The drive for efficiency and long battery life implies that power considerations play a key role in designs—from battery-powered mobile devices and electric vehicles to industrial and utility power systems. A variety of instruments has a role to play in power-analysis applications—from general-purpose oscilloscopes to dedicated power analyzers. Subtle challenges abound, however, and whatever approach you choose, it’s important to beware of potential sources of inaccuracy.
Wilson Lee, technical marketing manager at Tektronix, said power analysis applies to a wide range of application areas, involving problem solving from initial device level characterization to production test. At each stage, he said, an effective power-analysis strategy “… requires design and test engineers alike to delve into complex measurements that require ultraprecise, higher resolution measurements in order to optimize power efficiency and performance.”
Lee said engineers face several specific challenges:
- making high-precision power measurements, particularly in very low-power applications;
- simultaneously sourcing and measuring voltage and current with high resolution and accuracy;
- finding an effective way of simulating any battery model; and
- troubleshooting power-related issues in applications that go across the time and frequency domains.
Mike Hoyer, applications engineer at HBM Test and Measurement, offered his own list of power-analysis challenges engineers are facing:
- They are contending with more than three phases and often the lack of proper test equipment.
- They are performing multimotor or hybrid testing and again often lack a test system capable of performing the electrical and the mechanical testing.
- They face shortening test cycles from taking the measurement to getting to the result, which might be an efficiency map. The process can take days or weeks today.
Pursuing higher efficiency
According to Bob Zollo, solution architect for battery testing at Keysight Technologies, “Our customers, and the industry overall, are seeking to create higher efficiency power conversion to make the world greener or to increase runtime on battery-powered devices, from mobile electronics to electrical vehicles (where runtime means increased driving range).” Unfortunately, he added, “As devices become more efficient, it becomes increasingly difficult to measure efficiency.”
He explained that as efficiency pushes up over 90% and close to 98% or 99%, “The power loss during conversion becomes difficult to measure, as the loss is an ever increasingly small number on top of an increasingly large number.” He cited as an example a 100-W power converter with 95% efficiency. An oscilloscope with 3% measurement error could indicate that the efficiency is anywhere from 89% to 101%. The scope is simply not accurate enough to be useful.
The February issue of EE-Evaluation Engineering includes an article1 by Bill Gatheridge and Sam Shearman of Yokogawa that describes the types of instruments and systems—including dedicated power analyzers, data-acquisition systems and data recorders, and general-purpose instruments like oscilloscopes with dedicated power-analysis software tools—able to make power measurements. It also addresses the advantages and disadvantages of each.
One instrument that Yokogawa offers for power analysis is the WT800E precision power analyzer (Figure 1). Introduced last September, it was engineered to obtain highly precise and simultaneous measurements on the input and output of power-conversion devices and to improve equipment evaluation efficiency by facilitating simultaneous power measurements.
To measure the distorted voltage or current waveforms that energy-saving switching techniques can cause, the WT1800E employs 16-bit 2-MS/s ADCs to make power measurements from 0.1 Hz to 1 MHz. Basic power-measurement accuracy at 50/60 Hz is 0.05% of reading plus 0.05% of range.
For electric-motor testing, the WT1800E offers an optional “motor evaluation” that enables a single WT1800E to measure all the electrical power parameters along with rotation speed, torque, mechanical power, synchronous speed, slip, motor efficiency, and total system efficiency.
Applications that require continuous automatic testing of EV/PHV/motor drives and other rotating devices with varying speed can benefit from the new capability to automatically set the measurement interval. The WT1800E offers nine data update rates from 50 ms to 20 s that can be set manually or automatically.
The WT1800E also can perform maximum peak power tracking measurements in photovoltaic power-generation applications, and it includes a power-integration function that measures the amount of power sold or purchased in grid interconnection applications. Autoranging during integration and the vendor’s “average active power” function make it possible to measure power consumption under conditions where the power fluctuates greatly.
Several options assist with direct connection to sensors, simplifying tests by avoiding the use of separate hardware. A new current sensor power option, for example, can power up to six current sensors directly with a ±15-V supply. Support for the Modbus/TCP protocol enables connection with PLCs and recorders.
Hoyer at HBM said his company addresses the test and optimization of inverter-driven electrical machines in both automotive as well as “generic” industrial applications. The company focuses on test-rig-only (not mobile) testing.
His company’s offerings to meet power-analysis challenges, he said, include the HBM eDrive solution (Figure 2), which is scalable from three to 51 power channels to address three-phase, greater than three-phase, multimotor, and hybrid applications. It performs electrical and mechanical data acquisition in one box. Integrated analysis allows motor-map result generation in minutes (in real time with very short acquisition cycles per set point).
HBM, Hoyer said, offers options such as the eDrive dedicated software suite to facilitate the setup, acquisition, and analysis of electrical motor parameters; high-voltage probes up to 7.2 kVrms; isolated digitizers supporting even higher voltage; and a full line of digital torque transducers.
Hoyer concluded, “We not only measure efficiency (like a standard power analyzer), we give insights into the drive control and thus enable the user to optimize this and to improve efficiency.” The company offers tools to implement a real-time space-vector strategy as well as dq0 (direct-quadrature-zero) transformations (aka Park and Clarke transforms).
Analyzers and meters
Andrew Fretz, applications engineer, Hioki USA, said his company’s diverse lineup of power analyzers, power-quality analyzers, and power meters covers the gamut of power-analysis applications, including mobile battery-powered devices, industrial electric motors, electric vehicles, and utility/grid systems. “Hioki’s instruments are designed and developed for today’s most demanding electrical and electronic industries,” he said. “Whether in the laboratory performing product development or in the field capturing real-world data, our advanced instruments provide the necessary electrical statistics to drive scientific conclusions.”
When asked what main challenges customers face, he said, “Accuracy of test results is always in the forefront of thoughts and concerns when power evaluations are being conducted.”
He continued, “Our flagship PW6001 power analyzer not only offers exceptional accuracy but also incorporates a control menu structure and touchscreen graphical interface that make otherwise complex operations intuitive. Customers consistently tell us that navigating the instruments control menu inspires confidence.” Specifications include 5-MHz sampling speed, an 18-bit A/D converter, and 80-dB at 100-kHz common-mode rejection ratio.
“Our newly released PW3390 power analyzer updates the popular legacy model with improved basic power accuracy, widened frequency bandwidth, and a current sensor phase correction function,” he said, adding, “Power quality analysis in the field can be accomplished with our PW3198 (Figure 3), a ruggedized portable instrument that field engineers trust and routinely rely on.”
The company also supports measurement of power consumption of individual pieces of electrical equipment with its PW333X Series power meters. One of the five different models in this family will fit the wide variety of applications they are intended to serve, Fretz said.
He added, “Our in-house designed and developed current transducers are some of the most accurate in the world. Both our clamp-on configurations and highest precision pull-through designs offer wide-bandwidth and broad temperature range for today’s demanding applications.”
He noted that some applications do not require the highest-level comprehensive data that the company’s power-quality analyzers provide. “When simpler power consumption analysis is needed for an entire facility or just one circuit breaker panel within a facility, our PW3360 power demand analyzer becomes the perfect choice,” he said. “Detailed statistical data in easy-to-interpret formats allows facility managers to take control of their energy
Four power-analysis markets
Teledyne LeCroy, according to a spokesperson, serves four “power analysis” markets:
- power-semiconductor-device power analysis;
- switch-mode power-supply (single-phase) power analysis;
- inverter, drive, and motor (single-phase and three-phase) power analysis; and
- digital power-management (rail voltage) power analysis.
Specific relevant products feature probes for power electronics applications, including the HVD Series high-voltage differential probes, available with 1-, 2-, or 6-kV safety ratings. They achieve 65-dB CMRR at 1 MHz and 1% accuracy and offer wide differential-voltage ranges.
Teledyne LeCroy also offers a high-voltage fiber optically isolated probe, which it previewed at the IEEE Energy Conversion Congress and Expo (ECCE) 2016 exhibition last September in Milwaukee. The HVFO103 has 140-dB CMRR and is suitable for upper-side gate drives, floating control/sensor signals, and EMC, EFT, ESD, and RF immunity testing.
And in November, the company introduced the RP4030 active voltage rail probes, which have a 4-GHz bandwidth, ±30V offset, and low attenuation/noise. They support a variety of coaxial connections including solder-in leads, U.FL (de facto standard developed by Hirose) and MCX (micro coaxial) receptacles, and browser tips.
Concurrent with the RP4030’s debut, the company also introduced its MIPI System Power Management Interface (SPMI) serial decoder, which monitors and correlates SPMI serial bus messages with DC power/voltage rail changes. These two products are suitable for testing line or battery-powered computing and embedded systems that use digital power management ICs to reduce power consumption and increase system efficiency. They add to the capabilities already provided by the HDO8108 (1-GHz, eight-channel, 12-bit) and the HDO9404 (4-GHz, four-channel, 10-bit) high-definition oscilloscopes.
And finally, Teledyne LeCroy’s DA1855A differential amplifier has 100-dB CMRR with 10x gain and precision offset adjust. It is suitable for both device conduction and switching loss measurements as well as current-sense measurements.
Power supplies and solar inverters
Lee at Tektronix said his company addresses a range of power-analysis application markets: traditional AC power generation, AC/DC power supplies, solar inverters, and high-power components requiring test, and characterization. The company also supports ultralow-power measurements required in IoT and wireless sensor node applications as well as battery life-cycle simulation.
He cited several specific Tektronix instruments that can serve in power analysis. He described the SMU 2450 as “the industry’s first and only touchscreen source-measurement unit,” delivering up to 1-kW pulse power with 0.02% accuracy and 6.5 digits of resolution. “It has best-in-class low-current resolution of 0.1 fA, 15 times faster low-current settling time, and a best high-speed sampling rate of 1 MS/s.” He added, “Pulse testing enables testing of high-power semiconductors at wafer level without damaging the parts due to overheating or changing their characteristics due to temperature rise.”
In addition, he said the DMM7510 7.5-digit DMM features a touchscreen interface and a high-speed, 18-bit digitizer. It stores up to 27 million records, and its current sensitivity enables measurement of the low deep-sleep drain currents from low power RF devices.
Lee also cited the 4200A-SCS parameter analyzer, used to characterize device I-V and C-V performance with one setup that maximizes test quality and reduces test time. The 2281S battery simulator enables battery simulation on any battery type—covering state of charge, amp-hour capacity, equivalent series resistance, and open-circuit voltage; it can emulate battery performance from full charge to total discharge.
The PA3000 power analyzer with up to four channels, Lee said, is suitable for high-efficiency compliance test, supporting single- and three-phase applications with ±0.04% basic voltage and current accuracy and 10-mW standby power measurement capability. And the 2380 electronic load is suitable for power efficiency test in constant current, constant voltage, constant resistance, and constant power modes.
Tektronix oscilloscopes also are applicable for power analysis. The MDO4000C mixed-domain oscilloscope synchronizes RF, analog, and digital channels—“giving unprecedented insight into your power design,” Lee said. “The MDO4000C combines up to six instruments including a function generator and a built-in spectrum analyzer. The additional Power Analysis Application Module enables quick and accurate analysis of power quality, switching loss, harmonics, safe operating area, modulation, ripple, and slew rate (dI/dt and dV/dt).”
Finally, Tektronix offers IsoVu probes, which employ optical communications and power-over-fiber technology for complete galvanic isolation. “When combined with an oscilloscope equipped with the TekVPI interface (such as the MDO4000C), it is the first, and only, measurement system capable of accurately resolving high bandwidth differential signals in the presence of large common-mode voltage,” Lee said. “Apart from being the only system with complete optical isolation and high common-mode rejection, it also combines a 1-GHz bandwidth and a 2,000-V common-mode voltage range, [and it supports] 50-V differential voltage measurements.”
Power-conversion electrical test
Zollo at Keysight said his company’s IntegraVision power analyzers (Figure 4) are focused on electrical test of power-conversion systems. “Our high accuracy, fast digitizer, and single-shot measurement capabilities are targeted at testing AC/DC power conversion systems, DC/DC converters, DC/AC inverters, and other pure electrical devices. These power-conversion systems are found in many end devices, such as solar inverters, AC/DC power supplies, battery chargers, electrical-vehicle inverters, and electric-vehicle onboard chargers.”
Zollo elaborated on the IntegraVision family. “The PA2201A is a two-channel version suitable for measuring DC or single-phase AC power, he said. “The PA2203A is a four-channel version suitable for measuring DC or three-phase AC power. Here, a channel represents a simultaneous voltage measurement and current measurement along with calculation of instantaneous power.”
IngtegraVision, Zollo said, is the first power analyzer that combines accurate power measurements with a touch-driven oscilloscope visualization capability in a single instrument, with the user interface based on technology from Keysight’s InfiniiVision 6000 X-Series oscilloscope, including its 12.1-inch multitouch capacitive touchscreen with pinch, zoom, and scroll capabilities. Offering 0.05% basic accuracy and 16-bit resolution, he said, “The power analyzer enables engineers to characterize power consumption under highly dynamic conditions with 5-MS/s digitizing speed and 2-MHz bandwidth.”
When asked about options, Zollo replied, “The Keysight IntegraVision was designed to be a self-contained instrument that did not require users to have costly additional accessories and software. Each channel is configured with a built-in highly accurate 2-A current-measurement shunt, a 50-A current-measurement shunt, and an input for a current probe or transducer when more than 50 A is needed. By offering both low and high current shunts on every channel, the user won’t find himself with an analyzer that is sized improperly for the task at hand.” He added that the instrument supports a variety of current probes designed for use with Keysight oscilloscopes as well as non-Keysight probes. “Our goal was to be compatible with accessories already on hand so that the users can reuse the accessories they already have at their disposal,” he said.
Radio communications and power
Rohde & Schwarz cites long battery life as a key criterion for mobile devices as well as for embedded systems and chips for IoT and M2M applications. To address such applications, the company offers a system (Figure 5) for testing battery life in all operating modes. It consists of an R&S CMW radio communication tester, the new R&S RT-ZVC power probe, and R&S CMWrun sequencer software.
During testing, the radio communication tester manages the communications with the DUT and places the DUT in the various operating modes. The power probe acquires current and voltage readings at defined test points on the DUT. Sequencer software controls the process and delivers detailed measurement reports to the user. The user can precisely correlate the events occurring at the mobile interface with the DUT’s power consumption. The R&S RT-ZVC probe offers sufficient dynamic range to permit measurements from low currents in standby or sleep mode to large currents when the DUT transmits at maximum power.
The probe’s multichannel design makes it possible to simultaneously acquire and correlate the power at up to four different test points. Users can compare the power consumption of individual subcomponents, such as an application processor and the RF transmit unit, against the total power consumption within a realistic signaling scenario controlled by the R&S CMW500.
The power probe was designed specifically for the R&S CMW family of radio communication testers. The R&S CMWrun automation software enables long-term monitoring of automated signaling test scenarios as needed for performance tests, regression tests, and acceptance tests. Test scenarios support measurement and correlation for the new 3GPP features for reducing power consumption in machine-to-machine applications, such as power save mode and enhanced discontinuous reception.
The R&S RT-ZVC’s multichannel design enables it to measure power by taking a voltage and a current reading and then multiplying them in real time. The power probe also automatically calculates the minimum, maximum, average, and rms values for voltage, current, and power. The probe is available with two or four power measurement channels. The individual current and voltage signals are sampled at 5 MS/s for a time resolution of 200 ns for each reading. As a result, small, transient signal changes can be acquired—for example, to specify the start-up behavior of chip components.
The R&S RT-ZVC is designed for input voltages of ±15 V, and the measurement range for input currents can be varied from 4.5 μA to 10 A. A vertical resolution of 18 bits for sampled signals makes it possible to cover the required dynamic range from nanoamps to amps. The power values calculated by multiplying the current and voltage pairs are averaged (method selectable by the user) and then output over the integrated USB interface, keeping the data volume under control even for long-term acquisitions.
Power analysis will only become more challenging as engineers pursue goals ranging from 10-year battery life in IoT edge devices to multi-hundred-mile ranges for electric vehicles. Depending on the application, optimum power-analysis solutions will continue to extend from oscilloscopes to dedicated power analyzers. With regard to the former category, a spokesperson for Siglent said the company is planning a power-analysis option for its new SDS2000X family of oscilloscopes; the option is scheduled for release this summer. You can be sure that power analyzers will continue to evolve as well, as vendors work to provide accuracies concomitant with engineers’ push for ever higher efficiencies.
For more information
- Gatheridge, B., and Shearman, S., “Selecting the right instrument for electrical power measurement applications,” EE-Evaluation Engineering, February 2017, p. 16.