measuring floating inductor current in a truesine inverter application

Jamie Morken · 2008-01-22T16:35:00+00:00

Hi,I am trying to make a true sine inverter outputting 120VAC 60Hz,and am using 200kHz for the fet switch. Also using software PWMcontrol with either of one or the other of these two algorithms:method1: (uses high speed DAC)if inductor current > voltage error, pulse offif inductor current > current_limit, pulse offif time > limit pulse off (limit is our max dutycycle for this PWM period)method2: (uses high speed ADC)if inductor current > current_limit, pulse offDuty cycle = ((desired voltage - current voltage) * gain) - (Inductor current * gain2)For the current sensing I was thinking of using a hall effect sensor,like the "S22P025S05" from Tamura,which has an operating bandwidth of up to 200kHz, but this is still tooslow to do cycle by cycle current limiting unless a larger inductor isused than is otherwise necessary for the circuit. Is there a higherbandwidth hall sensor that could work for this?Also I was thinking about using a current sensing resistor and thenfeeding this directly into an ADC floating at the high voltage of the120VAC, and using optoisolators on the ADC SPI interface.Another possible way to interface to a current sensing resistor wouldbe to use a high common mode voltage differential amplifier, like theAD629.What would be other good ways to measure this high frequencyfloating current?cheers,Jamie

Jan 22, 2008 21 Replies

Rate this thread:

Jamie Morken 18 years ago

formatting link

The LEM ones look pretty neat:

formatting link

Good datasheets too, so with increasing frequency, it looks like the gain of the sensor increases, so the output current is more than actual?

I guess that is why they have such fast step response to current spikes,

0.1uS in this datasheet:

formatting link

I thought I would have to use a current shunt and fast opamp for cycle by cycle current limiting, but I guess these can be used solely for this, in a 200kHz SMPS.

Are the Tamura parts:

formatting link

Suitable for cycle by cycle current limiting at 200kHz PWM frequency as well?

cheers, Jamie

Vote

Terry Given 18 years ago

formatting link

buried in the digieky text is the frequency spec, 50kHz (35kHz for some), so I guess not. I'm using the LAH-25s for a couple of jobs at the moment.

Cheers Terry

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required