Week-7 Challenge: DC Motor Control
EV Live Batch 21.
1 Aim:
1. A. Explain a MATLAB demo model named ‘Speed control of a DC motor using BJT H-bridge’.
Ans:
Here we have to explain the speed control of a dc motor using bjt h bridge by different various plues generator.
The matlab demo model of speed control of a DC motor using BJT H- bridge . 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 IV). Therefore, the IGBT block can be used to model the BJT device .
Simulation Model:
=> The IGBT block does not simulate the gate current controlling the BUT 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 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%.
=> The H-bridge consists of four BJT/Diode pairs (BJT simulated by IGBT models) Two transistors are switched simultaneously: Q1 and Q4 or 02 and 03. When Ol and 04 are fired a positive voltage is applied to the motor and diodes D2 D3 operate as free-wheeling diodes when Q and Q4 are switched off. When Q2 and 03 are fired, a negative voltage is applied to the motor and diodes DI-D4 operate as free wheeling diodes when Q2 and 03 are switched off.
=> Initially, we run MATLAB demo Speed control of a DC motor using BJT H bridge with all it's default values and different pulse width(duty cycle) 70%, 50%, and 40%.
=> When we run the model with 1 sec, we get following three plot results.
Results Of Output of IGBT and DIODE Current:
=> When we run the model the output current diode of IGBT.
Output with DUTY CYCLE 70%:
=> The motor starts in a positive direction with a duty cycle of 70% (mean DC voltage of 180V). At t= 1.00 sec., the armature voltage is suddenly reversed and the motor runs in a negative direction.
=> 'Scope' shows motor speed, armature current, and load torque and 'Currents' shows currents flowing in BJT Q3 and diode D3.
Output with DUTY CYCLE 50%:
=> The motor starts in a positive direction with a duty cycle of 50% (mean DC voltage of 180V). At t= 1.00 sec., the armature voltage is suddenly reversed and the motor runs in a negative direction.
Output with DUTY CYCLE 40%:
=> The motor starts in a positive direction with a duty cycle of 40% (mean DC voltage of 180V). At t= 1.00 sec., the armature voltage is suddenly reversed and the motor runs in a negative direction.
1 B. Comment on the armature current shoot-up from the scope results.
Ans:
=> From 1st plot we can see that the current plot has initially very high value and then becomes steady and after that shows same path in the - ve direction.
=> In these three plots the value of this current shoot up is decreasing and the 3d plot has almost smooth current flow.
=> To get steadier and smoother current floe we need to decrease and control the duty cycle.
=> This shoot up happens because of the switching in the circuit that cause heat losses during switching. To avoid these losses, we use HEAT SINK material to dissipate the heat. From this the motor can change its direction of rotation easily and very smoothly.
2 Aim: Develop a 2-quadrant chopper using simulink & explain the working of the same with the relevant results. (Refer to article - Multiquadrant operation of motor )
Ans: Here we have to create the 2-quadrant chopper using simulink model.
Simulation Model:
=> Here in this simulink model we take compounds are pulse generator block, MOSFET block, NOT gate block , DC voltage source block , Diode block Current measurement block, Voltage measurement block, series RLC branch block, Scope block from the simulink libray browser.
=> In this model pluse generator connect to the logic operator to mosfet and here voltage source 1 given value is 20 V and voltage source 2 given value is 25 V the output connect to the scope.
=> Now connect the circuit as per circuit shown in above.
=> Let the voltage of dc voltage source1 is 20 volts.
=> Let us consider an series rlc branch and select inductor L. thus block works as a load.
=> To consider LE load i.e, motor load, and dc voltage source2 of 25 volts 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 other mosfet will get off and when other 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%.
Two Quadrant Type - A Chopper or Type - C Chopper:
=> Type C chopper is obtained by connecting type –A and type –B choppers in parallel.
=> We will always get a positive output voltage V as the freewheeling diode FD is present across the load.
=> When the chopper is on the freewheeling diode starts conducting and the output voltage v will be equal to V .
=> The direction of the load current i will be reversed.
=> The current i will be flowing towards the source and it will be positive regardless the chopper is on or the FD conducts.
=> The load current will be negative if the chopper is or 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 might be positive or negative.
=> The power flow may be life the first quadrant operation ie 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 my cause a short circuit in supply lines.
=> For regenerative braking and motoring these type of chopper configuration is used.
Two Quadrant Type - B Chopper or Type - D Chopper:
=> The circuit diagram of the type D chopper is shown in the above figure below.
=> When the two choppers are on the output voltage v will be equal to V .
=> When v0= – Vs the two choppers will be off but both the diodes D1 and D2 will start conducting.
=> V the average output voltage will be positive when the choppers turn-on the time T will be more than the turn off time T its shown in the wave form below.
=> As the diodes and choppers conduct current only in one direction the direction of load current will be always positive.
=> The power flows from source to load as the average values of both v and i is positive.
=> From the wave form it is seen that the average value of V is positive thus the forth quadrant operation of type D chopper is obtained.
=> From the wave forms the Average value of output voltage is given by V0= (Vs Ton -Vs Toff )/T = Vs .(T on-Toff )/T.
Result:
=> The voltage waveform is not going less than zero. the minimum value of voltage is zero and maximum value is always in the positive direction.
=> How ever in current waveform, the current is decreases.
=> The current may be positive as well as negative. and the pulse amplitude is 10 thus from pulse waveform we can see that the pulse amplitude is 10.
3 Aim: Explain in a brief about operation of BLDC motor.
Ans:
Working Of BLDC Motor:
=> The principles for the working of a BLDC motor are the same as for a brushed DC motor, internal shaft position feedback In case of a brushed DC motor, feedback is implemented using a mechanical commutator and brushes.
=> With a in BLDC motor, it is achieved using multiple feedback sensors.
=> The most commonly used sensors are hall sensors and optical encoders Hall sensors work on the hall- effect principle that when a current-carrying conductor is exposed to the magnetic field, charge carriers experience a force based on the voltage developed across the two sides of the conductor.
=> If the direction of the magnetic field is reversed, the voltage developed will reverse as well For Hall effect sensors used in BLDC motors whenever rotor magnetic poles (N or S) pass near the hall sensor, they generate a HIGH or LOW level signal, which can be used to determine the position of the shaft.
=> In a commutation system-one that is based on the position of the motor identified using feedback sensors-two of the three electrical windings are energized at a time as shown in figure.
=> The GREEN winding labeled (001 is energized as the NORTH pale and the BLUE winding labeled as '010" is energized as the SOUTH pole Because of this excitation, the SOUTH pole of the rotor aligns with the GREEN winding and the NORTH pale aligns with the RED winding labeled 100 in order to move the rotor, the RED and BLUE windings are driergized in the direction shown in figure.
=> This causes the RED winding to become the NORTH pole and the BLUE winding to became the SOUTH pole.This shifting of the magnetic leid in the stator produces torque because of the deveopment of repulsion (Red winding NORTH NORTH alignment) and attraction forces (BLUE winding NORTH-SOUTH alignment) which moves the rotor in the clockwise direction.
=> This torque is at its maximum when the rotor starts to move, but it reduces as the two fields align to each other. Thus, to preserve the torque or to build up the rotation, the magnetic field generated by stator should keep switching.
=> To catch up with the field generated by the stator, the rotor will keep rotating. Since the magnetic field of the stator and rotor both rotate at the same frequency, they come under the category of synchronous motor.
=> This switching of the stator to build up the rotation is known as commutation. For 3-phase windings, there are 6 steps in the commutation, Lo, 6 unique combinations in which motor windings will be energized.
Advantages Of BLDC Motor:
=> Less overall maintenance due to absence of brushes.
=> Reduced size with far superior thermal characteristics.
=> Higher speed range and lower electric noise generation.
=> It has no mechanical commutator and associated problems.
=> Higher dynamic response due to low inertia and carrying windings in the stator.
=> Less electromagnetic interference.
=> Low noise due to absence of brushes.
Disadvantages Of BLDC Motor:
=> These motors are costly.
=> Electronic controller required control this motor is expensive.
=> Requires complex drive circuitry.
=> Need of additional sensors.
Applications Of BLDC Motor:
=> Computer hard drives and DVD/CD players.
=> Electric vehicles, hybrid vehicles, and electric bicycles.
=> Industrial robots, CNC machine tools, and simple belt driven systems.
=> Washing machines, compressors and dryers.
=> Fans, pumps and blowers.
Conclusion:
=> MATLAB demo model named Speed control of a DC motor using BJTH bridge is studied and the the armature current shoot-up is studiod and The Four Quadrant Chopper DC Drive (DC7) block is also studied and Compare it with the H-bridge model.
=> 2 quadrant chopper using simulink model is made and the Various results obatined is studied.
=> Operation of BLDC motor is studied.
Note:
In this I didn't Menstion 1C Question Because Of In this EV Live Batch 21 Rasheed ahmed told to us,Please Check.