Stability Assessment of Current Controller with Harmonic Compensator for LCL-Filtered Grid-Connected Inverter under Distorted Weak Grid

Abstract

An assessment of the stability and performance of current controllers with harmonic compensators is presented for an inductive-capacitive-inductive (LCL)-filtered grid-connected inverter under distorted weak grid conditions. By using two typical current control schemes which are the direct current controller with the capacitor current-based active damping and integral-resonant state feedback current controller, the closed-loop system stability and current control performance are investigated in the presence of both uncertain grid impedance and distorted grid. Even though the controller stability has been investigated under weak grid in several studies, the stability assessment of the entire current control scheme, including the harmonic resonant controllers, still needs a further comprehensive investigation. The system stability is analyzed by obtaining the movement of the closed-loop poles in the discrete-time domain when the grid impedance varies. To fully study the impact of distorted weak grid condition on the LCL filters, three LCL filter parameter sets giving the resonance frequency in different frequency bands are chosen for the purpose of evaluating the system robustness and grid-injected current quality. In order to support the presented theoretical analyses, comprehensive simulation and experimental results based on 32-bit DSP TMS320F28335 to control 2 kVA grid-connected inverter are presented in terms of grid current quality and control stability in the environment of both uncertain grid impedance and distorted grid.

Weak-Grid Tolerant Positive- and Negative-Sequence Current Control of Voltage-Source Converters

“…respectively, where z +/− 1,2 are the reference-tracking zeros. The locations of the zeros in (11) depend on the gains k + t and k + c . Analogously, the locations of the zeros in (12) depend on the gains k − t and k − c .…”

“…Since the two zeros in the reference-tracking transfer functions (11) and ( 12) can be placed freely, two pole-zero cancellations can be achieved. Consequently, the reference-tracking dynamics under nominal conditions depend only on the two remaining poles.…”

“…In the indirect pole placement approaches [7]- [18], the closed-loop poles are placed indirectly by choosing the statefeedback gains through optimization. Various optimization methods for computing the state-feedback gains have been proposed, e.g., linear quadratic regulator (LQR) design [7]- [11], linear matrix inequality (LMI) optimization [12], [13], combination of LQR and LMI [14], combination of a genetic algorithm (GA) and LMI [15], particle swarm optimization [16], H ∞ design [17], and steady-state Kalman filter design [18]. By examining the collection of pole maps produced by these methods, a clear trend can be observed.…”

Impedance-Based Stability Analysis of Grid-Connected Inverters under the Unbalanced Grid Condition

“…For long-distance transmission lines, the line impedance and transformer impedance cannot be ignored, and various faults may occur throughout the line, which make the grid extremely sensitive to vulnerability and unbalance [6][7][8]. Due to the complex interaction between inverters and the weak and unbalanced power grid, there are many oscillation events caused by inverters in the power system [9,10]. Hence, the stability analysis of a grid-connected inverter system is significant for improving the utilization rate of renewable energy and maintaining the stable operation of the whole power system [11,12].…”

Adaptive PI + VPI Harmonic Current Compensation Strategy under Weak Grid Conditions

“…The new energy distributed generation system has been widely expanded under the guidance of the goal of "carbon dioxide emission peak" and "carbon neutrality", along with the scattered location of distributed generation systems, long-distance transmission lines and multiple transformers often used for interconnection. The connection of distributed generation systems to the public power grid leads to an increase in grid impedance that cannot be ignored, making the public power grid exhibit weak grid characteristics with a low short circuit ratio (SCR) [1][2][3]. According to IEEE standard 1204-1997, the grid is a weak one when the SCR < 3.…”