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Motor Control ICs Forum Discussions

JasonLEE
Level 4
Level 4
First like received First solution authored 50 replies posted

hello.

I'm curious about this part.

What is the difference between single shunt and leg shunt?

Can you tell me the pros and cons?

please answer about my question.

thank you

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1 Solution
LinGuohui
Moderator
Moderator
Moderator
100 replies posted 10 likes received 100 sign-ins

Hi @JasonLEE 

Both of leg & single shunt are used for current reconstruction, This is the basis of FOC.

For leg shunt:

1.Hardware. Leg shunt minimum required two ADC of MCU and  corresponding circuit hardware(eg: OP, shunt resistance).

2.Calculation. Leg shunt direct read IU,IV. IW = -IU -IV

3.Current sampling time.  Leg shunt, We sampling the current at the zero vector. This is the actual phase current, don't have other driver noises. And the zero vector always wide enough for ADC sample and conversion.

LinGuohui_0-1670463331718.png

4.Sample range. Leg shunt, the phase current is signed(+or-), so we always offset the sample signal to 1/2 Vref. So the sample range is 1/2 Vref.

For single shunt.

1.Hardware. Single shunt need only one ADC and corresponding circuit hardware. Less than leg shunt.

2.Calculation. Same as leg shunt.

3.Current sampling time. Current sampling at active vector. Different vectors represent different current signals. Because the sampling at active vector, the current signal is bad than leg shunt.

LinGuohui_1-1670464163915.pngLinGuohui_2-1670464319336.png

When the desired voltage vector is at sector cross-over regions or when the magnitude of the desired voltage vector is low. The duration of one or both active vectors is too short to guarantee reliable sampling of
winding current data. The current sampling will be distorted. To solve this problem, MCE provide Minimum Pulse Width PWM ,Phase Shift PWM andLow Noise Phase Shift PWM theory(more information, please refer MCESW-RM-UserManual 2.1.7)

LinGuohui_3-1670465066696.png

4.Sampling range. Single shunt, the current signal is always positive, so the sampling range is greater than leg shunt.(Notice: this is only for motor. if work at regeneration mode, The sampling range is same when use leg shunt, but opposite range with single shunt.  )

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1 Reply
LinGuohui
Moderator
Moderator
Moderator
100 replies posted 10 likes received 100 sign-ins

Hi @JasonLEE 

Both of leg & single shunt are used for current reconstruction, This is the basis of FOC.

For leg shunt:

1.Hardware. Leg shunt minimum required two ADC of MCU and  corresponding circuit hardware(eg: OP, shunt resistance).

2.Calculation. Leg shunt direct read IU,IV. IW = -IU -IV

3.Current sampling time.  Leg shunt, We sampling the current at the zero vector. This is the actual phase current, don't have other driver noises. And the zero vector always wide enough for ADC sample and conversion.

LinGuohui_0-1670463331718.png

4.Sample range. Leg shunt, the phase current is signed(+or-), so we always offset the sample signal to 1/2 Vref. So the sample range is 1/2 Vref.

For single shunt.

1.Hardware. Single shunt need only one ADC and corresponding circuit hardware. Less than leg shunt.

2.Calculation. Same as leg shunt.

3.Current sampling time. Current sampling at active vector. Different vectors represent different current signals. Because the sampling at active vector, the current signal is bad than leg shunt.

LinGuohui_1-1670464163915.pngLinGuohui_2-1670464319336.png

When the desired voltage vector is at sector cross-over regions or when the magnitude of the desired voltage vector is low. The duration of one or both active vectors is too short to guarantee reliable sampling of
winding current data. The current sampling will be distorted. To solve this problem, MCE provide Minimum Pulse Width PWM ,Phase Shift PWM andLow Noise Phase Shift PWM theory(more information, please refer MCESW-RM-UserManual 2.1.7)

LinGuohui_3-1670465066696.png

4.Sampling range. Single shunt, the current signal is always positive, so the sampling range is greater than leg shunt.(Notice: this is only for motor. if work at regeneration mode, The sampling range is same when use leg shunt, but opposite range with single shunt.  )

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