Synchronous motor drive

Synchronous motor drive, motor drive,power electronics

1. Laxmi Institute of Technology, Sarigam GTU Synchronous motor drive Subject : Power Electronics-2 (2150907 ) Presented by: Electrical [6 th Sem] SR.NO. NAME ENROLL NO. 1 PATIL GAURAV D. 150863109012 2 RAUT RITESH I. 150863109013 3 ROHIT VINAY K. 150863109014

2. Synchronous Motors Construction Stator identical to that of a three-phase induction motor – now called the “armature” Energize from a three-phase supply and develop the rotating magnetic field Rotor has a DC voltage applied (excitation) Rotor could be a permanent-magnet type Operation Magnetic field of the rotor “locks” with the rotating magnetic field – rotor turns at synchronous speed

3. Synchronous Motors A synchronous motor is the same physical machine as a generator, except that the direction of real power flow is reversed Synchronous motors are used to convert electric power to mechanical power Most synchronous motors are rated between 150 kW (200 hp) and 15 MW (20,000 hp) and turn at speed ranging from 150 to 1800 r/min. Consequently, these machines are used in heavy industry At the other end of the power spectrum, we find tiny single-phase synchronous motors used in control devices and electric clocks P , Q V t Motor

4. Operation Principle The field current of a synchronous motor produces a steady-state magnetic field B R A three-phase set of voltages is applied to the stator windings of the motor, which produces a three-phase current flow in the windings. This three-phase set of currents in the armature winding produces a uniform rotating magnetic field of B s Therefore, there are two magnetic fields present in the machine, and the rotor field will tend to line up with the stator field , just as two bar magnets will tend to line up if placed near each other. Since the stator magnetic field is rotating, the rotor magnetic field (and the rotor itself) will try to catch up The larger the angle between the two magnetic fields (up to certain maximum), the greater the torque on the rotor of the machine

5. Application of Synchronous Motors Synchronous motors are usually used in large sizes because in small sizes they are costlier as compared with induction machines. The principal advantages of using synchronous machine are as follows: Power factor of synchronous machine can be controlled very easily by controlling the field current. It has very high operating efficiency and constant speed. For operating speed less than about 500 rpm and for high-power requirements (above 600KW) synchronous motor is cheaper than induction motor. In view of these advantages, synchronous motors are preferred for driving the loads requiring high power at low speed; e.g ; reciprocating pumps and compressor, crushers, rolling mills, pulp grinders etc.

6. Salient-Pole Rotor Excitation Windings

7. Salient-Pole Rotor with brushless excitation

8. Synchronous Motor Starting Get motor to maximum speed (usually with no load) Energize the rotor with a DC voltage

9. Salient-Pole Motor operating at both no-load and loaded conditions Angle δ is the power angle , load angle , or torque angle

10. Rotor Structure Permanent-magnet or wound with a field winding

11. Synchronous Motor Drive Controller based on steady state operation

12. Self-controlled synchronous motor drive employing load commutated thyristor inverter Drive operating in true synchronous mode is shown in Fig. Frequency command is applied to a voltage source inverter through a delay circuit so that rotor speed is able to track the c angel in frequency. A flux control block changes stator voltage with frequency to maintain a constant flux below rated speed and a constant terminal voltage above rated speed. This scheme is commonly used for the control of multiple synchronous reluctance or permanent magnet motors in fiber spinning, textile and paper mills where accurate speed tracking between the motors is required.

13. Load-Commutated Inverter (LCI) Drive Used in very large power ratings

14. LCI Drive Controller Line converter controls the dc-link current

15. Operation of variable frequency control of multiple synchronous motor drive A self-controlled synchronous motor drive employing a load commutated thyristor inverter is shown in Fig. In large power drives wound field synchronous motor is used. Medium power drives also employ permanent magnet synchronous motor. The drive employs two converters, which are termed here as source side converter and load side converter. The source side converter-is a 6-pulse line-commutated thyristor converter described in Sec. 5.12. For a firing angle range 0 5 a, 5 90°, it works as a line-commutated fully controlled rectifier delivering positive Vds and positive id, and for the range of firing angle 90° 5 c4 5 180° it works as a line-commutated inverter delivering negative Vds and positive /d.

16. When synchronous motor operates at a leading power factor, thyristors of the load side convener can be commutated by the motor induced voltages in the same way, as thyristors of a line-commutated convener are commutated by line voltages. Commutation of thyristors by induced voltages of load (here load is a motor) is known as load commutation. Firing angle is measured by comparison of induced voltages in the same way as by the comparison of line voltages in a line commutated convener. Converter operates as an inverter producing negative Vdt and carrying positive for 90° 5 at < 180°. For 0 $ al 5 90° it works as a rectifier giving positive Vd ,. For 0 5 a, 5 90°, 90° 5 at 5 180° and with Vds > I/ di , the source side convener works as a rectifier and load side convener as an inverter, causing power to flow from ac source to the motor. thus giving motoring operation. When firing angles arc changed such that 90° 5 a, < 180 °.

17. Self controlled mode of operation of synchronous motor Self Control Mode In self control mode, the supply frequency is changed so that the synchronous speed is same as that of the rotor speed. Unlike, Separate control mode where the control inverter frequency is from an independent oscillator . Here the pulse train from position sensor may be delayed external command. The self controlled motor has the properties of a DC motor both under steady state and dynamic conditions and therefore, is called commutator less motor.