Yufei Dong

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.

P-i-N diode chip temperature extraction method by investigation into maximum recovery current rate di/dt

P-i-N Diode chip temperature is a significant indicator when evaluating the reliability of high power converters. Firstly, the limitation of the forward voltage drop for high power P-i-N diode thermal sensitive electrical parameter (TSEP) is explored. In conventional two-level converter, the commutation is occurred between upper and lower devices. By detailed analysis of the upper P-i-N diode reverse recovery process with lower non-ideal IGBT commutation behavior, the inherent relationship between the maximum recovery current rate did/dt and chip temperature is disclosed. As a result, the maximum did/dt during the recovery period is chosen as 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 Kelvin emitter and power emitter under different temperatures, the maximum recovery rate did/dt can be readily determined. Finally, a dynamic switching characteristics test platform based on half bridge topology is used to experimentally verify the theoretical analysis. The results show that the dependency between diode chip temperature and maximum recovery did/dt is approximately linear. This leads to a 3-D look-up table that can be used to estimate on-line P-i-N diode chip temperature.

An enhanced energy harvesting method based on resonant current transformer for high voltage AC cable monitoring equipment

With the development of smart grid, a large amount of monitor equipment is employed to supervise the condition of power cable. Because of its convenience, extracting electric energy from cable via a current transformer is a promising technique used in power supply for these pieces of monitoring equipment. In this paper, an enhanced energy harvesting method based on current transformer in resonant state is proposed. In this method, a resonant capacitor is adopted to resonate with the equivalent magnetizing inductor of the current transformer. Therefore the reactive power on the inductor is compensated, thus the power harvested from the power cable is dramatically increased. Furthermore, the lower side diodes of the conventional rectifier are superseded by fully controllable switches. With the proposed control scheme and PI compensation, the output voltage can be regulated when the primary side current varies in a wide range. The method is verified by a 20W prototype.

Engineering design for structure and bus bar of 1.2MVA hybrid clamped five-level converter module

Engineering design of structure and bus bar for a three phase 1.2MVA hybrid clamped five-level (HCFL) converter module is presented in this paper. Firstly, the commutation characteristics of the HCFL topology are analyzed. Based on the analysis, a decoupling structural design is proposed to eliminate the negative effect of high frequency current. Secondly, a laminated design for bus bar is employed to decrease the overshoot voltage of switching devices. Finally, a single phase prototype is built to verify the effectiveness of the proposed design method for the 1.2MVA HCFL.

Module Multilevel-Clamped Composited Multilevel Converter (M-MC 2 ) with Dual T-Type Modules and One Diode Module

A modular multilevel-clamped composited multilevel converter (M-MC²) is proposed. M-MC² enables topology reconfiguration, power device reuse, and composited clamping. An advanced five-level converter (5L-M-MC²) is derived from the concept of M-MC². 5L-M-MC² integrates dual three-level T-type modules and one three-level neutral point clamped module. This converter can also integrate dual three-level T-type modules and one passive diode module by utilizing the device reuse scheme. The operation principle and SPWM modulation are discussed to highlight converter performance. The proposed M-MC² is comprehensively compared with state-of-the-art five-level converters. Finally, simulations and experimental results are presented to validate the effectiveness of the main contributions of this study.

An equivalent power test scheme for modular multilevel converters (MMCs)

For modular multilevel converters (MMCs), it is important to investigate the electromagnetic and electrothermal performance of sub-modules for design validation and optimization. This paper presents an equivalent test scheme for sub-modules, which has the clear advantages of system simplicity and reduced facility requirements. Firstly, the detailed analysis on the output features of sub-modules demonstrates that submodules working in a real MMC system can be equivalent to a controlled voltage source, which consists of two independent components, the dc and ac components, respectively. Furthermore, the test circuit composed of two identical sub-modules is introduced and the corresponding control strategy is further designed to ensure the equivalence of the test scheme presented. Finally, the simulation and experiment results reveal that the sub-module behaviors under different operating conditions of MMC can be closely emulated with the proposed test scheme, which provides a convenient way to evaluate the reliability of sub-modules.