Challenge

Week-7 Challenge: DC Motor Control

When used for power-switching applications, the Bipolar Junction Transistor (BJT) operates as an IGBT.
When it is conducting (BJT operating in the saturated region), a forward voltage Vf is developed between the 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. A pulse generator controls the switch. The DC motor uses the preset model (5 HP 24V 1750 rpm).
It simulates a fan-type load (where load torque is proportional to the square of speed).
The armature means voltage can be varied from 0 to 240 V when the duty cycle 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 & Q4 or Q2 & Q3.
When Q1 & Q4 are fired, a positive voltage is applied to the motor and diodes D2-D3 operate as free-wheeling diodes when Q1 & Q4 are switched off.
When Q2 & Q3 are fired, a negative voltage is applied to the motor and diodes D1-D4 operate as free-wheeling diodes when Q2 & Q3 are switched off.

At 75% duty cycle, we can see that the current plot has initially a very high value and then becomes steady; it shows the same path in the negative direction.

At 55% duty cycle, we can see that the current shoot-up decreases and then becomes steady. In the negative direction, it has initially a high value and then it becomes steady.

Comparison between Four-Quadrant Chopper DC Drive and H-bridge

Four-Quadrant Chopper DC Drive	H-bridge
To change the motor direction, the polarity has to be changed.	To change the motor direction, the current signal has to be interrupted.
It can operate in all 4 modes: Forward motoring, forward braking, reverse motoring and reverse braking.	It can operate in two modes: Forward and Reverse.
It has broader torque and power output ranges.	It uses a single pulse generator which gives little torque and power output range.
It can be achieved up to 400 V.	It can be achieved up to 350 V.
In this, the current has chopped values.	In this, the current has continuous values.
Regenerative braking is possible.	Regenerative braking is not possible.
Two PI regulator (speed regulator and current regulator) is used to obtain the electromagnetic torque needed to reach the desired speed & control the armature current and stabilize the system.	PI regulator is not used.
Four-quadrant chopper is an electronic switch that is used to interrupt one signal under the control of another.	H-bridge is an electronic circuit that switches the polarity of the voltage applied to the load.
It is used to refer to numerous types of electronic switching devices and circuits used in power control and signal applications.	It is often used in Robotics and other applications to allow DC motors to run forward and backwards.

Two-quadrant chopper operation occurs in 2 modes: motoring and braking modes.
The chopper permits a change in the polarity of terminal voltage keeping the direction of the current constant.

In the figure, S1 & S2 are the choppers working as electronic switches and D1 & D2 are the feedback diodes.
Assuming continuous conduction, both S1 & S2 operate simultaneously.
When they are ON the load current Id increases, with the rate of rising depending upon the back emf and torque of the machine.
When they are OFF, the load current is fed to the supply through diodes D1 & D2. The current decreases in this stage.
From the figure, it is clear that the load voltage is effectively negative when the diodes conduct.
The average value of the output voltage of the chopper
Vda is zero for a = 0.5, the output voltage is an ac waveform with an average voltage equal to zero.
For a > 0.5, the average value of the dc voltage is negative. The chopper works in the regeneration mode.
The power flows from the load to the supply and the dc machine operates as a generator.
For the control ratio of 0.5, the operation is similar to the inversion of a line commutated converter (α > 90).
For a > 0.5, the chopper has the normal operation. The power flows from the supply to the load. This operation of the chopper is similar to the rectification of a line-commutated converter (α < 90).
For a = 0.5, the load voltage is zero.

Simulink model:

When used for power-switching applications, the Bipolar Junction Transistor (BJT) operates as an IGBT.
When it is conducting (BJT operating in the saturated region), a forward voltage Vf is developed between the collector and emitter (in the range of 1V). 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 PWM generator controls the switch. The DC motor uses the preset model (5HP 24V 1750rpm).
It simulates a fan-type load (where Load torque is proportional to the 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%.
This model consists of two BJTs/Diodes connected parallel to the DC motor. When Q1 is fired, a positive voltage is applied to the motor and diode D2 operates as a free-wheeling diode when Q1 is switched OFF.
When Q2 is fired, a negative voltage is applied to the motor and diode D1 operates as a free-wheeling diode when Q1 is switched OFF.
The motor starts in the positive direction with a duty cycle of 75% (mean DC voltage of 180 V). At t = 0.5 sec., the armature voltage is suddenly reversed and the motor runs in the negative direction.

BLDC motor works on a principle of the Lorentz force which states that whenever a current-carrying conductor is 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 the BLDC motor, the current-carrying conductor is stationary and the permanent magnet is moving.
When the stator coils get a supply from the source, it becomes an 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 a trapezoidal shape.
Due to the force of interaction between the electromagnet stator and permanent magnet rotor, the rotor continues to rotate.
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 aligns with the stator poles which causes the motor to rotate.

Ship work like this
in your own course.