The SPWM (Sinusoidal PWM) method is a relatively mature one, and currently uses a wider PWM method. An important conclusion in the aforementioned sampling control theory is that the effects of the narrow impulses with equal impulses and different shapes are basically the same when they are applied to the inertia. The SPWM method is based on this conclusion. The PWM waveform, which is equivalent to the sine wave, and the SPWM waveform, which is equivalent to the sine wave, is used to control the on/off of the switching device in the inverter circuit to make the area of ​​the pulse voltage output. It is hoped that the output sine wave has the same area in the corresponding interval, and the frequency and amplitude of the output voltage of the inverter circuit can be adjusted by changing the frequency and amplitude of the modulated wave.
Spwm application introductionapplication
Principle of SA8281 SPWM Wave Generator and Its Application in Frequency Converter
The pulse width modulation technique controls the on and off of the switching elements by a certain law to obtain a set of rectangular pulse waveforms of equal width and not equal width for approximating the sinusoidal voltage waveform. The application of pulse width modulation technology in inverters greatly promotes the development of modern power electronics technology and modern speed control systems. In recent years, due to the continuous emergence of field-controlled self-shutdown devices, the corresponding high-frequency SPWM (sinusoidal pulse width modulation) technology has been widely used in motor speed regulation. SA8281 is an integrated circuit for three-phase SPWM wave generation and control introduced by MITEL. It has convenient interface with microprocessor, built-in waveform ROM and corresponding control logic. After setting, it can independently generate three-phase PWM waveform. The intervention of the microprocessor is required when the output frequency or amplitude needs to be changed, and the microprocessor only controls it in a small amount of time, thereby enabling the detection of the entire system. Protection and control, etc. The inverter based on SA8281 and 89C52 has a simple circuit. full functioning. The performance price ratio is high. Good reliability and other advantages.
MCU generation
Many single-chip microcomputers used in the market have the function of generating SPWM control waveforms, and the external waveform driving circuit can drive the power bridge to achieve the purpose of inverter. It should be said that as long as the microcontroller with the PWM module and the timer module can accomplish this task.
The specific implementation is to first assign the sine table to the array. Then, the PWM waveform generation module enters an interrupt every PWM cycle, and changes the value of the PWM comparator according to the sine table in the ISR, and sequentially cycles.
The output SPWM wave signal is converted into a sine waveAs shown in the figure below is a conversion circuit. In the circuit, TC1427 is an amplifying circuit, and R11, C47 and R14, C49 are both RC low-pass filters.
For good sine wave output and improved drive capability of the circuit,
The figure above is a second-order active low-pass filter that directly converts the output PWM signal into a sine wave through a filter and then amplifies it through a power amplifier.
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