Introduction
The following measurement example demonstrates use of the Teledyne LeCroy MDA810 Motor Drive Analyzer to characterize a battery-powered, three-phase motor drive and brushless DC motor. The characterization in this case comprises static and dynamic analysis of electrical and mechanical shaft power output.
Static and Dynamic Analysis
The device under test is a battery-powered drill purchased from a local retailer. Figure 1 shows acquisition waveforms of the DC bus and drive output. Also shown are analog torque/speed signals, digital Hall sensor speed signals, and per-cycle waveforms and torque vs. speed X-Y plots.
The screen capture’s display grid area is in four quadrants in this example, bearing tab labels of DC Bus, Drive Output, Mechanical, and Torque vs. Speed. The former three quadrants contain both full acquisitions taken over 2 seconds (200 ms/div) (the left side of each quadrant) and zoom traces of the highlighted areas (the right side of each quadrant). Note that the MDA800 can display vertical zoom traces as well as horizontal zoom traces, as can be seen in the DC Bus quadrant (Z6), providing a more detailed view of small changes in voltage amplitude.
The Mechanical traces comprise analog torque and speed signals from a Magtrol dynamometer (top half of Mechanicals quadrant) and Hall sensor signals from the motor drive circuitry. From these acquisitions, we calculate all of the mean speed and torque values shown in the Mean Value Numerics table at bottom (see the inset).
Clicking on those mean values opens the per-cycle waveform plot of torque vs. speed seen at bottom right. In this example, XY plots augment the per-cycle plot. Using the MDA800’s Zoom + Gate mode further enhances the analysis by using only the data from the zoom trace to create the per-cycle and XY plots.
Comparison to Other Analysis Methodologies
One could undertake analysis of a brushless DC motor and its associated drive circuitry in other ways, namely using a traditional power analyzer, such as those available from Yokogawa, Zimmer, and other suppliers; or a four-channel, 8-bit oscilloscope. The power analyzer performs the static analysis but not the dynamic analysis. Nor does it provide the MDA800’s Zoom + Gate facility to isolate a section of interest within an acquisition for analysis. It is able, however, to characterize the motor and drive’s input/output efficiency with 0.25% accuracy, although such accuracy generally is not necessary in this application. Further, the MDA800 allows calculation of speed from brushless Hall sensor signals while the power analyzer does not.
Meanwhile, the oscilloscope is only able to acquire and display voltage signals and has limited calculation capabilities in this application. The MDA800, on the other hand, delivers powerful analysis capabilities in its ability to plot measurement results vs. time. In this fashion, the instrument makes it easy to spot dynamic changes in data.
Lastly, the MDA810 also functions as a full-featured 8-channel, 12-bit high bandwidth oscilloscope, making it uniquely capable of correlating drive system control activities or other signals with motor or drive power behaviors.
Conclusion
Thanks to its deep and varied analysis capabilities, the MDA800 provides a far more insightful view into the performance of brushless DC motors and their drive circuitry. The ability to plot dynamic changes over time for attributes such as torque and speed can be an invaluable tool in troubleshooting such systems. When coupled with the MDA800’s long acquisition memory, that facility enables users to leap far beyond static mean measurements into the domain of full dynamic analysis.
