Control of DC motors

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Description

Control of DC motors

Advancement in technology affects the demands of industries seeking optimal efficiency. As such, automatic control plays a key role in the development of engineering and science in general. Control of DC motors is a common practice in many industries today and this requires the incorporation of DC motor controller. Controllers such as the Proportional and Integration (PI) Controller are ideal for fostering efficiency in DC motors. This project focused mainly on utilizing the PI controller for the purpose of controlling the speed of a DC motor. The first portion entails simulation whereby the DC motor is designed and the PI controller is tuned through software tuning pursuant to the Ziegler-Nicholas specifications. The second portion involves implementing the simulation. As a result, the PI controller utilized in this project is able to control the speed of the DC motor based on the results of the simulation and exercises.Control of DC motors

Keywords: speed, control, motor, response, effect, compare.

 

 

 

 

 

 

Introduction

In this contemporary age, there is hardly any industrial application whereby there is no utilization of DC motors. The prevalence of DC motors in industrial applications can be attributed to the low cost maintenance, particularly in DC motors without brushes, resilience of DC motors over a vast array of applications, ease of control and low price. Some of the industrial applications where DC motors are frequently utilized include paper mills, machine tools, textile industry, robotics and electric traction. In majority of the applications of speed control of DC motors, the current in the armature winding is varied and the current in the field winding is kept constant or vice versa, resulting in remarkable speed control performance using discordant values. The objective in these applications include Control of DC motors

  • Track the speed command by setting the output speed at a desired level.
  • Attain this desired speed level in minimum time without the process resulting in huge overshoots and settling times.

In most cases, the closed loop operation with PI controllers in the outer speed loop and inner current loop is utilized for speed control. This design is facilitated by setting and analyzing time/frequency domains. In as much as the speed response derived from PI controllers set with the above specifications may be satisfactory, they may not be the best depending on the situation since they do not present any constraint on undershoot, overshoot or settling time. Based on this understanding, the requisite PI controller parameters must be optimally designed through Zeigler-Nicholas ultimate cycle tuning scheme or genetic algorithms.

The goal of this project is to determine and design an optimal PI controller for controlling speeds by implementing PI controller based on various signal type, amplitude, frequency, offset and control parameters entries in order to determine the speed response and compare the results of experiments and simulations in controlling the speed of DC motors. This project will determine the optimal PI controller that can control the speed of DC motors effectively. Given that the performance of a machine is a prominent factor in this project, as well as, in industrial application, this project will assess the performance and efficiency of a DC motor by determining the effect of set-point weight, tracking triangular signals and determining and comparing speed response in various exercises or applications.

 

Conclusion-control of DC motors

A proportional controller (Kp) will have the effect of decreasing the rise time and decrease, but never eradicate the steady-state error. On the other hand, an integral control (Ki) will have the effect of eradicating the steady-state error. However, it may result in the transient response being worse. The effects of each of P and I controllers, that is, Kp and Ki on a closed-loop system on a DC motor are illustrated in the table below.

Controller respond Overshoot Rise Time S-S error Settling Time
Kp Increase Decrease Decrease Small Alteration
Ki Increase Decrease Eradicate Increase

 

It is imperative to note that these correlations may not be accurate or register the same results every time because Ki and Kp are dependent of each other. This means that altering one of these variables can alter the effect of the other two. Therefore, this table is a reference based on an experiment of using PI controllers to control speed.

The process of selection of controller parameters or specifications to meet the given performance requirements or targets is referred to as controller tuning. Ziegler and Nicholas came up with rules for tuning PI controller that can be implemented in the design of a speed control system with known mathematical models. These rules give a stable operation for the system. Nonetheless, in some cases the resulting system may evince a significant maximum overshoot specifically in the step response. In such a situation, series of fine tuning should be undertaken until a favorable outcome is obtained.