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بسم الله الرحمن الرحيم. The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department. POWER ELECTRONICS . EELE 5450 — Summer 2012. Instructor: Eng. Jalal Al Roumy. Lecture 16. Chapter six.

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## POWER ELECTRONICS

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**بسم الله الرحمن الرحيم**The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department POWER ELECTRONICS EELE 5450— Summer 2012 Instructor: Eng. Jalal Al Roumy Lecture 16**Chapter six**A Free-Wheeling Diode DC Motor Drive Using the Jones Chopper This circuit is frequently referred to as a chopper circuit.**Chapter six**Operation of the Jones Commutation circuit The Jones circuit is an efficient commutating method to turn off the main SCR in the dc chopper circuit. The circuit characterized by class D commutation (charged capacitor switched by SCR2 and T1) (Ton and Toff can be varied)**Chapter six**Operation of the Jones Commutation circuit Initially SCR1 and SCR2 are not conducting and the side B of the capacitor C is charged to a negative voltage (from last SCR2”on”).**At time t1 SCR1 is triggered ,and the current passed through**the load. Commutating current through SCR1,L2, D2 and C charges up the capacitor to opposite polarity, B is positive**The capacitor retains its charge until SCR2 is triggered at**t3**The discharged of capacitor C reverse biased SCR1 and turn**it off.**C again charges up with A positive(energy in L1) and SCR2**turns off because its current falls below the holding value when C is recharged.**The autotransformer action of T1 induced voltage in L2 of**correct polarity for charging the commutating capacitor to a voltage > VB**The bottom plate (B) of capacitor C reaches a peak value at**t5.**Since Vc (at t5) is charged to a voltage greater than VB, D2**is again forward biased. C discharges to a value lower than VB .**The blocking voltages across SCR1 and SCR2 also changes (t5**to t6). The turn off time of SCR2 must be less than the time from t5 to t6.**The discharging of C stop at t7 when current through L2**falls to zero.**Chapter six**Design of the Jones commutation circuit The basic design of the commutating circuit involves the proper choice of ‘C’ and autotransformer T1**Chapter six**Design of the Jones commutation circuit • The magnitude of the commutating capacitor is dependent on the following circuit parameters: • Maximum motor current to be commutated, Im. • Turn-off time,t0, of SCR1. • The battery voltage, VB. End of Lecture

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