Dilong On Board Charger Adopts Advanced PFC+LLC Solution

In recent years, with the continuous development of new energy electric vehicles, more and more electric vehicles have entered thousands of households and become a means of transportation for people. On Board Charger (OBC) has become a standard charging device for every household electric vehicle due to its convenient and fast charging feature. Therefore, the development of high-efficiency, compact, lightweight, high reliability, and high power density OBC is of great significance for the rapid development of the electric vehicle industry.

The on board charger developed and produced by Dilong adopts a two-stage structure of PFC+LLC, which has significant advantages such as high efficiency, small size, light weight, stable and reliable operation, and high power density.

The front-end adopts an interleaved parallel Boost PFC rectification structure, which is mainly responsible for improving the power factor of the power supply. By adjusting the phase and amplitude of the input current and input voltage, the current waveform and voltage waveform are made as consistent as possible, thereby reducing harmonic distortion and improving energy utilization efficiency.

As shown in the figure below, the waveform of the power supply without PFC structure in the front stage of Figure 1 at the AC input terminal is compared with the waveform of the power supply with PFC structure in the front stage of Figure 2 at the AC input terminal.

It can reduce power density, volume, and weight while doubling the power level, and also reduce input and output current ripple, shaping it into a sine wave with a power factor of ≥0.998, minimizing harmonic pollution caused to the power grid during charging.

The rear stage adopts full bridge LLC resonant transformation technology, which achieves zero voltage switching (ZVS) at both ends of the switching tube through capacitors and inductors in the resonant cavity, thereby reducing switching losses and improving conversion efficiency. It can achieve ZVS of the power switching tube in the full load range and ZCS of the secondary rectifier diode, improving the efficiency of the on-board charger and achieving a wide range of output.

In the research and design of on board chargers, Dilong combines PFC with LLC, with the PFC part responsible for improving power factor and generating a stable DC voltage. This DC voltage is then sent to the LLC converter for further voltage conversion and frequency adjustment, which can achieve a wide range of input voltage regulation and output voltage stability while maintaining the high efficiency of on board chargers.