The basic principle of pulse width modulation (PWM): The control method is to control the on and off of the switching device of the inverter circuit, so that the output end can get a series of pulses with equal amplitude, and use these pulses to replace the sine wave or the required waveform. That is to say, a plurality of pulses are generated in the half period of the output waveform, so that the equivalent voltage of each pulse is sinusoidal waveform, and the output is smooth and the low-order harmonics are few. By adjusting the width of each pulse according to certain rules, the output voltage and frequency of the inverter circuit can be changed.
For example, by dividing the sinusoidal half-wave waveform into N equal parts, the sinusoidal half-wave can be regarded as a waveform composed of N pulses connected to each other. The pulse widths are equal to ∏/n, but the amplitudes are different, and the top of the pulse is not a horizontal line, but a curve. The amplitudes of each pulse change according to the sinusoidal law. If the above pulse sequence is replaced by the same number of equal amplitude and unequal width rectangular pulse sequence, the midpoint of the rectangular pulse and the corresponding sinusoidal equivalence midpoint coincide, and the rectangular pulse and the corresponding sinusoidal part area (impulse) is equal, a set of pulse sequence is obtained, which is called PWM waveform. It can be seen that the pulse width varies according to the sine rule. According to the same impulse equivalent effect, the PWM waveform and the sine half wave are equivalent. For sine negative half cycle, PWM waveform can also be obtained in the same way.
In the PWM waveform, the amplitude of each pulse is equal. To change the amplitude of the equivalent output sine wave, only the width of each pulse can be changed according to the same proportion coefficient. Therefore, in the AC-DC-AC inverter, the output pulse voltage of the PWM inverter circuit is the amplitude of the DC voltage.
According to the above principle, the width and interval of each pulse in PWM waveform can be calculated accurately after the sine frequency, amplitude and the number of pulses in half period are given. According to the result of calculation, the PWM waveform can be obtained by controlling the on-off of all switching devices in the circuit.
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2.Modified sine wave output.
3.High frequency design.
4.Optional input voltage range.
5.Full automatic and silent operation.
7.Auto change AC-DC.
10.Three-steps intelligent charging control to recharging.
11.LCD display, audible and visual alarm.