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

• Journal of Power Electronics
• /
• v.16 no.2
• /
• pp.490-497
• /
• 2016

The analysis of the switch status of each unit module of a cascaded multi-level inverter reveals that the working condition of the switch of a chopper arm causes unnecessary switching under the conventional unipolar sinusoidal pulse width modulation (SPWM). With an increase in the number of cascaded multilevel inverters, the superposition of unnecessary switching gradually occurs. In this work, we propose an improved SPWM strategy to reduce switching in cascaded multilevel inverters. Specifically, we analyze the switch state of the switch tube of a chopper arm of an H-bridge unit. The redundant switch is then removed, thereby reducing the switching frequency. Unlike the conventional unipolar SPWM technique, the improved SPWM method greatly reduces switching without altering the output quality of inverters. The conventional unipolar SPWM technique and the proposed method are applied to a five-level inverter. Simulation results show the superiority of the proposed strategy. Finally, a prototype is built in the laboratory. Experimental results verify the correctness of the proposed modulation strategy.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.27 no.12
• /
• pp.133-140
• /
• 2013

Cascaded H-Bridge multi-level inverters can be implemented through the series connection of single-phase modular power bridges. In recent years, multi-level inverters are becoming increasingly popular for high power applications due to its improved harmonic profile and increased power ratings. This paper presents a control method for balancing the dc-link voltage and ride-through enhancement, a modified pulse width-modulation Compensation algorithm of cascaded H-bridge multi-level inverters. During an under-voltage protection mechanism, causing the system to shut down within a few milliseconds after a power interruption in the main input sources. When a power interruption occurs finish, if the system is a large inertia restarting the load a long time is required. This paper suggests modifications in the control algorithm in order to improve the sag ride-through performance of ac inverter. The new proposed strategy recommends maintaining the DC-link voltage constant at the nominal value during a sag period, experimental results are presented.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.16 no.3
• /
• pp.283-292
• /
• 2011

This paper proposed a new multi-level inverter topology based on a H-bridge with two switches and two diodes connected to the DC-link. The output voltage of the proposed topology is quite closer to a sinusoidal waveform compared with a typical single phase inverter. The proposed multi-level inverter is applicable to a power conditioning system for renewable energy sources, and it can be also used as a building block of a cascaded multi-level inverter for a high voltage application. In case of conventional H-bridge type or NPC type multi-level inverter, 8 controllable switches are used to obtain a 5 level output voltage, but the proposed multi-level inverter requires only 6 controllable switches. Thus the circuit configuration is quite simple, reliable and cost-effective implementation is possible. The efficiency can be improved owing to the reduction of the switching loss. A new PWM method based on POD modulation is suggested which requires only one carrier signal. The switching sequence to make the capacitor voltage balanced is also considered. The feasibility is studied through simulation and experiment.

• Proceedings of the KIPE Conference
• /
• 2000.07a
• /
• pp.321-324
• /
• 2000

멀티-레벨 인버터 구조는 크게 세 가지가 있다 NPC 구조, 플라잉 커패시터 구조, 그리고 H-bridge 단위 인버터 셀을 종속적으로 연결한 cascaded 구조가 그것이다. 이중에서 cascaded 구조는 지금까지 홀수 레벨만 존재하는 것으로 알려졌다 본 논문에서는 이것을 짝수 레벨로 확장한 새로운 구조를 제안하고 홀수 짝수 레벨 모두에 적용이 가능한 새로온 PWM 기법을 제안하고자 한다. 제안한 기법은 컴퓨터 시뮬레이션 및 실험으로 그타당성을 입증하고자 한다.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2005.11a
• /
• pp.200-201
• /
• 2005

This paper is analyzed a new modulation method of OSW(Optimized Sine-Wave) modulation strategy for cascaded H-bridge multi-level inverter. The inverter structure was modified with the maximum output voltage level, and the switching angle was calculated easily to adjust the requested Vrms of the output. The suggested modulation method could make output waveform very close to the ideal sine wave, and the THD value was improved also remarkably.

• Proceedings of the KIPE Conference
• /
• 2005.07a
• /
• pp.651-654
• /
• 2005

In this paper, an efficient switching pattern to equalize the size of transformer is proposed for a multi-level inverter employing cascaded transformers. It is based on the prior selected harmonic elimination PWM(SHEPWM) method. Because the maximum magnetic flux imposed on each transformer becomes exactly equal each to each, all transformers can be designed with the same size regardless of their position. Therefore, identical full-bridge inverter units can be utilized, thus improving modularity and manufacturability. The fundamental idea of the proposed switching pattern is illustrated and the analyzed theoretically. The validity of the proposed switching strategy is verified by experimental results.

• Journal of Power Electronics
• /
• v.8 no.2
• /
• pp.171-180
• /
• 2008

One of the major problems in electric power quality is the harmonic contents. There are several methods of indicating the quantity of harmonic contents. The most widely used measure is the total harmonic distortion (THD). Various switching techniques have been used in static converters to reduce the output harmonic content. This paper presents and compares the two harmonic optimization techniques, known as optimal minimization of the total harmonic distortion (OMTHD) technique and optimized harmonic stepped-waveform (OHSW) technique used in multi-level inverters with unequal dc sources. Both techniques are very effective and efficient for improving the quality of the inverter output voltage. First, we describe briefly the cascaded H-bridge multi-level inverter structure. Then, we present the switching algorithm for the inverter based on OHSW and OMTHD techniques. Finally, the results obtained for the two techniques are analyzed and compared. The results verify the effectiveness of the both techniques in multi-level voltage-source inverter with non-equal dc sources, clarifying the advantages of each technique.

• Journal of the Korean Society for Railway
• /
• v.9 no.6 s.37
• /
• pp.761-765
• /
• 2006

At present, harmonic currents cause serious problems in power conversion system using the semiconductor switching device. Also some of the conversion system provokes harmonic currents against to the main power supply system and causes hindrances for the system. Main power impedance of the traditional LC passive filter method, influences on the filter characteristics and amplifies the harmonics when resonance phenomenon is occurred. And the traditional existing 2 level inverter systems show the limit in capacity of voltage and current in case of occurring sudden load change. So, to solve this problem active filter which uses cascaded H-bridge multi level inverter has been designed and ex-filter system circuits were totally investigated. With multi level active filtering system not only the size of filter but also the size of filter for transformer can be reduced by half and so as to the weight, while the capacity of inverter can be double sized and wave forms can be compensated exactly and precisely. Also by the benefit of the increase in rating capacity, the various currents owing to the load fluctuation can be dealt more steadily. In order to simulate the wave form of harmonics based on the measured data on the AC 25kV high speed Domestic Commercial railway, it was simulated with PSCAD/EMTDC and PSIM. Based on the results of this demonstration, the power supply system and inverter system would be more stable and also promoting its efficiency.

• Journal of Power Electronics
• /
• v.12 no.3
• /
• pp.509-517
• /
• 2012

This paper presents control strategies for cascaded H-bridge multilevel active power filters (APFs). A current loop controller is implemented using a proportional-resonant (PR) regulator, which achieves zero steady-state error at target frequencies. The power balancing mechanism for the dc-link capacitor voltages is analyzed and a voltage balancing controller is presented. To mitigate the picket-fence effect of the conventional FFT algorithm under asynchronous sampling conditions, the Hanning Windowed-FFT algorithm is proposed for reference current generation (RCG). This calculates the frequency, amplitude and phase of individual harmonic components accurately and as a result, selective harmonic compensation (SHC) is achieved. Simulation and experimental results are presented, which verify the validity and effectiveness of the devised control algorithms.