DC-Link Voltage Control of a Grid-Connected Solar Photovoltaic System for Fault Ride-Through Capability Enhancement

Abstract

The high penetration level of solar photovoltaic (SPV) generation systems imposes a major challenge to the secure operation of power systems. SPV generation systems are connected to the power grid via power converters. During a fault on the grid side; overvoltage can occur at the direct current link (DCL) due to the power imbalance between the SPV and the grid sides. Subsequently; the SPV inverter is disconnected; which reduces the grid reliability. DC-link voltage control is an important task during low voltage ride-through (LVRT) for SPV generation systems. By properly controlling the power converters; we can enhance the LVRT capability of a grid-connected SPV system according to the grid code (GC) requirements. This study proposes a novel DCL voltage control scheme for a DC–DC converter to enhance the LVRT capability of the two-stage grid-connected SPV system. The control scheme includes a “control without maximum power point tracking (MPPT)” controller; which is activated when the DCL voltage exceeds its nominal value; otherwise, the MPPT control is activated. Compared to the existing LVRT schemes the proposed method is economical as it is achieved by connecting the proposed controller to the existing MPPT controller without additional hardware or changes in the software. In this approach, although the SPV system will not operate at the maximum power point and the inverter will not face any over current challenge it can still provide reactive power support in response to a grid fault. A comprehensive simulation was carried out to verify the effectiveness of the proposed control scheme for enhancing the LVRT capability and stability margin of an interconnected SPV generation system under symmetrical and asymmetrical grid faults.

Harmonic Analysis and Control of Grid-Connected Solar PV Inverter under Normal and LVRT Operating Modes

“…The proposed control strategy is evaluated in a 100-kW solar PV array system linked to a 25-kV grid provided on the Matlab website [18]. The fault is created at t = 0.5 s and after 0.15 s is eliminated.…”

Grid Fault Ride Through Capability of Voltage Controlled Inverters for Photovoltaic Applications

“…By proposing a comprehensive design predictive control system, the incorporation of solar power into utility with grid (FRT) capability was explored [7][8][9]. A control system using Direct current link voltage for a dc-dc converter has proposed to increase LVRT performance of the two-stage on-grid PV inverter [10]. A control system designed to increase the (FRT) capability by measuring both the DC chopper and the current boundary based on the reactive power needed at fault time [11][12][13][14].…”

Sizing of dc-link capacitor for a grid connected solar photovoltaic inverter

“…Recently photovoltaic systems are actively researched as a sustainable power solution (7,8) . The PV sources can be operated in standalone or grid connected mode (9,10) . In order to inject the photovoltaic generated power to ac grid usually power electronic inverters are used with some standards and requirements (11,12) .…”