Application of magnetic integration technology in asymmetric half-bridge current doubler rectifier converter-EEWORLD

Collect

1 Introduction

With the continuous increase in the clock frequency of communication equipment and computers, the requirements for low-voltage/high-current output power supplies are getting higher and higher. To increase power density, it is necessary to reduce the volume and reduce losses. People usually use the method of increasing frequency to achieve miniaturization, but due to the limitations of magnetic components, the high-frequency method has certain limitations: on the one hand, the increase in frequency will be limited by the efficiency of the whole machine; on the other hand, the increase in frequency will lead to a rapid increase in core loss. In order to reduce core loss, the core is generally used at a reduced rating when working at high frequency, and the core utilization rate is reduced, which limits the reduction in the volume of magnetic components. In order to further reduce the volume and loss of magnetic components and ensure good performance of the converter, people have studied the application of magnetic integration technology. Magnetic integration technology is to wind two or more discrete magnetic components of the converter on a pair of magnetic cores and concentrate them together in terms of structure. The use of magnetic integration technology can reduce the volume, weight and loss of magnetic components, reduce current ripple, and improve filtering effects, which is of great significance to improving the performance and power density of power supplies.

2 Circuit structure and magnetic component structure

When studying circuit topology, we should not only consider the problem from the perspective of circuit topology, but also pay attention to combining the circuit topology scheme with the possible integration scheme of magnetic components to achieve the best combination of circuit structure and magnetic component structure.

2.1 Circuit structure

Figure 1 Asymmetric half-bridge current doubler rectifier converter circuit
The asymmetrical half bridge (Asym. HB) current doubler rectifier (CDR) converter circuit is shown in Figure 1. This circuit structure is chosen because it is simple and efficient, and CDR is beneficial to reducing the loss of the secondary winding of the transformer. There are three discrete magnetics (DM) in the circuit of Figure 1, transformer T, inductor LO1 and LO2. This article mainly uses magnetic integration technology to integrate these three magnetics together, thereby reducing the loss and volume of magnetics. The magnetics after DM integration are called integrated magnetics (IM).

2.2 Magnetic structure

Using the source transfer equivalent transformation method, the transformation process of IM is given as follows:

(a) DM-CDR circuit

(b) IM-CDR circuit proposed by C. Peng

(d) Combining the windings of the IM in (c) yields the IM proposed by Wei Chen

[page]

(e) IM obtained by splitting the winding of the IM in (d)

(f) Changing the winding connection method of the IM in (e) to obtain an improved IM
Figure 2 The transformation process of IM in the asymmetric half-bridge current doubler rectifier circuit
Figure 2 (a) is a simplified DM-CDR circuit from Figure 1. Figure 2 (b) is the IM-CDR circuit first proposed by C. Peng. Using the source transfer equivalent transformation method, the number of turns of the secondary winding of the magnetic component shown in Figure 2 (b) remains unchanged and is split into two, resulting in Figure 2 (c). Let R1, R2, and Rc be the magnetic resistance of the three magnetic columns of the magnetic core, respectively, and the equivalent magnetic circuit of Figure 2 (c) in one working cycle can be drawn: when the voltage between points a and b is positive, the output voltage is applied to both ends of c and d, c is positive and d is negative, φ1 increases, φ2 decreases, and the equivalent magnetic circuit is Figure 3 (a); when the voltage between points a and b is negative, the output voltage is applied to both ends of e and d, e is positive and d is negative, φ2 increases, φ1 decreases, and the equivalent magnetic circuit is Figure 3 (b). It can be seen from the equivalent magnetic circuit that when the voltage between points a and b is positive, the magnetic motive force generated by the inductance and the secondary side of the transformer is completely offset in the magnetic circuit corresponding to φ2; when the voltage between points a and b is negative, the magnetic motive force is offset to zero in the magnetic circuit corresponding to φ1. According to the results of the magnetic circuit analysis, the secondary winding of the transformer and the inductance winding of the IM in Figure 2 (c) are combined to obtain Figure 2 (d), which is the IM proposed by Wei Chen. Compared with Figure 2 (b), Figure 2 (d) omits the secondary winding of the transformer and reduces the connection terminals of the IM, which is very beneficial to reducing the copper loss and volume of the magnetic parts. However, the windings in Figure 2 (d) are located in three magnetic columns respectively, and there must be a large leakage inductance, which will reduce the performance of the converter. To overcome this problem, the source transfer transformation method can be used to split the primary side ab winding into two and move it to the side column, as shown in Figure 2 (e). In Figure 2 (e), the winding of the IM is divided into two parts, which are wound on the two side columns of the magnetic core respectively. By changing the connection mode of the winding on a magnetic column in Figure (e) (actually changing the same-name ends of the windings), an improved IM-CDR circuit is obtained, as shown in Figure 2 (f). When changing the winding connection mode, the windings on the same magnetic column should be changed at the same time, so that the same-name ends between the windings on the same magnetic column remain relatively unchanged. Compared with Figure 2 (d), Figure 2 (e) can reduce the alternating magnetic flux of the column in the magnetic core, which is also beneficial to reducing the primary current.

(a)Vab>0 (b)Vab<0
Figure 3 Equivalent magnetic circuit of the magnetic component shown in Figure 2 (c)

3 Simulation waveforms

Comparing Figure 2 (e) and Figure 2 (f), it can be concluded that the flux coupling effects are different in the two different modes. When the flux generated by the windings enhance each other, it is a forward coupling mode; otherwise, it is a reverse coupling mode. Obviously, Figure 2 (e) is a forward coupling mode, and Figure 2 (f) is a reverse coupling mode.

A------Reverse coupling center column alternating flux
B, C------Alternating magnetic flux of two side columns
D------Forward coupling center column alternating flux
Figure 4 Alternating magnetic flux of the column in two different integration methods

Figure 5: Magnetic flux ripple coefficients of two integration methods with different duty cycles
[page] PSpice simulation of the above two coupling methods can be obtained as shown in Figure 4. It can be concluded from Figure 4 that the alternating magnetic flux of the middle column is the sum of the alternating magnetic flux of the two side columns. The forward coupling method increases the alternating magnetic flux of the middle column, and the reverse coupling method reduces the alternating magnetic flux of the middle column, that is, it reduces the maximum magnetic density of the middle column, thereby reducing the volume of the magnetic component.
Figure 5 shows the magnetic flux ripple coefficient of the middle column under two different integration methods when the duty cycle D changes. The size of the duty cycle D can be adjusted by PWM. In the reverse coupling (Figure 2 (f)), the alternating magnetic flux generated by the two side columns is reduced in the middle column, especially when D = 0.5, the alternating magnetic flux generated by the two side columns is completely offset in the middle column, and the ripple coefficient is zero; while in the forward coupling (Figure 2 (e)), regardless of the value of the duty cycle D, the ripple coefficient is always 1.
From the above comparison, it can be concluded that the reverse coupling integration method is more conducive to reducing the alternating magnetic flux of the middle column, reducing the maximum magnetic density of the middle column, reducing the volume and loss of the middle column, and thus reducing the volume and loss of the entire magnetic component.

4 Efficiency curve

In order to illustrate the effect of magnetic integration, the efficiency curves of forward coupling and reverse coupling (Figure 6) and the efficiency curve when the input voltage changes during reverse coupling (Figure 7) are given.

Figure 6 Efficiency curves of two integration methods with different output powers
Figure 6 shows that the efficiency in the reverse coupling mode is significantly higher than that in the forward coupling mode. As far as the reverse coupling mode is concerned, it can be seen from Figure 6 that the efficiency of the converter increases with the increase of load before the output power reaches 700W; it is the highest at about 700W, about 94.6%, and then decreases with the increase of load. This is because when the load is small, the loss of the power device in the converter accounts for a small proportion, while other losses account for a large proportion, and this part of the loss is much less sensitive to load changes than the device loss. Therefore, when the load is small, as the load increases and the output power increases, the proportion of other losses gradually decreases, and the converter efficiency increases; when the load increases to a certain extent, the loss of the power device becomes the main part of the loss. Since the power device used is a MOS device, the conduction loss is proportional to the square of its current effective value, and the output power is proportional to the load current, so the efficiency will show a downward trend as the load increases.

Figure 7 Efficiency curves for reverse coupling at different input voltages
Figure 7 shows the efficiency of the converter in the input range of 300-400V. Although the Asym HB converter is more suitable for constant input voltage, its efficiency is not less than 91.6% in the input range of 300-400V.

5 Conclusion

The magnetic integration technology can be used to integrate the two discrete inductors and a transformer in the asymmetric half-bridge current doubler rectifier converter into a core structure, which effectively reduces the alternating magnetic flux of the middle column, thereby reducing the volume of the magnetic parts and the core loss, and improving the power density.
However, the asymmetric half-bridge current doubler rectifier circuit and magnetic integration technology still have shortcomings. For example, CDR will increase the primary side loss of the converter and the loss of the filter inductor; the loss of the secondary side rectifier is also the main factor limiting the efficiency of the converter; due to the limitations of the existing magnetic core and the influence of scattered magnetism, magnetic integration technology will increase copper loss while reducing iron loss. For example, the air gap of IM is large, and the increase in copper loss may offset the core loss reduced by magnetic integration. All these shortcomings will also promote the further development of circuit topology and magnetic integration technology.

References

[1] CPES, “Asymmetrical Half Bridge with Current Doubler”, 3-28-3-33, April 2002.
[2] Chen Qianhong, “Application of Magnetic Integration Technology in Switching Power Supplies”, PhD Dissertation, Nanjing University of Aeronautics and Astronautics,
September 2001.
[3] Chen Qianhong, “High Efficiency, Low Voltage Output Forward-Flyback Converter Using Magnetic Integration Technology”, Transactions of the Chinese Society of Electrotechnical Engineering,
Vol. 17, No. 1, February 2002.
[4] Chen Wei, Luo Henglian, Li Zheyuan, Zhou Xunwei, Xu Peng, “
Research on Planar Integrated Inductor Scheme for Multi-module Interleaved Quasi-square Wave (QSW) DC/DC Power Converter”, Proceedings of the 13th National Power Technology Annual Conference, pp.37~40.
[5] Bo Yang and Fred C.Lee, Alpha J.Zhang and Guisong Huang, “LLC Resonant Converter for
Front End DC/DC Conversion” IEEE 2002 , pp.1108~1112.

Reference address：Application of magnetic integration technology in asymmetric half-bridge current doubler rectifier converter

Previous article：Application of Phase-Locked Loop in Frequency Modulation and Demodulation Circuit
Next article：Research on four-quadrant rectification of electric locomotive based on space voltage vector

Popular Resources
Popular amplifiers