The power conversion circuit of the inverter generally includes a push-pull inverter circuit, a full-bridge inverter circuit and a high-frequency boost inverter circuit. The main circuits are shown in Figures 1 and 3 respectively.
In the push-pull inverter circuit shown in Figure 1, the center tap of the step-up transformer is connected to the positive power supply, and the two power tubes work alternately to obtain AC output. Because the power transistors are connected to the common ground, the driving and control circuits are simple, and the transformer has a certain leakage inductance, which can limit the short-circuit current, thus improving the reliability of the circuit. The disadvantage is that the utilization rate of the transformer is low, and the ability to drive the inductive load is poor.
The full-bridge inverter circuit shown in Figure 2 overcomes the shortcomings of the push-pull circuit, the power switch tubes T1, T4 and T2.
The phase of T3 is reversed, and the phases of T1 and T2 are 180° different from each other. Adjust the output pulse width of T3 and T4, and output the effective value of the AC voltage.
change accordingly. Since the circuit has the function of making T5 and T6 conduct together, it has a freewheeling loop, and the output voltage will not be distorted even for inductive loads. The disadvantage of this circuit is that the power tubes of the upper and lower bridge arms do not share the same ground, so a special drive circuit or an isolated power supply must be used. In addition, in order to prevent the common-state conduction of the upper and lower bridge arms, a circuit must be designed to be turned off first and then turned on between T3, T6 and T4, T6, that is, a dead time must be set, and the circuit structure is more complicated.
Figure 3 shows the circuit principle of a high-frequency step-up inverter. Since the output of the push-pull circuit and the full-analysis circuit must be equipped with a step-up transformer, the work-amount step-up transformer is large in size, low in efficiency, and expensive. With the development of power electronic technology and microelectronics technology, high-frequency boost conversion technology is used to realize high power density inverter.
The front-stage booster circuit of this inverter circuit adopts a push-pull structure (T1.T2), but the operating frequency is above 20kHz. The booster transformer B1 adopts high-frequency magnetic core material, so it is small in size, light in weight, and has high frequency inversion. After the transformation, it is converted into high-frequency alternating current through a high-frequency transformer, and then high-voltage direct current (generally above 300V) is obtained through a high-frequency rectifier and filter circuit, and then reversed through the power frequency full-bridge inverter circuit (T3, T4, T5.T6) With this circuit structure, the power density of the inverter circuit is greatly improved, the no-load loss of the inverter is correspondingly reduced, and the efficiency is improved. The disadvantage of this circuit is that the circuit is complex and the reliability is lower than the above two circuits.