Modern oscilloscope analysis software can help engineers perform faster and more repeatable measurements. The new MSO Series 4 B is one such oscilloscope, recently released with a more powerful processor system to accelerate analysis for power converter designers at a price accessible to many professional designers.
Some benchtop oscilloscopes, like the MSO Series 4 B, can be equipped with three differential voltage probes, three current probes, and analysis software for measuring the output of industrial motor controllers.
Power Measurements in AC/DC and DC/DC Converters:
Power measurement and analysis packages facilitate measurements in AC/DC and DC/DC converters, from input stages to switching, control loops, and output stages. The Advanced Power Measurement and Analysis (4-PWR) option is one such package. The software automates the setup process for key power measurements, including AC line input measurements for frequency, RMS voltage and current, crest factor (voltage and current), real, reactive, and apparent power, power factor, and phase. Measurements of switching loss and magnetic loss help engineers make incremental changes to achieve fractional improvements with the latest broadband power devices. It also allows in-circuit measurement of the safe operating area (SoA) of switching devices. Bode plots can be used to evaluate the stability of power supply control loops. The fastest processor in the new version of the Series 4 B accelerates the calculations underlying these measurements for a faster refresh rate.
The power measurement and analysis software automatically performs calculations to measure switching losses in power converters. The red line represents VDS and the green line represents ID. The software configures the orange line, which displays the power loss during switching.
Measurements Support Transition to Wideband Devices.
The transition from silicon to silicon carbide (SiC) and gallium nitride (GaN) switching devices has placed even more pressure on measurement systems. For these devices, accurate switching assessment requires a much wider measurement bandwidth to accommodate faster response times. Until recently, switching measurements on the high side of half-bridge switching stages were nearly impossible. Any measurements relative to the switching node suffered distortion due to the high common-mode voltage signals impacting the differential signal. A relatively new class of probes uses optical isolation to achieve common-mode rejection of 80 dB at 1 GHz and higher at lower frequencies. The MSO Series 4 B is compatible with optically isolated IsoVu probes and is therefore capable of measuring switching signals of 100 V/ns or faster.
Special analysis software for dual-pulse testing is also available to assist designers in transitioning to widebandgap switching technology. The instrument's processing power is used to automate configurations, measurements, and calculations that help designers measure the switching and on-resistance parameters crucial for supporting power design, timing, and reverse recovery characteristics of the diodes.
Dual pulse tests are commonly used to evaluate the performance of FETs and IGBTs in circuit, under conditions that approach full power operation or beyond.
Three-Phase Power Analysis and Motor Controllers:
Controller and inverter designers face similar challenges. Most modern motor controller systems use pulse-width modulation (PWM) to control the frequency, and therefore the speed, of a motor. Pulse-width modulation makes stable measurements of these signals difficult. Manually determining the correct combination of filters and triggers to achieve stable waveforms is challenging, but it is a requirement for consistent measurements.
They often have three-phase outputs, which can complicate connections and configurations. The wiring configuration determines the calculations used in power analysis, so it is important to understand and select the correct wiring configuration to obtain the expected results. These configurations apply to both the inputs and outputs of the motor controllers. Improper probing of the motor controller system and poor connection integrity are common causes of errors when performing motor controller measurements.
In addition to measuring the controller output, measurements are also important for evaluating the performance of the controller's input stages, such as harmonics, power, and power factor. While it's possible to export raw waveforms to a spreadsheet or other analysis program, the process is time-consuming and requires careful calculations.
For these reasons, a good view of a motor controller system using an oscilloscope requires careful configuration, stable waveforms, and robust measurement algorithms provided by application software designed for this purpose. The enhanced performance of the 4B series makes it ideal for three-phase measurements of power systems and motor control systems that were previously only feasible on high-end oscilloscopes.
Three-phase analysis software can help obtain stable measurements on the PWM outputs of motor controllers. The phasor diagram quickly displays the relative phase and magnitude of the three voltages and currents.
Using 6 Channels to Measure Three-Phase Systems:
The output of motor controllers and inverters is typically a 3-wire system, meaning it lacks a neutral conductor or the system is balanced and there is no neutral current. Power in these systems can be accurately measured using only 2 voltage and 2 current channels on oscilloscopes by employing the "two-wattmeter method." This requires two voltage channels and two current channels, with the voltage channels connected phase-to-phase and one phase acting as a reference. This can be done with a 4-channel oscilloscope.
However, the inputs to an industrial variable frequency drive (VFD) are more likely to use a 4-wire system with a neutral conductor. In that case, three wattmeters must be used. The three-wattmeter configuration requires six oscilloscope channels: three for voltages and three for currents. Although several oscilloscopes offer 8 input channels, the MSO Series 4 B is one of the few professional-quality oscilloscopes available with 6 analog inputs.
We're taking test automation to the next level.
Like all Tektronix instruments, the MSO Series 4 B is equipped with industry-standard command interfaces and communication buses such as USB and Ethernet. It also includes high-speed APIs, tools, and software to optimize test development time and execution performance. To simplify instrument control, Tektronix provides access to native instrument drivers that translate instrument commands into familiar constructs in a chosen programming language. Users can choose from Python, LabVIEW®, CVI, MATLAB, C, C#, .NET, or virtually any other language and access free tutorials, scripts, examples, and videos, as well as learn more using our programming reference guides.
In conclusion
, tools for power converter measurements, dual-pulse testing, precise probes, and three-phase measurements help designers obtain fast and repeatable measurements and bring their projects to market more quickly. The increased underlying computational performance of professional oscilloscopes like the MSO Series 4 B brings the computational performance levels of high-end oscilloscopes to the engineer's bench, further accelerating the design process and improving ease of use.
About the author:
Andrea Vinci is Senior Technical Marketing Manager at Tektronix. He holds a Master's degree in Electronics from the University of Padua. Before joining marketing, he worked as an RF designer, test manager, applications engineer, and later in sales as a business developer in EMEA. His experience includes test solutions for semiconductors, power electronics, and energy storage applications.
