1. Instructor: Eng. Jalal Al Roumy
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

2. A Free-Wheeling Diode DC Motor Drive Using the Jones Chopper
Chapter six
A Free-Wheeling Diode DC Motor Drive Using the Jones Chopper
This circuit is frequently referred to as a chopper circuit.

3. Operation of the Jones Commutation 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)

4. Operation of the Jones Commutation circuit
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”).

5. 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

6. The capacitor retains its charge until SCR2 is triggered at t3

7. The discharged of capacitor C reverse biased SCR1 and turn it off.

8. 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.

9. The autotransformer action of T1 induced voltage in L2 of correct polarity for charging the commutating capacitor to a voltage > VB

10. The bottom plate (B) of capacitor C reaches a peak value at t5.

11. 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 .

12. 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.

13. The discharging of C stop at t7 when current through L2 falls to zero.

14. The cycle repeats itself when SCR1 is again triggered.

15. Design of the Jones commutation circuit
Chapter six
Design of the Jones commutation circuit
The basic design of the commutating circuit involves the proper choice of ‘C’ and autotransformer T1

16. Design of the Jones commutation circuit
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