Contents I. Introduction
With the increasing enhancement of emission standards for non-road mobile machinery by the government, the emphasis on energy conservation and emission reduction in construction machinery has grown significantly. As a result, the development and application of electric forklifts have gradually gained attention [1]. The hydraulic lifting system of forklifts is typically controlled by valve control or pump control systems [2]. Pump control systems have higher efficiency compared to traditional valve control systems but may suffer from low responsiveness and unstable control issues [3]–[7]. Pump-controlled systems can be broadly classified into volumetric pump control speed regulation and variable speed pump control speed regulation. Among them, variable speed pump control can better leverage the excellent control performance of the motor [8]. To enhance the output performance of variable speed pump control, numerous scholars have conducted research in this area. Pasca introduced a PID upper output limit to the variable displacement pump control, thereby reducing system overshoot, fluctuations, stabilization time, and average absolute error [9]. Wei improved the PID parameters using a combined adaptive speed tracking control strategy involving NNMRAC, SOA, fuzzy control algorithm, and PID controller. The performance of this strategy was then compared with traditional speed control strategies like PSO-PID and GA-PID. As a result, the average overshoot of the output speed for a fixed-displacement motor was reduced by approximately 23.2%, and the steady-state settling time was shortened by around 30.1% [4]. Ye conducted a comparison in the pump-controlled hydraulic walking system, evaluating state chart module control, Z-N frequency response PID control, and a PID parameter self-tuning method based on genetic algorithms (GA). This study concluded that the PID parameter self-tuning control based on the backpropagation (BP) algorithm showed no overshoot. Additionally, the time required for the PID parameter self-tuning control based on BP algorithm to achieve dual motor synchronous speed was 36.55%, which is shorter than that of the GA self-tuning PID controller. As a result, dual-motor reached the target speed synchronously in a shorter duration, leading to smooth operation of the hydraulic system [10]. Zhang installed an accumulator in the hydraulic system, which is significantly reduced the starting and braking time of the power unit, as well as the startup power demand [11]. However, the current control of pump-controlled systems primarily targets issues related to control performance, such as excessive overshoot, low responsiveness, and unstable control, while limited emphasis on optimizing the electric motor control algorithms themselves.
