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

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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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