H bridge driver and current magnitude and direction sense

[bunalmis]

h bridge current sensing

I use H bridge and inductive load. Waveform of load current is sinusoidal and frequency is DC to 1 KhZ. (I use sinus modulated pwm signal.)

I add small resistor to gnd line for sensing current. Voltaje drop on the this resistor is proportional by current of load, but this voltage drop does not give any idea for current direction.

I take samples from resistor voltage at the every 20 microsecond.
Current magnitude and direction are very importand data, because i use this two values for feedback value of current regulator.

Inductance current waveform is sine wave and current and voltage not same phase. (Frequency range between DC to 1Khz)

How I can learn the current direction?. (indepented from load type.)
I dont want to use expensive sensors (LEM, HP or IRF current IC)
Dou you have any simple idea for this problem?

I dont want to use current transformer because load current may be DC if i reduce the frequency.

(H bridge voltage value is 100V)

 

[Tornado]

magnitude direction sense

Hi Bunalmis

I think the voltage across the sense resistor is always positive.
so you cannot detect current direction, you probably need some
steering logic combined with the DIR signal and a current
amplifier/comparator to do this.

Tornado

 

[bunalmis]

h bridge change polarity

Hii Tornado,

Can you draw principle schematics or can you explain.

Inductance strore the current and if you change the polarity of DIRection signal, current direction dont change at the same time. This is produce a dificulty for learning of current direction.

I am looking zero crossing points. This area give more usuful data for the direction crossing.

But :

Current sense circuit has opamp and ADC. Offset values and ground noise produce indefinitieness at the around of zero. (I wrote software for sensing of current direction but system wrong work near zero)


Yes I know problem will finish if i use the expensive sensors.

But I am looking more idea.

 

[nec3]

proteus h-bridge

Two optocouplers one for the route of SW1 and the other for SW2.
outputs of the coupler will show the current direction... leds may need current shunt in paralel.

 

[bunalmis]

current sensing in dc h-bridges

This type method lost the precison of direction data at the near zero cross. (Led not work and I dont know the current direction.)

If i add the active circuits (opamp, transistor..) we need floating voltage for opamp power. (switching capacitor may be solve the power problem)

But more idea.

 

[bunalmis]

h-bridge transformer driver

We can sense the curent direction if we add two resistor.

But we need matched power resistor. Else opposite signed but same magnitude currents give different results.

This methode also good for learning circulation current direction.

But i am looking more idea.

 

[alphi]

magnitude and direction of current

Use R to test current,
use DIR and sw3's diode voltage to test real current.

 

[alphi]

sence, magnitude, direction

it is like to full bridge phase shift soft switchmode power supply.
Pls ref to this type smps topology.

 

[Tornado]

current sense smps h bridge

In the position of SW3 SW4 you can use current sense mosfets,
to control the H-Bridge you need something like UC3638 from
TI/Unitrode.
Also check Maxim for High-Side, Current-Sense Amplifiers with
Voltage Output

**broken link removed**

it has an output that goes plus or minus depending on the direction of the current thru the 2 current sense resistors.

Tornado

 

[Tornado]

max4080 examples

Hi Bunalmis, I designed a circuit in Proteus demo for detecting SWs current and outputing a 5V logic level for direction.
Please check it. Caps need to be calculated for noise rejection.

Tornado

 

[bunalmis]

h-bridge current controlled load

I dont have proteus may you send jpeg or gif format?

 

[Tornado]

current limiting an h bridge

OK here is:

JPEG, GIF and PNG format

Tornado

 

[bunalmis]

h-bridge driver current direction

Thanks Tornado,

Your sense circuit good. System needs two sense resistor this is small disadvantage.

Do you have any idea for single sense resistor?

Are there another methode for current directions.
(other then hall effect components)

 

[Tornado]

h bridge current sense circuit

OK here is another circuit similar to previous with a single sense resistor in series with the load, check it. Component values have to be calculated
for your application.

Tornado

 

[barny451]

current sense in h-bridge opamp

It isn't very clear why you think you want to measure the polarity of the current; if you're looking for a zero crossing, this would look like a minimum in the measured current through the sense resistor, and to detect this you don't need the polarity of the current through the load before and after the minimum.

Also, if there's so much noise on the measured current, you are unlikely to be able to improve the detection of zero-crossing simply by knowing the polarity of the current through the load.

And, if the load *is* purely resistive+inductive, the current through it won't carry on increasing when the PWM switches direction, because the phase-shift can't exceed 90 degrees; the current through the sense resistor is never more than the current being put into the load through the MOSFETs.

Therefore, if you want to limit the load current because you don't want to damage the MOSFETs, you also don't need to know the polarity of the current because if 10A is flowing through the sense resistor then 10A is flowing through two of the MOSFETs.

So, what are you trying to achieve? And, is the load a simple resitor+inductor?

HTH
barny