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How the inverter works?
- Aug 06, 2018 -

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Basic structure of inverter

The direct function of the inverter is to convert DC power into AC power. The core of the inverter is the inverter switching circuit, referred to as the inverter circuit. The circuit performs the function of inverter through conduction and turn off of power electronic switches. The on and off of power electronic switching devices require certain driving pulses, which may be regulated by changing a voltage signal. A circuit that generates and regulates the pulse. It is usually called a control circuit or a control loop. The basic structure of the inverter device includes the protection circuit, the output circuit, the input circuit, the output circuit and so on.

How the inverter works?

1. Working principle of fully controlled inverter

Is the normally used single-phase output full-bridge inverter main circuit, the ac components are IGBT Q11, Q12, Q13, Q14. PWM pulse width modulation (PWM) is used to control the conduction and cutoff of IGBT tube.

When the inverter circuit is connected to the dc power supply, it is first connected by Q11, Q14, Q14 and Q13, then the current is output from the positive pole of the dc power supply, and then it is returned to the negative pole of the power supply through Q11, L or the transformer primary coil figure 1-2, and Q14. When Q11 and Q14 are cut off, Q12 and Q13 are conductive, and the current from the positive terminal of the power supply passes through Q13 and the transformer primary coil 2-1. At this time, positive and negative alternating square waves have been formed on the primary coil of the transformer. By using high frequency PWM control, two pairs of IGBT tubes are repeated alternately, generating ac voltage on the transformer. As a result of LC ac filter, the output end forms sine wave ac voltage. When Q11 and Q14 are off, in order to release the storage energy, the secondary tubes D11 and D12 are connected in parallel at the IGBT to return the energy to the dc power supply.

2. Working principle of semi-controlled inverter

The semi-controlled inverter USES thyristor elements. The main circuit of the improved parallel inverter is shown in figure 4. In the figure, Th1 and Th2 are thyristor working alternately. If Th1 is set to trigger the conduction first, the current flows through the transformer through Th1. The conduction is triggered by pressing Th2. Due to the anode of Th2 plus reverse bias, Th1 is off and returns to the blocking state. Thus, the Th1 and Th2 are switched, and then the capacitor C is recharged in reverse polarity. In this way, alternating current flows to the primary stage of the transformer, where alternating current is obtained at the secondary level of the transformer.

In the circuit, inductance L can limit the discharge current of commutation capacitance C, prolong the discharge time, and ensure that the circuit shutdown time is greater than that of the thyristor, without the need for capacitors with large capacity. D1 and D2 are two feedback diodes, which can release the energy in inductor L and return the rest energy to the power source to complete the energy feedback.