Week-7 Challenge: DC Motor Control

STUDY-1 :

1. Run MATLAB demo ‘Speed control of a DC motor using BJT H-bridge’. Modify the model such that armature current doesn’t shoot up when motor changes direction from forward to reverse.

In simulink, open " Speed Control of a DC motor BJT H-bridge model " by using the help section.

The Bipolar Junction Transistor (BJT) when used for power switching applications, operates as an IGBT.

The armature mean voltage block parameter is 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 .
• Two transistors are switched simultaneously: Q1 & Q4 or Q2 & Q3.
• On the time of Q1 and Q4 are switched off, a positive voltage is applied to the motor and diodes D2-D3 operates.
• 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 operates on the time of Q2 and Q3 are switched off.

working principle of speed control of DC motor using BJT H-Bridge mode :

The motor starts rotaing in the positive direction with the duty cycle of 75%(dc voltage at 180V). When t=0.5 sec then the armature voltage is gradually starts reversing and then the motor runs in negative direction.

current represents current flowing in this bipolar jumction Transisitor Q3 and the respective didode D3. Adding the diode in forward direction for the transistors, to give a path for the current.

Before the phase width in 75% the reults of the IGBT current and the diode current shows in below dialoge box

while the phase width in the 75% the shoot up is maximum in that case.

while changing the phase width from 75% to 45%, the varriation results accoured like in the below dialoge box shown here:

Results :

Pulse-Width Modulation (PWM) is the method that reducing the average power delivered by an electrical signal, here by deducing the effictive chopping it up into discrete parts. PWM works well with digital controls,which because of their on/off characteristics, can easily set the required duty cycle.

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

H-Bridge model using BJT :

(1). H-Bridge model consists of four IGBT diode pairs.

(2). here maximum voltage achieved is 300V to 350V.

(3). Torque and the output power bandwidth are narrower as it is restricted to use single pulse generator.

(4). The range of armature current has lesser values comparitvely since only two pairs of IGBT and diode models are functioning at a time.

Four Quadrant Chopper DC Drive (DC7) block :

(1). due to presence of DC-AC converters, DC7 block model has the previlage to vary the magnitude of voltage to the desired level.

(2).the maximum level of voltage can be achieved is 400V which on phase reversal becomes 200V.

(3). it has broader range of torque and output power compared to the former.

(4). the use of four Quadrant Chopper DC Drive block gives the armature curent more degrees of freedom.

3. Make a suitable EV model using DC7 block and make result report.

Making of suitable EV model setup using DC7 block with the help of matlab help document section,

the new EV modeled block is below,

EV model of DC7 Block :

In this DC7 block the speed reference block is replaced as the slider gain block to achieve like a drive cycle which wil statisfy the requirement of the EV model input.

and mainly the load torque is replaced by the load torque function of Tm = 24.7+0.0051w^2 is used as a load input here.

here the EV model is battery pack is AC source as shown in the above figure.

RESULT :

the achieved parameters fullfill the requirements of the EV model.