# Design and Verification of a Modular Reconfigurable Test Platform for Electric Tractors
## 1 Introduction  
Traditional tractors with diesel engines emit pollutants, such as nitrogen oxide and particulate matter [1, 2]. To lower the levels of toxic exhaust, many manufacturers of agricultural equipment and researchers around the world have devoted considerable resources for developing electric tractors (ETs) to make them more environmental-friendly and energy-efficient [3]. Similar to electric vehicles, ETs can be divided into two main categories: hybrid electric tractors (HETs) and battery electric tractors (BETs). The HET uses two energy sources to propel the tractor. At present, one type of energy source is an engine supplied by fuel, and the other is a battery plus electric motor drive. In hybrid electric tractors, there are three configurations. The first is a series hybrid, where the engine provides electric power to the electric motor(s) driving the wheels and agricultural equipment, featuring an indirect mechanical connection with the propelling wheels and the power takeoff (PTO) shaft. However, it remains to be determined if this configuration can allow battery recharge from the electric grid and offer a significant range in the purely electric mode; its type of model is called a plug-in hybrid. Here, we regard the plug-in hybrid as a special type of series hybrid. The second is a parallel hybrid, where the engine and the electric motor(s) are mechanically connected with a mechanical coupling device (e.g., a fixed-gear set and a planetary gear set), allowing the components to directly supply their torque to the driving wheels or PTO shaft. The third is a series-parallel hybrid, which combines the series and parallel hybrid configurations into one package and allows one to change the powertrain configuration from series to parallel via the engagement or disengagementof one or two clutches, and vice versa. BETs are propelled only by their onboard electric motor(s), which are powered by the battery (recharged from the power grid). According to the number of drive motors, BETs can be classified into three categories: (i) single-motor drive, (ii) dual-motor drive, and (iii) four-motor drive (called all-wheel-drive). In recent years, scholars have investigated the powertrain configurations of ETs by building test benches or fabricating prototypes. For a BET with the single-motor drive system, [PERSON] et al. [4; 5; 6] studied the drive force and transmission efficiency characteristics of a mini tractor with a rated power of 5 kW by developing a BET test bench composed of a series direct current (DC) motor, a magnetic powder brake, and a measurement control system. To study the electric energy consumption of tractors used in a greenhouse, a battery-electric tractor prototype with a single-motor drive system was fabricated and studied via a performance trial in [7]. To research the characteristics of small and medium-sized tractors used in hilly and mountainous areas, [PERSON] et al. [8] proposed a test platform with a three-axis direct-connected electric drive system to conduct experiments, including tests of the external characteristics transmission efficiency, noise, and reliability. Test benches and prototypes of single-motor drive systems for tractors can also be found in [9; 10; 11; 12] and allow one to study the electric efficiency characteristics under different farming operations. Furthermore, each configuration has variable architectures of the powertrain in terms of the inclusion of hybrid electric tractors and BETs in multi-motor drive powertrains. For hybrid electric powertrains, [PERSON] et al. [13; 14; 15] proposed a coupling device suitable for the requirements of farming operations, using the concept of a power-split from parallel hybrid electric vehicles as a reference to design a parallel hybrid tractor test bench to verify the performance of the coupling device.