This article describes the different types of measurement equipment required for power electronic systems.
Performance of an electromechanical system is determined by the performance of individual power electronic components and switching devices. Hence, there is a need for accurate measurement of responses of power electronics, and other electrical and physical parameters. This article describes the different types of measurement equipment required for power electronic systems.
To select a measuring instrument for testing these systems, it is necessary to understand the testing parameters at various development stages. Test and measurement (T&M) equipment enable predictive and preventive inspections to minimise the risk of defects, accidents or electronic systems breakdowns. You can also derive optimum efficiency and operation for all kinds of troubleshooting.
Faster switching power electronic devices
The trend in power electronics is to push the operating frequencies higher to reduce size, weight and cost of the systems. This requires faster switching power electronic devices, such as SiC and GaN MOSFETS, and diodes. To test and characterise such devices, you need faster measurement devices like higher bandwidth oscilloscopes and power analysers.
For design and architecture stages, key factors that help select test instruments include high-frequency dynamic behaviour, static behaviour, fast inverter switching, trigger for individual waveforms and overshoot on pulses. Measurement at this stage requires mixed-signal oscilloscopes with multiple channels.
Dynamic behaviour of power electronics can be measured with a scopecorder (oscilloscope-cum-data acquisition recorder). A data acquisition recorder handles a wide range of power measurements and captures high-resolution details with a 12- or 16-bit ADC. A spacecorder carries out complex calculations to measure power factor, active power and harmonics using a digital signal processor.
Dynamic parameters such as switching times (Trise, Tfall, Tdelay or Trr) use high- bandwidth oscilloscopes. Static parameter measurements need curve tracers and parametric analysers. Static parameters include VCEon, VDS, RDSon, VF, VGE and leakage currents using curve tracers. Switching energies such as Eon, Eoff and Err are measured using high-bandwidth current probes and oscilloscopes with math functions.
Quality control measures
Power analysis, conversion efficiency and harmonics are measured for efficiency validation. A power analyser measures efficiency, total harmonic distortion and power factor correction of circuits. For these, the test power analyser should be of high accuracy and high stability. It should have calibration ability that can measure highly distorted current and voltage waveforms accurately.
Online inspection and troubleshooting are important to reduce costs and downtime, and improve the efficiency of various electronic components. For online inspection, thermal imagers are useful for PCBs and SMD cards, for fault diagnosis and research purposes. This is due to their high IR resolutions of 320×240 pixels and 640×480 pixels. These can also be used for the mass production of electronic components for monitoring, processing and quality control.
T&M equipment for power electronics
Nitin Shetty, chief executive officer, Convergent Technologies, says, “A galvanically-isolated solution like Tektronix TIVM Series IsoVu can resolve high-bandwidth differential signals up to 2500Vpk in the presence of large common-mode voltages. The latest T&M technology for power electronics is 8-channel, 12-bit ADC and deep memory MSO 5 series oscilloscope.
“MSO is available with eight high-resolution channels, easy-to-use user interface and a large HD touchscreen display along with advanced IsoVu probing solutions. It is suitable for designing an inverter, optimising a power supply and testing communication links. It measures across a current shunt resistor, debugging electromagnetic interference or electrostatic discharge issues, and eliminates ground loops in a test setup.”
Convergent Technologies offers multiple solutions. These include:
- 4-, 6- or 8-flexi channel, 12-bit resolution Tektronix MSO5 oscilloscope with advanced power analysis solutions for three-phase power electronics, automotive electronics, power supply design and DC-to-DC power converters
- Battery-operated Tektronix TPS2000 series oscilloscope with fully-isolated and floating channels
- Single- and three-phase power analysers: PA3000and PA1000 series from Tektronix
Vijay Bolloju, manager – applications engineering, Rohm Semiconductors, says, “The requirement of power systems for automotive systems have increased considerably due to heavy electric vehicles and their development activities. This necessitates low-voltage and high-current power supplies to characterise system performance. Efficiency, total harmonic distortion and power factor correction of the systems are measured using regulated AC and DC supplies and power analysers.”
He adds, “We provide SiC MOSFET technology and full SiC modules, an extensive series of SiC products like MOSFETS, Schottky barrier diodes and more. We also have regulated AC and DC power supplies, electronic loads, LED load simulators, high-bandwidth oscilloscopes with math functions and spectrum analyser packages. Torque simulators such as Magtrol are used for testing motor drives. Low-footprint, precise current probes are used for measuring the currents in circuits.”
Parag Yelegaonkar, business development manager, Testo India, says, “Our latest and most advanced solutions are electrical instruments for inspecting electrical components and circuit failure threats. These ensure longevity and efficiency of various power electronic components that control and regulate the flow of electrical energy.
“Our unique clamp meters and multimeters are intuitive, can measure several parameters in a single component and have patented features. The new range of thermal imagers with smartphone integration are designed to deliver networked thermography mostly used for predictive and preventive maintenance in electric and power sectors. Wireless operation, with the ease of saving and transferring data over networks, makes these user-friendly, interactive and cost-effective.”
Measuring current is always a challenge, as the current probes tend to be bulky and invasive. High-bandwidth compact current probes measure low currents (<5A). These are needed to test low-power systems like ceiling fans and other consumer appliances.
To test high-speed power devices such as SiC and GaN MOSFETs, higher bandwidth measuring equipment are needed to capture fast-rising switching waveforms.
Equipment for measuring electromagnetic compatibility and surge tests tend to be quite expensive. Low-cost pre-compliance test equipment can expedite the design process.
Power quality, switching loss, harmonics, ripple, modulation and safe operating area measurements are other challenges in power electronics. These can be overcome by using latest and faster testing devices.