## 1 Introduction  
In large wind turbine systems, stable control of power output cannot be achieved solely by the generator. This necessitates the use of efficient variable pitch control technologies. Variable pitch systems are mainly divided into three types: electric motor-driven, hydraulic cylinder-driven, and hydraulic motor-driven [1]. Among these, hydraulic cylinder variable pitch systems using servo valves for control have become increasingly sophisticated through prolonged research and development. [PERSON] et al. systematically analyzed the evolution and advantages of hydraulic pitch systems [2]. [PERSON] et al. investigated the impact of pitch control on wind turbine load reduction [3]. However, traditional hydraulic systems suffer from significant overflow losses and poor pollution resistance, as documented by [PERSON], [PERSON] et al. [4]. To address these challenges, servo pump control systems have emerged as a promising alternative. These systems operate by coaxially connecting a servo motor to a fixed-displacement pump, which directly drives a hydraulic cylinder [5; 6]. This configuration offers several distinct advantages. [PERSON], [PERSON] et al. demonstrated that controlling the flow rate through servo motor speed adjustment significantly reduces energy losses compared to valve-controlled systems [7]. [PERSON], [PERSON] et al. quantified these efficiency improvements through comprehensive experimental studies [8]. [PERSON], [PERSON] conducted an analysis of energy losses in hydraulic systems using CFD methods, further validating these findings [9]. The closed-loop design of servo pump control systems brings additional benefits. [PERSON], [PERSON] et al. compared a novel self-contained electro-hydraulic cylinder with traditional valve-controlled actuators, demonstrating through experiments that the former saves 62% energy in a typical work cycle and exhibits excellent energy recovery capabilities [10]. [PERSON], [PERSON] et al. designed a variable-displacement bi-directional pump-controlled electrohydraulic system, improving the system's energy efficiency by directly controlling the pump with a variable-speed motor and achieving significant energy savings in simulations [11]. [PERSON], [PERSON] investigated energy losses in hydrostatic drives with hydraulic cylinders and proposed methods to reduce energy losses in proportional control systems, thereby enhancing the overall energy efficiency of the system [12]. [PERSON], [PERSON] and [PERSON], [PERSON] et al. developed a high-efficiency electrohydraulic actuator with energy regeneration capabilities, with the experimental results showing that the system's energy efficiency can reach up to 84.7% and recover up to 81.8% of the actuator's energy during the auxiliary phase [13]. [PERSON], [PERSON] et al. optimized motor control strategies to reduce energy losses and avoid the use of expensive variable-displacement pumps, further enhancing the system's energy efficiency [14]. These studies collectively demonstrate that pump-controlled systems can achieve both energy efficiency and reliable operation simultaneously. However, implementing servo pump control in wind turbine pitch systems faces several significant challenges. [PERSON] et al. observed that pump-controlled systems exhibit pronounced nonlinearities in pump flow mapping and mechanical dynamics, which they addressed using an adaptive compensation approach [15]. [PERSON] and [PERSON] pointed out that an electro-hydraulic servo system involves complex interactions between valves and pumps, with nonlinearities and clearances that can reduce control accuracy and system stability. They proposed a clearance compensation method using a Hopfield neural network to address these nonlinear issues, enhancing system stability and accuracy by adjusting neural network parameters [16]. Additionally, [PERSON], [PERSON] et al.