Please recall that for a sine wave, RMS voltage and current values relate to the equivalent DC values. Thus I will suggest that, for the most part, you stay with the RMS values for the analysis. For a DC motor application I think all you will need is suitably sized transformer and diode rectifiers and can eliminate any regulation circuitry including capacitors. As I suspect that a transformer with a 220/200 ratio may be difficult to obtain, a 1:1 isolation transformer may do the trick. Assuming a full wave rectifier, the resultant DC output will be 250 Vdc with no load. and somewhat below that when under load. If the output, under load, is 220 Vdc, this will be only 10% over the rated 200 Vdc for the motor. Motors, especially those of the ratings described, should be able to handle an applied voltage of 10 & over the nominal. Regards.

 

my project is to drive dc motor by PWM so i will use MOSFET in the output of rectifier as a chopper class A
the motor is 220Vdc so i will limit the duety cycle in 70%.
i think thats good , isnt it?

My aplogies, I should have read the whole thread. If I had I would have seen the above.

I still think you can get by with a 1:1 transformer. But now you could add an SCR based controller that can will modulate the unfiltered full wave rectified DC voltage to get the speed control you want. The circuitry used to control the gate of the SCR would be similar to that of a light dimmer. This concept needs to have the full wave rectified DC voltage applied to the SCR unfiltered so that the SCR turns off every half cycle. If you limit the duty cycle to 70% then, even with 200 Vdc(rms), you will be below the 200 Vdc rating of the motor. Regards.

 

ok,
i will use the 1:1 transformer which is for insolation
and N-channel power Mosfet to control the speed of motor
i think that MOSFET or MCT is easier to use than SCR beacause it doesnt need commutaion circuit.and about the the mosfet gate i will use gate driver
which between pic and mosfet
also the mosfet connected to the low side
and add freewheeling diod parallel with the motor.
my software is stopped know ,as it repair i will add the circuit
ist good man?

 

i know that if the the input of rectifier is 220Vac
the output is 1.4*Vin=314Vdc
is it true?
if its true i can use transformer with 220:155
so 155*1.4=220Vdc
which is the motor nominal voltage

 

One point which hasn't been mentioned in all of the foregoing discussion is the VA rating of the required transformer.

Depending upon the running duration and loading of the motor, I would not select a transformer rated below 1500VA at the minimum. It will also require sufficient core stack size to provide good regulation for a temperature rise of up to 45 - 50C above ambient. Such a transformer is not exactly small and if my 1KVA transformer is anything to go by, would weigh in the region of 20Kg.

 

h.d. Early on SgtWookie asked why you need a 220 Vdc rectifier and you answered with a drive for a dc motor. Now, I will expand the original question by asking what will the motor be driving?

If the application is something like a fan or a conveyor belt you most likely will be able to get away with using the motor and mechanical system to dampen or integrate the 100 Hz in the rectified dc power and do away with capacitors in the rectifier. This will allow the full wave wave rectified 220 Vac input to be used as if were 220 Vdc given that the rms value of the recified and non-integated dc power is 220 Vdc. You need not worry about the peak voltage of 314 volts (I was in error earlier).

However, if the mechanical system - such as an audio turntable (2 hp?) or a robot - will not allow for a 100 Hz ripple, you may have to consider external integration, e.g. capacitive filters, in the rectifier. In this case the integrated rectified voltage will be higher than 220 Vdc. How much higher, depends on the amount of filtering, the capacity of the filters and the load.

I realize that using the raw, rectified and non-integrated dc voltage together with a PWM driver circuit will require some tricky software to scale the PWM output to take the semi-sinusoidal voltage into account but I will leave this open for discussion.

Regards.

 

h.d. Early on SgtWookie asked why you need a 220 Vdc rectifier and you answered with a drive for a dc motor. Now, I will expand the original question by asking what will the motor be driving?

If the application is something like a fan or a conveyor belt you most likely will be able to get away with using the motor and mechanical system to dampen or integrate the 100 Hz in the rectified dc power and do away with capacitors in the rectifier. This will allow the full wave wave rectified 220 Vac input to be used as if were 220 Vdc given that the rms value of the recified and non-integated dc power is 220 Vdc. You need not worry about the peak voltage of 314 volts (I was in error earlier).

However, if the mechanical system - such as an audio turntable (2 hp?) or a robot - will not allow for a 100 Hz ripple, you may have to consider external integration, e.g. capacitive filters, in the rectifier. In this case the integrated rectified voltage will be higher than 220 Vdc. How much higher, depends on the amount of filtering, the capacity of the filters and the load.

I realize that using the raw, rectified and non-integrated dc voltage together with a PWM driver circuit will require some tricky software to scale the PWM output to take the semi-sinusoidal voltage into account but I will leave this open for discussion.

Regards.

thanks for interest,
the application is treadmill
and the motor used to drive the treadmill conveyor,but donr well get what you mean about the frequency,so if you can tell me more explain or website can i study the topuc from it.
and about the PWM i will use MOSFET conreolled by pwm signal from the
PIC16F877A.

 

h.d. I have attached a graphic of a full wave rectifier circuit with waveforms I found on wikipedia. The graphic shows an ac input to a transformer which in your case will be 220 Vac at 50 Hz. After the transformer, the graphic then shows a diode bridge circuit with the resulting, full wave rectified waveform. These semi-sinusoidal pulses are at 2 x the input frequency or 100 Hz. If the transformer ratio is 1:1 the RMS value of the voltage created by these pulses will be 220 Vdc.

For a treadmill I do not think you will need to smooth the semi-sinusoidal voltage as the treadmill's mechanical system itself will do the smoothing and no one will be able to detect any remaining vibration caused by the 100 Hz ripple in the voltage. However, scaling and synchronizing the PWM control in software to the semi-sinusoidal voltage will be a challenge.

Integrating or smoothing the semi-sinusoidal pulses with filter capacitors will create a dc voltage that will be higher than 220 Vdc, as much as 314 Vdc at no load. This dc voltage will be easier to control with the microcontroller. But, like the transfomer, you may need very large capacitors capable of working at a miniumum working voltage of 400 Vdc.

Regards.

 

i do the model with transformer and filter ,
i get that results
the capacitor is 4mF

 

The graphic shows an ac input to a transformer which in your case will be 220 Vac at 50 Hz. After the transformer, the graphic then shows a diode bridge circuit with the resulting, full wave rectified waveform. These semi-sinusoidal pulses are at 2 x the input frequency or 100 Hz. If the transformer ratio is 1:1 the RMS value of the voltage created by these pulses will be 220 Vdc.

The RMS value of the DC pulses will be 220V. Their peak value will be 312V.

 

see the attached image
i will use the first one in addition to freewheeling diod parallel with the load,
and MOSFET in sereis with load in low side,to control the voltage,
but is thier calculation to determine the value of capacitor(filter)?
or choice it rouphly as 10mF?​

 

thanks for interest,
the application is treadmill
and the motor used to drive the treadmill conveyor,but donr well get what you mean about the frequency,so if you can tell me more explain or website can i study the topuc from it.
and about the PWM i will use MOSFET conreolled by pwm signal from the
PIC16F877A.

Since the application is a treadmill you won't need to use a transformer.

Look at the data sheet for a typical 2HP PMDC motor controller as made by KB Electronics
http://www.kbelectronics.com/data_sheets/kbpc_240d.pdf
and its accompanying manual
http://www.kbelectronics.com/manuals/kbpc_240d.pdf
The 230Vac is connected directly into the controller and the output DC is internally fixed at 180V for maximum rated torque.

 

rherber1
thanks for replay
the controller which you talk about is good
but i should designe the controller and the power circuit,so i search a bout how to designe that and to be stable and robust in my application

 

h.d. I have attached another graphic taken from the same wikipedia page I referenced before. This graphic shows how a circuit using a thyristor, e.g. SCR or Triac, can be used to control the output from a full wave rectified, but unfiltered, power supply. The thyristor is triggered to turned on at some time following a zero point. The thyristor turns off at the next zero point.

This is similar to PWM control where the PWM signal can be used to control the point at which the thyristor is triggered relative to the zero point. With reference to the graphic, think of the time between the zero point and the trigger, shown in blue, as being created by a pulse of a variable width. This pulse or PWM signal will have to be synchronized to the zero point to create the trigger signal at the desired time.

If the thyristor is turned on just after the zero point almost all of the available energy is output. If the thyristor is turned on 1/4 * 1/50 seconds or 5 milliseconds after the zero point the output energy is 50% of the total energy available. If the thyristor is turned on more than 5 milliseconds after the zero point the output energy is less than 50% of the total energy available. I will note that the output energy vs. the timing offset is not linear. Here, you may want to add some software to scale the PWM or trigger signal so the input control is linear.

I think that the approach using a filtered DC supply and a MOSFET driven with a PWM control circuit is more complex than it needs to be for a treadmill.

Regards.

 

why do you think that PWM with MOSFET is complex
comparing to the SCR ,i think its the same concept
also SCR you need commutation circuit.

 

Speed control of an AC motor is very complex indeed. PWM with MOSFET on a DC motor is the way most devices work.

 

Speed control of an AC motor is very complex indeed. PWM with MOSFET on a DC motor is the way most devices work.

i agree with you
to apply PWM in AC motors and get a wide spedd control range
you ahould varey the voltage an frequency wich is complex.