• Title/Summary/Keyword: In-grid Condition

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A Novel Harmonic Compensation Method for the Single Phase Grid Connected Inverters (단상 계통연계 인버터를 위한 새로운 고조파 보상법)

  • Khan, Reyyan Ahmad;Ashraf, Muhammad Noman;Choi, Woojin
    • Proceedings of the KIPE Conference
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    • 2018.07a
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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.

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Improved Phase and Harmonic Detection Scheme using Fast Fourier Transform with Minimum Sampling Data under Distorted Grid Voltage (최소 샘플링의 고속푸리에 변환을 이용한 비정상 계통의 향상된 위상추종 및 고조파 검출 기법)

  • Kim, Hyun-Sou;Kim, Kyeong-Hwa
    • The Transactions of the Korean Institute of Power Electronics
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    • v.20 no.1
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    • pp.72-80
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    • 2015
  • In distributed generation systems, a grid-connected inverter should operate with synchronization to grid voltage. Considering that synchronization requires the phase angle of grid voltage, a phase locked loop (PLL) scheme is often used. The synchronous reference frame phase locked loop (SRF-PLL) is generally known to provide reasonable performance under ideal grid voltage. However, this scheme indicates performance degradation under the harmonic distorted or unbalanced grid voltage condition. To overcome this limitation, this paper proposes a phase and harmonic detection method of grid voltage using fast Fourier transform (FFT). To reduce the calculation time of FFT algorithm, minimum sampling data is taken from the voltage measurement to determine the phase angle and the magnitude of harmonic components. An experimental test setup for a grid-connected inverter system has been constructed. By comparative simulations and experiments under various abnormal grid voltage conditions, the proposed scheme has been proven to effectively track the phase angle of the grid voltage.

Analysis of the Flow in Square Cavity Using CIP Method in Non-staggered Grid Arrangement (비엇갈림 격자계에서 CIP법을 이용한 캐비티내의 유동해석)

  • Lee, Jung-Hee;Kang, Joon;Im, Do-Kiun;Kim, Charn-Jung
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1821-1826
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    • 2003
  • In this study, we discuss CIP method, which can treat compressible/incompressible problem and multi-phase problem. We can apply this method to the general equations by using CCUP. In this paper, non-staggered grid arrangement and predictor-corrector method are used to enhance later development and the solution accuracy and convergence performance. To validate the numerical algorithm proposed in this paper, the two-dimensional unsteady flow in the driven cavity is simulated. The numerical results of this subject using the present algorithm are compared with other numerical results. As a result, it is prived that the present scheme gives stable and improved solutions, and the results even coarse grid are in good agreement with other result using a fine grid arrangement.

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Direct Power Control Scheme of Improved Command Tracking Capability for PMSG MV Wind turbines

  • Kwon, Gookmin;Suh, Yongsug
    • Proceedings of the KIPE Conference
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    • 2015.07a
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    • pp.361-362
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    • 2015
  • This paper proposes a Direct Power Control (DPC) scheme of improved command tracking capability for Permanent Magnet Synchronous Generator (PMSG) Medium Voltage (MV) Wind Turbines. Benchmarking is performed based on a neutral point clamped three-level back-to-back type voltage source converter. It is introduced to design the DPC modeling and propose DPC scheme of a three-level NPC (3L-NPC) converter. During the fault condition in wind farms, the proposed control scheme directly controls the generated output power to the command value from the hierarchical wind farm controller. The proposed control scheme is compared with conventional control scheme as respect to loss and thermal analysis. The DPC scheme of improved command tracking capability is confirmed through PLECS simulations. Simulation result shows that proposed control scheme achieves a much shorter transient time in a step response of generated output power. The proposed control scheme makes it possible to provide a good dynamic performance for PMSG MV wind turbine to generate a high quality output power under grid fault condition.

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An Improved Harmonic Compensation Method for a Single-Phase Grid Connected Inverter (단상 계통연계 인버터를 위한 개선된 고조파 보상법)

  • Khan, Reyyan Ahmad;Choi, Woojin
    • The Transactions of the Korean Institute of Power Electronics
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    • v.24 no.3
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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.

Power demand pattern analysis for electric appliances in residential and commercial building (주택 및 사무용 빌딩 내 전기기기의 전력 수요 패턴 분석)

  • Noh, Sung-Jun;Lee, Soon-Jeong;Lee, Sang-Woo;Kim, Kwang-Ho
    • Journal of Industrial Technology
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    • v.30 no.A
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    • pp.9-15
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    • 2010
  • Recently, Smart Grid is a emerging topic in power and communication industry. Smart Grid refers to a evolution of the electricity supply infrastructure that monitors, protects, and intelligently optimize the operation of the interconnected elements including various type of generators, power grid, building/home automation system and end-use consumers. In order to successful implementation of Smart Grid, energy management function will be the key factor that coordinates and optimally controls the various loads according to the operating condition and environments, and the load patterns in residential and commercial building will be required as fundamental element for load management. In this study, we collects many types of energy usage data of electric appliances, analyze their load curves, and make the general load patterns for electrical appliance.

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Stability Enhancement of a Hybrid Micro-grid System in Grid Fault Condition

  • Ambia, Mir Nahidul;Al-Durra, Ahmed;Caruana, Cedric;Muyeen, S.M.
    • Journal of international Conference on Electrical Machines and Systems
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    • v.2 no.2
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    • pp.225-231
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    • 2013
  • Low voltage ride through capability augmentation of a hybrid micro-grid system is presented in this paper which reflects enhanced reliability in the system. The control scheme involves parallel connected multiple ac-dc bidirectional converters. When the micro-grid system is subjected to a severe voltage dip by any transient fault single power converter may not be able to provide necessary reactive power to overcome the severe voltage dip. This paper discusses the control strategy of additional power converter connected in parallel with main converter to support extra reactive power to withstand the severe voltage dip. During transient fault, when the terminal voltage crosses 90% of its pre-fault value, additional converter comes into operation. With the help of additional power converter, the micro-grid system withstands the severe voltage fulfilling the grid code requirements. This multiple converter scheme provides the micro-grid system the capability of low voltage ride through which makes the system more reliable and stable.

Battery Charge and Discharge Optimization for Vehicle-to-grid Regulation Service (전력 보조서비스 제공을 위한 전기자동차 충/방전 최적화)

  • Kim, Wook-Won;Shin, Hong-Yul;Kim, Jin-O;Kim, Kyu-Ho
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.63 no.8
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    • pp.1033-1038
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    • 2014
  • Electric vehicles should be connected to power system for charge and discharge of battery. Besides vehicle's battery is charged for a power source, it is also reversibly possible to provide power source from battery to power system. Researches on battery usage for regulation resources have been progressed and could cause cost increase excessively because they distribute regulation capacity equally without considering the battery wear cost of SOC, temperature, voltage and so on. This causes increase of grid maintenance cost and aggravate economical efficiency. In this paper it is studied that the cost could be minimized according to the battery condition and characteristic. The equation is developed in this paper to calculate the possible number of charge and discharge cycle, according to SOC level and weighting factors representing the relation between battery life and temperature as well as voltage. Thereafter, the correlation is inferred between the battery condition and wear cost reflecting the battery price, and the expense of compensation is decided according to the condition on battery wear-out of vehicle. In addition, using realtime error between load and load expectation, it is calculated how much regulation capacity should be provided.

The Strap Vibration Characteristics in $5{\times}5$ Grid Exposed to Axial Flow (축방향 유속에 노출된 $5{\times}5$ 지지격자 스트랩의 진동특성)

  • Kim, Kyoung-Hong;Park, Nam-Gyu;Kim, Kyoung-Ju;Suh, Jung-Min
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2012.04a
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    • pp.911-916
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    • 2012
  • It is important to identify dynamic characteristics of nuclear fuel components. Since the fuel always exposed to turbulent flow, the dynamic contact between grids and rods is one of the fuel failure modes. The dynamic behavior of grids in nuclear fuels is quite complex, since two pairs of spring support are placed in the limited space. The strap in a cell has single spring and double dimples and this paper focuses on investigation of the grid strap(Test Fuel Strap, TFS) vibration in one cell. To identify the grid strap vibration, modal analysis of the strap is performed using Finite Element Method (FEM). Modal testing on a $5{\times}5$ grid structure without rods is performed. The modal testing results are compared to analytic results. In addition, random test considering rod effect is performed about a $5{\times}5$ grid with rods under real contact condition in the air. Finally, the strap vibration of a $5{\times}5$ fuel bundle in INvestigation of Flow INduced vIbraTion(INFINIT) facility is measured in real fluid velocity condition without heating. It is shown that modal frequencies from the test are almost equal to those peak frequencies in the INFINIT test.

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UNSTEADY AERODYNAMIC ANALYSIS OF HELICOPTER ROTOR BLADES USING DIAGONAL IMPLICIT HARMONIC BALANCE METHOD (중첩 격자 기법이 적용된 대각 내재적 조화균형법을 이용한 헬리콥터 로터 블레이드의 비정상 공력 해석)

  • Im, D.K.;Choi, S.I.;Kim, E.;Kwon, J.H.;Park, S.H.
    • Journal of computational fluids engineering
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    • v.17 no.1
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    • pp.70-77
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    • 2012
  • In this paper, diagonal implicit harmonic balance method with overset grid technique is applied to analyze helicopter rotor blade flow in hover and forward flight condition. The chimera grid need interpolation time with sub-grid and background grid in moving problem such as forward flight on every time step. Present method is available enough to reduce the grid module interpolation time. In order to demonstrate present method, Caradonna & Tung's and AH-1G rotor blades are used and the results are compared to other researchers' result and experimental data.