Currently, electrical systems in thermal power plants are beginning to be incorporated into distributed control systems (DCS). The need for joint simulation of electrical systems and thermal automation systems is emerging. Compared with thermal systems, electrical systems have many differences in control requirements and operation. The main characteristics of electrical systems, such as the high reliability and fast action speed of automatic protection devices for electrical equipment, and the complex operating mechanisms and low operating frequency of electrical equipment, all require that after the electrical system of the unit is incorporated into the DCS control, the control system must have high reliability. In addition to being able to realize normal start-up, shutdown and operation, it is especially required to be able to realize the real-time display of various data and statuses under abnormal operation and accident conditions, and provide corresponding operation guidance and emergency handling measures to ensure that the automatic control of the electrical system works under the safest and most reasonable operating conditions. The characteristics of electrical systems have led to the use of specialized software in power system simulation research for many years, which has been carried out separately from the simulation of power plant thermal control systems. With the development and improvement of open computer technology, it has become possible to use general simulation software to realize simulation analysis of various types of processes. For example, the application of MATLAB to power system simulation has long been valued [1]. Reference [1] introduced the conversion of the electromagnetic transient analysis software package PSCAD/EMTDC for real-time digital simulation of power systems to MATLAB in 1997, realizing a general open and visual technology. With its powerful matrix operation capabilities, simple plotting functions, visual simulation and rich algorithm toolbox, MATLAB has become a powerful development tool for scientific research and engineering technicians [2], and has been widely used in various types of thermal control systems of power plants. Reference [3] introduced the technology of using MATLAB to realize visual simulation of industrial processes. However, for power system engineers, conventional simulation tools are inadequate for accurately and quickly conducting customized simulation studies of circuits and more complex electrical systems according to engineering needs. This is because if each link is represented by a simplified transfer function, many important details will be ignored; if the basic modules (such as switches and triggers) provided by Simulink in MATLAB are used to construct the model, it is quite time-consuming and laborious. Although PSPICE can be used to realize the simulation of electronic circuits, PSPICE is mainly suitable for the microelectronics field and is difficult to combine with the complex algorithms and advanced control theories required for power system design. To date, a large number of electrical system simulation analyses still use dedicated software packages [4]. This paper will explore the method of using MATLAB to realize power system simulation analysis and design by combining the PowerSystemBlockset in MATLAB. By utilizing the interface between MATLAB and high-level languages ​​such as FORTRAN, we can also inherit the experience of power system simulation analysis over the years. 1 Introduction to the PowerSystemBlockset MATLAB version 5.2 and above provides the Powerlib PowerSystemBlockset library. The Powerlib PowerSystemBlockset library uses Simulink as its operating environment and covers the simulation models of basic components and systems commonly used in electrical engineering disciplines such as circuits, power electronics, electrical drives, and power systems. It can not only realize the calculation and simulation of power systems in the time domain and frequency domain, such as calculating the law of electrical parameters changing with time when the power system is subjected to disturbances or parameter changes, but also can be widely used in high voltage DC transmission, FACTS controller design, power system harmonic analysis, and simulation analysis calculations in the field of power electronics. After running Simulink, you can open Blocksets & Toolboxes to call up the PowerSystemBlockset library. You can also directly type Powerlib in the MATLAB command window to call it up. The Powerlib electrical system module library consists of six sub-module libraries as shown in Figure 1. (1) Power supply module library: including DC voltage source, AC voltage source, AC current source, controllable voltage source and controllable current source, etc. (2) Basic component module library: including series RCL load/branch, parallel RCL load/branch, linear transformer, saturated transformer, current transformer, circuit breaker, N-phase distributed parameter line, single-phase type II lumped parameter transmission line and surge discharger, etc. (3) Power electronics module library: including diode, thyristor, GTO, MOSFET and ideal switch, etc. To meet the simulation requirements of different purposes and improve the simulation speed, there is also a simplified thyristor model, as shown in Figure 2. (4) Motor module library: including excitation device, water turbine and its regulator, asynchronous motor, synchronous motor and its simplified model and permanent magnet synchronous motor, etc. Figure 3 shows a simplified synchronous motor model. (5) Connection module library: including ground, neutral point and bus (common point). (6) Measurement module library: including current and voltage measurement. Based on the six basic sub-module libraries, more complex modules can be combined and encapsulated as needed and added to the required module library. As shown in Figure 4, the three-phase electrical system in the PowerlibExtras module library is constructed and encapsulated using the modules in the six basic sub-libraries. The “LookUnderMasy” command can be used to open each module and view its internal structure to understand the construction method and rules. The PowerlibExtras module library also includes: root mean square calculation, active and reactive power calculation, Fourier analysis, programmable timer and synchronous trigger pulse generator, etc. 2 Basic operating principle and use The Powerlib module in the electrical system module library is somewhat different from the regular Simulink module. Therefore, in Simulink, there is an initialization process before simulation to convert the system containing the Powerlib module into the equivalent coefficients that Simulink can simulate. The specific operation is as follows: (1) Call the Power2sys function to divide all modules into regular modules and Powerlib modules. The Powerlib modules are further divided into linear modules and nonlinear modules. (2) Call the Power2sys function to obtain the network topology of the module, get its parameters, and assign a node number to each electrical node. (3) Call the Circ2sys function to obtain the state space model of the linear module (the state variables are inductor current and capacitor voltage). (4) Call the Power2sys function to obtain the Simulink model of the nonlinear module based on the internal predefined model of Simulink. After initialization, Simulink starts simulating this system. The Power2sys and Circ2sys functions can be called directly in the MATLAB command window in the form of command line, and are more flexible in use. They can construct modules that are not in Powerlib (such as current transformers with more than 3 windings), which will not be elaborated here. Of course, the above complex preprocessing process is shielded from the user. The modules in the electrical system module library are used in a similar way to regular Simulink modules. Just copy them into your own model and set the appropriate parameters. However, Powerlib modules and regular Simulink modules are two different types of modules. Therefore, for simulation models that use both types of modules at the same time, there will inevitably be signal flow between the two types of modules, which requires an intermediate interface module. Specifically, when signals from Simulink modules are sent to Powerlib modules, a controllable voltage source or controllable current source module should be used as an intermediate link, depending on its nature. Conversely, when signals from Powerlib modules are fed back to the control system constructed by Simulink modules, a current or voltage measurement module should be used. Because the Power2sys function checks each module in the model to be an electrical system module during simulation initialization, it can slow down the simulation speed to some extent for large-scale systems. To avoid this negative impact, Power2sys can be artificially prevented from checking regular modules by adding a "$" symbol before the module name of regular modules and subsystems containing regular modules, such as "$PID". However, it must be ensured that all modules within the subsystem are regular modules. PowerGUI is a powerful tool provided by the electrical system module library. It allows for convenient calculation and display of steady-state values ​​of various state and measurement variables in the system using a graphical user interface (GUI); it allows modification of the system's initial state to start simulation from any initial condition, avoiding long transition periods; and it can also calculate and initialize the power flow of a three-phase power grid including motors. Using Powergui, simply copy the data into the model, open it, and you can view and configure it. 3. Example of Power Electronics Simulation in TLAB Many electrical system simulation examples can be found in the demos, such as power filters, HVDC, distributed parameter lines, transformers, transient analysis, and three-phase diode rectification. The thyristor rectifier circuit built using the electrical system module library in this paper is shown in Figure 5. The system supplies power to the RL load through a single-phase, single-pulse thyristor rectifier circuit. The thyristor gate trigger pulse is provided by the timer Timerl. The simulation parameters are: rectifier load R = 0.5Ω, L = 6.5mH. Thyristor module on-resistance R = 0.001Ω, inductance L = le - 5H, forward voltage U = 0.8V, bypass resistance R = 20Ω, and capacitance C = 4e - 6F. The line load can also be represented in reactance form. When feeding back the signal from the thyristor module in Powerlib to the Simulink filter display module (Ufilter), a current and voltage measurement module is used. Figure 6 shows the simulated voltage and current waveforms displayed on the oscilloscope Ufilter. These curves are completely consistent with the experimental waveforms analyzed in theory.