Week-7 Challenge: DC Motor Control
1) A) Explain a MATLAB demo model named 'Speed control of a DC motor using BJT H-bridge'.
Aim ) The Main aim is to explain speed control of dc motor by using BJT H-bridge in MAtlab
H-Bridge:-
The H-bridge is a rather simple circuit,containing four switching element,with the load at the center, in an H-like configuration.
A H-bridge is essentially four switches that allow the polarity of the supply applied to a motor to be attached both ways round . Thus, the motor can be driven both clockwise or counter clockwise.
It consists of a pair of high- and low-side switches with the motor connected between the two pairs.
The engagement of the switches has to be carefully implemented as enabling a high- and low-side pair results in a short-circuit of the power source, something that rarely ends well.
Therefore, the designer has to ensure That only a diagonally opposed pair of high-/low-side switches can be engaged at any moment in time.
Simple Image of H-bridge:-
The basic operation of the H-bridge circuit diagram are given below:-
Thus the H-brige is driven both clockwise(Forward ) or counter-clockwise(Reverse).
Forward operation :-
Fig-Forward Operation
In this operation The the swithcing flow is (Q1-D1-M-D4-Q4), That means the Q1 switch is high polarity and Q4 switch becoms Low polarty then the Bridge circuit acts as forward direction.
Reverse Operatio:-
Fig-Reverse Operation
In this operation The the swithcing flow is (Q3-D3-M-D2-Q2), That means the Q3 switch is high polarity and Q2 switch becoms Low polarty,then the Bridge circuit acts as Reverse direction.
MATLAB demo model named ‘Speed control of a DC motor using BJT H-bridge:-
This model can be get by type the Command "power_Hbridge" In MATLAB command window.
Then the new Simulink window opende with MODEL OF BJT H-bride of Dc moter as followes:-
Simulink model:-
Explanation :-(Major Blocks)
BJT H-Bridge:-
Fig--> BJT H-Bridge
Here the H-Bridge is designed by using the BJT Semicundector switches with following parameters:-
The Bipolar Junction Transistor (BJT) when used for power switching applications, operates as an IGBT. When it is conducting (BJT operating in the saturated region), a forward voltage Vf is developed between collector and emitter (in the range of 1 V). Therefore, the IGBT block can be used to model the BJT device.
The IGBT block does not simulate the gate current controlling the BJT or IGBT. The switch is controlled by a Simulink signal (1/0).
DC Motor used in the simulink model:-
The DC motor uses the preset model (5 HP 24V 1750 rpm). It simulates a fan type load (where Load torque is proportional to square of speed). The armature mean voltage can be varied from 0 to 240 V when the duty cycle (specified in the Pulse Generator block) is varied from 0 to 100%.
The H-bridge consists of four BJT/Diode pairs (BJT simulated by IGBT models). Two transistors are switched simultaneously: Q1 and Q4 or Q2 and Q3. When Q1 and Q4 are fired, a positive voltage is applied to the motor and diodes D2-D3 operate as free-wheeling diodes when Q1 and Q4 are switched off. When Q2 and Q3 are fired, a negative voltage is applied to the motor and diodes D1-D4 operate as free-wheeling diodes when Q2 and Q3 are switched off.
DC moter Block Parameter:-
Fig-->Configaration DC Moter Fig->Parameters Of Dc Moter
Pulse width Modulation(PWM):-
Parameter Block :-
Fig-> Parameter Block(PWM)
Pulse Width Modulation(PWM) is a modulation technique that generates variable-width pulses to represent the amplitude of an analog input signal.The length of time that a pulse is in a given state (High/Low) is the "width" of a pulse wave. Here the term comes the duty cycle which represents in percentage values.
The Pulse gnerator given by a pulse width of 75% and period of 2e-3 seconds.The motor parameters of the torque and field voltage and armature voltages are taken as default values of the model.
Results scope Plot :-
BJT and Diode Currents Plots :-
Scope->BJT & Diode Currents
>>From the above scope the top scope is regarding BJT currents and bottem scope is for Diode Currents.
>> We can observe that the During the 1 sec period of cycle upto 0.5 sec the BJT gets no current output while Diode consiste of 38 Amps nearly
>> after 0.5sec The diode showes 0Amps Currents but the BJt is acivated and peak current vakue at 0.52 sec is nearly 65 amps.
Moter side plots :-
Scope -> Plots For Moter Charactaristics
>> From The Above Graph
Top Plot for--> angular Speed of Moter (W)-in Rpm
From this Graph we can observe that the Dc moter gets accelartion from 0 Rpm to 1000 Rpm with in 0.5 sec and , deseleration start from 0.5 , At 0.6 sec the Rpm starts its negetavi direction (Regenation time ) and the moterSpeed becoms -1000 RPm. upto 1sec time.
Middle Plot for--> Armature Current (Ia)-Amp
>>From this Graph we can observe that the Dc moter Armature current (Ia) is raises 0 to nearly 40 amps with interval of 0sec to 0.1 sec
>>After 0.1 sec -0.5 sec the Armature currents becoms very very loe this can be seeen in above graph.
>>From 0.5 sec to 0.6 sec The armature gets the -ve Current of vakue -40 amps nearly
>> After 0.6 sec to 1 sec we can observe the armature current as nearly very tiny value (-ve).
Bootem Plot ->Load torque (Nm)
>>The load torque follows the speed waveform in the positive direction.when the negative direction it follows the armature current current and the speed waveform.
Conclusion :- FromUsing the BJT H-Bridge controller the speed of DC moter will be controlled
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1) (B) Comment on the armature current shoot-up from the scope results.
Aim) The mainnn is by using BJT H-bride explain the armature current shoot-up from the scope results.
Armature Current(Ia):-The Output of Armature current will be basically depend on the input signal %duty cycle
The Armature current Shoot up can be Observed by following 2 type % of Duty cycle cases :-
Case 1) The basic model of BJT H-Bridge uses the inpu signal as PWM tehcinique with 75% of duty cycle
Pulse width Modulation(PWM):-
Parameter Block :-
Fig-> Parameter Block(PWM)
Then the Output results as followes :-
Scope -> Plots For Moter Charactaristics
Middle Plot for--> Armature Current (Ia)-Amp
>>From this Graph we can observe that the Dc moter Armature current (Ia) is raises 0 to nearly 40 amps with interval of 0sec to 0.1 sec
>>After 0.1 sec -0.5 sec the Armature currents becoms very very loe this can be seeen in above graph.
>>From 0.5 sec to 0.6 sec The armature gets the -ve Current of vakue -40 amps nearly
>> After 0.6 sec to 1 sec we can observe the armature current as nearly very tiny value (-ve).
>>From the above the armature current shoot-up at the starting of the armature current a sudden rise in the waveform we had noticed .
>>To reduce the sudden rise in the armature current we will the reduce the duty cycle of the pulse width modulation
Case 2) The model of BJT H-Bridge uses the inpu signal as PWM tehcinique with 50% of duty cycle
Then the Output results as followes :-
Scope -> Plots For Moter Charactaristics
Middle Plot for--> Armature Current (Ia)-Amp
>>The difference between two case (1) and case (2) graphs, The armature current in Case(2) graph having a no sudden rise at the starting of the armature current.
>>If we further reduced the pulse width modulation the negative of the rise will get reduced.
Conclusion :- With increse the Duty cycle % we can get the Sudden Rise in Armater current in fraction of sec
This sudden rise of armature current will be redused by reducing the duty cycle %
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1)(C)Refer to the help section of ‘The Four-Quadrant Chopper DC Drive (DC7) block’. Compare it with the H-bridge model.
Aim) The main is camparision between "The Four-Quadrant Chopper DC Drive (DC7) block" and "H-bridge model".
Chopper :-A dc‐to‐dc converter, also known as dc chopper, is a static device which is used to obtain a variable dc voltage from a constant dc voltage source.
Choppers are widely used in trolley cars, battery-operated vehicles, traction motor control, control of large numbers of dc motors, etc. They are also used as dc voltage regulators.
Choppers are of two types:(Based on Output Voltage)
(1) Step‐down choppers
In this choppers, the output voltage will be less than the input voltage.
(2) Step‐up choppers.
In this step‐up choppers output voltage will be more than the input voltage.
According to their working(four quadrants) :-
We can classify chopper circuits as type A, type B, type C, type D and type E.
Type A:-(First quadrant chopper)->The output voltage and current both must be positive.
Type B:->The output of the voltage is positive and the current is negative.
Type C:- >The output voltage is positive and current can be either positive or negative
Type D:- > The output current is positive and the voltage can be either positive or negative
Type E:-(Four quadrant chopper) -> The both output voltage and current can be either positive or negative.
The Four-Quadrant Chopper DC Drive (DC7) block:-
This can obtained in MATLAB using command window "dc7_example" type this command
Then the new windoe will open in Simulink as followes :-
Explanantion :-
From thi simulink model the armature voltage is provided by an IGBT converter controlled by two regulators.
The converter is fed by a 515 V DC bus obtained by rectification of a 380 V AC 50 Hz voltage source. In order to limit the DC bus voltage during dynamic braking mode, a braking chopper has been added between the diode rectifier and the DC7 block.
The first regulator is a speed regulator, followed by a current regulator.
The speed regulator outputs the armature current reference used by the current controller in order to obtain the electromagnetic torque needed to reach the desired speed. The speed reference change rate follows acceleration and deceleration ramps in order to avoid sudden reference changes that could cause armature over-current and destabilize the system.
The current regulator controls the armature current by computing the appropriate duty ratios of the 5 kHz pulses of the four IGBT devices (Pulse Width Modulation).
For proper system behaviour, the instantaneous pulse values of IGBT devices 1 and 4 are opposite to those of IGBT devices 2 and 3. This generates the average armature voltage needed to obtain the desired armature current. In order to limit the amplitude of the current oscillations, a smoothing inductance is placed in series with the armature circuit.
H-Bridge model:-
The H-bridge is a rather simple circuit,containing four switching element,with the load at the center, in an H-like configuration.
A H-bridge is essentially four switches that allow the polarity of the supply applied to a motor to be attached both ways round . Thus, the motor can be driven both clockwise or counter clockwise.
It consists of a pair of high- and low-side switches with the motor connected between the two pairs.
The engagement of the switches has to be carefully implemented as enabling a high- and low-side pair results in a short-circuit of the power source, something that rarely ends well.
Therefore, the designer has to ensure That only a diagonally opposed pair of high-/low-side switches can be engaged at any moment in time.
Simple Image of H-bridge:-
The basic operation of the H-bridge circuit diagram are given below:-
Thus the H-brige is driven both clockwise(Forward ) or counter-clockwise(Reverse).
Forward operation :-
Fig-Forward Operation
In this operation The the swithcing flow is (Q1-D1-M-D4-Q4), That means the Q1 switch is high polarity and Q4 switch becoms Low polarty then the Bridge circuit acts as forward direction.
Reverse Operatio:-
Fig-Reverse Operation
In this operation The the swithcing flow is (Q3-D3-M-D2-Q2), That means the Q3 switch is high polarity and Q2 switch becoms Low polarty,then the Bridge circuit acts as Reverse direction.
Comparasion between "The Four-Quadrant Chopper DC Drive (DC7) block" and "H-bridge model":-
Comaprision Link :-
Link:->> Comparision.xlsx
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2. Develop a 2-quadrant chopper using simulink & explain the working of the same with the relevant results. (Refer to article - Multiquadrant operation of motor )
Aim) The main aim is Develop a 2-quadrant chopper using simulink
Chopper :-
A dc‐to‐dc converter, also known as dc chopper, is a static device which is used to obtain a variable dc voltage from a constant dc voltage source.
Choppers are widely used in trolley cars, battery-operated vehicles, traction motor control, control of large numbers of dc motors, etc. They are also used as dc voltage regulators
2-Quadrant Chopper :-
In this type of Chopper, the average voltage will be always positive but the average load current might be positive or negative. The two Switches 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 freewheeling diode starts conducting and the output voltage v0 will be equal to Vs. The direction of the load current 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 diode D2.
Basic Circuit image of 2-quadrant chopper:-
Simulink model:-
For creating the 2-quadrant chopper By usnig Simlink-Simscape blocks are as followes:
Pulse generator:- To generate pulse to input signal
dc voltge source:- To give the input signal to chopper
IGBt :- To creating the Switching sdevices
Diode :- To use for Unidirection output signal
Current measurement:- to measure the output Current
Voltage measure ment:- To measure the output voltage signal
Scope :- to plot the Output signals
Power gui:- Set simulation type, simulation parameters, and preferences.
Simulink model :-
procedure :-
>>first connect the parallale 2 leg for creating the switching operations
>>one leg is with IGBT block and 2nd leg with diode block(for sending the input signal to output in uni directiion only.
>> A Dc(12 volts ) supply is connected accros the IGBT Switching legs
>>After that a Pulse genaerator is used to generate gate pulses to IGbt
>> By using Not (logic) gate we sending the signal to Q2.
>>> while Q1 is in active mode then Q2 is rest mode this will obtained from using the NOt loghic gate.
>> at load side we connect the Induction motor load consisits inductance and resistance by using the Serie RLC branch.
Noe By using the Voltage measurement and current measurent Blocks we can get the output voltage and current.
>> the Output pulses along Current and Voltage will plotted by using the Scope.
Output Scopes:-
>>from above graph (Top plot for Q2 and Bottem Plot for Q2)
we can observed that the while Q1 is on then Q2 value is Zero position.
Current and Voltage plot:-
>> from above graph we can observe that the
>>Top plot is for current value Bottom plot is for voltge value
>> current plot We can see the starting current gets a spkie value 0.9 amps in between 0sec to 0.9 sec.
>> After that The currents getszeero position.
>>Voltage plot we can see the voltage Spike in terms of pulses in load side.
Conclusion :-2-quadrant chopper using simulink id developed and output scopes are explained .
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3. Explain in a brief about operation of BLDC motor?
Aim) The main is explaination regarding operation of BLDC motor.
BLDC moter:-
A BLDC Motor (known as brushless DC motor) is a permanent magnet synchronous electric motor which is driven by direct current (DC) electricity and it accomplishes electronically controlled commutation system instead of a mechanically commutation system. BLDC motors are also referred as trapezoidal permanent magnet motors.
Commutation is the process of producing rotational torque in the motor by changing phase currents through it at appropriate times.
BLDC motor employs electrical commutation with permanent magnet rotor and a stator with a sequence of coils. In this motor, permanent magnet (or field poles) rotates and current carrying conductors are fixed.
Fig-> BLDC motor image
Construction of BLDC Motor:-
BLDC motors can be constructed in different physical configurations. 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.
A commutator-brushes arrangement helps in achieving unidirectional torque in a typical dc-Motor Obviously, commutator and brush arrangement is eliminated in a brushless dc motor. Here, an integrated inverter/switching circuit is used to achieve unidirectional torque. That is why these motors are, sometimes, also referred as 'electronically commutated motors'.
Just like any other electric motor, a BLDC motor also consists of two main parts a stator and a rotor.
Permanent magnets are mounted on the rotor of a BLDC motor.
The stator is wound for a specific number of poles. Also, a control circuit is connected to the stator winding. Most of the times, the inverter/control circuit or controller is integrated into the stator assembly. This is the basic constructional difference between a brushless motor and a typical dc motor.
Stator Constriction:-
Fig -> Stator Part Of BLDC
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.
For robotics, automotive and small actuating applications, 48 V or less voltage BLDC motors are preferred. For industrial applications and automobile systems, 100 V or higher rating motors are used
Rotor Constriction:-
Fig-> Rotor Part
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.
Working principle:-
Stator windings of a BLDC motor are connected to a control circuit (an integrated switching circuit or inverter circuit). The control circuit energizes proper winding at the proper time, in a pattern which rotates around the stator.
Permanent magnets on the rotor try to align with the energized electromagnets of the stator, and as soon as it aligns, the next electromagnets are energized. Thus, the rotor keeps running.
The layout of a DC brushless motor can vary depending on whether it is in ''Out runner'' style or ''Inrunner” style''.
Out runner: –
The field magnet is a drum rotor which rotates around the stator. This style is preferred for applications that require high torque and where high rpm isn’t a requirement.
Fig->Outerrotor BLDC motor working animation
In runner :-
The stator is a fixed drum in which the field magnet rotates. This motor is known for producing less torque than the out runner style, but is capable of spinning at very high rpm.
Fig->Inner rotor BLDC motor working animation
Advantages:-
- Less overall maintenance due to absence of brushes
- Reduced size with far superior thermal characteristics
- Higher speed range and lower electric noise generation.
- It has no mechanical commutator and associated problems.
- High efficiency and high output power to size ratio due to the use of permanent magnet rotor
- High speed of operation even in loaded and unloaded conditions due to the absence of brushes that limits the speed.
- Smaller motor geometry and lighter in weight than both brushed type DC and induction AC motors.
Applications :-
Brushless DC motors (BLDC) use for a wide variety of application requirements such as varying loads, constant loads and positioning applications in the fields of industrial control, automotive, aviation, automation systems, health care equipments etc.
- Computer hard drives and DVD/CD players.
- Electric vehicles, hybrid vehicles, and electric bicycles.
- Industrial robots, CNC machine tools, and simple belt driven systems.
- Washing machines, compressors and dryers.
- Fans, pumps and blowers.
Conclusion:- The operation of BLDC motor is explained.
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Results :-
1)(A) MATLAB demo model named 'Speed control of a DC motor using BJT H-bridge is explained.
(B)Armature current shoot-up from the scope results are explained
(C)Comaprision Link :-
Link:->> Comparision.xlsx
2)Conclusion :-2-quadrant chopper using simulink id developed and output scopes are explained .
3) Conclusion:- The operation of BLDC motor is explained.
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