Simulation of Soft Start Process of Asynchronous Motor Based on MATLAB Huang Yigang 2, Huang Huagao, Ji Guoyu 2 (1. School of Electrical Engineering, Zhejiang University, Hangzhou 310027, China; 2. Nanchang University, Nanchang 330029, China) Explain the processing and establishment of the main link module of soft start The complete simulation system model is given, and finally the simulation results are given and the examples are verified.
1 Introduction Asynchronous motors are widely used. With the development of society and the advancement of production technology, in many occasions, the starting performance of asynchronous motors has also risen.
In many existing starting parties, soft start stands out because of its convenient control, feedback closed-loop control, and good smoothness. It is favored and domestic development research is in the ascendant. The simulation research on the soft start of asynchronous motor is undoubtedly of great significance. The traditional use of Folran or C language modeling and programming simulation method has some obvious shortcomings: the programming efficiency is not high enough, the program debugging is annoying, and the dynamic characteristic curve is not convenient. Since the soft start system includes circuits, power electronics, motors, and control, it increases the difficulty of traditional method simulation.
In recent years, especially after the addition of the electrical system module library (PowwSystemBlockset) in Matlab 5.2 in 1998, the application of Matlab in China for electrical simulation has sprung up. Before this, Matlab was widely used in the field of control. The electrical system module library uses the Simulk dynamic system modeling and simulation software under Matlab as the operating environment, covering the basic components and system simulation models commonly used in electrical engineering such as circuits, power electronics, and motors. The use of modules is similar to the conventional Simulink module. Based on the electrical system module library, this paper uses Matlab to establish a simulation model of asynchronous motor soft start system and simulate it.
2 Asynchronous motor soft start soft starter is gradually developed on the basis of motor speed control device, also known as decompression starter (SSRVS). It adopts a three-phase AC voltage regulating circuit composed of a thyristor power element (SCR). By controlling the conduction angle of the thyristor power component, the voltage applied to the motor is automatically increased gradually, and the motor is gradually accelerated from the stopped state to the running state, and finally The main circuit schematic diagram runs stably at rated voltage. The basic schematic diagram of the main circuit is shown.
The principle of the soft start system circuit is as shown.
The control loop is generally composed of a voltage synchronization signal sampling and processing circuit, a signal detection circuit, a start control circuit, a protection control circuit, and a phase shift control circuit.
The sampling and processing circuit is the reference for the phase shift control trigger pulse to ensure the accuracy between the trigger pulse phase and the main loop voltage phase.
The signal detection circuit detects signals such as current magnitude and power factor angle, and provides a basis for current limiting control and protection action.
Soft start core and key. Choose a reasonable control strategy to achieve a soft start.
The circuit principle of the soft start system is protected by overcurrent, phase failure, phase sequence and overheating to ensure safe and reliable operation of the motor.
A phase shift signal is issued to control the magnitude of the firing angle to change the degree of opening of the thyristor to achieve adjustment of the input voltage of the motor.
3 soft start simulation 3.1 asynchronous motor mathematical model asynchronous motor mathematical model is a high-order, nonlinear, strongly coupled multivariable system, its dq model in two-phase rotating coordinate system is: the equation of motion equation L转矩 equation The amount of (') indicates the amount of rotor deflection seen from the stator side.
The asynchronous motor model provided in the Matlab electrical system module library is based on the dq model of the rotor rotating coordinate system. Its standard form module (Asy-chiomousMachineSIUnits) is shown as input, A, B, C and output a, b, respectively The three-phase line connection of the stator and the rotor, the three-phase windings of the stator and the rotor of the module are all set to the star connection method, and the neutral point cannot be used externally. The output of the rotor of the standard form asynchronous motor module dedicated multiplex resolver is usually Directly shorted or connected to an external circuit. Tm is the motor load torque input, mS1 is a vector output with 20 motor quantities, and at the same time, a dedicated multiplexer (ASMMeasurementDemux) () is provided in the module library to separate the various quantities of the output motor. Values, such as stator, rotor three-phase current, motor speed, electromagnetic torque, etc., these outputs can be directly observed with a simulated oscilloscope.
3.2 The simulation model of the asynchronous motor soft start system is the simulation model of the asynchronous motor soft start system established by Simulink. It is mainly composed of three-phase AC voltage source, synchronization, pulse generation, three-phase AC voltage regulation, motor and measurement, current feedback and start control. The structure division is basically the same as that of the asynchronous motor soft start system. Compared with other modules, the pulse generation subsystem module and the startup control subsystem module add a '' symbol before the module name. This is because during the simulation initialization process, Simulink has a function (powei2sys) to check each module in the model one by one. For the electrical system module, if it is, then the conversion, and vice versa, in order to avoid checking the Simulink conventional module to speed up the simulation, Simulink can add a '' in front of the subsystem module name, but must ensure that all the subsystems are Simulink Modules, the two subsystem modules mentioned above meet this condition.
The following is a discussion on how to build these main link modules: the single-phase power supply is only available in the electrical system module library, and there is no ready-made three-phase AC power supply module. We can use three single-phase AC power supplies to connect by star. By setting the correct phase sequence and amplitude relationship, it is simply combined and packaged into a module. It is only necessary to directly set the line voltage and frequency of the three-phase AC power supply of the module. The internal structure is as shown.
The synchronization link module and the three-phase bridge type three-phase AC voltage source asynchronous motor soft start simulation model flow circuit are different, the control angle of the three-phase AC voltage regulation circuit is a = 0, and the synchronization signal should be Take the power phase voltage signal instead of the line voltage. Its internal model, for example, has three input ports and three output ports. Since the electrical system module is essentially different from the conventional Simulink module, the intermediate interface module must be used for the signal flow between the two types of modules. Therefore, depending on the nature, the voltage measurement module is used as the input electrical signal and the output Simulink signal. Intermediate interface.
The additional module library of the electrical system (P (we- gives a synchronous six-pulse generator can meet the general requirements, of course, according to the actual needs, according to the mechanism of the synchronous pulse generation, using the Simulink conventional module to build this link module. In the simulation model system, the module modified on the basis of the synchronous six-pulse generator module in the above library is used, and the wide pulse triggering is adopted, and the internal model map is omitted here.
The practical application of the soft start system is usually to use the current transformer to obtain the feedback signal, through the rectification, filtering and other signal processing links to obtain a signal that faithfully reflects the starting current (generally the effective value), which is not simple to implement, but in the simulation In the modeling, the effective value of the starting current can be easily obtained, because in the additional module library, the measurement sub-library (MeasuremaUs) provides the effective value, and the measurement module (RMS) can be directly utilized, which is very convenient.
The soft start is essentially a step-down start, the key is to limit the starting current. The realization process is that the starting voltage is gradually increased from a given voltage value to a constant after the given limiting current, and after the constant starting voltage is excessively high, the starting voltage continues to rise again, so The final rated full pressure is reached. According to the internal model of the package module, the input current feedback signal iback and the current limit set value iref are compared by an adder, and the current deviation is compared by a hysteresis loop. If the feedback signal is greater than a given value, the output is output. If the value is 0, the output is 1. When the voltage rise rate control uincr value is multiplied by the hysteresis output, an integral value is used to generate a signal whose value is linearly increased by 0 from the rising slope. When the product value is 0, The output of the integral link remains unchanged. The starting voltage starting set value uini is compared with the integrated output value, and the deviation is limited to a range of output values ​​by a saturation link (Saturation) and sent to the output end. The values ​​of uini and the saturated output range both indicate the magnitude of the firing angle a.
The three-phase AC voltage regulation link module is the soft start feature of the asynchronous motor. The internal model, such as the pulse output from the pulse generation link, is supplied to each thyristor via the selector Selector and the multi-channel signal resolver Demux. The order of triggering between them. Six thyristor modules (Thristor) are selected from the power system sub-module of the electrical system module library to form three pairs of bidirectional anti-parallel thyristor circuits. To avoid the generation of algebraic loops, the thyristor component parameters Lon can be set small enough, but Can not be 0, considering the inductive load with motor, need to set Rs and Cs, so as not to affect the simulation rationality, Rs can take large resistance (such as 1e6), Cs can take inf, the rest of the parameters are selected according to the actual situation.
Simulation results and experimental results of the three-phase AC voltage regulation module 3.3 Using the above simulation model, the no-load start of the asynchronous motor soft start system of the “Dawer†tank with 75IKW frequency conversion unit was simulated (current limit RMS 400A). Numerical simulation algorithm: ode15s, relative error: 1e-3, absolute error: 1e-3. Since the starting time of the soft start system is relatively long (about half a minute), the waveform of the whole starting process is inconvenient, for the sake of clarity, The local starting current waveforms of the initial stage of the starting, the intermediate stage of the current limiting and the ending stage of the starting are respectively extracted and enlarged, and the corresponding experimental waveforms are also listed for comparison (0).
From 0 we can see that the simulated waveform is basically consistent with the experimental waveform.
(a) Start initial stage simulation current waveform (a) Start initial stage experimental current waveform (b) Current limiting stage local simulation current waveform (1/) Current limiting stage local experimental current waveform (c) Start end stage simulation current waveform (c Start-up section experimental current waveform 0 simulation waveform and experimental waveform 4 Conclusion This paper aims to establish a simulation model for asynchronous motor soft start system using Matlab/Simulink and electrical system module library. The simulation is efficient, accurate and intuitive, which lays a foundation for subsequent in-depth analysis and research. At the same time, the subsystem modules established in the simulation model have certain reference value, and can be easily transplanted, which reduces the repetitive workload of simulation research in related fields in the future.
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