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Electrolytic capacitorless STATCOM with both inductive and capacitive VAR compensation modes
Mohammad Sameer Irfan,Young-Tae Jeon,Mohamed Atef Tawfik,Ashraf Ahmed,Joung-Hu Park 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.8
This paper proposes an effective VAR source established as a cascaded H-bridge (CHB) static compensator (STATCOM), which is based on the flux cancellation method. The conventional CHB-STATCOM uses a low-frequency large capacitor as a source. The required capacitance value of the capacitor increases as a function of the amount of VAR produced to compensate the power system. The proposed topology is based on flux cancellation. Therefore, the source of VAR in this case is not limited by the capacitors or the power decoupling transformer size. The sub-module (SM) of the proposed topology comprises of a CHB module with power decoupling circuits. The double-frequency ripple powers on the sub-module (SM) capacitors, which have a phase shift of 120° with respect to each other. The ripple powers are derived from each of the three phases toward a common magnetic core to cancel each other out. An isolated bidirectional triple port dual half-bridge converter is utilized for the flux cancellation process. In this converter, the main challenges are leakage inductances and the high voltage insulation among the three windings of the high-frequency transformer. An αβ-frame-based model is proposed, using the generalized state-space averaging method, for the flux cancellation circuit. Furthermore, the size is significantly reduced by the proposed method, since a small sub-module capacitance of a few microfarads is sufficient to operate the CHBSTATCOM. The analysis and the controller design process are presented, followed by simulation and hardware validations.
Irfan, Mohammad Sameer,Ahmed, Ashraf,Park, Joung-Hu,Seo, Chulhun Institute of Electrical and Electronics Engineers 2017 IEEE transactions on power electronics Vol. No.
<P>In this paper, a novel DHB power-decoupling control scheme without current sensor is proposed for single-phase inverters. As electrolyte capacitors are conventionally used; however, these capacitors limit ripple current capability and circuit reliability. Film capacitors improve the ripple current capability, size reduction, and circuit reliability. Conventionally, non-isolated topologies are used for power decoupling. The volume of the decoupling capacitor per unit energy in isolated bidirectional power decoupling topologies is reduced as compared to nonisolated due to unrestricted voltage across the decoupling capacitor. Voltage-fed Phase-Shift Dual Half-Bridge (DHB) is preferred with film capacitors as it has the least number of components in isolated bidirectional topologies. However, in DHB, power decoupling controller is a challenge as current control is conventionally required. The challenge has been overcome with novel current-sensorless dc link ripple rejection control. The controller has the advantage of current-sensorless configuration especially when it needs information from inverter phase-lock-loop (PLL). The proposed power decoupling control scheme is independent of the inverter control and universal. A new dynamic analysis has been carried out by taking into account the input-voltage dynamics. The advantage of the DHB is that it has single pole behavior and, hence, sufficient bandwidth can be obtained. Simulations and experiments have been performed to verify the analysis of the power decoupling control scheme and the capability of film-capacitor DHB for power decoupling.</P>
Irfan, Mohammad Sameer,Shin, Jong-Hyun,Park, Joung-Hu The Korean Institute of Electrical Engineers 2018 Journal of Electrical Engineering & Technology Vol.13 No.2
This paper presents a novel power decoupling control scheme with the bidirectional buck-boost converter for primary-side regulation photovoltaic (PV) micro-inverter. With the proposed power decoupling control scheme, small-capacitance film capacitors are used to overcome the life-span and reliability limitations of the large-capacitance electrolytic capacitors. Then, an improved flyback PV inverter is employed in continuous conduction mode with primary-side regulation for the PV power conditioning. The proposed power-decoupling controller shares the reference for primary side current regulation of the flyback PV inverter. The decoupling controller shapes the input current of the bidirectional buck-boost converter. The shared reference eliminates the phase-delay between the input current to the bidirectional buck-boost converter and the double frequency current at the PV primary current. The elimination of the phase-delay in dynamic response enhances the ripple rejection capability of the power decoupling buck-boost converter even with small film capacitor. With proposed power decoupling control scheme, the additional advantage of the primary-side regulation of flyback PV inverter is that there is no need to have an extra current sensor for obtaining the ripplecurrent reference of the decoupling current-controller of the power-decoupling buck-boost converter. Therefore, the proposed power decoupling control scheme is cost-effective as well as the size benefit. A new transient analysis is carried out which includes the source voltage dynamics instead of considering the source voltage as a pure voltage source. For verification of the proposed control scheme, simulation and experimental results are presented.
Irfan, Mohammad Sameer,Tawfk, Mohamed Atef,Ahmed, Ashraf,Park, Joung-Hu The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.2
Cascaded multilevel inverter cells produce double-grid frequency ripples that require a large electrolytic capacitor bank for every cell, resulting in reduced system reliability and lifespan. This paper proposes a new generalized power-decoupling methodology that is applicable to any three-phase cascaded multilevel inverter topology. The proposed flux cancellation method is based on forcing a three-phase double-frequency ripple into the core of a three-phase transformer. The flux components from each phase, which are phase-shifted by 120°, cancel each other inside the core. Therefore, no power-decoupling capacitor is required in this method. A three-port bidirectional isolated converter is proposed to cancel the three-phase 120 Hz pulsating power in a single high-frequency (HF) core. High-leakage inductances and imbalances among the ports of a HF transformer are a topographical challenge. The imbalance in leakage inductances can be reduced by improving the winding schemes. However, increased leakage and imbalance among the three ports are unavoidable under high voltages because of the need for higher isolation. A universal solution involves the application of a phase shift-based controller to obtain balanced and reduced voltage ripples among the three DC links. This paper presents the dynamic analysis and controller design procedure. Results of the prototype hardware confirm the suitability of the proposed power-decoupling methods.