two-quadrant converter t1 conducts v a = v dc q1q2 vava iaia t1 t2 d1 +va-+va- d2 iaia + v dc
Post on 14-Dec-2015
217 Views
Preview:
TRANSCRIPT
Two-quadrant converter
T1 conducts va = Vdc
Q1Q2
Va
Ia
T1
T2
D1
+
Va
-
D2
ia
+
Vdc
Two-quadrant converter
Q1Q2
Va
Ia
T1
T2
D1
+
Va
-
D2
ia
+
Vdc
D2 conducts va = 0 T1 conducts va = Vdc
Quadrant 1 The average voltage is made larger than the back emf
Two-quadrant converter
Q1Q2
Va
Ia
T1
T2
D1
+
Va
-
D2
ia
+
Vdc
T2 conducts va = 0
Quadrant 2 The average voltage is made smaller than the back emf, thus forcing the current to flow in the reverse direction
Two-quadrant converter
Q1Q2
Va
Ia
T1
T2
D1
+
Va
-
D2
ia
+
Vdc
D1 conducts va = Vdc
5
Chopper fed DC drive Four-quadrant Chopper
+ Va Q1
Q2
Q3
Q4
D1 D3
D4D2
+
Vdc
Q1 & Q4 is ON
Current Flow : Vdc + _ Q1 _Motor_Q4_Vdc-
Current Ia & Va are positive
Operates in First Quadrant
Forward Motoring
Va
Ia
6
Chopper fed DC drive Four-quadrant Chopper
+ Va Q1
Q2
Q3
Q4
D1 D3
D4D2
+
Vdc
Q1 is OFF & Q4 is ON. Inductor current has to flow in the same Direction.
Diode D2 is FB
Inductor Current freewheels through D2 & Q4
Output Voltage is Zero
7
Chopper fed DC drive Four-quadrant Chopper
+ Va Q1
Q2
Q3
Q4
D1 D3
D4D2
+
Vdc
Q4 is OFF. Q2 is ON. Load is not connected with the source.
Back Emf drives the current through Q2 & D4
8
Chopper fed DC drive Four-quadrant Chopper
+ Va Q1
Q2
Q3
Q4
D1 D3
D4D2
+
Vdc
Q2 is OFF. Diode D1 is FB
Current flows through D4 & D1
Current Ia is negative & Va is positive.
Operates in second quadrant.
Va
Ia
Forward Braking
9
Chopper fed DC drive Four-quadrant Chopper
- Va +Q1
Q2
Q3
Q4
D1 D3
D4D2
+
Vdc
Q3 & Q2 is ON
Current Flow : Vdc + _ Q3 _Motor_Q2_Vdc-
Current Ia & Va are negative
Operates in third Quadrant
10
Chopper fed DC drive Four-quadrant Chopper
- Va +Q1
Q2
Q3
Q4
D1 D3
D4D2
+
Vdc
Q3 is OFF. Q2 is ON. Current has to be continuous.
Diode D4 is FB
Current flows through Q2,D4 & (Eb,La,Ra)
11
Chopper fed DC drive Four-quadrant Chopper
- Va +Q1
Q2
Q3
Q4
D1 D3
D4D2
+
Vdc
Q4 Is ON & Q2 is OFF.
Back emf Drives the current through Q4 – D2 - MOTOR
12
Chopper fed DC drive Four-quadrant Chopper
- Va +Q1
Q2
Q3
Q4
D1 D3
D4D2
+
Vdc
Q4 IS Turned Off,
D3 is FB
Current Flows through Va+ - D3 – D2 – Va-
Va is negative. But current Ia is positive
Operates in fourth quadrant
13
14
15
16
17
top related