B.Tech(EEE)_SOLID STATE DRIVES AND CONTROL_EE0401_4TH YEAR_7TH SEMESTER_
- 2. INTRODUCTION Modern machinery or Production systems such as rolling mills, textile mills, domestic application machines consist of a large number of different parts. Each of these different parts are assigned for a definite function with different modes of motions which requires control. Systems employed for motion control are called Drives and may employ any of prime mover types, such as diesel engines, steam engines, electric motors, etc. Drives employing electric motors along with its controller are known as Electrical Drives which this course is concerned. ELECTRICAL DRIVES
- 3. Advantages of Electrical Drives •They have flexible control characteristics. - The steady state and dynamic characteristics of electrical drives can be shaped to satisfy load requirements. Employment of semiconductor devices like thyristors, power transistors, IGBTs, GTOs, digital ICs, microprocessors made the control characteristics more flexible. Starting and braking is usually simple and easy to operate. •They are available in wide range of torque, speed and power. •Electrical motors have high efficiency, low no load losses, and considerable short time overload capacity.
- 4. • They are adaptable to almost any operating conditions Such as explosive and radioactive environments, submerged in liquids, etc. • Can operate in all the four quadrants of speed- torque plane. • Do not pollute the environment. • Unlike other prime movers, there is no need to refuel or warm-up the motor. • They are powered by electrical energy which has a number of advantages over other forms of energy etc..
- 5. PARTS OF ELECTRICAL DRIVES •Electrical drive has the following major parts: - - Power source - Power modulator - Control unit - Motor - Load • There are large number of loads and each load has its own specific requirements. Load is a machinery designed to accomplish a given task; eg. Washing machines, machine tools, drills, pumps, etc. • Usually load requirements can be specified in terms of speed and torque demands.
- 6. •A Motor having speed-torque characteristics and capabilities compatible to the load requirements is chosen. Block Diagram of an electrical Drive Sourc e Power Modulator Motor Load Sensing unit Control unit Input command
- 7. POWER SOURCE •Power sources are usually are AC (fixed voltage fixed frequency) and DC (fixed voltage ) • In electrical drive system, electrical motors use mainly these two types of electrical power sources. • Ac source can be single phase or three phase from utility transmission or other sources. • Dc source can be from dc generator, converted from AC, battery bank, etc. •For the control of Dc motors one requires, variable dc voltage source, whereas for ac motors one requires either fixed frequency variable voltage, variable frequency fixed voltage or variable frequency variable voltage ac sources. •These motor requirements are met by different convertors and their combinations.
- 8. POWER MODULATOR • Power modulator performs one or more of the following four functions. i) Modulates flow of power from the source to the motor in such a manner that motor is imparted speed- torque characteristics required by the load. ii) During transient operations, such as starting braking and speed reversal, it restricts source and motor currents within permissible values. iii) Converts electrical energy of the source in the form suitable to the motor. i.e., if the source is DC and an induction motor is to be used, then the power modulator is required to convert DC into AC. (convertors) iv) Selects the mode of operation of the motor, i.e. motoring or braking.
- 9. • Controls for power modulators are built in control unit which usually operates at much lower voltage and power levels. The control unit may also generate command signal which adjusts the operating point of the drive and for the protection of power modulator and motor . Sensing of certain drive parameters, such as motor current and speed, may be required either for protection or for closed loop operation. •Power modulators can be classified in to : - a) Convertors b) Variable impedances c) Switching circuits
- 10. a) Convertors: - • Convertors are devices needed when nature of the available electrical power is different than what is required for the motor. Convertors can be: - 1. AC to DC convertors (Rectifiers) Uncontrolled rectifiers (Diode rectifiers ) used to get dc Supply of fixed voltage from ac supply of fixed voltage. Controlled convertors used to get Variable voltage dc supply from fixed ac supply. eg. - Fully controlled thyristors rectifier; - Half controlled thyristors rectifier; - Transformer with taps and rectifiers; - Rectifiers with self
- 11. 2. Ac voltage controllers or regulators Autotransformer of Fixed turns ratio Fixed voltage 1 or 3-phase ac Lower (fixed) AC voltage Fixed voltage 1 or 3-phase ac Transforme r with taps Variable voltage AC Fixed voltage 1 or 3-phase ac Thyristors voltage controllers Variable voltage AC Fixed voltage 1 or 3-phase ac Magnetic amplifier Variable voltage AC
- 12. 3.Choppers or Dc converters • They are used to get DC Variable voltage from fixed dc voltage and are designed using semiconductor devices such as power transistors, IGBTs, GTOs, power MOSFETs and thyristors. 4. Inverters • Inverters are employed to get a variable frequency ac supply from a dc supply. Fixed voltage DC Semiconductor Chopper Variable voltage DC Fixed voltage DC PWM Semiconductor inverter Variable frequency and Variable voltage AC
- 13. 5.Cycloconverters; • Are used to convert fixed voltage and frequency ac to variable voltage and variable frequency ac. They are built from thyristors and are controlled by firing signals from control unit. b) Variable impedances Variable resistors are commonly used for the control of low cost dc and ac drives and are also needed for dynamic braking of drives. Fixed frequency And Fixed voltage ac Cycloconverters Variable frequency And variable voltage ac
- 14. -Variable resistors may have two (full and zero) or more steps and can be controlled manually or automatically. Step-less variation of resistance can be obtained using a semiconductor switch in parallel with a fixed resistor. C) Switching Circuits Switching operations are required to achieve any one of the following; - for changing motor connections to change its quadrant of operation; - for changing motor circuit parameters in discrete steps for automatic starting and braking control; - for operating motors and drives according to a predetermined sequence; - to provide interlocking to prevent maloperation; - to disconnect motor when abnormal operating conditions occur. Switching operations in motor’s power circuits are carried out by contactors, relays (electromechanical, solid state), limit switches, PLCs etc.
- 15. Assignment 1 1. State the essential parts of electrical drives. What are the functions of power modulators? 2. State and explain the function of various converters. 3. What are the main factors which decide the choice of electrical drives for a given application? 4. What is the current status of AC and DC drives? 5. Write a brief note on the sources employed in electrical drives.
- 16. Power Electronic Systems What is Power Electronics ? A field of Electrical Engineering that deals with the application of power semiconductor devices for the control and conversion of electric power Power Electronics Converters Load Controller Output - AC - DC Input Source - AC - DC - unregulated Reference POWER ELECTRONIC CONVERTERS – the heart of power a power electronics system sensors
- 17. Power Electronic Systems Why Power Electronics ? Power semiconductor devices Power switches ON or OFF + vsw − = 0 isw + vsw − isw = 0 Ploss = vsw× isw = 0 Losses ideally ZERO !
- 18. Power Electronic Systems Why Power Electronics ? Power semiconductor devices Power switches - Vak + ia G K A - Vak + ia K A - Vak + ia G K A
- 19. Power Electronic Systems Why Power Electronics ? Power semiconductor devices Power switches D S G + VDS - iD G C E + VCE - ic
- 20. Power Electronic Systems Why Power Electronics ? Passive elements High frequency transformer + V1 - + V2 - Inductor + VL - iL + VC - iC
- 21. Power Electronic Systems Why Power Electronics ? Power Electronics Converters sensors Load Controller Output - AC - DC Input Source - AC - DC - unregulated Reference IDEALLY LOSSLESS !
- 22. Power Electronic Systems Why Power Electronics ? Other factors: • Improvements in power semiconductors fabrication • Decline cost in power semiconductor • Advancement in semiconductor fabrication • ASICs • FPGA • DSPs • Faster and cheaper to implement complex algorithm • Power Integrated Module (PIM), Intelligent Power Modules (IPM)
- 23. Power Electronic Systems Some Applications of Power Electronics : Power rating of < 1 W (portable equipment) Tens or hundreds Watts (Power supplies for computers /office equipment) Typically used in systems requiring efficient control and conversion of electric energy: Domestic and Commercial Applications Industrial Applications Telecommunications Transportation Generation, Transmission and Distribution of electrical energy kW to MW : drives Hundreds of MW in DC transmission system (HVDC)
- 24. Modern Electrical Drive Systems • About 50% of electrical energy used for drives • Can be either used for fixed speed or variable speed • 75% - constant speed, 25% variable speed (expanding) • Variable speed drives typically used PEC to supply the motors AC motors - IM - PMSM DC motors (brushed) SRM BLDC
- 25. Modern Electrical Drive Systems Classic Electrical Drive for Variable Speed Application : • Bulky • Inefficient • inflexible
- 26. Modern Electrical Drive Systems Power Electronic Converters Load Motor Controller Reference POWER IN feedback Typical Modern Electric Drive Systems Power Electronic Converters Electric Energy - Unregulated - Electric Energy - Regulated - Electric Motor Electric Energy Mechanical Energy
- 27. Modern Electrical Drive Systems Example on VSD application motor pump valve Supply Constant speed Variable Speed Drives Power In Power loss Mainly in valve Power out
- 28. Modern Electrical Drive Systems Example on VSD application Power In Power loss Mainly in valve Power out motor pump valve Supply motor PEC pump Supply Constant speed Variable Speed Drives Power In Power loss Power out
- 29. Modern Electrical Drive Systems Power In Power loss Mainly in valve Power out Power In Power loss Power out motor pump valve Supply motor PEC pump Supply Constant speed Variable Speed Drives Example on VSD application
- 30. Modern Electrical Drive Systems Electric motor consumes more than half of electrical energy in the US Fixed speed Variable speed HOW ? Improvements in energy utilization in electric motors give large impact to the overall energy consumption Replacing fixed speed drives with variable speed drives Using the high efficiency motors Improves the existing power converter–based drive systems Example on VSD application
- 31. DC drives: Electrical drives that use DC motors as the prime mover Regular maintenance, heavy, expensive, speed limit AC drives: Electrical drives that use AC motors as the prime mover Less maintenance, light, less expensive, high speed Modern Electrical Drive Systems Overview of AC and DC drives Easy control, decouple control of torque and flux Coupling between torque and flux – variable spatial angle between rotor and stator flux
- 32. Before semiconductor devices were introduced (<1950) • AC motors for fixed speed applications • DC motors for variable speed applications After semiconductor devices were introduced (1960s) • Variable frequency sources available – AC motors in variable speed applications • Coupling between flux and torque control • Application limited to medium performance applications – fans, blowers, compressors – scalar control • High performance applications dominated by DC motors – tractions, elevators, servos, etc Modern Electrical Drive Systems Overview of AC and DC drives
- 33. After vector control drives were introduced (1980s) • AC motors used in high performance applications – elevators, tractions, servos • AC motors favorable than DC motors – however control is complex hence expensive • Cost of microprocessor/semiconductors decreasing –predicted 30 years ago AC motors would take over DC motors Modern Electrical Drive Systems Overview of AC and DC drives
- 34. Overview of AC and DC drives Extracted from Boldea & Nasar Modern Electrical Drive Systems
- 35. Power Electronic Converters in ED Systems Converters for Motor Drives (some possible configurations) DC Drives AC Drives DC Source AC Source AC-DC-DC AC-DC AC Source Const. DC Variable DC AC-DC-AC AC-AC NCC FCC DC Source DC-AC DC-DC-AC DC-DC DC-AC-DC
- 36. Power Electronic Converters in ED Systems Converters for Motor Drives Configurations of Power Electronic Converters depend on: Sources available Type of Motors Drive Performance - applications - Braking - Response - Ratings
- 37. Power Electronic Converters in ED Systems DC DRIVES Available AC source to control DC motor (brushed) AC-DC-DC AC-DC Controlled Rectifier Single-phase Three-phase Uncontrolled Rectifier Single-phase Three-phase DC-DC Switched mode 1-quadrant, 2-quadrant 4-quadrant Control Control
- 38. Q1 Q2 Va Ia T1 T2 D1 + Va - D2 ia + Vdc D2 conducts va = 0 Va Eb T1 conducts va = Vdc Quadrant 1 The average voltage is made larger than the back emf DC DRIVES AC-DC-DC DC-DC: Two-quadrant Converter Power Electronic Converters in ED Systems
- 39. Q1 Q2 Va Ia T1 T2 D1 + Va - D2 ia + Vdc D1 conducts va = Vdc DC DRIVES AC-DC-DC DC-DC: Two-quadrant Converter Power Electronic Converters in ED Systems
- 40. Q1 Q2 Va Ia T1 T2 D1 + Va - D2 ia + Vdc T2 conducts va = 0 Va Eb D1 conducts va = Vdc Quadrant 2 The average voltage is made smallerr than the back emf, thus forcing the current to flow in the reverse direction DC DRIVES AC-DC-DC DC-DC: Two-quadrant Converter Power Electronic Converters in ED Systems
- 41. DC DRIVES AC-DC-DC DC-DC: Two-quadrant Converter + vc 2vtri vc + vA - Vdc 0 Power Electronic Converters in ED Systems
- 42. leg A leg B + Va Q1 Q4 Q3 Q2 D1 D3 D2 D4 + Vdc va = Vdc when Q1 and Q2 are ON Positive current Power Electronic Converters in ED Systems DC DRIVES AC-DC-DC DC-DC: Four-quadrant Converter
- 43. leg A leg B + Va Q1 Q4 Q3 Q2 D1 D3 D2 D4 + Vdc va = -Vdc when D3 and D4 are ON va = Vdc when Q1 and Q2 are ON va = 0 when current freewheels through Q and D Positive current Power Electronic Converters in ED Systems DC DRIVES AC-DC-DC DC-DC: Four-quadrant Converter
- 44. va = -Vdc when D3 and D4 are ON va = Vdc when Q1 and Q2 are ON va = 0 when current freewheels through Q and D Positive current va = Vdc when D1 and D2 are ON Negative current leg A leg B + Va Q1 Q4 Q3 Q2 D1 D3 D2 D4 + Vdc Power Electronic Converters in ED Systems DC DRIVES AC-DC-DC DC-DC: Four-quadrant Converter
- 45. va = -Vdc when D3 and D4 are ON va = Vdc when Q1 and Q2 are ON va = 0 when current freewheels through Q and D Positive current va = -Vdc when Q3 and Q4 are ON va = Vdc when D1 and D2 are ON va = 0 when current freewheels through Q and D Negative current leg A leg B + Va Q1 Q4 Q3 Q2 D1 D3 D2 D4 + Vdc Power Electronic Converters in ED Systems DC DRIVES AC-DC-DC DC-DC: Four-quadrant Converter