Week-7 Challenge: DC Motor Control

1

a)I cant get the actual demo model, but model is shown in mathworks website. Here for H bridge four IGBT’s along with anti parallel diodes is used. Gate signals for each of the IGBT is generated by using required armature voltage as input.There are four anti parallel diodes connected across IGBT’s.The DC motor used is saperately excited of which speed and torque can be measured.

Current flowing through IGBT’s and diodes can be seen in scope. Motor Speed armature current are seen in scope. An artificial load torque requirement is generated by actual speed and gain block and this load torque is given as input to motor block, the motor is operated in vector control with sensor. Four quadrant operation can be obtained using this model

b)The armature current is because as it is a vector control, the current varies with respect

c)The model using DC7 block is also more or less same as regular H Bridge but it used PWM signal to generate gate pulses for H Bridge.

2.

The two quadrant operation of DC motor is realised using IGBT and diodes. Two quadrant operation means forward motoring and forward breaking. In this operation direction of current is reversed during breaking but voltage polarity remains same.

During motoring operation IGBT 1 conducts and motor is in forward motorning mode. When power supply is turned off freewheeling diode conducts the stored energy in motor. Motor electrical breaking can be applied by turning ON IGBT 2 or generated power can be fed back to source through Diode 1 called regenerative breaking.

When in regeneration mode direction of current is reversed and it can be seen in scope. Model and Screen shot attached

3

BLDC stands for brushless direct current motor. A BLDC motor uses a permanent magnet a rotor. In a normal DC motor armature winding and fielding windings are present. Field winding creates permanent magnetic field. When a current carrying conductor is placed inside a magnetic field a force is exerted on it (based on the direction of current with respect to magnetic field). Because of this force motion of the shaft is observed. But as the shaft rotates the current direction in carrying conductor remains same at new position with respect to magnetic field, no force is exerted on rotor. For continuous motion of rotor a commutator segment is used. A commutator segment changes the direction of current in armature coils such that the rotor current carrying conductors are aligned with field properly to get max torque.

In case of BLDC motor as permanent magnet is present no commutator is required in rotor. If stator when exited by DC power generates constant flux, both rotor and stator produces constant flux, there is no net resultant torque exerted on the rotor. This is why BLDC motor is not a self-starting motor and it is useless without its drive. The stator winding of DC motor is fed supply through an inverter drive. This drive produces a time varying voltages which in turn produces a time varying flux. The rotor permanent magnet tries to align with the varying field, hence shaft motion is observed. The job of mechanical commutator is replaced by inverter and hence the name electrically commutated motor. The operation to some extent matches with ac induction motor as stator is producing a rotating magnetic flux.