Speed control of AC motor

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1

Hi all, I well played with dc motors, now i want to try ac motors,

I googled and found http://playground.arduino.cc/Main/ACPhaseControl

actually the topic is not only related to arduino we can use any MCU, but i always first try with arduino then extend my work to others ---- AVR, PIC, 8051, Raspberry pi, FPGA/CPLD…

OK the above tut uses the following components,

for zero crossing detection H11AA1

for triac control MOC3052

triac some other

but unfortunately i could not find the main components viz. H11AA1, MOC3052, and the triac on some local market.

so i decided to use substitutes and come up with following,

H11AA1 substitute with MCT2E and bridge rectifier, transformer

MOC3052 substitute with MOC3021

Triac i use BT 136

I planned the following schematic pls see attached images :

zero Crossing Detector :

zeroCrossDetector_zpsz1hubmr4.png997×511 25.1 KB
http://i1374.photobucket.com/albums/ag4 … hubmr4.png

triac switch :

switch_zpssntwixel.png1022×511 12.9 KB
http://i1374.photobucket.com/albums/ag4 … twixel.png

now before ordering the components i need your advice as i know i am going to play with AC mains, pls first check the circuit ---- is everything OK ?

if any thing wrong etc pls tell me.

i selected R1 to be 1k in zeroCrossDetector is it OK and safe for the MCT2E ?

pls reply soon, so that i can order the parts and start further…

thanks in advance

2

1000 ohms for R1 is okay for now, but you may need to play with the value to get the sensitivity you desire. But first note that your circuit as drawn won’t detect zero crossings, because the end of R1 not connected to the optoisolator is actually connected to the filtered bridge output voltage - somewhere around +17V. Therefore the optoisolator’s output will go low any time that either AC transformer output lead is less than about 15.5V (which is always going to be the case. I recommend connecting this lead of R1 to the ground (which is also the center tap of the transformer output). This way the optoisolator’s output will be low whenever either AC lead is more negative than -1.5V, which occurs outside of the zero crossing region.

In addition, the BT136 requires on the order of 20-30mA trigger current, so R2 in the TRIAC circuit will probably need to be on the order of 120 to 240 ohms (180 ohms is common with 120Vac mains). You may also need to reduce R1 in this circuit to get enough current flowing in the optoisolator’s input LED.

Finally, phase control is most useful for speed control of “universal” (brushed) AC motors; it is not very effective for induction motors, and can cause excessive current draw.

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I took a course in electrical machines many many years ago, and to my recollection, you need to change the frequency …

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Indeed, the most effective means of controlling the speed of an induction motor is to vary the frequency of the AC supply. This is usually accomplished by rectifying the mains to DC and then using H-bridge MOSFET or IGBT devices connected to a microcontroller that controls the gate drive circuitry to generate a sine wave (or similar) AC output.