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

Some Test Result about Current Sensor

Limei Zhao

07/23/2003

Current Sensor (1)

* No filter added* Output signal has too much noise* High pressure to current sensor

* If add filter, spend too much space

Current Sensor-- Test Result (1)

* Green signal is motor phase current* Red signal is output signal from current sensor

Current Sensor (2)

3 current sensors are needed and only two channel go to DSPbecause they cause signals transform delay

Current Sensor (3)

Open 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

Current Sensor (4)

LEM LTS 15-NP 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

Current Sensor (5)

* Some methods to improve resolution:

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

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

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

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.

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=0.07728A=77.28mA--- when motor peak phase current is 13.9A, phase current will have a 77.28mA difference at every 1 -- smaller will better

* Motor phase current simulation result

Conclusion

Another DC power supply is needed

Will try to decrease VREFHI and increase VREFLO to increase accuracy