5 research outputs found
Body diode reliability investigation of SiC power MOSFETs
A special feature of vertical power MOSFETs, in general, is the inbuilt body diode which could eliminate the need of having to use additional anti-parallel diodes for current freewheeling in industrial inverter applications: this, clearly, subject to their demonstration of an acceptable level of reliability. Recent improvements in Silicon Carbide (SiC) power MOSFET device manufacturing technology has resulted in their wider commercial availability with different voltage and current ratings and from various manufacturers. Hence, it is essential to perform characterisation of its intrinsic body diode. This paper presents the reliability assessment of body diodes of latest generation discrete SiC power MOSFETs within a 3-phase 2-level DC-to-AC inverter representing realistic operating conditions for power electronic applications
Wide Band Gap Power Semiconductor Devices and their Applications
DC power supplies are being widely used in almost every modern day appliance. Basic DC power supply should only consist of AC/DC rectification unit with bulk capacitor. But irregular current drawn by rectifier pollutes the power system. Standards related to power quality puts a limit on harmonics that are being injected by a device into power system. To comply with standards Power factor correction (PFC) circuits are employed with rectification unit. Addition of an extra unit, puts a limit on overall efficiency of power supply. Advent of Wide Band Gap (WBG) power semiconductor devices have provided us with the opportunity to improve the efficiency of existing electronic circuits with relatively simple control schemes. According to recent research, it has been forecasted that GaN based devices are ideal choice for medium voltage and high speed applications. However, SiC based devices are estimated to take over high voltage applications.
Conventional PFC circuit based on bridged CCM average current controlled Boost converter was chosen for this study. Simulation was made to compare the performance of GaN, SiC and Si based switches. Results from simulation revealed that 38% reduction in switching losses can be achieved by using GaN HEMT instead of Si MOSFET. Practical evaluation was performed on Transphom Totem Pole PFC and All in One Power supply. Both of these devices are based on GaN HEMTs. Totem pole PFC is the major breakthrough achieved by GaN HEMT in the field of PFC circuit. Very low reverse recovery of switches made it possible to implement this circuit with very high efficiency for high power applications. 94% efficiency was observed during evaluation of DC power supply, which validates the claim of superior performance of WBG devices
Design and Evaluation of High Efficiency Power Converters Using Wide-Bandgap Devices for PV Systems
The shortage of fossil resources and the need for power generation options that produce little or no environmental pollution drives and motivates the research on renewable energy resources. Power electronics play an important role in maximizing the utilization of energy generation from renewable energy resources. One major renewable energy source is photovoltaics (PV), which comprises half of all recently installed renewable power generation in the world. For a grid-connected system, two power stages are needed to utilize the power generated from the PV source. In the first stage, a DCDC converter is used to extract the maximum power from the PV panel and to boost the low output voltage generated to satisfy the inverter side requirements. In the second stage, a DC-AC inverter is used to convert and deliver power loads for grid-tied applications. In general, PV panels have low efficiency so high-performance power converters are required to ensure highly efficient PV systems.
The development of wide-bandgap (WBG) power switching devices, especially in the range of 650 V and 1200 V blocking class voltage, opens up the possibility of achieving a reliable and highly efficient grid-tied PV system. This work will study the benefits of utilizing WBG semiconductor switching devices in low power residential scale PV systems in terms of efficiency, power density, and thermal analysis.
The first part of this dissertation will examine the design of a high gain DC-DC converter. Also, a performance comparison will be conducted between the SiC and Si MOSFET switching devices at 650 V blocking voltage regarding switching waveform behavior, switching and conduction losses, and high switching frequency operation.
A major challenge in designing a transformerless inverter is the circulating of common mode leakage current in the absence of galvanic isolation. The value of the leakage current must be less than 300mA, per the DIN VDE 0126-1-1 standard. The second part of this work investigates a proposed high-efficiency transformerless inverter with low leakage current. Subsequently, the benefits of using SiC MOSFET are evaluated and compared to Si IGBT at 1200 V blocking voltage in terms of efficiency improvement, filter size reduction, and increasing power rating. Moreover, a comprehensive thermal model design is presented using COMSOL software to compare the heat sink requirements of both of the selected switching devices, SiC MOSFET and Si IGBT.
The benchmarking of switching devices shows that SiC MOSFET has superior switching and conduction characteristics that lead to small power losses. Also, increasing switching frequency has a small effect on switching losses with SiC MOSFET due to its excellent switching characteristics. Therefore, system performance is found to be enhanced with SiC MOSFET compared to that of Si MOSFET and Si IGBET under wide output loads and switching frequency situations. Due to the high penetration of PV inverters, it is necessary to provide advanced functions, such as reactive power generation to enable connectivity to the utility grid. Therefore, this research proposes a modified modulation method to support the generation of reactive power. Additionally, a modified topology is proposed to eliminate leakage current
Novel TCAD-based Signal-Flow Graph Approaches for the Stability Analysis of Power Semiconductor Devices
Technological innovation in power electronics is desired to realize the social demand for the spread of renewable energy and the promotion of electrification of automobiles to achieve carbon neutrality. Power devices are key components in power electronics, and their performance has been improving. As their performance improves, the occurrence of unstable behaviors such as oscillation and noise in power device packages and circuits can cause system failures. Hence, a new design technology to ensure the stable operation is required. In this study, a novel design method is proposed and applied to oscillation phenomena of SiC-MOSFETs and Si-IGBTs during short-circuit operation. The effectiveness of the method is demonstrated by comparing the results calculated using the proposed method and the results obtained using conventional methods and experimental results. In chapter 1, the requirements for power semiconductors in the international effort to achieve zero CO2 emissions in 2050 are summarized. Then, the trend of research and development on the improvement of power device characteristics for smaller and higher efficiency power conversion systems is discussed, focusing on Si-IGBT and SiC-MOSFET. In chapter 2, previous studies on oscillation phenomena and its suppression are summarized, which can become issues as the power devices are improved. These previous studies can be classified into two categories: one based on equivalent circuits and the other based on device physics. However, there has not been sufficient discussion on the oscillation phenomenon that strongly couples circuits and devices, which is becoming more important as power devices become more high-performance. Technology computer aided design (TCAD) mixed mode simulation can handle both circuits and device physics, however, it is difficult to use it for realistic device design due to the large amount of calculation. In Chapter 3, a new method based on the S-parameter and the signal flow graph (SFG) is introduced to analyze the circuit stability. This method allows us to calculate the frequency response of the output current to the external field maintaining the response of the carrier distribution and electric field inside the device. The signal gain for the focused operating mode can be easily calculated by applying Masonâs rule to the SFG. Additionally, the stability analysis using the Nyquist plot enables not only the judgment of the system stability with respect to the design parameters but also the quantitative evaluation of the stable/unstable margin. In Chapter 4, the usefulness of the proposed method is verified by applying it to the oscillation phenomenon of SiC-MOSFETs during Type II short-circuit operation. The S-parameters are calculated from the TCAD model for a commercial SiC-MOSFET, and stability analysis is carried out using the SFG. The dependence of the gate resistance required for oscillation suppression obtained from the mixed mode simulation of TCAD is compared with the results obtained from the proposed method. The agreement between the proposed method and the results of TCAD mixed mode simulation is confirmed. Stability analysis is conducted for both the mode in which a single switching device oscillates by coupling with parasitic elements of the circuit and the mode in which oscillation occurs through switching devices connected in parallel. The characteristics of each mode during short-circuit operation are clarified, and the stability phase diagram in the design parameter space is calculated for each mode by taking advantage of the computational speed. It is shown that which mode becomes unstable depends on the design parameters. In Chapter 5, the proposed method is applied to the oscillation phenomenon of Si-IGBTs under Type II short-circuit operation and the oscillation mechanism is investigated. Experimental results revealed that the oscillation occurred during Type II short-circuit operation and it can be suppressed by increasing the gate resistance. The resistance required for oscillation suppression decreases as the collector voltage increases. The stability analysis is conducted using the proposed method. It is confirmed that the calculated critical gate resistance decreases as the collector voltage increases. The results are in good agreement with the experimental results. The internal behavior of the device under the oscillation state is also analyzed. During the short-circuit operation, a high electric field region is formed at the boundary between the base and drift layers, and the carrier distribution at both ends of the plasma region is modulated through the electron-hole plasma. This modulation becomes more responsive when the collector voltage is smaller. In Chapter 6, the development potential of the proposed method and future challenges are discussed. This study presents a new method for accelerating the development of power devices and power electronics systems that contribute to CO2 reduction, which is becoming an international effort. This method provides an integrated approach for managing the multilevel design hierarchy, from devices to power conversion systems. 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