Test & Measurement

Motor drive analysers based on eight channel oscilloscope

2nd March 2015
Mick Elliott

Teledyne LeCroy’s MDA800 Series of Motor Drive Analysers (MDAs) combine three-phase power analyser static (steady-state) calculations, unique dynamic three-phase power and mechanical motor analysis capabilities, as well as high bandwidth (1 GHz) embedded control system debug in a single instrument.

The MDAs are based on the HDO8000 oscilloscope platform and are standard with 8 input channels (16 digital channels optional) with 12-bit resolution, 2.5 GS/s sample rate, up to 1 GHz bandwidth and up to 250 Mpts/ch acquisition memory. A complete set of serial trigger/decode and analysis software options, and a wide variety of voltage and current probes are available to use with the MDAs.

Designers and manufacturers of motors, motor drives, variable frequency drives, variable speed drives, industrial automation and motion control equipment manufacturers are all potential users. Design engineers that integrate motors into their designs (vehicles, power tools, appliances, elevators, fans, blowers, compressors, pumps, etc.) will utilise the product to validate proprietary controls and complete drive system designs. For engineers who design three-phase systems without motors, the MDAs can be used for basic three-phase power system analysis and debug as well.

A complete drive system is a complex mix of three-phase power electronics, motor/mechanical analogue and digital sensors, and embedded controls, with a complex variety of analogue, digital, serial data and pulse-width modulated (PWM) signals. Conventional 8-bit oscilloscopes are able to capture higher-speed embedded control system or power transistor activities. Power Analysers are a single-use tool for measuring input/output “black-box” drive power and efficiencies, but provide limited or no waveform capture for embedded control or drive system debug.

The MDA permits waveform captures from the drive three-phase power section, individual power transistors, and embedded control system, and performs coincident three-phase power analysis of the power section waveforms in one high-performance instrument, enabling debug and analysis of all aspects of the complete motor drive.

Various voltage, current, power (real, apparent, and reactive), phase angle/power factor, and efficiency parameters are calculated on acquired voltage and current waveforms and displayed in a Numerics table. The table is user-configurable and is displayed along with the acquisition waveform, and corresponds to information normally provided by a Power Analyser that measures in a “static” (steady-state) operating mode.

Additionally, the MDA provides numerical calculations under dynamic operating conditions. Waveforms showing any per-cycle measurement parameter variation can be “synthesised” and displayed by simply selecting a table value.

This Waveform is time-correlated with other waveforms acquired by the MDA and can be used to correlate complex drive behaviors to other control or power system waveforms, and to debug drive system problems. Statistical detail of the measurement set can also be displayed. This additional information goes well beyond what is provided by a Power Analyser.

The long acquisition memory in the Motor Drive Analysers (up to 250 Mpts/Ch) provides capabilities for motor, motor drive, and three-phase power dynamic response analysis. For example, 25 seconds of continuous acquisition capture is possible at a sample rate of 10 MS/s. This permits complete understanding of dynamic drive behaviors, such as startup, application of load, or fast changing load conditions, and correlation of drive response problems to control system instructions or power section failures.

An intuitive, graphical user interface provides setup/connection guidance. Setup capability is provided for any combination of single-phase or three-phase drive input/output, and supports both two- and three-wattmeter calculation methods and a line-line to line-neutral voltage conversion. Using the two-wattmeter method, drive input/output and motor output efficiencies can be measured using the eight inputs on the HDO8000 oscilloscope.

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