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Electrohydraulic Systems Control
Published in Qin Zhang, Basics of Hydraulic Systems, 2019
The key difference between an open-loop and a closed-loop controller is that the open-loop does not use a feedback but the closed-loop does. As illustrated in Figure 9.2(b), a closed-loop control system measures the current system output, compares it with the set point, and alters the control action if there is an error keeping the output as close to the set point (the input) as possible. In other words, a closed-loop control system is a self-adjusting system as the output data flows back to the starting point of the control system, often through a specific amplifier to convert the measured output data to the same form as the control system input, making the controller adjust accordingly to minimize the error between expected and actual outputs. Closed-loop controls could be a better choice when (1) measurement of the output is feasible; (2) the process has a certain degree of predictability; (3) the system may become unstable; and (4) the output is sensitive to external disturbances. Systems requiring accurate control of their output normally use closed-loop control.
Closing the Loop
Published in Richard J. Jagacinski, John M. Flach, Control Theory for Humans, 2018
Richard J. Jagacinski, John M. Flach
A solution to this control problem is to use a closed-loop controller. A closed-loop controller is one that monitors its own behavior (output) and responds not to the input, per se, but to the relation between the reference input (e.g., desired temperature) and the output. This capacity to respond to the relation between reference input and output is called feedback control. Figure 2.2 shows a negative feedback control system. The output in this system is fed back and subtracted (hence negative) from the input. The attender then operates on the difference between one set of inputs and the output. This difference is called the error and the inputs that are compared to the output are generally referred to as the reference, or command, inputs. Those inputs that enter to the right of the attender are referred to as disturbances.
Introduction to Mechatronic Systems
Published in Bogdan M. Wilamowski, J. David Irwin, Control and Mechatronics, 2018
An open-loop controller is the simplest controller that computes its input into a system using only the current state. Open-loop control is useful for well-defined systems where the relationship between the input and the resultant state can be modeled by a mathematical formula. However, the varied dynamic characteristics of a real controlled system resulting in the feedback of error based on direct measurable input and output signals is essential to avoid the problems of the open-loop controller. Closed-loop controllers have several advantages over open-loop controllers, such as disturbance rejection, guaranteed performance even with model uncertainties, higher stability, reduced sensitivity to parameter variations, and improved reference-tracking performance. A common closed-loop controller architecture is the PID controller, which is appropriate when the process or system is linear and time invariant. It looks at the current value of error, the integral of the error over a recent time interval, and the current derivative of the error to determine not only how much of correction to apply but for how long. In summary, the proportional controller is capable of reducing the rise time, but never of eliminating the steady-state error. The integral action contributes to the effect of eliminating the steady-state error, but it may make the transient response worse. The derivative function induces the effects of increasing the stability of the system, reducing the overshoot, and improving the transient response.
Application of CS-PWM rectifier for the operation and control of wind-driven generators
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Mahaboob Subahani Akbarali, Senthilkumar Subramaniam, Kumaresan Natarajan
Keeping a constant DC output voltage of 220 V at the rectifier output terminals the performance of the entire system for different values of DC power output (Pdc) was simulated for a speed of 1500 rpm. Figure 9(a) shows variations of generator terminal voltage, generator line current, rectifier input current, capacitor line current, DC load voltage, and current for a step increase in output power from 800 W to 1600 W. During this change in power output, an increase in the rectifier input current was observed with sinusoidal shaping of the waveform. A slight decrease in the generator terminal voltage and an increase in generator line current were observed, yet the closed-loop controller maintains the DC load voltage constant. Also, the system performance is verified for a step decrease in load from 1600 W to 800 W and the results are shown in Figure 9(b).
FPGA-based closed-loop monitoring and control of doubly fed induction generator with single inverter and battery for wind energy conversion
Published in Australian Journal of Electrical and Electronics Engineering, 2018
K. A. Nikhil, P. Bharath Chandra, M. R. Jawahar, S. Moorthi, M. P. Selvan, N. Kumaresan
Figure 10(a) shows the variation of the electrical quantities for a change in speed. Initially, the stator voltage and frequency of the system has been brought to 415 V, 50 Hz at a speed of 1200 rpm. After setting the stator voltage and frequency to 415 V, 50 Hz at 1200 rpm, experiment has been done on DFIG for the speed change of 1200–1260 rpm with the same load resistance. As the speed increases, the air-gap voltage momentarily increases which in turn increases the stator voltage. The frequency of the stator voltage also increases instantly, which is controlled by change in frequency at rotor side. The stator voltage has been brought to set value by the closed-loop controller within seconds. Similar experiment has been conducted for a change in speed from 1260 rpm to 1190 rpm which is depicted in Figure 10(b).
Optimal robust state-feedback control of nonlinear systems: minimal time to target
Published in International Journal of Control, 2021
An example provided in Section 6 demonstrates the superiority of optimal feedback controllers. In this example, an optimal closed-loop controller achieves a significantly shorter time-to-target than an optimal open-loop controller. In addition, the outcome of optimal closed-loop control is less sensitive to uncertainties and errors present in the controlled system's model, thus providing more robust performance than the performance achieved by an optimal open-loop controller.