At the heart of modern power electronics converters are power semiconductor switching devices. The emergence of wide bandgap (WBG) semiconductor devices, including silicon carbide and gallium nitride, promises power electronics converters with higher efficiency, smaller size, lighter weight, and lower cost than converters using the established siliconbased devices. However, WBG devices pose new challenges for converter design and require more careful characterization, in particular due to their fast switching speed and more stringent need for protection. Characterization of Wide Bandgap Power Semiconductor Devices presents comprehensive methods with examples for the characterization of this important class of power devices. After an introduction, the book covers pulsed static characterization; junction capacitance characterization; fundamentals of dynamic characterization; gate drive for dynamic characterization; layout design and parasitic management; protection design for double pulse test; measurement and data processing for dynamic characterization; cross-talk consideration; impact of three-phase system; and topology considerations.
Inspec keywords: power semiconductor devices; network topology; semiconductor device models; capacitance; wide band gap semiconductors
Other keywords: parasitic management; cross-talk; junction capacitance characterization; gate drive; layout design; dynamic characterization measurement; three-phase system; topology; double pulse test protection design; wide bandgap power semiconductor devices; pulsed static characterization; data processing
Subjects: Power semiconductor devices; Network topology; General electrical engineering topics
This book focuses on how to characterize the emerging wide bandgap (WBG) power semiconductor switching devices, including silicon carbide (SiC) and gallium nitride (GaN) devices. Power semiconductor switching devices are at the heart of modern power electronics converters. Today's commercial power semiconductor devices are still dominated by the mature and well-established silicon (Si) technology. Since the advent of Si thyristors in the 1950s, Si power semiconductor devices have gone through many generations of development in the last 60 years and are approaching material theoretical limitations in terms of blocking voltage, operation temperature, and conduction and switching characteristics. These intrinsic physical limits become a barrier to achieving higher performance power conversion.
The static I-V characteristics of a power device describe its behavior in steady-state. Pulsed I-V characterization is usually performed with a curve tracer to establish the on-resistance, maximum current capability, and maximum voltage capability of the device. Some of the static characteristics are also used to interpret later dynamic test results. While most of this procedure can be found in the user manual for the test equipment (i.e., curve tracer), the unique properties of WBG devices require special care and considerations that may be overlooked in such general instructions. This chapter will describe these considerations, the desired deliverables of static characterization, and the tests required to produce them.
This chapter will describe the procedures and methodology for characterizing the equivalent capacitances of a WBG power device, including the individual capacitances between each electrical terminal of the device and the conventionally reported lumped capacitance parameters. These capacitances, often in the form of curves as functions of operating conditions, have inherent value in selecting an appropriate device for a given application, as well as creating accurate simulation models and interpreting dynamic characterization data.
This chapter introduces the fundamentals of dynamic characterization. Starting from the switching commutation analysis in an actual power electronics converter, the simplified test circuit for dynamic characterization is derived such that not the whole converter will be needed for the test. Then, fundamentals of DPT based on the simplified test circuit are introduced, including operation principle, configuration, and setup. Detailed DPT design and control are discussed. In the end, according to the design theory, a case study is given. Two-level voltage source converter is the focused topology in the following description, since it is the one of the most widely used converter types.
In this chapter, focuses on the gate drive design in switch/switch-based DPT circuit for dynamic characterization of WBG devices, as shown in Figure 5.2. First, gate drive fundamentals and unique design considerations for WBG devices are presented. Second, key power device characteristic parameters used for gate drive design are highlighted, which are some of the characteristics already obtained in static characterization described in previous chapters. Third, detailed gate drive design is introduced based on the basic functional blocks. Finally, leveraging the gate drive design criteria, a case study based on a 1,200 V SiC MOSFET is given. It is noted that although gate drive illustrated in this chapter is for WBG device dynamic characterization, its basic theory and design consideration can be utilized for the gate drive design in actual WBG-based power electronics converters.
The high-speed switching performance of WBG devices poses unique challenges for circuit layout design and parasitics management. This chapter aims at understanding the impact ofparasitics on the switching behavior, investigating the layout design principle for a DPT board, and presenting several case study examples to illustrate the way to apply this design theory in actual implementations.
Today, WBG power devices are often expensive or sampled in limited quantities. In addition, intrinsic characteristics of WBG semiconductors enable WBG devices with very high voltage capability, for example, 10 kV SiC MOSFETs. Thus, due to the limited availability, high cost, and unique capability of devices, proper protection for WBG device DPT is important. The protection includes two categories: one is to protect DUT and DPT circuit, and the other is for the operator safety, especially when testing high-voltage WBG devices. In summary, short-circuit and overcurrent protection is critical for WBG-based dynamic characterization.
This chapter describes the techniques for measurement and post-processing of dynamic characterization data collected using the methodology described in Chapters 4-7. Measurement is a crucial consideration in performing an effective DPT. The oscilloscope, voltage probes, current sensors, and their connection to the test circuit must be carefully selected and designed. Following the test, the data processing can be implemented with any computation tool or programming language. This chapter discusses the generalized algorithms and methodologies as well as some example code and post-processing results implemented in MATLAB®. These data processing techniques allow the experimenter to analyze the dynamic behavior of the device under test and calculate key device characteristics.
When introducing fundamentals of dynamic characterization in Chapter 4, we started from a three-phase voltage source converter, which is a widely applied circuit for many applications, and derived a simplified configuration to equivalently evaluate the switching behavior of WBG devices. With this assumption, details of the DPT have been comprehensively discussed including DPT basics, gate drive, layout design, protection, measurement, and data processing in previous chapters. However, the observed switching performance of WBG devices in power converters is almost always worse than test results by DPT with the common observation of slower switching speed and higher switching losses. Therefore, starting from this chapter, we will revisit the assumptions made for the simplification of the dynamic characterization in DPT, and better understand the impacting factors and limitations of the switching performance in a practical system. As a result, we will either modify the conventional DPT to characterize the switching behavior more accurately for an actual converter or will develop solution(s) to address the adverse effects of the identified limitations on the switching performance such that the conventional DPT results can still be valid and used. We highlight key elements that can potentially affect the switching characteristics in a three-phase PWM voltage source inverter. Within the switch/switch-based phase-leg configuration of a single phase, gate drive, parasitics, and interference between the lower and upper switches (i.e., cross-talk) are the critical elements for high-speed switching performance of WBG devices; while in the entire three-phase converter system, other phase-legs, heatsink, and motor/cable load are potential limitations for fast switching speed behavior. Among these six potential impacting factors, gate drive and parasitics have been covered in the conventional DPT and discussed specifically in Chapters 5 and 6. This chapter focuses on the cross-talk. Within this chapter, first, the mechanism causing the cross-talk is discussed and unique challenges for WBG devices are analyzed. Then, practical solutions to mitigate the cross-talk are summarized and their effectiveness is compared. Finally, the methodology to evaluate the impact of cross-talk on the dynamic characterization is described. Two case studies based on (1) GaN transistor and (2) SiC MOSFET are presented to quantify the influence of cross-talk for the WBG dynamic characteristics.
This chapter focuses on the limitations and impacting factors of switching performance of WBG devices in a three-phase power converter, and their influences on the accuracy of the dynamic characterization results based on the conventional DPT.
In addition to the two-level phase-leg based voltage source converter that has been the focus in prior chapters, there are many other widely used converter types in practical applications, such as current source converters and multilevel voltage source converters. For the fast WBG devices, their switching behavior becomes more susceptible to parasitics and noise of the application circuit. Therefore, the dynamic characterization results based on the conventional two-level phase-leg DPT, even considering the influence of three-phase system as discussed in Chapter 10, usually cannot match well with the actual switching performance in other non-two-level-phase-leg based topologies. This chapter aims at investigating the impacting factors on the switching performance originated from practical topologies that are not based on the simple two-level phase-leg configuration. The main focus here is the hard switching-based topology where the dynamic characteristics of devices would significantly affect the power converter performance. Two typical representatives, including current source converter and three-level active neutral-point clamped (ANPC) converter, are selected to understand the difference of switching commutation loop and the influence on the switching performance between these non-two-level-phase-leg based converters and the conventional two-level phase-leg based DPT. First, based on the typical modulation scheme, the switching commutation of each topology is analyzed. Accordingly, the switching loops are derived and compared with those in the conventional DPT. Considering more complicated topologies versus the conventional DPT circuit, the critical non-operating devices that are beyond the main switching commutation loop but will affect the switching performance of the operating switch are identified; and then their influence on the dynamic characterization is described. Finally, based on these case studies, a general discussion is given to summarize the impact of other non-two-level-phase-leg based topologies on the dynamic characterization.
This Appendix presents a list of equipment and components within the categories of: DPT main components; measurement; tape and wire; soldering; fixture, connector, kits; mechanical; personal protection equipment.
This Appendix presents various computer listings for dynamic characterisation data processing code, relevant to wide band gap power semiconductor devices.