Presentation on theme: "Instructor: Eng. Jalal Al Roumy"— Presentation transcript:
1Instructor: Eng. Jalal Al Roumy بسم الله الرحمن الرحيمThe Islamic University of GazaFaculty of EngineeringElectrical Engineering DepartmentPOWER ELECTRONICSEELE 5450 — Summer 2012Instructor: Eng. Jalal Al RoumyLecture 16
2A Free-Wheeling Diode DC Motor Drive Using the Jones Chopper Chapter sixA Free-Wheeling Diode DC Motor Drive Using the Jones ChopperThis circuit is frequently referred to as a chopper circuit.
3Operation of the Jones Commutation circuit Chapter sixOperation of the Jones Commutation circuitThe 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)
4Operation of the Jones Commutation circuit Chapter sixOperation of the Jones Commutation circuitInitially SCR1 and SCR2 are not conducting and the side B of the capacitor C is charged to a negative voltage (from last SCR2”on”).
5At 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
6The capacitor retains its charge until SCR2 is triggered at t3
7The discharged of capacitor C reverse biased SCR1 and turn it off.
8C 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.
9The autotransformer action of T1 induced voltage in L2 of correct polarity for charging the commutating capacitor to a voltage > VB
10The bottom plate (B) of capacitor C reaches a peak value at t5.
11Since Vc (at t5) is charged to a voltage greater than VB, D2 is again forward biased. C discharges to a value lower than VB .
12The 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.
13The discharging of C stop at t7 when current through L2 falls to zero.
14The cycle repeats itself when SCR1 is again triggered.
15Design of the Jones commutation circuit Chapter sixDesign of the Jones commutation circuitThe basic design of the commutating circuit involves the proper choice of ‘C’ and autotransformer T1
16Design of the Jones commutation circuit Chapter sixDesign of the Jones commutation circuitThe 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