闭环控制系统(精选.)

闭环控制系统许多实时嵌入式系统使作出控制决策。

这些决策通常是由软件和基于硬件反馈的基础上由它控制（被称为机械）。

这些反馈通常采用的是模拟传感器，可以通过一个A / D转换器读取他形式。

例如：传感器可能代表位置，电压，温度或其他任何适当的参数。

每样提供软件和附加信息基础控制决策。

闭环控制的基本知识基于反馈原理建立的自动控制系统。

所谓反馈原理，就是根据系统输出变化的信息来进行控制，即通过比较系统行为（输出）与期望行为之间的偏差，并消除偏差以获得预期的系统性能。

在反馈控制系统中，既存在由输入到输出的信号前向通路，也包含从输出端到输入端的信号反馈通路，两者组成一个闭合的回路。

因此，反馈控制系统又称为闭环控制系统。

反馈控制是自动控制的主要形式。

自动控制系统多数是反馈控制系统。

在工程上常把在运行中使输出量和期望值保持一致的反馈控制系统称为自动调节系统，而把用来精确地跟随或复现某种过程的反馈控制系统称为伺服系统或随动系统。

反馈控制系统由控制器、受控对象和反馈通路组成。

比较环节，用来将输入与输出相减，给出偏差信号。

这一环节在具体系统中可能与控制器一起统称为调节器。

以炉温控制为例，受控对象为炉子；输出变量为实际的炉子温度;输入变量为给定常值温度,一般用电压表示。

炉温用热电偶测量，代表炉温的热电动势与给定电压相比较，两者的差值电压经过功率放大后用来驱动相应的执行机构进行控制。

同开环控制系统相比，闭环控制具有一系列优点。

在反馈控制系统中，不管出于什么原因（外部扰动或系统内部变化），只要被控制量偏离规定值，就会产生相应的控制作用去消除偏差。

因此，它具有抑制干扰的能力，对元件特性变化不敏感，并能改善系统的响应特性。

但反馈回路的引入增加了系统的复杂性，而且增益选择不当时会引起系统的不稳定。

为提高控制精度，在扰动变量可以测量时，也常同时采用按扰动的控制（即前馈控制）作为反馈控制的补充而构成复合控制系统。

一个闭环系统采用反馈来衡量实际的系统运行参数，如温度，压力，流量，液位，转速控制。

这种反馈信号发送回的地方是较理想的系统设定点控制器。

该控制器发一个误差信号，即启动纠正措施和驱动器输出设备所需的值。

在直流电动机驱动上很容易说明上述情况，转速表提供了一个反馈电压是成正比的实际运动速度。

闭环系统具有以下特点：1、一个参考或设定点的建立是所需的操作系统控制的周围。

2、过程变量反馈信号，“告诉”在什么时候该系统控制器实际运作。

3、一个控制器的比较与系统反馈，并生成一个误差信号，表示期望与实际点和系统运行的系统参考值的差额。

4、最后一个元素或控制机制是对系统的错误反应，使之达到平衡。

这个系统可能是一个气动控制阀，电子定位器，定位电机，可控硅或晶体管逆变器，一个加热元件，或其他控制设备。

5、系统优化要素，修改通过引入数学常数定制控制的具体应用，提供系统稳定的控制操作，并调整系统的响应时间。

在过程控制系统中的这些调整内容是：比例，积分和微分（PID）的功能。

在电子系统，如发电机电压调节器和马达驱动，典型调试整定包括：（1）增益，控制器的误差放大器，从而影响系统的稳定性和响应时间放大系数；（2）稳定性提供了一个时间延迟反馈的变化反应，以防止振动，并降低系统的“狩猎”；（3）反馈调整它控制的反馈信号，对体系的平衡设定点振幅；（4）升压这是在交流和直流电动机驱动器用来提供额外的低端扭矩；（5）红外补偿，提供了一个控制信号，对于IR降（电压降），其中在直流电机由于增加了电流通过电枢绕组电枢发生补偿。

反馈极性在闭环系统，反馈信号可以是再生（同相）或退化（内异相）。

再生反馈时存在的极性或相位关系的行为，是以援助或增加的主要控制信号来补偿。

如果反馈的幅度足够大或出现振荡发散（这是在无线电频率的振荡器操作中使用的主要）。

当在再生反馈控制系统，用这些在红外补偿，有过多的反馈效应，必须限制，否则将导致不稳定的情况。

退行性反馈另一方面，将挫伤振荡和生产体系的稳定。

在退化反馈，相位关系或反馈信号极性行为取消或降低有关的主要控制信号。

反馈极性是至关重要的和适当的反馈极性时，必须确定调试设备的单独控制和反馈装置组成。

这不是用一个包裹安装在一起，控制和反馈装置是预先作为一个完整的系统安装好的。

在直流电动机驱动器这个例子中，运算放大器作为一个总结逆变器配置的利用。

这种配置需要参考和反馈信号的极性相反，因为放大器的输出（误差）将是输入电压（这里参考数学总结是积极的反馈为负）。

当一个差分放大器使用时，参考和反馈将是相同的极性，因为放大器的输出（误差）将两个输入电压的数学差异。

一个开关控制的例子比例控制是主要的选择开关控制。

如果目前的工厂之间的输出，其所需的值（目前的错误）差异较大，软件也许应该改变驱动信号了很多东西。

如果错误是小，它应该改变它只是一点点。

换句话说，我们总是希望这样的变化：比例其中P是一个常数比例增益由系统的设计集。

例如，如果使用的PWM驱动信号，它可以采取介于0％和100％工作周期的任何值。

如果驱动器上的信号是20％占空比和输出误差在余下的则是小，我们可能只需要调整到18％或19％，达到该工厂所需的输出。

如果比例增益选择得好，当时的工厂需要达到一个新的设定值将尽可能短，超调（或冲），并尽量减少振荡。

不幸的是，单是没有比例控制在所有控制应用提供足够的。

一个或更多的响应时间，超调的要求，振荡可能无法履行其在任何比例增益设置。

单比例控制的最大问题是，你要达到新的预期值迅速减少，为了避免过冲和波纹。

建议迅速作出反应的高比例增益;尽量减少过冲和振荡，建议小比例增益。

实现在同一时间都可能无法在所有的系统。

幸运的是，我们通常有（或可以得出）对工厂的产量变化率的信息。

如果输出是变化很快，过冲有可能还在后面。

在这种情况下，我们可以减少比例，由比例控制器更改大小。

对一个信号的变化率也被称为及其衍生物。

在当前的时间导数是简单的价值从以前的样本改变目前的1。

这意味着，我们应该减去一个变化：微分其中D是一个不断衍生收益。

唯一的其他东西，我们需要做的是保存在内存中前面的示例。

在实践中，比例，微分（PD）的控制器工作。

最终的结果是一个具有超调量远低于比1比例控制器单独纹波较慢的响应时间。

积分剩下的一个问题是，PD控制本身并不能完全解决一直到所需的输出。

事实上，在不同的比例增益，这是完全可能的是，PD控制器将最终解决的输出值是远从理想。

出现该问题，如果每个单独的误差仍然低于比例部分起作用的起始值。

（你说的误差是3，P= 1 / 8，使用整数的数学。

）的导数项不会有什么作用，除非输出正在发生变化。

别的东西需要向驱动装置设定值。

这些是整体所必须的。

一个积分是随着时间的总和在这种情况下，在全厂上下过去的错误和输出，即使积分增益系数，我通常是小，一个持久的错误，最终导致数额增长较大，积分项强制在驱动器中信号的变化。

在实践中，积累误差通常是限制在一些最大和最小值。

总之，在开关和比例控制的两种闭环控制的基本技术中。

然而，衍生工具及/或整体而言，有时添加比例控制器，以改善某一植物的反应定性性质。

当所有三个名词一起使用，首字母缩写用来描述控制器的PID。

Closed Loop Control System Many real-time embedded systems make control decisions. These decisions are usually made by software and based on feedback from the hardware under its control (termed the plant). Such feedback commonly takes the form of an analog sensor that can be read via an A/D converter. A sample from the sensor may represent position, voltage, temperature, or any other appropriate parameter. Each sample provides the software with additional information upon which to base its control decisions.Basics of Closed-Loop ControlEstablished based on the feedback control system theory. The so-called feedback principle, in accordance with changes in the information system output control, that is, by comparing the system behavior (output) and the deviation between the expected behavior, and the elimination of bias in order to achieve the desired system performance. In the feedback control system, there was not only the signal from the input to output prior to the pathway, also contain input from the output to the signal feedback path, the two form a closed loop. Therefore, the feedback control system, also known as closed loop control system. Feedback control is the main form of control. Most of the feedback control system control system. In engineering often to run the expectations manipulation to output and consistent feedback control system, known as automatic adjustment system, to be used to accurately follow or replicate a process known as feedback control system or servo system .Feedback control system by the controller, the controlled object and the feedback path formed. More links, for subtracting the input and output, error signal is given. This link may be in specific systems, together with the controller, referred to as regulators. With temperature control, for example, the controlled object for the stove; output variables for the actual oven temperature; input variables for a given constant temperature, usually expressed with the voltage. Temperature measurement using thermocouples, on behalf of the thermal emf and the furnace temperature for a given voltage compared to the difference between the voltage through the power amplified to drive the corresponding actuator control. Compared with open loop control system,closed-loop control has a number of advantages. In the feedback control system, for whatever reason (external disturbances or changes within the system), as long as the amount of deviation from the specified value to be controlled, it will generate the appropriate control action to eliminate bias. Therefore, it can inhibit the ability of interference, not sensitive to the device characteristics and can improve the system's response. However, the introduction of feedback loops to increase the complexity of the system, but choose not to then the gain will cause system instability. To improve the control precision can be measured in the disturbance variables, they often also used by disturbance of the control (ie, feedforward control) as a supplement to constitute a feedback control complex control systems.A Closed-Loop system utilizes feedback to measure the actual system operating parameter being controlled such as temperature, pressure, flow, level, or speed. This feedback signal is sent back to the controller where it is compared with the desired system setpoint. The controller develops an error signal that initiates corrective action and drives thefinal output device to the desired value. In the DC Motor Drive illustrated above, the tachometer provides a feedback voltage which is proportional to the actual motor speed. Closed-Loop Systems have the following features：1.A Reference or Set Point that establishes the desired operating point around which the system controls.2.The process variable Feedback signal that “tells” the controller at what point the system is actually operating.3.A Controller which compares the system Reference with the system Feedback and generates an Error signal that represents the difference between the desired operating point and the actual system operating value.4.A Final Control Element or mechanism which responds to the system Error to bring the system into balance.This may be a pneumatically controlled valve, an electronic positioner, a positioning motor, an SCR or transistor power inverter, a heating element, or other control device.5.System Tuning Elements which modify the control operation by introducing mathematical constants that tailor the control to the specific application, providesystem stabilization, and adjust system response time. In process control systems these tuning elements are: Proportional, Integral, and Derivative (PID) functions. In electrical systems, such a generator voltage regulators and motor drives, typical tuning adjustments include:(1).Gain, the amplification factor of the controller error amplifier, which affects both system stability and response time;(2).Stability which provides a time-delayed response to feedback variations to prevent oscillations and reduce system “hunting”;(3).Feedback an adjustment which controls the amplitude of the feedback signal that is balanced against the system set-point;(4).Boost which is used in AC and DC motor drives to provide extra low-end torque;(5).IR Compensation which provides a control signal that compensates for the IR Drop (V oltage Drop) which occurs in the armature windings in DC machines due to increased current flow through the armature.Feedback PolarityIn closed-loop systems, feedback signals may be either Regenerative (in-phase) or Degenerative (out-of-phase). Regenerative feedback exists when the feedback polarity or phase relationship acts to aid or boost the main control signal. If the amplitude of the feedback is sufficiently large oscillations will be developed. (This is the principal used in the operation of radio frequency oscillators.) When regenerative feedback is used in control systems, such in the case of IR Compensation, the effect of excessive feedback must limited, otherwise instability will result.Degenerative feedback, on the other hand, will dampen oscillations and produce system stability. In degenerative feedback, the phase relationship or polarity of the feedback signal acts to cancel or reduce that of the main control signal.Feedback polarity is critical and proper feedback polarity must be determined when commissioning equipment which consists of separate control and feedback devices. This is not a concern to the installer of a packaged system where the control and feedback devices are pre-wired as a complete system.In the example DC Motor Drive, an operational amplifier configured as a summing inverter is utilized. This configuration requires that the reference and feedback signals be of the opposite polarity because the amplifier output (error) will be the mathematical sum of the input voltages (here the reference is positive and the feedback is negative). When a differential amplifier is used, the reference and feedback will be of the same polarity because the amplifier output (error) will be the mathematical difference of the two input voltages.An example of on-off controlProportional control is the primary alternative to on-off control. If the difference between the current plant output and its desired value (the current error) is large, the software should probably change the drive signal a lot. If the error is small, it should change it only a little. In other words, we always want a change like:Proportionwhere P is a constant proportional gain set by the system's designer.For example, if the drive signal uses PWM, it can take any value between 0% and 100% duty cycle. If the signal on the drive is 20% duty cycle and the error remaining at the output is small, we may just need to tweak it to 18% or 19% to achieve the desired output at the plant.If the proportional gain is well chosen, the time the plant takes to reach a new setpoint will be as short as possible, with overshoot (or undershoot) and oscillation minimized.Unfortunately, proportional control alone is not sufficient in all control applications. One or more of the requirements for response time, overshoot, and oscillation may be impossible to fulfill at any proportional gain setting.The biggest problem with proportional control alone is that you want to reach new desired outputs quickly and avoid overshoot and minimize ripple once you get there. Responding quickly suggests a high proportional gain; minimizing overshoot and oscillation suggests a small proportional gain. Achieving both at the same time may not be possible in all systems.Fortunately, we do generally have (or can derive) information about the rate ofchange of the plant's output. If the output is changing rapidly, overshoot or undershoot may lie ahead. In that case, we can reduce the size of the change suggested by the proportional controller.The rate of change of a signal is also known as its derivative. The derivative at the current time is simply the change in value from the previous sample to the current one. This implies that we should subtract a change of:Differentialwhere D is a constant derivative gain. The only other thing we need to do is to save the previous sample in memory.In practice, proportional-derivative (PD) controllers work well. The net effect is a slower response time with far less overshoot and ripple than a proportional controller alone.IntegrationA remaining problem is that PD control alone will not always settle exactly to the desired output. In fact, depending on the proportional gain, it's altogether possible that a PD controller will ultimately settle to an output value that is far from that desired. The problem occurs if each individual error remains below the threshold for action by the proportional term. (Say the error is 3, P = 1/8, and integer math is used.) The derivative term won't help anything unless the output is changing. Something else needs to drive the plant toward the setpoint. That something is an integral term.An integral is a sum over time, in this case the sum of all past errors in the plant output，Even though the integral gain factor, I, is typically small, a persistent error will eventually cause the sum to grow large and the integral term to force a change in the drive signal. In practice, the accumulated error is usually capped at some maximum and minimum values.In summary, on-off and proportional control are the two basic techniques of closed-loop control. However, derivative and/or integral terms are sometimes added to porportional controllers to improve qualitative properties of a particular plant's response. When all three terms are used together, the acronym used to describe the controller is PID.最新文件仅供参考已改成word文本。