Power and Efficiency Measurement of Motors and Inverters

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Power and Efficiency Measurement of Motors and Inverters


High-precision power consumption and efficiency evaluations of  motors and inverters used in EVs and robots are required. In an evaluation, it is important to observe the transient instantaneous power and voltage and current waveforms during acceleration and deceleration as well as during steady state.

Simultaneous measurement of motor torque, rotational speed, other sensor signals, and control data is also required for verification within a wide operating range.


High-precision, wide-band power and efficiency measurement
Direct input of voltage and current
Wide range of voltage measurement from low to high voltages
Fast measurement of fluctuating power
Synchronous display of power parameters and waveforms of input voltage, current, etc.
Simultaneous measurement of motor torque and rotational speed
IEC harmonic, voltage fluctuation/flicker test
Synchronous measurement with an oscilloscope or data logger
Report creation with data


Yokogawa’s power meters / WT series of power analyzers, to which current and voltage can be directly input, include the WT5000 Precision Power Analyzer with high bandwidth (up to 1 MHz), high accuracy (maximum accuracy of ± 0.03%), and up to 7 inputs, and the PX8000 Precision Power Scope, which offers both “High-precision power measurement" and "Waveform measurement with improved time resolution“, providing more accurate power and efficiency testing.

Direct input supports small current to large current, low voltage to high voltage.
High-precision DC/AC signal simultaneous measurement and power/efficiency measurement
Large-current and high-voltage model available (up to 50 A, 1000 V)
Testing of up to 3000 Apeak with AC/DC current sensor series
Evaluation of 2 systems, up to 4 motors (WT5000 /MTR1, /MTR2 option)
A wide variety of line and frequency filters, including an anti-aliasing filter, allows high-accuracy measurement of harmonic components with a motor rotational speed as the fundamental frequency along with the measurements over the entire measurement band.
Harmonic test according to IEC/JIS, voltage fluctuation/flicker test according to IEC (WT5000)
Synchronous measurement between the WT5000,  the ScopeCorder DL950 and the Mixed Signal Oscilloscope DLM5000




nApplication example

Evaluation of up to 4 motors (WT5000)

In EV development, it is necessary to evaluate multiple motors at the same time. Simultaneous evaluation of 4 motors is required especially in the development of four-wheel drive vehicles.

With the /MTR1 and /MTR2 options, a single WT5000 provides simultaneous evaluation of 4 motors. These options can also be used to measure rotational speed, direction and electrical angles from the input of A, B and Z phase signals of two motors.

Evaluation of up to 4 motors (WT5000)

Waveform data streaming at up to 2 MS/s, synchronous measurement of highly precise power values and waveforms (WT5000)

Synchronized with normal power parameter measurements, the voltage/current waveforms and torque/rotational speed data of the same measurement period , on which the power calculations are based, can be continuously streamed to a PC at up to 2 MS/s without any gaps (/DS option).

By analyzing both numerical values and waveforms at the same time, it is possible to analyze in more detail how changes in noise on the waveform or changes in the control state affect the power values and each parameter through the changes in the waveform.

In an efficiency map creation where a combination of rotational speed and torque is tested, not only the efficiency data, but also the waveform data synchronized with power value calculation results can be saved. Additionally, you can always back up the original data of voltage/current waveforms, which  may be required in evaluation reports.

Waveform data streaming (up to 2 MS/s)

Waveform data streaming (up to 2 MS/s)

Basic characteristics test of voltage, current, torque and rotational speed

Testing of I-V, S-T, and  I-T characteristics

The X-Y display and mathematical functions of the PX8000 Precision Power Scope can be used to convert the rotational speed and torque data to time-series data for each cycle to evaluate the I-V characteristics (current-voltage phase characteristics), S-T characteristics (rotational speed-torque), I-T characteristics (current-torque), and other motor characteristics.

Basic characteristics test of voltage, current, torque and rotational speed

Transient power measurement of motors and inverters

The PX8000 Precision Power Scope has 100 MS/s, 20 MHz bandwidth, and 12-bit resolution to accurately capture high-speed inverter waveforms and perform instantaneous transient power calculations.

In addition, torque and rotational speed can be input together with voltage/current electrical signals, enabling evaluation of inverter efficiency, motor efficiency and overall efficiency of an inverter-driven motor.

Transient power measurement of motors and inverters

IEC/JIS standard test

With the Precision Power Analyzer WT5000 (with /G7  option) and IS8011/IS8012 Harmonic/Flicker Analysis  Software, you can complete tasks from IEC/JIS Harmonic/Flicker standard compliance assessment up to test report output without any specialized knowledge.

IEC/JIS standard test

Harmonics standard test

You can import the harmonic data measured by the WT5000 with /G7 option to a PC and perform harmonics tests according to IEC/JIS standards by using the IS8011/IS8012 Harmonic/Flicker Analysis  Software. With the CT200 current sensor, you can test large equipment over 16 A/phase (IEC61000-3-12).


Voltage fluctuation and flicker standard test

The WT5000 with the /G7 option can measure voltage fluctuation and can conduct a flicker test, according to IEC61000-3-3 standard. This option shows a trend of parameters such as dc, dmax and Pinst (instantaneous flicker sensation). To capture test results, this option generates a comprehensive test report.

nSynchronous Measurement with ScopeCorder DL950

The combination of Precision Power Analyzer WT5000, ScopeCorder DL950, and Integrated Software Platform IS8000 enables  simultaneous recording and display of highly reliable  power measurements calibrated to national standards and high speed, high precision voltage/current and motor torque waveforms. Motors and inverters can be evaluated accurately and efficiently.

Synchronous Measurement with ScopeCorder DL950

nPower calculation function of Oscilloscope and ScopeCorder

You can use the power calculation function of the Oscilloscope or ScopeCorder, if you only need rough power measurements, rather than the high-precision power measurements using a power analyzer.

DLM5000 /G03 Power supply analysis option

It can measure power parameters automatically for up to four pairs of voltage and current waveforms, such as active power, apparent power, reactive power and power factor.

DL950 /G05 Power math function option

The DL950 calculates the conversion efficiency from the input and output power of an inverter and analyzes the effects of harmonics caused by external disturbances while capturing mechanical variations in motor speed and torque.

Also, the DL950 can trigger on the trend waveforms of power parameters.

Related Industries

Related Products & Solutions

IS8000 Integrated Software Platform

  • IS8000 comprehensive test and measurement software
  • Accelerate engineering workflow 
  • Integrate timing, control, and data collection from multiple instruments

PX8000 - Precision Power Scope

  • Transient/Start-up Waveform Capture & Power Analysis
  • Harmonics, Cycle by cycle and FFT analysis

WT1800E - High-Performance

  • Power, Harmonics (THD) Measurements (up to 500th order)
  • Electrical & Mechanical Efficiency of Inverters and Motors in EV and HEV



WT5000 - Precision Power Analyzer

  • Precision power analyzer with superior accuracy
  • 7 swappable input elements
  • 4 motor inputs
  • Harmonics test compliant to IEC 61000-3-2

Power Analyzers and Power Meters

Measure characteristics of devices that generate, transform or consume electricity. Also called power meters or wattmeters, these devices measure parameters such as true power (watts), power factor, harmonics, and efficiency.

Precision Making