Electric Drives EEP 436 Course Contents PDF

Electric Drives EEP 436 Course Contents: Components and Properties of electric drive systems. Types of loads and Four-quadrant operation. Motor Sizing Thermal consideration and duty Types DC Drives: o Fundamentals of DC machine Speed Control. o...

Electric Drives EEP 436 Course Contents: Components and Properties of electric drive systems. Types of loads and Four-quadrant operation. Motor Sizing Thermal consideration and duty Types DC Drives: o Fundamentals of DC machine Speed Control. o Open-loop and closed-loop speed control Induction Motor (IM) Drives: o Fundamentals of IM Speed Control. o 3-phase voltage source inverters (VSI). o 3-phase AC voltage controllers. o Open loop V/f speed control. o Closed loop V/f speed control. o Braking techniques. Electric Drives Dr. Ayman Abdel-Khalik 1 o Vector control and DC machine control analogy. Electric Drives Text Book 1. Fundamentals of Electrical Drives, Mohamed El-Sharkawy, Brooks/Cole, 2000. 2. Electric Drives: An Integrative Approach, Ned Mohan. 3. The induction Machine Handbook, I. Boldea, S. Nassar. Type Marks Projects 5 Assessment Lab. 20 Mid term 25 Final Exam 50 2 Motion Control and Servo Systems In control engineering, a servomechanism is an automatic device that uses error-sensing negative feedback to correct the action of a mechanism. It comprises a built-in position/speed feedback mechanism to ensure the output is achieving the desired position/speed. Drive systems that employ Electric Motors as prime movers are called Electric Drive Systems. The combination of electric motor, transmission and control equipment is nominated as Electric Drive Systems 3  Reasons for Using Variable Speed Drives (VSDs) There are many and diverse reasons for using VSDs. Some applications, such as paper making machines, cannot run without them while others, such as centrifugal pumps, can benefit from energy savings. In general, VSDs are used to: 1. Match the motor speed/torque to the process requirement. 2. Save energy and improve efficiency. 4 WARD LEONARD System for Variable Speed Applications Ward Ward Leonard control system is introduced by Henry Ward Leonard in 1891. Disadvantages Disadvantages very costly (Multi- machine system). low efficiency. Large size and weight. 5 Types of Electric Drives Based on the motor type, the electric drive systems are classified into: 1) DC Drive systems Pros: Simple control. Cons: Regular maintenance, heavy, expensive, limited speed. They are usually proposed for applications requiring high performance such as tractions, elevators, servos servos,, etc. 2) AC drive systems Pros: Less maintenance, lighter, less expensive, wide speed 6 Types of Electric Drives Before power electronics development: DC drives were commonly have been used in Variable Speed + High Performance Applications. AC drives were usually employed in Fixed Speed Applications. After introducing Vector Control of AC drives in 1980, the AC drives have now been favored in most industrial applications with the notable cost drop in semiconductor devices and microprocessors microprocessors.. 7 Types of Electric Drives Classical Drive Systems: Motors are directly fed from mains Solid State Drives: Best suitable for VSDs applications The trade-off between the two types depends on many factors including: Technology and application. Performance Capabilities. Motor cost. Additional System Component Costs. 8 Components of Solid –State Drive Systems 9 1) Power Source Available supplies are commonly: DC: Batteries, fuel cells, photovoltaic AC: Single- or three-phase utility. These supplies are even unregulated or fixed voltage/frequency supplies. 10  2) Driving Motor Electric motors exhibit wide variations of torque-speed characteristics suitable for different mechanical loads. The basic criterion in selecting an electric motor for a given drive application is to meet the required power level and performance during steady-state as well as dynamic operations. DC motors motors:: Permanent magnet or wound field motor AC motors motors:: Induction, Synchronous, PMSM, Brushless DC. Special motors motors:: Universal motors, switched reluctance motors (SRM), stepper motors, etc. 11 2) Driving Motor (Cont.) The machine selection depends on the following: a) Electrical considerations c) Size and ratings of motors Running Load duty cycle characteristics Heating and cooling time Starting characteristics constants of the electric motor Speed control Overload capacity Braking characteristics d) Cost considerations b) Mechanical consideration Initial cost Type of enclosure Running cost Type of bearings Transmission Noise 12 3) Power Electronic Converter PEC (or Power Modulator) Function: To provide a regulated power supply. PEC depends on the motor type and the available supply. May be a single power converter or a combination of different converters. 13  4) Controller The controller complexity depends on the performance requirements. Can be classified into: Analogue: Inflexible. Digital: Configurable. PLCs, DSPs/Microprocessor: flexible and can perform complex control functions. Electric (or Galvanic) isolation between control and power circuits is mandatory for: 1) Safety. 2) avoiding malfunction/damaging of control circuit. 14  5) Mechanical Loads Loads are classified into: 1) Active loads They are associated with either gravitational or elastic deformation of bodies such as spring action. Appears as a result to the change in potential energy. 2) Passive loads They are mainly due to friction, shear or deformation in non-elastic bodies. Always opposes motion (speed and torque are in opposite directions). Such as lathes, fans, and pumps. 15 Passive Load 16 Basic Types of Passive Loads 1) Dry Friction Load ((Torque Torque independent of speed speed)) Such as pumping of water or gas against constant pressure. 2) Viscous friction loads ((Torque Torque linearly dependent on speed speed)) Such as eddy current brakes, machine tools, servo. 3) Torque proportional to the square of speed Such as fans, centrifugal pumps, and propellers. 4) Torque inversely proportional to the speed Such as milling, lathes, and boring machines. 17 Advantages of Solid-State Electric Drives The solid-state drives have many outstanding merits over classical drive systems, including including: Flexible control characteristics: The steady-state and dynamic characteristics of electric drives can easily be shaped to satisfy the load requirements. Available in wide range of torque and speed. Adaptable to different operating conditions in normal and hazardous environments. Automatic fault detection and ride-through capability. 18 Advantages of Solid-State Electric Drives (Cont.) They easily offer a four-quadrant operation. Energy saving and high efficiency. High power factor operation. Facility for remote control. Compactness and less floor space. Quiet. 19  Forms of Electric Drive systems 1) Individual Electric Drive (Single-motor, single-load drives): This is the most common form of electric drive. A single motor is is It dedicated to aflexible safer and single load. in spite of the associated higher initial cost. Applications include household equipment, drills, fans, hard disc, washers, and dryers. 20 Forms of Electric Drive systems (Cont.) 2) Line Shaft or Group Drives: They consist of a single electric motor driving multiple loads through a common line shaft and/or driving belts. Advantages: Low initial cost. Motor rating will be less than the summation of individual loads. Disadvantages: Motor failure yields a whole system shut down. Inflexible speed control, high noise, and high mechanical losses. 21 Forms of Electric Drive systems (Cont.) 3) Multi-Motor Drives: Several motors are used to drive a single mechanical load. Applications such as airplane actuation system, cranes and robots 22 Driving Cycle Intervals of A Drive System Any driving cycle usually comprises acceleration, steady-state operation, and deceleration intervals. 23 Dynamic Equations of Electric Drives The dynamic equations of an electric drive is governed by the Newton’s second law of motion. The simplest drive system comprises a rotating load directly coupled to the motor. Te : Motor torque. TL : Equivalent load torque Jeq : Equivalent inertia (Jeq = Jm+JL) beq : Equivalent friction (beq = bm+bL) Keq : Equivalent stiffness Note: All values should be referred to the motor side. 24 Steady-State Stability Stability condition Operating point A is stable, but B is unstable Technical Seminar 25 Gear Input/output relations Assuming 100% gear efficiency, then: 26 Gear Transmission (Speed reducer) 27 Equation of Motion Translational motion (Newton’s law) Rotational motion : Accelerating torque which presents during speed transients 28 Equation of Motion Combination of rational and translational motions Equivalent moment inertia of the linearly moving mass 29 How To Refer System to Motor Side The load is coupled to the motor through a gearbox with a ratio nm : nL. The concept of referring depends on the fact that the kinetic energy and power transferred from the motor to load do not change through the gear system. 30 Translational to Rotating Motion For same kinetic energy, then, 31 Example Find the equivalent motor torque, inertia, and friction 1) Cylindrical load: 2) Winch load: 4) Viscous friction: 5) Fan: 3) Dry friction: 32  Motion Profiles There are two commonly used motion profiles: Trapezoidal velocity profile (for analysis) S-curve velocity profile (practical) The trapezoidal velocity profile is popular due to its simplicity. The S-curve velocity profile leads to smoother motion. 33 Motion Profiles The jerk (also called jolt) of trapezoidal velocity profile is infinite at four points in this motion profile due to the discontinuities in the acceleration at corners of the velocity profiles. S-curve motion profiles reduce abrupt acceleration changes and thereby smooth out the motion. 34 Example A single-axis conveyor vehicle is designed. The vehicle is driven in x-axis via toothed belt with the following parameters and the shown speed profile: Parameter Value Mass to be transported M = 400kg Wheel diameter D = 0.14m Max. Speed Max. acceleration/deceleration Distance travelled S = 2m Cycle time 7s Gearbox ratio 10 Mechanical efficiency η = 100% Specific travelling resistance Motor inertia Jm=0.0065kg.m2 35 Load Side (Linear Motion) 36 Load Side (Angular motion) 37 Motor Side(Angular motion) 38 Effect of Gearing-Equivalent System Inertia For previous example 39 Load and Motor Steady-State Torque 40 Total Torque Rated torque: RMS of the torque curve 41 Four-Quadrant Operation During a driving cycle, the machine may act as a motor in either directions of rotation, or in some instances as a generator or brake depending on the terminal conditions. 42 Four-Quadrant Operation T and N directions under different quadrants of a complete driving cycle. 43 Four-Quadrant Operation Using Hoisting System The weight of the counterweight is adjusted to be higher than the unloaded cage and less than the 200+400 loaded one (Typically ½ the weight 300k 200k 300k = 600kg g of fully loaded cabin). g g In quadrants 1 & 3, the machine runs as a motor (Speed and torque have the same directions). In quadrants 2 & 4, the machine acts as a generator or brake 300k (Speed and torque have opposite g 200k 300k 600k g g g directions). 44 Motor Sizing What is Sizing? Finding the best motor for certain application. There are many factors are used to determine the best motor. What is Sizing? Motion profile Must be balanced Cost Inertia against others Resolution requirements Speed Environment Acceleration Power requirements Torque. Physical size limitation Regenerative capacity Overload capacity 45 Four Key Sizing Factors 1. Inertia Ratio 2. Speed 3. Max torque at rated speed 4. RMS torque at rated speed JMotor is found in catalog JLoad represents the equivalent total load inertia at the motor side (calculated) Torque-speed capability curve 46 Inertia Ratio Specification 5:1 typical 2:1 or less for highest dynamic performance 10:1 or higher when performance is not critical Ease of control loop tunning and machine dynamic performance go up as inertia ratio goes down. However, low inertia ratio may entail oversized motor, which can be avoided by using gear transmission. 47 Speed-Torque Curve 48 Motor Rating The RMS torque point of the torque profile must lay in the continuous region. 49 Max and RMS Torques Maximum torque at the application speed ideally falls in the intermittent region. If falls in the continuous region, this indicates an over sized motor. RMS torque is equivalent to steady-state torque. 50 YASKAWA SigmaSelect https://www.youtube.com/watch?v=4MaGqSQfYOk&ab_channel=YaskawaAmerica https://www.youtube.com/watch?v=ZqupnFfCj7k&ab_channel=YaskawaAmerica 51 Selection of Motor Rating and Thermal Considerations Generally, the motor size and rating depend upon the following factors:- 1. Heating effects 2. Load conditions and duty type 3. Load Inertia 4. Environmental Conditions Technical Seminar 52 Motor Heating and Cooling Technical Seminar 53 Motor Thermal Model 54 Heating and Cooling Time Constants 55 Insulation Classes for Electric Motors NEMA motor insulation classes describes the ability of motor insulation in the windings to handle heat. There are four insulation classes in use namely: A, B, F, and H. All four classes identify the allowable temperature rise from an ambient temperature of 40° C (104° F). Classes B and F are the most common in many applications. Temperature rises in the motor windings as soon as the AC motor is started. Maximum Maximum Maximum Winding Hot-spot Over Class Ambient Temperature Rise Temperature Temperature (°C) Temperature (°C) (°C) (Tmax)(°C) A 40 60 5 105 B 40 80 10 130 F 40 105 10 155 H 40 125 15 180 56 Insulation Classes for Electric Motors (Cont.) If the motor is operated at a higher winding temperature, service life will be reduced. A As a rule, a 10° C increase in the operating temperature above the allowed maximum can cut the motor’s insulation life expectancy in HALF. Hot-spot Over Temperature Allowance Each insulation class has a margin allowed to compensate for the motor’s hot spot. The hot-spot is a point at the center of the motor windings where the temperature is higher. As can be seen from the above table, hot-spot over temperature allowance for A, B, F and H are respectively 5°C, 10°C, 10°C and 15°C. When replacing a motor, extreme care must be taken not to choose a motor with the wrong insulation class. It is advisable therefore to replace a motor with one having an equal or higher insulation class. Replacement with one of lower temperature rating could result in premature failure of the motor. 57 Example Technical Seminar 58 IEC 60034-1 electric motor duty cycles For an electrical motor, number of starting and braking per unit of time have a large incidence on the internal temperature. The IEC (International Electrotechnical Commission) publishes IEC 60034-1, Rotating electrical machines - Part 1: Rating and performance, which contains classifications for duty cycles to describe motor operating conditions. It is vital to know the differences between these duty cycles and to note what mode of operation each rating refers to. Importantly, establishing the duty cycle of a motor and drive for a given application will help to save costs. 59 Duty type S1 – Continuous running duty Operation at a constant load maintained for sufficient time to allow the machine to reach thermal equilibrium. 60 Duty Type S2 – Short-time duty Constant-load operation for a given period of time, less than required to reach thermal equilibrium, followed by a pause to restore thermal equilibrium between the machine and the surrounding coolant at around 20° C. Ex: S2 60min 61 Duty type S3 – Intermittent periodic duty Series of identical cycles, each with a period of operation and a pause. The starting current in this type of duty is such that it has no significant effect on heating. Recommended values for the cyclic duration factor are 15, 25, 40, and 60 percent. Ex: S3 15% 62 Duty type S4 – Intermittent periodic duty with starting Series of identical cycles, each with a significant starting period, a period of constant-load operation and a pause 63 Motor Nameplate 64 Electric Motor Ingress Protection (IP) Ratings The Ingress Protection (IP) rating of a motor shows how well it protects against both water and solid foreign objects such as dust. Usually found on the motor nameplate, this information is crucial when choosing an electric motor as it ensures that the enclosure can protect the motor from the environment it is operating in. 65 IP Ratings 66