杜怿, 孙旭, 孙延东, 肖凤, 朱孝勇, 毛怡, 严序康. 电动拖拉机PC-DSPM电机电子变极策略与分析[J]. 农业工程学报, 2023, 39(8): 44-53. DOI: 10.11975/j.issn.1002-6819.202212084
    引用本文: 杜怿, 孙旭, 孙延东, 肖凤, 朱孝勇, 毛怡, 严序康. 电动拖拉机PC-DSPM电机电子变极策略与分析[J]. 农业工程学报, 2023, 39(8): 44-53. DOI: 10.11975/j.issn.1002-6819.202212084
    DU Yi, SUN Xu, SUN Yandong, XIAO Feng, ZHU Xiaoyong, MAO Yi, YAN Xukang. Electronic pole-changing strategy and analysis for PC-DSPM motor in electric tractors[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2023, 39(8): 44-53. DOI: 10.11975/j.issn.1002-6819.202212084
    Citation: DU Yi, SUN Xu, SUN Yandong, XIAO Feng, ZHU Xiaoyong, MAO Yi, YAN Xukang. Electronic pole-changing strategy and analysis for PC-DSPM motor in electric tractors[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2023, 39(8): 44-53. DOI: 10.11975/j.issn.1002-6819.202212084

    电动拖拉机PC-DSPM电机电子变极策略与分析

    Electronic pole-changing strategy and analysis for PC-DSPM motor in electric tractors

    • 摘要: 针对田间作业和转场运输等不同工况时的行驶速度需求,该研究提出使用双凸极变极永磁(pole-changing doubly-salient permanent magnet,PC-DSPM)电机作为电动拖拉机的驱动电机,通过变极获得驱动电机的多种机械特性。基于气隙磁场调制理论,将PC-DSPM电机气隙磁场中的主要工作谐波分为2组,采用电子变极改变电枢绕组连接方式,从而选择不同组别的气隙磁场谐波参与机电能量转换,形成PC-DSPM电机3种运行模式。根据不同模式下的转矩-转速曲线,选取电机在恒功率区的2个变极切换点,并据此将拖拉机的运行速度划分为0~7.7、7.7~10.5和10.5~32.7 km/h共3个区间。为实现平滑变极,构建自抗扰控制和跟踪微分器的PC-DSPM电机变极策略。与采用自抗扰控制的阶跃响应变极相比,虽然2个切换点处的变极时间分别延长至400和600 ms,但变极过程中dq轴电流过渡平稳,转矩波动分别下降8.5%和11.8%,转速恒定在920和1 250 r/min。研究结果可为实现电动拖拉机多工况高效运行及变极永磁电机平滑切换提供理论参考。

       

      Abstract: Abstract: Benefiting from driving by an electric motor, an electric tractor is one of the most effective means to realize green agricultural production with high efficiency, zero emission, and low noise. The field and road operating conditions can usually occur in electric tractors. Specifically, the typical speed of the former is 2-7, and 7-10 km/h, whereas, the latter is mainly used in the condition of transportation with the speed of 20-35 km/h. The speed of an electric tractor can be in the discrete form in the very wide range of speed regulation. In this study, a pole-changing doubly-salient permanent magnet (PC-DSPM) motor was proposed using the PC operation. Different output characteristics were also obtained to meet the special operation of electric tractors. The working components were firstly selected as the 2, 4, 10, and 16 pole-pairs harmonics with the higher amplitude, according to the general air-gap field modulation. Then, four working harmonics were divided into two groups, in terms of the slot pitch angles. As such, the coil electromotive force (EMF) phasor graphs under the working harmonics of Group 1 were totally different from that of Group 2, in order to achieve the PC operation using different winding connections. Three kinds of armature winding connections were then designed using the coil EMF phasor graphs. Thus, three operating modes of the PC-DSPM motor were achieved to select one or two groups of working harmonics in the electromechanical energy conversion using the filtering effect of armature winding. Two PC switching points were determined in the constant power region with the mechanical characteristic curves of the PC-DSPM motor under three modes. The motor speed was divided into low (0-920 r/min), medium (920-1 250 r/min), and high speed (1 250-3 900 r/min). In terms of the gear-box with a fixed ratio of 18 and the wheels with a diameter of 0.8 m, the speeds of electric tractors in the three modes were 0-7.7, 7.7-10.5, and 10.5-32.7 km/h, respectively, in order to meet the speed demands of field and road operations. Furthermore, an electronic PC method was proposed to change the current angles and the armature winding connection for continuous PC operation. Two sets of three-phase windings were controlled by a six-leg inverter under the dual three-phase control theory. The current angle in each coil was then controlled independently. Active disturbance rejection control (ADRC) was designed in the current loop of the control system for the PC-DSPM motor. The real-time disturbance was reduced and then suppressed during the PC process. In addition, a tracking differentiator (TD) was also used to arrange the switching of the current angle. The current was smoothed without overshoot after arrangement. The simulation and experimental analysis of the PC-DSPM motor were performed at the first PC switching point (920 r/min, 4.75 N·m), and the second one (1 250 r/min, 3.4 N·m). The operation transitions were shifted from mode Ⅲ to Ⅱ, and the mode Ⅱ toⅠ in the PC-DSPM motor under the current phase. The performances during TD-based electronic PC operation using ADRC were compared with the traditional step response. The current loop of the latter also adopted the ADRC strategy, indicating the better performance of TD electronic PC. The results showed that during the PC processes at the first switching points, although the PC transient time were prolonged to 400 ms when the tracking differentiator electric PC strategy was adopted, the switching of current in d-axis presented a smooth trend from 3.6 and 3 A to 4.6 and 0.2 A, and current in q-axis also presented a smooth trend from 2.7 and 3.2 A to 1.5 and 4.7 A. Similarly, the PC transient time were prolonged to 600 ms when the tracking differentiator electric PC strategy was adopted at the second PC switching point, but the switching of current in d-axis presented a smooth trend from 4.2 and 1.2 A to 0.2 and 4.2 A, and current in q-axis also presented a smooth trend from 0.2 and 4 A to 4 and 0.2 A, respectively, so that the torque ripple of PC-DSPM motor were reduced 8.5% and 11.8%, respectively, compared with those of the step PC method. Thus, the speed of motor can be stable at 920 and 1 250 r/min. The research provided a better solution to expend speed range for field operations and road operations of electric tractors and realize a smooth PC switching of PC permanent magnet motors.

       

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