-Leonard Motor Generation System

Ward-Leonard Motor Generation System

Introduction:

A control system generally controls, regulates, and updates its output continuously based on present inputs, nature of the system, and the past outputs. In other words, there is a feedback mechanism that is inherent in the system, and is called a closed loop control system. For example, adding an emitter resistance to a common emitter amplifier, results in a negative feedback mechanism in the amplifier system – if the output current increases, the input voltage decreases accordingly so as to reduce the output current; if the output current decreases, then the input voltage increases in order to raise the output current level. Negative feedback thus ensures that the output is always controlled to stay within an optimal range. Similarly other systems may exhibit a positive feedback mechanism. In either case, a control system can be represented as follows:

Figure 1: Control System representation

In Figure 1, G represents the forward loop function and Fb represents the feedback function. In case the Fb function is absent, the system is reduced to an open loop system.

The most popular representation of control systems is using the ‘Block Diagram’ approach (Balakrishnan, 1988). Each component in the system is represented as a block, with its role represented as a mathematical function. From the block diagram representation, the overall function of the system, called the transfer function, is obtained. The transfer function of a system is defined as O/p(s)I/p(s), where O/p(s) and I/p(s) denote the output and input functions of the system respectively, denoted in Laplace form. It is important to note that for Transfer system analysis, the initial conditions need to be zero. Further, the transfer function model does not support analysis of Multiple Input Multiple Output (MIMO) systems, where modelling becomes very complicated.

The disadvantages associated with the transfer function model led to the state...