With rising energy costs and concerns over the efficient delivery of power, Power Factor Correction (PFC) has become common in industrial and commercial electrical systems. Typical applications of PFC circuits are PFC pre-regulators for SMPS and electronic ballasts for fluorescent, HID or LED lighting. Since most equipments require a DC source, the AC power is converted to DC by a power conversion equipment or power supply whose first stage is an AC-to-DC conversion stage. The resulting DC output is then provided to further stages. This AC-to-DC stage immediately follows the AC source and generally consists of a rectifier with a capacitive filter. Rectifiers are non-linear devices which cause current pulses with high peak amplitude and short duration drawn from the power supply. This type of current results in increased network losses, harmonic content, and radiated emissions. At high power levels, these effects become more pronounced.
Most power conversion applications such as SMPSs for PCs use the PFC stage as the first stage in an AC-to-DC converter to improve the overall efficiency of power distribution and minimize losses. An important factor that decide the power quality in an electrical system is Power Factor (PF). It is defined as the ratio of Real Power to Apparent Power. An ideal electrical appliance has a PF of 1.0 and draws minimum current from the supply by drawing zero Reactive Power and only the Real Power required to perform the work. A PFC stage improves PF close to 1.0 by minimizing the reactive power drawn by a load from the supply. This is achieved by making the input current drawn from the system sinusoidal and in phase with the input voltage. This reduces losses in a power line and power generator, resulting in the improvement of power quality and efficiency.
Electrical equipments use two types of PFC: Passive PFC and Active PFC. Passive PFC is used in many electrical appliances or loads such as resistive heaters, incandescent lamps, and constant speed induction and synchronous motors. These loads are linear loads with low PF, which means that when a sinusoidal voltage is applied to them, the current drawn by the load follows the voltage waveform. Passive PFC uses a passive network of capacitors or inductors to improve the PF. Disadvantages to using a passive PFC approach include requirement of larger inductors or capacitors and less effectiveness at improving the PF.
In contrast, Active PFC is common with non-linear loads such as battery chargers, electronic ballasts, variable frequency drives, and switching mode power supplies (SMPS), which cause current to vary with the voltage and distort the current drawn from the system. Further, these loads cause the current and voltage to have nonsinusoidal waveforms containing distortions. Multiple harmonics of fundamental frequency are created and superimposed upon the original signal. As these harmonics increase the reactive power, the Power Factor (PF) reduces below 1.0. An electrical system with harmonics can cause damage to equipments such as transformers and capacitor banks. Serious resonant conditions can also be created which can cause considerable damage to electrical equipments. Active PFC uses power electronics to change the waveform of current drawn by a load to improve the power factor. Some types of the active PFC are buck, boost, buck-boost and synchronous condenser.
Designers are faced with the challenge of incorporating an appropriate PFC stage in power supplies while meeting other requirements such as active and standby mode power consumptions and EMI limits. Current Energy Star guidelines for computers call for a power factor of ≥ 0.9 at 100% of rated output in the PC’s SMPS. In recent designs, SMPSs with passive PFC are able to achieve PF of about 0.7–0.75, SMPSs with active PFC, up to 0.99 PF, while a SMPSs without any PFC have a power factor of only about 0.55–0.65. An Active PFC generally involves use of PFC controller ICs to implement the PFC stage in a power supply. The ICs provide integrated protection circuits dedicated for robust operation in the intended application and protection from overvoltage, undervolatge, overcurrent and brownout conditions. The ICS are intended to meet the demands of a range of medium and high power power supply designs with crucial energy and cost saving features.
Mentioned below are some reference designs of Power Factor Correction circuits with all the required documentation:-
- PFC using Interleaved CCM: This reference design presents a 1.2 kW interleaved PFC converter with 390 VDC output and universal input. If the circuit is subjected to 20% to 100% loads, it achieves efficiencies greater than 95% at 115 Vac and greater than 97% at 230 Vac. For same load range and inputs, the Power factor is greater than 0.98. The design consists of two boards – the main board with power train components and a daughter board with necessary control circuitry to drive the power train. The control is based on the UCC28070 continuous current mode interleaved PFC controller from TI. More on this Reference Design
- Direct PFC Reference Design: This reference design explains a cost-effective direct PFC algorithm. The design implements average current mode control of Power Factor Correction (PFC). Freescale’s MC56F8013 digital signal controller (DSC) is used to implement both fast current and slow voltage loops. The DSC also controls the PFC power switch. The design works from a 230VAC Input voltage and provides a maximal output power of 750W. The solution integrates all required fault protections such as input over-current, input under-voltage, input over-voltage, etc. More on this Reference Design
- Interleaved Power Factor Correction (IPFC) Design: This reference design is an Interleaved Power Factor Correction (IPFC) converter. This system is implemented with a 16-bit fixed point dsPIC DSC (Digital signal controller). The IPFC converter uses two boost converters, which are parallel coupled and are 180º out of phase current controlled with respect to each other. Apart from hardware design guidelines and MATLAB modeling, this design also explains how to install and configure the IPFC reference board. More on this Reference Design
- 350W PFC Design with CCM: This reference design can be integrated in a variety of applications that require a high-performance PFC stage at the AC-DC front-end of their designs. The design implements a continuous conduction mode (CCM) boost converter for achieving power factor correction (PFC) with the help of a IR1152 PFC IC from International Rectifier. Designed to be operated from 85-264VAC universal input voltage, the design delivers 350W continuous output power. Using an optimized PCB layout, the design includes several features such as AC line sag, system overcurrent & overvoltage. The design shows less than 10% Total Harmonic Distortion (THD) and EN61000-3-2 Class D standard compliance. More on this Reference Design
- Design of 100W PFC: This reference design is an active power factor correction (PFC) controller for boost PFC application which operates in the critical conduction mode. A design of a 100W output power converter is explained along with a power factor correction (PFC) efficiency of 90%. The design includes schematics, bill of material and theory of operation. More on this Reference Design