• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.59-60
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• 2012

Cascaded H-bridge 멀티레벨인버터의 스위칭 패턴을 기본파 생성을 위한 저주파 동작과 파형 개선 목적의 고주파 PWM 스위칭 패턴으로 구분하여 스위칭 손실을 감소시킬 수 있지만 입력단의 DC 독립전압원은 각 H-bridge 모듈이 담당하는 출력전압의 레벨에 따라 용량의 차이가 발생한다. 이는 각 H-Bridge 모듈 스위치의 전류 스트레스 차이를 의미하며, 이로 인해 H-bridge 모듈별 수명 차이를 발생시킨다. 본 논문에서는 용량 창이에 따른 모듈 특성 개선과 인버터 수명 문제를 해결하기 위하여 기존의 다중 반송파 정현 펄스폭 변조방식에 스와핑 스위칭 방법을 적용하여 Cascaded H-bridge 멀티레벨인버터에 적용함으로써 스위칭 손실 개선과 함께 각 H-bridge 별 담당 부하 전력을 동일하게 하여 동일 전류 정격 스위치의 사용을 가능하게 한다. 제안된 스와핑 스위칭 패턴을 PD, POD, APOD방식으로 구현하고 이론적 분석과 시뮬레이션을 통해 타당성을 검증한다.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.2
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• pp.190-196
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• 2013

It presents a unification of buck-boost and flyback converter for driving a cascaded H-bridge multilevel inverter with a single independent DC voltage source. Cascaded H-bridge multilevel inverter is useful to make many output voltage levels for sinusoidal waveform by combining two or more H-bridge modules. However, each H-bridge module needs an independent DC voltage source to generate multi levels in an output voltage. This topological characteristic brings a demerit of increasing the number of independent DC voltage sources when it needs to increase the number of output voltage levels. To solve this problem, we propose a converter combining a buck-boost converter with a flyback converter. The proposed converter provides independent DC voltage sources at back-end two H-bridge modules. After analyzing theoretical operation of the circuit topology, the validity of the proposed approach is verified by computer-aided simulations using PSIM and experiments.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.1022-1028
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• 2005

This paper is presented the analysis results and simulation results of cascaded H-bridge 7 level inverter with various modulation index. Stepped waveform having number of switching was used to eliminate harmonic components. Switching angles according to modulation index are calculated numerically. Therefore, 3 times of switching with 7 level topology and QWS(Quarter Wave Symmetry) could eliminate 5th and 7th harmonics. The harmonic characteristics are compared to those of space vector modulation method which known as common modulation method in industrial field. Stepped waveform method showed higher ability to reduce, especially lower order of harmonics.

• Journal of Power Electronics
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• v.12 no.4
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• pp.567-577
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• 2012

This paper introduces a new scheme to balance the DC bus voltages of a cascaded H-bridge converter which is used as a Distribution Static Synchronous Series Compensator (D-SSSC) in electrical distribution network. The aim of D-SSSC is to control the power flow between two feeders from different substations. As a result of different cell losses and capacitors tolerance the cells DC bus voltage can deviate from their reference values. In the proposed scheme, by individually modifying the reference PWM signal for each cell, an effective balancing procedure is derived. The new balancing procedure needs only the line current sign and is independent of the main control strategy, which controls the total DC bus voltages of cascaded H-bridge. The effect of modulation index variation on the capacitor voltage is analytically derived for the proposed strategy. The proposed method takes advantages of phase shift carrier based modulation and can be applied for a cascaded H-bridge with any number of cells. Also the system is immune to loss of one cell and the presented procedure can keep balancing between the remaining cells. Simulation studies and experimental results validate the effectiveness of the proposed method in the balancing of DC bus voltages.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1763-1772
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• 2016

To reduce system complexity and implementation costs, fully-controlled H-bridge (FHB) modules and diode H-bridge PFC (DHB) modules are cascaded to form a hybrid cascaded H-bridge rectifier (HCHR). In this paper, the advantages of such a HCHR over other cascaded rectifiers are analyzed depending on the numbers of FHB modules and DHB modules. Therefore, to assign proper numbers to these two kinds of modules for the HCHR, a configuration determination method is investigated under balanced and imbalanced loads. Three principles are also presented to guide the configuration determination for the HCHR. In addition, the constraints for selecting the step-up ratio and filter inductance are derived based on a phasor diagram analysis. The proposed configuration determination method is validated by simulations under three different conditions in the PSIM environment. Finally, experiments are carried out on a scaled-down prototype where the configuration can be easily adjusted. The feasibility of the proposed theory is then verified by experimental results.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1161-1162
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• 2011

본 논문에서는 독립된 DC 입력전원을 요구하는 Cascaded H-bridge 멀티레벨 인버터를 단일 입력전원으로 구동시키기 위한 회로 구조를 제안한다. 변압기 포화를 방지하기 위해 채용되는 리센 권선을 가지는 포워드 컨버터의 구조를 변경한 것으로 리셋 권선에 의해 전원으로 회생되는 에너지가 출력단으로 전달되도록 변경된다. 제안된 회로 구조의 입출력전압과 스위치의 도통비와의 관계를 이론적으로 분석하고 시뮬레이션을 통해 타당성을 검증한다.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.270-271
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• 2017

Cascaded NPC/H-bridge 인버터의 기존 Level-Shift PWM에서는 한 stack에서 전력 및 손실 불균형이 발생하게 된다. 이에 따라 손실 불균형을 개선하기 위해 새로운 Level Shift PWM을 개발하였고, PSIM 9.14를 통해 기존의 PWM 기법들과 비교 분석 하였다.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2067-2075
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• 2016

Cascaded H-bridge multilevel inverters are currently used because it enables the integration of various sources, such as batteries, ultracapacitors, photovoltaic array and fuel cells in a single system. Conventional modulation schemes for multilevel inverters have concentrated mainly on the generation of a low harmonic output voltage, which results in less effective utilization of connected sources. Less effective utilization leads to a difference in the charging/discharging of sources, causing unsteady voltages over a long period of operation and a reduction in the lifetime of the sources. Hence, a charge balance control scheme has to be incorporated along with the modulation scheme to overcome these issues. In this paper, a new approach for charge balancing in symmetric cascaded H-bridge multilevel inverter that enables almost 100% charge balancing of sources is presented. The proposed method achieves charge balancing without any additional stages or complex circuit or considerable computational requirement. The validity of the proposed method is verified through simulation and experiments.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.2
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• pp.197-201
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• 2013

Cascaded H-bridge multilevel inverter requires independent DC voltage sources to produce multi output voltage levels. When it needs to generate more levels in the output voltage wave, the number of independent DC voltage sources usually limits its extension. To solve this problem, we propose a cascaded H-bridge multilevel inverter employing a front-end flyback converter for unifying input DC voltage sources. After theoretical analysis of the proposed circuit, we verify the validity of the proposed inverter using computer-aided simulations and experiments.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.323-324
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• 2015

Recently, asymmetrical cascaded H-bridge multilevel inverter started to be highlighted as an alternative for the symmetrical cascaded H-bridge. The topology has a small number of part count compared to the symmetrical with higher number of levels. However, it has a drawback of the modulation index limitation which is relatively higher than its symmetrical counterpart, which causes a necessity of an extra voltage pre-regulator. In this paper, the single-sourced pre-regulator is unified with an inner single switch DC/DC converter isolated by coupled inductor. It leads to cost and size reduction. The proposed topology is verified using simulation results.