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Thyristor-based variable-frequency power supplies and IGBT-based variable-frequency power supplies share many similarities in terms of their load resonance methods and basic structure; for example, both can be designed as series variable-frequency power supplies or parallel variable-frequency power supplies. The structure of such devices is mostly based on a AC-DC-AC circuit: the mains AC power is first converted into DC power through a rectification stage (usually a DC power supply with adjustable voltage), and then this DC power is transformed into AC power with adjustable voltage and frequency via an inverter stage. In both thyristor-based and IGBT-based variable-frequency power supplies, the rectification stage consists of rectifying thyristors (rectifier diodes), and they all include a filtering stage made up of smoothing reactors or filter capacitors. The main difference between the two is the inverter section of the variable-frequency power supply: in the former, it is composed of thyristors along with the associated trigger circuit, while in the latter, it is made up of IGBTs together with their corresponding trigger circuit. In other words, the main difference between the two is that the inverter component in a thyristor-based variable-frequency power supply is a thyristor, while in an IGBT-based variable-frequency power supply it is an insulated-gate bipolar transistor (IGBT). Due to the differences in the type and technical characteristics of these inverter components, their associated trigger circuits, as well as the methods of triggering, turning off, and commutation, also differ. Therefore, to compare the technical features of the two, it is first necessary to compare the thyristors and IGBTs as well as their trigger and drive mechanisms.