Modeling and simulation of direct output current control for LCL-interfaced grid-connected inverters with parallel passive damping

J. Mod. Power Syst. Clean Energy

Liu

Wang

2017

Active damped LCL-filter-based inverters have been widely used for grid-connected distributed generation (DG) systems. In weak grids, however, the phase-locked loop (PLL) dynamics may detrimentally affect the stability of grid-connected inverters due to interaction between the PLL and the controller. In order to solve the problem, the impact of PLL dynamics on small-signal stability is investigated for the active damped LCL-filtered grid-connected inverters with capacitor voltage feedback. The system closed-loop transfer function is established based on the Norton equivalent model by taking the PLL dynamics into account. Using an established model, the system stability boundary is identified from the viewpoint of PLL bandwidth and current regulator gain. The accuracy of the ranges of stability for the PLL bandwidth and current regulator gain is verified by both simulation and experimental results.

Section: Introductionmentioning

confidence: 99%

Impact of phase-locked loop on stability of active damped LCL-filter-based grid-connected inverters with capacitor voltage feedback

J. Mod. Power Syst. Clean Energy

Liu

Wang

2017

“…1, where an LCL filter is used to attenuate the high-frequency harmonics due to switching [18,19]. The control objective is to inject sinusoidal currents into the grid, which complies with the relevant IEEE Standard [6].…”

Section: Proposed Control Strategymentioning

confidence: 99%

“…The single-line diagram of the control structure for threephase grid-connected inverter is shown in Fig. 4, where C(s) is the current controller, K is the pulse width modu- Abc-frame complex-coefficient filter and controller based current harmonic elimination strategy 89 lation (PWM) gain, R 2 is the resistor used for the passive damping [19], and U g is the grid voltage. The grid current can be derived from Fig.…”

Section: Proposed Control Strategymentioning

confidence: 99%

Abc-frame complex-coefficient filter and controller based current harmonic elimination strategy for three-phase grid connected inverter

J. Mod. Power Syst. Clean Energy

Guerrero

2016

Current quality is one of the most important issues for operating three-phase grid-connected inverter in distributed generation systems. In practice, the grid current quality is degraded in case of non-ideal utility voltage. A new control strategy is proposed for the three-phase gridconnected inverter. Different from the traditional method, our proposal utilizes the unique abc-frame complex-coefficient filter and controller to achieve the balanced, sinusoidal grid current. The main feature of the proposed method is simple and easy to implement without any frame transformation. The theoretical analysis and experimental test are presented. The experimental results verify the effectiveness of the proposed control strategy.

“…The direct output current control (Guo, et al, 2010) is used for the grid-connected power converter to enhance the system steady-state and dynamic performances. Aside from that, an additional impedance 2 2 g g R jL + and two switches (S1 and S2) are used for testing the dynamic performance of the proposed impedance estimation method.…”

Section: T a T X T B T U T Y T C X Tmentioning

confidence: 99%

New grid impedance estimation technique for grid-connected power converters

Sun

et al. 2014

J Engin Res

Grid impedance estimation is crucial for operating and controlling of grid-connected converters, especially with the high penetration of renewable energy sources into microgrid and smart grid. One of the technical challenges is how to fast and accurately estimate the grid impedance, even under the distorted and unbalanced conditions. Many impedance estimation methods have been presented in the past decades. Most of them intentionally inject one or more disturbance signals, low frequency or high frequency, to excite the grid response. And then the grid impedance can be estimated by the voltage/current information of two steady-state operating points before and after the disturbance. However, these injected disturbances will deteriorate the power quality due to harmonics caused by the injected disturbances. In order to mitigate the problem, a new impedance estimation method is presented in this paper. Its basic idea lies in the inherent switching feature of the grid-connected power converter. The unique feature is that the proposed new grid impedance can be easily estimated, even under distorted and unbalanced grid voltage conditions with no need of the intentionally injected disturbance signals any more. First of all, the system equivalent impedance circuit is analyzed to clarify the proposed method, along with a theoretical comparison with the conventional one. Aside from that, an interesting estimation of voltage and current switching components are presented for determining the grid impedance with two well-defined equations. And then, the performance tests are carried out and the results verify the effectiveness of the proposed method. Finally, a typical application of the proposed method is presented and discussed.