I. What is a block diagram

Block diagram, also known as block diagram or structure diagram, has the characteristics of image and intuition. We say that there are four basic symbols that make up a block diagram, namely, signal lines, comparison points, boxes of transmission links and lead-out points. Block diagram element block diagram: indicates the functional relationship of one-way transmission of input and output. Signal line: a straight line with an arrow, indicating the flow direction of the signal, and the time function or image function of the signal is marked next to the straight line.

An element that adds and subtracts two or more input signals at a comparison point (synthesis point, synthesis point). "+"means addition and "-"means subtraction. You can omit the "+"sign. Note: the quantity of addition and subtraction must have the same quantity rigidity. The branch point (extraction point, measurement point) indicates the position where the signal is measured or extracted. Note: The signals extracted at the same location are identical in size and nature.

Second, the system block diagram drawing

For a system, when the working principle and signal transmission of the system are clear, the block diagrams of all links can be connected together according to the basic connection form of block diagrams to form a system block diagram. Considering the load effect, the differential equations or transfer functions of each part of the system are listed separately and represented by blocks. According to the signal flow direction of each component, the block diagram of the system can be obtained by connecting each block in turn with signal lines.

System block diagram-also a system mathematical model. A perfect control system usually includes feedback structure, so it is also called closed-loop control system. Usually, there are two kinds of external signals (excitation) received by the control system: one is the useful signal or excitation that we actively apply, or it is called input signal, given value, reference input, etc. , often expressed as r(t); The other is the signal passively applied by the system, which is called disturbance.

Or interference, noise, etc. , often expressed by n(t). The transfer function of feedback control system can be obtained by establishing the differential equation model of feedback control system and directly carrying out Laplace transform under zero initial condition. The transfer function can also be obtained by simplifying the structure diagram of the feedback control system.