selected examples of electric power measurements in drive
TRANSCRIPT
Selected Examples of Electric Power Measurements
in
Drive Systems
Power Electronics Event
June 19, 2019
Timothy Hertstein
© Copyright 2019
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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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 [email protected]
+49 (0) 6171 88832 97
www.zes.com