Design and manufacture of a lead-acid battery charger

With the development of various electric vehicles, the demand for power battery chargers will increase. The quality of the charger is related to the performance and life of the battery, and the intelligence of the charger itself is related to the user's convenience and management issues such as power system electricity billing. Different batteries have different characteristics and different charging strategies. If the charger of one battery is well made, it is easy to expand the technology to other battery types. This topic is practical and targeted at the training of talents in the field of electric racing.

Main functional indicators:

The input voltage is single-phase 50HZ ±10%, and the voltage effective value fluctuation range is 220V ±20%, that is, the effective value is 176V-264V;

Output DC rated voltage 50V;

Add power factor correction at the input end, power factor 90%;

The initial charging efficiency is greater than 80%;

Input current distortion is less than 4%;

The charging process is divided into stimulation, fast charging and floating charging;

With temperature detection function, the charging strategy can be changed according to the battery and ambient temperature;

It has a friendly human-machine interface and can adjust the charging strategy;

Cooling method: air cooling.

Overall block diagram of the main circuit:

EMI filter circuit:

C1 and L1 form the first stage EMI filtering

C2, C3, C4 and L2 form the second stage filter.

L1, L2 are common mode inductors

Rectification and power factor correction circuit:

Rectifier bridge:

Current flowing through the diode ID = 3.55A

Diode reverse voltage V=373V

Considering the actual working conditions, BR601 (35A/1000V) is selected;

Power Factor Correction:

Solution: BOOST topology has low output resistance, simple hardware circuit and control, and mature technology, so BOOST structure is selected;

Chip selection: TI's UCC2801 9 can control the power output to 100W-2KW, and the power factor can be increased to 0.95, which meets the design requirements, so this chip is selected for this design;

Circuit Diagram

DC-DC main topology:

Solution options:

When the switch tube is subjected to peak current and voltage, the output power of the full-bridge is twice that of the half-bridge. When the power is greater than 500W, the full-bridge is more suitable than the half-bridge. Therefore, this design adopts the full-bridge topology.

Power switch tube selection:

After rectification and filtering, the maximum voltage is 373V, and the maximum primary current is 3.5A. Considering the actual working conditions, choose FQA24N50

(24A/500V/0.2Ω)

Output rectifier diode:

The maximum reverse voltage that the rectifier diode has to withstand is 100V and the current is 10A. Considering the actual working conditions, we choose MUR3060 (600V/30A)

Full bridge circuit diagram:

Rectification and filtering output circuit:

Driving circuit:

The PWM signal is isolated by an optocoupler and enters the half-bridge driver chip IR2110 through an inverter. The Q1 and Q2 half-bridge driver circuits are shown in the figure. The Q3 and Q4 driver circuits are the same as this circuit.

Auxiliary power supply:

This design system uses a separate auxiliary power supply for power supply. The system block diagram is as follows:

This power supply system can provide stable 12V, 5V, -12V voltage with high efficiency.

Intelligent control circuit design:

Power PWM control section

The power core control chip used in this design is the SG3525 chip from General Motors, USA. The control circuit is shown in the figure:

Sampling circuit

Thermal protection circuit

This designed system can detect the battery temperature and charger temperature. When the battery is overheated, the PWM output waveform will be turned off, causing the circuit to stop working. At the same time, the microcontroller will alarm. When the charger is overheated, the air cooling system will be turned on. If the temperature continues to rise, the charger will stop working.

Overcurrent, short circuit protection circuit

When the current is too large, exceeding 12A, the circuit will limit the current and alarm. Before the charger starts, a short circuit detection will be performed. When the resistance is less than 0.5Ω, the circuit is considered to be faulty and an alarm will be issued.

System software structure

Four-stage charging control strategy:

Analysis of the four-stage charging strategy:

Activation charging: After the charger starts working, the microcontroller collects the battery terminal voltage for detection. If the voltage is too low, it means that it has been over-discharged. In order to avoid excessive charging current, small current activation is implemented.

Constant current charging: Constant current charging is 10A.

Constant voltage charging: The constant voltage charging voltage is 59V.

Trickle float charge: When the charging current drops to 0.1 times of the constant current, that is, 1A, trickle float charge is used.

The four-stage charging strategy ensures that the battery can be activated and repaired in the early stage of charging, making the battery more durable, and can be fully charged without overcharging in the final stage.

Power system anti-interference

Hardware anti-interference technology

Power supply EMC design: The rectifier diode uses Schottky diode as the rectifier tube, the switch tube loop adds RCD network, the input end adds EMI filter circuit, and the transformer design is optimized.

Optimize PCB board layout and routing.

Software anti-interference technology

Adopt remote interception technology between program modules.