基于myRIO的电动拖拉机驱动控制器设计与室内试验

由于传统的内燃机拖拉机污染严重,噪音大,不适合工作在温室大棚等空间封闭狭窄的场合,开发小型电动拖拉机的需求变得日益迫切。设计了一种小型电动拖拉机用的永磁直流无刷电动机控制器,该控制器以myRIO为控制核心,智能化程度高,满足电动拖拉机运输、作业时多种动力工况要求。控制器外围电路包括MOSFET(metal-oxide-semiconductor field-effect transistor,金属-氧化物半导体场效应晶体管)功率放大、栅极驱动、电流保护、低电压保护和温度保护等电路。运用Lab VIEW/FPGA图形化编程环境,编写了ARM实时处理器控制流程和FPGA(field-programmable gate array,现场可编程门阵列)I/O驱动程序,软件由启动、驱动、欠压保护、过流保护、过热保护等子VI程序组成。通过样机试验表明,电动拖拉机工作正常,空载时启动电流为120 A,带载时启动电流为164 A,驱动时序符合直流无刷电动机要求。该设计方案解决了驱动控制器开发困难的问题,为电动拖拉机智能化的发展提供了参考。

Motor controller design and indoor experiment for electric tractor based on myRIO

Abstract: It is well known that off-road vehicles contribute a huge amount of pollution to air, and studies have shown that renewable electric vehicles (EVs) decrease petroleum consumption and consequently reduce criteria emissions under nearly all circumstances. Diesel tractors exhaust CO, NOx PM10 and pollutants that are harmful to human body. As a consequence, diesel tractors are not allowed to work in some limited and closed environments such as greenhouse. It is imperative that a kind of small electric tractor with less noise, zero emission and more comfort should be developed with the least delay. A brushless direct current (BLDC) motor drive is characterized by higher efficiency and lower maintenance. Therefore, it is necessary to have a low-cost but effective BLDC motor controller. This research develops a new low-cost method for the design of BLDC motor controller and designs a BLDC motor controller for a small electric tractor. The BLDC motor controller includes cybernetics core and controller peripheral circuits, and modular design idea is proposed. The advanced intelligent controller uses the myRIO as a cybernetics core, and the myRIO uses the latest Zynq technology from Xilinx, which features an FPGA integrated with a processor running a real-time OS that can meet the requirements of intelligent control for electric tractor. The myRIO is coupled with an onboard accelerometer, programmable LEDs (light emitting diodes) and analog and digital I/O, and USB port helps modular design ideas come to life. The controller peripheral circuits include power amplifier MOSFET gate drive, current protection, low voltage protection and temperature protection, which meet the tractor's transportation and working demands under different power conditions. Programs are developed in real-time processor ARM and I/O driver software in FPGA to the control flow in graphical programming environment. Main control and protection algorithms run in real-time OS; at the same time the driving timing sequence algorithms run in FPGA, and the algorithms with 2 different execution rates are isolating. In this way, it not only reduces the real-time processor's load, but also improves the accuracy and reliability of the controller. The software includes starter, driving, low-voltage protection, overcurrent protection, thermal protection and other sub-VI programs. The electric tractor prototype tests show that BLDC motor controller works properly with maximum starting current 120 A under zero load condition and 164 A under loaded condition with overcurrent detection. Under starting condition, after performing several experiments, when duty cycle of the PWM signal is set as 60% and the frequency is set as 10 kHz in initial stage, the better motor starting torque can be obtained, and amplitude of starting current is also limited. The sequence of motor drive voltages meets the requirement of the BLDC motor excellently with the help of hall position sensors. It is concluded that the modular design idea of developing a BLDC motor controller that combines cybernetics core and controller peripheral circuits is practicable. In the whole testing process, the disadvantage of the impact force does not exist, and less vibration and lower noise make the tractor driver more comfortable when it is working. The design proposal combining myRIO as control core and peripheral circuit solves the difficult problems of developing drive controller, it promotes the development of the intelligent electric tractor.