1. Power conversion circuit
From the perspective of power conversion function, there are the following four categories:
(1) Converting alternating current to direct current, i.e., AC/DC conversion. The conversion circuit that performs this function is generally called a rectifier circuit or rectifier.
(2) Converting direct current to alternating current, i.e., DC/AC conversion. The conversion circuit that performs this function is generally called an inverter circuit or inverter.
(3) Converting one type of direct current to another, i.e., DC/DC conversion. This conversion achieves a change in the amplitude or polarity of DC voltage (current), and is generally called a DC/DC conversion circuit or DC/DC converter.
(4) Converting one type of AC power into another, i.e., AC/AC conversion. This conversion achieves the transformation of AC voltage (current) and frequency. The former is called an AC voltage regulating circuit (e.g., voltage regulator, current regulator), and the latter is called a frequency converter (or frequency converter). Sometimes it is also necessary to change the number of phases (e.g., single-phase to three-phase or three-phase to single-phase, etc.).
The four types of conversion circuits mentioned above are collectively referred to as “converter technology” in terms of their technology. These circuits can be used individually or in combination. For example, a common conversion method involves directly rectifying the mains power (single-phase or three-phase) into DC, then using an inverter circuit to convert it into high-frequency AC (adjustable pulse width positive and negative rectangular pulses or adjustable pulse frequency quasi-sine pulses), and finally rectifying it back into DC to supply the load. In the high-frequency conversion stage, pulse width modulation is used to stabilize the output DC voltage. This is the commonly used circuit mode for high-frequency switching power supplies, employing a combined conversion method (containing two rectifications and one inversion).
2. Control Method
During the conversion process, besides operating the power devices in a linear state, they often operate in a switching state, converting electrical energy according to a set timing sequence under the action of control signals. The operation of the devices involves the transfer of current between various branches, hence the term “commutation.” For circuits composed of semi-controlled devices, since the devices themselves have no switching capability, external conditions are often used to turn off the conducting devices during the commutation process. Successful commutation is a necessary condition for the normal operation of semi-controlled circuits; therefore, the commutation process is the main content of the analysis of this type of circuit, and commutation technology is the core of this type of conversion technology.
In the AC /OC conversion process, a high-frequency conversion stage is often introduced to achieve the goals of reducing the size and weight of power supply equipment, improving efficiency, and enhancing dynamic characteristics. The conversion frequency is generally from tens of kilohertz to hundreds of kilohertz. In the 1970s, the development of DC linear regulated power supplies powered by 50Hz AC mains to DC switching regulated power supplies with a switching frequency of 100Hz was hailed as the “100Hz revolution.” However, in just over 10 years, the conversion frequency of switching power supplies has reached over 100Hz.