Tektronix is working to improve efficiency using subsystem power measurements. When it comes to traction inverters and motors Tektronix is working towards a high standard. The addition of SiC power semiconductors and measurements of the subsystems in those inverters and motors means more efficiency and a more compact inverter.
EV architects are using different motor designs with new traction inverter designs. These new hybrid structures are ideally suited to the demands of electric conveyance.
Techniques for a repeatable inverter measurement system. There are different motors in EVs, but all need to apply PWM voltage signals to the motor stator. They do this to create three sinusoidal currents spaced 120º apart.
The modulation of the high-voltage input is performed by high-voltage IGBTs or MOSFETs with switching frequencies that usually range from 20 to 100 kHz. The most important system design for this switching is minimizing energy loss while maintaining safe timing systems.
When analyzing critical inverter signals, pulse-width modulation and multi-phase current are critical. These waveforms present challenges for oscilloscopes as well as the engineers who rely on these measurements.
Being able to measure and observe these waveforms is a vital part of optimizing the inverter’s robustness, power density, reliability, and efficiency.
In these instances, the introduction of a 6 and 8-channel oscilloscope has simplified the study of 3-phase systems. In the case of inverters, there is a need for special measurements as well. There are two factors to take into consideration.
- 3-phase systems must be analyzed for voltage, current, angle, and power in individual phases as well as the total system measurements. For observing the magnitudes, angles, and balance a set of Phasor diagrams work well.
- In order to get stable repeatable measurements the PWM signals must be paid special attention, as they are the hardest to trigger on. A stable time reference is necessary, to get accurate readings.
Understanding system behavior under changing motor loads can be a key measurement to understand. Test conditions that can assess power density and efficiency under a number of circumstances are needed.
An oscilloscope with a long record length can store enough information during the run to provide relevant results in waveform and plots. The uses of high-speed data can’t be ignored here, this gives an engineer the capability to zoom in on a particular area of the waveform to pinpoint a problem. Many power analyzers typically support calibrated 3-phase measurement but don’t provide high-speed sampling rate data.
For a continued in-depth look into traction inverter and motor measurements and testing, access the Tektronix advice page here.
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