The relationship between MATLAB SIMULINK, the control cycle, and the sampling frequency (withdress)
Recently, I have encountered problems that need to set up a control cycle in the simulation. I have been shared for a while, and I will share my understanding. Welcome to discuss it together.
The meaning of three concepts
Stepman: Setting up in "Model Configratuon Parameters" above Simulink, see Figure 1 for details. In fact, it is MATLAB to solve differential equations. Δ t \Delta t ΔtThe size, if it is a step-long, Matlab will neglect the steps until the result meets the error requirements; if it is a long way, you can set your own size.
Figure 1 Step length setting
Control cycle: This problem does not encounter in the simulation, but will encounter in actual control. Because the microcontroller responsible for control is not possible to send an instruction from a period of time, there is a control cycle, or the control frequency is used.
Sampling frequency: The core of control is feedback, the controller needs the output of the system to give the next control command, but the system output is a continuous signal, but we need a discrete signal, so it involves the sampling frequency when measurement. That is how long I measure the output of a system.
Three concepts
In general, the step size <sampling cycle <control cycle and preferably an integer multiple relationship (if I am not an error).
Because the step size is a step time, (a bit like the CPU's frequency) is inevitable, the sampling period is small than the control cycle because the control is based on the feedback, and the sampling cycle can add a filter. Eliminate noise.
How do three concepts implement in Simulink simulation?
The step size can be set directly in Simulink. The control cycle and sampling cycle need to be implemented through "Zero-Order Hold".
Figure 2 shows a circuit simulation of the control period of 4 ms, the sampling period is 2 ms, and Fig. 3 is the simulation result. It can be seen that the simulation delay of 0.04s.
Figure 2: Simulation example
Figure 3: Result curve
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