Researcher Sun Xiaofeng, Pan Wei, Shen Hong, Shen Yanfeng, and Li Wei, researchers of the Key Laboratory of Power Electronics Energy Conservation and Transmission Control in Yanshan University (Yanshan University), wrote in the 24th issue of Journal of Electrical Engineering, in 2017, on the traditional current-type transformation The present invention has a shutdown voltage spike problem and a hard switching phenomenon, and proposes a resonant high-voltage side modulation current-type bidirectional DC converter.
By introducing variable frequency control and high-voltage side modulation strategy, the converter can realize natural commutation and zero current shutdown (ZCS) of the low-voltage side switching tube, eliminating the voltage spike of the low-voltage side switching tube. Firstly, the working principle of the forward and reverse working modes of the circuit is analyzed. Then, the detailed characteristics analysis and design of the converter are carried out. Finally, a 400W prototype is built and tested. The experimental results verify the advantages and feasibility of the proposed circuit topology and control strategy.
In new energy applications, energy storage systems are essential. A bidirectional converter is required between the energy storage components (battery and supercapacitor) and the high voltage bus to achieve energy exchange [1, 2]. Compared with voltage-type converters, current-mode converters can reduce current ripple and extend battery life [3] for better performance [4]. Therefore, there is a need for a current mode bidirectional converter as an interface circuit for an energy storage component and a high voltage bus.
The current type bidirectional DC converter has the characteristics of simple structure [5], low current ripple on the low voltage side, low switch conduction loss, high voltage gain [6], high utilization of the transformer, and is suitable for low voltage and high current applications. When the conventional current-mode DC converter is in the operating mode, due to the leakage inductance of the transformer, the voltage switch at the low-voltage side of the switch will generate severe voltage spikes, which greatly limits the power level and switching frequency of the converter [7].
In response to the above problems, scholars have proposed many improved topologies and control schemes. In the literature [8-10], an active clamp circuit is introduced to solve the turn-off voltage spike problem, and the zero voltage turn-on (ZVS) of the switch is realized. The literature [11,12] adopts frequency conversion control, which maintains the advantage of simple structure of the current-type two-inductor converter. Although the turn-off voltage spike is suppressed, the voltage peak is still maintained at more than 3 times of the transformer primary voltage. At the same time, the schemes in the above documents are all one-way boost mode, and the two-way flow of energy cannot be realized.
In [13], a bidirectional control scheme is proposed: in the forward working mode, the fixed-frequency PWM control is adopted, and the high-voltage side modulation scheme is added, which can realize the natural commutation and zero-current shutdown of the low-voltage side switching tube (Zero Current Switching). , ZCS), eliminates the turn-off voltage spike; in the reverse mode of operation, the converter uses variable frequency control, the low-voltage side is used as a current-doubler circuit, and synchronous rectification technology is added; however, the modulation methods of the two modes are different. Therefore, smooth switching between forward and reverse is not possible.
In [14], a bidirectional frequency conversion control scheme is proposed: both the forward working mode and the reverse working mode adopt frequency conversion control, and the ZVS of the low voltage side switching tube is realized by using the transformer leakage inductance and the parasitic capacitance resonance of the low voltage side switching tube; However, the low-voltage side switch still has a turn-off voltage peak of more than three times, and the voltage peak increases as the power increases.
In this paper, a resonant high-voltage side-modulated current-mode bidirectional DC converter is proposed. The control scheme is variable frequency control plus high-voltage side modulation strategy. The scheme combines the advantages of the above two schemes, realizes smooth switching of forward working and reverse working, and realizes ZCS and ZVS of the low-voltage side switching tube through the high-voltage side modulation strategy and resonance control, and the low-voltage side switching tube The turn-off voltage peak is limited to twice the primary voltage of the transformer, eliminating the turn-off voltage spike; at the same time, the high-voltage side switch can also achieve ZVS in the full power range.
Figure 1 Current type bidirectional DC converter circuit
in conclusion
In this paper, a resonant high-voltage side modulation bidirectional DC converter is proposed. Through theoretical analysis and experimental verification, the DC converter has the following advantages:
1) Bidirectional flow of energy and high voltage gain can be achieved by controlling the duty cycle and frequency.
2) The low-voltage side switch tube realizes the natural commutation of the switch tube and ZCS.
3) By introducing the resonance control, the turn-off voltage spike of the low-voltage side switch tube is eliminated, and the ZVS of the low-voltage side switch tube is realized.
4) Due to the ZVS of the high-voltage side switch, the current is independent of the power of the circuit, so the high-side switch can achieve ZVS in the full power range.
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