## 1 Introduction  
The number of renewable energy sources connected to the public grid is increasing significantly, due to the deregulation of electric power distribution industries and environmental issues. Among these renewable sources, photovoltaic (PV) technology will play an important role in the future of electricity generation. In the past, PV sources were commonly used in isolated and stand-alone applications. Nowadays, PV systems are commonly connected to the public grid and the generated power is sold, with advantageous price ratings fixed by governmental policies. The high penetration of solar photovoltaic (SPV) systems has resulted in several technical problems in the grid. The grid codes (GCs) are strictly adhered to in order for grid-connected SPV systems to avoid adverse effects on the power system [1; 2; 3]. Among the grid codes, the low-voltage ride-through (LVRT) capability of solar PV is important. According to the widely adopted E.ON Netz GmbH code, the PV system should be kept connected to the grid during grid disturbances, to provide dynamic grid support [4]. Extensive studies have been performed on enhancement of the LVRT of SPV systems via hardware solutions. A direct current (DC)-breaking chopper circuit can be coupled across the DCL to satisfy the GC with respect to the LVRT [5]. However, this method requires additional components, and dissipates a large amount of power during the fault condition. In research by [PERSON] and [PERSON] [6] an alternative approach for LVRT enhancement was proposed, by connecting the energy storage system (ESS) with the DCL to avoid excess energy being applied to the DC-link capacitor. However, this control method not only increases cost, but also requires frequent maintenance. The insertion of a series dynamic braking resistor (SDBR) improves the voltage sag by introducing impedance at the fault point [7]. This approach will enhance the LVRT capability of the PV system. However, the selection of the optimal resistance value for the SDBR is a challenging task. In [PERSON]'s work [8], an LVRT capability enhancement scheme for a hybrid PV-fuel cell system is proposed, in which a dump load is inserted to maintain an active power balance, DCL voltage, and grid currents within their limits under fault conditions. The dump loads used in the system will increase the power loss on the system in this method. In [PERSON] et al. [9], fault-current limiters (FLCs) are proposed to reduce DCL fluctuations. Additionally, a novel intelligent damping controller (NIDC) has been proposed for the static synchronous compensator (STATCOM) to enhance the transient stability of the hybrid power multi-system [10]. However, all of the above approaches involve additional hardware costs. Looking for alternatives to the above hardware-based approaches, several studies have been performed to augment the LVRT of SPV systems by modifying the control strategies. In [PERSON] et al. [11], an LVRT strategy based on positive and negative sequence control schemes is proposed for large-scale PV plants; however, the proper active power injection and the DC link over voltage control during a grid disturbance are not discussed widely. The active and reactive power control for grid balance of the PV system under a grid fault is proposed in the work by [PERSON] et al. [12], however the DC-link over-voltage is not considered. In [PERSON] et al. [13], an LVRT capability improvement strategy is proposed which is based on decreasing the output power delivery of the SPV system via controlling the DC-DC boost converter proportion compared to the level of voltage sag, so that the PV generation system can maintain the power balance during grid voltage differences. Simultaneously, the grid inverter delivers the specified reactive current to the grid according to the E.ON Netz GmbH code. However, the performance of the proposed control strategy in real environmental conditions, including variable irradiance and temperature, was not discussed.