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After discharging the battery of an electric vehicle, the direct current is used to pass the battery in the opposite direction from the discharge current to restore its working capacity. This process is called battery charging. When the battery is charged, the positive pole of the battery is connected with the positive pole of the power supply, and the negative pole of the battery is connected with the negative pole of the power supply. The voltage of the charging power supply must be higher than the total electromotive force of the battery. There are two charging modes: constant current charging and constant voltage charging.
The conventional charging system was designed according to internationally accepted rules of thumb prior to 1940. The most famous of these is the "ampere-hour rule" : the number of amperes charged should not exceed the number of ampere-hours left to charge the battery. In practice, the speed of conventional charging is limited by the temperature rise and gas generation of the battery during charging. This phenomenon has important implications for the minimum time necessary to charge batteries.
Constant current charging method is to adjust the output voltage of the charging device or change the series resistance of the battery to keep the charging current intensity unchanged. The control method is simple, but because the acceptable current capacity of the battery is gradually decreased with the charging process, to the late charging, charging current is used for electrolytic water, gas generation, so that the gas is too much, therefore, often choose stage charging method.
This method includes two-stage charging method and three-stage charging method
Charging stations for electric vehicles
Charging stations for electric vehicles
(1) The two-stage method adopts the quick charging method combining constant current and constant voltage. First, charge to a predetermined voltage value by constant current, and then change to constant voltage to complete the rest of the charging. In general, the conversion voltage between the two stages is the constant voltage of the second stage.
(2) Three-stage charging method at the beginning and end of charging using constant current charging, with constant voltage charging in the middle. When the current decays to a predetermined value, the second stage is converted to the third stage. This method can reduce the gas output to a minimum, but as a quick charging method, it is limited.
(1) The two-stage method adopts the quick charging method combining constant current and constant voltage. First, charge to a predetermined voltage value by constant current, and then change to constant voltage to complete the rest of the charging. In general, the conversion voltage between the two stages is the constant voltage of the second stage.
(2) Three-stage charging method at the beginning and end of charging using constant current charging, with constant voltage charging in the middle. When the current decays to a predetermined value, the second stage is converted to the third stage. This method can reduce the gas output to a minimum, but as a quick charging method, it is limited.
The voltage of the charging power supply remains constant throughout the charging time, and the current decreases gradually as the terminal voltage of the battery increases. Compared with constant current charging method, its charging process is closer to the optimal charging curve. Fast charging with constant voltage, due to the initial charging battery electromotive force is low, charging current is very large, with the charging, the current will gradually reduce, therefore, only a simple control system.
This charging method has little electrolytic water and avoids battery overcharging. But in the early charging current is too large, the battery life has a great impact, and easy to make the battery plate bending, resulting in the battery scrap. Due to this shortcoming, constant voltage charging is rarely used, only when the charging power supply is low and the current is high. For example, when a car is running, the battery is charged at constant voltage.
(1) Pulse charging method, this charging method not only follows the battery inherent charging acceptance rate, but also can improve the battery charging acceptance rate of electric vehicles, thereby breaking the limit of the battery index charging acceptance curve, which is the new development of the battery charging theory.
Charging stations for electric vehicles
Charging stations for electric vehicles
(2) 2REFLEXTM fast charging method, this technology is a patent technology in the United States, it is mainly facing the charging object is nickel-cadmium battery. Because it adopts a new charging method, it solves the memory effect of nickel-cadmium battery, so it greatly reduces the fast charging time of the battery. The charging method of lead-acid battery and the detection method of the charging state are very different from the nickel-cadmium battery, but they can borrow REFLEXTM charging method of a working cycle including forward charging pulse, reverse instantaneous discharge pulse, stop charging to maintain three stages.
(3) Variable current intermittent charging method, which is based on constant current charging and pulse charging, as shown in FIG. 7. It is characterized by changing constant current charging section to limited-voltage variable current intermittent charging section. In the early stage of charging, the method of variable current intermittent charging is adopted to ensure that the charging current is increased and most of the charging quantity is obtained. At the later stage of charging, a constant voltage charging section is used to obtain the overcharge amount and restore the battery to a fully charged state. Through intermittent stop charging, the battery by the chemical reaction of oxygen and hydrogen combined by absorbing the have time to make the concentration polarization and ohm polarization naturally get eliminated, thus reduce the battery internal pressure, make the next round of constant-current charging can more smoothly, the battery can absorb much more power.
(4) Variable voltage intermittent charging method. On the basis of variable current intermittent charging method, variable voltage intermittent charging method was proposed, as shown in Figure 8. The difference with variable current intermittent charging method is that the first stage is not intermittent constant current, but intermittent constant voltage. In each constant-voltage charging stage, because it is constant-voltage charging, the charging current naturally decreases in accordance with the exponential law, in line with the characteristics of the acceptability of battery current gradually decreases with the charging process.
(5) Variable voltage and current wave intermittent positive and negative zero pulse rapid charging method, combined with the advantages of pulse charging method, ReflexTM rapid charging method, variable current intermittent charging method and variable voltage intermittent charging method, variable voltage and current wave positive and negative zero pulse intermittent rapid charging method has been developed and applied. Pulse charging method charging circuit control generally has two kinds:
1) The amplitude of pulse current is variable, while the frequency of PWM signal is fixed;
2) The amplitude of pulse current is fixed and the frequency of PWM signal is adjustable.
Pulse current amplitude and PWM signal frequency are fixed, PWM duty ratio is adjustable, on this basis, join the intermittent stop phase, can be in a shorter time to charge more power, improve the battery charging capacity.