POWER ELECTRONICS
description
Transcript of POWER ELECTRONICS
![Page 1: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/1.jpg)
POWER ELECTRONICS
Instructor: Eng. Jalal Al Roumy
The Islamic University of GazaFaculty of EngineeringElectrical Engineering Department
الرحمن الله بسمالرحيم
EELE 5450 — Summer 2012
Lecture 17
![Page 2: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/2.jpg)
HALF-BRIDGE WITH RESISTIVE LOAD
![Page 3: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/3.jpg)
HALF-BRIDGE WITH RESISTIVE LOAD
![Page 4: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/4.jpg)
Chapter seven
HALF-BRIDGE INVERTER WITH RESISTIVELOAD AND CAPACITIVE ELEMENTS
In the circuit shown, capacitors replace the centre-tapped battery, and a single battery acts as the d.c. source.
![Page 5: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/5.jpg)
Chapter seven
HALF-BRIDGE INVERTER WITH RESISTIVELOAD AND CAPACITIVE ELEMENTS
C1 and C2 are each charged to Vb/2 prior to switching. When Q1 is switched on, C1 capacitor voltage is applied across the load, load current flows and exponentially decays until Q1 is switched off.
![Page 6: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/6.jpg)
Chapter seven
HALF-BRIDGE INVERTER WITH RESISTIVELOAD AND CAPACITIVE ELEMENTS
Q2 is switched on to connect C2 as a reverse voltage across the load. Load current flows in reverse through the load, exponentially decaying until Q2 turns off and Q1 turns on to repeat the cycle.
![Page 7: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/7.jpg)
Chapter seven
HALF-BRIDGE INVERTER WITH RESISTIVELOAD AND CAPACITIVE ELEMENTS
Load voltage
![Page 8: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/8.jpg)
Chapter seven
HALF-BRIDGE INVERTER WITH RESISTIVELOAD AND CAPACITIVE ELEMENTS
Example Vb = 40V, C 1 - C 2 = 200μF, R1 = 10Ω and an inverter frequency
of 100Hz. Assuming ideal switches, determine maximum and minimum values of load voltage, assuming the waveform is symmetrical.
![Page 9: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/9.jpg)
Chapter seven
HALF-BRIDGE INVERTER WITH RESISTIVELOAD AND CAPACITIVE ELEMENTS
Example Vb = 40V, C 1 - C 2 = 200μF, R1 = 10Ω and an inverter frequency
of 100Hz. Assuming ideal switches, determine maximum and minimum values of load voltage, assuming the waveform is symmetrical.
![Page 10: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/10.jpg)
Chapter seven
![Page 11: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/11.jpg)
Chapter seven
![Page 12: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/12.jpg)
Chapter seven
HALF-BRIDGE WITH PURELY INDUCTIVELOAD
With resistive loads, at the half-cycle period Q1 is switched off and Q2 is switched on. The load current changes instantaneously from the maximum positive to the maximum negative value.
With inductive loads, instantaneous reversal is impossible. In fact, if an inductive load was turned off with maximum current and there was no alternative path for the current to flow, the current collapse would be very rapid, and the induced voltage, e = L di/dt, would be very large. This voltage would appear across the transistor switch in reverse and could destroy it.
![Page 13: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/13.jpg)
Chapter seven
HALF-BRIDGE WITH PURELY INDUCTIVELOAD
To protect the transistor from this inductive surge, feedback diodes are connected in anti-parallel across the transistor to provide a path for the current to decay.
![Page 14: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/14.jpg)
Chapter seven
HALF-BRIDGE WITH PURELY INDUCTIVELOAD
When Q1 switches off at maximum positive current, the inductive voltage VL reverses its polarity, the voltage rises above Vb2 and forward biases D2, allowing the decay of current until load current zero, Then Q2 will start the flow of current in the negative direction.
![Page 15: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/15.jpg)
Chapter seven
HALF-BRIDGE WITH PURELY INDUCTIVELOAD
When negative current reaches its maximum value, Q2 switches off, VL reverses, rising above Vbl and forward biasing diode D1, until load current zero, Q1 will then allow current to grow in the positive direction and the cycle is repeated.
![Page 16: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/16.jpg)
Chapter seven
HALF-BRIDGE WITH PURELY INDUCTIVELOAD
![Page 17: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/17.jpg)
Chapter seven
HALF-BRIDGE WITH PURELY INDUCTIVELOAD
![Page 18: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/18.jpg)
Chapter seven
HALF-BRIDGE WITH PURELY INDUCTIVELOAD
![Page 19: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/19.jpg)
Chapter seven
HALF-BRIDGE WITH PURELY INDUCTIVELOAD
![Page 20: POWER ELECTRONICS](https://reader035.fdocuments.us/reader035/viewer/2022062310/56816437550346895dd5ff6e/html5/thumbnails/20.jpg)
Chapter seven
End of Lecture