Introduction to the system of power battery charge

Power batteries have two charge methods: slow charge and fast charge, and the power battery charge is different. So, how can we choose the right charge method we want according to the introduction of power battery charge?

According to the charge method used to select the appropriate battery, this article will introduce the charge function, method, battery pack charge method, charger and other aspects. The purpose is to enumerate the knowledge of charge power batteries and provide better concrete ideas.

1. Power battery charge function

Restore the battery to its rated capacity as soon as possible. That is, under the premise of restoring battery capacity, the shorter the charge time, the better.

Eliminate the adverse consequences caused by the battery in the discharge process, and repair the battery performance damage caused by deep discharge, polarization, etc. Recharge the battery to overcome the adverse effects caused by battery self-discharge.

2. Power battery charge method

There are two ways of power battery charge: conventional charge method and fast charge method.

① Conventional charge method

The conventional charge method, also known as the traditional power battery charge, only requires plugging the plug of the car charger into the parking lot or a power socket at home to charge, so the charge process is generally completed by yourself independently.

During the charge process, the battery voltage changes, and understanding more of the car battery voltage will facilitate the process. It is characterized by taking power directly from the low voltage lighting circuit, the charge power is small. 

It is powered by the standard grid power supply, and the typical charge time is 8–10 h (the soc reaches more than 95%). There are three conventional charge ways: constant current charge method, constant voltage charge method, and stage charge method.

● Constant current charge method

During the charge process, the power battery charge type that keeps the charge current constant is called constant current charge. Constant current charge has the following characteristics:

• During the charge process, the charge current is constant, but the charge voltage changes.

That is, during the charge process, the terminal voltage of the battery continues to rise, in order to ensure the constant charge current, the charge power supply voltage or regulating load should change at any time.

• Batteries with different terminal voltages can be charged in series.
• Long charge time.
• The size of the charge current can be determined according to the type of charge and battery capacity.

● Constant voltage charge method

During the charge process, the voltage applied to both ends of the battery remains unchanged, which is called constant voltage charge. Constant voltage charge has the following characteristics:

During charge, the charge voltage remains unchanged. If the charge voltage is too low, the battery will be undercharged. If the charge voltage is selected too high, the battery will continue charge after it is fully charged, and the charge at this time is overcharged.

At the beginning of constant voltage charge, the battery electromotive force is small, so the charge current is very large. In the middle and late stages of charge, the anode potential becomes higher and the cathode potential becomes lower. So the electromotive force increases, and long-term undercharge is formed, which affects the battery's service life.

● Stage charge method

The ways comprises a two-stage charge method and a three-stage charge method. The two-stage method adopts a fast power battery charge combining constant current and constant voltage.

The three-stage power battery charge uses constant current charge at the beginning and end, and constant voltage charge in the middle. When the current decays to a predetermined value, it is converted from the second stage to the third stage.

This operation minimizes gas output, but is somewhat limited when used as a fast power battery charge. Since the stage power battery charge way uses both constant current charge and constant voltage charge, the advantages of both power battery charge means can be combined.

② Fast charge method

Fast charge is a way of bringing a battery to a fully charged state in a short time with a high charge current. The fast charger has a lot of power, generally greater than 30 kW, and adopts a three-phase, four-wire 380 V power supply. Its typical charge time is 10–30 min.

This kind of power battery charge has a certain impact on the battery life, which cannot be charged quickly, because accepting a large amount of power in a short period of time will cause the battery to overheat.

Commonly used fast power battery charge ways include pulse charge, Reflex TM fast charge, the variable current intermittent charge, variable voltage intermittent charge.

● Pulse fast charge

The mean is to first charge the battery with a pulse current, then stop charge for a period of time, then charge the battery with a pulse current, and so on.

● Reflex TM fast charge

This kind of power battery charge alleviates the memory effect problem of nickel-cadmium batteries and greatly reduces the time for fast battery charge. A ReflexTM fast charge cycle consists of three stages: forward pulse charge, reverse transient pulse discharge and decharge maintenance.

● Variable current charge intermittently

This road for power battery charge is based on constant current charge and pulse charge, and is characterized in that the constant current charge section is changed to a voltage limiting variable current intermittent charge section.

● Variable voltage intermittent charge

The variable voltage intermittent charge mean differs from the variable current intermittent charge mean in that the first stage is not intermittent current setting, but intermittent voltage setting.

● Amplitude modulation/frequency modulation charge method

The amplitude modulation and frequency power battery charge way combines the advantages and generally adopts the following three control technologies:

• The pulse current amplitude is variable, and the frequency at which the charge/discharge switching tube (PWM) signal is driven is fixed.
• The pulse current amplitude does not change, and the frequency of the PWM signal is adjustable.
• The pulse current amplitude does not change, the frequency of the PWM signal is fixed, and the duty cycle of the PWM signal is adjustable.

3. Power battery pack charge method

Due to the differences in manufacturing process, material, use environment and wiring among the many power batteries in the battery pack, it is inevitable that there will be inconsistencies between individual batteries.

The use of the charger to directly charge the battery pack as a whole will inevitably lead to an aggravation of inconsistency between individual batteries, and over voltage charge of individual batteries.

Similarly, the presence of inconsistencies between individual cells can also lead to over discharge of individual cells during battery pack discharge. At this time, the concept of battery hookup needs to be introduced, which is the process of combining two or more batteries into a battery pack in which they can change the voltage or battery capacity.

Therefore, we can choose the appropriate power battery charge technoligy according to the voltage and capacity. According to different operating means, the charge of electric vehicle power battery packs can be divided into two charge sides: ground charge and on-board charge.

① Ground charge

Ground charge occurs when the vehicle is replenished and the disassembled battery is replenished and charged by the ground charge system.

The use of ground charge is conducive to battery maintenance, improving battery life and vehicle efficiency, but it puts forward higher requirements for vehicles and battery replacement equipment. There are two types of ground charge: charge in seperate boxes and the whole set.

● charge in separate boxes

Each charger charges a battery box in the battery pack and communicates with the battery management unit of the battery box to complete charge control. This power battery charge is conducive to improving the balance of the battery pack and extending the service life of the battery pack. 

But the number of chargers is large, the connection between the battery pack and the charger is large, the monitoring network is complex, and the cost is high.

● Charge the whole set

The number of chargers is small, and the monitoring network is simple, but compared to the single-box charge, the balance of the battery pack is poor, and the service life is low.

② On board charge method

On board charge means that when the vehicle is replenished, the charger and the charge vehicle are connected through the charge plug, and the battery can be charged directly without removing it from the vehicle. There are two types of chargers used for onboard battery charge.

One is the charger installed and carried with the car, called the on-board charger. Usually, the power is small. The charge time is long, so it is also supplemented with slow charge, which is suitable for charge at night and operating electric vehicles during the day.

The second type is a non-on-board charger, which generally guarantees that the vehicle can be charged within 30 minutes to ensure that the vehicle travels more than 50 km. It mostly uses AC 380 V industrial grid charge, and the charge speed is faster, so it is also called fast charge.

In electric vehicles that have been commercially produced, in order to meet the application of these two chargers, it is common to set up both on-board charge machines and fast charge interfaces on the vehicle.

4. The power battery charger

A charger is a device connected to the AC grid to provide DC power for rechargeable energy storage systems such as lifepo4 batteries, nickel metal hydride battery, fuel cell and so on. It is generally composed of a control unit, a metering unit, a charge interface, a power supply interface, and a human-computer interaction interface.

It can realize charge measurement and other functions and has multiple functions such as reverse polarity, overload, short circuit, overheating, delayed start, soft start, power off memory automatic start, and so on.

● The type of charger

• On-board charger

Small power, can only provide small current slow charge, long charge time.

• Non-on-board chargers

It can be divided into three types: AC charge pile, DC charge pile and AC and DC charge pile.

• Conductive chargers

The power supply part of the conductive charger is mechanically connected to the receiving part, that is, the output end of the charger is directly connected to the charge interface of the electric vehicle through the power cable.

• Inductive chargers

The inductive charger uses the principle of electromagnetic energy transfer to transmit electrical energy to the electric vehicle by electromagnetic induction coupling.

And there is no direct mechanical connection between the power supply part and the power receiving part, and the energy transfer between the two depends only on the conversion of electromagnetic energy.

• Wireless charge

There are three types of electromagnetic induction charge, magnetic resonance charge and microwave charge.

5. Performance requirements for chargers

• Safe
• Easily use
• Economy.
• Highly efficient.
• Low pollution to the grid.
• Intelligent charge management

Intelligent charge management is an intelligent charge management mode jointly carried out by the charger's charge management system and the onboard BMS (battery management system) without excessive manual intervention.

Concerning the charge stations, a fully functional charge station consists of five basic parts: a power distribution area, a monitoring area, a charge area, a battery replacement area, and a battery maintenance area.

6. Conclusion

Knowing more about power batteries can be of great help in battery selection. First of all, understand the power battery charge function and ways of powering the battery. We can learn that there are two roads, conventional charge and fast charge, and their range of use. The power battery charge of the power battery pack on both the ground and the vehicle can also help you make a more suitable choice.

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