DC Choppers and Converters

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What type of switches are GTO, BJT, MOSFET, MCT, IGBT, and IGCT?

Partially-controlled switches

Uncontrolled switches

Semi-controlled switches

Fully controlled switches (correct)

Which of the following is a First Quadrant converter?

Three-phase controlled rectifier

Step-down choppers

Diode rectifier (correct)

AC controller

What is the range of the average output voltage Vo,dc in a step-down chopper?

0 to Vi

-Vi to +Vi (correct)

Vi to 2Vi

-Vi to 0

What are the two parameters of the control function in fully controlled switches?

Tsw and d Signup and view all the answers

What is the quadrant of operation when vo is positive and io is negative?

Second Quadrant Signup and view all the answers

What are the most common fully controlled switches used presently?

MOSFET and IGBT Signup and view all the answers

What is the range of the magnitude control ratio M?

0 ≤ M ≤ 1 Signup and view all the answers

What is the expression for the output current Io,dc in terms of the input voltage Vi, magnitude control ratio M, and resistance R?

(MVi - E)/R Signup and view all the answers

What is the condition for the inductor current to be approximated to a constant?

The inductor current is approximated to a constant Signup and view all the answers

What is the expression for the current ripple ΔIo in terms of the input voltage Vi, magnitude control ratio M, switching frequency Ts, and inductance L?

M(1-M)TsVi/L Signup and view all the answers

What is the quadrant of operation of the chopper in Example 1?

Quadrant I Signup and view all the answers

What is the value of the average output voltage of the chopper in Example 1?

80 V Signup and view all the answers

What is the value of the AC component of the armature current in Example 1?

0.5 A Signup and view all the answers

What is the ripple factor of the output voltage in Example 1?

0.2 Signup and view all the answers

What is the magnitude control ratio, M, defined as?

Vo,d/Vi Signup and view all the answers

What is the differential equation of the load in terms of the output current?

L(di_o/dt) + Ri_o + E = Vo Signup and view all the answers

What is the general form of the solution to the differential equation of the load?

i_o(t) = (Vo-E)/R + i_o(to) e^(-(R/L)(t-to)) Signup and view all the answers

What is the expression for the output voltage of the chopper in terms of the periodic binary switching variable x1?

Vo = x1 Vi Signup and view all the answers

What is the duty ratio of switch S1, denoted by?

d1 Signup and view all the answers

What is the expression for the average output voltage, Vo,dc, in terms of the duty ratio d1?

Vo,dc = d1 Vi Signup and view all the answers

What is the range of the magnitude control ratio, M, for a 1st Quadrant Chopper?

0 < M <= 1 Signup and view all the answers

What is the physical significance of the duty ratio, d1, in the context of the chopper circuit?

It represents the fraction of time for which the switch S1 is ON Signup and view all the answers

Study Notes

DC Choppers

Fully controlled switches include: GTO, BJT, MOSFET, MCT, IGBT, IGCT, and others
The most common ones are MOSFET and IGBTs

Control Function

The control function has two parameters: Tsw (switching period) and d (duty ratio)
d = Ton / Tsw, where Ton is the on-time of the switch

Quadrant of Operation

Converter quadrant is identified by the polarity of output voltage and current
Four quadrants:
- First Quadrant: vo and io are positive
- Second Quadrant: vo is positive and io is negative
- Third Quadrant: vo and io are negative
- Fourth Quadrant: vo is negative and io is positive

Step-Down Choppers

The average output voltage, Vo,dc, depends linearly on the duty ratio of the chopper switches
The magnitude control ratio, M, is defined as Vo,dc / Vi
Vo,dc can be adjusted in the range of -Vi to +Vi

Output Current

The differential equation of the load is: L(di/dt) + Ri + E = vo
The output current has a general solution of the form: io(t) = (vo - E) / R + (E - vo) / R * e^(-R(t-to) / L)

First Quadrant Chopper

The output voltage can be expressed as: vo = x1 * Vi
The duty ratio, d1, is defined as: d1 = Ton / Tsw

Output Voltage and M Range

The average output voltage, Vo,dc, is: Vo,dc = d1 * Vi
The range of M is: E / Vi <= M <= 1, which implies d1,min = E / Vi

Output Current Approximation

The output current can be approximated as: Io,dc = M * Vi / R
The current ripple, ΔIo, is: ΔIo = M(1 - M) * Tsw * Vi / L

Example Problem

A step-down chopper with a magnitude control ratio of 0.4 operates a dc motor with an armature EMF of 70 V and armature resistance of 0.5 Ω
The average output voltage and current can be calculated using the formulas above
The AC component of the armature current and ripple factor of the current can be calculated using the approximate analysis formulas

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Learn about the different types of fully controlled switches and their applications in DC choppers, as well as the control function and quadrants of operation.