A Lyapunov function based current controller to control active and reactive power flow in a three phase grid connected PV inverter under generalized grid voltage conditions

S. Dasgupta,S. N. Mohan,S. K. Sahoo,S. K. Panda 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

In this paper, a novel control system is proposed to control the active and reactive grid power flow in a three phase grid connected PV inverter. The control system not only controls the grid power but also reduces the grid current THD in the presence of typical non-linear loads in parallel with grid at the point of common coupling (PCC). The proposed control system also takes care of not only the grid voltage unbalance but also the unbalance in the connecting line side inductors. The stability of the proposed control system is ensured by the direct method of Lyapunov. The proposed control system is not only simple to implement in the digital form but also provides superior performance over the conventional multiple PI or resonant control methods. A new grid connected inverter modeling technique is also proposed to take care of unbalances in the inverter system. Experimental results are provided to show the efficacy of the proposed control system.

Overview of Multi-functional Grid-connected Inverter and Its Application in Micro-grid

Tieyan Zhang,Xuefeng Yang,Yan Zhao 보안공학연구지원센터 2016 International Journal of Grid and Distributed Comp Vol.9 No.8

A comprehensive review on inverter topologies and control strategies for grid connected photovoltaic system

Zeb, Kamran,Uddin, Waqar,Khan, Muhammad Adil,Ali, Zunaib,Ali, Muhammad Umair,Christofides, Nicholas,Kim, H.J. Elsevier 2018 RENEWABLE & SUSTAINABLE ENERGY REVIEWS Vol.94 No.-

<P><B>Abstract</B></P> <P>The application of Photovoltaic (PV) in the distributed generation system is acquiring more consideration with the developments in power electronics technology and global environmental concerns. Solar PV is playing a key role in consuming the solar energy for the generation of electric power. The use of solar PV is growing exponentially due to its clean, pollution-free, abundant, and inexhaustible nature. In grid-connected PV systems, significant attention is required in the design and operation of the inverter to achieve high efficiency for diverse power structures. The requirements for the grid-connected inverter include; low total harmonic distortion of the currents injected into the grid, maximum power point tracking, high efficiency, and controlled power injected into the grid. The performance of the inverters connected to the grid depends mainly on the control scheme applied. In this review, the global status of the PV market, classification of the PV system, configurations of the grid-connected PV inverter, classification of various inverter types, and topologies are discussed, described and presented in a schematic manner. A concise summary of the control methods for single- and three-phase inverters has also been presented. In addition, various controllers applied to grid-tied inverter are thoroughly reviewed and compared. Finally, the criteria for the selection of inverters and the future trends are comprehensively presented.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The global PV market and classification of PV systems. </LI> <LI> Various inverter topologies presented in a schematic manner. </LI> <LI> Review of the control techniques for single- and three-phase inverters. </LI> <LI> Selection guide for choosing an appropriate inverter topology based on specific application. </LI> </UL> </P>

Stability Analysis of Grid-Connected Inverters with an LCL Filter Considering Grid Impedance

Xiao-Qiang Li,Xiao-Jie Wu,Yi-Wen Geng,Qi Zhang 전력전자학회 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.5

Under high grid impedance conditions, it is difficult to guarantee the stability of grid-connected inverters with an LCL filter designed based on ideal grid conditions. In this paper, the theoretical basis for output impedance calculation is introduced. Based on the small-signal model, the d-d channel closed-loop output impedance models adopting the converter-side current control method and the grid-side current control method are derived, respectively. Specifically, this paper shows how to simplify the stability analysis which is usually complemented based on the generalized Nyquist stability criterion (GNC). The stability of each current-controlled grid-connected system is analyzed via the proposed simplified method. Moreover, the influence of the LCL parameters on the stability margin of grid-connected inverter controlled with converter-side current is studied. It is shown that the stability of grid-connected systems is fully determined by the d-d channel output admittance of the grid-connected inverter and the inductive component of the grid impedance. Experimental results validate the proposed theoretical stability analysis.

Stability Analysis of Grid-Connected Inverters with an LCL Filter Considering Grid Impedance

Li, Xiao-Qiang,Wu, Xiao-Jie,Geng, Yi-Wen,Zhang, Qi The Korean Institute of Power Electronics 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.5

Under high grid impedance conditions, it is difficult to guarantee the stability of grid-connected inverters with an LCL filter designed based on ideal grid conditions. In this paper, the theoretical basis for output impedance calculation is introduced. Based on the small-signal model, the d-d channel closed-loop output impedance models adopting the converter-side current control method and the grid-side current control method are derived, respectively. Specifically, this paper shows how to simplify the stability analysis which is usually complemented based on the generalized Nyquist stability criterion (GNC). The stability of each current-controlled grid-connected system is analyzed via the proposed simplified method. Moreover, the influence of the LCL parameters on the stability margin of grid-connected inverter controlled with converter-side current is studied. It is shown that the stability of grid-connected systems is fully determined by the d-d channel output admittance of the grid-connected inverter and the inductive component of the grid impedance. Experimental results validate the proposed theoretical stability analysis.

Resonant Damping Analysis of Output Filter of Grid-Connected Inverters

Zhou XiaoJie 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.4

The design performance of the grid-connected inverter directly determines the quality of the grid-connected output current as an interface between the distributed power generation system and the power grid. Grid-connected inverters usually use output fi lters to attenuate high-frequency harmonics, and output fi lters’ fi ltering performance directly determines the system's performance. Based on the analysis of the existing output fi lter topology and fi ltering performance, an LLCLC-type grid-connected inverter output fi lter is proposed. To suppress fi lter resonance spikes for stable system operation, R s and R s - C s methods are used to damp the LCL-type, LLCL-type and LLCLC-type fi lters. The damping eff ect on resonant spikes and high-frequency harmonic attenuation is thoroughly analyzed and compared for diff erent damping methods applied to diff erent fi lters. The analysis shows that LCL-type and LLCL-type fi lters have the same characteristic that the better the damping eff ect, the worse its trapping eff ect on the switching frequency harmonics. However, the trapping eff ect of LLCLCtype fi lters on switching frequency harmonics is not weakened by damping, so its overall fi ltering eff ect will be signifi cantly better than that of LCL-type and LLCL-type fi lters under the same device volume cost, which is an outstanding advantage of LLCLC-type fi lters. Both simulation and experimental results verify the correctness and eff ectiveness of the proposed LLCLC-type output fi lter structure and resonant spike damping technique. v The design performance of the grid-connected inverter directly determines the quality of the grid-connected output current as an interface between the distributed power generation system and the power grid. Grid-connected inverters usually use output fi lters to attenuate high-frequency harmonics, and output fi lters’ fi ltering performance directly determines the system's performance. Based on the analysis of the existing output fi lter topology and fi ltering performance, an LLCLC-type grid-connected inverter output fi lter is proposed. To suppress fi lter resonance spikes for stable system operation, R s and R s - C s methods are used to damp the LCL-type, LLCL-type and LLCLC-type fi lters. The damping eff ect on resonant spikes and high-frequency harmonic attenuation is thoroughly analyzed and compared for diff erent damping methods applied to diff erent fi lters. The analysis shows that LCL-type and LLCL-type fi lters have the same characteristic that the better the damping eff ect, the worse its trapping eff ect on the switching frequency harmonics. However, the trapping eff ect of LLCLCtype fi lters on switching frequency harmonics is not weakened by damping, so its overall fi ltering eff ect will be signifi cantly better than that of LCL-type and LLCL-type fi lters under the same device volume cost, which is an outstanding advantage of LLCLC-type fi lters. Both simulation and experimental results verify the correctness and eff ectiveness of the proposed LLCLC-type output fi lter structure and resonant spike damping technique.

Investigation of Instability in Multiple Grid-Connected Inverters with LCL Output Filters

Fariba Asghari,Arash Safavizadeh,Hamid Reza Karshenas 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

This paper deals with the instability and resonant phenomena in distribution systems with multiple grid-connected inverters with an LCL output filter. The penetration of roof-top and other types of small photovoltaic (PV) grid-connected systems is rapidly increasing in distribution grids due to the attractive incentives set forth by different governments. When the number of such grid-connected inverters increases, their interaction with the distribution grid may cause undesirable effects such as instability and resonance. In this paper, a grid system with several grid-connected inverters is studied. Since proportional-resonant (PR) controllers are becoming more popular, it is assumed that most inverters use this type of controller. An LCL filter is also considered at the inverters output to make the case as realistic as possible. A complete modeling of this system is presented. Consequently, it is shown that such a system is prone to instability due to the interactions of the inverter controllers. A modification of PR controllers is presented where the output capacitor is virtually decreased. As a result, the instability is avoided. Simulation results are presented and show a good agreement with the theoretical studies. Experimental results obtained on a laboratory setup show the validity of the analysis.

Performance Improvement of Grid-Connected Inverter Systems under Unbalanced and Distorted Grid Voltage by Using a PR Controller

Jong-Hyun Lee,Hae-Gwang Jeong,Kyo-Beum Lee 대한전기학회 2012 Journal of Electrical Engineering & Technology Vol.7 No.6

This paper proposes a control method for grid-connected inverter systems under unbalanced and distorted grid voltage. The proposed method can reduce the power ripple caused by the unbalanced condition and compensate for the low-order harmonics of the output currents caused by the distortion of grid voltage. To reduce the power ripple, our method replaces the two conventional PI controllers with one PR controllers in the stationary frame. PR controllers can implement selective harmonic compensation without excessive computational requirements; the use of these controllers simplifies the method. Both the simulated and experimental results agree well with the theoretical analysis.

An Improved Harmonic Compensation Method for a Single-Phase Grid Connected Inverter

칸 레이안,최우진,Khan, Reyyan Ahmad,Choi, Woojin The Korean Institute of Power Electronics 2019 전력전자학회 논문지 Vol.24 No.3

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.

An Improved Harmonic Compensation Method for a Single-Phase Grid Connected Inverter

칸레이안,최우진 전력전자학회 2019 전력전자학회 논문지 Vol.23 No.3

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.