Week-7 Challenge: DC Motor Control

 EV BATCH:17

 Aim:

To develop the model by using the matlab and describe the BLDC motor.

 objective:2Develop a 2-quadrant chopper using simulink & explain the working of the same with the relevant results. (Refer to article - Multiquadrant operation of motor )

expanation:

• By refered with an article the 2nd quadrant chopper can be developed by using the simulink.
• In this type of chopper,the average voltage will bealways positive but the average load current might be positive or negative
• The two switches of CH1 and CH2 should not be turned on simultaneously  as the combined action may cause a short circuit in supply lines.
• for regenerative braking and motoring these type of chopper configuration is used.
• we will always get a positive output voltage V0 as the freewheeling diode FD is present across the load.
• when the chopper CH1 is on the current flows from source to load. the inductor stores energy.when CH1 turn off The I0 will be reversed.the current I0 will be flowing towards the source.the load current will be negative when the CH2 is on.The current completes its path through the diode D2.
• we have develop a model by using the below figure 2 as a referance 

----figure (1)

-----figure (2)

model:

• the below model will represent the 2nd quadrant chopper.

• here we used the MOSFET transister.
• Metal Oxide Silicon Field Effect Transistors commonly known as MOSFETs are electronic devices used to switch or amplify voltages in circuits.
• It is a current controlled device and is constructed by three terminals. The terminals of MOSFET are named as follows:
• Source
• Gate
• Drain
• Body

• The dc voltage source which having this voltage source provides the constant voltage at the output is called a dc source.
• In this source, the electrons move in the same direction, so its polarity will not vary.
• The output voltage of this source will remain the same, it will not vary with the time.
• there are two voltage source used the first one with a voltage of 24v.

• the second voltage source with the 12v.

• The pulse generator which is used to  specify a fixed-step solver for models that contain time-based pulse generators.
• However, in this case, Simulink computes a fixed sample time for the time-based pulse generators.
• It then simulates the time-based pulse generators as sample-based.

plots:

• The below plot is represent the current measurement and as well as the voltage measurement in the scope.
• the current folws is starts with a square wave is a non-sinusoidal periodic waveform in which the amplitude alternates at a steady frequency between fixed minimum and maximum values, with the same duration at minimum and maximum.
• In an ideal square wave, the transitions between minimum and maximum are instantaneous.

 objective 3:Explain in a brief about operation of BLDC motor.

BLDC motor:

• A brushless DC motor (known as BLDC) is a permanent magnet synchronous electric motor which is driven by direct current (DC) electricity.
• In simple words, a BLDC has no brushes and commutator for having unidirectional torque rather integrated inverter / switching circuit is used to achieve unidirectional torque.
• That is why these motors are, sometimes, also referred as Electronically Commutated Motors.
• BLDC motors are also referred as trapezoidal permanent magnet motors.
• In this motor, permanent magnet (or field poles) rotates and current carrying conductors are fixed.
•  Hall sensors or rotary encoders are most commonly used to sense the position of the rotor and are positioned around the stator.
• The rotor position feedback from the sensor helps to determine when to switch the armature current.
• The efficiency of BLDC motors is typically 85 to 90 percent, whereas as brushed type DC motors are 75 to 80 percent efficient.
• There are wide varieties of BLDC motors available ranging from small power range to fractional horsepower, integral horsepower and large power ranges.

CONSTRUCTION OF BLDC MOTOR:

• Like any other electric motor, a BLDC motor also has a stator and a rotor.
• Here we will consider Stator and Rotor each separately from construction point of view.

BLDC Stator:

• Depending on the stator windings, these can be configured as single-phase, two-phase, or three-phase motors. However, three-phase BLDC motors with permanent magnet rotor are most commonly used.
• The construction of this motor has many similarities of three phase induction motor as well as conventional DC motor. This motor has stator and rotor parts as like all other motors.

• Stator of a BLDC motor made up of stacked steel laminations to carry the windings.
• These windings are placed in slots which are axially cut along the inner periphery of the stator.
• These windings can be arranged in either STAR or DELTA. However, most BLDC motors have three phase star connected stator.
• Each winding is constructed with numerous interconnected coils, where one or more coils are placed in each slot. In order to form an even number of poles, each of these windings is distributed over the stator periphery.

• The stator must be chosen with the correct rating of the voltage depending on the power supply capability.

Rotor

• BLDC motor incorporates a permanent magnet in the rotor.
• The number of poles in the rotor can vary from 2 to 8 pole pairs with alternate south and north poles depending on the application requirement.
• In order to achieve maximum torque in the motor, the flux density of the material should be high.
• A proper magnetic material for the rotor is needed to produce required magnetic field density.

• FERRITE magnets are inexpensive, however they have a low flux density for a given volume.
• Rare earth alloy magnets are commonly used for new designs. Some of these alloys are Samarium Cobalt (SmCo), Neodymium (Nd), and Ferrite and Boron (NdFeB).
• The rotor can be constructed with different core configurations such as the circular core with permanent magnet on the periphery, circular core with rectangular magnets, etc.

Hall Sensors

• Hall sensor provides the information to synchronize stator armature excitation with rotor position.
• Since the commutation of BLDC motor is controlled electronically, the stator windings should be energized in sequence in order to rotate the motor.
• Before energizing a particular stator winding, acknowledgment of rotor position is necessary. So the Hall Effect sensor embedded in stator senses the rotor position.
• Most BLDC motors incorporate three Hall sensors which are embedded into the stator.
• Each sensor generates Low and High signals whenever the rotor poles pass near to it.
• The exact commutation sequence to the stator winding can be determined based on the combination of these three sensor’s response.

Working Principle and Operation of BLDC Motor

• BLDC motor works on the principle similar to that of a conventional DC motor, i.e., the Lorentz force law which states that whenever a current carrying conductor placed in a magnetic field it experiences a force.
• As a consequence of reaction force, the magnet will experience an equal and opposite force.
• In case BLDC motor, the current carrying conductor is stationary while the permanent magnet moves.

• When the stator coils are electrically switched by a supply source, it becomes electromagnet and starts producing the uniform field in the air gap.
• Though the source of supply is DC, switching makes to generate an AC voltage waveform with trapezoidal shape.
• Due to the force of interaction between electromagnet stator and permanent magnet rotor, the rotor continues to rotate.
• Consider the figure below in which motor stator is excited based on different switching states.
• With the switching of windings as High and Low signals, corresponding winding energized as North and South poles.
• The permanent magnet rotor with North and South poles align with stator poles causing motor to rotate.
• Observe that motor produces torque because of the development of attraction forces (when North-South or South-North alignment) and repulsion forces (when North-North or South-South alignment).
• By this way motor moves in a clockwise direction.

• The motor continuous rotation depends on the switching sequence around the coils. As discussed above that Hall sensors give shaft position feedback to the electronic controller unit.
• Based on this signal from sensor, the controller decides particular coils to energize.
• Hall-effect sensors generate Low and High level signals whenever rotor poles pass near to it. These signals determine the position of the shaft.

ANIMATION OF BLDC:

conclusion :

• The two quadrant chopper will be developed successfully by using the matlab simulink.
• The BLDC motor can be described succesfully.