Central issue:
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* The basic principle of intelligent variable pulse charging technology
* Basic principle of segmented constant current charging intelligent control technology
solution:
* Intelligent variable pulse charging technology and segmented constant current charging intelligent control technology
An important manifestation of the green revolution is green transportation. Electric vehicles have emerged as the times require, and their market demand has also shown an increasing trend. Electric vehicles have long charging time, and charging is difficult as a problem in the promotion and application of electric vehicles. Therefore, the research of fast charging technology has a great impact on the development of electric vehicles, and has far-reaching significance. At present, the research results of the more mature fast charging technology mainly include intelligent variable pulse charging technology and segmented constant current charging intelligent control technology.
The basic principle of intelligent variable pulse charging technology:
The variable pulse fast charging system is mainly composed of a rectifier and a power converter, as shown in Figure (1).
According to the real-time detection of the battery terminal voltage, charging current, temperature, dynamic internal resistance and other information, the fast charger implements the charging current pulse width T1, the intermittent time T2, and the discharging current according to the mass charging law by using an intelligent control algorithm. The segmentation adjustment of the pulse T3 eliminates the polarization phenomenon of the charged battery pack, so that the battery pack is in a better current receiving state at all times, and the charging speed and the charging efficiency are improved. The specific control process is: first, charging with a wider charging pulse, the terminal voltage of the battery rises, when the charging time T1 is reached, the charger suspends charging, and when the charging intermittent time reaches T2, the charger continues to be charged, so repeated, as shown in the figure (2) shown.
When the voltage rises to the set voltage value V1, according to the setting of the program, the duty cycle of the charging pulse is reduced, and the battery is charged. When the battery terminal voltage reaches the set value V2, the charger intermittently suspends charging; The voltage automatically adjusts the duty cycle of the output pulse. After a short time to stop charging, the polarization voltage of the battery drops rapidly, and the cycle is repeated until the battery end charging voltage V3 is reached.
For the first time, the fast charger realizes intelligent real-time adjustment of the pulse charger charging pulse according to the actual state of charge (current, voltage, temperature, dynamic internal resistance, etc.) of the charged battery, and raises the charger and the charged battery to one. The system problem is comprehensively considered, and the charger has a wider applicability by introducing an intelligent adjustment algorithm.
The basic principle of segmented constant current charging intelligent control technology:
The segmented constant current charging intelligent control circuit is shown in Figure (3). The circuit is controlled by the CPU, which can detect the temperature of the rechargeable battery and the charging environment, time the battery charging, and control the segmented constant current charging process by using the voltage and current of the battery during charging.
Segmented constant current charging makes the actual charging current curve of the battery close to the charging acceptable current curve, which is an effective method for realizing rapid charging of the battery. The capacity gradient method is used to determine the standard parameters of the constant current charging termination, reduce the gradient constant of the stepped constant current charging current, and supplement the protection control of stopping the charging when the battery temperature is too high, so that the intelligent fast charging control of the power battery can be realized.
First, the phase constant current charging termination standard of the segmented constant current charging intelligent control technology adopts the capacity gradient method, that is, the capacity gradient parameter dU / dC is used as the phase constant current charging termination judgment standard. According to the constant current charging characteristic curve of the battery, the charging termination capacity gradient parameter is determined. During the charging process, the controller samples the charging voltage with a set frequency, calculates the capacity gradient value under I ( n), and sets the charging value. The termination capacity gradient standard is compared, and it is judged based on the comparison result whether or not the current phase constant current charging is terminated.
Secondly, the segmented constant current charging intelligent control technology can make the actual charging current curve closer to the charging acceptable current curve by reducing the constant current value falling gradient (increasing the number of segments). The initial constant current value I(1) of the battery is determined by experiments, and the current reduction amplitude of the phase constant current charging is reduced. If the time to reach the charge termination capacity gradient value is short after the charge current is reduced (set a minimum charge time), the magnitude of the current drop is appropriately increased. The piecewise constant current charging current curve is shown in Figure (4).
Finally, the charging safety assurance control parameter of the segmented constant current charging intelligent control technology is set to the battery temperature. Set the maximum battery temperature limit. If the battery temperature reaches the limit during charging, stop charging immediately. When the battery temperature drops to the normal temperature, the charging current is appropriately reduced to continue charging until the constant current charging is completed, thereby ensuring the charging safety.
The test results show that the intelligent variable pulse charging technology and the segmented constant current charging intelligent control method can effectively shorten the charging time, improve the charging efficiency and prolong the battery life.
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