• Journal of international Conference on Electrical Machines and Systems
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• 제1권2호
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• pp.70-78
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• 2012

Due to the variable nature of renewable energy resources and power demand by consumers, it is difficult to operate a power system installed with only one type of renewable energy resource. Grid-based renewable generation may be the only solution to overcome this problem. The conventional approach based on a low-voltage converter with power frequency transformer is commonly employed for grid connection of offshore renewable energy systems. Because of the heavy weight and large size of the transformer, the system can be expensive and complex in terms of installation and maintenance. In this paper, an 11-kV series connected H-bridge (SCHB) multilevel voltage source converter (VSC) is proposed to achieve a compact and light direct grid connection of renewable energy systems. This paper presents the design, simulation and analysis of a five level (5L)-SCHB and an eleven level (11L)-SCHB VSC for 11-kV grid-based renewable energy systems. The performance, cost, modulation scheme and harmonic spectra of the converter are analyzed.

• Journal of Power Electronics
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• 제15권3호
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• pp.786-795
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• 2015

In this paper, an active damping control scheme for LLCL filters based on the PR (proportional-resonant) regulator is proposed for grid-connected three-level T-type PWM converter systems. The PR controller gives an infinite gain at the resonance frequency. As a result, the oscillation can be suppressed at that frequency. In order to improve the stability of the system in the case of grid impedance variations, online grid impedance estimation is applied. Simulation and experimental results have verified the effectiveness of the proposed scheme for three-phase T-type AC/DC PWM converters.

• Journal of Power Electronics
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• 제9권1호
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• pp.109-116
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• 2009

This paper addresses the output control of a utility-connected double-fed induction machine (DFIM) for wind power generation systems (WPGS). DFIM has a back-to-back converter to control outputs of DFIM driven by the wind turbine for WPGS. To supply commercially the power of WPGS to the grid without any problems related to power quality, the real and reactive powers (PQ) at the stator side of DFIM are strictly controlled at the required level, which in this paper is realized with the Fuzzy PI controller based on the field orientation control. For the Sinusoidal Pulse Width Modulation (SPWM) converter connected to the rotor side of DFIG to maintain the controllability of PQ at the state side of DFIM, the DC voltage of the DC link capacitor is also controlled at a certain level with the conventional Proportion-Integral (PI) controller of the real power. In addition, the power quality at the grid connected to the rotor side of DFIM through the back-to-back converter is maintained in a certain level with a PI controller of the reactive power. The controllers for the PQ at the stator side of DFIM, the DC link voltage of the back-to-back inverter and the reactive power at the grid connected to the rotor side of DFIM are designed and simulated in the PSIM program, of which the result verifies the performance of the proposed controllers.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1945-1954
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• 2017

In recent years, several LCL filter design methods for different converter topologies have been published, many of which use analytical expressions to calculate the ideal converter AC voltage harmonic spectrum. This paper presents the LCL filter design methodology but the focus is on presentation and validation of the non-iterative filter design method for a grid-connected three-phase two-level PWM-VSC. The developed method can be adapted for different converter topologies and PWM algorithms. Furthermore, as a starting point for the design procedure, only the range of PWM carrier frequencies is required instead of an exact value. System nonlinearities, usually omitted from analysis have a significant influence on VSC AC voltage harmonic spectrum. In order to achieve better accuracy of the proposed procedure, the system nonlinear model is incorporated into the method. Optimal filter parameters are determined using the novel cost function based on higher frequency losses of the filter. An example of LCL filter design for a 40 kVA grid-connected PWM-VSC has been presented. Obtained results have been used to construct the corresponding laboratory setup and measurements have been performed to verify the proposed method.

• 전력전자학회논문지
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• 제27권3호
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• pp.192-199
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• 2022

In DC distribution systems, a TAB converter employing multiple transformers is one of the most widely used topologies due to its high power density, modularizability, and cost-effectiveness. However, the conventional control technique for a grid-connected mode in the TAB converter cannot maintain its reliability for an islanding mode under a blackout situation. In this paper, the islanding mode control technique is proposed to solve this issue. To verify the relative stability and dynamic characteristics of the control technique, small-signal models of both the grid connected and the islanding mode are derived. Based on the small-signal models, PI controllers are designed to provide suitable power control. The proposed control technique, the accuracy of small-signal models, and the performance of the controllers are verified by simulations and experiments with a 1-kW prototype TAB converter.

• Journal of Electrical Engineering and Technology
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• 제9권3호
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• pp.1119-1124
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• 2014

High temperature superconducting magnetic energy storage (HTS SMES) is known as an effective solution to significantly decrease the voltage and power fluctuations of grid connected wind power generation system (WPGS). This paper implements an effective control scheme of a back-toback converter with shunt-connected HTS SMES for the frequency regulation of an islanded microgrid. The back-to-back converter is used to connect the WPGS to the grid. A large-scale HTS SMES is linked to the DC side of the back-to-back converter through a two-quadrant DC/DC chopper. An adaptive control strategy is implemented for the back-to-back converter and the two-quadrant DC/DC chopper to improve the efficiency of the whole system. The performance of the proposed control system was evaluated in a test power system using PSCAD/EMTDC. The simulation results clearly show that the back-to-back converter with shunt-connected HTS SMES operates effectively with the proposed control strategy for stabilizing the power system frequency fluctuations.

• 전기전자학회논문지
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• 제23권4호
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• pp.1280-1287
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• 2019

계통 연계 형 양방향 PCS 기술은 분산 형 신재생 에너지 스마트 그리드를 구현하기 위한 기술이며, 방대한 스마트 그리드 시스템 중 태양광 모듈로부터 수집된 전력 및 상용 계통전원을 이용하여 상시 전력을 충전하였다가 필요시 저장된 전력을 저압 계통 측으로 방출할 수 있도록 하는 하이브리드형 에너지 저장 장치이다. 이를 위해 MPPT 기능이 포함된 PV입력 전력변환기와 배터리 충·방전을 위한 양방향 전력변환기 및 DC Link 전압을 3상 380V AC 계통으로 출력하고 필요할 경우 계통전력을 AC/DC변환하여 양방향 DC/DC컨버터를 통해 배터리로 충전기능을 수행하는 인버터로 구성된 3개의 전력변환기 구조를 갖는 PCS를 설계 및 개발하였다. 현재 이 시스템을 정전 및 화재사고에 취약한 제주의 사이트에 적용하여 실증 및 운영하고 있다.

• 조명전기설비학회논문지
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• 제27권1호
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• pp.76-84
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• 2013

The renewable energy sources is raising for use of grid connected systems, for which higher power quality requirements are being issued. A grid connected converter requires a LC-filter stage, this one is lightly damped for efficiency constraints. Hence, it is subject to resonance if excited by the converter current harmonics or pre-exciting grid voltage harmonics. In this paper, an active damping technique employing notch filter for damping of the resonance frequency is introduced. This technique doesn't need to additional sensors. In addition, it is simple to apply for various systems. Monitoring of the resonance frequency ensures the stable operation of the proper connection and disconnection of the grid. This paper proposes the estimating method of a resonant frequency to determine the cut-off frequency of the notch filter. This method is validated by both simulation and experimental results.

• 전력전자학회논문지
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• 제19권3호
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• pp.276-282
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• 2014

In a single-phase grid-connected power system consisting of a dc-dc converter and a dc-ac converter, the current drawn from renewable energy sources has a tendency to be pulsated and contains double-fundamental frequency ripple components, which results in several drawback such as a power harvesting loss and a shortening of the energy source's life. This paper presents a new double-fundamental current reduction-scheme with a fast dc-link voltage loop for two-stage dc-dc-ac grid connected systems. In the frequency domain, an adequate control design is performed based on the small-signal transfer function of a two-stage dc-dc-ac converter. To verify the effectiveness of proposed control algorithm, a 1 kW hardware prototype has been built and experimental results are presented.

• 전력전자학회논문지
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• 제9권4호
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• pp.397-404
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• 2004

본 논문에서는 농형유도발전기를 이용한 계통연계형 풍력발전시스템의 가변속제어 기법이 제안된다. 농형유도발 전기는 간접벡터제어 방식으로 동작되는데 d-축 전류에 의해 여자가 제어되고 q-축 전류에 토크가 제어된다. 이 토크제어에 의해 발전기는 풍속의 변화에 대해서 항상 최대전력을 발생하도록 가변속 제어된다. 발전된 전력은 back-to-back PWM 컨버터에 의해 계통으로 공급된다. 계통측 컨버터는 q-축 전류 제어에 의해 직류링크 전압을 제어하고 d-축 전류 제어에 의해 계통측 역률을 제어할 수 있다. 제안된 기법은 M-G세트로 구성된 터빈시뮬레이터를 이용하여 실험적으로 검증된다.