1. Some Test Result about Current Sensor
Limei Zhao
07/23/2003

2. Current Sensor (1) * No filter added * Output signal has too much
noise
* High pressure to current sensor
* If add filter, spend too much
space

3. Current Sensor-- Test Result (1)
* Green signal is motor phase current
* Red signal is output signal from current sensor

4. Current Sensor (2)
3 current sensors are needed and only two channel go to DSP
because they cause signals transform delay

5. Current Sensor (3) Open loop current sensor Close loop current sensor
cheaper
Lighter
Higher ability to withstand sustained overload
Close loop current sensor
Fast response
Excellent linearity
Less susceptible to electrical noise
low temperature drift
Preferred in high frequency circuits
Quick response and noise immunity to high di/dt

6. Current Sensor (4) LEM LTS 15-NP V_out=2.5 ± 0.625*I_in/IPN
IPN Primary nominal r.m.s. current 15 At
IP Primary current, measuring range 0 .. ± 45 At
V_out=2.5 ± 0.625*I_in/IPN

7. Current Sensor (5)
* Some methods to improve resolution:

8. Current Sensor (6) For new motor LEM LA100-P Supply voltage : +12-15V
IPN Primary nominal r.m.s. current: 100 At
IP Primary current, measuring range: 0 .. ± 150 At
Price: $30.80

9. Current Sensor-- Test Result (2)
* Using same power supply with power board
* A lot of noise exists – from power ground
* The red signal is output from current sensor – phase A and extend waveform
* The green signal is motor current – phase A

10. Current Sensor-- Test Result (4)
* Using separate DC power supply
* The red signal is output from current sensor – phase A
* The green signal is motor current – phase C

11. Current Sensor-- Test Result (5)
The isolated power supply can enhance current sensor performance by preventing digital switching noise of the logic circuitry that can be present on VSS and VCC from coupling into the current sensor analog stage.

12. DSP ADC Interface For DSP ADC :
Input signal voltage < VREFHI = 3.3 V and > VREFLO = 0 V
Absolute resolution = 3.22 mV at VREFHI = 3.3 V and VREFLO = 0 V
As VREFHI decreases, VREFLO increases, or both, the absolute accuracy increase
Current sensor corresponding resolution:
3.22*10^-3=0.625*Ip/15  Ip= A=77.28mA
--- when motor peak phase current is 13.9A, phase current will have a 77.28mA difference at every 1 -- smaller will better

13. * Motor phase current simulation result

14. Conclusion Another DC power supply is needed
Will try to decrease VREFHI and increase VREFLO to increase accuracy