Control method and process for current-source dual-transformer bidirectional DC-DC converters

Issuing time:2023-05-16 16:43

Bidirectional dc-dc converters are widely used in energy storage systems, electric vehicles and solid-state transformers. Dual active bridge converter (dab) has been widely used because of its inherent zero voltage turn-off (zvs), high power density and electrical isolation. The traditional voltage source type dab consists of two active full Bridges and a high-frequency transformer. Various control methods have been proposed in the previous literature. The traditional single phase shift control can realize zero voltage turn-off of all switching tubes, but it has to face problems such as high average current and peak current when the primary side voltage matching ratio deviates from 1, which leads to the instability of the system and the reduction of efficiency. In order to minimize the peak value of leakage current, control methods such as double phase shift and three phase shift control have been applied, but such control methods often need to develop off-line tables to generate control variables, which is difficult to achieve real-time control. Meanwhile, the peak value of input current ripple is still large, which will reduce the life of energy storage devices such as batteries. Therefore, current-source dab is a better choice to extend voltage gain range and minimize charge/discharge current ripple. Under proper design, current-source dab can realize natural zero voltage shutdown, which is a feature that other topologies do not have. The traditional current source type dab is not suitable for the case of wide range voltage input and wide range voltage output, so the hybrid bridge topology of dual transformers can be used as a solution. The addition of a transformer can extend the voltage gain while avoiding increasing the number of switching tubes. The traditional control strategy keeps the voltage duty cycle at the low voltage side at 50% and realizes the current pulsation at the low voltage side at zero, which is good for the life of energy storage devices such as batteries at the low voltage side. When the secondary side adopts the volt-second balance control strategy, it may still produce large leakage current ripple to achieve zero voltage shutdown, resulting in large leakage current peak value and reduced reliability.


Technical implementation elements:


In order to solve the problem that the converter cannot realize a wide voltage input range and a wide output voltage range under bidirectional power current, and the leakage inductance current is not optimized enough, the control method for a bidirectional dc-dc converter with a double transformer of current source type disclosed in the invention shall solve the following technical problems: A control method for minimizing peak leakage current and effective value is provided. The wide input voltage range and wide output voltage range of the converter as well as the peak leakage current and effective value are optimized by fully digital control of low voltage level duty ratio on the low voltage side of the transformer, high level duty ratio on the high voltage side and voltage phase shift Angle between the low voltage side and high voltage side of the transformer. The wide range of soft switching of all switching tubes is realized, the on-loss and circulation loss of the converter are reduced, and the efficiency of the converter is improved.


Scheme implementation


The invention discloses a control method for a current source type double transformer bidirectional dc-dc converter. The current source type double transformer bidirectional dc-dc converter comprises a main circuit and a control circuit; The main circuit mainly consists of a full bridge circuit on the high voltage side, a high frequency transformer and a hybrid bridge circuit on the low voltage side. The control circuit includes a controller and a drive circuit. The current source type bi-directional hybrid bridge dc-dc converter obtains the duty cycle of zero level on the high voltage side by giving the output voltage, and realizes the matching of the output voltage measurement of the transformer. By determining the relationship between the high level duty cycle and phase shift Angle on the low voltage side, the zero level duty cycle on the high voltage side and the number of turns of the two transformers, the above variables are controlled to make the converter work in the mode of minimizing the peak current, optimize the peak value of leakage current and effective value, and realize the wide range of soft switching of all switching tubes, so as to improve the conversion efficiency of the converter.