Control Strategy of Bidirectional Power Converter for Mobile Energy Storage Vehicles based on Wide-Gain Variable-Mode Multi-Control Fusion

The LLC converter is a key component of the bidirectional power converter for mobile energy storage vehicles (MESV), it is difficult to obtain small gains at low power levels, so the power control in the pre-charging stage of the Li-ion battery cannot be achieved. In addition, the bus voltage may be lower than the peak grid voltage due to LLC reverse gain limitation. The low SoC of the lithium battery will result in the inverter not being able to connect directly to the grid. Aiming at these problems, a dual-mode switching full-bridge LLC control strategy is proposed to expand the range of pre-charge gain. In the reverse mode, the voltage gain is boosted by the gate signal on the asynchronous primary and secondary sides, and enables the inverter to be successfully connected to the grid. A 1.5 kW experimental platform was built to verify the strategy. Compared with the traditional single-mode pulse frequency modulation (PFM) control, the voltage control range was expanded from 58V-100V to 38V-100V, which met the control requirements in the pre-charging stage of lithium batteries. the inverter reverse gain is increased to 1.4. the problem is solved that the low SoC grid-connected total harmonic distortion (THD) does not meet the standard. Finally, the feasibility and effectiveness of this method are verified.