Week-7 Challenge: DC Motor Control

Objective 1:- 

(A) Explain a MATLAB demo model named ‘Speed control of a DC motor using BJT H-bridge’.

Introduction:- 

A DC motor controller has many forms.Here we are learning an h-bridge motor driver circuit.

So what? It is easy to do with a transistor or MOSFET drivers. And they are high performance, too.

Firstly we are understanding the general operation of BJT H-bridge DC motor speed controller.

* In-circuit, we see that all switches are the open states. No the current flowing in the circuit, cause the DC motor can’t work.

*Forwarding mode:-When having the S1-switch (closed) and S3 (closed). 

It causes the motor to get the current. As we notice that the current flowing into the positive terminal of the motor.

Making the DC motor rotated in features of forwarding form. Or Rotate clockwise.

*Reversed  mode:-

And, If both S4 and S2 are closed together. The Motor also get current that flow through them. But it will don’t the same first form. Because that current will flow through the negative of motor cause current reversed or Rotated back counter-clockwise direction. 

We will try to use all the transistors as the switch. When a base of transistors gets the current electricity. It causes the transistor running and the DC motor will rotate, too.

The Diodes D1, D2, D3 & D4 are called catch diodes and schottky diodes. The top end of the bridge is connceted to power suply which is a battery source and botton end is grounded.

Model Discription:- 

1)- The basic operation of the model is similar to switch operation which i have explained above. Firstly Q1 & Q3 will energize then current will flow through Q1 to motor to Q4, so motor will energize and it will rotate in forward direction. Same as When Q2 & Q3 will energize the motor will rotate in backword direction.

2)- The important factor is when Q1 & Q2 or Q3 & Q4 will be close at the same time so we have just created a very low resistance path for power supply and ground effectively short circuiting your power supply. This condition is called shoot through and quickly destroy the bridge when this will occur. 

3)- The BJT when used for power switching application, 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 1V). Therefore the iGBT block can be used to model the BJT device.

4)- DC motor used 5HP, 24V, 1750RPM. It simulated a fan type load (Where load torque is proptional to square of the speed). The armature mean voltage can be varied from 0-240V when the duty cycle varied from 0 to 100%.

5)- During operation of Q1 & Q4 after switching of diode D2 & D3 work as a freewheeling diode. sme as during operation of Q2 & Q3 after switching of diode D1 & D4 work as a freewheeling diode. 

Thus from the above graph we can say that for 0- 0.5 sec the current floes through diode D3 and from 0.5-1sec the current floes through Q3.

The motor starts in the positive direction with a duty cycle of 75%(means DC voltage is 180V) at t=0.5 sec, the armature voltage is suddenly reversed and the motor runs in the negative direction. 

 The waveform for speed, armature current and load torque is shown in the above graph. from armature current graph, we can see that at starting there is sudden spike increases in current at 0 sec also at 0.5 sec. We can see that as the voltage gets changed in the circuit the speed of the motor also changed. 

In the transition of positive to negative direction of rotation was observe a high surge in current, this is due to the transient switching occuring in the circuit. as there is already cuurent flowing in the circuit & on changing of the switches after 0.5sec, the current in the circuit adds to the changed direction of current and we observe a surge.  

(C) Refer to the help section of ‘The Four-Quadrant Chopper DC Drive (DC7) block’. Compare it with the H-bridge model.

Introduction:-
A four quadrant chopper is a chopper which can operated in all the four quadrants. The power can flow either from source to load or load to source in this chopper. In first quadrant, a Class-E chopper acts as a step-down chopper whereas in second quadrant it behaves as a step up chopper. This type of chopper is also known as Class-E or Type-E chopper. This article describes the working principle and operation of Class-E chopper with the help of circuit diagram.
Working Principle / Operation of Class-E Chopper:
The circuit of a four quadrant chopper or class-E chopper basically consists of four Semiconductor switches CH1 to CH4 and four diodes D1 to D4. The four diodes are connected in anti-parallel. The circuit diagram of this type of chopper is shown below.

In the above circuit diagram, the choppers are numbered CH1 to CH4. For first quadrant operation CH1 is made ON, for second quadrant operation CH2 is made ON and so on. To better understand the working of four quadrant chopper, we will discuss its operation separately for each quadrant.
First Quadrant Operation:
For first quadrant operation, CH4 is kept ON, CH3 is kept OFF and CH1 is operated. When both CH1 & CH4 are ON simultaneously, the load gets directly connected to the source and hence the output voltage becomes equal to the source voltage. This essentially means that vo = vs. It may be noted that the load current flows from source to load as shown by the direction of io.
When CH1 is switched OFF, the load current free wheels through CH4 and D2. During this period, the load voltage and current remains positive.
Thus, both the output voltage vs and load current io are positive and hence, the operation of chopper is in first quadrant. It may be noted that, Class-E chopper operates as a step-down chopper in this case.
Second Quadrant Operation:
To obtain second quadrant operation, CH2 is operated while keeping the CH1, CH3 & CH4 OFF. When CH2 is ON, the DC source in the load drives current through CH2, D4, E and L. Inductor L stores energy during the On period of CH2.
When CH2 is turned OFF, current is fed back to the source through D1, D4. It should be noted at this point that (E+Ldi/dt) is more than the source voltage Vs. As load voltage Vo is positive and Io is negative, it is second quadrant operation of chopper. Since, the current is fed back to the source, this simply means that load is transferring power to the source. Kindly read step-up chopper for detailed analysis and better understanding.
For second quadrant operation, load must contain emf E as shown in the circuit diagram. In second quadrant, configuration operates as a step-up chopper.
Third Quadrant Operation:
To obtain third quadrant operation, both the load voltage and load current should be negative. The current and voltage are assumed positive if their direction matches with what shown in the circuit diagram. If the direction is opposite to what shown in the circuit diagram, it is considered negative. One important thing to notice is that the polarity of emf E in load must be reversed to have third quadrant operation. Circuit diagram of Class-E chopper for third quadrant operation is shown below.
For third quadrant operation, CH1 is kept off, CH2 is kept ON and CH3 is operated. When CH3 is ON, load gets connected to source and hence load voltage is equal to source voltage. But carefully observe that the polarity of load voltage vo is opposite to what shown in the circuit diagram. Hence, vo is assumed negative. Let us now see what is the status of load current io. It may be seen that io is flowing in the direction opposite to shown in the circuit diagram and hence negative.
Now, when CH3 is turned OFF, the negative load current free wheels through the CH2 and D4. In this manner, vo and io both are negative. Hence, the chopper operates in third quadrant.
Fourth Quadrant Operation:
To obtain fourth quadrant operation, CH4 is operated while keeping CH1, CH2 and CH3 OFF. The polarity of load emf E needs to be reversed in this case too like third quadrant operation.
When CH4 is turned ON, positive current flows through CH4, D2, L and E. inductance L stores energy during the time CH4 is ON. When CH4 is made OFF, current is fed back to the source through diodes D2, D3. Here load voltage is negative but the load current is always positive. This leads to chopper operation in fourth quadrant. Here, power is fed back to the source from load and chopper acts as a step-up chopper.
The operation of a four quadrant chopper or Class-E chopper is summarized in the figure below.

Comparison of 4 quadrant chopper and BJT H bridge:-

1)- The 4 quadrant chopper works in all four modes like
* Forward motoring
* Forward breaking
* Reverse motoring
* Reverse breaking

But the BJT H bridge model works

* Forward motoring

* Reverse motoring 

2)- To chnage the direction of rotation of motor from forward to reverse and vice cersa, the current signals get transited from one to other switch while in h bridge model, the direction of motor is chnaged by changing the polarity of current.

3)- The 4 quadrant chopper have high switching frequency while h bridge model have low switching frequency.

4)- The armature current in 4 quadrant chopper have a littile spike at transition from one to other switch because of high switching frequency while h bridge model have high spike of current.

5)- The 4 quadrant choper is generally used in industrial application while h bridge model is used in robotics.

Objective 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 )

Result:- Two quadrant chopper is also called Type C chopper.Type C chopper is obtained by connecting Type A and type B chopper is parallel. We will always get a positive output voltage Vo at the freewheeling diode FD is present across the load. When the chopper is on the Frewhheling diode starts conducting and the output voltage Vo will be equal to Vs.The direction of the load current Io will be reversed. The current Io will be flowing towards the source and it will be positive regardlesss the chopper is on or the FD conducts. The load current will be negative if the chopper oi off and the diode D2 conducts. We can say the chopper and FD operate together as type A chopper in first quadrant. In the second quadrant the chopper and D2 will operate together as type B chopper.

The average voltage will be always positive but the average load current migt be positive or negative. The power flow may be life the first quadrant operation i.e. from source to load or from load to source like the second quadrant operation.The two choppers should not be turned on simultaneously as the combined action may cause a short circuit in the supply lines. For regenerative braking and motoring these types of chopper configuration is used. 

Two quadrant model using simulink:-

Let us take two mosfet blocks and diodes blocks and connect it as shown in circuit diagram. 

The DC voltage source is connected as shown.

Let the DC voltage source is 24Volts.

Let us consider an series RLC branch block and select inductor L. Thus block works as a load.

To consider LE load as motor load and DC voltage source of 12V is also connected in series with inductor.

The pulse generator block is used to create gate pulse. The not gate is used in the model so that the two MOSFET will not get closed at the same time otherwise short circuit will occur due to use of not gate, when one MOSFET is on the first MOSFET will get off.

The amplitude of pulse generator is kept 10 so that we can clearly see the pulses at scope and let period be 0.02 seconds and let pulse width be 50%. 

 The voltage waveform is not going less than zero. The minimum value of voltage is zero and maximum value is always in the positve direction.

However in the current waveform the current increases and decreses. the current may be positive as well as negative and the pulse amplitude is 10 thus pulse waveform we can see that the pulse is 10.

Link:- https://drive.google.com/file/d/1Rx8vCjNLuNoewmY3FqD6-LL3oTuLPjVe/view?usp=sharing

Objective3:-  Explain in a brief about operation of BLDC motor.

Introduction:- 

Understanding the principle and application of high efficiency motors: 1 of 3.A motor converts supplied electrical energy into mechanical energy. Various types of motors are in common use. Among these, brushless DC motors (BLDC) feature high efficiency and excellent controllability, and are widely used in many applications. The BLDC motor has power-saving advantages relative to other motor types.

The simplest type of motor is the brushed DC motor. In this type of motor, electrical current is passed through coils that are arranged within a fixed magnetic field. The current generates magnetic fields in the coils; this causes the coil assembly to rotate, as each coil is pushed away from the like pole and pulled toward the unlike pole of the fixed field. To maintain rotation, it is necessary to continually reverse the current—so that coil polarities will continually flip, causing the coils to continue “chasing” the unlike fixed poles. Power to the coils is supplied through fixed conductive brushes that make contact with a rotating commutator; it is the rotation of the commutator that causes the reversal of the current through the coils. The commutator and brushes are the key components distinguishing the brushed DC motor from other motor types.

Fixed brushes supply electric energy to the rotating commutator. As the commutator rotates, it continually flips the direction of the current into the coils, reversing the coil polarities so that the coils maintain rightward rotation. The commutator rotates because it is attached to the rotor on which the coils are mounted.

Controlling:- 

hows the relationship between energized phases and flux. As you can see, switching sequentially through modes 1 through 6 will cause the rotor to turn clockwise through one rotation. The speed of rotation can be controlled by controlling the rate at which the phases change. We use the name “120-degree conducting control” to the 6-mode control method described here.

Advantages:-

One big advantage is efficiency, as these motors can control continuously at maximum rotational force (torque). Brushed motors, in contrast, reach maximum torque at only certain points in the rotation. For a brushed motor to deliver the same torque as a brushless model, it would need to use larger magnets. This is why even small BLDC motors can deliver considerable power.

The second big advantage—related to the first—is controllability. BLDC motors can be controlled, using feedback mechanisms, to delivery precisely the desired torque and rotation speed. Precision control in turn reduces energy consumption and heat generation, and—in cases where motors are battery powered—lengthens the battery life.

BLDC motors also offer high durability and low electric noise generation, thanks to the lack of brushes.

Applications:-washing machines, air conditioners, and other consumer electronics, spin hard disc drives, drive vacuum machines and more recently, they are appearing in fans, where their high efficiency has contributed to a significant reduction in power consumption.

Future:- 

1)- We can expect to see BLDC motors used in a wider range of applications in the future. For example, they will probably be widely used to drive service robots—small robots that deliver services in fields other than manufacturing.

2)- But BLDC motors are better suited to controlling the force. And with a stepper motor, holding the position of a structure such as a robot arm would require a relatively large and continuous current. With a BLDC motor, all that would be required is a current proportionate to the external force