VFD

Question 1

What is the most common control scheme in vfds is?

Answer 1

PWM

pulse width modulation

Question 2

Pulse width modulation (PWM) use several techniques to control a motor circuit. What are they?

Answer 2

Space vector modulation

Direct torque control

Vector control

V/Hz control

Question 3

The rapid switching that is achived by a vfd inverter is achived by?

Answer 3

IGBT

Insulated gate bipolar transistors

Question 4

What are 3 advantages of the integration of a VFD into a motor driven system

Answer 4

Enhanced energy efficiency

Provide a soft start function

Minimize inrush current

Question 5

What can a vfd control?

Answer 5

Speed

Acceleration

Deceleration

Question 6

What is the formula for synchronus speed?

Answer 6

Question 7

Besides speed control of a motor what can VFDs control?

Answer 7

Acceleration

Deceleration

torque

Overall performance management

Question 8

VFD is an essential component in?

Answer 8

Modern motor control systems

Question 9

What does VFD stand for?

Answer 9

Variable frequency drive

Question 10

What is used to optimize and minimize harmonic distortion and can achive higher voltage outputs than traditional PWM methods?

Answer 10

Space vector modulation

Question 11

What is an advanced control technique that provides a more direct control of the motor’s magnetic flux and torque?

Answer 11

Direct torque control

Question 12

What involves controlling the magnitude and phase of the motor control voltage?

Answer 12

Vector control

Question 13

What maintains a constant voltage to frequency ratio to ensure constant flux in the motor?

Answer 13

V/Hz control

Question 14

How does a vfd control the speed of a motor?

Answer 14

It will pulse dc using pwm to stimulate a sinwave

Question 15

What are the major components of a vfd?

Answer 15

RIFC

Rectifiers

Inverter

Filter

Controller

Question 16

A 6 pulse rectifier is a

Answer 16

Three phase full wave rectifier

Question 17

A 12 pulse rectifier is?

Answer 17

Two three phase full wave rectifiers.
One rectifier will have a 30 degree shift

Question 18

An 18 pulse rectifier is?

Answer 18

3 full wave rectifiers.
Their supply voltage is 20 degrees out of phase.

Question 19

Why are IGBTs a staple in vfds?

Answer 19

Due to their ability to rapidly turn on and off

Question 20

How long does it take an IGBT to switch on or off?

Answer 20

They can be switched on in 100 - 500 ns.
Switched off in 250 - 2000 ns

Question 21

The terminals and function of the IGBT are?

Answer 21

GEC

Gate - control terminal

Emitter- negative terminal

Collector - positive terminal

Question 22

What must be done to switch an IGBT on and off?

Answer 22

Switch on - apply positive voltage to the gate

Switching off - remove voltage from gate

Question 23

What is created by the insertion of an LC filter between the rectifier and the gate?

Answer 23

Dc-Link

Question 24

Squirrel cage induction motors are? (Designed to be powered by vfds)

Answer 24

Inverter ready

Inverter duty

Vector duty

Question 25

Non- induction motors types are? (Designed for vfds)

Answer 25

Permanent magnetic ac motors Wound field Reluctance motors

Question 26

What happens when you increase the carrier frequency of a motor?

Answer 26

Reduces high pitch noise Increase damage caused by harmonic currents

Question 27

Controlling a VFDs applied power to a motor is achieved through two basic types of control schemes. What are they?

Answer 27

Open loop - doesn't require feedback Closed loop - precise control

Question 28

A VFD can accomplish motor breaking in three ways. What are they?

Answer 28

Dynamic breaking Line regenerative breaking Dc injection breaking

Question 29

What are the benefits of auto tuning a vfd?

Answer 29

Enhances efficiency Improves overall motor performance

Question 30

What is the initial electrical process of a vfd?

Answer 30

Adjusting the switching frequency of the ac output

Question 31

What does the V/Hz control method maintain to ensure constant flux in the motor?

Answer 31

Constant voltage to frequency ratio

Question 32

How must a voltage source be matched for a motor connected to main VFD?

Answer 32

Output voltage must be the same as the motor's voltage

Question 33

What is required when a vfd is used with a single phase input to power a three phase motor?

Answer 33

The vfd may need to be oversized

Question 34

Harmonics and voltage transients will?

Answer 34

decrease the lifespan of a motor.

Question 35

What is the purpose of the DC link section of a VFD?

Answer 35

Filters the pulsating DC voltage

Question 36

The DC Link section is made up of a/an?

Answer 36

inductor in series. and a capacitor in parallel with the output

Question 37

Answer 37

10 Volts ÷ Hz

Question 38

A 3-phase motor is known to have 10 poles. If this motor is connected to a VFD which is outputting 20 Hz. The synchronous speed of the motor is __ RPM.

Answer 38

240

Question 39

A PWM inverter that utilizes ,__ __ __ is used to optimize and minimize harmonic distortions?

Answer 39

Space vector modulation

Question 40

A PWM inverter that utilizes __ __ __ tends to have more control of the motors magnetic flux than other methods of PWM methods.

Answer 40

Direct torque control

Question 41

A PWM inverter that utilizes __ __ __ can achieve higher output voltages than traditional PWM methods

Answer 41

Space vector modulation