DO_AN_DIEN_TU_CONG_SUAT điều khiển tốc đọ động cơ điện một chiều

Table of contents Page Introduction Chapter 1: Introduction to DC motors 1.1 General introduction to separately-excited dc motor a Structure characteristics of DC electric motor b Operating principles of DC electric motor c Equation of mechanical properties of separately-excited DC d Speed adjustment methods 1.2 General introduction about rectifiers a General concept b Classification of overpressure hashers c Semi-conduction device Thyristor Chapter 2: Design of a speed regulator for an separately-excited dc motor 2.1 Project assignmenst 2.2 Speed adjustment method of separately-excited dc motor by pulse PWM 2.2.1 PWM pulse modulation method 2.2.2 Working principle of PWM 2.2.3 Method to generate PWM for control Chapter 3: Design of the control circuit and simulating control circuits 4 6 14 14 14 15 18 18 18 18 19 21 22 3.1 General structure of the control circuit 3.2 Control circuit diagram calculation 3.2.1 Section create square pulse and ariangle carrier voltage 3.2.2 Circuit comparison pulse 3.2.3 Circuit control (Udk) 3.2.4 Pulse amplification 3.2.5 Power circuit 22 Chapter 4: Conclusion Reference 32 23 23 25 27 28 29 33 Introduction With the increasing growth of industries in both width and depth, electricity and electric machines play a very important role, indispensable in most industries and daily life human activity It is always one step ahead of the premise but also the key to the success of an industrial production system There is no country or any manufacturing industry that does not use electricity or electrical machines Due to the advantages of the AC system: easy to manufacture, easy to transmit , both the generator and the AC motor have a simple structure and large capacity, easy to operate AC (electric motor) is increasingly widely and popularly used However, DC motors still hold a certain position as in the transportation industry, and generally in devices that require a wide range of speed control (such as steel rolling machines, big tools, electric locomotives ) Although compared with induction motors to manufacture DC motors of the same size, the cost is more expensive due to the use of more non-ferrous metals, more complicated commutation preservation but due to the advantages of which DC machines are still indispensable in modern 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 asynchronous motor cannot be met by itself or if it can be met, the associated converter equipment (such as an inverter ) is very expensive, then is DC motors These can be adjusted widely and precisely, while the circuit structure is simpler 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 of electricity The pressure ranges from a few hundred to 1000v The development direction is to improve the material lift, improve the economic performance of the engine and build larger capacity machines, which is a large and complex problem, so with limited knowledge of Within this topic, I cannot mention many major problems, but only mention the problem of designing DC pulse hash to adjust the reversing speed of an independent dc motor according to the deserve This is one of the most commonly used methods 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 and characteristics 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 and dynamic part The stationary part or the stator, also known as the engine excitation, is the part generated from field it includes: +) Magnetic circuit and excitation wire outside the magnetic circuit (if the motor is excited electromagnet), the magnetic circuit is made of ferromagnetic tape (cast steel, solid steel) Cord excitation winding, also known as excitation winding, is made of electromagnetic wires the solenoid coil 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 Magnetic iron core made of technical steel sheets electricity or carbon steel 0.5 to mm thick pressed and spread tightly In the electric motor small steel can be used The magnetic pole is fastened to the housing by bolts The field winding is wound with insulated copper wire and each winding is uniform is thoroughly insulated into one block, impregnated with insulating paint before placing on the magnetic pole The field coils are placed on these magnetic 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 winding structure make it look like a main magnetic pole winder The auxiliary magnetic 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 medium electric motors, thick steel is often bent and welded, in large electric machines often use cast steel Sometimes in small electric motors use cast iron make the case +) Other parts: Machine cover: To protect the machine from falling foreign objects and damaging the cord wrapped and safe from electrical touch In small and compact electric machines The machine also works as a bearing bracket In this 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 spring pressed tightly to the neck contribute The brush box is fixed on the brush holder and insulated with the rack Price the brush can be rotated to adjust the brush position to the right place, after the adjustment is complete, use the screw 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 the wire are connected with copper plates called commutators, those commutators are insulated with each other and insulated from the shaft is called a commutator or commutator The crank on the commutator is a pair of coal embers made of graphite coal and 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 both sides and then pressed tightly to reduce the loss due eddy currents cause On the steel sheet, there is a groove shape stamping so that after being pressed again, put the cuff on In the average engine or more people still stamp ventilation holes so that when pressed into the iron core, they can create ventilation holes along the axis In larger electric motors the iron core is generally 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 the coil and the iron core In small DC motors, the armature iron is directly pressed axis In large electric motors, a rotor is placed between the shaft and the iron core Use a rotor 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 is usually made of coated copper wire insulation In small machines with a capacity 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, the winding is carefully insulated from the groove of the steel core In order to avoid being thrown out by the rotation due to centrifugal force, a wedge is used at the mouth of the groove Squeeze or tighten the cuff The wedge 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 a circular shaft Two shaft ends round using two V-shaped tiles pressed tightly together Between the rim and round cylinder is also the way electricity by mica The tail of the commutator is slightly raised to weld the ends of the wires 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 The conductors whose electric current is in the magnetic field will bear the force that causes the rotor to rotate, the direction of force is determined by the lefthand rule When the armature has been rotated half a turn, the positions of the guides swapped Due to the integer current collector, the magnetic force is applied constant When rotating, the conductors cutting off the magnetic field are induced by electrical stress the direction of the electromotive force is determined by the rule 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 1.1: Principle diagram of separately-excited DC motor Figure 1.2: Principle diagram of parallel-excited DC motor -According to the principle diagram in the figure and figure 2, the voltage balance 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: Eư (1.3) Or we can write: Eư = Ke.ф.n (1.4) And: ω (1.5) Thanks to magnetic effect on armature wire when there is an electric current, rotor spin under effects of the torque turned: M = K.ф.Iư (1.6) From system of equations (1) and (2) we can plug out equation of mechanical properties indicate relationship ω = f(I) of separately-excited dc motor as follows: ω (1.7) 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 fully energized at zero speed This occurs when starting the engine and when the engine is running but is stopped because of jam or overload is not pulled Electric Inm this is large and often equal: Inm = (10 ÷ 20)Idm (1.10) It may cause a fire or damage to the engine if the phenomenon persists for a long time 1.1.4 Speed adjustment methods When choosing a speed regulation system with a certain adjustment method for a production machine, care should be taken so that the tuning characteristics adhere to the specification requirements of the production machine load Thus, the working system will ensure quality and stability requirements When considering the mechanical characteristic equation of separatelyexcited dc motor, we know the dependence ω=f(M) of electrical parameters U, ф, Rư These varying parameters will give them different mechanical properties therefore, for the same load torque, the engine speed will be different for different mechanical properties As such, separately-excited dc motor can be speed adjusted by the following methods: +) Speed regulation by varying armature voltage Rư=const Rf=0 Ф=фdm=const When changing the voltage applied to the armature windings, we have their mechanical properties with different no-load rates, parallel and of the same rigidity The voltage U can only be changed on the downside (U Urc then Ura = + Ubh, when Uđk < Urc then Ura = -Ubh If the control voltage is applied to the door (-), and the jagged voltage (+) we have: So when Uđk > Urc then Ura = -Ubh, when Uđk < Urc, then Ura = + Ubh Figure 3.6: Simulation comparison pulse Thus, the voltage to be compared must be the same sign to change the output state And the maximum difference between the two state gates when working must not exceed the allowable limit of the selected OA type 25 3.2.3 Circuit control (Udk) -Circuit to create voltage Udk used in control circuit Figure 3.7: Circuit to create voltage Udk -The integral component of the PI circuit will cause adjustment delay because it takes time to integrate, in which the value of capacitor C1 has a decisive influence on the speed of the system (R77 is involved in the Kp component It is not used to adjust Ki), so it must depend on the actual system to calculate C10 Figure 3.8: Simulation comparison pulse 26 3.2.4 Pulse amplification -Both T1 and T2 bulbs are selected under the same voltage conditions to withstand the ECS source number Regarding the current, the bulb T1 selects according to the current through the primary winding I1 of the pulse transformer: Of which: Ig: Dong controls the valve opening k: ratio of primary and secondary turns Figure 3.9: Pulse amplification -After selecting T1 to have the amplification factor β1, T2 will be chosen, so that the T2 bulb is always smaller than T1 due to the current being times smaller Resistor R1 chooses from a well saturated open condition for T1,T2and does not overload the front stage of the pulse amplification: 27 Figure 3.10: Simulation amplifier pulse -If the voltage to the pulse amplifier is negative, it is necessary to secure the protective diode for the transistors D2 or Dz, to prevent overvoltage causing burns to the balls as they switch from lead to lock 3.2.5 Powerr circuit Figure 3.11: Powerr circuit 28 -Engine calculation: Engine parameters: P = 1.5kW, Uđm = 500V, Idm = 50A, nđm = 2000 v / Rated spee dof engine: (rad/s) 0.079 (Ώ) Figure 3.7: Simulation signal voltage -Select Diode: Power diodes are selected based on the basic factors: load current, selected scheme, heat dissipation conditions, operating voltage The basic parameters of the diode valve are calculated as follows after ignoring the pressure drop onthe valves: Average current flows through the diode with rated motor current value: Iđm=50A Choosing the cooling mode is a valve with a radiator blade with enough surface volume and a ventilation fan, then allow the allowable working current to flow through the valve to 50% Iđm At that time, the flow through the valve needs to be selected: Ki.Imax = 50/0.5 = 100 (A) Through the graphs we see: The maximum reverse voltage placed on each valve (ignoring the pressure drop on each valve) is: UNgmax = E = 600V Select the overvoltage factor ku =2 =>Ungv = ku.Ungmax = 2.600 =1200 V -Selection of Thyristor: Calculate the average current flowing through the valve: 29 Through the analysis of the above force circuits we see: Average current flows through the valve Iμ : IS = γ It with the value of the motor rated current is Iđm = 50 (A) + Select the cooling mode is a valve with a heat vent with enough surface area and a ventilation fan, then the allowable working current to run through the valve is up to 50% Idm At that time, the current through the valve should be selected: Iđmv = ki Imax =50 / 0.5 = 100 (A) Through the graphs we see: The maximum reverse voltage applied to each valve (ignoring the pressure drop on the valves) is Ungmax = E = 1200 (V) Select the overvoltage factor ku = => Ungv = ku.Ungmax = 2.600 = 1200 (V) 30 Chapter 4: Conclude After a semester of project implementation with the enthusiastic guidance of instructor Pham Thi Thuy Linh, we have completed the project of Power Electronics subject with the topic “Designing a speed regulator for an separately-excited dc motor” and achieved the following results: - Understand the structure and operating principle of a separately-excited dc motor - Applying the principle of speed adjustment method of separately-excited dc motor by pulse PWM - Know the design and calculate the force circuit - Know how to design and calculate control circuits The simulation results show that the force circuit and control circuit work well to meet the actual requirements set out That proves the correctness of the designed circuit This result can be the basis for the circuit design in practice However, due to the limited time and limited qualifications, this project cannot avoid its shortcomings We would like to thank our instructor Pham Thi Thuy Linh for his wholeheartedly helping us complete this project 31 Reference [1] Nguyen Binh: Power electronics [2] Vo Quang Lap: The Transformation Technique [3] Vo Minh Chinh, Pham Quoc Hai, Tran Trong Minh, Power Electronics Science and Technology Publishing House, 2004 [4] Electronic components manual [5].The software the simulation: PSIM, Tina, Multisim, Pspice, Matlab 32