Research and Implementation of Variable Frequency Speed ​​Regulating System Based on SVPWM

1 Introduction In the AC motor Frequency control, the PWM control has been widely used, among which the classic sine pulse width modulation (SP-WM), which mainly focuses on making the output voltage of the inverter as close to the sine wave as possible. The fundamental components of the PWM voltage wave are as large as possible and the harmonic components are as small as possible, but this method is only an approximation and the ability to suppress harmonics is limited. The voltage space vector pulse width modulation (SVPWM) regards the inverter and the motor as one and controls the motor to obtain a circular rotating magnetic field with a constant amplitude. It can obviously reduce the harmonic content of the output voltage of the inverter and the harmonic loss of the motor, reduce the torque ripple, and the maximum amplitude of the output line voltage of the inverter is the DC side voltage, which is more than the sinusoidal pulse. Wide-modulation inverter output voltage is higher than 15%. With the improvement of SVPWM control technology, ordinary single-chip microcomputer can't meet high-precision control requirements more and more. The application of digital signal processor (DSP) can achieve good control accuracy. This paper presents its digital solution based on the characteristics of the TMS320F240 DSP.

2 Principle of Voltage Space Vector Pulse Width Modulation In AC motor variable-voltage variable-frequency speed control systems, three-phase voltage-type inverters can be expressed equivalently by the six switching elements represented. The phase voltage and line voltage of the motor depend on it. Corresponding to the state of the six power switches of the upper and lower legs of the inverter, the vector 1 and the phase voltage are switched. Therefore, all the control functions are completed by it, which is easy to implement and has high control accuracy.

The 6-channel SVPWM signal output from the DSP is used to control the IPM through a high-speed optical isolator. The voltage and current sensors are used to detect the voltage and current in real time and send it to the DSP for processing. The desired rotational speed is obtained by constant voltage-frequency ratio control of u/f=constant. In order to enhance the anti-interference ability of the system and the stability of the system work, the working power of the DSP and its peripheral circuits is provided by the switching power supply, and the digital power supply of the system is separated from the analog power supply.

Coupling unipolar control method) analyzes and compares the advantages and disadvantages of these two control methods from the output voltage harmonics, switching losses, reliability, etc.: 2(1)3 current sine wave, current ripple has also been effective Inhibition; by the figure locomotive inverter air conditioner, it has high control precision and stable operation. Practice certificate 8(b) shows that the utilization ratio of DC voltage is higher; and it can be seen from (c) that the variable frequency speed control system has good effects.

As we know, the inverter output current harmonics obtained by this method are relatively small,