converterinduction motorvfd
I am implementing a Variable frequency Drive control of single phase induction motor. I am little bit confused about the V/f ratio and voltage level.
i boosted voltage upto 380V for Inverter . if i operate the motor at 220 volt with 50 HZ. so the 220/50 = 4.4 . am i right . otherwise i have to use (1.414*220/50)=6.2
how can i calculate the modulation index.
please help me i am confused about the calculation of V/f constant Control techniques .
There is no way to calculate the Starting Current or Locked Rotor Current (LRA) without more information!
Single-phase or three-phase? NEMA Motor Design B, C or D?
What does academic education's sake mean? A voltage of 15V with a power of 132kW is meaningless for an induction motor. You just can't make up numbers. You are also using \$P = V\ I\$, which is DC power.
You'd be better off looking up a motor nameplate and going from there.
Take a 150hp, 1789rpm, 460V, Design B, Code G, 3-phase induction motor. So rated current is 163A, with a power factor of 0.897 lagging and an efficiency of 96.2%.
Code G gives you locked rotor kVA on a per hp basis. Locked rotor kVA will allow you to calculate LRA. Code G = 5.6 up to but not including 6.3. Worst case = 6.3.
$$150hp \times 6.3 = 945 kVA$$
$$ S = \sqrt {3}\ V_{Line}\ I_{Line} $$ $$ I_{Line} = \frac {S} {\sqrt {3}\ V_{Line}} = \frac {945 kVA} {\sqrt {3} \times 460V} = 1,186A $$
LRA will be between 1,102A and < 1,186A vs 163A or 676% to 728% of full-load current.
The RPM is determined by the frequency and does not directly effect the current. The current is more closely related to torque. Some useful relationships are:
Motor speed RPM = 120 X Frequency (Hz) / Number of motor poles (4 poles for the Tesla I think)
Input power to the motor, Watts = Volts X Amps X Square Root of 3 X Power Factor
Horsepower output = Torque (Ft-Lbs) X RPM / 5252
Input Power X Efficiency = Output Power
1 Horsepower = 746 Watts
The Tesla motor is very efficient, 0.95 or higher
For constant torque operation, the voltage applied to the motor is proportional to frequency.
The Tesla motor can provide constant torque up to some frequency limit. Above that, the voltage does not increase any more (or perhaps it increases at a slower rate). That allows the motor to provide constant power.
Re. Test Data
It appears that the voltage and current for the test data are battery voltage and current. The power at the battery is just watts = voltage X current. The inverter is between the battery and the motor. The Tesla inverter efficiency is also quite high, perhaps 0.95 or higher.
Best Answer
Any power magnetic component running from AC will magnetically saturate the core if the volt.seconds starts to be exceeded i.e. too many volts of the same polarity for too long and you get trouble.
Volts per hertz is exactly the same measure because hertz are cycles per second hence V/f are volt.seconds per cycle.
So if in one cycle of AC the volts.seconds gets too big you get magnetic saturation problems.
For variable frequency drives and induction motors, as speed is ramped down by lowering frequency so volts must also fall to prevent saturation.
For any particular motor it's volt.seconds will be determined by the motor manufacturer or specifier so I can't help you in that respect other than to say that if a motor is OK for 220V AC RMS at 60 Hz then at 30 HZ (half speed) you should have a pretty good reason for running at a voltage level higher than 110 V AC RMS.