Trade-off study of heat sink and output filter volume in a GaN HEMT based single phase inverter

This paper presents the trade-off study of heat sink and output filter volume of a GaN HEMT based single phase inverter. The selected topology is three-level Active Neutral point Clamped (ANPC) inverter, and the main aim is to explore the benefits of the GaN HEMTs at 600 V blocking class on the system level efficiency, and power density under wide range of operating conditions. The paper starts by introducing the inverter topology, selected PWM scheme and followed by the device features, static and dynamic characterisation and continues with presenting and discussing the results of extensive experimental and analytical characterisation. After this, the impact of GaN HEMTs on inverter volume is discussed in terms of heat sink and output filter volume analysis under different switching frequency and heat sink temperature conditions. The calculation of heat sink volume and single stage LC output filter volume are presented with respect to experimental results of single phase prototype. The findings from static, dynamic characterisation and single phase prototype results clearly show that GaN HEMT has excellent switching performance under wide load current and heat sink temperature conditions. The high performance of the inverter lead to reduction of the combined total volume, including output filter and heat sink volume

Single-phase T-type inverter performance benchmark using Si IGBTs, SiC MOSFETs and GaN HEMTs

In this paper, benchmark of Si IGBT, SiC MOSFET and GaN HEMT power switches at 600V class is conducted in single-phase T-type inverter. Gate driver requirements, switching performance, inverter efficiency performance, heat sink volume, output filter volume and dead-time effect for each technology is evaluated. Gate driver study shows that GaN has the lowest gate driver losses above 100kHz and below 100kHz, SiC has lowest gate losses. GaN has the best switching performance among three technologies that allows high efficiency at high frequency applications. GaN based inverter operated at 160kHz switching frequency with 97.3% efficiency at 2.5kW output power. Performance of three device technologies at different temperature, switching frequency and load conditions shows that heat sink volume of the converter can be reduced by 2.5 times by switching from Si to GaN solution at 60°C case temperature, and for SiC and GaN, heat sink volume can be reduced by 2.36 and 4.92 times respectively by increasing heat sink temperature to 100°C. Output filter volume can be reduced by 43% with 24W, 26W and 61W increase in device power loss for GaN, SiC and Si based converters respectively. WBG devices allow reduction of harmonic distortion at output current from 3.5% to 1.5% at 100kHz

Novel multilevel hybrid inverter topology with power scalability

In this paper, a novel multilevel hybrid inverter is presented. The inverter is based on 2 floating capacitors and 16 active switches for five-level voltage waveform between the output of the inverter and neutral point of DC link. The proposed inverter structure, switching states and commutation scheme for different output voltage levels are presented. The proposed topology is simulated and verified experimentally. The simulation results show that proposed topology can achieve higher efficiency in comparison to state-of-the-art hybrid topologies due to reduced conduction and switching losses at low modulation index and light load conditions. Experimental results show that the converter is successfully operated up to 1 kV DC link voltage and 12 kW output power

High-frequency modulated secondary-side self-powered isolated gate driver for full range PWM operation of SiC power MOSFETs

The present work proposes a solution for an isolated gate driver suitable for SiC MOSFETs. The driver is implemented by means of two small magnetic transformers, to provide the turn-on and turn-off gate signals, as well as the power required for an adequate gate control. The operation is based on the modulation of the PWM pulses with a high frequency (HF) square-waveform signal. The resulting modulated AC waveform is applied to the primary side of the first transformer, and reconstructed at the secondary side to obtain the gate driving signal. Simultaneously, the HF modulating signal is connected to the primary of the second transformer, to provide the required gate drive voltage levels and power at the secondary side, ensuring full range duty ratio operation. Given that both primary side signals are HF symmetrical waveforms, saturation is avoided at both transformers, for any duty ratio operation. Therefore, the proposed solution provides galvanic isolation for power and gate signal transfer with very small core sizes, allowing for an overall size reduction vs. conventional solutions. This enables much more compact designs, which are critical in high-power density applications and multilevel converters. After describing the basic operation, experimental results on a prototype are shown, thus demonstrating the feasibility of the proposed solutio

Wide-bandgap semiconductor based power converters for renewable energy systems

The demand for low carbon economy and limited fossil resources for energy generation drives the research on renewable energy sources and the key technology for utilisation of renewable energy sources: power electronics. Innovative inverter topologies and emerging WBG semiconductor based devices at 600 V blocking class are the enabling technologies for more efficient, reliable and accessible photovoltaic based electricity generation. This thesis is concerned with the impact of WBG semiconductor based power devices on residential scale PV inverter topologies in terms of efficiency, volume reduction and reliability. The static and dynamic characterisation of the Si and WBG based devices are carried out, gate drive requirements are assessed and experimental performance comparison in a single phase inverter is discussed under wide range of operating conditions. The optimisation of GaN HEMT based single phase inverter is conducted in terms of converter efficiency, switching frequency and converter volume. The long term mission-profile based analysis of GaN and Si based devices is conducted and impact of WBG devices under low and high switching frequency conditions in terms of power loss and thermal loading are presented. Finally, a novel five-level hybrid inverter topology based on WBG devices is proposed, simulated and experimentally verified for higher power applications

Wide-bandgap semiconductor based power converters for renewable energy systems

The demand for low carbon economy and limited fossil resources for energy generation drives the research on renewable energy sources and the key technology for utilisation of renewable energy sources: power electronics. Innovative inverter topologies and emerging WBG semiconductor based devices at 600 V blocking class are the enabling technologies for more efficient, reliable and accessible photovoltaic based electricity generation. This thesis is concerned with the impact of WBG semiconductor based power devices on residential scale PV inverter topologies in terms of efficiency, volume reduction and reliability. The static and dynamic characterisation of the Si and WBG based devices are carried out, gate drive requirements are assessed and experimental performance comparison in a single phase inverter is discussed under wide range of operating conditions. The optimisation of GaN HEMT based single phase inverter is conducted in terms of converter efficiency, switching frequency and converter volume. The long term mission-profile based analysis of GaN and Si based devices is conducted and impact of WBG devices under low and high switching frequency conditions in terms of power loss and thermal loading are presented. Finally, a novel five-level hybrid inverter topology based on WBG devices is proposed, simulated and experimentally verified for higher power applications

Experimental demonstration of an optimised PWM scheme for more even device electro-thermal stress in a 3-Level ANPC GaN inverter

GaN device as one potential power electronics device has been gained much attention recently. One of the power conversion systems, ANPC inverter using GaN HEMT is potentially considered to be prospective usage of low loss and high efficiency. In this work, we demonstrate one optimised PWM scheme aims at balancing the device electro-thermal stress based on Parma PWM to control 3-Level ANPC GaN inverter. The method is to decrease the loss for switches account for the large loss and increase the loss for switches with less thermal stress initially. The simulation and experimental results prove the effectiveness of the optimised PWM in controlling the loss distribution

Reliability-driven assessment of GaN HEMTs and Si IGBTs in 3L-ANPC PV inverters

In this paper, thermal loading of the state-of-the-art GaN HEMTs and traditional Si IGBTs in 3L-ANPC PV inverters is presented considering real-field long-term mission profiles (i.e., ambient temperature and solar irradiance). A comparison of Si IGBT against GaN HEMT with three different possibilities: 1) with TIM at 10 kHz, 2) without TIM at 10 kHz, and 3) with TIM at 300 kHz has been performed. The assessment results indicate lower thermal stress with GaN HEMT devices at 10 kHz in comparison to Si IGBT. At high switching frequencies, the results show significant system level cost savings can be achieved without compromise of operating efficiency with GaN HEMTs. Both simulations and experimental tests are provided to demonstrate the thermal loading analysis approach. More important, the proposed analysis and comparison approach can be used for lifetime and reliability analysis of wide-bandgap devices

Built-in reliability design of a high-frequency SiC MOSFET power module

A high frequency SiC MOSFET-based three-phase, 2-level power module has been designed, simulated, assembled and tested. The design followed a built-in reliability approach, involving extensive finite-element simulation based analysis of the electro-thermo-mechanical strain and stress affecting the switch during both manufacturing and operation: structural simulations were carried out to identify the materials, geometry and sizes of constituent parts which would maximize reliability. Following hardware development, functional tests were carried out, showing that the module is suitable for high switching frequency operation without impairing efficiency, thus enabling a considerable reduction of system-level size and weight