Power electronics used to control DC motors

Question 1

what is the duty cycle

Answer 1

time on/(time on+time off)

Question 2

why is a diode nescasary in a DC chopper circuit

Answer 2

current must decay slowly to stop infitinite volatge in the inductor

Question 3

what is voltage across an inductor with change in current

Answer 3

V=L*di/dt

Question 4

what are problems with high current ripple

Answer 4

it causes pulsating torques/higher accoustic noise and additional loss in the sttor core

Question 5

what is current ripple and why is it caused

Answer 5

the voltage chopping creates the inductor discharging and charging causing the current to change

Question 6

what is the best why to minimise losses from curren ripple

Answer 6

high frequency switching

Question 7

what is a major benefit of reaching >20kHz frequncy

Answer 7

It can’t be heard by humans

Question 8

3 advantages of 3 phase transmission

Answer 8

conduction advantage - can transmit 3x whuth one more wire
constant power
rotating magnetic field

Question 9

why must any houses be connected together in 3 phase system

Answer 9

the usage must be even to have a blanced 3 phase system