​Application of low-voltage MOS in multi-level inverters-YFW diode

Application of low-voltage MOS in multi-level inverters

Multi-level inverter is a new type of inverter. Conventional inverter with a single switching device on a single bridge arm. Multilevel inverters contain multiple series switching devices on a single bridge arm to fine-grained control of the output voltage. The sine wave output by the inverter is differentiated, and the more the number of differentials, the closer it is to the sine wave. Common multi-level inverters are three-, five-, and seven-level inverters. Its power switching element works at a lower frequency, so that the switching loss of the power element is reduced, the electromagnetic interference generated is smaller, and the inverter is more efficient. The disadvantage is that a larger number of power switching components are required, and the technical requirements for drive modulation and test verification are higher.

Bridge circuits are commonly found as part of common two-level inverter circuits. It is composed of two bridge arms, which are divided into single-phase and three-phase according to different application scenarios in practical applications. MOS transistors Q1 and Q2 are located between the voltage source and the ground wire, and the required voltage is output from the midpoint by controlling the on/off of Q1 and Q2.
The working waveform of the two-level inverter is shown in the figure, the output voltage has two levels, when Q1 is on, Q2 is turned off is U (voltage source voltage), and when Q1 is turned off, Q2 is on 0 (ground voltage).
A two-level inverter has only one switching device in each arm, while a multi-level inverter has multiple switching devices in series in each arm.

The duty cycles are Q1 and Q2 on, Q2 and Q3 on, Q3 and Q4 on, respectively. The output voltage has three levels, Q1 and Q2 are U when they are on, Q2 and Q3 are U/2 when they are on, and Q3 and Q4 are 0 when they are on.
If the voltage source voltage of the above two inverters is U, the output voltage amplitude of the two-level inverter is U theoretically, because the output voltage is U and 0, and the voltage applied on each diode is also U. The amplitude of the output voltage of the three-level inverter is U/2, and since the output voltage is U, U/2, and 0, then the voltage applied to each diode is also U/2. Therefore, for a 3-level inverter, the voltage applied to each switching diode becomes half that of a 2-level inverter, and a diode with a withstand voltage reduced by half can be used.

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