DO_AN_DIEN_TU_CONG_SUAT điều khiển tốc đọ động cơ điện một chiều

+ Main magnetic pole: Is the part that generates the magnetic field, including the iron core and the coil excitation iron core outer core.. In larger electric motors the iron core isgene

Table of contents

1.1 General introduction to separately-excited dc motor 4

a Structure characteristics of DC electric motor 4

b Operating principles of DC electric motor 6

c Equation of mechanical properties of separately-excited DC 6

1.2 General introduction about rectifiers 14

b Classification of overpressure hashers 14

c Semi-conduction device Thyristor 15

Chapter 2: Design of a speed regulator for an

2.2.3 Method to generate PWM for control 21

Chapter 3: Design of the control circuit and simulating

3.1 General structure of the control circuit 22

3.2 Control circuit diagram calculation 23

3.2.1 Section create square pulse and ariangle carrier

With the increasing growth of industries in both width and depth,electricity and electric machines play a very important role, indispensable inmost industries and daily life human activity It is always one step ahead ofthe premise but also the key to the success of an industrial productionsystem There is no country or any manufacturing industry that does not useelectricity or electrical machines

Due to the advantages of the AC system: easy to manufacture, easy totransmit , both the generator and the AC motor have a simple structure andlarge capacity, easy to operate AC (electric motor) is increasingly widelyand popularly used However, DC motors still hold a certain position as inthe transportation industry, and generally in devices that require a widerange of speed control (such as steel rolling machines, big tools, electriclocomotives ) Although compared with induction motors to manufacture

DC motors of the same size, the cost is more expensive due to the use ofmore non-ferrous metals, more complicated commutation preservation butdue to the advantages of which DC machines are still indispensable inmodern production

The advantage of DC motors is that it can be used as an electric motor

or a generator in different working conditions But the biggest advantage of

DC motors is speed regulation and overload capacity If an asynchronousmotor cannot be met by itself or if it can be met, the associated converterequipment (such as an inverter ) is very expensive, then is DC motorsThese can be adjusted widely and precisely, while the circuit structure issimpler and the control circuit is of high quality

Today, the efficiency of small-capacity DC motors is about 75% ÷85%, and in medium and large-capacity electric motors are about 85% ÷94% The maximum capacity of DC motors is about 100000kw ofelectricity The pressure ranges from a few hundred to 1000v Thedevelopment direction is to improve the material lift, improve the economicperformance of the engine and build larger capacity machines, which is alarge and complex problem, so with limited knowledge of Within this topic,

I cannot mention many major problems, but only mention the problem ofdesigning DC pulse hash to adjust the reversing speed of an independent dcmotor according to the deserve This is one of the most commonly usedmethods today to adjust DC motors independently of the need to reverse the

motor to be rotated symmetrically It is an economically efficient method It

is highly functional and widely used for its outstanding features andcharacteristics

Chapter 1: Introduction to DC motors

1.1 General introduction to separately-excited dc motor.

1.1.1 Structure characteristics of DC electric motors.

DC motors can be divided into two main parts: the stationary anddynamic part

The stationary part or the stator, also known as the engine excitation, is thepart generated from field it includes:

+) Magnetic circuit and excitation wire outside the magnetic circuit (if themotor is excited electromagnet), the magnetic circuit is made offerromagnetic tape (cast steel, solid steel) Cord excitation winding, alsoknown as excitation winding, is made of electromagnetic wires the solenoidcoil is now connected in series

+) Main magnetic pole: Is the part that generates the magnetic field,

including the iron core and the coil excitation iron core outer core Magneticiron core made of technical steel sheets electricity or carbon steel 0.5 to 1

mm thick pressed and spread tightly In the electric motor small steel can beused The magnetic pole is fastened to the housing by bolts The fieldwinding is wound with insulated copper wire and each winding is uniform isthoroughly insulated into one block, impregnated with insulating paintbefore placing on the magnetic pole The field coils are placed on thesemagnetic poles connected in series

+) Secondary magnetic pole: The auxiliary magnetic pole is located on the

main magnetic poles Steel core of magnetic pole The filler is usually made

of solid steel and on the side the auxiliary magnetic pole has a windingstructure make it look like a main magnetic pole winder The auxiliarymagnetic pole is attached to the housing thanks bolts

+)Not magnetic: Magnetic hips are used as magnetic circuits to connect the

magnetic poles, at the same time as shell machine In small and mediumelectric motors, thick steel is often bent and welded, in large electricmachines often use cast steel Sometimes in small electric motors use castiron make the case

+) Other parts:

Machine cover: To protect the machine from falling foreign objects anddamaging the cord wrapped and safe from electrical touch In small andcompact electric machines The machine also works as a bearing bracket Inthis case the lid is usually made of cast iron

Brush structure: To bring current from the part to outward Brush structure.The charcoal consists of a brush placed in the brush box thanks to a springpressed tightly to the neck contribute The brush box is fixed on the brushholder and insulated with the rack Price the brush can be rotated to adjustthe brush position to the right place, after the adjustment is complete, use thescrew to fix it.

- Rotating part or rotor: Including the following main parts

+) The part that generates electromotive force includes:

Magnetic circuit is made of ferromagnetic material (technical steel foil)folded together

On the magnetic circuit there are slots for inserting the armature winding

Armature coil: Consisting of many wires connected together according to a

rule certain Each winding consists of many turns of wire the wires of thewire are connected with copper plates called commutators, thosecommutators are insulated with each other and insulated from the shaft iscalled a commutator or commutator

The crank on the commutator is a pair of coal embers made of graphite coaland closely coupled the commutator by springs

+) Armature iron core: Used to conduct magnetic, often using electrical

engineering steel plates 0.5mm thick, coated with thin insulation on bothsides and then pressed tightly to reduce the loss due eddy currents cause Onthe steel sheet, there is a groove shape stamping so that after being pressedagain, put the cuff on In the average engine or more people still stampventilation holes so that when pressed into the iron core, they can createventilation holes along the axis In larger electric motors the iron core isgenerally divided into a small section, between those sections, is a gap called

a ventilation gap When the wind blower blows through the gaps to cool thecoil and the iron core

In small DC motors, the armature iron is directly pressed axis In largeelectric motors, a rotor is placed between the shaft and the iron core Use arotor rack can save electrical engineering steel and reduce rotor weight

+) Armature winding: Armature winding is the part that generates the

electromotive force and with current flowing, the armature winding isusually made of coated copper wire insulation In small machines with acapacity of less than a few Kw, a wired cord is often used round section In

medium and large machines, a rectangular cross-section is often used, thewinding is carefully insulated from the groove of the steel core.

In order to avoid being thrown out by the rotation due to centrifugal force, awedge is used at the mouth of the groove Squeeze or tighten the cuff Thewedge can be made of bamboo, wood or bakelit

+) Commutator: Commutator consists of many copper plates which are

plated with equal insulation the mica layer is 0.4 to 1.2mm thick and forms acircular shaft Two shaft ends round using two V-shaped tiles pressed tightlytogether Between the rim and round cylinder is also the way electricity bymica The tail of the commutator is slightly raised to weld the ends of thewires winding element and commutator plates are easy

1.1.2 Operating principles of DC electric motor.

When DC is applied, there is electricity in the armature winding Theconductors whose electric current is in the magnetic field will bear the forcethat causes the rotor to rotate, the direction of force is determined by the left-hand rule

When the armature has been rotated half a turn, the positions of the guidesswapped

Due to the integer current collector, the magnetic force is applied constant.When rotating, the conductors cutting off the magnetic field are induced byelectrical stress the direction of the electromotive force is determined by therule of right hand, at Eư motor in the opposite direction of the current Iư so

Eư is called electromotive force moving Then we have the equation: U = Eư+ Rư

1.1.3 Equation of mechanical properties of separately-excited dc motor.

-Separately-excited dc motor: excitation coil powered from an independent

DC source with the power supply for the rotor

Figure 1.2: Principle diagram of parallel-excited DC motor.

Figure 1.1: Principle diagram of

separately-excited DC motor.

-According to the principle diagram in the figure 1 and figure 2, the voltagebalance equation of the armature circuit can be written (rotor) as follows:

Uư = Eư + (Rư + Rp).Iu (1.1)Inside:

- Uư is the motor armature voltage

-Eư is the electromotive force of the motor

-Rư is the armature coil resistance

-Rp is the armature circuit auxiliary resistance

-Iư is the motor armature current

Rư = rư + rct + rcb + rcp (1.2)

rư reactive armature coil

rct contact resistance between brush and commutator

rcb reactive offset coil

rcp reactive filler roll

Electromotive force armature proportional to rotation speed of rotor:

From equation (5) plug out Iư instead equation (6) we can:

ω (1.8)Inside: is ideal idle speed

Δω = is reduce speed

Can be represented in another format:

ω = ω0 – Δω (1.9)

Figure 1.3: Equation of mechanical properties of separately-excited dc

motor

Torque Mnm and Inm is the short-circuit torque and the short-circuit current It

is worth torque engine current maximum and maximum when fullyenergized at zero speed This occurs when starting the engine and when theengine is running but is stopped because of jam or overload is not pulled.Electric Inm this is large and often equal:

It may cause a fire or damage to the engine if the phenomenon persists for along time

1.1.4 Speed adjustment methods.

When choosing a speed regulation system with a certain adjustment methodfor a production machine, care should be taken so that the tuningcharacteristics adhere to the specification requirements of the productionmachine load Thus, the working system will ensure quality and stabilityrequirements

When considering the mechanical characteristic equation of excited dc motor, we know the dependence ω=f(M) of electrical parameters

separately-U, ф, Rư These varying parameters will give them different mechanicalproperties therefore, for the same load torque, the engine speed will bedifferent for different mechanical properties As such, separately-excited dcmotor can be speed adjusted by the following methods:

+) Speed regulation by varying armature voltage.

Rư=const

Rf=0

When changing the voltage applied to the armature windings, we have theirmechanical properties with different no-load rates, parallel and of the samerigidity

The voltage U can only be changed on the downside (U<Udm) so this methodonly allows for deceleration adjustment

Figure 1.4: Speed regulation by varying armature voltage

Assume the motor is operating at point A on mechanical property 1corresponding to voltage U1 on the armature When reducing the voltagefrom U1 to U2, the motor changes the working point from point A ofmagnitude ωA on line 1 to point D with a smaller speed on line 2(corresponding to voltage U2)

Figure 1.5: The process of speed changes when adjusting the voltage

No load speed:

Speed drop: Ic=const

The worship of artificial specialties:

Regulates the speed of an independent magnetic dc motor by voltagevariation armature has the following characteristics:

- The lower the voltage, the smaller the dynamic speed

-Smooth adjustment throughout the adjustment range

- Mechanical property hardness remains constant throughout the adjustmentrange

- The absolute deceleration over the entire tuning range for a torque is thesame Speed drop

relative will be greatest at the lowest mechanical properties of the range.Therefore, the relative speed error (static error) of the lowest mechanicalperformance does not exceed the permissible error for the full range ofadjustment

- The adjustment range of this method can be: D ~ 10: 1

- Speed can only be adjusted on the downward side (since it can only bechanged with Uư ≤ Uđm)

- This adjustment method requires a power supply in order to be able tosmoothly change the output voltage

+) Adjust speed by varying flux.

To change the motor flux, we change the inrush current of the motor throughone resistor in series in the field of excitation Obviously this method onlyallows to increase the input resistance excitation circuit, that is, theexcitation current can only be reduced (Ikt ≤ Iktđm), so that the fluxreduction side When the flux is reduced, the properties are steeper and have

a greater no-load rate

Figure 1.6: Adjustable speed of separately-excited dc motor by changing the

flux flux method

- Mechanical property stiffness decreases with decreased flux.

- Can be smoothly adjusted in the adjustment range: D ~ 3: 1

- Speed changes can only be adjusted on the upside

- As the mechanical property slope increases with decreasing flux, theproperties intersect each other and, therefore, with load is not large (M1), thespeed increases when the flux decreases In high load area (M2), speed can

be increased or decrease depending on the load In fact, this method is onlyused at the load area not too large compared to the intended level

- This method is very economical because speed regulation is done in a fieldwith current excitation is (1 ÷ 10)% of the rated current of the armature Lowadjustable losses

+) Adjust the speed by varying the resistance in the armature circuit.

In principle, this method allows for adjustment thanks to a change inresistance, but since the rotor is large, switching resistance will be difficult.Practically often use convertible resistance level

Figure 1.7: Adjustment of separately-excited dc motor by changing armature

- The hardness of artificial mechanical properties:

Features of the speed regulation method by varying the resistance in thearmature circuit:

- The armature circuit resistance increases, the greater the mechanicalproperty slope, the softer the mechanical property and the degree the poorspeed stability, the greater the speed error

- The method allows speed change adjustment on the downward side only(since it can only be incremented resistor)

- Because of the speed adjustment by adding resistance to the armaturecircuit, the power loss is below the greater the heat form on the resistor

- The range of adjustment depends on the load torque value The smaller theload (M1), the adjustable range smaller In general, this method gives theadjustment range: D ≈ 5: 1

1.2 General introduction to DC pulse hashing.

1.2.1 General concept.

The permissible direct-voltage pulse hash from the direct current source U,produces voltage Ura which is also DC voltage but can be adjusted

Figure 1.8: General diagram and output voltage pattern

Ura is a square (ideal) array of pulses with a pitch and rest t2 The outputvoltage is equal to the average value of the pulse voltage: Ura = γ.Us (γ =t1 / T) The basic principle of these converters is to periodically use the law

of the power semiconductor valves to adjust the coefficient to ensure achange in the mean voltage across the load

1.2.2 Classification of overpressure hashers.

- Parallel pulse hash set

- Series pulse voltage hash

- Mixed series parallel and series pulse voltage hash

1.2.3 Semi-conduction device Thyristor.

+)Structural features:

A thyristor is a solid statesemiconductor device with four layers ofalternating P- and N-type mate rials It acts exclusively as a bistable switch,conducting when the gate receives a current trigger, and continuing toconduct until the voltage across the device is reversed biased, or until thevoltage is removed (by some other means) There are two designs, differing

in what triggers the conducting state In a three-lead thyristor, a small current

on its Gate lead controls the larger current of the Anode to Cathode path In

a two-lead thyristor, conduction begins when the potential differencebetween the Anode and Cathode themselves is sufficiently large (breakdownvoltage)

BBD

Figure 1.9: Thyristor.

+) Symbols: PNP or NPN.

+) Volt-amp characteristics:

-Thyristors in Forward Biased State:

When anode is made positive, the PN junctions at the ends are forwardbiased and center junction (NP) becomes reverse biased It will stay inblocked (OFF) mode (also known as Forward Blocking Stage) till the time it

is triggered by Gate current pulse or the applied voltage reaches the forwardbreakover voltage

Triggering by Gate Current Pulse – When it is triggered by the gate currentpulse, it starts conducting and will act as a close switch The Thyristorsremains in the ON-state, i.e it remains in the latched state Here the gateloses its control to turn off the device

Triggering by Forward Breakover Voltage – When a forward voltage isapplied, a leakage current starts to flow through the blocking (J2) in themiddle junction of Thyristors When voltage exceeds the forward break overvoltage or critical limit, then J2 breaks down and it reaches to the ON state.When the Gate current (Ig) is increased, it reduces the blocking area and sothe forward break over voltage is reduced It will turn ON when a minimumcurrent called latching current is maintained

When the gate current Ig = 0 and anode current falls below a certain valuecalled holding current during the ON state, it again reaches to its forwardblocking state

Figure 1.10: Voltage Ampere (VI) Characteristics of Thyristor.

-Thyristors in Reverse Biased State:

If the anode is negative with respect to cathode, i.e., with the application ofreverse voltage, both PN junctions at the end i.e J1 and J3 become reversebiased and the centre junction J2 becomes forward biased Only a smallleakage current flows through it This is the reverse voltage blocking mode

or OFF state of Thyristor

When the reverse voltage is increased further, then at a certain voltage,avalanche breakdown of J1 and J2 occurs and it starts conducting in thereverse direction The maximum reverse voltage at which a thyristor startsconducting is known as Reverse Breakdown Voltage