3. Source-side power factor correction technology
Source-side (also known as input-side) power factor correction (A) technology is proposed for power electronic devices with nonlinear loads consisting of rectification and capacitor filtering. Its main purpose is to reduce the harm of high-order harmonics generated by electrical equipment to the power grid. These high-order harmonics in the load current not only increase losses on transmission lines and waste a lot of electrical energy, but also affect the normal operation of other nearby electrical equipment.
Power factor correction, abbreviated as PFC, improves the power factor on the source side in two main ways: passive power factor correction and active power factor correction. The former primarily targets power supply systems and large factories and mines where low power factor is caused by numerous inductive motor loads. The correction method involves connecting appropriate capacitors in parallel at the grid inlet to make the λ value as close to 1 as possible, achieving energy saving—what we commonly call reactive power compensation. The latter mainly targets switching power supply loads. Due to the rapid development of computers, program-controlled telephone exchanges, and other technologies in recent years, switching power supplies and uninterruptible power supplies (UPS) have been widely adopted. The input side of these power supply devices often operates in a non-linear manner with direct rectification and capacitor filtering, which has led to widespread attention and application of PFC technology.
Power factor correction method: The basic idea of active power factor correction is to perform full-wave rectification on the input AC voltage, perform DC-DC conversion on the rectified voltage, and make the input current automatically follow the voltage waveform after full-wave rectification through appropriate control, so that the input current is sinusoidal. Although PFC is also a switching power supply, it is significantly different from traditional switching power supplies.
(iv) Power Conversion Circuit Technology
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.