Three-winding coupled inductor for higher voltage gain of the transformer

With a three-winding coupled inductor, switched-capacitor technology, and cascade structure, the converter achieves higher voltage gain.

The input inductance of the converter effectively reduces the input current ripple, which reduces the input supply stress. In addition, the leakage inductance energy of the coupled inductor is recycled by the output terminal, and the voltage spike of the switching transistor can be suppressed and the voltage stress can be reduced while improving the efficiency.

The working principle of the cascaded high-gain power converter with three-winding coupled inductor and the steady-state performance of the converter in continuous conduction mode are analyzed in detail. Finally, a 30V input, 380V/0.3A output experimental prototype was built. The experimental results verified the correctness of the theoretical analysis.

As the penetration rate of renewable energy continues to increase, photovoltaic cells and fuel cells play an increasingly important role in their grid connection. Due to the low output voltage (less than 50V) of photovoltaic cells and fuel cell units, high-gain power converters need to be boosted to DC high voltage (usually 380V or 760V) to meet the requirements of the latter stage. The traditional Boost converter has limited actual voltage gain, high voltage and current stress, and low efficiency, which cannot meet the above application requirements [6].

In general, methods for boosting converter gain are: converter cascade, output series, coupled inductor, and increased switched capacitor. Although the converter cascade can effectively improve the voltage gain, it has the disadvantages of complicated topology and control mode, and the loop design is relatively difficult.

By sharing the switching tube, the circuit topology and control of the conventional cascaded Boost converter are simplified. However, the number of components in the cascade structure is still large, and the device voltage stress is high. To this end, a cascade structure is adopted, and a switched capacitor is introduced to further increase the voltage gain and reduce the voltage stress of the device. However, the number of cores in the topology is large and the system cost is high. Converter output series is another effective solution to boost voltage gain.

The output of the Boost converter and the Flyback converter are connected in series, and the high voltage gain is achieved through inductive coupling and common switching transistors, which simplifies the circuit topology. On this basis, a new high-gain topology is proposed by combining the converter cascade with the output series.

By designing the turns ratio of the coupled inductor, the above two converters can reasonably distribute the output capacitor voltage and the diode stress, and the leakage inductance energy is recovered by the output terminal, but when a very high voltage gain is required, there is a large core volume and leakage. Problems such as high inductance, high device stress, and large input current ripple. In addition, some scholars have proposed a high-gain scheme for three-winding coupled inductors [21-23]. This scheme can increase the flexibility of voltage gain adjustment while increasing the voltage gain, and the voltage stress distribution of the device is more reasonable.

This paper presents a cascaded high gain power converter with a three-winding coupled inductor. Based on the high gain scheme in [23], the converter proposed in this paper only needs to add one inductor and one diode, which can achieve higher voltage gain while preserving the advantages of the original scheme.

In addition, compared to the original input current interrupt, the newly added inductor can effectively reduce the input current ripple and reduce the input power stress. At the same time, the proposed converter reduces the three-way series output in the original scheme to two serial outputs, which can reduce the capacity and volume of the output capacitor and increase the power density of the converter.

Figure 2 High gain power converter topology presented in this paper

Figure 3 The equivalent circuit of the high gain power converter proposed in this paper

in conclusion

In this paper, a cascaded high-gain power converter with three-winding coupled inductor is proposed, and its working principle is analyzed in detail. Finally, the prototype is designed and built for experimental verification. Experiments show that the converter proposed in this paper has the following characteristics:

1) The topology requires only a single switch tube, and the control and drive are simple and reliable.

2) A higher voltage gain is achieved by using a three-winding coupled inductor, switched capacitor technology, and cascading.

3) By rationally designing the turns ratio of the three-winding coupled inductor, flexible distribution of output capacitance and diode voltage stress can be achieved.

4) The leakage inductance energy is recovered by the output end, which improves the efficiency and suppresses the voltage spike at both ends of the switch tube and reduces the voltage stress of the switch tube. Therefore, high-voltage switching devices with low withstand voltage can be selected to further improve conversion efficiency.

5) The input inductor effectively reduces the input current ripple and reduces the input power stress, which is beneficial to prolong the life of photovoltaic cells and fuel cells in renewable energy systems.

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