First, the working principle of the fully controlled inverter: It is the full-bridge inverter main circuit of the single-phase output that is usually used, and the AC components adopt IGBT tubes Q11, Q12, Q13, Q14. The IGBT tube is turned on or off by PWM pulse width modulation.

When the inverter circuit is connected to the DC power supply, it is turned on by Q11 and Q14, and Q1 and Q13 are turned off. Then the current is output from the positive pole of the DC power supply. After Q11, L or sense, the primary coil of the transformer is shown in Figure 1-2, to Q14. To the negative pole of the power supply. When Q11 and Q14 are turned off, Q12 and Q13 are turned on, and the current is returned from the positive pole of the power supply through Q13, the inductance of the primary coil of the transformer 2-1 to the return of Q12 to the negative pole of the power supply. At this time, on the primary coil of the transformer, a positive and negative alternating square wave has been formed, and by the high frequency PWM control, the two pairs of IGBT tubes are alternately repeated to generate an alternating voltage on the transformer. Due to the action of the LC AC filter, the output forms a sinusoidal AC voltage.

When Q11 and Q14 are turned off, in order to release the stored energy, the diodes D11 and D12 are connected in parallel at the IGBT to return the energy to the DC power source.

Second, the semi-controlled inverter working principle: the semi-controlled inverter uses thyristor components. The main circuit of the improved parallel inverter is shown in Figure 4. In the figure, Th1 and Th2 are thyristors that work alternately. When Th1 is first triggered to conduct, current flows through the transformer through Th1, and due to the induction of the transformer, the commutating capacitor C is charged to a large supply voltage twice. Pressing Th2 is triggered to turn on, because the anode of Th2 is reverse biased, Th1 is turned off, and the blocking state is returned. Thus, Th1 and Th2 are commutated, and then capacitor C is charged in reverse polarity. The thyristors are alternately triggered in such a way that the current flows alternately to the primary of the transformer, and alternating current is obtained at the secondary of the transformer.

In the circuit, the inductor L can limit the discharge current of the commutating capacitor C, prolong the discharge time, and ensure that the circuit off time is greater than the turn-off time of the thyristor, without requiring a capacitor with a large capacity. D1 and D2 are two feedback diodes that release the energy in the inductor L and return the remaining energy to the power supply to complete the energy feedback.