In modern power storage and application, batteries, as a key energy storage device, are widely used in automobiles, uninterruptible power supplies (UPS), solar power systems, and many other scenarios. The charging method has a crucial impact on the performance, lifespan, and safety of batteries. Constant voltage charging, as a commonly used charging method, can, to a certain extent, ensure the charging effect and stability of batteries. So, how exactly is constant voltage charging of batteries achieved?
I. Circuit Design for Constant Voltage Charging
(I) Linear Regulated Power Supply Circuit
A linear regulated power supply circuit is a basic method for achieving constant voltage charging. It mainly consists of a regulating transistor, a reference voltage source, a comparator amplifier, and a sampling resistor. The reference voltage source provides a stable reference voltage. The sampling resistor samples the voltage across the battery terminals and compares the sampled voltage with the reference voltage. The comparator amplifier outputs a control signal based on the comparison result, adjusting the conduction level of the regulating transistor to change the charging current and maintain a constant voltage across the battery terminals.
The advantages of linear regulated power supply circuits are stable output voltage, low ripple, and smoother battery charging. However, their disadvantages are also quite obvious. Because the regulating transistor operates in the linear amplification region, it consumes a lot of power, resulting in low power efficiency and severe heat generation, especially during high-current charging.
(II) Switching Power Supply Circuit
Switching power supply circuits are widely used in modern constant voltage charging. They convert the input DC voltage into a high-frequency pulse voltage by switching a high-frequency transistor on and off, and then rectify and filter it to obtain a stable DC output voltage. In the control section of the switching power supply, pulse width modulation (PWM) or pulse frequency modulation (PFM) techniques are used to regulate the output voltage.
During constant-voltage charging, the battery terminal voltage is monitored in real time by a feedback circuit and compared with the set constant-voltage value. When the battery voltage is lower than the set value, the control circuit increases the on-time of the switching transistor (PWM) or increases the switching frequency (PFM) to raise the output voltage and increase the charging current. When the battery voltage approaches or reaches the set value, the control circuit decreases the on-time of the switching transistor or decreases the switching frequency to lower the output voltage and decrease the charging current, thereby achieving constant-voltage charging.
The advantages of switching power supply circuits are high efficiency, the ability to achieve constant voltage charging over a wide power range, and small size and light weight. However, they also have some disadvantages, such as relatively large output voltage ripple, requiring more complex filtering circuits to reduce the impact of ripple on the battery; at the same time, the high-frequency switching action of the switching power supply may generate electromagnetic interference, requiring corresponding shielding and filtering measures.
II. Control Strategies and Algorithms
(I) Simple Voltage Feedback Control
The simplest constant-voltage charging control strategy is open-loop control based on voltage feedback. A fixed charging voltage is set and applied directly to the battery terminals. However, this method does not account for changes in the battery's internal resistance, temperature, and other disturbances during charging, resulting in poor charging accuracy and stability. In practical applications, this simple control method is rarely used alone.
(II) PI Control Algorithm
The proportional-integral (PI) control algorithm is a commonly used closed-loop control algorithm with wide applications in constant-voltage charging. The PI controller adjusts the charging current by performing proportional and integral calculations on the deviation of the battery terminal voltage (the difference between the set voltage and the actual voltage) and outputting a control signal. The proportional element responds quickly to voltage deviations, while the integral element eliminates steady-state errors, gradually stabilizing the battery terminal voltage near the set value.
PI control algorithms are relatively simple and easy to implement, and can improve the accuracy and stability of constant voltage charging to a certain extent. However, they also have some limitations, such as being sensitive to parameter changes, and the PI parameters may need to be readjusted under different operating conditions to achieve the best control effect.
(III) Intelligent Control Algorithm
With the development of intelligent control technology, some advanced intelligent control algorithms are gradually being applied to the field of constant voltage charging of batteries. For example, fuzzy control algorithms transform expert experience and knowledge into fuzzy rules, fuzzify parameters such as voltage and current during the charging process, and then perform reasoning and decision-making based on the fuzzy rules to output control signals. Fuzzy control does not rely on precise mathematical models, has strong robustness to changes in system parameters and disturbances, and can adapt to charging of batteries under different types and operating conditions.
Achieving constant-voltage charging of batteries requires comprehensive consideration of circuit design, control strategies, and various factors during the charging process. By rationally selecting the circuit topology, employing advanced control algorithms, and ensuring proper preparation before charging, monitoring and protection during charging, and post-charging processing, constant-voltage charging of batteries can be effectively achieved, improving charging efficiency, extending battery life, and ensuring safe and reliable operation. With continuous technological advancements, constant-voltage charging technology for batteries will continue to develop and improve, providing even better solutions for power storage and application.
