Download How To Significantly Improve Efficiency Testing of Electrical Motors

How To Significantly Improve Efficiency Testing
of Electrical Motors, Inverters and Generators
Continuous and synchronous acquisition of electrical and
mechanical raw data for review, verification and analysis
eDrive Testing - Overview
• 
Why improve efficiency testing of motors, inverters and generators?
•  Increasing the efficiency of electrical motors, inverters and generators
provides significant growth and improvement in…
•  Electrical vehicles, primarily the distance a vehicle can travel
•  Cars
•  Buses
•  Trucks
•  Power-generation systems, resulting in optimized energy
•  Aircraft – APUs - auxiliary power units
•  Trains
•  Ships
•  Power generators (i.e. wind energy)
•  Elevators
•  Electrical appliances using PWM motors
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eDrive Testing - Overview
• 
How can we improve efficiency testing?
•  Traditional test methods have reached limitations for improving efficiency
•  Primarily designed for steady state testing
•  New test methods are required to significantly improve efficiency
•  Via continuous and synchronous acquisition of electrical and mechanical signals
• 
In this presentation we’ll…
•  Review traditional efficiency testing methods and limitations
•  Introduce a new test method to greatly improve efficiency testing
•  Present ways to safely, accurately, synchronously and continuously measure,
high voltages, currents, torque, speed, temperature, vibration…
•  Show calculations and waveforms for electrical and mechanical power and efficiency
•  Illustrate how to verify results
•  Show methods to perform motor and inverter analysis
•  Offer a list of articles, case studies and white papers for further details
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eDrive example: The electrical drive train in a car (or APU in reverse)
Battery
• 
Electrical
motor
Vehicle chassis with
2/4 driven wheels
Transmission
Components in an electrical drive train (simplified)
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Frequency
inverter
Battery
Frequency inverter
Electrical motor (with transmission)
Chassis
To improve range there are three possibilities:
•  Less weight
•  Better battery technology (capacity, lifetime, usage, drive profile adaption)
•  Higher efficiency (conversion, recuperation)
•  Currently the efficiency of electrical cars is at 50 – 60 % (battery to road)
•  This is due to dramatically changing conditions:
battery status, load, temperature, accelaration, driver habit…..
-> Improve inverter, motor, their matching and increase inverter „intelligence“
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eDrive: DAQ requirements on electrical (hybrid) drive train
Battery
Frequency
inverter
Battery voltage and current
* Voltages up to 1000 V DC
* Currents up to 300 A DC
* Battery / cell temperatures
* Electrical power
up to 100 kW
Electrical
motor
Frequency inverter output
voltages and currents
* Voltages up to +/-500 V AC,
n phases, modulated
* Currents up to 500 A AC
* Inverter temperature
* Electrical power
up to 100 kW
Efficiency frequency inverter
TorqueSensor
Vehicle chassis
Electrical motor output
* Torque
* RPM
* Rotor position
* Motor temperature
* Mechanical power
up to 100 kW
Efficiency electrical motor
Efficiency electrical drive
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eDrive: Measuring efficiency – the typical method
Battery
Electrical
motor
Frequency
inverter
ϑ
Battery voltage and current
Various slow speed measurement types,
i.e. just using DMM´s
ϑ
TorqueSensor
Vehicle chassis
ϑ
Frequency inverter output
n-phase power meter
(plus extra oscilloscope)
Electrial motor output
Torque transducer and DAQ system
for torque and speed
Problems:
1.  Difficult time synchronization between different systems
2.  Data storage in different systems & different formats
3.  No continuous raw data available for verification or analysis
4.  Slow calculation cycles of power meters
and questionable results in dynamic load changes
5.  No documented algorithms for power analysis, no verification possible
User comment:
„Sometimes we measure
efficiency larger 1.
We can´t believe that, but
we can´t analyse further
as we have no raw data.
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eDrive: Enhanced requirements on data acquisition
• 
Simple system configuration
•  One system for all different signals
•  Voltage, current, torque, speed, position, temperatures, vibration...
•  Easy setup
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Reliable acquisition
•  Simultaneous sampling of electrical and mechanical power
•  No phase shift caused by different data acquisition systems
•  Continuous storage to hard disc
•  One data format for all acquired data
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Faster, better results
•  Analysis per half cycle with documented, traceable algorithms
•  Verification of results and advanced analysis based on raw data
• 
Easier system integration
•  Open data format
•  Modern software interfaces
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eDrive: Current measurement at e-motor input – three methods *
Current transformers
•  High accuracy and high bandwidth
•  High effort in installation
Current clamps
•  Low accuracy and limited bandwidth
•  Easy to use
Current shunts
•  High accuracy and high bandwidth
•  Very difficult to measure
( mV signal on high frequency CMV ~ 500 V)
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eDrive: Voltage measurement at electrical motor input *
Passive isolated probe
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+/- 1000 V measurement range
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High bandwidth, low phase shift
Differential active probe
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Needs isolation amplifier (or probe)
•  Problem with probe is low accuracy
Isolation amplifier
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eDrive: Torque and RPM measurement at electrical motor output
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For the mechanical signals torque transducers are used
•  It‘s important to use a very accurate torque transducer
• 
A torque transducer acquires
•  Torque (M)
•  Speed (n)
•  And also Reference pulse (rotor position)
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The mechanical power delivered at the drive shaft is computed as:
Pmech = 2 x 𝛑 x n x M
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in [ ​𝑵𝒎/𝒔 ]
This formula delivers the instantaneous mechanical power
•  But for accurate efficiency calculation,
the mechanical power should be calculated
over the same cycle as the electrical power
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eDrive: New testing concept
Battery
Battery output
Frequency
inverter
Temperatures
via satellite
Current clamp / transformer
with shunt / Probe
Electrical
motor
Inverter output
Vehicle chassis
Transmission
Temperatures
via satellite
Current clamp / transformer
with shunt / Probe
eMotor output
One or two Torque transducer
Advantages:
1.  Continuous storage of all raw
data for verification and analysis
2.  Synchronous acquisition of all data
3.  Storage of all data in one system / format / file
4.  LIVE power calculations per half cycle
Optical
network
PC in control area
5.  LIVE scope and FFT displays
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eDrive: Hardware components to improve measurements
• 
One mainframe to acquire all signals
•  Voltages, currents, torque, speed, vibration...
•  200 MB/s continuous streaming to 500 GB SSD
• 
Isolated 1 kV input card
•  6 isolated channels, ±20 mV to ±1000 V, isolation 1,000 Vrms
•  Direct connection to HV signals without probes
•  Sample rate 2 MS/s @ 18 bit per channel
•  Accuracy 0.1%
•  One torque & speed channel per board
• 
Plug-on artificial star module
•  Creates artificial star point for 3 phase measurements
•  Plugs directly into the card to minimize cabling
• 
Optional, remote temperature satellite
•  16 channels type K or T
•  Keeps TC cables short for signal fidelity
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eDrive SW SETUP: Setting up the test in one single, simple menu
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eDrive LIVE: Numerical results *
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eDrive LIVE: Numerical results and scope *
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eDrive LIVE: Numerical results and scope and FFT *
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eDrive REVIEW: Typical signals, continuously acquired for 1 minute *
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eDrive REVIEW: Overview, zoom and 2nd zoom window *
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eDrive: Single phase voltage, current and the spectrum *
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eDrive ANALYSIS: Some basic math (simplified) *
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Input signals (to be measured)
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Voltage
Current
Torque
Speed
=u
=i
=M
=n
Power calculations (simplified)
•  True power
P
=
MEANcycle ( u x i )
•  Apparent power
S
=
( RMScycle u ) x ( RMScycle i )
•  Mechanical power
Pmech
=
MEANcycle ( 2 x 𝛑 x n x M )
Efficiency calculation
•  Efficiency electrical motor
η (Eta) = Pmech / P
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eDrive: “Cycle” detection (shown: current i_1) *
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To compute any power result the “cycles” of the signals are needed
Detecting the cycles via zero crossings is difficult due to noise
Advanced algorithms are needed to detect each cycle
•  result can be shown for verification
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eDrive: “Cycle detect” verification *
• 
The “cycle detect” integrity can be checked by computing the cycle frequency
•  Cycle frequency must not have peaks or drops ( = double / missing cycles)
•  Must be the same “wave shape” as rpm
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eDrive: Efficiency calculation – Formula Examples *
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Cycle detection
• 
RMS of voltage and
currrent per phase
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Instantaneous power
per phase
• 
True power per phase/total
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Mechanical power
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Motor efficiency
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eDrive: Some computed results *
Top to bottom: Mechanical power, Electrical power (P,S), Motor Efficiency
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eDrive: Other analysis possibilities *
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Advanced motor/inverter analysis on raw data using formula database
Potential Motor analysis
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Equivalent circuit diagram
Iron losses
Main inductance
Starting currents
Armature currents
Airgap torque
Torque ripple / cogging torque
Saturation effects
a
Potential Inverter analysis
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Space vector (α,β) transformation (Clarke)
dq0 transformation (Park)
Frequency & amplitude of fundamental
THD of voltage and current
Switching frequency
Modulation method & Inverter control behaviour
Re
α
i
ic
iβ
Im,
β
b
ia=iα
ib
c
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eDrive: Space vector transformation *
From the known signals u1, u2, u3 and i1, i2, i3
the space vectors uα, uβ and iα, iβ are calculated
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eDrive: New concept for e-motor/inverter testing – Summary *
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Use one system to connect to all signals being high voltage,
currents, torque, speed, temperatures, vibration…..
• 
All signals are sampled simultaneously and displayed live
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Sampling is done with high sample rate and high resolution
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Continuous raw data storage allows verification and analysis
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Setting up the measurement is done in one simple menu
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Power calculations are done LIVE and per half cycle
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A formula database can offer all the tools needed
for further, detailed motor and inverter analysis
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More detailed information
•  www.hbm.com/edrive
• 
Articles
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Brochures
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Case studies
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Datasheets
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White papers
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