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This paper presents the comparison of various current control strategies employed for an interleaved power factor correction (PFC) boost converter for improving the power quality. The major control strategies discussed in this paper are: peak current control, average current control, hysteresis control, borderline current control and non-linear control. These strategies are implemented in MATLAB/SIMULINK and the performance of the proposed converter is compared under open loop and closed loop operation. From the results, the input current waveform was close to input voltage waveform implying improved power factor and reduced total harmonic distortion for nonlinear current control technique. Experimental results validate the proposed method.

The power-electronics products are employed for a variety of applications such as power supplies for microelectronics, household electric appliances, electronic ballasts, battery charging, motor drives, power conversion circuits, etc., but this leads to rich current harmonics at the supply side. Therefore, Power Factor Correction (PFC) is necessary for AC-DC converters in order to fulfill the requirements of international standards. PFC will reduce the harmonics in the supply current and boost the efficiency of the system. Even though numerous methods have been suggested to resolve the problem of low power factor, it is important to make the supply power factor to unity. In order to meet the standards of IEC 6l000-3-2 Electromagnetic compatibility (EMC): harmonic current limits, achieve high power factor and reduced harmonics, power factor corrected converters are commonly employed in various types of switching power supply [

Interleaved boost converter is one of the most popular choices for high power factor converter. This type of converter provides an output voltage greater than the input voltage and also it operates at maximum duty ratio. The boost converter is supplied from a full wave rectified line voltage and operated so that the input current follows the input voltage and it is generally preferred because of its simple construction. Power factor correction (PFC) [

Various techniques are available for shaping the line current, and also they are supported by integrated circuits [

The paper is organized as follows: Section 2.1 gives a brief idea of the interleaved boost converter. Section 2.2 analyzes the effect of the ripple steering technique in detail. Section 3 deals about the design of interleaved boost converter. Section 4 analyzes the operation of interleaved boost PFC converter with different current control strategies. Section 5 gives the comparison between the proposed control techniques and the open loop configuration of interleaved boost PFC with ripple steering technique. The analysis is made in terms of input current, input voltage, output voltage and total harmonic distortion with the help of simulation results. A prototype has been built and tested, and the experimental results are presented in Section 6.

Power factor correction (PFC) interleaved boost converter is a popular topology for high level switching power supply to improve the power factor (PF). An interleaved boost converter provides benefits of component availability, high efficiency, high power density and low harmonics compared to conventional converters. Hence it has been extensively used in numerous applications. The important features for these type of converters is the current cancellation effect thereby reduces the size, weight and cost of the filters. It also identifies the differential mode EMI noise hence suitable for input filter design, input and output side capacitor selection.

The interleaved boost converter is simply two traditional boost converters with half the power rating as a result the input bridge rectifier must have the same power rating as the conventional power factor corrected boost converter. And also design equations will be alike to that of conventional converters. Interleaved boost converters are usually employed for high input-current and high input to output voltage conversion applications. The added benefit of interleaving is that ripple currents are reduced at both input and output side. There is an increased efficiency by splitting the output current into “n” pathways; considerably it reduces the power and inductor losses. Here the interleaved structure is presented for boost converter to improve the efficiency of the PFC converter [

Interleaved boost converter with ripple steering technique is employed to achieve active power-factor correction. This ripple steering technique is also called as coupled magnetic filter technique and it is implemented to IBC topology in this paper. The concept of zero-ripple or ripple-free input current is not new. It was originally used to reduce weight and increase power density of the converter. Generally, a zero-ripple phenomenon is achieved by using the coupled inductor technique in a modified boost converter. Based on the zero-ripple input current concept, various PFC converters with separate inductors and EMI filter requirements can be found in the literature [

Designing an interleaved boost converter includes the following steps:

Since the number of phases chosen in this paper is two, 50% of the duty cycle will be the best choice. And also D = 0.5 gives less ripples when compared to other duty ratios. The duty ratio is calculated as,

where,

This paper uses two phases, as the number of phases is increased the ripples will be minimum. But increasing the number of phases will increase the cost and complexity of the circuit. Therefore the number of phases is chosen as two.

The inductor and capacitor values can be found using the formula given below.

where,

where

The main objective of this paper is to present the current control design techniques and experimental results for the proposed converter. An open loop control technique is often used in simple processes because of its simplicity and low cost, especially in systems where feedback is not significant. Generally, to obtain a more accurate control of the circuits, closed loop systems are designed to automatically achieve and maintain the desired output condition by comparing it with the actual condition. It does this by generating an error signal which is the difference between the output and the reference input. By adopting current control techniques [

A schematic circuit diagram of PFC interleaved boost converter under peak current control [

when the sum of the positive ramp of the inductor current (i.e. the switch current) and an external ramp (i.e. compensating ramp) touches the sinusoidal current reference. Usually, this reference can be attained by multiplying a scaled replica of the rectified line voltage v_{g} times the output of the voltage error amplifier, which sets the current reference amplitude. In this way, the reference signal is naturally synchronized and always proportional to the line voltage, which is the condition to obtain unity power factor. Whenever the inductor current crosses zero, switch is turned ON and as it reaches the reference current, the flip-flop is reset and the switch is turned OFF. Obviously the ramp compensation can improve the quality of the input line current, which means the amplitude of the ripple is decreased significantly. Owing to the large output capacitance, the output voltage ripple can be neglected. Therefore, the time-varying mathematical mode of PFC boost converter can be expressed as a first order differential equation as follows:

where

In most of the power electronic converter applications the output variable is the voltage and is involved in the outer loop. The variable within the inner loop is current, this is the reason this technique is called as average current control technique. The average current controlled interleaved boost PFC converter, is designed to operate in CCM, it may transit to DCM when the load becomes light.

Firstly the inductor current is sensed and filtered by a current error amplifier whose output drives a PWM modulator. Hence the inner current loop tends to limit the error among the average input current i_{g} and the reference. The converter works in CICM, so the same considerations done with regard to the peak current control can be applied. The average of inductor current is taken as reference and the inductor current is forced to go after it. The switch is turned ON whenever the inductor current reaches zero and switch is turned OFF when the inductor current falls below the reference.

We know that the rectified input voltage of the boost converter can be expressed as follows:

where

The average value of the inductor current is programmed to sinusoidal shape for achieving the PFC function. Under different input voltage and load conditions, the average current controlled technique may operate in all CCM or partly CCM/DCM. When the converter operates in CCM, the duty cycle

where

and when the inductance current is more than the upper current reference, power switch is turned OFF. The boost converter is being operated at continuous current mode (CCM). For the hysteresis control, the inductance current is switching at a variable switching frequency. The switch must be turned ON while zero crossing of the line voltage for restraining very high switching frequency. In order to avoid too high switching frequency, the switch can be kept open near the zero crossing of the line voltage so introducing dead times in the line current.

In this type of control approach the ON time of the switch will remain constant during the line cycle and the switch is turned ON when the inductor current falls to zero. Therefore the converter operates at the boundary between Continuous and Discontinuous Inductor Current Mode. The freewheeling diode is turned OFF softly and the switch is turned ON at zero current. So the commutation losses are also reduced. And also the higher current peak increase the device stresses and conduction losses will lead to heavier input filters. This is a type of hysteretic control in which the lower reference I_{V}, ref is zero anywhere. The principle scheme is shown in

Nonlinear carrier controllers are proposed for high power factor boost rectifiers with low total harmonic distortion [

The simulation results of the different current control strategies for interleaved boost converter are discussed here. The converter is designed with the simulation parameters as shown in _{d}, Displacement factor K_{θ} and the power factor. Two phase interleaved boost converter with ripple steering technique for different control techniques are simulated using MATLAB/SIMULINK.

Parameters | Values |
---|---|

V_{in} | 24 V |

V_{o} | 42 V |

R | 100 Ω |

C | 400 µF |

f_{s} | 50 KHz |

L_{m} | 60 mH |

D | 0.5 |

For an ideal sinusoidal input voltage, the power factor can be expressed as the product of distortion factor and the displacement factor.

where

The distortion factor

The following equations link total harmonic distortion to power factor:

where φ is the angle between voltage and current, PF is the power factor, THD is the total harmonic distortion.

The simulation results of the interleaved boost converter with ripple steering technique are shown in

The simulation results of the average current control technique are shown in

Simulation results of hysteresis current control technique are shown in

The simulation results of the borderline current control technique are shown in

technique.

The simulation results of the nonlinear switch current control technique are shown in

The simulation results of the nonlinear inductor current control technique are shown in

From the above table, it is inferred that the total harmonic distortion is minimum for the nonlinear inductor

current control technique and also it is noted that the supply power factor is closer to unity, for the proposed converter with the closed loop configuration compared to open loop configuration.

An experimental prototype was built to verify the operation of the proposed two phase interleaved boost converter with ripple steering for Non-linear current control technique. A photograph of the prototype is shown in

RMS voltage, output ripple voltage and supply power factor of the proposed two-phase IBC with nonlinear inductor current technique are shown from Figures 16-18. For an input voltage of 24 V an output voltage of 33 V is obtained in

Control Techniques | THD% | Supply Power factor |
---|---|---|

Open loop configuration | 12.17 | 0.859 |

Peak Current | 11.63 | 0.885 |

Average Current | 8.28 | 0.896 |

Hysteresis | 4.81 | 0.897 |

Borderline | 3.19 | 0.905 |

Non Linear/switch current | 3.11 | 0.913 |

Non Linear/inductor current | 2.84 | 0.92 |

This paper deals with several current control techniques specifically developed for active power factor correction. A comparative analysis of the performance parameters of peak current control, average current control, hysteresis control, borderline current control and non-linear control techniques has been carried out. From the results it is found that the, non-linear current control technique affords the least total harmonic distortion and hence, the best power factor, which validates its choice for power factor correction. The simulation results are validated experimentally. Therefore, nonlinear inductor current control will be a suitable technique to improve the power factor.

The author gratefully acknowledges the support provided by her supervisor Dr. R. Seyezhai and thanks the management of Loyola-ICAM College of Engineering and Technology for encouraging the research work.

A. Inba Rexy,R. Seyezhai, (2016) Investigation of Current Control Techniques of AC-DC Interleaved Boost PFC Converter. Circuits and Systems,07,307-326. doi: 10.4236/cs.2016.74027