###### Abstract  
Modular multilevel converter (MMC)-based VSC system has become attractive around the world for renewable energy integration. Instead of a dynamic braking resistor, this work proposes an active power reduction technique for PV systems to support the fault ride through (FRT) of the MMC-HVDC system. In addition, it develops a battery control strategy to improve transient performance during solar radiation and temperature change due to partial shading of the PV panels. Besides, a control technique for the battery to regulate the surplus energy in the HVDC transmission network is developed. Furthermore, the proposed control scheme optimally integrates solar energy using the modified incremental conductance method. A feedforward controller was employed to create a standalone AC grid. The complete system has been implemented in real-time digital simulation (RTDS). The results confirm the efficacy of active power reduction technique to protect the HVDC link voltage and battery control strategy for the improvement of transient performance during the irradiance and temperature changes. Besides, it improves the low voltage ride-through capability during balanced and unbalanced disturbances at the point of common coupling. MMC detailed model; modified incremental conductance method; PV; active power reduction; battery; balanced fault; unbalanced fault +
Footnote †: journal: Applied Physics Letters  
_Applied Physics Letters_  
Due to the advancement in the semiconductor switch and converter design over the decades, the HVDC transmission system has become attractive for renewable energy integration. Besides, the VSC-HVDC system has the ability of asynchronous interconnections, no issue of sub-synchronous resonances, reactive charging current and skin effect, ability to resist the AC fault propagation, real and reactive power controllability, and power reversal capability without changing voltage polarity [4; 5]. Low loss and modular characteristics have made the modular multilevel converter (MMC) attractive for remotely located renewable energy interconnection over the HVDC line [6; 7; 8]. Due to a large number of submodules, MMC produces almost ideal sine wave voltage. It significantly reduces harmonic pollution at the point of common coupling and minimizes the cost of filtering. Like AC system, MMC-HVDC system also suffers a stability problem due to faults at the point of common coupling of AC grids if proper action is not taken. Series-connected resistor-based bridge type fault current limiter has been discussed for a two-level VSC-HVDC system to mitigate different kinds of faults in [9; 10]. However, this approach keeps a large number of semiconductor switches turned on at normal operating conditions, resulting in continuous conduction loss. The unbalanced fault analysis has been carried out for offshore energy-connected HVDC systems [11; 12]. However, the detailed model was not considered, and no experimental result was presented in [11; 12]. As the fault at the point of common coupling reduces the converter capability to deliver power, HVDC link voltage could go beyond its threshold. Fast communication-based centralized control, power reduction, power-sharing, and coordination among the converter stations have been discussed in [13; 14; 15; 16]. Nevertheless, it requires a large bandwidth for communication and a reliable system. The active current is reduced from the wind turbine by controlling the electrical torque, which in turns reduces the overall electrical power injection [17; 18; 19]. However, response time is slow and not appropriate to mitigate the fast energy build up in the HVDC link during a fault in the AC side. The wind power is also reduced by detecting the grid frequency over the high bandwidth communication link during the fault [18]. The offshore wind farm output power could be reduced by decreasing the modulation index of the converter, which results in a significant reduction of power but a maintained converter-rated current [20].