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Introduction
Mining hydraulic excavators are widely used in mining and earthmoving operations owing to their compact structure, large driving force, and high production efficiency [1]. Under the dual background of severe energy crises and reduced carbon emissions, intelligent operation and energy saving of mining hydraulic excavators have received wide attention [2, 3]. Compared with traditional excavators, hybrid excavators have gained attention in the past decade because they can maintain the working points of engines and thus improve their economic performance. However, owing to the complex structure, difficult control, and limited efficiency of diesel engines, their energy-saving effects are limited. Currently, manufacturers favor pure electric-driven hydraulic excavators because of their better economic performance, lack of pollution, and easy control [4]. Furthermore, trailed-electric excavators are widely used because many open-pit mines and construction sites have power supply conditions [5].
The swing system can be optimized to further improve the energy efficiency of mining excavators. The current swing systems of mining excavators operate as follows: When mining excavators use a valve-controlled hydraulic motor system to drive a swing platform, the braking energy of swing platform is converted into heat energy through overflow loss, resulting in energy waste [6]. When mining excavators use a closed pump-controlled hydraulic motor system to drive a swing platform, part of the swing braking energy is recovered only when the other actuators and swing platform move simultaneously [7]. When the electric motor drives swing platform, the braking energy is quickly converted into electrical energy and returned to the common DC bus [8]. Therefore, based on an electric motor-driven main pump, an electric motor-driven swing platform for mining excavators is more conducive to energy-saving and intelligent operation [9]. However, excessive peak power and dramatic fluctuations in the DC bus voltage may result in temporary power outages, thereby affecting production [10].
To ensure that the DC bus voltage is maintained within a small range of variation and to reduce the peak power of the grid, Caterpillar proposed supercapacitors as electrical energy storage units that could effectively reduce peak power of the grid, reduce downtime, improve service life, and increase energy utilization [11]. In addition, scholars have applied electrical energy storage systems (ESSs) to many fields and conducted extensive research on their energy management strategies (EMSs), such...