• 전력전자학회논문지
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• 제21권4호
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• pp.364-372
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• 2016

In this paper, a voltage controller for the seamless transition of a grid-connected inverter for ESS is proposed. The single-phase inverter is operated as a current controller when the grid is connected and as a voltage controller in the stand-alone mode when the grid is disconnected. Generally, in the case of grid recovery, the overcurrent may flow into the system because of the mismatch phase between the inverter output and grid voltages. The proposed controller resolves the overcurrent problem through phase delay problems with initial value feed-forward control of the integrator when the grid voltage is restored. The effects of the control method are simulated through PSIM, and the usefulness of the control method is verified through experiments.

• 전력전자학회논문지
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• 제28권1호
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• pp.22-29
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• 2023

A grid-connected inverter can be used in grid-connected or stand-alone modes. Generally, a grid-connected inverter operates in a grid-connected mode, but the inverter operates in stand-alone mode if grid faults occur. In the stand-alone mode, the grid-connected inverter must supply electric power to a critical load that needs to receive stable power even though grid faults occur. Generally, three-phase loads are used as critical loads, but a single phase is configured in some cases. In these conditions, the critical load is required to unbalance the load power consumption, which makes the three-phase load voltage unbalancd. This unbalanced voltage problem can cause fatal problems to the three-phase critical loads, and thus must be addressed. Hence, this paper proposes an algorithm to solve this unbalanced voltage problem by the individual phase current control. The proposed method is verified using Psim simulation and experiments.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 춘계학술대회 논문집 에너지변화시스템부문
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• pp.228-230
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• 2009

Nowadays, the LCL-filter type becomes an attractive grid interfacing for grid-connected Voltage Source Inverter (VSI). LCL-filter can render the current harmonics attenuation around the switching frequency by using smaller inductance than L-filter. This paper presents a study about the LCL-filter design for single-phase grid-connected inverter in Photovoltaic (PV) system. According to the expected current ripple, the inductances of the filter can be determined. Based on the absorbed reactive power on capacitor, the capacitance can be calculated. Due to the theoretical analysis, a LCL-filter based single phase grid connected inverter control system are simulated. The studied simulation results are given to validate the theoretical analysis.

• 조명전기설비학회논문지
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• 제24권5호
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• pp.129-135
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• 2010

화석에너지의 고갈과 환경오염 문제를 해결하기 위한 대안인 신재생 에너지를 이용하는 분산발전 시스템은 핵심 구성 요소인 PWM 인버터의 전력제어가 요구된다. 본 논문에서는 단상 계통연계 인버터 시스템의 전력제어를 위해 계통 임피던스를 고려한 SRF(synchronous-reference-frame) 전력제어 방법을 제안한다. 제안한 SRF 전력제어 방법은 복잡한 계통 임피던스의 추정 없이 계통 임피던스의 공칭값(nominal value)에 기반해 단상 인버터에 전압 기준값(reference)을 제공하여 독립운전 모드와 계통연계 모드에서 모두 운전이 가능함을 나타내었다. 또한, 유효전력과 무효전력의 독립적인 제어가 가능한 장점을 가진다. 계통을 포함하는 시뮬레이션을 통해 제안한 SRF 전력제어 방법의 타당성을 검증한다. 시뮬레이션 결과는 제안한 SRF 전력제어 방법을 통해 단상 계통연계 인버터 시스템의 전력 흐름을 적절히 제어할 수 있음을 보여주고 있다.

• 전력전자학회논문지
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• 제24권3호
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• pp.169-180
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• 2019

Grid codes for grid-connected inverters are essential considerations for bulk grid systems. In particular, a low-voltage ride-through (LVRT) function, which can contribute to the grid system's stabilization with the occurrence of voltage sag, is required by such inverters. However, when the grid voltage is under zero-voltage condition due to a grid accident, a zero-voltage ride-through (ZVRT) function is required. Grid-connected inverters typically have phase-locked loop (PLL) control to synchronize the phase of the grid voltage with that of the inverter output. In this study, the LVRT regulations of Germany, the United States, and Japan are analyzed. Then, three major PLL methods of grid-connected single-phase inverters, namely, notch filter-PLL, dq-PLL using an active power filter, and second-order generalized integrator-PLL, are reviewed. The proposed PLL method, which controls inverter output under ZVRT condition, is suggested. The proposed PLL operates better than the three major PLL methods under ZVRT condition in the simulation and experimental tests.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2018년도 전력전자학술대회
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• pp.144-146
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• 2018

In order to meet the harmonics standards such as IEEE 519 and P1547 the output quality of a grid connected inverter should satisfy a certain level of Total Harmonic Distortion (THD) value. However, the output quality of an inverter gets degraded due to the grid voltage harmonics, the dead time effects and the nonlinearity of the switches, which all contributes to a higher THD value of the output. In order to meet the required THD value for the inverter output under the distorted grid condition the use of harmonic controller is essential. In this paper a novel feedforward harmonic compensation method is proposed in order to effectively eliminate the low order harmonics in the inverter current to the grid. In the proposed method, unlike the conventional harmonic control methods, the hamonic components are directly compensated by the feedforward terms generated by the PR controller with the grid current in the stationary frame. The proposed method is simple in implementation but powerful in eliminating the harmonics from the output. The effectiveness of proposed method is verified through the PSIM simulation and the experiments with a 5kW single phase grid connected inverter.

• 전력전자학회논문지
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• 제24권3호
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• pp.215-227
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• 2019

Grid-connected inverters should satisfy a certain level of total harmonic distortion (THD) to meet harmonics standards, such as IEEE 519 and P1547. The output quality of an inverter is typically degraded due to grid voltage harmonics, dead time effects, and the device's turn-on/turn-off delay, which all contribute to increasing the THD value of the output. The use of a harmonic controller is essential to meet the required THD value for inverter output under a distorted grid condition. In this study, an improved feedforward harmonic compensation method is proposed to effectively eliminate low-order harmonics in the inverter current to the grid. In the proposed method, harmonic components are directly compensated through feedforward terms generated by the proportional resonant controller with the grid current in a stationary frame. The proposed method is simple to implement but powerful in eliminating harmonics from the output. The effectiveness of the proposed method is verified through simulation using PSIM software and experiments with a 5 kW single-phase grid-connected inverter.

• 전기학회논문지P
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• 제66권4호
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• pp.236-241
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• 2017

This paper presents a single-phase grid connected voltage-ed inverter with a power decoupling circuit. In the single-phase grid connected voltage-ed inverter, it is well known that a power pulsation with twice the grid frequency is contained in the input power. In a conventional voltage type inverter, electrolytic capacitors with large capacitance have been used in order to smooth the DC voltage. However, lifetime of those capacitors is shortened by the power pulsation with twice grid frequency. The authors have been studied a active power decoupling(APD) method that reduce the pulsating power on the input DC bus line, this enables to transfer the ripple energy appeared on the input DC capacitors into the energy in a small film capacitor on the additional circuit. Hence, extension of the lifetime of the inverter can be expected because the small film capacitor substitutes for the large electrolytic capacitors. Finally, simulation and experimental results are discussed.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2008년도 하계학술대회 논문집
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• pp.91-93
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• 2008

In this paper, novel phase angle following algorithm for the single phase grid-connected inverter is proposed. Gird-connected inverter needs phase angle detection for synchronization grid voltage with the inverter output. In case of single phase grid-connected inverter, zero crossing detection and virtual 2-phase PLL using digital all pass filter or digital low pass filter are used conventionally. But these methods have a weakness for harmonics, noises and ripples. The proposed method of PLL achieve DFT(Discrete Fourier Transform) using Goertzel algorithm. It can extract fundamental voltage of grid. As a results, it can obtain phase angle using digital all pass filter without effect of harmonics, noises and ripples. Simulation results are presented to demonstrate the effectiveness of the proposed algorithm.

• Journal of Power Electronics
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• 제11권4호
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• pp.561-567
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• 2011

This paper presents a high-efficiency power conditioning system (PCS) for grid-connected photovoltaic (PV) modules. The proposed PCS consists of a step-up DC-DC converter and a single-phase DC-AC inverter for the grid-connected PV modules. A soft-switching step-up DC-DC converter is proposed to generate a high DC-link voltage from the low PV module voltage with a high-efficiency. A DC-link voltage controller is presented for constant DC-link voltage regulation. A half-bridge inverter is used for the single-phase DC-AC inverter for grid connection. A grid current controller is suggested to supply PV electrical power to the power grid with a unity power factor. Experimental results are obtained from a 180 W grid-connected PV module system using the proposed PCS. The proposed PCS achieves a high power efficiency of 93.0 % with an unity power factor for a 60 Hz / 120 Vrms AC power grid.