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Challenges and Solutions for power electronics testing applications

Technical Overviews

Challenges and Solutions for Power Electronics Testing Applications

Introduction

The term power electronics encompasses a wide range of applications, from small power converters used in personal computers to large scale electric power generation/transmission systems. Because power electronics is essential to these functions, having robust and reliable power electronics circuits is extremely important. In addition, the need for more efficient circuits with smaller form factors continues to increase as concerns over CO2 emissions drive the ongoing shift to alternative energy sources.

Challenges Facing Power Electronics Applications

All power electronics applications require some sort of power conversion system. For this reason, all over the world companies are continuously working on improving the performance, efficiency, and reliability of these systems. Power conversion systems are also being used in new applications as they replace conventional systems. For instance, internal combustion engines are gradually being replaced by hybrid and electric alternatives to reduce fossil fuel consumption. Hydraulic actuators in airplanes are being replaced with electric motor based actuators to improve aircraft safety and reliability.

Many modern vehicles employ hybrid powertrains to improve fuel efficiency. Hybrid systems typically have one inverter circuit for DC-DC converter electrical motor control and one for the regenerative circuit that converts kinetic energy (e.g. from braking, coasting, etc.) into electrical energy stored in the system’s battery. Both of these inverter circuits use many IGBTs (Insulated Gate Bipolar Transistors), diodes, capacitors, resistors and inductors, and these components need to be able to handle very large voltages and currents. For instance, the most popular hybrid automobile today uses voltages of up to 650 V and currents of more than 200 A. Component reliability under a wide range of operating conditions (from freezing cold to hot and humid conditions) is also extremely important, since any failure could cause serious injury to the car’s driver or passengers.

Component weight is another factor that affects energy efficiency because the inductors and capacitors used in the powertrain are in general large and heavy. Since higher operating frequencies allow smaller components to be used, wide band gap (WBG) devices such as SiC MOSFETs and GaN FETs (which can operate at higher frequencies than silicon devices) are gradually replacing IGBTs in switching circuits. Of course, the power devices and components used in the circuit are critical parts that cannot fail under any situation.

What Should Power Circuit Designers Do?

Power electronics engineers have to develop highly efficient, safe and reliable electric circuits, so the evaluation of final circuit characteristics is very important. It is therefore mandatory to evaluate the efficiency of the entire circuit, including verifying current and voltage waveforms at each circuit node. To achieve this, a detailed understanding of the power devices and components used in the circuit is necessary. This is especially true for the power devices (such as IGBTs and MOSFETs) used in the circuit, since their performance often dictates the efficiency, safety and reliability of the entire circuit. Unfortunately, device manufacturer supplied datasheet information is often insufficient to meet these needs. The datasheet conditions are often different from actual use conditions, and the supplied information often has large margins with no information on device variation. This makes it hard to design reliable and efficient circuits using only the information supplied by the device and component manufacturers.

Maximizing circuit efficiency through optimal device selection

Maximizing circuit performance and efficiency requires more data than conventional curve tracers can supply. In particular, as switching frequencies increase switching loss and drive loss begin to dominate device power loss. This makes characterization of device capacitances, gate resistance and gate charge extremely important. However, since these parameters are difficult to measure many power electronics engineers do not attempt them. The B1506A solves this issue with its ability to not only automatically measure all of these parameters, but also with its capability to use the extracted parameters to perform power loss calculations.

B1507A Power Device Capacitance Analyzer

If you already have a conventional curve tracer or production power device tester for DC characterization but lack capacitance measurement capability, then the B1507A can bridge this gap in your testing resources. It provides automatic transistor input, output and reverse transfer capacitance measurement capability at high voltage bias (up to 3 kV), as well as the ability to measure gate resistance. In addition, the abilities to measure breakdown voltage up to 3 kV and to accurately characterize leakage currents down to the sub-pA level can reveal device characteristics that conventional test equipment (such as curve tracers) cannot detect. These features are also effective to detect counterfeit or substandard power devices.

The B1507A supports both package device testing and on-wafer device testing. Therefore, it supports the needs of power electronics circuit designers, incoming inspection engineers, failure analysis engineers and power semiconductor device engineers.

Power device switching characterization

Switching characteristics are an important part of component level test, and Keysight has both oscilloscopes and pulse generators that can help evaluate these parameters.

The InfiniVision 3000/4000/6000 X series oscilloscopes provide good bandwidth and resolution at a reasonable cost, and they support both current and voltage probes. The 81110A pulse generator is also able to provide voltage pulses fast and large enough to characterize automotive components.

DC-DC Converter IC evaluation

A benchtop SMU with two channels can simplify the otherwise complicated test setup necessary to perform DC-DC converter characterization. Figure 16 shows two test set ups for DC-DC converter IC load regulation evaluation; the first uses 2 digital multimeters, 2 DC voltage sources and a load resistor while the second uses a 2-channel SMU.

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