With the aggravation of energy crisis, resource exhaustion and air pollution, China has established new energy vehicles as a strategic emerging industry. As an important part of electric vehicles, vehicle chargers have both theoretical research value and important engineering application value. FIG. 1 shows the structure block diagram of vehicle charger with the combination of front STAGE AC/DC and rear stage DC/DC.
When the car charger is connected to the power grid, it will produce certain harmonics, pollute the power grid, and affect the stability of the electric equipment. In order to limit the amount of harmonics, the International Electrotechnical Commission developed the harmonic limit standard iec61000-3-2 for electrical equipment, and China also issued the NATIONAL standard GB/T17625. In order to comply with the above standards, on-board chargers must undergo power factor correction (PFC). PFC AC/DC converter supplies power to the rear DC/DC system on the one hand, and auxiliary power supply on the other hand. The design of PFC AC/DC converter directly affects the performance of car charger.
In view of the volume and harmonics of pure electric vehicle chargers have harsh requirements, this design uses active power factor correction (APFC) technology. APFC has a variety of topologies. The Boost topology has the advantages of simple driving circuit, high PF value and special control chip, so the main circuit of the Boost topology is selected. Considering various basic control methods, the average current control method with advantages of low harmonic distortion, insensitivity to noise and fixed switching frequency is selected.
This article in view of the power of 2 kW all-electric car charger, considering the harmonic content, volume and anti-jamming performance design requirements, the key research PFC AC/DC converter, contains the system main circuit and control circuit design, and on the basis of the study, in the study of system simulation and experimental tests verify
2 PFC AC/DC converter main circuit design
The main circuit of PFC AC/DC converter is composed of output filter capacitor, switching device, boost inductor and other components, and its parameters are designed as follows.
2.1 Output filter capacitance
The output filter capacitor can filter out the output voltage ripple caused by the switching action and maintain the output voltage in a certain range. The selected device should better realize the above two functions.
The control circuit adopts double closed-loop structure: the outer loop is voltage loop and the inner loop is current loop. The current loop controls the input current of the main circuit and tracks the reference current to achieve power factor correction. The output voltage of the voltage loop and the output reference voltage are compared by the voltage error amplifier. The output signal, the feedforward voltage and the input voltage are calculated by the multiplier to obtain the input reference current of the current loop. By adjusting the current loop, the driving signal of the main circuit switch tube is generated to achieve the power factor correction of the system and output a stable DC voltage. The multiplier is mainly used for signal multiplication. Here, this paper focuses on thedesign of voltage loop and current loop.
Post time: Jun-20-2022