• Title/Summary/Keyword: Grid connected

Search Result 871, Processing Time 0.101 seconds

Single Phase Grid Connected Voltage-ed Inverter Utilizing a Power Decoupling Function (전력 디커플링 기능을 가진 단상 계통연계 전압형 인버터)

  • Lee, Sang-Wook;Mun, Sang-Pil;Park, Han-Seok
    • The Transactions of the Korean Institute of Electrical Engineers P
    • /
    • v.66 no.4
    • /
    • pp.236-241
    • /
    • 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.

Dual Current Control Scheme of a Grid-connected Inverter for Power Quality Improvement in Distributed Generation Systems (분산 전원 시스템의 전력품질 향상을 위한 계통연계 인버터의 이중 전류제어 기법)

  • Kim, Kyeong-Hwa
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
    • /
    • v.29 no.9
    • /
    • pp.33-41
    • /
    • 2015
  • To improve the power quality of distributed generation (DG) systems even in the presence of distorted grid condition, dual current control scheme of a grid-connected inverter is proposed. The proposed current control scheme is achieved by decomposing the inverter state equations into the fundamental and harmonic components. The derived models are employed to design dual current controllers. The conventional PI decoupling current controller is used in the fundamental model to control the main power flow in DG systems. At the same time, the predictive control is applied in the harmonic model to suppress undesired harmonic currents to zero quickly. To decompose the voltage inputs and state variables into the fundamental and harmonic components, the fourth order band pass filter (BPF) is designed in the discrete-time domain for a digital implementation. For experimental verification, 2kVA prototype of a grid-connected inverter has been constructed using digital signal processor (DSP) TMS320F28335. The effectiveness of the proposed strategy is demonstrated through comparative simulation and experimental results.

Power Quality Improvement for Grid Connected Inverters under Distorted and Unbalanced Grids

  • Kim, Hyun-Sou;Kim, Jung-Su;Kim, Kyeong-Hwa
    • Journal of Power Electronics
    • /
    • v.16 no.4
    • /
    • pp.1578-1586
    • /
    • 2016
  • A power quality improvement scheme for grid connected inverters, even in the presence of the disturbances in grid voltages due to harmonic distortions and three-phase imbalance, is presented for distributed generation (DG) power systems. The control objective is to force the inverter currents to follow their references with robustness even under external disturbances in grid voltages. The proposed scheme is realized by a disturbance observer (DOB) based current control scheme. Since the uncertainty in a system can be effectively canceled out using an estimated disturbance by the DOB, the resultant system behaves like a closed-loop system consisting of a disturbance-free nominal model. For experimental verification, a 2 kVA laboratory prototype of a grid connected inverter has been built using a digital signal processor (DSP) TMS320F28335. Through comparative simulations and experimental results under grid disturbances such as harmonic distortion and imbalance, the effectiveness of the proposed DOB based current control scheme is demonstrated.

Droop Control Scheme of a Three-phase Inverter for Grid Voltage Unbalance Compensation

  • Liu, Hongpeng;Zhou, Jiajie;Wang, Wei;Xu, Dianguo
    • Journal of Power Electronics
    • /
    • v.18 no.4
    • /
    • pp.1245-1254
    • /
    • 2018
  • The stability of a grid-connected system (GCS) has become a critical issue with the increasing utilization of renewable energy sources. Under grid faults, however, a grid-connected inverter cannot work efficiently by using only the traditional droop control. In addition, the unbalance factor of voltage/current at the common coupling point (PCC) may increase significantly. To ensure the stable operation of a GCS under grid faults, the capability to compensate for grid imbalance should be integrated. To solve the aforementioned problem, an improved voltage-type grid-connected control strategy is proposed in this study. A negative sequence conductance compensation loop based on a positive sequence power droop control is added to maintain PCC voltage balance and reduce grid current imbalance, thereby meeting PCC power quality requirements. Moreover, a stable analysis is presented based on the small signal model. Simulation and experimental results verify the aforementioned expectations, and consequently, the effectiveness of the proposed control scheme.

Grid-Connected Three-Phase Inverter System with Sub Inverter using Combination Type UPFC Structure

  • Park, Seong-Mi;Vi, Le Thi Tuan;Jeong, Da-Woom;Park, Sung-Jun;Park, Jang-Sik
    • Journal of the Korean Society of Industry Convergence
    • /
    • v.23 no.4_1
    • /
    • pp.559-567
    • /
    • 2020
  • As the renewable energy market grows, grid-connected inverters have been improving and expanding in several fields in recent years because energy conversion devices are the main components of solar systems. In this paper, a high-precision new grid-connected three-phase inverter system is proposed. The proposed system consists of a main inverter, a sub inverter and a transformer. The main inverter operates at a low switching frequency and high power and transmits power to the grid. A sub-inverter connected in series with the transmission line through a matching transformer operates at lower power than the main inverter to provide input values to the transformer. The transformer acts as a power supply according to the voltage compensation value. This study is based on the principle of operation of the UPFC(Unified Power Flow Controller) structure used to regulate power flow in AC transmission lines. The grid-connected inverter system proposed in this paper is implemented with high precision and high resolution. The proposed system was verified through its ability to enhance and ensure the safety of the proposed system through simulation and experiment.

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
    • /
    • /
    • pp.144-146
    • /
    • 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.

  • PDF

A Novel Three-Phase Four-Wire Grid-Connected Synchronverter that Mimics Synchronous Generators

  • Tan, Qian;Lv, Zhipeng;Xu, Bei;Jiang, Wenqian;Ai, Xin;Zhong, Qingchang
    • Journal of Power Electronics
    • /
    • v.16 no.6
    • /
    • pp.2221-2230
    • /
    • 2016
  • Voltage and frequency stability issues occur in existing centralized power system due to the high penetration of renewable energy sources, which decrease grid absorptive capacity of them. The grid-connected inverter that mimics synchronous generator characteristics with inertia characteristic is beneficial to electric power system stability. This paper proposed a novel three-phase four-wire grid-connected inverter with an independent neutral line module that mimics synchronous generators. A mathematical model of the synchronous generator and operation principles of the synchronverter are introduced. The main circuit and control parameters design procedures are also provided in detail. A 10 kW prototype is built and tested for further verification. The primary frequency modulation and primary voltage regulation characteristics of the synchronous generator are emulated and automatically adjusted by the proposed circuit, which helps to supports the grid.

Mode Switching Smooth Control of Transient Process of Grid-Connected 400 Hz Solid-State Power Supply System

  • Zhu, Jun-Jie;Nie, Zi-Ling;Zhang, Yin-Feng;Han, Yi
    • Journal of Power Electronics
    • /
    • v.16 no.6
    • /
    • pp.2327-2337
    • /
    • 2016
  • The mode-switching control of transient process is important to grid-connected 400 Hz solid-state power supply systems. Therefore, this paper analyzes the principle of on-grid and islanding operation of the system with or without local loads in the grid-connected process and provides a theoretical study of the effect of different switching sequences on the mode-switching transient process. The conclusion is that the mode switch (MS) must be turned on before the solid-state switch (STS) in the on-grid process and that STS must be turned off before the MS in the off-grid process. A strategy of mode-switching smooth control for transient process of the system is proposed, including its concrete steps. The strategy utilizes the average distribution of peak currents and the smooth adjustment of peak currents and phases to achieve a no-shock grid connection. The simulation and experimental results show that the theoretical analysis is correct and that the method is effective.

Design of LCL-filter for Grid-Connected Three-Phase Inverters Using a Discontinuous PWM Method (DPWM 방식을 적용한 3상 계통 연계 인버터의 LCL-필터 설계)

  • Lee, Jung-Rok;Seo, Seung Gyu;Lee, Kyo-Beum
    • The Transactions of The Korean Institute of Electrical Engineers
    • /
    • v.65 no.3
    • /
    • pp.419-427
    • /
    • 2016
  • This paper proposes a design method of LCL-filter for a grid-connected three-phase inverter using a discontinuous PWM (DPWM) method. When using a DPWM method, many harmonic voltages are generated in the inverter output compared to a continuous PWM (CPWM) method. Therefore, an optimized grid-connected filter design is required for a DPWM method. The proposed design method provides generalized formula to design accurate LCL-filter without trial and error procedures. An inverter side inductance is designed by analyzing the current ripple injected to the grid. The Optimized parameters of LCL-filter can be designed by analyzing the total harmonic distortion (THD) and the ripple attenuation factor of the output current. The proposed LCL filter design method is demonstrated by simulation and experimental results.

Analysis of Current Control Stability using PI Control in Synchronous Reference Frame for Grid-Connected Inverter with LCL Filter (LCL 필터를 사용하는 계통연계형 인버터의 동기좌표계 PI 전류제어 안정도 해석)

  • Jo, Jongmin;Lee, Taejin;Yun, Donghyun;Cha, Hanju
    • The Transactions of the Korean Institute of Power Electronics
    • /
    • v.21 no.2
    • /
    • pp.168-174
    • /
    • 2016
  • In this paper, current control using PI controller in the synchronous reference frame is analyzed through the relationship among bandwidth, resonance frequency, and sampling frequency in the grid-connected inverter with LCL filter. Stability is investigated by using bode plot in frequency domain and root locus in discrete domain. The feedback variable is the grid current, which is regulated by the PI controller in the synchronous reference frame. System delay is modeled as 1.5Ts, which contains computational and PWM modulator delay. Two resonance frequencies are given at 815 Hz and 3.16 kHz from LCL filter parameters. Sufficient phase and gain margins can be obtained to guarantee stable current control, in case that resonance frequency is above one-sixth of the sampling frequency. Unstable current control is performed when resonance frequency is below one-sixth of the sampling frequency. Analysis results of stability from frequency response and discrete response is the same regardless of resonance frequency. Finally, stability of current control based on theoretical analysis is clearly verified through simulation and experiment in grid-connected inverters with LCL filter.