• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.496-497
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• 2014

본 논문은 Cascaded H-bridge 멀티레벨 인버터의 출력 전압 레벨 수의 증가를 위한 모델과 스위칭 기법을 제안한다. 제안하는 모델은 기존의 Cascaded H-bridge 멀티레벨 인버터 구조에서 각 H-bridge 모듈의 출력단에 변압기를 연결하고, 변압기 2차측을 직렬로 연결한 모델이다. 이 구조에서 다수의 변압기의 턴비는 동일하고, 1개의 변압기 턴비만이 다른 턴비를 갖게된다. 따라서 1개의 변압기 턴비를 조절하여 출력전압의 전압 레벨수를 증가시킬 수 있다. 스위칭 방법은 기존에 멀티레벨 인버터에서 주로 사용되는 Level-shifted PWM 방식을 이용하여 간단하게 구현할 수 있다. 제안하는 모델의 검증을 위하여 시뮬레이션을 수행하여 제안하는 모델의 타당성을 확인한다.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2272-2283
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• 2016

This paper proposes a power conditioning system (PCS) for distributed photovoltaic (PV) applications using an asymmetric cascaded multilevel inverter with a single PV source. One of the main disadvantages of the cascaded multilevel inverters in PV systems is the requirement of multiple isolated DC sources. Using multiple PV strings leads to a compromise in either the voltage balance of individual H-bridge cells or the maximum power point tracking (MPPT) operation due to localized variations in atmospheric conditions. The proposed PCS uses a single PV source with a flyback DC-DC converter to facilitate a reduction of the required DC sources and to maintain the voltage balance during MPPT operation. The flyback converter is used to provide input for low-voltage H-bridge cells which processes only 20% of the total power. This helps to minimize the losses occurring in the proposed PCS. Furthermore, transient analyses and controller design for the proposed PCS in both the stand-alone mode and the grid-connection mode are presented. The feasibility of the proposed PCS and its control scheme have been tested using a 1kW hardware prototype and the obtained results are presented.

• Proceedings of the KIPE Conference
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• 2003.07b
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• pp.593-597
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• 2003

Multilevel power conversion technology has received increasing attention recently for high power applications. The converters with the technology are suitable for high voltage and high power applications due to their ability to synthesize waveforms with better harmonic spectrum and apply for the high voltage equipment with a limited voltage rating of device. In the family of multilevel inverters, the topologies based on cascaded H-bridges are particularly attractive because of their modularity and simplicity of control. This paper presents multilevel inverter with cascaded H-bridge for large-power motor drives. The main features of this drive 1) reduce harmonic injection 2) can generate near-sinusoidal voltages, 3) have almost no common-mode voltage; 4) are low dv/dt at output voltage; 5)do not generate significant over-voltage on motor terminal; The topology of the developed product is presented and the feasibility study of the inverter on 3300v 1MVA 7-level H-bridge type was tarried out with experiments.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.3
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• pp.239-246
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• 2006

This paper suggests a new modulation strategy for step pulse type multi-level inverter. The proposed strategy is simple to determine the switching angles without regard to increase of levels. Designed to extract the equivalent RMS value compared to ideal sine wave from inverter, it can be applied effectively to high level step pulse inverter. Also this paper proposed modulation strategy for modified H-bridge 13 level inverter which has different cell source voltages with simulation and experiment. The modulation characteristics from simulation and experiment, agreed very well with tracing sine wave about modified structure of cascaded H-bridge multi-level inverter.

• 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 Electrical Engineering and Technology
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• v.10 no.2
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• pp.574-585
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• 2015

This paper aims to improve the performance of conventional direct torque control (DTC) drives proposed by Takahashi by extending the idea for 5-level inverter. Hybrid cascaded H-bridge topology is used to achieve inverter voltage vector composed of 5-level of voltage. Although DTC is very popular for its simplicity but it suffers from some disadvantages like- high torque ripple and uncontrollable switching frequency. To compensate these shortcomings conventional DTC strategy is modified for five levels voltage source inverter (VSI). Multilevel hysteresis controller for both flux and torque is used. Optimal voltage vector selection from precise lookup table utilizing 12 sector, 9 torque level and 4 flux level is proposed to improve DTC performance. These voltage references are produced utilizing a hybrid cascaded H-bridge multilevel inverter, where inverter each phase can be realized using multiple dc source. Fuel cells, car batteries or ultra-capacitor are normally the choice of required dc source. Simulation results shows that the DTC drive performance is considerably improved in terms of lower torque and flux ripple and less THD. These have been experimentally evaluated and compared with the basic DTC developed by Takahashi.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2278-2288
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• 2017

Multilevel converter topologies are widely used in many applications. The cascaded H-bridge multilevel inverter (CHBMI), which is one of many multilevel converter topologies, has been introduced as a useful topology in high and medium power. However, it has a drawback to require a lot of switches. Therefore, the reliability of CHBMI is important factor for analyzing the performance. This paper presents a simple switch fault diagnosis method for single-phase CHBMI. There are two types of switch faults: open-fault and short-fault. In the open-fault, the body diode of faulty switch provides a freewheeling current path. However, when the short-fault occurs, the distortion of output current is different from that of the open-fault because it has an unavailable freewheeling current flow path due to a disconnection of fuse. The fault diagnosis method is based on the zero current time analysis according to zero-voltage switching states. Using the proposed method, it is possible to detect the location of faulty switch accurately. The PSIM simulation and experimental results show the effectiveness of proposed switch fault diagnosis method.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.45-46
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• 2013

멀티레벨 고압인버터 토폴로지 중 저압 Power Cell를 이용하여 고압을 출력하는 Cascaded 방식이 산업계에서는 널리 사용되고 이다. 최근 제품화된 Cascaded 방식은 크게 두 가지 형태로 구분할 수 있다. 저압 Power Cell에 단상 H-Bridge를 이용한 Cascaded H-Bridge 멀티레벨 인버터와 단상 NPC(Neutral Point Clamped) 토폴로지를 적용한 Cascaded NPC 멀티레벨 인버터이다. 이 중 Cascaded NPC 멀티레벨 인버터의 경우 적은 수의 셀을 사용하여 CHB와 동일한 출력 레벨을 생성할 수 있으며, NPC 방식의 고압 인버터 고유의 장점을 모두 구현할 수 있다. 반대로 CHB Type과 NPC type의 단점인 복잡한 구조의 Phase Shift Transformer와 DC_Link 중성점 전압이 변동하는 단점 또한 나타나게 된다. 본 논문에서는 Cascaded NPC 멀티레벨 인버터의 이러한 단점을 극복하기 위한 새로운 방식의 Phase Shift Transformer와 NPC Power Cell의 중성점 전압 변동을 줄일 수 있는 기법에 대해 설명하고 이 기법에 대한 타당성을 모의시험을 통해 검증하였다.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.1
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• pp.59-65
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• 2021

This study proposes a dead-time implementation method suitable for cell voltage control of a cascaded H-bridge (CHB) inverter. The PWM module of an existing microcontroller cannot generate a maximum voltage due to the dead-time effect when used as the cell controller of the CHB inverter. In the proposed method, the operation method of the PWM module was changed without using the dead time module included in the existing microcontroller, so that the cell output voltage can be increased to the maximum voltage without voltage discontinuity. During the maximum voltage generation period, the full turn-on state can be maintained without unnecessary switching. The validity of the proposed method is confirmed through an experiment.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.6
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• pp.620-627
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• 2004

As h-bridge multilevel inverter is connected with series of single phase power cell, so it obtain high voltage using low voltage power semi-conductor and output voltage similar to sine wave. In this topology, the number of power cell increases in proportion to the output voltage level. Therefore, there are drawbacks that are responsibility against operating ability of main controller and signal wire increase. However, we can overcome this problems by the substitution of serial communication for the PWM signal in power cell control. Additionally, it has merits of reliability and maintenance. This paper deals with the synchronization and phase-shift method of power cell PWM using CAN(Controller Area Network) communication interrupt in H-bridge multilevel inverter. The advantages of proposed method are signal-line simplification using serial communication between main controller and cell controller, burden reduction in main controller, modularization of power cell, easy protection of each power cell, expandability improvement and reliability increase of control signal and power cell. This paper establishes propriety and reliability of proposed method through experiment of 13-level H-bridge multilevel inverter.