Week-7 Challenge: DC Motor Control

1.

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 BIT device.
The IGBT block does not simulate the gate current controlling the BIT or IGBT. The switch is controlled by a Simulink signal (1/0). 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 O to 240 V when the duty cycle (specified in the Pulse Generator block) is varied from O to 100%.
The H-bridge consists of four BJT/Diode pairs (B]T 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.

Case 1:
'Speed control of a DC motor using BJT H-bridge' - 5HP 240V 1750RPM
Field Voltage = 300
Torque TL Mechanical input

Case 2:
'Speed control of a DC motor using BJT H-bridge' - 5HP 240V 1750RPM
Field Voltage = 150
Torque TL Mechanical input

2.

The Four-Quadrant Chopper DC Drive (DC7) block
The Four-Quadrant Chopper DC Drive (DC7) block represents a four-quadrant, DC-supplied, chopper drive for DC motors. This drive features
closed-loop speed control with the four-quadrant operation.
The main advantage of this drive, compared with other DC drives, is that it can operate in all four quadrants (forward motoring, reverse
regeneration, reverse motoring, and forward regeneration). In addition, due to the use of high switching frequency DC-DC converters, a lower
armature current ripple (compared with thyristor-based DC drives) is obtained. However, four switching devices are required, which increases
the complexity of the drive system.
The Four-Quadrant Chopper DC Drive block uses these blocks from the Electric Drives
• Speed Controller (DC)
• Regulation Switch
• Current Controller (DC)
• Chopper

H-bridge model -
The H-Bridge block represents an H-bridge motor driver. The block has the following two Simulation mode options:
PWM - The H-Bridge block output is a controlled voltage that depends on the input signal at the PWM port. If the input signal has a value
greater than the Enable threshold voltage parameter value, the H-Bridge block output is on and has a value equal to the value of the Output
voltage amplitude parameter. If it has a value less than the Enable threshold voltage parameter value, the block maintains the load circuit using
one of the following three Freewheeling mode options:
• One semiconductor switch and one freewheeling diode
• Two freewheeling diodes
• Two semiconductor switches and one freewheeling diode
Averaged - This mode has two Load current characteristics options:
• Smoothed
• Unsmoothed or discontinuous

3. A Brushless DC Electric Motor (BLDC) is an electric motor powered by a direct current voltage supply and commutated electronically instead of by brushes like in conventional DC motors. BLDC motors are more popular than the conventional DC motors nowadays, but the development of these type of motors has only been possible since the 1960s when semiconductor electronics were developed.