外文翻譯--改善電磁閥和液力偶合器的控制(編輯修改稿)
2025-06-26 06:47 本頁面
【文章內(nèi)容簡介】 than with the intelligent control techniques. However, even though many solutions have been suggested [6], tuning a PIDcontroller still remains a difficult task, especially in systems where trail and error methods are not acceptable. A disadvantage of PIDcontrol is its restricted ability to acmodate system nonlinearities. The solenoid valve and drain coupling bination lends itself to the application of PID control. By controlling the switching of the valve, the motor/coupling torque could maintain a predetermined pattern. The system dead time is short enough not to contribute significantly to system nonlinearity, in which case PIDcontrol may be applied. The control equation is described as follows [7]: ? ? ? ? ? ? ? ? ? ? ? ?? ?[ 1 2 1 2 ]C s i d sT K E n E n T T E n T T E n E n E n? ? ? ? ? ? ? ? ? ? ? ? ? ? [1] where: E error, difference between set point and observed value T required torque change [Nm] Kc proportional gain Td derivative time constant [s] Tj integral time constant [s] Ts sample time constant [s] n sample number. Contrary to the conventional PID approach Eq. (1) determines the change required relative to the current torque (△ T) and not the amount of torque required as a function of the error. This is a quicker and more convenient way to determine the output, since no numeric integration or differentiation is required. The number n refers to the current error measurement, n –1 to the previous measurement and n 2 to the one before that. The time between measurements is critical. A too short sampling time can result in excessive equipment cycling, while a too long sampling time can result in overshoot and instability [8]. The constants Kc,Tj Td are originally determined theoretically according to the wellknown ZIEGLERNICHOLS method [6]. These values serve as a starting point from where further fine tuning was done experimentally. The effect of each of these constants on the controller’s performance has been described by SMITH [3] and can be summarised as follows [7]: A small value of Kc produces large overshoot but gives good stability, while larger values of Kc reduce the overshoot but increase equipment cycling. Small values of Tj eliminate constant errors quickly, but result in rapid cycling of control equipment. In turn, large values of Tj cause constant errors to occur. A small value of Td causes large overshoot, while a large value of Td increases the reaction time, which results in increased stability. Although the valve can only be switched on or off, it is still possible to control the switching as if it were a linearly varying valve by controlling the time for which it is switched on or off. By applying Eq. (2), △ T is converted to a duty cycle, which is defined as follows: Duty cycle = max 100[%]ontt ? [2] where: ont time for which the valve is switched on ( max0 ontt?? ) [s] maxt time between each sample which also represents maximum time for which the valve can be switched on during one interval (tmax = sT )[s]. In fact the conversion may be done in several ways ranging from a simple proportional relationsh
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