Advanced Power Conversion Systems Research Articles

A Proposed Single-Input Multi-Output Battery-Connected DC–DC Buck–Boost Converter for Automotive Applications

In the realm of electric vehicles (EVs), achieving diverse direct current (DC) voltage levels is essential to meet varying electrical load demands. This requires meticulous control of the battery voltage, which must be adjusted in line with specific load characteristics. Therefore, the integration of a well-designed power converter circuit is crucial, as it plays a pivotal role in generating different DC voltage outputs. In this study, we also consider the incorporation of two additional doubler/divider circuits at the end of the proposed converter, further enhancing its capacity to produce distinct DC voltage levels, thus increasing its versatility. The standout feature of the proposed converter lies in its remarkable ability to amplify DC voltages significantly. For instance, when the input battery voltage is set at 48 VDC with a duty cycle (D) of 0.8, the resulting output demonstrates a remarkable augmentation, producing voltages 18, 36, and 72 times higher than the input voltage. Conversely, with a reduced D of 0.2 while maintaining the input voltage at 48 VDC, the converter yields diminished voltages of 0.1875, 0.375, and 0.75 times the initial voltage. This adaptability, based on the parameterization of D, underscores the converter’s ability to cater to a wide range of voltage requirements. To oversee the intricate operations of this versatile converter, a high-speed DSP-based controller system is employed. It utilizes the renowned PID approach, known for its proficiency in navigating complex, nonlinear systems. Experimental results validate the theoretical and simulation findings, reaffirming the converter’s practical utility in EV applications. The study introduces a simple control mechanism with a single power switch, high efficiency for high-power applications, wide voltage range, especially with VDC and VMC cells, and continuous current operation for the load in CCM mode. This study underscores the significance of advanced power conversion systems in shaping the future of electric transportation.

Behavior, Switching Losses, and Efficiency Enhancement Potentials of 1200 V SiC Power Devices for Hard-Switched Power Converters

Semiconductor power devices are the major constituents of any power conversion system. These systems are faced by many circumscriptions due to the operating constraints of silicon (Si) based semiconductors under certain conditions. The emergence and persistence evolution of wide bandgap technology pledge to transcend the restrictions imposed by Si based semiconductors. This paper presents a thorough experimental study and assessment of the performance of three power devices: 1200 V SiC cascode, 1200 V SiC MOSFET, and 1200 V Si IGBT under the same hardware setup. The study aims to capture the major attributes for each power device toward determining their realistic potential applications. The switching performance of each power device is studied and reported. As the gate resistance is a crucial factor in a power device characterization, an extensive analysis of hard-switching losses under different separated turn-on and turn-off gate resistances is also performed and discussed. To appraise the fast switching capability, the switching dv/dts and di/dts are measured and analyzed for each power device. Furthermore, insights are provided about the dependency of switching energy losses on the power device current and blocking voltage. This paper also focuses on evaluating the operations and the performances of these power devices in a hard-switched dc-dc converter topology. While using of 1200 V SiC Schottky diode in the converter design with each power device, the high switching frequency operations and efficiency of the converter are reported and thoroughly explored. The SiC cascode exhibited superior performance when compared to the other two power devices. The results and analyses represent guidelines and prospects for designing advanced power conversion systems.

Advanced Power Conversion System for Motor Drive in Electrified Vehicles.

This paper presents a power conversion system for six-switch BLDC motor drive and fourswitch BLDC motor drive. Brushless DC (BLDC) motor drive have the advantage of high efficiency, high power density and low maintenance. These advantages make BLDC motor drive be widely used in industrial applications. In addition, the four-switch inverter will reduce the cost of the system with less switches. However, the problem of torque pulsation of four- switch BLDC motor drive is an intrinsic problem. To reduce torque pulsation, a novel DC/DC converter whose name is multi-purpose bi-directional DC/DC converter will be proposed in the thesis. This DC/DC converter with diode-assisted network will help improve boost ratio for the input of the BLDC motor drive. For the control system, PI controllers are used to control DC/DC converter and hysteresis control is employed for BLDC motor drive. Though there are other advanced methods for control, the PI controllers and hysteresis control can reduce the complexity of the whole system. Both six-switch and four-switch BLDC motor drives with the proposed system are simulated in PSIM software and the results are compared and discussed.

Finite‐Control‐SetModel Predictive Control for Asymmetrical CascadedH‐BridgeMultilevelGrid‐ConnectedInverter with Flying Capacitor

The multilevel inverter is the most advanced power conversion system, whose main advantage is to improve power quality and efficiency. Cascaded H‐bridge (CHB) multilevel inverter is a kind of inverter that can be selected in the field of motor drive systems, electric vehicles and photovoltaic grid‐connected power generations. However, the CHB multilevel inverters require a great deal of independent direct current (dc) power supplies, which makes the realization of these inverters very complicated in practical applications. In this article, model predictive control for CHB inverter with flying capacitors is proposed to improve the above drawbacks. Simulation and experimental results show that voltage balance of the flying capacitor can be maintained and simultaneously the output voltage of the inverter normally. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Novel Deep Space Nuclear Electric Propulsion Spacecraft

The space industry is expanding at an increasing rate. While most efforts are currently focused on Earth and lunar orbits, it is only a matter of time before affordable exploration missions into deep space become more prevalent. Nuclear electric propulsion (NEP) with large quantities of power have been theorized for such missions with many advantages over traditional solar panels and radioisotope power sources. Key among NEP issues has been the power conversion system, often falling upon dynamic cycles over solid-state options like thermoelectric generators (TEGs) because of low efficiencies. Howe Industries has conceptualized a deep space probe capable of transporting cube satellites (CubeSats) and other payloads to deep space utilizing NEP based on an advanced TEG power conversion system with efficiencies that would challenge traditional dynamic power conversion cycles. Experimentation at a TRIGA research reactor has shown a potential for 20 to 50 times increase in electrical conductivity of potential thermoelectric materials, which would correlate to large increases in efficiencies over traditional TEGs.

(Invited) RKP Vanadium Flow Battery and its Application

Vanadium flow battery(VFB) is deemed to be one of the most promising technologies for large-scale industrial energy storage, due to its attractive features like flexible capacity, active thermal management, long cycle life and high safety. Dalian Rongke Power Co., Ltd. (RKP) has been devoted to the fundmental study and advanced research of Vanadium flow battery applications. It has become one of the world-leading enterprises in VFB development, manufacturing and delivery industry. The products have evolved from earlier indoor structure to the latest containerized system designs. More than a dozen VRFB systems have been deployed and end products have been launched into operations across the world over the past decades. The 500kW/2MWh VFB product was developed for the large scale energy application, which is consisted of 16 cell stacks. The high integration level, low shunt current loss, low auxiliary power supply consumption and high reliability were achieved. The novel cell stack is designed by optimizing the key materials and cell stack structure, which can achieve a better performance and higher reliability at a relatively low cost. The energy efficiency(EE) could reach 80% at the rated power of 33kW, and the current density could be improved to 140~150 mA/cm2.The cycle life test indicated that no obvious performance decay was found even after 10000 cycles. The advanced two-stage power conversion system (PCS) was selected in order to realiaze the independent control of each sub-systems, which would improve the overall reliability ultimately. The AC/AC energy efficiency could reach 70% at the rated power of 500kW. The 500kW/2MWh VFB product has been installed in power plants for wind and solar energy storage and has obtained better application effect. The world largest battery system, a 200MW/800MWh VFB peaking power plant conducted by RKP, is currently in progress in Dalian, China. The purpose is to improve the Northeast grid resiliency and facilitate smooth integration of renewables. A 500kW/2MWh VFB product is the minimum storage unit of the project. Each unit product could be controled independently. The foreseeable success of the project would exert great influence on the development of the flow battery in the future. In this presentation, new technolgy and product developments of vanadium flow battery at RKP will be introduced and further challenges will be addressed as well.

Corrosion resistance of alumina-forming alloys against molten chlorides for energy production. I: Pre-oxidation treatment and isothermal corrosion tests

Advanced components in next-generation concentrating solar power (CSP) applications will require advanced heat-transfer fluids and thermal-storage materials that work from about 550°C to at least 720°C, for integration with advanced power-conversion systems. To reach the cost target, less-expensive salts such as molten chlorides have been identified as high-temperature fluid candidates. High-strength alloys need to be identified and their mechanical and chemical degradation must be minimized to be used in CSP applications. Approaches for corrosion mitigation need to be investigated and optimized to drive down corrosion rates to acceptable levels—in the order of tens of micrometers per year—for achieving a long system lifetime of at least 30 years. Surface passivation is a good corrosion mitigation approach because the alloy could then be exposed to both the liquid and the vapor phases of the salt mixture. In this investigation, we pre-oxidized the alumina-forming alloys Inconel 702, Haynes 224, and Kanthal APMT at different temperatures, dwelling times, and atmospheres to produce the passivation by forming protective oxides at the surface. The pretreated alloys were later corroded in molten MgCl2 – 64.41wt% KCl at 700°C in a flowing Ar atmosphere. We performed electrochemical techniques such as open-circuit potential followed by a potentiodynamic polarization sweep and conventional long-term weight-change tests to down-select the best-performing alloy and pre-oxidation conditions. The best corrosion results were obtained for In702 pre-oxidized in zero air at 1050°C for 4h. Metallographic characterization of the pre-oxidized alloys and of the corroded surfaces showed that the formation of dense and uniform alumina scale during the pre-oxidation appears to protect the alloy from attack by molten chloride.

Design and Control of Modular Multilevel Converters for Battery Electric Vehicles

New advanced power conversion systems play an essential role in the extension of range and life of batteries. This paper proposes a new modular multilevel converter with embedded electrochemical cells that achieves very low cell unbalancing without traditional balancing circuits and a negligible harmonic content of the output currents. In this new topology, the cells are connected in series by means of half-bridge converters, allowing high flexibility for the discharge and recharge of the battery. The converter features a cell balancing control that operates on each individual arm of the converter to equalize the state of charge of the cells. The paper shows that the proposed control does not affect the symmetry of the three-phase voltage output, even for significantly unbalanced cells. The viability of the proposed converter for battery electric vehicles and the effectiveness of the cell balancing control are confirmed by numerical simulations and experiments on a kilowatt-size prototype.

통계학적 비교 기법을 이용한 태양광 모듈의 고장 유무 검출에 관한 연구

In recent years, many investigations about photovoltaic power systems have been significantly carried out in the fields of renewable power energy. Such research area generally includes developments of highly efficient solar cells, advanced power conversion systems, and smart monitoring systems. A generic objective of fault detection and diagnosis techniques is to timely recognize unexpected faulty of dynamic systems so that economic demage occurred by such faulty is decreased by means of engineering techniques. This paper presents a novel fault detection approach for photovoltaic power arrays which are electrically connected in series and parallels. In the proposed fault detection scheme, we first measure all of photovoltaic modules located in each array by using electronic sense systems and then compare each measurement in turn to detect location of fault module through statistic computation algorithm. We accomplish real-time experiments to demonstrate our proposed fault detection methodology by using a test-bed system including two 20 watt photovoltaic modules.

Design Option of Heat Exchanger for the Next Generation Nuclear Plant

The next generation nuclear plant (NGNP), a very high temperature gas-cooled reactor (VHTR) concept, will provide the first demonstration of a closed-loop Brayton cycle at a commercial scale, producing a few hundred megawatts of power in the form of electricity and hydrogen. The power conversion unit for the NGNP will take advantage of the significantly higher reactor outlet temperatures of the VHTRs to provide higher efficiencies than can be achieved with the current generation of light water reactors. Besides demonstrating a system design that can be used directly for subsequent commercial deployment, the NGNP will demonstrate key technology elements that can be used in subsequent advanced power conversion systems for other Generation IV reactors. In anticipation of the design, development, and procurement of an advanced power conversion system for the NGNP, the system integration of the NGNP and hydrogen plant was initiated to identify the important design and technology options that must be considered in evaluating the performance of the proposed NGNP. As part of the system integration of the VHTRs and the hydrogen production plant, the intermediate heat exchanger is used to transfer the process heat from VHTRs to the hydrogen plant. Therefore, the design and configuration of the intermediate heat exchanger are very important. This paper describes analyses of one stage versus two-stage heat exchanger design configurations and simple stress analyses of a printed circuit heat exchanger (PCHE), helical-coil heat exchanger, and shell-and-tube heat exchanger.

99/03076 Granular filtration in a fluidized bed

Successful development of advanced coal-fired power conversion systems often require reliable and efficient cleanup devices which can remove particulate and gaseous pollutants from high-temperature high-pressure gas streams. A novel filtration concept for particulate cleanup has been developed at the Morgantown Energy Technology Center (METC) of the U.S. Department of Energy. The filtration system consists of a fine metal screen filter immersed in a fluidized bed of granular material. As the gas stream passes through the fluidized bed, a layer of the bed granular material is entrained and deposited at the screen surface. This material provides a natural granular filter to separate fine particles from the gas stream passing through the bed. Since the filtering media is the granular material supplied by the fluidized bed, the filter is not subjected to blinding like candle filters. Because only the inflowing gas, not fine particle cohesive forces, maintains the granular layer at the screen surface, once the thickness and permeability of the granular layer is stabilized, it remains unchanged as long as the in-flowing gas flow rate remains constant. The weight of the particles and the turbulent nature of the fluidized bed limits the thickness of the granular layer on the filter leading to a self-cleaning attribute of the filter. This paper presents work since then on a continuous filtration system. The continuous filtration testing system consisted of a filter, a two-dimensional fluidized-bed, a continuous powder feeder, a laser-based in-line particle counting, sizing, and velocimeter (PCSV), and a continuous solids feeding/bed material withdrawal system. The two-dimensional, transparent fluidized-bed allowed clear observation of the general fluidized state of the granular material and the conditions under which fines are captured by the granular layer.

Forty years of experience on closed-cycle gas turbines

In this paper the 40 years of experience on closed-cycle gas turbines (CCGT) is emphasized to substantiate the claim that this prime-mover technology is well established. European fossil-fired plants with air as the working fluid have been individually operated over 100,000 hours, have demonstrated very high availability and reliability, and have made money for their operator owners. Following the initial success of the small air closed cycle gas turbine plants, the next step was the exploitation of helium as the working fluid for plants above 50 MWe. The first fossil fired combined power and heat plant at Oberhausen, using a helium turbine, plays an important role for future nuclear systems and this is briefly discussed. The combining of a modern reactor (HTGR) and an advanced proven power conversion system (CCGT) represents the most interesting and challenging project to engineers in the closed cycle gas turbine field. The benefits of the nuclear gas turbine power plant are such that the worldwide efforts to bring it into use should increase rapidly since the role it can play in meeting energy goals is significant. The key to acceptance of the CCGT in the near term is the introduction of a small nuclear cogeneration plant (100–300 MWe) that utilizes the waste heat, and thus demonstrates a very high fuel utilization efficiency; aspects of such a plant are outlined in this paper.

Alkali Metal Space Power Technology Applicable to National Energy Research and Development

The nation's space power program developed an alkali metal technology potentially applicable to its future energy needs. The space power system was designed to utilize a nuclear reactor with a primary lithium loop and a secondary boiling/condensing potassium loop driving a potassium vapor turbine/electrical generator. Considerable design, manufacture, test, and evaluation efforts were expended in the successful demonstration of the boilers, condensers, turbines, seals, valves, pumps, and other components. Much of that high-temperature, Rankine cycle technology can be used as a basis for advanced power conversion systems; these might include fossil and nuclear fueled plants, central solar power systems or solar power satellites.