VFD Testing, Modeling, and ControlBernie Lesieutre
BPA Synchrophasor Meeting, Portland April 21, 2010 1
Tests Overview
Purpose: Measure the response of variable frequency drive running
• Fan (7.5 HP)• Pump (7.5 HP)
with the goal to • Develop suitable load model• Design grid responsive controls
2
Tests
Our typical suite of tests:• voltage ramp• voltage steps• voltage sags• voltage oscillations• frequency steps• frequency ramps• frequency oscillations
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Fan Test Arrangement
Measurements: • Input voltage and currents • VFD DC link voltage• Motor speed
Compute: Active and Reactive Powers4
Calculations: Positive Sequence
Voltage Ramp
Positive Sequence, fundamental frequencypf ≈0.99 laggingP≈1500 W Q≈200 VAR
P
Q
Vfd – current/power drawn
iaThe current drawn by the VFD is NOT sinusoidal, and has strong harmonics.
RMS calculations:P≈ 1500 W Q≈1300 VARPf ≈ 0.75 lagging
“Rabbit Ears”
YIKES!
We look at fundamental frequency calculations in this presentation
Voltage Steps – Active Power
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Voltage Steps: Reactive Power
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Voltage Ramp: Active Power
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Voltage Ramp: Reactive Power
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Voltage Oscillations
Q
PV
Small oscillations noted in active and reactive power responses:• Low frequency active power response follows steady-state response• Higher frequency?
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Pump Test Arrangement
Measurements: • Input voltage and currents • VFD DC link voltage• Motor speed
Compute: Active and Reactive Powers12
Voltage Steps: Active Power
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Voltage Steps: Reactive Power
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Voltage Ramp: Active Power
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Voltage Ramp: Reactive Power
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Matlab Simulation Model
Rectifier PWM Inverter
IMInput
open loopvolts/hertzcontrol
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Simulation – Voltage Steps
(protection is not represented in the Matlab model)18
Simulation: Voltage Ramp
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Simulation: Voltage Oscillation
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Next Steps
Rectifier PWM Inverter
IMInput
open loopvolts/hertzcontrol
Grid Responsive Control
speed command
VFD
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Control Objective
Control the VFD to make the VLF/IM load• Voltage response appear as constant current• Frequency response D = 10.
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Control Objective
Control the VFD to make the VLF/IM load• Voltage response appear as constant current• Frequency response D = 10.
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Voltage Ramp Test - ActualFAN
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Voltage Ramp Test - ControlsFAN
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Voltage Step Test - Actual FAN
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Voltage Step Test - ControlsFAN
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Frequency Responsive ControlsFAN
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