For the type E chopper to be operated in the fourth quadrant

Question

Examoogle · Accepted Answer

only one switch is operated

Explanation: A Type E chopper, also known as a four-quadrant chopper, operates in the fourth quadrant when both the output voltage $V_o$ and output current $I_o$ are negative. This is achieved by specifically operating only one switch (typically CH4) while the load current freewheels through the corresponding antiparallel diode.

Working Principle: In the fourth quadrant, the chopper functions as a boost converter where power flows from the load to the source (regeneration). When switch CH4 is ON, the load energy is stored in the load inductance. When CH4 is OFF, the energy stored in the load inductor is released back to the source through the feedback diode D2, resulting in negative terminal voltage and positive current relative to the load, but defining the fourth quadrant operation relative to source terminals.

Key Formulas: $V_o = V_s(D-1)$ — Output voltage during fourth quadrant operation; $P_{out} = V_o I_o$ — Negative power signifies regenerative braking

Key Points: Type E chopper allows bi-directional power flow.; Fourth quadrant: Negative voltage, Positive current (regenerative mode).; Only one switch (CH4) is toggled to modulate the energy return to source.; Antiparallel diodes provide the path for current during the OFF state.

Advantages: Allows four-quadrant operation of DC motors.; Enables efficient regenerative braking.

Disadvantages: Complex control circuit required.; Higher switching losses compared to single-quadrant choppers.

Applications: DC Electric Locomotive braking.; Industrial motor drives requiring precision speed control.

Additional Info: In a Class E chopper, CH1/D1, CH2/D2, CH3/D3, and CH4/D4 constitute the four legs.. Operation in Quadrant IV is specifically associated with the conduction of CH4 and D2.

Answer: A is correct — Only one switch is operated to control the regenerative power transfer from the load back to the DC source.

Exam Tip: Always remember that in multi-quadrant choppers, quadrants I and III represent motoring, while II and IV represent regenerative braking.

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