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Electric Machines
Published in Patrick Hossay, Automotive Innovation, 2019
A better approach is offered by a modern digital control method called pulse width modulation (PWM). The core of PWM is essentially a switch that can turn a signal off and on very quickly. By accurately controlling the amount of time the signal is on as a percentage of the total cycle, called duty cycle, and the frequency of the cycle, we can create an output that behaves like a precisely defined constant voltage. So, while the signal behaves like low voltage, it is in fact a very rapid succession of full-voltage pulses. As a result, power loss is small, though loss still occurs during the actual switching, called switching loss, but this can be reduced with improved control logic. Essentially, the goal of all this is to digitally encode a precisely modulated analog signal. To get a particular speed at a given load, a simple lookup table can be used to define the PWM duty cycle needed to produce the targeted motor speed (Image 4.11).
An Introduction to Control Systems
Published in Arthur G.O. Mutambara, Design and Analysis of Control Systems, 2017
Discrete data control systems differ from continuous-data systems in that the signals at one or more points of the system are in the form of either a pulse train or a digital code. Usually, discrete-data control systems are subdivided into sampled-data and digital control systems. Sampled-data control systems refer to a more general class of discrete-data systems in which the signals are in the form of pulse data. A digital control system refers to the use of a digital computer or controller in the system, so that the signals are digitally coded, such as in binary code. In general, a sampled-data system receives data or information only intermittently at specific instants of time. A sampled-data system can also be classified as an AC system since the signal of the system is pulse modulated.
Sensor Systems in Engineering
Published in Clarence W. de Silva, Sensor Systems, 2016
In digital control, a digital computer (e.g., a microcontroller) serves as the controller. Virtually, any control law may be programmed into the control computer. Control computers have to be fast and dedicated machines for real-time operations where processing has to be synchronized with plant operation and actuation requirements. This requires a real-time operating system. Apart from these requirements, control computers are basically not different from general-purpose digital computers. They consist of a processor to perform computations and to oversee data transfer, memory for the storage of programs and data during processing, mass-storage devices to store information that is not immediately needed, and input or output devices to read in and send out information (i.e., for interfacing with other components of the control system).
Predicting the effects of task jitter in digital control systems
Published in Australian Journal of Electrical and Electronics Engineering, 2022
Long Tran, P. J. Radcliffe, Liuping Wang
Digital control systems have largely supplanted analogue controllers due to their key advantages such as low cost, high accuracy, flexibility, and reliability (Santina and Stubberud 2010a). A digital controller requires a sampler to convert the continuous signal to a discrete signal (Feuer and Goodwin, 2010) then apply the control law in the digital domain. Modern digital controllers often include an operating system and are empowered to process multiple tasks each with its own schedule. This schedule may vary according to the CPU load, task priority, and the scheduler. This variation is called task jitter (Pereira, Paladini, and Schaf 2012; Marti et al. 2001) and it does affect control system performance. The jitter issue means that a real-time system designer has two conflicting goals, to choose an inexpensive controller but one with enough capacity so that task jitter will not compromise performance. A bad choice can result in an overly expensive system or unacceptable performance.
Improved Dynamic Performance of the Fuel Cell-Fed Boost Converter Using Super Twisting Sliding Mode Control Strategy
Published in IETE Journal of Research, 2023
F. Punnya Priya, K. Latha, K. Ramya
Also, analog nonlinear controllers have undesirable characteristics such as variable switching frequency and non-zero steady-state error. Moreover, in analog implementation, complex mathematical functions of nonlinear control, such as multiplication and division functions, are very slow and expensive, whereas digital control is capable of doing it with less computational time.