• 전력전자학회논문지
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• 제18권6호
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• pp.579-586
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• 2013

This paper proposes a mode transition algorithm between the grid-tied and the stand-alone operations for the single-phase inverter with the energy storage system. For the grid-tied operation, the dc-link voltage and the output current are required to be control. For the stand-alone mode, both the output voltage and the output current should be regulated. In order to mitigate a falling-off in control performance during transients in mode change, the load power estimation and the current selection schemes are proposed. The proposed method allows an optimized current reference is selected to reduce an output voltage drop and an excessive over-current in transient. To verify the effectiveness of the proposed method, both the simulation and the experiments for a 3kW single-phase inverter with the energy storage system have been conducted. From the results, it has been confirmed that the proposed method reduces a transient error as well as implementing smooth mode transition.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2010년도 하계학술대회 논문집
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• pp.216-217
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• 2010

This paper presents a new software-based on-line dead-time compensation technique for single-phase grid-connected photovoltaic (PV) inverter system. To improve the mitigation of dead-time effect around the zero-crossing point of phase current, a selective harmonic elimination of instantaneous feedback current is used as an additional part of conventional current control scheme. Simulation and experimental results are shown to verify the effectiveness of proposed compensation method in the grid-connected power distributed generation systems.

• 한국태양에너지학회 논문집
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• 제37권3호
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• pp.13-22
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• 2017

Anti-islanding scheme of grid-connected inverter is a key function of standards compliance, since unintentional islanding results in safety hazards, reliability, and many other issues. Therefore, many anti-islanding schemes have been researched, however, most of them have problems, which deteriorate performance of islanding detection under parallel-operation. Therefore, this paper proves the reason of problems and proposes a new anti-islanding scheme that has precise islanding detection under parallel-operation in single-phase and three-phase system. Finally, both simulation and experimental result validate the proposed scheme.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.924-925
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• 2008

There are many types of grid-connected inverter controllers, PI controller based is the most popular methods. But, a common PI control is produced zero-steady state error and phase delay in sinusoidal reference. Synchronous reference frame or DQ transform based controller is capable for reducing both of zero-steady state error and phase delay is. But DQ transform based controller has cross-coupling component which difficult to analyze the system in single phase model. In this paper, to obtained single phase model of the system, DQ transform based controller is analyzed in two techniques. The first is by neglecting cross-coupling. The second is eliminated cross-coupling component by decoupling method. By these two techniques, single phase model is obtained. Then, the single phase model is analyzed to evaluate its performance in stability and frequency response, through Root Locus and Bode diagram, respectively. MATLAB and PSIM simulation is used to verify the analysis. Simulation result is shown; cross-coupling component has no significant influent to the controller.

• Journal of Power Electronics
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• 제7권2호
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• pp.174-180
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• 2007

In this paper, a simple control method for two-stage utility grid-connected photovoltaic power conditioning systems (PCS) is proposed. This approach enables maximum power point (MPP) tracking control with post-stage inverter current information instead of calculating solar array power, which significantly simplifies the controller and the sensor. Furthermore, there is no feedback loop in the pre-stage converter to control the solar array voltage or current because the MPP tracker drives the converter switch duty cycle. This simple PCS control strategy can reduce the cost and size, and can be utilized with a low cost digital processor. For verification of the proposed control strategy, a 2.5kW two-stage photovoltaic grid-connected PCS hardware which consists of a boost converter cascaded with a single-phase inverter was built and tested.

• 조명전기설비학회논문지
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• 제23권5호
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• pp.72-79
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• 2009

태양 에너지는 재생 가능하고 오염이 없는 특성으로 바람직한 에너지 원이다. 계통에 이용하기 위해서는 dc-dc 컨버터와 계통 연계 do-ac 인버터가 필요하다. dc-dc 컨버터는 태양광 시스템이 높은 dc전압에 동작하기 위하여 필요하고, 인버터는 계통에 연결하기 위하여 필요한 전압과 주파수를 만들어 내는데 필요하다. 본 논문에서는 첫째로 단상 계통 연계 인버터에서 전류 루프 전달 함수가 유도되고, 둘째로 컨버터 측에서 컨덕턴스 증가 방식의 MPPT 방식이 제안하여 인버터 측에 최대 전력을 공급하는데 있다. 시뮬레이션 결과가 계통에서 태양광 인버터 시스템의 성능과 특성을 보여준다.

• Journal of Power Electronics
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• 제12권4호
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• pp.578-586
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• 2012

In this paper a single-phase Cascaded H-Bridge (CHB) inverter for photovoltaic (PV) applications is presented. Based on the presented mathematical analysis, a novel controller is introduced which adjusts the inverter power factor (PF) and manipulates the distribution of the reactive power between the cells to enhance the operating range of the CHB inverter. The adopted control strategy enables tracking of the maximum power point (MPP) of distinct PV strings and allows independent control of the dc-link voltages. The proposed controller also enables the inverter to operate under heavily unbalanced PV conditions. The performance of the CHB inverter and the proposed controllers are evaluated in the PSCAD/EMTDC environment. A seven-level CHB-based grid connected laboratory prototype is also utilized to verify the system performance.

• Journal of Power Electronics
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• 제18권1호
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• pp.212-224
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• 2018

For maintaining a reliable and secure power system, this paper describes the design and implement of a single-phase grid-connected inverter with an enhanced phase-locked loop (PLL) and excellent power control performance. For designing the enhanced PLL and power regulator, a full-bridge voltage-controlled inverter (VCI) is investigated. When the grid frequency deviates from its reference values, the output frequency of the VCI is unstable with an oscillation of 2 doubling harmonics. The reason for this oscillation is analyzed mathematically. This oscillation leads to an injection of harmonics into the grid and even causes an output active power oscillation of the VCI. For eliminating the oscillation caused by a PLL, an oscillation compensation method is proposed. With the proposed method, the VCI maintains the original PLL control characteristics and improves the PLL robustness under grid frequency deviations. On the basis of the above analysis, a power regulator with the primary frequency and voltage modulation characteristics is analyzed and designed. Meanwhile, a small-signal model of the power loops is established to determine the control parameters. The VCI can accurately output target power and has primary frequency and voltage modulation characteristics that can provide active and reactive power compensation to the grid. Finally, simulation and experimental results are given to verify the idea.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2018년도 추계학술대회
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• pp.95-97
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• 2018

The power quality of Single Phase Grid-Connected Inverters (GCIs) has received much attention with the increasing number of Distributed Generation (DG) systems. However, the performance of single phase GCIs get degraded due to several factors such as the grid voltage harmonics, the dead time effect, and the turn ON/OFF of the switches, which causes the harmonics at the output of GCIs. Therefore, it is not easy to satisfy the harmonic standards such as IEEE 519 and P1547 without the help of harmonic compensator. To meet the harmonic standards a certain kind of harmonic controller needs to be added to the current control loop to effectively mitigate the low order harmonics. In this paper, the harmonic compensation is performed using a novel robust harmonic compensation method based on Digital Lock-in Amplifier (DLA). In the proposed technique, DLAs are used to extract the amplitude and phase information of the harmonics from the output current and compensate it by using a simple PI controller in the feedforward manner. In order to show the superior performance of the proposed harmonic compensation technique, it is compared with those of conventional harmonic compensation methods in terms of the effectiveness of harmonic elimination, complexity, and implementation. The validity of the proposed harmonic compensation techniques for the single phase GCIs is verified through the experimental results with a 5kW single phase GCI. Index Terms -Single Phase Grid Connected Inverter (SPGCI), Harmonic Compensation Method, Total Harmonic Distortion (THD) and Harmonic Standard.

• 전력전자학회논문지
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• 제20권6호
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• pp.517-525
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• 2015

A grid connected inverter must be operated as the main electricity source under an isolated condition caused by the grid problem. Conventionally, the dual loop controller is used for the grid inverter, and the controller is used for control under the stand-alone mode. Generally, the PI(Proportional - Integral) controller is highly efficient under a synchronous reference frame, and stable control can be available. However, in this synchronous frame-based control, high-quality DSP is required because many sinusoidal calculations are necessary. When the PI control is conducted under a stationary frame, the controller constructions are made simple so that they work even with a low-price micro controller. However, given the characteristics of the PI controller, it should be designed with the phase of reference voltage considered. Otherwise, the phase delay of the output voltage can occur. Although the current controller also has a higher bandwidth than the voltage controller, distortion of the voltage is difficult to avoid only by the rapid response of the PI controller, as a sudden load change can occur in the nonlinear load. In this study, a new control method that solves the voltage controller bandwidth problem and rapidly copes with it even in the nonlinear load situation is proposed. The validity of the proposed method is proved by simulation and experimental results.