High Power Converter System Research Articles

A Unified Capacitor Stress Emulation Method for High-Power Converter Applications

This paper proposes a unified capacitors stress emulation method, which has two unique test capabilities: 1) concurrent electrical stress emulation to AC capacitors and DC capacitors; 2) different electrical stress levels (including different ripple current, ripple voltage, and DC voltage) can be individually controlled for the testing samples. It preserves the advantages of a recently reported method with a minimum required power supply and is robust to testing sample degradation. This method is suitable for application-oriented stress emulation testing with different types of DC / AC capacitors and multiple electrical stresses in high power converter systems. The circuit architecture and testing ability of this method are presented. Moreover, analytical models are derived to size the key components to realize various testing requirements. Proof-of-concept experimental results are presented to verify the feasibility of the proposed test method.

系統連系変換器の高調波共振現象に対する組み合わせ補償制御と補償安定性

This paper presents a theoretical discussion on a combined-compensation control method and its stability on harmonic resonance for grid-connected converters. The interaction between the grid impedance and the grid-connected converter potentially creates harmonic resonance. The compensation control with a combination of a digital filter and a virtual impedance is an effective solution for this problem. The theoretical analysis developed in this study reveals that the proper use of the two control schemes enhances the availability of grid-connected converters. Simulated results obtained from a three-phase high-power converter system verify this analysis.

Planar Common-Mode EMI Filter Design and Optimization for High-Altitude 100-kW SiC Inverter/Rectifier System

Silicon-carbide (SiC) devices are receiving popularity for high-power converter systems in aircraft due to many advantages over silicon counterparts. However, the electromagnetic interference (EMI) problems are more serious with the SiC devices operating at higher switching speeds and higher switching frequencies. The common-mode (CM) EMI filter design of the high-power SiC converter is especially challenging for high-altitude applications due to the harsher requirements of insulation and heat dissipation. The optimization of the parameters and physical design of a CM EMI filter in a 100-kW SiC inverter/rectifier system operating at 50 000 ft is conducted in this article to obtain the highest power density. The effect of the switching frequency on the EMI filter volume and the total power density of the converter system is analyzed. The lower breakdown voltage of air and the higher thermal resistance of natural convection make the conventional design of the CM choke infeasible at high altitudes. A printed circuit board (PCB)-based planar CM choke is designed with the consideration of partial discharge (PD) and heat dissipation at the altitude of 50 000 ft. The structure of the CM choke is optimized with embedded electric-field shielding plates, which controls the electric-field intensity in the air below 300 V/mm. The PCB windings improve the efficiency of heat dissipation at high altitudes and reduce the profile of the CM choke. A Pareto optimization is conducted to minimize the size of the choke and the volume of the final design is only 155 cm3. The experimental results show that the CM noise is reduced effectively with the CM EMI filter. PD is not observed even at the altitude of 50 000 ft and the thermal performance is excellent with a current of 190 A. With the optimization and the dedicated design of the CM EMI filter, the power density of the converter system is up to 33.3 kW/L.

Gate Drivers for Medium-Voltage SiC Devices

Extensive research in wide-bandgap material technology such as silicon carbide (SiC) has led to the development of medium-voltage (MV) power semiconductor devices with blocking voltages of 3.3 to 15 kV. When these devices are used in various applications, they are exposed to a high peak voltage stress and a very high $dv/dt$ (50–100 V/ns). These impose stringent requirements on the gate driving stage for these devices in terms of featuring a high isolation voltage capability along with a high $dv/dt$ ruggedness, which makes it necessary to have an ultralow coupling capacitance between primary and secondary sides of the gate drivers. One of the key issues in achieving this MV insulation pertains to the necessary clearance and creepage requirements, as defined in IEC 61800-5-1 standards. While the successful operation of these gate drivers is demonstrated in MV converter applications such as solid-state transformers, and MV grid-connected inverters, substantial research needs to be carried out to improve the gate drivers’ performance and provide a plug-and-play solution. This article aims to comprehensively review these gate drivers and consolidate various required design features concerning their galvanic isolation stage, based on normal and short-circuit operation of MV high-power converter systems. Different device short-circuit protection schemes for these gate drivers are explored in detail. Additional applications and functionalities of the gate drivers, including gate drivers used in the series-connection of MV devices and intelligent gate drivers, are also provided in brief. Based on prior research, this review aims to provide design choices and guidelines for the gate drivers, accelerating the growth and deployment of MV SiC devices for field applications.

Bond Wire Damage Detection and SOH Estimation of a Dual-Pack IGBT Power Module Using Active Power Cycling and Reflectometry

High thermal and electrical stress, over a period of time tends to deteriorate the health of power electronic switches. Being a key element in any high-power converter systems, power switches, such as insulated-gate bipolar junction transistors (IGBTs) and metal-oxide semiconductor field-effect transistors, are constantly monitored to predict when and how they might fail. A huge fraction of research efforts involves the study of power electronic device reliability and development of novel techniques with higher accuracy in the health estimation of such devices. Until today, no other existing technique can determine the number of lifted bond wires and their locations in a live IGBT module, although this information is extremely helpful to understand the overall state-of-health of an IGBT power module. Through this article, a new method for online condition monitoring of IGBTs and IGBT modules using spread spectrum time-domain reflectometry has been proposed. Unlike traditional methods, this research work concentrates at the gate terminals (low voltage) of the device instead of looking at the collector side. In addition, the RL-equivalent circuit to represent a bond wire has been developed for the device under test and simulated in CST Studio Suite to measure the reflection amplitudes. Experimental results were obtained using a prototype reflectometry hardware, and both the simulation and experimental results have been compared. These results prove that a single measurement is sufficient to predict the failure of the device instead of looking at the traditional precursor parameter (VCEON). With only two sets of measurements, it is possible to locate the aged device inside a module and detect the number of bond wire liftoffs associated with that device.

Energy balancing in modular multilevel converter systems

Abstract The modular multilevel converter (MMC) is a well-known solution for medium and high voltage high power converter systems. This paper deals with energy balancing of MMCs. The analysis includes multi-converter systems. In order to provide clear view, the MMC control system is divided into hierarchical levels. Details of control and balancing methods are discussed for each level separately. Finally, experimental results, based on multi-converter test setup, are presented.

Inductor Characteristics Analysis in High Power Interleaved Buck Converter

Inductor in high power converter system increases production cost, volume and core loss proportional to the power. To decrease these disadvantages, this paper analyzed the characteristic of parallel-inductor and coupled-inductor in interleaved system with simulation. As a result, it is confirmed that two-phase interleaved non-coupled buck-converter has the best characteristic among three types converter.

Optimized Integrated Harmonic Filter Inductor for Dual-Converter-Fed Open-End Transformer Topology

Many high-power converter systems are often connected to the medium-voltage network using a step-up transformer. In such systems, the converter-side windings of the transformer can be configured as an open end, and multilevel voltage waveforms can be achieved by feeding these open-end windings from both ends using the two-level dual converter. An $LCL$ filter with separate converter-side inductors for each of the converter is commonly used to attenuate the undesirable harmonic frequency components in the grid current. The magnetic integration of the converter-side inductors is presented in this paper, where the flux in the common part of the magnetic core is completely canceled out. As a result, the size of the magnetic component can be significantly reduced. A multiobjective design optimization is presented, where the energy loss and the volume are optimized. The optimization process takes into account the yearly load profile and the energy loss is minimized, rather than minimizing the losses at a specific operating point. The size reduction achieved by the proposed inductor is demonstrated through a comparative evaluation. Finally, the analysis is supported through simulations and experimental results.

Development of a Modular High-Power Converter System for Battery Energy Storage Systems

The integration of storage systems into the grid is becoming increasingly important due to the growing amount of volatile power sources. This paper shows a theoretical approach for designing a modular battery energy storage system (BESS) for medium voltage grids (Fig. 1). Typically, this system is scalable in power rated from 5 MW up to 100 MW with a storage capacity of several hours. The flexibility of power rating and energy capacity allows the set-up of BESS for versatile applications. Using power electronic building blocks (PEBBs) a converter for DC grids and AC grids can be built. In this paper, the chosen topology for the AC solution is the cascaded cell converter. The focus is to determine the optimum number of levels, the modulation technique to avoid microcycles of the batteries and to present the efficiency. A formula to calculate the parasitic capacitance of lead-acid batteries is shown and verified by measurements, which is important for the design of such a converter system. Moreover, a new charging strategy for LiFePO4 - the chosen battery technology for the proposed storage system - is introduced, which prolongs the battery’s life, reduces the charging time and decreases the life cycle cost. The proposed charging strategy and battery technology compared to lead-acid batteries is also economically evaluated.