Selected Examples of Electric Power Measurements in Drive Systems Power Electronics Event June 19, 2019 Timothy Hertstein
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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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