The Tektronix MSO68B6IMDA Inverter Motor Drive Analysis Software for MSO68B Units helps engineers design better and more efficient three-phase motor drive systems, taking full advantage of the advanced user interface, six or eight analog input channels, and 'High Res' mode (16 bits) on the 6 Series B MSO. The MSO68B 6-IMDA solution provides fast, accurate, and repeatable results for electrical measurements on industrial motors and drive systems for AC induction motors, permanent magnet synchronous motors (PMSM), and brushless DC (BLDC) motors. It can be configured to measure DC to three-phase AC converters, such as those used in the electric vehicles.

Measurements and analysis on three-phase power systems are inherently more complex than on single-phase systems. Although oscilloscopes can capture voltage and current waveforms with high sample rates, further calculations are required to produce key power measurements from the data. The oscilloscope based three-phase solution allows to capture three-phase voltage and current waveforms with higher sample rates - longer record lengths using the HiRes acquisition mode that goes up to 16-bits with the support of automated measurements produce key power test results. The Power converters based on Pulse Width Modulation (PWM), such as variablefrequency motor drives, can complicate measurements since it is very important to extract precise zero crossings for the PWM signals, thus making an oscilloscope a recommended test tool for validation and troubleshooting for motor designers. Special software, designed to automate power analysis on inverters, motors, and drives, greatly simplifies important three-phase power measurements on PWM systems and can help engineers get faster insights into their designs.

Measurement overview

Three-phase power converters such as variable frequency drives require a range of measurements during the design process. The Inverters, Motors, and Drives Analysis package for the 6 Series B MSO automates key electrical measurements which are grouped into the Electrical Analysis group. The measurements can be configured to measure the Input or Output wiring configuration.

The measurements can be set to measure 1V1I (1-Phase-2-Wire), 2V2I (1-Phase-3-Wire), 2V2I (3-Phase-3-Wire), 1V1I (1-Phase 2-Wire DC) or 3V3I (3-Phase-3-Wire), and 3P4W (3-Phase-4-Wire) to support various supply and motor configurations. Measurements can be performed lineto- line or line-to-neutral, to support delta and wye or star configurations.

Harmonics

Power waveforms are rarely textbook sinusoids. Harmonics measurements break down non-sinusoidal voltage or current waveforms into their sinusoidal components, indicating the frequency and amplitude for each component.

Harmonics analysis can be performed up to 200th harmonic order. The maximum harmonic order can be set to suit the user's needs by specifying the range in the measurement configuration. THD-F, THD-R and fundamental values are measured for each phase. Measurements can be evaluated against the IEEE-519 or IEC 61000-3-2 standard, or custom limits. Test results can be recorded in a detailed report indicating pass/fail status.

The Harmonics plot shows the test results for all three phases grouped together so that the user can correlate the test results between the phases. The plot also shows the test results visually. The harmonics bars are highlighted in green during a pass condition, and highlight to red when it exceeds the test limits. This gives a quick insight to the user when debugging for harmonics design.

Power quality

This measurement provides critical three-phase power submeasurements including frequency and RMS magnitudes of voltage and current; crest factors of voltage and current; PWM frequency; and phase angle for each phase. It also displays the sum of true power, the sum of reactive power, and the sum of apparent power components.

Additionally, in the Line-Neutral configuration, this measurement displays True Power, Reactive Power, and Apparent Power components of all three-phases.

Voltage and current vectors can be displayed on a phasor diagram so the user can quickly judge phase shift for each phase and the balance among phases. Each vector is represented by an RMS value and phase is computed using the Discrete Fourier Transform (DFT) method.

The Power quality measurement can be configured to provide critical three-phase power measurements on the output side, including frequency and RMS magnitudes of voltage and current; crest factors of voltage and current; PWM frequency; true power; reactive power; apparent power; power factor; and phase angle for each phase.

Efficiency

Efficiency measures the ratio of the output power to input power. The MSO68B 6-IMDA solution supports efficiency of three-phase AC and Inverter configurations. By using the 2V2I method, three-phase efficiency can be measured using eight oscilloscope channels (2 voltage and 2 current sources on the input side and 2 voltage and 2 current sources on the output side). The solution calculates efficiency at each phase (for 3V3I configuration) and the total (average) efficiency of the system based on the different input and output wiring combinations.

Ripple analysis

Ripple is defined as the residual or unwanted AC voltage on a constant DC component. It is typically measured on the DC bus. This measurement helps to understand how efficiently the signal is getting converted from AC-DC on the input side, and the impact of unwanted components on the PWM signal on the output side.

Dynamic measurements using trend analysis

A common requirement in motor drive analysis is an ability to look at the motor response over longer test times, records, and an extended number of acquisitions to monitor the DUT behavior over varying load conditions. This dynamic measurement helps to understand optimal designs and interdependency between different parameters like voltage, current, power, frequency, and their variance based on the load conditions. The user can manually zoom into the specific region of interest to look at test results at the particular region of the waveform.

MSO68B 6-IMDA solution offers two unique trend plots on the power quality measurement to support such requirements:

Time trend plot

Acq trend plot

Each plot has its advantages and can be used to plot the supported sub-measurements under power quality measurement. The time trend plot shows the measured value per cycle, or for an acquired waveform (a record), while the acq trend plot shows a mean of the measured value per record, over each of the acquisitions. The acquisition count can be set by the user during the test configuration. This allows users to capture long records of data to perform deep record analysis and understand the dynamic behaviors of the motor response. The plots can be saved as a CSV file for post-processing.

Report generation

The MSO68B 6-IMDA software simplifies data collection, archiving, documentation of the design, and development process. It supports the report generation in MHT or PDF formats with pass/fail results for easy analysis.