A COMPARITVE STUDY BETWEEN VECTOR CONTROL AND DIRECT TORQUE CONTROL OF INDUCTION MOTOR USING MATLAB SIMULINK Submitted by Fathalla Eldali Department of Electrical and Computer Engineering For the Degree of Master of Science Colorado State University Fall 2012 1 WHEN HAVE I BEEN INTERESTED IN MOTOR DRIVE AND MATLAB? BSC Senior Design LIM + PLC MATLAB/Simulink as A Modeling TOOL 2 THESIS OUTLINES Introduction Induction Motor Principles Induction Motor Modeling Electric Motor Drives Vector Control of Induction Motor Direct Torque Control Theoretical Comparison Vector Control and Direct Torque Control Simulation Results Simulation Results in the normal operation case The effect of Voltage sags and short interruption on driven induction motors The characteristics of the voltage sag and short interruption 3 Conclusion & Future Work INTRODUCTION Motors are needed Un driven Motors and power consumption Power Electronics, DSP revolution help Rectifiers Inverters Sensors Control Systems Theories 4 OLD STUDIES & MOTIVATION Many studies have been done about FOC & DTC individually Few studies were published as a comparison studies as [17-19] Voltage Sag & Short Interruption faults were not considered in the comparison 5 INDUCTION MOTOR PRINCIPLES Nikola Tesla first AC motors 1888 AC motors -Induction Motors -Permanent Magnet Motors Why are Induction Motors are mostly used ? Supplied through stator only Easy to manufacture and maintain Cheap 6 INDUCTION MOTOR CONSTRUCTION Stator : laminated sheet steel (eddy current loses reduction) attached to an iron frame stator consists of mechanical slots insulated copper conductors are buried inside the slots and then Y or Delta connected to the source. 7 Two Types of Rotor A-wound rotor: -Three electrical phases just as the stator does and they (coils) are connected wye or delta. B-squirrel-cage’s rotor -contains bars of aluminum or copper imbedded in the rotor, which are short circuited at the end of each bar by an end disc 8 INDUCTION MOTOR ROTOR TYPES (A) WOUNDED ROTOR (B) SQUIRREL-CAGE ROTOR. 9 ELECTRIC AC MOTOR DRIVES Practically, induction motor doesn’t work at its rated speed Switching the (motor) on/off is possible by mechanically stressful decreasing the rotation speed is a better way to save energy and reduce mechanical stress 10 PURPOSES OF ELECTRIC AC MOTOR DRIVES 11 INDUCTION MOTOR MODELING To model IM, We should know the electrical and mechanical equations that describe it in the transient and steady state The Electrical equations are for the Voltage, current, Flux The Mechanical equations for the speed, position and Torque 12 IDEALIZED CIRCUIT MODEL OF THREE PHASE INDUCTION MACHINE 13 ELECTRICAL EQUATIONS 14 MECHANICAL EQUATIONS 15 MACHINE MODEL IN ARBITRARY REFERENCE FRAMES Purpose of those Transformations: Eliminate the effect of inductance changing with time It is more convenient to be used in Unbalanced voltage cases. The other advantage is that we can observe any variable at any instance. 16 17 RELATIONSHIP BETWEEN ABC AND QD ARBITRARY COORDINATE REFERENCE FRAMES. 18 INDUCTION MOTOR MODELING MATLAB/SIMULINK Three phase to d-q stationary reference frame d-q stationary frame to d-q synchronous frame Electromagnetic Torque Equation modeling 19 THREE PHASE TO D-Q STATIONARY REFERENCE FRAME u[1] 1 Vas Vqs_s Vqs-s Vbs f(u) 2 Vds_s Vds-s Vcs 20 D-Q STATIONARY FRAME TO D-Q SYNCHRONOUS FRAME 1 Vds_s Mux 2 f(u) 1 Vqs_s Vqs_e Fcn f(u) 2 Vds_e Fcn1 Mux Repeating Sequence 21 ELECTROMAGNETIC TORQUE AND SPEED EQUATION MODELING 22 1 Iqs-e Product1 2 Idr-e Gain4 Add -K- 1 Te Te 3 Ids-e 4 Product Iqr-e 1 Te 1 -K- 1 s Wm Speed 1/J Integrator TL B 23 Gain2 Vqs-e d(Iqs-e)/dt Vas d(Iqr-e)/dt u[1] Vqs_s Vqs_e Ids-e Iqs-e Vbs Iqs-e Vqs-s Idr-e Iqs-e Te Subsystem1 f(u) Vds_s Vds_e Vcs Iqs-e Vds-e Vds-s Wr d(Ids-e)/dt Idr-e d-q (S) To d-q (E) Transformation Iqs-e 1 Te -K- Iqr-e Ids-e s Gain1 Ids-e Ids-e Integrator d(Idr-e)/dt Ids-e Iqr-e Subsystem2 Electromagnetic Torque Calculation Vqr-e d(Iqr-e)/dt d(Iqs-e)/dt B Ids-e 0 Wr Gain2 Iqr-e Idr-e Constant Subsystem3 Step Vdr-e d(Idr-e)/dt Iqs-e Wr Iqr-e Idr-e d(Ids-e)/dt Subsystem 24 Overall IM Model 1-VECTOR CONTROL OF INDUCTION MOTOR Torque in separately excited dc motor Principles of vector control of Induction motor Torque equations for Vector Control Vector Control MATLAB/SIMULINK 25 TORQUE IN SEPARATELY EXCITED DC MOTOR 26 SIMPLE REPRESENTATION OF SEPARATELY EXCITED DC MOTOR. 27 PRINCIPLES OF VECTOR CONTROL OF INDUCTION MOTOR 28 PRINCIPLES OF VECTOR CONTROL (DECOUPLING BETWEEN ROTOR FLUX AND TORQUE) 29 DERIVATION OF THE ORIENTATION CONDITION 30 PROCEDURE IN THREE MAIN POINTS 31 THE PROCEDURE USING MATLAB/SIMULINK 32 33 The last step is to convert the gotten component of stator current in stationary reference frame to the desired three phase currents to be the base of control the inverter 34 THE SIMULINK MODEL OF THE FIELD ORIENTATION CONTROL (FOC) OF INDUCTION MOTOR. Scope Time 0.8 -K- ids iabc Landa_r* . ids iabc* N Vabc Vabc iqs iabc* Te iqs iabc Landa_s ev iqs* th Determing the state th Reference PI of the PWM TL Speed Current decoupling Landa_dr Output controller Landa_qr Terminator To Workspace IM1 Load Stator currents Rotor flux angle Actual speed 35 Overall FOC Model 2-DIRECT TORQUE CONTROL The basic concept of (DTC) method was proposed by Takahashi and Noguchi in 1986 It is more used in controlling the induction motor because it is considered a simple and robust method It has a very fast response and simple structure which makes it to be more popular used in industrial world It implies a comparative control of the torque and the stator fluxes which must fall into two separate certain bands (limits) to be applicable 36 SPACE VECTOR MODULATION OF THREE PHASE VOLTAGE SOURCE INVERTER WITH DTC voltage vector is shifted (lag or lead) with respect to the stator flux vector by an angle which is not more than 90°, this causes the flux to increase and vice versa The torque is then directly controlled by selecting the inverter situation in order to boost the stator flux up or buck it down. 37 SV-PWM 38 SV-PWM 39 BASIC PRINCIPLES OF SWITCHING TABLE 40 THE HYSTERESIS BAND CONTROLS THE STATOR FLUX VOLTAGE AND Increase Increase Increase Decrease 41 Decrease Decrease Decrease Increase THE SIMULINK MODEL OF DIRECT TORQUE CONTROL (DTC) OF INDUCTION MOTOR. 0.8 Landa_s* Output Interpreted iabc ev Te* Relay Vabc MATLAB Fcn N Relay1 Repeating PI MATLAB Fcn Te Sequence Landa_s TL th Step IM Scope3 42 Overall DTC Model LOOK-UP TABLE (SWITCHING TABLE) Sectors I II III IV V VI FU TU V2 V3 V4 V5 V6 V1 FU TD V6 V1 V2 V3 V4 V5 FD TN V7 V0 V7 V0 V7 V0 FD TU V3 V4 V5 V6 V1 V2 FD TD V5 V6 V1 V2 V3 V4 FD TN V0 V7 V0 V7 V0 V7 43 THEORETICAL COMPARISON VECTOR CONTROL AND DIRECT TORQUE CONTROL 44 SIMULATION RESULTS DTC Vs. FOC Speed Electromagnetic Torque Flux Three phase current 45 MOTOR SPEED RESPONSE. FOC DTC 400 350 300 250 200 Motor speed (r.p.m) Motor speed 150 100 50 0 0 1 2 3 4 5 6 7 Time (sec) 46 TORQUE RESPONSE FOC DTC 47 FLUX RESPONSE FOC DTC 0.9 0.9 0.8 0.8 0.7 0.7 0.6 0.6 0.5 0.5 0.4 0.4 Stator Flux (Wb) Stator Flux (Wb) 0.3 0.3 0.2 0.2 0.1 0.1 0 0 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Time (sec) Time (sec) 48 THREE PHASE MOTOR CURRENT FOC DTC 4 20 3 15 2 10 1 5 0 0 -1 Three phase motor current (Amp) motor current phase Three Three phase motor currenr (Amp) motor currenr phase Three -5 -2 -10 -3 -4 -15 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Time (sec) Time (sec) 49 THE DISTORTION OF THREE PHASE CURRENT FOC DTC 50 THE EFFECT OF VOLTAGE SAGS AND SHORT INTERRUPTION ON DRIVEN INDUCTION MOTORS (ASD) is considered as one of the sensitive loads to the voltage sag and short interruption That might cause the motor protection relay to trip, because the undervoltage of the DC link The ac current, which is feeding the motor, increases. The speed usually deviates and the torque varies [29] 51 THE CHARACTERISTICS OF THE VOLTAGE SAG AND SHORT INTERRUPTION Two main types of Voltage Sag and interruptions Balanced and Unbalanced 7 types of sags could happen as shown 52 SIMULATION RESULTS FOR THE CHOSEN PQ ISSUES The voltage sag types, which are used in this project thesis, are Type A (Balanced) and Type B (Unbalanced). The short interruption is applied on the two driving techniques too. 53 SIMULATION RESULTS FOR THE CHOSEN PQ ISSUES The affected DC Link Voltage For FOC Vs. DTC , I observe the following: Speed Variation Three Phase Current 54 THE AFFECTED DC LINK VOLTAGE One phase short interruption’s effect on DC link voltage (Type B) 55 DC VOLTAGE WAVE SHAPE UNDER THE EFFECT OF TWO TYPES OF VOLTAGE SAG CONDITION 56 TABLE THE DC LINK VOLTAGE IN DIFFERENT VOLTAGE SAG PERCENTAGES AND DIFFERENT DURATIONS (TYPE A) Sag Duration (Cycles) 18 cycles 22 cycles 26 cycles 30 cycles Voltages Sag (%) 20 % 314.75 314.6 314.51 314.2 40 % 236.5 236.4 236.4 236.4 60 % 159.7 156.28 156.26 156.26 80 % 155.4 126.2 102.49 83.55 100 % (interruption) 155.3 126.15 102.4 83.15 57 THE DC LINK VOLTAGE IN DIFFERENT VOLTAGE SAG PERCENTAGES AND DIFFERENT DURATIONS (TYPE A) 350 DC link in the normal operation is 400 Volt 18 cycles 22 cycles 26 cycles 300 30 cycles 250 200 DC link DC Voltage (Volt) 150 100 50 58 20 30 40 50 60 70 80 90 100 Voltage Dip (Sag) % SPEED VARIATION (DEVIATION) VOLTAGE SAG TYPE A FOC DTC 70 100 18 cycles 18 cycles 90 22 cycles 60 22 cycles 26cycles 26 cycles 80 30cycles Motor Stall 30 cycles 50 70 60 40 50 30 40 Speed Drop % from speed the Drop desired Speed 30 20 % from speed the desired Drop Speed 20 10 10