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simul.pptx
1. INTRODUCTION
• In the modern electric drive system power electronics converters are used as power controller.
• DC drives are widely used in applications requiring adjustable speed control and are less costly and
less complex than AC drives.
• The speed of DC motors can be adjusted above or below rated speed. Their speed above rated speed are
controlled by field flux control and below rated speed is controlled by armature voltage control.
• For controlling the speed of DC motor chopper as power converter and PI as controller are used.
2. CHOPPER
• A chopper is a static power electronic device which converts fixed DC input voltage to a variable DC
output voltage.
• It is also considered as a DC equivalent of an AC transformer since they behave in an identical manner.
• The electric automobiles are also use choppers for their speed control and braking.
• Chopper system offer smooth control, high efficiency, faster response and regeneration facility.
3. OPERATION OF CLASS-E CHOPPER
• The circuit of a four quadrant chopper or class-E chopper basically consists
of four semiconductor switches CH1 to CH4 and four diodes D1 to D4.
• The four diodes are connected in anti-parallel.
4. FIRST QUADRANT OPERATION
• CH4 : ON CH3 : OFF & CH1 is operated
• When both CH1 & CH4 are ON simultaneously, the load gets
directly connected to the source and hence Vo = Vs and load current
flows from source to load.
• When CH1 is switched OFF, the load current free wheels through
CH4 and D2. During this period, the load voltage and current
remains positive.
• Class-E chopper operates as a step-down chopper in this case.
5. SECOND QUADRANT OPERATION
• CH2 is operated while keeping the CH1, CH3 & CH4 OFF.
• When CH2 is ON, the DC source in the load drives current through
CH2, D4. Inductor stores energy during the ON period of CH2.
• When CH2 is turned OFF, current is fed back to the source through
D1, D4.
• As load voltage Vo is positive and Io is negative, it operates as a
step-up chopper.
6. THIRD QUADRANT OPERATION
• CH1 is kept OFF, CH2 is kept ON and CH3 is
operated.
• When CH3 is ON, Vo= -Vs.
• When CH3 is turned OFF, the negative load
current free wheels through CH2 and D4.
7. FOURTH QUADRANT OPERATION
• CH4 is operated, while keeping CH1, CH2 and CH3 OFF.
• When CH4 is turned ON, positive current flows through CH4, D2.
Inductance stores energy during CH4 is ON.
• When CH4 is made OFF, current is fed back to the source through diodes
D2, D3.
• Here load voltage is negative but the load current is always positive.
• Chopper acts as a step-up chopper.
8. APPLICATIONS
The type-E choppers are used in –
• Switch Mode Power Supply (SMPS) System
• DC motor as speed controllers
• DC voltage boosters
• Battery chargers
• Railway systems
• Electric cars
• Signal processing systems
9. ADVANTAGES OF CHOPPER DRIVES
• Quick response
• Flexibility in control
• High energy efficiency
• Light weight & compact control unit
• Less ripples in armature current
• Ability to control down to very low speeds
