Step-up switched-capacitor multilevel inverter employing multiple inputs with reduced switches

Wang, Yaoqiang,Wang, Zhe,Liu, Wenjun,Zhang, Yun,Wang, Kewen,Liang, Jun The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.7

A large device count, weak boosting capability, and DC voltage imbalance are common issues in conventional multilevel inverters. In this paper, a novel multilevel inverter is presented that can generate the desired number of output levels with reduced devices by using new switched-capacitor circuits (SCCs). The two input sources and capacitors in the SCC can be switched in parallel and series modes. In the parallel mode, the capacitor voltage of the SCC is charged to the DC source voltage, which inherently solves the capacitor voltage imbalance issue without any auxiliary circuits. In the series mode, the capacitor can be used as an alternative source, which helps achieve a high voltage gain. The multiple input sources of the SCC make the proposed topology suitable for application in renewable energy generation systems where several DC sources are available. Instead of an H-bridge module, a structure with two half-bridges and two switches is used as a polarity generation circuit at the load terminal. The input sources of two SCCs can be selected as symmetric and asymmetric patterns, which can result in a great number of output voltage levels. The circuit topology, operational principle, modulation strategy, capacitor analysis, and performance comparisons of the inverter are described in this paper. In addition, experimental results verify the feasibility and validity of the inverter.

Bypass arm based DC fault isolation scheme for MMC‑HVDC systems

Yaoqiang Wang,Ruyin Sun,Yanxun Guo,Kewen Wang,Jun Liang 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.8

High voltage direct current transmission based on a modular multilevel converter (MMC-HVDC) is an effective method to solve the grid connection of the new energy. A DC fault is an issue that must be solved for MMC-HVDC. This paper proposes a protection scheme for HVDC converters to quickly suppress DC fault current without increasing the operation loss. By employing a bypass arm in conjunction with a switch-type zero-loss current limiter (SZCL), most of the DC current in the bridge arm fl ows through the bypass arm so the fault current of the power devices is reduced. There are a number of main advantages of this scheme. The fault isolation time can be greatly shortened, the cost of the system is effectively reduced, the steady-state operation loss of the system does not increase, the operation of the AC-grid can be maintained stably when a DC fault occurs, and the overcurrent impulse to the AC-grid is reduced. The proposed scheme is applicable to two-terminal systems and the DC grid, especially for faults at the converter outlet of the DC grid. Simulation results using PSCAD/EMTDC show the superiority of the proposed scheme when compared with other schemes and a comparison of the costs shows the feasibility of the proposed scheme in practical applications.

A Nine-Level Switched-Capacitor Step-Up Inverter with Low Voltage Stress

Wang Yaoqiang,Ye Juncheng,Wang Kaige,Nie Fuquan,Li Gen,Liang Jun 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.2

This paper proposes a nine-level switched-capacitor step-up inverter (9LSUI) which can achieve a quadruple voltage gain with single dc source. Differing from other switched-capacitor inverters, the voltage stress of switches is effectively reduced due to the elimination of H-bridge, and the peak inverse voltage of all switches is kept within 2Vdc. In addition, the proposed inverter is able to integrate inductive load, and the capacitor voltage self-balancing can be achieved without any auxiliary circuits. Moreover, the topology structure can be flexibly extended to raise the output levels, and the peak inverse voltage of switches can remain constant with the increase of sub-modules in the extended structure. Comprehensive comparisons are performed to verify the outstanding advantages of the proposed inverter. Finally, the steady-state and dynamic performance of the proposed inverter is validated through an experimental prototype, and the experimental results are provided to prove the theoretical analysis.

A modular switched‑capacitor multilevel inverter featuring voltage gain ability

Yaoqiang Wang,Juncheng Ye,Ruohan Ku,Yuchen Shen,Gen Li,Jun Liang 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.1

This article presents a modular switched-capacitor multilevel inverter which uses two capacitors and a single dc source to obtain triple voltage gain. It is worth noting that the inherent inversion capacity removes the H-bridge, which can efficaciously diminish the voltage stress of switches, and the maximum voltage stress (MVS) on devices is kept within 2Vdc. Additionally, the proposed topology is able to integrate inductive load, and the capacitor voltage self-balancing can be achieved. Moreover, the modular structure also has an expandable topology which can generate more levels and raise the voltage gain by using multiple switched-capacitor units, meanwhile the voltage stress on power switches can be kept within 2Vdc. Furthermore, comprehensive analysis and comparison with other multilevel inverters have been implemented to certify the superiority of the proposed topology. Finally, the steady-state and dynamic performance of the proposed topology is examined through a seven-level inverter prototype, the validity and practicability of the topology are verified by simulations and experiments.

Extendable space‑type switched‑capacitor multilevel inverter with fault‑tolerant capability

Yaoqiang Wang,Hengtai Zhang,Jinmu Lai,Kewen Wang,Jun Liang 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.6

Low reliability is one of the main concerns in terms of multilevel inverters (MLI) due to the presence of a large number of switches and capacitors. Therefore, the fault-tolerant operation of MLIs has recently gained a great deal of attention. An extendable space-type switched-capacitor MLI topology with fault-tolerant characteristics is proposed in this paper. The proposed inverter employs a single direct-current voltage source and three capacitors to output staircase voltage levels with low distortion. The proposed topology is capable of tolerating open-circuit faults due to the separated charging paths of the inverter. Under pre-fault and post-fault operations, it preserves capacitor voltage balancing, voltage boost capability, as well as the ability to supply inductive loads. Furthermore, the voltage stresses of the switches and the voltage ripples of the capacitors are decreased or remain under post-fault operations. The proposed topology has been validated with a laboratory prototype in both dynamic and steady-state operations.

Flexible cascaded multilevel inverter with multiple operation modes

Wang, Yaoqiang,Du, Guanyu,Liang, Jun,Qin, Ming The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.3

In this paper, a flexible cascaded multilevel inverter is proposed with a wide operational range. The inverter can change its topology structure to operate in three modes by a bidirectional switch unit. The nine-level or five-level mode of the inverter is adopted to optimize the output waveform when the input power is low. To decrease power losses, the three-level mode of the inverter is adopted to reduce the number of active switch devices when the input power is high. The topology and modulation strategy of the proposed inverter are presented and analyzed. The total losses and current THD of the inverter are calculated. In addition, simulations and experiments are conducted. The obtained simulation and experimental results indicate the correctness and feasibility of the proposed inverter and its modulation strategy.

Novel extensible multilevel inverter based on switched‑capacitor structure

Yaoqiang Wang,Juncheng Ye,Ruohan Ku,Yi Wang,Jun Liang 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.9

Multilevel inverters (MLIs) play an important role in research on renewable energy conversion. However, in traditional designs, the high-voltage stress of switching devices and the large number of switches limit the wide application of theinverter. To ameliorate these problems, this paper proposes a switched-capacitor multilevel inverter (SCMLI). When compared with traditional MLIs, the proposed SCMLI utilizes a switched-capacitor structure, where the capacitors can achieve voltage self-balancing without auxiliary methods. Thus, it permits changes of the positive and negative polarity of the output level without the need for an H-bridge. In addition, with the augment of the level in the expanded SCMLI structure, the maximum blocking voltage can be kept constant. To show the advantages of the proposed structure, an extensible single dc source five-level SCMLI prototype has been built. Through a comparative analysis with different topologies, this paper also presents the advantages of the proposed topology in terms of the output voltage gain, number of output levels, and voltage stress. Finally, the correctness and feasibility of the proposed inverter are validated by extensive experiments.

Enhanced activity and hydrothermal stability of Rh-based three-way catalyst for emission control from motorcycles with the assistance of monoethanolamine

Li Lan,Jinfeng Wang,Shanhu Chen,Dacheng Li,Hongmei Li,Dayu Liu,Wei Wang,Yaoqiang Chen 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.71 No.-

In this work, an advanced Rh/CeO2–ZrO2 (Rh/CZ) three-way catalyst was synthesized with the assistanceof monoethanolamine. Compared with conventional Rh/CZ, the dispersion and oxidation state of Rhspecies, as well as the hydrothermal aging resistance are remarkably modified. That is, upon agingtreatment, conventional Rh/CZ undergoes severe agglomeration of Rh species and formation of largeamount of reduction-resistive RhO2, resulting in serious catalyst deactivation. Fortunately, after theintroduction of monoethanolamine, the sintering of Rh species and transformation into inactive RhO2upon aging are effectively suppressed. Consequently, improved reducibility and advanced three-waycatalytic activity are achieved for the modified catalyst.

Enhanced activity and stability of the monolithic Pt/SiO2–Al2O3 diesel oxidation catalyst promoted by suitable tungsten additive amount

Yanli Liang,Ming Zhao,Jianli Wang,Mengmeng Sun,Shanshan Li,Yufen Huang,Lin Zhong,Maochu Gong,Yaoqiang Chen 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.54 No.-

A series of the modified Pt/SiO2–Al2O3 diesel oxidation catalysts with different WO3 loading were prepared through co-impregnation method. With an optimum additive loading of 2 wt% WO3, the catalyst significantly improved the performance and its stability. Compared to the free-tungsten sample, the catalyst increased the maximum conversion of NO by 5–10% and decreased the reaction temperature for 30% NO conversion by 7–28 C. It was found that there exist the electron and structure interaction between platinum and tungsten species. The interactions can generate and maintain more Pt sites in metallic state for the catalytic oxidation with enhanced activity and stability.

Designed synthesis and characterization of nanostructured ceria-zirconia based material with enhanced thermal stability and its application in three-way catalysis

Jie Deng,Yi Zhou,Shanshan Li,Lei Xiong,Jianli Wang,Shandong Yuan,Yaoqiang Chen 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.64 No.-

Three CeO2–ZrO2–Y2O3–La2O3 (CZ) nanomaterials with controllable crystallite size were prepared by a simple co-precipitation method combined with hydrothermal treatment at different temperatures. The material CZ-180 possesses a high surface area of 43.6 m2 g−1 and a low reduction temperature of 344 °C simultaneously even after aging at 1000 °C for 4 h. Moreover, with improving hydrothermal temperature, the incorporation of rear earth metals was accelerated and surface properties were modified. And higher Pd dispersion and larger proportion of active Pd2+ species were achieved on the modified surface of CZ-180. Consequently, the supported catalyst Pd/CZ-180 shows a superior three-way catalytic performance.