Haoze Luo

Topology Review and Derivation Methodology of Single-Phase Transformerless Photovoltaic Inverters for Leakage Current Suppression

Single-phase voltage source transformerless inverters have been developed for many years and have been successful commercial applications in the distributed photovoltaic (PV) grid-connected systems. Moreover, many advanced industrial topologies and recent innovations have been published in the last few years. The objective of this paper is to classify and review these recent contributions to establish the present state of the art and trends of the transformerless inverters. This can provide a comprehensive and insightful overview of this technology. First, the generation mechanism of leakage current is investigated to divide the transformerless inverters into asymmetrical inductor-based and symmetrical inductor-based groups. Then, the concepts of dc-based and ac-based decoupling networks are proposed to not only cover the published symmetrical inductor-based topologies but also offer an innovative strategy to derive advanced inverters. Furthermore, the transformation principle between the dc-based and ac-based topologies is explored to make a clear picture on the general law and framework for the recent advances and future trend in this area. Finally, a family of clamped highly efficient and reliable inverter concept transformerless inverters is derived and tested to offer some excellent candidates for next-generation high-efficiency and cost-effective PV grid-tie inverters.

Junction Temperature Extraction Approach With Turn-Off Delay Time for High-Voltage High-Power IGBT Modules

Thermo-sensitive electrical parameter (TSEP) approaches are widely employed in the junction temperature extraction and prediction of power semiconductor devices. In this paper, the turn-off delay time is explored as an indicator of a TSEP to extract the junction temperature from high-power insulated gate bipolar transistor (IGBT) modules. The parasitic inductor LeE between the Kelvin and power emitter terminals of an IGBT module is utilized to extract the turn-off delay time. Furthermore, the monotonic dependence between the junction temperature and turn-off delay time is investigated. The beginning and end point of the turn-off delay time can be determined by monitoring the induced voltage veE across the inductor LeE. A dynamic switching characteristic test platform for high-power IGBT modules is used to experimentally verify the theoretical analysis. The experimental results show that the dependency between IGBT junction temperature and turn-off delay time is near linear. It is established that the turn-off delay time is a viable TSEP with good linearity, fixed sensitivity, and offers nondestruction on-line IGBT junction temperature extraction.

Online High-Power P-i-N Diode Chip Temperature Extraction and Prediction Method With Maximum Recovery Current di / dt

P-i-N diode chip temperature is a significant indicator when evaluating the reliability of high-power converters. The feasibility of state-of-the-art thermosensitive electrical parameter (TSEP) extraction strategies for a high-power module is investigated and the limitations of using forward voltage drop for high-power P-i-N diode TSEP are explored. In the widely employed half-bridge topology, by detailed analysis of the upper antiparallel diode reverse recovery process due to lower nonideal insulated-gate bipolar transistor switching behavior, the inherent monotonic relationship between the maximum recovery current rate did/dt and chip temperature is disclosed. The maximum did/dt during the recovery period is chosen as the better TSEP, which can accurately reflect P-i-N diode chip temperature variation. Fortunately, by monitoring the negative peak voltage on the parasitic inductor between the Kelvin and power emitters under different temperatures, the maximum recovery rate did/dt can be readily determined. Consequently, additional passive components are not required for P-i-N diode chip temperature extraction, which is practical and cost-effective for high-power applications. Finally, a dynamic switching characteristics test platform based on a half-bridge topology is designed and adopted to experimentally verify the theoretical analysis. The experimental results show that the dependence between P-i-N diode chip temperature and the maximum recovery did/dt is approximately linear. This leads to a 3-D lookup table that can be used to estimate online P-i-N diode chip temperature.

Theoretical Evaluation of Stability Improvement Brought by Resonant Current Loop for Paralleled LLC Converters

This paper presents a digitally master-slave controlled parallel system of multiple LLC resonant converters with an inner resonant current control loop in each module. Theoretical analysis of the stability of individual modules and the system with an inner resonant current loop is proposed based on the envelop model, which reveals the principle of the performance improvement brought by the resonant current control loop. Moreover, the inner resonant current loop eliminates the differences in small-signal characteristics among different static operating points, thus facilitating the voltage loop design. The analysis of parallel operation and a complete control loop design guide for paralleled LLC resonant converters is presented based on a small-signal model rather than on software simulation. Finally, the stability analysis and design are elaborated and verified through a 16-kW experimental system of four modularized LLC resonant converters.

Decoupling-Controlled Triport Composited DC/DC Converter for Multiple Energy Interface

In this paper, a decoupled controlled triport dc/dc converter is derived by combining two bidirectional single-phase buck-boost converters and one isolated full-bridge converter for multiple input source applications. The power density is improved, and the circuit structure is simplified because the power devices are completely shared in the primary side. Furthermore, the pulsewidth modulation plus phase-shift control strategy is introduced to provide two control freedoms and achieve the decoupled voltage regulation within a certain operating range. The duty cycle of the bidirectional buck-boost converters is adopted to balance the voltage between the two primary input terminals, while their phase angle is applied to regulate the accurate secondary voltage. Furthermore, zero-voltage-switching soft-switching operation is provided for all of the primary power switches due to the inherent phase-shift control scheme. Moreover, the two filter inductors in the bidirectional buck-boost converters and the isolated transformer in the full-bridge topology are integrated and replaced by the winding-cross-coupled inductors to reduce the component numbers and simplify the magnetic structure. Finally, a 1-kW prototype is built to verify all theoretical considerations, and it is shown that the proposed topology is particularly advantageous in the distributed power generation system with multiple energy sources.

Asymmetrical Duty Cycle-Controlled LLC Resonant Converter With Equivalent Switching Frequency Doubler

In the conventional full-bridge LLC converter, the duty cycle is kept as 0.5 and the phase-shift angle of the half-bridge modules is 0° to be a symmetrical operation, which makes the resonant tank operating frequency only equal to the switching frequency of the power devices. By regulating the duty cycles of the upper and lower switches in each half-bridge module to be 0.75 and 0.25 and the phase-shift angle of the half-bridge modules to be 180°, the asymmetrical duty cycle controlled full-bridge LLC resonant converter is derived. The proposed asymmetrical duty cycle controlled scheme halves the switching frequency of the primary switches. As a result, the driving losses are effectively reduced. Compared with the conventional full-bridge LLC converter, the soft-switching condition of the derived asymmetrical controlled LLC converter becomes easier to reduce the resonant current. Consequently, the conduction losses are decreased and the conversion efficiency is improved. The asymmetrical control scheme can be also extended to the stacked structure for high input voltage applications. Finally, two LLC converter prototypes both with 200-kHz resonant frequency for asymmetrical and symmetrical control schemes are built and compared to validate the effectiveness of the proposed control strategy.

A Short-Circuit Safe Operation Area Identification Criterion for SiC MOSFET Power Modules

This paper proposes a new method for the investigation of the short-circuit safe operation area (SCSOA) of state-of-the-art SiC MOSFET power modules rated at 1.2 kV based on the variations in SiC MOSFET electrical parameters (e.g., short-circuit current and gate–source voltage). According to the experimental results, two different failure mechanisms have been identified, both reducing the short-circuit capability of SiC power modules with respect to discrete SiC devices. Based on such failure mechanisms, two short-circuit safety criteria have been formulated: 1) the short-circuit-current-based criterion; and 2) the gate-voltage-based criterion. The applicability of these two criteria makes possible the SCSOA evaluation of SiC MOSFETs with some safety margins in order to avoid unnecessary failures during their SCSOA characterization. SiC MOSFET power modules from two different manufacturers are experimentally tested in order to demonstrate the procedure of the method. The obtained results can be used to have a better insight of the SCSOA of SiC MOSFETs and their physical limits.

Online junction temperature extraction with turn-off delay time for high power IGBTs

High power insulated gate bipolar transistor (IGBT) modules are widely used in the wind power generator systems, electric locomotives, high voltage direct current transmission, etc. In such safety-critical and cost-sensitive applications, IGBT module reliability drawn research focuses. Research shows that IGBT reliability is closely related to junction temperature. In this paper, a junction temperature extraction method is presented based on device turn-off delay time. Module internal parasitic inductance is utilized to extract turn off delay time, and its temperature characteristics are analyzed. Experimental verification involves monitoring high power IGBT switching characteristics offline. The junction temperature extraction method based on turn-off delay time due to module parasitic inductance is viable and effective.

Modern IGBT gate driving methods for enhancing reliability of high-power converters — An overview

Abstract This paper presents a survey of existing gate driving approaches for improving reliability of Insulated Gate Bipolar Transistors (IGBTs). An extensive and various lists of techniques are introduced and discussed, including fast detection, identification and protection against IGBT failures, also considering cost-effective solutions. Gate-driver circuit solutions to improve short-circuit robustness, overload, voltage and current overshoots withstanding capability are first introduced to cope with abnormal conditions severely affecting lifetime expectation. Later, some advanced, state-of-the-art control techniques are discussed to minimize the real-mission-profile stresses in terms of voltage and current stresses to the device, together with, not least, temperature variations. Future challenges and perspectives are finally discussed at the end of the paper.

Online High-Power P-i-N Diode Junction Temperature Extraction with Reverse Recovery Fall Storage Charge

This paper proposes a method to extract the junction temperature of high-voltage and high-power p-i-n diodes. It is investigated that the swept-out charge during reverse recovery current fall time is affected by junction temperature variation, which makes the swept-out charge a possible thermo-sensitive electrical parameter (TSEP). Thanks to the specific package of high-power IGBT modules with p-i-n diodes, the swept-out charge of a p-i-n diode can be measured by the induced voltage