## 1 Introduction  
Late in the last century, in order to meet the needs of deep-water gas and oil exploitation, subsea equipment suppliers began to develop and improve the all-electric subsea control technology [1]. The all-electric Subsea Production Control System (AE), a leading-edge and breakthrough technology, which didn't need hydraulic fluid and was driven completely by electric power, was proposed and developed [2]. The key benefits of the AE system compared to the conventional Multiple Electric-Hydraulic Control System (MEH) are as follows [3; 4; 5; 6; 7; 8; 9; 10]: the simplified system structure, enhanced control performance, improved system reliability and availability, increased the oil recovery factor and environmental friendliness. Furthermore, the advantages of AE system also include: the decreased power consumption [11; 12], reduced Capital expenditure(CAPEX) and Operatingexpenditure(OPEX) [13; 14; 15; 16], strengthened intelligence [17; 18]. Therefore, with the improvement of key techniques of the AE system, the AE system will replace the MEH system as a trend in the future [19; 20; 21]. The all-electric subsea gate valve actuator is one of the critical components of the AE system [6; 7], which is used to open and close the production gate valve for the subsea Xmas tree. Its performance directly affects the reliability and safety of the AE system. Similar to the traditional hydraulic-driven subsea gate valve actuator, in the opening and closing processes of the valve, the all-electric subsea gate valve actuator is required to have a failsafe close ability, Remotely Operated Vehicle(ROV) override function, subsea ambient pressure compensation and valve position indication [22; 23]. The all-electric subsea gate valve actuator uses the motor as the actuation unit, and the service life cycle of the motor is lower than that of the hydraulic cylinder. Therefore, to ensure the high reliability of the actuator, the actuation device should be designed with regard to redundancy [24]. In addition, the subsea gate valve is a normally open valve. When the valve is opened, the power system needs to resist the resilience of the failsafe closing mechanism, which consumes a lot of energy in long term operation [25]. Thus, to reduce the energy consumption, the low-power holding mechanism is required for the all-electric subsea gate valve actuator to ensure that the valve remains open with small power consumption. The research and development of all-electric subsea gate valve actuators are in the early phase. A few oil companies like Cameron and FMC have carried out relevant research on it. Cameron's all-electric subsea gate valve actuator realized the opening and closing operation of the subsea gate valve through a high-power \"drive\" motor, and was equipped with a low-power \"clutch\" motor to ensure that the valve remained open by means of a friction-based mechanism. Further, a closing spring was used as the failsafe close solution [6; 7]. FMC's all-electric subsea gate valve actuator powered the built-in motion control system via locally stored power from rechargeable batteries and capacitors to open and close the subsea gate valve and was equipped with the ROV interface. No springs were required to move a valve to a failsafe position [8; 11]. At present, the all-electric subsea gate valves actuator of each oil company are still in the initial application stage, and the key technology of has not yet matured. [PERSON] [26] developed a functional design specification for the all-electric subsea gate valve actuator and proposed a design for an all-electric subsea gate valve actuator, as well as the motor control system layout based on the specification. [PERSON] [27] discussed failsafe solutions of the all-electric subsea gate valve actuator and created the calculation method of the peak load and the applied torque of the actuator. [PERSON] [24] proposed the multi-motor parallel redundant method to drive the valve and designed the structure of an all-electric subsea valve actuator.