Control Strategy for Grid Connected Inverters Under Unbalanced Network Conditions - A DOb Based Decoupled Current Approach

Abstract

Penetration of grid connected inverters (GCI) has arisen in power systems due to increasing integration of renewable sources. However, restrictive grid codes require that renewable sources connected to the grid with power electronic systems must be properly connected and appropriate currents must be injected to support stability of the grid under grid faults. Simultaneous injection of symmetrical positive and negative sequence currents is mandatory to support stabilization of grid at the instant of grid faults. Conventional synchronously rotating frame dq current controllers are insufficient under grid faults due to low bandwidth of PI controllers. This paper proposes a new grid current control strategy for grid connected voltage source inverters under unbalanced grid voltage conditions. A proportional current controller with a first order low pass filter disturbance observer (DOb) is proposed which establishes positive sequence power requirements and independently control negative sequence current components under unbalanced voltage conditions. The method does not need any parameter, since it estimates nonlinear terms with low pass filter DOb. Simulations are implemented in Matlab/Simulink platform demonstrating the effectiveness of proposed method.

Research on Safety Protection of Smart Microgrid Operation Control Based on Automatic Regulation

“…The weight parameter in equation ( 2) is reversely adjusted according to the error [11]. The weight is constantly adjusted through repeated training until the training error reaches the expected value.…”

Minimisation of power oscillations with a novel optimal control strategy for distributed generation inverter under grid faulty and harmonic networks

“…The PCI controller achieves more accurate and faster current regulation [23] than the traditional PI and PR controllers [45]. Improved traditional PI controller (29) is written in the following equation:…”

“…In [28], the fractional‐order PI controller has been improved to reduce harmonic component tracking error and to enhance the response of the system. In [29], disturbance observer‐based proportional decoupled current controller is presented for controlling negative sequences. In , for steady‐state errors and current tracking errors, the PR controller [3, 9, 30], direct power control algorithm [31], hysteresis control strategy [32], and the MPC [22, 33] or other advanced control techniques have been discussed for the current regulation.…”

Utilizing Full Degrees of Freedom of Control in Voltage Source Inverters to Support Micro-Grid with Symmetric and Asymmetric Voltage Requirements

“…The role of power converters is very unique since the converters are the interfaces enabling the synchronization, voltage control, current control and power flow control in the MG and SG [5,7,8]. A number of studies can be found in the literature regarding the control of three-phase VSI, specifically in view of controlling the imbalance of power in the MG [9][10][11][12][13]. All of these established works offer complexity, since they are designed to maintain pure sinusoidal voltages as the output of the VSI, whose conception dates back to the 1980s due to the stringent supply requirements of the three-phase motors [14][15][16][17].…”