What Is Power Factor Correction (PFC) Equipment?
A power factor correction (PFC) equipment is a specialized controller used to manage PFC equipment, which plays a crucial role in improving the power factor of electrical systems.
The power factor represents the ratio of active power to apparent power in an AC circuit. When AC voltage is supplied to a system with capacitive or inductive loads, it can result in phase differences in input current and the distortion of the waveform, leading to the generation of harmonic currents that negatively impact the power factor.
PFC equipment, which includes a PFC circuit, is designed to mitigate these issues, bringing the power factor closer to 1. A PFC controller is employed to regulate and control the PFC circuit.
Uses of Power Factor Correction (PFC) Equipment
PFC equipment is essential in AC-DC converters, which transform AC commercial power into DC. In cases where electronic equipment has a low power factor, it imposes an additional burden on power companies and other suppliers, as they need to provide extra power beyond what the load consumes.
Furthermore, harmonic currents caused by low power factors can damage power transmission and distribution equipment. International standards, such as IEC61000-3-2, set limits for harmonic currents, and electronic devices must adhere to these regulations.
Therefore, the use of PFC equipment is crucial to ensure compliance with these standards and to improve the power factor.
Principle of Power Factor Correction (PFC) Equipment
Power factor correction begins with the rectification of AC voltage by a diode bridge in an AC-DC converter. The voltage is then smoothed using a capacitor and converted into DC voltage. However, during this process, a phase difference develops between the voltage at both ends of the capacitor and the current flowing through it, leading to a phase difference between input voltage and current.
Additionally, because no current flows during the period when the input AC voltage is lower than the voltage at both ends of the capacitor, and charging current only flows during the period when the input AC voltage is higher, it results in a distorted current waveform, generating harmonic currents. These phase differences and harmonic currents are detrimental to the power factor.
To enhance the power factor, a PFC circuit is inserted between the diode bridge and the smoothing capacitor. This circuit, which operates similarly to a boost-type DC-DC converter, controls the switching elements to shape the input current waveform closer to a sine wave.
Structure of Power Factor Correction (PFC) Equipment
The PFC equipment’s circuit consists of components such as an inductor, a field effect transistor (FET), and a diode. The FET is a type of transistor that, when turned on or off, rapidly changes the current in the inductor. However, the inductor’s property of slowing down current changes results in a triangular wave for the current. Repeated switching control ensures the current waveform approximates a sine wave, enhancing the power factor.
Other Information on Power Factor Correction (PFC) Equipment
1. Circuit Method of PFC Circuit
Two main PFC circuit methods exist: a single method with one set of switches and an interleaved method with two sets of switches that can suppress ripple current by operating them with a 180-degree phase shift. Additionally, there are two operating modes: continuous current mode (CCM) for high-power applications (200 to 500 W) and current critical mode (CRM) for medium-power applications (100 to 200 W). The selection depends on the specific purpose and application requirements.
2. Active Power and Apparent Power
- Active Power
This represents the power consumed by the load and is not returned to the source (reactive power). - Apparent Power
Apparent power is the product of the root mean square (RMS) voltage and RMS current applied to the load. Both active and reactive power components are derived from apparent power. Therefore, the sum of active and reactive power equals apparent power.