Climate change concerns due to the rising amounts of the carbon gas in the atmosphere have in the last decade or so initiated a fast pace of technological advances in the renewable energy industry. Such developments in technology and the move towards cleaner sources of energy have made distributed generation (DG) from renewable resources more desirable. However, it is a known fact that rising penetrations of DG can have adverse impacts on the grid structure and its operation. The microgrid concept is a solution proposed to control the impact of DG and make conventional grids more suitable for large scale deployments of DG. Covering many aspects of the power systems and power electronics fields, microgrids have become a very popular research field. This paper reviews the background and the concept of a microgrid, the current status of the literature, on-going research projects, and the relevant standards. It also presents a review of the microgrid pilot projects around the world in further detail and discusses the potential avenues for further research.

Recent developments in microgrids and example cases around the world—A review

The thermal stress of power electronic components is one of the most important causes of their failure. Proper thermal management plays an important role for more reliable and cost-effective energy conversion. As one of the most vulnerable and expensive components, power semiconductor components are the focus of this paper. Possible approaches to control the semiconductor junction temperature are discussed in this paper, along with the implementation in several emerging applications. The modification of the control variables at different levels (modulation, control, and system) to alter the loss generation or distribution is analyzed. Some of the control solutions presented in the literature, which showed experimentally that the thermal stress can be effectively reduced, are reviewed in detail. These results are often mission-profile dependent and the controller needs to be tuned to reach the desired cost-benefit tradeoff. This paper analyzes also the many open questions of this research area. Among them, it is worth highlighting that a verification of the actual lifetime extension is still missing.

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Junction Temperature Control for More Reliable Power Electronics

This paper presents an active gate driver (AGD) for IGBT modules to improve their overall performance under normal condition as well as fault condition. Specifically, during normal switching transients, a di/dt feedback controlled current source and current sink is introduced together with a push-pull buffer for dynamic gate current control. Compared to a conventional gate drive strategy, the proposed one has the capability of reducing the switching loss, delay time, and Miller plateau duration during turn-on and turn-off transient without sacrificing current and voltage stress. Under overcurrent condition, it provides a fast protection function for IGBT modules based on the evaluation of fault current level through the di/dt feedback signal. Moreover, the AGD features flexible protection modes, which overcomes the interruption of converter operation in the event of momentary short circuits. A step-down converter is built to evaluate the performance of the proposed driving schemes under various conditions, considering variation of turn-on/off gate resistance, current levels, and short-circuit fault types. Experimental results and detailed analysis are presented to verify the feasibility of the proposed approach.

A di/dt Feedback-Based Active Gate Driver for Smart Switching and Fast Overcurrent Protection of IGBT Modules

This paper proposes a fault-tolerant control strategy for a T-type three-level inverter when an open-circuit fault occurs. The proposed method is explained by dividing fault into two cases: the faulty condition of half-bridge switches and neutral-point switches. In case of the open-circuit fault in a neutral-point switch, two methods will be proposed and compared based on thermal analysis and neutral-point voltage oscillation. The reliability of T-type inverter systems is improved considerably by the proposed algorithm when a switch fails. The proposed method does not require any additional components. Simulation and experimental results verify the validity and feasibility of the proposed fault-tolerant control strategy.

Reliability Improvement of a T-Type Three-Level Inverter With Fault-Tolerant Control Strategy

This paper proposes a new diagnosis method of an open-switch fault and fault-tolerant control strategy for T-type three-level inverter systems. The location of the faulty switch can be identified by the average of the normalized phase current and the change of the neutral-point voltage. The proposed fault-tolerant strategy is explained by dividing into two cases: the faulty condition of half-bridge switches and neutral-point switches. The performance of the T-type inverter system improves considerably by the proposed fault-tolerant algorithm when a switch fails. The proposed method does not require additional components and complex calculations. Simulation and experimental results verify the feasibility of the proposed fault diagnosis and fault-tolerant control strategy.

Diagnosis and Tolerant Strategy of an Open-Switch Fault for T-Type Three-Level Inverter Systems

New IGBT modules to realize advanced neutral-point-clamped (A-NPC) 3-level power converters have been developed for the first time. The power loss of the IGBT modules developed is minimized by using 6th generation IGBT and FWD and 2nd generation RB-IGBT dies, the stray inductance between each pair of main terminal is as low as 40nH, and the arrangement of the terminals are optimized for constructing small sized A-NPC 3-level power converters. The electrical properties of the IGBT modules developed are reported. The power conversion efficiencies and power losses of A-NPC 3-level inverters using IGBT modules developed are calculated and compared with those of NPC 3-level and normal 2-level inverters. Prototypes of UPS using A-NPC circuit and IGBT modules developed have been fabricated and tested. The power conversion efficiency of the prototype UPS of usually operating type exceeds 95%, which is higher than that of conventional products by more than 5 point.

New IGBT modules for advanced neutral-point-clamped 3-level power converters

An enhanced reverse blocking MMC with DC fault handling capability for HVDC applications

Compared with conventional direct matrix converter, two-stage matrix converter has similar input/output characteristic. Furthermore, two-stage matrix converter can be implemented and controlled much easier since it has a practical DC-link. RB-IGBT is employed to construct bi-directional switches in two-stage matrix converter, which reduces on-state voltage drop and power loss of the converter. In this paper, a gate drive circuit for RB-IGBT with short-circuit protection based on integrated chip EXB841 is proposed. Experimental results validate the good performance of the proposed circuit in terms of switching test, fault under load test and hard switching fault test. The proposed gate drive circuit has been applied to drive the RB-IGBT bi-directional switches in the rectifier stage of two-stage matrix converter. The implementation of 10 kW two-stage matrix converter prototype using RB-IGBT is presented, and the experimental results on the rectifier stage of two-stage matrix converter using RB-IGBT is shown to test the proposed gate drive circuit.

RB-IGBT gate drive circuit and its application in two-stage matrix converter

Compared with conventional direct matrix converter, two-stage matrix converter has similar input/output characteristic. Furthermore, two-stage matrix converter can be implemented and controlled much easier since it has a practical dc-link. RB-IGBT is employed to construct bi-directional switches in two-stage matrix converter, which reduces on-state voltage drop and power loss of the converter. In this paper, a gate drive circuit for RB-IGBT with short-circuit protection based on integrated chip EXB841 is proposed. Experimental results validate the good performance of the proposed circuit in terms of switching test, fault under load test and hard switching fault test. The proposed gate drive circuit has been applied to drive the RB-IGBT bi-directional switches in the rectifier stage of two-stage matrix converter. The implementation of 10kW two-stage matrix converter prototype using RB-IGBT is presented, and the experimental results on the rectifier stage of two-stage matrix converter using RB-IGBT is shown to test the proposed gate drive circuit.

Offshore wind power converter is usually packed in a closed cabinet equipped with water cooling to meet the moisture and salt spray prevention requirements When a sudden dip of wind speed happens, the generated power will reduce significantly, making power semiconductor device and cooling water's temperature reduced quickly While the air temperature inside cabinet decreases slowly Thus, the water-cooling panels and water pipes become cold spots When the temperature is below the dew temperature, the condensation will happen In this paper, the reactive power oriented thermal control is proposed, which control the reactive power circulating between the two parallel wind power converters to prevent condensation The circulating reactive power control the power semiconductor and water-cooling panels' temperature above the dew temperature In this paper, the reactive power oriented thermal control and anti-condensation method are analyzed Finally, the MATLAB/PLECS simulation is carried out to validate the feasibility of proposed method

Seiki Igarashi

Papers

New IGBT modules for advanced neutral-point-clamped 3-level power converters

An enhanced reverse blocking MMC with DC fault handling capability for HVDC applications

RB-IGBT gate drive circuit and its application in two-stage matrix converter

RB-IGBT gate drive circuit and its application in two-stage matrix converter

Thermal control method based on reactive circulating current for anti-condensation of wind power converter under wind speed variations