Small Signal Behaviour of DC Machine — Lesson 3

This lesson covers the concept of small signal modeling for DC machines. It explains how disturbances in the inputs applied to the DC machine, such as the voltage applied to the armature, field, and load, can cause small disturbances in the flow of armature current, field current, and speed. The lesson further elaborates on how these small signal equations can be used to derive relationships between the response considered as an output and the input applied. It also provides an in-depth understanding of how the small signal model can predict the response of the DC machine and how it compares with the actual large signal model. The lesson uses a 5HP DC machine as an illustrative example to explain the concept.

Video Highlights

00:14 - Introduction
01:29 - Detailed discussion on the small signal equations of the DC machine
05:31 - Discussion on how to solve the small signal equation and obtain the responses as dependent on the inputs
11:29 - Discussion on the relationship between the speed and the field voltage applied as the input
22:36 - Explanation of large signal model response
43:13 - Explanation of how the large signal model response and the small signal model response compare
47:41 - Discussion on the limitations of the stationary reference frame description and the need for an arbitrary reference frame

Key Takeaways

- Small signal modeling is a useful tool for understanding the behavior of DC machines under disturbances.
- The small signal equations derived from the disturbances in the inputs can be used to derive relationships between the output and input.
- The small signal model can accurately predict the response of the DC machine, especially when the disturbances are small.
- However, as the magnitude of the disturbances increases, the response estimated from the small signal model may deviate from the actual response.
- The small signal model can be used to model a variety of machines, including induction machines, DC machines, and synchronous machines.