Pulse Width Modulation Controlled DC Motor and H-Bridge
In this project, we are implementing dc motor controller using PWM, thereby regulating the speed of the motor and imple...
PWM CONTROLLED DC MOTOR and H-BRIDGE A Project Report
Harish Kumar Anjali Chugh Aman Pundir
(07414) (07428) (07429)
DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY HAMIRPUR-177005, HP (INDIA) APRIL, 2010
ACKNOWLEDGEMENT Apart from the efforts of us, the success of this project depends largely on the encouragement and guidelines provided to us by our Linear Integrated Circuits lecturer from time to time. We take this opportunity to express our gratitude to the person who has been instrumental in the successful completion of this project. We would like to show our greatest appreciation to our project guide,
Er. Vinod Kumar (Faculty of Electronics and Communication Engineering) Under the guidance of whom We feel motivated and encouraged every time we attend his lectures. Without his encouragement and guidance this project would not have materialized. We can’t say thank you enough for his tremendous support and help. We are grateful for his constant support and help. Thanking you for your kind anticipation in our project.
Harish Kumar (07414) Anjali Chugh (07428) Aman Pundir (07429) Nit Hamirpur, H.P.
CONTENTS Page No
A motor controller is a device or group of devices that serves to govern in some predetermined manner the performance of an electric motor. A motor controller might include a manual or automatic means for starting and stopping the motor, selecting forward or reverse rotation, selecting and regulating the speed, regulating or limiting the torque, and protecting against overloads and faults.
In this project, we are implementing dc motor controller using PWM, thereby regulating the speed of the motor and implementing the working of the H-bridge across the Load. A PWM controller typically contains a large reservoir capacitor and an H-bridge arrangement of switching elements (thyristors, Mosfets, solid state relays, or transistors). In particular, our circuit is based on power MOSFETs and IR2110 H-bridge driver IC.
PWM controls uses pulse width modulation to regulate the current sent to the motor. Unlike SCR controls which switch at line frequency, PWM controls produce smoother current at higher switching frequencies, typically between 1 and 20 kHz. At 20 kHz, the switching frequency is inaudible to humans, thereby eliminating the hum which switching at lower frequency produces. However, some motor controllers for radio controlled models make use of the motor to produce audible sound, most commonly simple beeps.
A pulse width modulator (PWM) is a device that may be used as an efficient light dimmer or DC motor speed controller. The circuit described here is for a general purpose device that can control DC devices which draw up to a few amps of current. The circuit may be used in either 12 or 24 Volt systems with only a few minor wiring changes. This device has been used to control the brightness of an automotive tail lamp and as a motor speed control for small DC fans of the type used in computer power supplies. The purpose of a motor speed controller is to take a signal representing the demanded speed, and to drive a motor at that speed. The controller may or may not actually measure the speed of the motor.
2) PRINCIPLE The speed of a DC motor is directly proportional to the supply voltage, so if we reduce the supply voltage from 12 Volts to 6 Volts, the motor will run at half the speed he speed controller works by varying the average voltage sent to the motor. A better way is to switch the motor's supply on and off very quickly. If the switching is fast enough, the motor doesn't notice it, it only notices the average effect. As the amount of time that the voltage is on increases compared with the amount of time that it is off, the average speed of the motor increases. This on-off switching is performed by power MOSFETs. A MOSFET (MetalOxide-Semiconductor Field Effect Transistor) is a device that can turn very large currents on and off under the control of a low signal level voltage. To control the speed of a d.c. motor we need a variable voltage d.c. power source. If we take a 12V motor and switch on the power to it, the motor will start to speed up: motors do not respond immediately so it will take a small time to reach full speed. If we switch the power off sometime before the motor reaches full speed, then the motor will start to slow down. If we switch the power on and off, quickly, the motor will run at some speed in between zero and full speed. This is exactly what a PWM controller does: it switches the motor on in a series of pulses. To control the motor speed, it varies (modulates) the width of the pulses - hence “Pulse Width Modulation”.
Consider the waveform above. If the motor is connected with one end to the battery positive and the other end to battery negative via a switch (MOSFET, power transistor or similar) then if the MOSFET is on for a short period and off for a long one, as in A above, the motor will only rotate slowly. At B the switch is on 50% and off 50%. At C the motor is on for most of the time and only off a short while, so the speed is near maximum. In a practical low voltage controller the switch opens and closes at 20 kHz (20 thousand times per second). This is far too fast for the poor old motor to even realize it is being switched on and off: it thinks it is being fed from a pure d.c. voltage. It is also a frequency above the audible range so any noise emitted by the motor will be inaudible. It is also slow enough that MOSFETs can easily switch at this frequency.
However the motor has inductance. Inductance does not like changes in current. If the motor is drawing any current then this current flows through the switch MOSFET when it is on. In order to remove the inductance effect, we use the main capacitor or boost capacitors. Thus following points can be incurred from the above discussion:
The Speed of the dc motor is dependent on the frequency of the resulting PWM signal.
Frequencies between 20Hz and 18 kHz may produce audible screaming from the speed controller and motors.
RF interference emitted by the circuit will be worse the higher the switching frequency we
3) COMPONENTS USED:
a) Resistors b) Capacitors c) Power MOSFETs d) ICs e) Schottky Diode f)
g) Voltage Regulator h) Power Supplies i)
a) Resistors: In all we are using around 4 resistors with all of them having Power ratings of ¼ watts and are axial head- Through hole - Carbon film fixed resistors.
R1, R2, R3, R4
b) Power MOSFETs: The MOSFETs used in this project are International Rectifier’s IRF3205 which can handle up to 115A drain current and 55V Drain to Source voltage. It has 0.008 Ohm RDS (on) resistance. For lower currents (~0-5A) heat dissipation will be too low. But if you will use this board for high current applications you should connect a heat sink .
Q1, Q2, Q3, Q4
And its datasheet as follows:
c) Capacitors: The capacitors that we are using in this circuit are Polyester and Electrolytic. The dielectric used in this capacitor is polyester and various other characteristics of Polyester capacitor are given as: a) Capacitance Range: 500pF- 10µF. b) Maximum Voltage: 600 V c) Maximum Operating Temperature: 125 °C d) Tolerance: ±10 e) Insulation Resistance: 10,000 MΩ
100nF Polyester Capacitor.
C1, C5, C6
100µF/16V Electrolytic Capacitor.
C3, C4, C7, C8
10µF/16V Electrolytic Capacitor
The Electrolytic Capacitor is used to eliminate ripples. The line carrying DC voltage has ripples or spikes in it; the capacitor evens out the voltage by absorbing the peaks and filling in the valleys.
d) Function Generator: The very function for the purpose of which we used function generator was to obtain pulses. As we have to give High and Low pulses to the pin No. 10 and 12 of the Low and High Side Driver IC. This enables us to produce a constant duty cycle which certainly isn’t helping in producing PWM as in contrast we require varying Duty cycle.
e) ICs: In our circuit, the IC we are using is half bridge MOSFET and IGBT driver IC which allow us to use four N-type transistors instead of two P-type and two N-type transistors, so as to result in the formation of the H-bridge. Thus, we are using two ICs and as such each IC is used to drive the half bridge.
IR2110 MOSFET AND IGBT DRIVER IC
And its datasheet as follows:
f) Schottky Diodes: The voltage drop is an important loss factor in the entire circuit, and that Schottky diodes can be used to increase efficiency. There are many types of Schottky diodes and any type will do, though only matters are the maximum current and voltage ratings. Types such as 1N5818 and 1N5822 are often mentioned; the 1N5822 being the highcurrent variant with the lowest resistance (and the thickest leads). However, both have a maximum reverse voltage of "only" 40V. Thus,
D2, D3, D4, D5, D6, D7
1N5822 SCHOTTKY RECTIFIER.
g) Signal Diode: The signal diode is used in this project for the purpose of build up of the auxiliary circuit for the conversion of 12V supply to 5V. This 5V is required for the functioning of the IR2110. The diode is reverse biased and is basically used for the rectification purposes as sometimes the 12V supply may contain some ac components. Thus
And the datasheet of it as follows:
h) Voltage Regulator: The positive voltage regulator is used in the auxiliary circuit so as to get a regulated output voltage of 5V. The voltage regulator we used is
And its datasheet as follows:
i) Power Supplies: The various power supplies we used for this project are as under given:
12V dc Supply: This supply is used for driving the voltage regulator as well as the Low and High Side Driver IC.
15V dc Supply: It is used to provide the voltage to the drain of two of the Power Mosfets.
5V dc Supply: This supply is basically obtained from the auxiliary circuit we have built along with the main circuit. The voltage regulator output gives us 5V supply which is required by the Low and High Side Driver IC.
4) CIRCUIT DIAGRAM:
The circuit diagram that we used in order to implement the project is as given under; in which the first part or the figure at the top left constitute the auxiliary circuit. The main function of this auxiliary circuit is to convert a 12V power supply to a regulated 5V power supply so that the same can be feed to the IR2110 IC.
5) SCHEMATICS DIAGRAM: In reference to the circuit diagram, the following schematic was simulated with the help of ORCAD tool.
D1N5818 D6 0Vdc
2 6 3 9 5 13
R9 7 1
2 R10 330
D4 M3 1N5814 IRF3205
COM VB VCC VDD VS VSS
COM VB VCC VDD VS VSS
1 10 12
R11 1k U1
V1 = 0 V2 = 4 TD = 0 TR = 0 TF = 0 PW = 4 PER = 0
V1 = 0V V2 = 4V TD = 0 TR = 0 TF = 0 PW = 4 PER = 0
10 12 11 2 6 3 9 5 13
12V R7 D2 1N5814
6) WORKING: Motor speed control of DC motor is nothing new. A simplest method to control the rotation speed of a DC motor is to control its driving voltage. The higher the voltage is, the higher speed the motor tries to reach. The working of this project can be studied by first understanding the workability of the PWM controller and then, the H-bridge. In the Pulse Width Modulation (PWM) method, the operating power to the motors is turned on and off to modulate the current to the motor. The ratio of "on" time to "off" time is what determines the speed of the motor. When doing PWM controlling, keep in mind that a motor is a low pass device. The reason is that a motor is mainly a large inductor. It is not
capable of passing high frequency energy, and hence will not perform well using high frequencies. Reasonably low frequencies are required, and then PWM techniques will work. Lower frequencies are generally better than higher frequencies, but PWM stops being effective at too low a frequency. The idea that a lower frequency PWM works better simply reflects that the "on" cycle needs to be pretty wide before the motor will draw any current (because of motor inductance). A higher PWM frequency will work fine if you hang a large capacitor across the motor or short the motor out on the "off" cycle. The reason for this is that short pulses will not allow much current to flow before being cut off. Then the current that did flow is dissipated as an inductive kick - probably as heat through the fly-back diodes. The capacitor integrates the pulse and provides a longer, but lower, current flow through the motor after the driver is cut off. In the simplest way the working of a PWM controller can be understood in the following manner. Consider the circuit below: this shows the drive MOSFET and the motor.
When the drive MOSFET conducts, current flows from battery positive, through the motor and MOSFET (arrow A) and back to battery negative. When the MOSFET switches off the motor current keeps flowing because of the motor's inductance. There is a second MOSFET connected across the motor; MOSFETs act like diodes for reverse current, and this is reverse current through the MOSFET, so it conducts. We can use a MOSFET like this (short its gate to its source) or we can use a power diode. However a not so commonly 32
understood fact about MOSFETs is that, when they are turned on, they conduct current in either direction. A conducting MOSFET is resistive to current in either direction or a conducting power MOSFET actually drops less voltage than a forward biased diode so the MOSFET needs less heat sinking and wastes less battery power. So, if the drive MOSFET is on for a 50% duty cycle, motor voltage is 50% of battery voltage and, because battery current only flows when the MOSFET is on, battery current is only flowing for 50% of the time so the average battery current is only 50% of the motor current. Main Capacitor: When the MOSFET switches off, it not only interrupts the motor current but it also interrupts the current flowing from the battery. The wires from the battery have inductance (so does the battery) so when this current is interrupted this inductance causes a voltage spike: in the circuit the main capacitor absorbs (most of) this spike. When the drive MOSFET turns on again, battery current is asked to flow quickly - which it cannot. The main capacitor supplies current during the period battery current is re-establishing. It will be apparent from the above that the work this capacitor does is extremely dependant on the loop inductance of the battery wires. Long wires will have a high inductance. H-Bridge configuration is commonly used in electrical applications where the load needs to be driven in either direction. A typical H-Bridge structure is shown below;
The term "H-bridge" is derived from the typical graphical representation of such a circuit. An H-bridge is built with four switches (solid-state or mechanical). When the switches S1 and S4 (according to the first figure) are closed (and S2 and S3 are open) a positive voltage will be applied across the motor. By opening S1 and S4 switches and closing S2 and S3 switches, this voltage is reversed, allowing reverse operation of the motor.
The switches S1 and S2 should never be closed at the same time, as this would cause a short circuit on the input voltage source. The same applies to the switches S3 and S4. This condition is known as shoot-through.
The H-Bridge arrangement is generally used to reverse the polarity of the motor, but can also be used to 'brake' the motor, where the motor comes to a sudden stop, as the motor's terminals are shorted, or to let the motor 'free run' to a stop, as the motor is effectively disconnected from the circuit. The following table summarises operation. S1 1 0 0 0 1
S2 0 1 0 1 0
S3 0 1 0 0 1
S4 1 0 0 1 0
RESULT Motor moves right Motor moves left Motor free runs Motor brakes Motor brakes
Now, summing up both the PWM controller and H-bridge part, we can very easily explain the working of our project and how the motor behaves at the output. We can explain the working of the project with the help of some figures. Consider a full bridge circuit given below;
To make the motor go forwards, Q4 is turned on, and Q1 has the PWM signal applied to it. The current path is shown in the diagram below in red. Note that there is also a diode connected in reverse across the field winding. This is to take the current in the field winding when all four MOSFETs in the bridge are turned off.
In under given figure, Q4 is kept on so when the PWM signal is off, current can continue to flow around the bottom loop through Q3's intrinsic diode:
To make the motor go backwards, Q3 is turned on, and Q2 has the PWM signal applied to it:
Now,Q3 is kept on so when the PWM signal is off, current can continue to flow around the bottom loop through Q4's intrinsic diode:
For regeneration, when the motor is going backwards for example, the motor (which is now acting as a generator) is forcing current right through its armature, through Q2's diode, through the battery (thereby charging it up) and back through Q3's diode:
Freewheeling Diode: They are also called as fly back diode, snubber diode, suppressor diode, or catch diode. Catch diodes (FD1, FD2, FD3, FD4) are often overlooked or just briefly mentioned in most H-bridge descriptions, but they are very important components. It is a diode used to eliminate fly back, the sudden voltage spike seen across an inductive load when its supply voltage is suddenly reduced or removed. The basic principle of it is very simple: while the bridge is on, two of the four switching elements will carry the current, the diodes have no role. However once the bridge is turned off the switches will not conduct current any more. By far the most common load for an H-bridge is an electric DC motor, which is an inductive load. During the on-time the motor will build an electromagnetic field inside it. When the switch is turned off, that field has to collapse, and until that happens, current must still flow through the windings. That current cannot flow through the switches since they are off, but it will find a way. The catch diodes are in the design to provide a low-resistance path for that collapse current and thus keep the voltage on the motor terminals within a reasonable range. Now, whenever a diode is conducting current, there will be a relatively constant voltage drop on it. This is called forward voltage drop and denoted as Vf. It is in the 5001000mV range for most components. Thus, in this way the motor speed and direction can be controlled by the proper application of Pulse having a varying duty cycle and proper switching of the power Mosfets.
7) APPLICATIONS Electronics Cooling All of Control Resources' DC & AC Controls can be used in electronics cooling applications for fan speed control to regulate temperature and reduce acoustical noise. Typical OEM (original equipment manufacturer) applications include file servers, ATE products, storage subsystems, medical devices and telecommunications equipment.
Medical Instruments & Power Supplies The Smart Fan is a temperature based fan speed control and temperature alarm circuit which is based on PWM, which can be mounted in the exhaust or inlet of any heat producing equipment
Telecommunications Equipment Control Resources specializes in fan speed control for telecommunication applications. The Smart Fan Multi SD, Multi SR, Vortex, and Fusion were specifically designed for telecommunications cooling applications. Features available with the Multi SD, Multi SR, Vortex, and Fusion include: Accepting diode OR'd dual power feeds from 10 to 75 VDC Soft start and current limiting Speed control for 12, 24, or 48 VDC fans Speed control based on temperature (thermistor), PWM DC signal or via a serial communication (I2C) bus Multiple programmable alarm and fan status outputs Voltage boost circuit that will maintain required voltage to the fan even when the supply voltage drops below what is needed Managed or intelligent FRU ATCA compliance. PWM controlled motor with H-bridge is mostly used in robotics, as it can handle both direction as well as speed simultaneously.
The main Disadvantages of PWM circuits are the added complexity and the possibility of generating radio frequency interference (RFI).
8) FUTURE ASPECTS
With certain modifications or rather, with certain attachments our project can be used for the construction of the Solar Seeker.
SOLAR SEEKER: It is a simple device that tracks a light source. Such a device can be used in satellites to keep the solar panels aligned with the sun, or in search and rescue robots that try to guide trapped people towards light. In order to implement the solar seeker we used two Cadmium Sulphide (CdS) photocells and a servo motor that rotated the photocells. The circuit diagram for its implementation is given as;
9) WEBSITES http://www.circuit-projects.com/ http://en.wikipedia.org/wiki/H_bridge http://en.wikipedia.org/wiki/Motor_controller http://www.4qdtec.com/pwm-01.html http://www.4qdtec.com/bridge.html http://www.modularcircuits.com/h-bridge_secrets1.htm http://www.tycoelectronics.com/aboutus/news/prodnews.asp?id=935 http://www.dprg.org/index.html http://www.mcmanis.com/chuck/robotics/projects/servo.html