The aim of this project is to control speed of permanent magnet DC motor by using technique called cascade control. In this project the working of PMDC motor, H-bridge using unipolar switching scheme, PI controller in current loop and speed loop of cascade control is first studied by simulating in MATLAB software and after that practically applied cascade control on PMDC motor using flexible inverter board. In this project dsPIC30F3010 is programmed and armature current and armature voltage is controlled by inner current loop and outer speed loop of coascade control. In this project investigation of effect of anti-windup C code on drive performance is done. The flexible board has microcontroller, current sensor and H-bridge circuit on it which will be used to supply voltage to PMDC motor. As a PMDC motor, DC motor rig is used which has two identical DC motor coupled together and one motor have encoder fitted on it and other motor have tacho-generator fitted on it.
Table of Contents
INTRODUCTION
HARDWARE
DC motor test rig
Flexible Inverter Board
RL Load and Current Clamp
dsPIC30F3010 microcontroller
In-circuit debugger unit (ICD3)
SOFTWARE
MPLAB X IDE
LABVIEW
MATLAB
Project Stages
BACKGROUND THEORY
Permanent Magnet DC Motor
Mathematical Model of PMDC Motor
Electrical Characteristics
Mechanical Characteristics
MATLAB simulation PMDC motor
H-Bridge
Four – Quadrant (4Q) operation of DC motor
Cascade speed control of Permanent DC Motor
Current Loop
Speed Loop
Optical Encoder
ADC CONVERSION
C Code
Experimental Results
CONTROL of LEG A and LEG B of H-BRIDGE
LEG-A of H-Bridge
LEG-B of H-Bridge
Role of Gate Driver IC IR2130
C Code
Experimental Results
UNIPOLAR PWM SWITCHING OF H-BRIDGE
Experimental results
CURRENT CONTROL
Experimental results
SPEED CONTROL
Experimental result
INNER CURRENT LOOP
Inner current Loop C Code
Experimental Results
OUTER SPEED LOOP
Outer speed loop C Code
Experimental result
Project Goals and Scope
This project aims to implement digital cascade speed control for a permanent magnet DC motor. The research focuses on modeling, simulating, and practically applying a cascade control strategy, utilizing a PI controller for both the inner current loop and the outer speed loop to optimize motor performance and protect the hardware from overcurrent conditions.
- Design and simulation of a PMDC motor model using MATLAB.
- Implementation of unipolar PWM switching schemes via an H-bridge converter.
- Development of a cascade control system using a dsPIC30F3010 microcontroller.
- Integration of current and speed feedback loops for improved stability.
- Practical testing and validation of the control system on a DC motor test rig.
Excerpt from the Book
Permanent Magnet DC Motor
A permanent magnet DC motor is a machine or device which converts electrical power to mechanical power using magnetic coupling. The voltage source provides electrical power while mechanical output power is rotation of rotor due attraction and repletion of stator magnetic field and armature magnetic field generated by rotor winding. A permanent magnet DC motor mainly consists of two components stator and rotor. [5]
The stator of PMDC motor consists of magnets which produce magnetic field called stator magnetic field (green dotted line in fig-11) and rotor (also called armature in DC machine) consists of many coils wound around iron core which produces magnetic field, when motor is connected to voltage source and this magnetic field is called armature field (red dotted line in fig-11 ). The phenomenon of opposing and attracting forces of the stator magnetic field and rotor magnetic field make armature (rotor) to rotate. Another way to analyse the reason for rotation of armature is that as electric current following through armature coil create armature magnetic field and the polarity of electric current (or direction of current flow) is changed constantly by commutator to make always make armature magnetic field perpendicular to stator magnetic field to maximise the torque. Since torque is equal to dot-product of force and length, so torque is maximum when angle is 90 degree. [5]
The commutator consists of two semi-circular copper segments fitted on the shaft at the end of rotor (armature) as shown in fig -11. Each rotor coil terminal is connected to a copper segment of commutator. Stationary brushes touch the copper segments and the coil on rotor gets connected to a stationary dc voltage supply by a near frictionless contact. [5]
Summary of Chapters
INTRODUCTION: Provides an overview of the PMDC motor structure and the role of H-bridge converters in variable speed applications.
HARDWARE: Details the physical setup, including the DC motor test rig, flexible inverter board, and the dsPIC30F3010 microcontroller.
SOFTWARE: Discusses the programming environment, specifically MPLAB X IDE, LABVIEW, and MATLAB simulation tools used for development.
BACKGROUND THEORY: Explains the mathematical modeling of the PMDC motor, H-bridge operation, and the theoretical foundation of cascade speed control.
ADC CONVERSION: Covers the process of converting analog signals to digital format within the microcontroller for feedback control.
CONTROL of LEG A and LEG B of H-BRIDGE: Analyzes the gate driver and PWM duty cycle control required to manage the motor phases safely.
UNIPOLAR PWM SWITCHING OF H-BRIDGE: Explains the switching scheme used to generate the desired armature voltage across the motor.
CURRENT CONTROL: Describes the practical implementation and measurement of current using RL loads before motor connection.
SPEED CONTROL: Explains the use of optical encoders for speed feedback and the calibration against tacho-generator output.
INNER CURRENT LOOP: Documents the development and performance testing of the fast-response armature current controller.
OUTER SPEED LOOP: Discusses the implementation of the outer loop, which dictates demand current based on speed error.
Keywords
Permanent Magnet DC Motor, PMDC, Cascade Control, H-Bridge, Unipolar PWM, PI Controller, dsPIC30F3010, Current Loop, Speed Loop, Optical Encoder, MATLAB Simulation, Digital Control, Armature Current, Microcontroller, Inverter Board.
Frequently Asked Questions
What is the primary objective of this project?
The main objective is to implement a digital cascade control system for a permanent magnet DC motor to maintain precise speed control while protecting the motor from overcurrent.
Which control technique is utilized in the study?
The study utilizes a cascade control technique, which features an inner current loop for protection and an outer speed loop for regulation.
Why is a cascade control structure used instead of a single loop?
Cascade control allows for faster response times in the inner loop, protecting the DC motor during stall or transient conditions while the slower outer loop handles overall speed regulation.
What hardware platform is used to implement the controller?
The system is implemented on a flexible inverter board powered by a dsPIC30F3010 microcontroller.
What is the role of the MATLAB simulations?
MATLAB is used to model the motor and control loops to determine optimal proportional (Kp) and integral (Ki) gains for the PI controllers before practical implementation.
How is the motor speed measured?
Motor speed is measured using an optical encoder attached to the motor shaft, which generates frequency signals proportional to the angular velocity.
What is the function of the H-bridge in this system?
The H-bridge acts as the power converter that supplies variable voltage to the DC motor, enabling speed and directional control through PWM switching.
How does the system prevent shoot-through faults?
The gate driver IC (IR2130) introduces a dead-time (typically 2µs) during switching to ensure that the upper and lower MOSFETs in a leg are not energized simultaneously.
How is the current sensor calibrated?
The current sensor has a specific offset voltage; the study calculates gain based on the output voltage variation relative to the current flowing through the sensor to enable accurate current measurement.
What were the main conclusions regarding the performance?
The project concludes that the digital cascade control functions effectively, as evidenced by the system's ability to maintain motor speed under varying load conditions and its successful limitation of armature current.
- Arbeit zitieren
- Ninad Gondhalekar (Autor:in), 2014, Cascade control of DC brushed motor, München, GRIN Verlag, https://www.grin.com/document/283511
