LCD Display Inverter

“The Inverter circuit corresponds to the rectifier circuit, and the conversion of direct current into alternating current is called inverter. When the AC side is connected to the power grid, that is, when the AC side is connected to a power supply, it is called active inverter; when the AC side is directly connected to the load, it is called passive inverter.

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The inverter circuit corresponds to the rectifier circuit, and the conversion of direct current into alternating current is called inverter. When the AC side is connected to the power grid, that is, when the AC side is connected to a power supply, it is called active inverter; when the AC side is directly connected to the load, it is called passive inverter.

Inverter circuits are widely used. Among the existing power sources, storage batteries, dry cells, solar cells, etc. are all DC power sources. When these power sources are required to supply power to an AC load, an inverter circuit is required. In addition, power Electronic devices such as frequency converters, uninterruptible power supplies, and induction heating power supplies for AC motor speed regulation are widely used, and the core part of their circuits are inverter circuits. Its basic function is to convert the DC power output from the intermediate DC circuit into an AC power with adjustable frequency and voltage under the control of the control circuit.

The switching state of the bridge inverter circuit is determined by the voltage signal applied to its control pole. The PN terminal of the bridge circuit is connected to the DC voltage Ud, and the A and B terminals are connected to the load. When T1 and T4 are open and T2 and T3 are closed, u0=Ud; on the contrary, when T1 and T4 are closed and T2 and T3 are open, u0=-Ud. Therefore, when each arm in the bridge turns on and off at the frequency f (determined by the repetition frequency of the control electrode voltage signal), the output voltage u0 will become an alternating square wave, and its amplitude is Ud. The repetition frequency is f, as shown in Figure 2, the fundamental wave can be expressed as the rectangular wave uo whose amplitude is Ud is expanded into a Fourier series: uo=4Ud/π (sinwt+1/3 sin3wt+1/5 sin5wt+ …) It can be seen from the formula that the frequency f of the control signal can determine the frequency of the output terminal, and the amplitude of the fundamental wave can be changed by changing the DC power supply voltage Ud, so as to achieve the purpose of inversion.

Commutation method:

1) Device commutation: The self-shutdown capability of the fully controlled device is used for commutation. The fully controlled device adopts this commutation method.

(2) Grid commutation: The grid provides the commutation voltage, as long as the negative grid voltage is applied to the device to be commutated.

(3) Load commutation: The commutation voltage is provided by the load. When the load is a capacitive load, that is, the load current leads the load voltage, the load commutation can be realized.

(4) Forced commutation: Setting an additional commutation circuit and forcing a reverse voltage commutation to the thyristor to be turned off is called forced commutation. It is usually realized by using the energy on the additional capacitor, also called capacitive commutation.