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Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor Catalogue THE PREFACE In the technological innovation and modernization of water, the problem of applying science and technology to regulated products is the most urgent issue Along with the development of a number of industries such as electronics, information technology Industry automation company has also developed dramatically Process production automation is very popular, can replace human labor, high productivity again, good product quality Along with the development of the power electronics industry, the application of DC motors and industry is very important The use of 1-way motors for Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor many purposes such as to ensure the technological requirements of the load To understand the role of electric drive system, power electronics and one-way electric motor through this subject project, under the guidance of Mr Nguyen Ngoc Khoat with the main content of the subject: Design a rectifier to control speed of a separately excited DC motor with the following parameters: 1) Single-phase controlled bridge rectifier; 2) DC motor: P = kW, Uđm = 180V, nđm = 980v/p, Iđm = 6A, Mc = 75%Mđm I sincerely thank Mr Nguyen Ngoc Khoat for his dedication and help for guiding, helping and creating favorable conditions for us to complete this topic We sincerely thank! Hà Nội, December 18th , 2020 Students : Tăng Thị Như Quỳnh Trần Thị Thu Thảo CHAPTER1: OVERVIEWOF DC MOTORS 1.1 General structure 1.1.1 Concept A DC motor is a DC machine that converts direct current into mechanical energy When a DC machine is operating in the motor mode, the input power is the electromechanical power and the output power is the mechanical power Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor Figure 1: DC motor 1.1.2 Components of dc motor DC motors can be divided into two main components: the stationary and the dynamic part Figure 2: Construction of DC motors 1- Plate, - Main pole with field coil, - Commutating with reel, - Ball bearing box, - Laminated, - Armature roll, 7- Brush equipment, - commutator, - Axis, 10 - Terminal box cover 1.1.3 Classification of DC motors DC motors are classified according to excitation into the following categories: • Independent DC motor: The armature and the exciter are supplied from two separate sources • Parallel dc electric motor: The field coil is connected in parallel with the armature • Series magnetic dc motor: The exciter coil is connected in series with the armature • Combined d.c electric motor: Consists of two excitation windings, one connected parallel to the armature, one connected in series with the armature Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor 1.1.4 Principle of DC motors DC motors operate based on the effect of a magnetic field on the wire frame with electric current flowing through the magnetic field When operating DC motors turn the electric current of direct current into mechanical energy 1.2 Speed – torque equation of DC motors 1.2.1 Electrical motor characteristics The mechanical characteristic of electric motors is the linearity between the speed and the speed of the motor:M = f(ω) 1.2.2 Wiring schematic diagram of an independent dc motors Independent DC motor: DC power is supplied to the armature and supplied to the exciter independently Figure 3: Wiring schematic diagram of separatedly excited dc motor • Equation of voltage balance: Uư = Eư +(Rư + Rf).Iư • Electromotive force of the engine armature: Eư = K • The electromagnetic torque of the motor: M = KIư • Speed – Current characteristic : (1.2) (1.4) Figure 4: Speed –Current • Speed – Torque characteristic : Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor (1.5) Figure 5: Speed – Torque 1.2.3 Natural Speed -Torque characteristic Natural mechanical properties: = f (M) when parameters such as U, I, R of the motor are the rated parameters on the natural mechanical properties we have a rated working point is (; ) - Each motor has only natural mechanical property • Natural Speed –Current characteristic: (1.6) • Natural Speed -Torque characteristic: (1.7) 1.2.4 Artificial Speed -Torque characteristic Artificial mechanical characteristics: = f (M) when the electrical parameters are not rated parameters or when the electric circuit has been added Rf, Lf - Each motor has many artificial mechanical properties • Speed -Torque characteristic: (1.8) 1.3 Methods of adjustment change engine speed DC 1.3.1 Change the auxiliary resistance in the armature circuit Speed -Torque characteristic: (1.9) We see that when we change Rf, ω_o = const and change, so we will be adjusted by the same ω_o and steeper as the larger Rf, with the same load, the lower the speed Figure 6: Speed adjustment characteristic when Rf changes Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor Adjustment characteristics: • Ideal constant idle speed • Only allows speed change adjustment on the downward side • As Rf increases, the greater the slope of the mechanical properties, the softer the mechanical properties ⇒ the lower the speed stability, the greater the speed error • Power loss in the form of heat on the auxiliary resistor If we increase Rfto a certain value, it will make M ≤ Mc so that the motor will not spin and the motor is in short circuit mode (ω = 0).From now on, we can change the Rf and the speed will remain 0, which means the engine speed cannot be adjusted anymore.Therefore this adjustment method is not a radical adjustment method Advantages: The changing device is very simple, often used for crane motors, elevators, lifters, and excavators Disadvantages: The lower the adjustment speed, the greater the input resistance value, the softer the mechanical properties, the reduced stiffness leads to poor speed stability when the load changes poorly The auxiliary losses are very large when adjusting, the lower the speed, the higher the auxiliary losses The Rfchange method is suitable only when starting the engine 1.3.2 Change of motor magnetic flux Speed -Torque characteristic: (1.10) We see that when changes, and Δω both change, so we will get the curves adjusted gradually and higher than the natural mechanical properties when ϕ is smaller, with the same load, the higher the speed when reducing the flux ϕ Figure 7: Speed adjustment characteristic by change ϕ Adjustment characteristics: • Decreasing the flux results in inversely proportional change of speed The lower the flux, the more ideal idle speed increases, and the greater the motor speed • Constant short-circuit current • Mechanical property stiffness decreases with decreased flux If is too small, it may cause the motor speed to exceed the permissible limit, or make the switching condition worse due to the increased armature current.Thus, to Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor ensure normal switching, it is necessary to reduce the armature current ⇒ the torque on the motor shaft rapidly decreases ⇒ the motor is overloaded Advantages: The speed adjustment method by varying the flux can be infinitely adjusted and gives the speed greater than the basic speed.The bouncing method is often used for machines such as: universal grinder, bed planer, The adjustment is done on the exciter circuit so the loss of energy is low, the equipment is simple so the price is low Disadvantages: Due to deep adjustment, β decreases, large static error, less stable with high speed.That means the deeper the adjustment, the larger Δω.So the more the characteristic is that the smaller the torque is until the smaller the load torque, the motor cannot run 1.3.3 Change of motor armature voltage Speed -Torque characteristic: (1.11) We see that when Uưchanges, changes and Δω = const, so we will be adjusted parallel by the property lines.But if you want to change Uư, you must have a DC power supply that can change the output voltage, often using a converter Figure 8: Speed adjustment characteristic by Uư change Adjustment characteristics: • The motor speed increases / decreases in the direction of increasing / decreasing the armature voltage • Variable both ideal no-load speed , and short-circuit current • Mechanical property hardness remains constant throughout the adjustment range • Speed can only be adjusted on the downward side because it can only be changed with UưUđm Advantages: The speed control method by varying the motor armature voltage will keep the characteristic line stiffness, so it is widely used in metal cutting machines.Ensuring economy, low energy loss, wide range of adjustment.If combined with the flux adjustment method, we can adjust the higher and smaller speeds than the rated speed Disadvantage: This method requires a power supply that can smoothly change voltage Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor 1.4 Conclusion Through the analysis of the three methods of adjusting the speed of a DC electric motor, the method of controlling the motor speed by changing the armature voltage is the best and most radical Therefore, we choose the method of varying armature voltage to control the speed of DC motors CHAPTER 2: ADJUSTMENT OF THE PHASE FULLY CONTROLLED BRIDGE RECTIFIER 2.1 General introduction 2.1.1 Concepts Rectifiers are static converters that convert the energy of a source with alternating quantities into a source other than DC quantities Applications: Power supply for DC loads such as DC motors, battery chargers, electrolytic plating, DC welding machines, electromagnets, high voltage direct current transmission,… 2.1.2 Classification Based on the number of phases supplied to the rectifier valves: phase, phase, phase, phase Based on the type of semiconductor valve: • Uncontrolled rectifier circuit • Full control rectifier circuit • Semi-controlled rectifier circuit Based on valve diagram: • Beam diagram: Number of valves is equal to number of phases supplied.The valves are matched with one end: Common anode or common cathode • Spherical diagram: Half of the valves have common Anode, half of the valves have common cathode 2.1.3 Characteristics of voltage and rectifying current 2.1.3.1 Rectifier voltage ud: The instantaneous value of the rectifier voltage uσ: Alternating components Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor Ud: Average value of rectifier voltage (2.2) p: Number of pulse pulses of rectifier voltage wave (2.3) fσ(1): Frequency of the AC component's 1st harmonic waveud f: Grid voltage frequency The effective value of the voltage rectifier: (2.4) Uσ: The effective value of the AC component voltage rectifiers 2.1.3.2 Rectifier current id: The instantaneous value of the rectifying current idσ: Alternating components (2.6) Uσ(n): The effective value of the nth harmonic wave component of alternating voltage rectifier : Angular frequency of a harmonic wave n-order AC component Flickering of the load current: Due to the ac component of the rectifier voltage If L → ∞ Iσ(n) → id= IdAbsolutely flat lines 2.2 Adjusting the floor screen full control 2.2.1 Principle circuit diagram (2.7) (2.8) (2.9) (2.10) Figure 1: Circuit diagram of a fully controlled single-phase bridge rectifier Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor 2.2.2 Working principle Figure 2: Diagram and graph of u, i of single-phase controlled bridge rectifier Consider at established work cycles: In () u1> Suppose T2, T4 are conducting the reactive current id = iT2 = iT4 = ipk> 0; T1, T3 are locked, ud< u1> and has control pulses T1, T3open id = iT1 = iT3> 0, T2, T4close, ud> In () u2> T1, T3T1, T3 are still conducting reactive current id = iT1 = iT3 = ipk> 0, ud< u2> and has control pulses T2, T4open id = iT2 = iT4> 0; T1, T3close, ud> Just like that, we will open control each pair of T1, T3, then T2, T4 separated by an angle 2.2.3 Rectifier voltage and current • Average value rectifier voltage: (2.11) • Average current across load: (2.12) • Average value of current through thyristor: (2.13) • Maximum locking and reverse pressure applied to the component: Um 2.2.4 Coincidence phenomenon Phenomenon is the state insect branches led thyristor in the same group at the same conductive switches 10 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor CHAPTER 4: DESIGN OF CONTROL NETWORK PART 4.1 General introduction 4.1.1 Thyristor control block diagram synchronized Th compare amplification Figure 1: Thyristor control block diagram The phase of the copper phase is responsible for generating the same voltage as URC (usually linear jagged voltage) that coincides with the voltage of the Thyristor The comparison stage is responsible for comparing the same voltage with the control voltage Udk, finding the moment when these two voltages are equal, then generate pulses at the output and send to the amplifier stage The pulse generator is responsible for creating a suitable pulse to open the Thyristor.Thyristor pulses to open are required: front slope is vertical, to ensure Thyristor open immediately when there is control pulse (usually this pulse type is needle pulse or rectangular pulse);enough width with pulse width greater than the Thyristor opening time, enough capacity, isolating the control circuit from the dynamic circuit (if the dynamic voltage is too large) 4.1.2 Requirements of the control circuit The control circuit is a very important step in the thyristor converter because it plays an important role in determining the quality and reliability of the converter door.The control circuit door requirement can be summarized in the following six main points: • Width of control pulse • Loudness control pulse • Requirements for tooth slope • Symmetry of pulses in control channels • Requirements for reliability: Control channel resistance must be small so that the Thyristor will not open automatically when the leakage current increases.Control pulses are less dependent on temperature fluctuations, source voltage fluctuations.It is necessary to eliminate inductive noise to avoid mistaken opening • Assembly and commissioning requirements: Replacement equipment for assembly and adjustment, each with a high ability to work independently 4.1.3 Control circuit duties Is to generate pulses at the desired times to open the dynamic valves of the rectifier 19 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor The function of the control circuit: • Adjustable control pulse position within a positive half cycle of voltage applied on thyristor cathode - cathode • Generate pulses open thyristor pulse width tx U-(A1) UB> During the negative half cycle: U+(A1)< U-(A1) UB< At OPAMP A2: When UB> => T1 close U-(A2)> U+(A2) We consider the integral circuit included: rheostatR3,capacitor C1, and OPAMP A2at that timeUđb = UC = Because UB = const linear function When UB< => T1 open UB< U-(A2), diode D1 close U-(A2) = UC1 = There is increased current through the capacitorThe voltage at UC is negative to balance the voltage to 20 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor 4.2.2 The stage of comparison Figure 1: Circuit diagram of comparison stitching Working Principle: Choose At OPAMP A3 => U-(A3) = ; U+(A3) = When URC + Uđk> U-(A3) > U+(A3) UD = Vcc WhenURC + Uđk< U-(A3) < U+(A3) UD = Vcc Figure 2: Waveform diagram 4.2.3 Stitch creating beam pulse For a circuit diagram, in order to reduce the power current for the amplifier stage and increase the number of open pulses, in order to ensure the thyristor is open reliably, it is common to generate beam pulses for the thyristors.The principle of pulsed pulse is that before entering the amplifier stage, we insert an AND gate with the input signal received from the comparator stage and from the beam pulse generator as shown compare beam pulse amplification Figure 3: Schematic of the beam pulse generation 21 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor Figure 4: Schematic diagram of pulsed pulse generator using algorithm amplifier • Working Principle: Assume at first outputUE = VccU+(A4) At this time, capacitor C is loaded in the direction from the output through R8 to GND, the more capacitor voltage is charged on the capacitor, until the voltage across the capacitor is equal to UC = U-(A4) > U+(A4) = then the UE will change to the saturation level UE = VccU+(A4) At this time, capacitor C will discharge in the opposite direction, the port capacitor discharge voltage across the capacitor decreases, until UC = U-(A4) < U+(A4) Capacitor C will start to charge again, the continuous charging and discharging process alternately creates a UE multivibrator pulse 4.2.4 Amplifier stitching Figure 4.5: Amplifier stitching circuit diagram With the task of generating a suitable pulse to open the thyristor as mentioned above, the final amplifier stage is usually designed with a power transistor as shown.To have a needle pulse sent to the thyristor, we use a pulse transformer (BAX), to be able to amplify the power we use transistors , diode and to protect and the primary winding BAX when locks suddenly 22 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor In fact the control pulse only needs a small width (about 10 ÷ 200 μs), but the opening time of the power transistors is long (up to a half cycle of 0.01s), causing the excess heat of the transistortoo large and the BAX primary winding size is large.In order to reduce the radiant capacity and the size of the BAX primary wire, you can add a cascade capacitor C3.According to this diagram, is only open for current to flow during the charging time, so their effective current is much smaller 4.2.5 Control circuit diagram Figure 4.6: Thyristor control circuit diagram Figure 4.7: Diagram of control circuit curves 23 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor 4.3 Contributing circuit parameters Control circuit is calculated from the request to open Thyristor, so we have basic parameters to calculate the control circuit: • Thyristor control voltage: = V • Thyristor control current: = = 0,18 A • Thyristor opening time: = 10 s • Width of control pulse: = 20s • Frequency control pulse: = kHz • The loss of symmetry allows: = • Voltage control circuit: U = 12V • Pulse amplitude drop: = 0,15 4.3.1 Pulse transformer calculation Select the core material is ferrite ferrite HM, the core has a toroidal shape that works on a part of the magnetization properties with ∆B = 0.3T, ∆H = 30A / m without air clearance • Transformer ratio: choose m = • The secondary voltage of the pulse transformer The secondary voltage of the pulse transformer: = = V • The voltage applied to the transformer voltage transformer secondary winding: = m = = 9V • Current level voltage of pulse transformer: = = 0,18A • The primary current of the pulse transformer: = = = 0,06A 4.3.2 Calculate the final amplification stage Select 2SC911 Power Tranzitor Type NPN transistor is silicon semiconductor • Voltage between Collector and Bazo when Emitter open circuit: = 40V • Voltage between Emitter and Bazo when Collector open circuit: = 4V • The maximum current the Collector could endure: = 500 mA • Power dissipation in Collector: = 1,7 W • The maximum temperature of the junction surface: = • Gain factor: • Collector max current: IC3max = 0,5 A • Collector's working current: • Base working current: = = 1,2 mA We see that with selected Thyristor type has quite small control capacity: = V, = 0,18 A Therefore, we only need one amplifier stage to control the Tranzitor Select the power source for the pulse transformer E = 15 V, with the source E = 15 V we must add resistor in series with the Emitter pole of T3.IC3 = I1 IE All the Diode in the control circuit use type 1N4009 with parameters: • Electricquota 24 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor • Maximum reverse voltage • Diode voltage for open through 4.3.3 Calculation of beam pulse generator selection Each control channel must use algorithm amplifiers, so we choose IC type TL084 by TexasInstrument, each of these ICs has op amps Figure 4.8: sewing beam pulse Parameter • Power supply voltage: choose Vcc = • The voltage difference between the two inputs: • Working temperature: T = 25 • Power Consumption: P = 0.68 W • Input impedance: • Output current: • Input current: • Allowable speed of voltage variation: ) The beam pulse generator circuit has frequency f,or beam pulse period: We have period of oscillation: Choose R6 =R7= 33 k thỡ T = 2ìR8ìC2ìln3 =40 às We have: R8ìC2=18,2 às Choose C2=0,01 àF =>R8= 1820 For the convenience of the circuit, we choose R8 as a 2kΩ resistor 4.3.4 Compute choosing the comparison layer Each control channel has an algorithm amplifier acting as a comparison layer, we choose IC type TL084 as above 25 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor In that sourceVcc = ± 12V, then input voltageA3,Uv = 12V The input current is limited toIlv < mA R4 = R5>=12 kΩ Choose R4 = R5 =15 kΩ, then the current is inA3: Ilv-max = =0,8 mA 4.3.5 Calculation of choosing a synchronous stage Capacitor voltage is formed by the charging of capacitor C1, on the other hand, to ensure a wide control range, the control angle α = ÷ 180º, the time constant of the capacitor load: Choose C1 = 0,1 then the resistanceR3 = For the convenience of adjustment when assembling R3 circuit, resistor R3 greater than 10 kΩ is usually selected for adjustment Select transistor T1 A564 type with the following parameters: PNP type Tranzitor made of Si Voltage between Emitter and Base at Collector circuit: UEBO = 7V Maximum current the Collector can withstand:IC-max = 100 mA Maximum temperature at the junction surface: TCP = 150º Amplifier coefficient: β = 250 The maximum current of the base: IB1 = =0,4 mA The resistance to limit the current to the Tranzitor base T1 is selected as follows: Select R2 satisfies the control: R2≥ = = 30 kΩ Select the copper phase voltage: UA = 15V The resistor R1 to limit the current entering the amplifier goes into the algorithm amplifier A1 usually chooses R1 so that the input current amplifies the algorithm: Iv< mA R1 == 15 kΩ Choose R1 = 15 kΩ 4.3.6 Calculate synchronous stitching half cycle 26 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor Figure 4.9: section synchro Control angle 165֯ Choose   With Choose R40 = 15kΩ, R21 = 10kΩ, R39 = 10kΩ = 40,6 (V) E 15 = = 15k Ω J 10−3 = 7,5° → time = 0, 278ms R∑ = α 4.3.7 calculate serrated half cycle U RE max Figure 4.10: jagged voltage generation = 10v, U dp = 220v, f = 50 Hz , E = ±15V With Choose OA is TL082, control angle Tp = 165°.10ms = 9, 617 ms 180° Choose diode (BZ.79)180 Choose capacitors 27 C = 220nF Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor U Dz = 31, 25 E.FP 15.9, 617.10 −3 → R8 = = ≈ 20k Ω U Dz C 31, 25.220.10−9 R8 = 20k Ω tn = 10ms − 9,167 ms = 0,833ms R5 ≤ U bh − 0, 12,5 − 0, = C U Dz E 220.10 −9 15 + + −3 tn R8 0,833.10 10.103 Z = 10k Ω R5 = 10k Ω 4.3.8 Choosing Diode for rectifier Effective current through the diode: Select diode with rated current: Maximum reverse voltage to which the diode is subjected: So choose a KYZ 70 diode with the following parameters: • Electricquota : • The maximum reverse voltage of the diode: 28 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor CHAPTER 5: DESIGN OF DYNAMIC COMPONENTS 5.1 Generation introduction For semiconductor rectifier when calculating as well as operating, we must pay special attention to the problem of overcurrent and overvoltage protection Because of the small size of the semiconductor valve, the small heat capacity and the large current temperature across the PN junction, it is very sensitive to current overload.a few hundredths of a second, therefore, fast-acting protection is required Semiconductor valves, on the other hand, are also very sensitive to overvoltages As long as there exists a reverse voltage greater than the permissible value for a few µs, the PN junction surface can be electrically penetrated 5.2 Over current protection When working with current flowing, the valves have a pressure drop, so there is power loss ∆P that generates heat to heat the semiconductor valve The fix is to use the radiator fins: Figure 1: Realistic heat dissipation images Power loss per Thyristor: 29 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor Heat dissipation surface area: Inside: : Thyristor maximum voltage drop Ilv: Thyristor working current ∆P: capacity loss : temperature difference with the environment Select the ambient temperature of 40C, the maximum working temperature of the Thyristor is125oC Select the temperature on the fins of the radiator is 80 oC = 8040 =40oC Km: radiant heat coefficient by convection and radiation Choose Km = W/m2.oC Choose a 6-blade radiator fins with the size of 10 cm each.The total heat dissipation area of the wing is:S= 62 10 10 = 1200 cm2 = 0,12 m2 5.3 Protect circuit chart of the motion circuit Figure 2: Circuit diagram of the protective circuit 30 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor Figure 7: Rectification section Figure 8: Comparison section 31 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor Figure 9: gain section Figure 5.10: Load voltage 32 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor REFERENCES [1] Sách hướng dẫn thiết kế điện tử công suất, Phạm Quốc Hải, Nhà xuất Khoa Học & Kĩ Thuật Hà Nội, 2009 [2] Giáo trình Điện tử công suất, Trần Trọng Minh, Nhà xuất giáo dục Việt Nam, 2012 [3] Cơ sở truyền động điện, Bùi Quốc Khánh – Nguyễn Văn Liên, Nhà xuất khoa học kĩ thuật, 2007 33 ... current transmission,… 2.1.2 Classification Based on the number of phases supplied to the rectifier valves: phase, phase, phase, phase Based on the type of semiconductor valve: • Uncontrolled rectifier... (2.8) (2.9) (2.10) Figure 1: Circuit diagram of a fully controlled single-phase bridge rectifier Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited... switches 10 Topic: Design of a Single-phase controlled bridge rectifier to control speed of a separately excited DC motor Figure 3: The phenomenon of 1-phase bridge rectification coincidence