_Article_  
Coordinated LVRT Control for a Permanent Magnet Synchronous Generator Wind Turbine with Energy Storage System  
[PERSON] 1, [PERSON] 2, [PERSON] 3 and [PERSON] 4,*(c)  
1 Department of AI Electrical Engineering, Pai Chai University, Daejeon 15540, Korea; [EMAIL_ADDRESS]  
2 Automation & Control Section, Department of Electronic Systems, Aalborg University, 9220 Aalborg East, Denmark; [EMAIL_ADDRESS]  
3 School of Electrical Engineering, Shandong University, Jinan 250061, China; [EMAIL_ADDRESS]  
4 School of Energy Systems Engineering, Chung Ang University, Seoul 06974, Korea  
* Correspondence: [EMAIL_ADDRESS]; Tel.: +82-02-820-5928 check for updates  
Received: 25 March 2020; Accepted: 22 April 2020; Published: 28 April 2020  
This study introduces a coordinated low-voltage ride through (LVRT) control method for permanent magnet synchronous generator (PMSG) wind turbines (WT) interconnected with an energy storage system (ESS). In the proposed method, both the WT pitch and power converters are controlled to enhance the LVRT response. Moreover, the ESS helps in regulating the dc link voltage during a grid fault. Previous LVRT methods can be categorized into strategies with or without an additional device for the LVRT. The latter scheme is advantageous from the perspective of no additional installation cost; in this case, pitch and converter controllers are used. Meanwhile, the former method uses an additional device for LVRT operation and hence, involves additional expense. However, it can effectively enhance the LVRT response by reducing the LVRT burden on the WT. Moreover, the additional device can be used for various WT power control applications and it is common that the ESS is interconnected to the WT for multiple objectives. Previous studies focused on these two aspects separately; hence, a method of coordinated control for an ESS and a WT is needed as more ESSs are required to connect to WTs for flexible wind power operation. The proposed method introduces a control method with different LVRT modes considering the ESS state of charge (SoC). When the WT does not have a sufficient inertial response operation range, the ESS reserve energy capacity is required for LVRT operation. This coordinated LVRT method employs both the WT and ESS controls when it is hard to handle the LVRT using the WT control alone at high wind speeds. In this case, power curve analysis is used to obtain the appropriate power reference during the fault period. In addition, a power reference is also used to ensure a safe operation. Using the proposed method, an ESS can be operated in a manner that is appropriate for WT operation, especially at high wind speeds. To validate the effectiveness of the proposed method, we considered two case studies. One study compares the LVRT response between the WT itself and the proposed method. The other research work compares the response of the conventional LVRT method that uses a WT and an ESS and with that of the proposed method. From these case studies, we concluded that the proposed method achieved a better performance while operating within the constraints of the WT rotor speed and ESS SoC limits.  
**Keywords:** coordinated controller; energy storage system; low voltage ride-through; pitch control; inertial response; wind turbine