Selected Examples of Electric Power Measurements

in

Drive Systems

Power Electronics Event

June 19, 2019

Timothy Hertstein

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ZES ZIMMER Electronic Systems GmbH

- The importance of synchronisation

- Why accuracy and bandwidth are necessary

- The influence of accuracy on efficiency and losses

- Aliasing and how to avoid it

- Requirements for DC link measurements

- How to measure sub-cycle behaviour

- Common mode errors and their prevention

Challenges & Pitfalls

2

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Drive system measurements: many sources, lots of data

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Power Spectrum (18kW, no load, close to VFD)

4

1,E-03

1,E-02

1,E-01

1,E+00

1,E+01

1,E+02

1,E+03

1,E+04

10,00 100,00 1000,00 10000,00 100000,00

Po

we

r/ W

att

Frequency / Hz

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Power Spectrum (4W, no load, 100m cable)

5

0,0001

0,001

0,01

0,1

1

10

10 100 1000 10000 100000 1000000 10000000

Po

we

r /

Wat

t

Frequency / Hz

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• Efficiency

• Drive/frequency converter

• Motor

• Motor drive combination

• DC link

• Residual ripple

• Start-up behaviour

• Error influences

• General observations

• Common mode errors

Typical drive system measurements

6

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Efficiency considerations

7

Electric Drive System

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ZES ZIMMER Electronic Systems GmbH

Influence of accuracy

88

100W

99W

101W

98W

97W

99W

Tolerance 0.1%

ηmax = 98.2%

ηmin = 97.8%

At 2W loss: +/- 0.198W ≙ 9.9%

Tolerance 0.2%

ηmax = 98,4%

ηmin = 97.6%

At 2W loss: +/- 0.396W ≙ 19.8%

Input Output

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Filter Dilemma

9

• Requirements for drive/motor efficiency measurements:

• Determination of broadband RMS power

• Undersampling not critical for RMS power measurement

• Requirements for measuring potentially torque-relevant portion at drive output:

• Isolation of fundamental

• FFT or filtering required

• Danger of aliasing!

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Risky: Sampling without Anti-Aliasing Filter

10

Broadband values

Sampling DigitalFilter

Narrowband values

e.g. fundamental of motor

e.g. power up to 10 MHz

!

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Safe, but laborious: repeated sampling

11

Broadband values

Signal

AAF Narrowband values

e.g. fundamental of motor

e.g. power up to 10 MHz

Signal

Repetition of test

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Safe: double, parallel sampling

12

Broadband values

Signal

AAF Narrowband values

e.g. fundamental of motor

e.g. power up to 10 MHz

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Novel approach: Dual Path

13

• Truly parallel measurement of broad-

and narrowband values only possiblewith additional hardware

• Aliasing risk eliminated

• Time-savings by eliminating repeat

measurements

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DC link measurements: residual ripple

14

• Overlay of low-amplitude AC voltage (≤ 5%) on top of

550-600V DC voltage

• Good dynamic range required

• Resolution sufficient?

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Motor start-up behaviour

15

0

1.000

2.000

3.000

4.000

5.000

6.000

7.000

8.000

9.000

10.000

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

P /

W

Zeit / s

Power at motor start-up

p-q Theory Power Components Calculations, João L. Afonso, Member, IEEE, M. J. Sepúlveda Freitas, and Júlio S. Martins,

ISIE’2003 - IEEE International Symposium on Industrial Electronics, Rio de Janeiro, 2003

“In three-phase electrical systems the

instantaneous real power presents

symmetries […], depending on the

system being balanced or not, and

having or not even harmonics.

Since the instantaneous zero-

sequence power presents an equal or

smaller symmetry period, the

instantaneous three-phase power, […]

, presents the same kind of

symmetries.

This paper suggests the utilization of a

sliding window, in a digital control

system, to calculate the mean value of

the instantaneous real power,

exploiting the symmetries described

above.“

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Influence of common-mode signals

Delta voltage

U12

Motor

Common-mode voltage

≈ Star voltage

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Common-mode errors: a simple test (Step 1)

17

Shorting voltage input

Filters deactivated!

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Common-mode errors: a simple test (Step 2)

18

Applying frequency converter phase voltage

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Common-mode error: numerical estimation

19

Measured value with shorted voltage channel:

UDC2 + UNOISE2 = 9mV

Measured value with frequency converter phase voltage applied:

UDC2 + UNOISE2 + UCM2 = 21mV

Common-mode voltage influence on measured value:

UCM = 21mV2 − 9mV2 ≈ 19mV

Relative influence common-mode signal at 180V phase voltage: 0,019V/180V ≈ -80dB

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p-q Theory Power Components Calculations, João L. Afonso, Member, IEEE,

M. J. Sepúlveda Freitas, and Júlio S. Martins,

ISIE’2003 - IEEE International Symposium on Industrial Electronics, Rio de

Janeiro, 2003

ZES ZIMMER Applikationsbericht 109 (Rev. 1.4): Elektrische Leistung und

Wirkungsgrad am Frequenzumrichter zuverlässig messen, Thomas Jäckle,

Oberursel, 2014

References

20

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Thank you very much for your attention!

Questions?

21

Timothy Hertstein

ZES ZIMMER Electronic Systems GmbH thertstein@zes.com

+49 (0) 6171 88832 97

www.zes.com