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.

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.

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.

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.

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.

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.

Experimental Study and Numerical Analysis on the Progressive Collapse Resistance of SCMS

Hua Huang,Yaoqiang Xian,Kailin Xi,Boquan Liu 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.1

With the Spokewise Cable-Membrane Structure (SCMS) of Foshan Century Lotus Sports Center (FCLSC) as the engineering background, this study analyzes the infl uence of the structure’s local cable damage on its holistic resistant behavior and investigates the resistance of SCMS against progressive collapse by means of scale model tests and ANSYS fi nite element analysis. Results indicate that SCMS exhibits good resistance against progressive collapse. After the upper radial cables or the lower radial cables break, their borne load is passed to the connected cables. Thus the collapse can be restricted within a limited area through the deformation and stress relaxation of the adjacent cables. In the design process, the cable system is divided into a fi nite number of partitions, and double cables could be used at the junctions of diff erent partitions to better control the damaged area. The inverted Y-type or the polystyle pier column should be chosen to enhance the resilience after collision or explosion.

Controllable synthesis of zone-distributed Pd over CeO2–ZrO2/Al2O3 as advanced three-way catalyst

Li Lan,Shanhu Chen,Hongmei Li,Hanmei Li,Wanxia Wu,Jie Deng,Yaoqiang Chen 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.58 No.-

Two optimally designed catalysts (Ce0.7Zr0.3O2/Pd/Al2O3, Pd/Ce0.7Zr0.3O2/Pd/Al2O3) were synthesized and compared with conventional Pd/Ce0.7Zr0.3O2/Al2O3. The characterization results reveal that for Pd/Ce0.7Zr0.3O2/Al2O3, Pd species undergo severe agglomeration and encapsulation during thermal aging process, leading to dramatic catalyst deactivation. While for the two optimized catalysts, some Pd species initially distributed on Al2O3 would migrate to the surface of CexZr1−xO2(CZ) grains upon aging treatment, resulting in enhanced Pd–CZ interaction, thus the two aged samples possess higher dispersion, larger amount of oxidized Pd2+ species and more oxygen vacancies compared with conventional Pd/Ce0.7Zr0.3O2/Al2O3-a. Consequently, modified reducibility and improved three-way catalytic performance are obtained, especially for Pd/Ce0.7Zr0.3O2/Pd/Al2O3-a.

Hydrothermal deactivation over CuFe/BEA for NH3-SCR

Qingjin Lin,Xi Feng,Hailong Zhang,Chenlu Lin,Shuang Liu,Haidi Xu,Yaoqiang Chen 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.65 No.-

Hydrothermal deactivation over CuFe/BEA and CuFe/BEA-HT for the selective catalytic reduction of NO with NH3 (NH3-SCR) were investigated with different characterizations. The hydrothermal treatment destroys BEA skeleton, losing acid sites reacting with the aerial NOx. H2-TPR and XPS reveal that the hydrothermal treatment could weaken the interaction between Cu/Fe species and the surrounding other atoms, causing the aggregation of isolated and low nuclearity copper/iron species. Aggregated copper/iron oxides depress the redox property of CuFe/BEA-HT, producing the lower concentration of NO2. Besides, results of in situ DRIFTS also indicate that both CuFe/BEA and CuFe/BEA-HT follow Eley–Rideal (E–R) mechanism at 225 °C.