CN113799654B - Balanced charging method for power battery of electric automobile - Google Patents

Abstract

The invention relates to a power battery equalizing charge method of an electric automobile, which is characterized in that a charge power supply is connected with the positive and negative poles of n battery equalizing units connected in series to charge the n battery equalizing units connected in series, each battery equalizing unit has the same structure and comprises a battery unit Bi, a first equalizing switch S1 and a second equalizing switch S2, and the battery unit Bi is connected in parallel with the equalizing switch S2 after being connected in series with the first equalizing switch S1; the equalizing charge method comprises a constant-current charge stage, a constant-voltage charge stage and an equalizing charge stage. The invention does not need a plurality of electric energy conversion devices, which are correspondingly connected with the single battery in parallel, saves the quantity of the electric energy conversion devices, does not need a plurality of wires to connect the single electric energy conversion device with a plurality of battery single bodies, greatly reduces the total length of the wires, has simple circuit structure and is easy to realize balance.

Description

A balanced charging method for power batteries of electric vehicles

Technical field

The invention belongs to the field of electric vehicles and relates to power battery balancing technology, and in particular to a power battery balancing charging method for electric vehicles.

Background technique

With the popularity of electric vehicles, the use of power batteries is also increasing. It is difficult for a single battery to meet the requirements of electric vehicles. Therefore, in the existing technology, multiple single batteries are generally connected in series to form a battery pack or battery pack, thereby increasing the overall capacity of the battery and improving the cruising range of electric vehicles. Since it is difficult to achieve consistent performance of individual cells in a battery pack, the discreteness of batteries after large-scale group application will seriously affect the cycle life of the battery. Effective balancing management can improve the cycle life of the battery.

In the existing technology, battery balancing technology is generally divided into two types, one is passive balancing and the other is active balancing.

Passive balancing is to connect switches and discharge resistors in parallel at both ends of the battery cell to achieve balancing by consuming the high-voltage battery power as heat energy. However, this balancing method has certain unsafe factors, is not conducive to energy saving and environmental protection, and is not suitable for high-power battery packs.

Active balancing is to return some of the power of the high-voltage battery to the battery circuit through the power conversion device or directly to the low-voltage battery. The energy storage components used are mainly capacitors or inductors. The battery pack is completed through repeated charging and discharging of the capacitors or inductors. Voltage balance of internal battery cells. Although this balancing method improves the utilization of electric energy, it will still cause consumption of electric energy during the balanced electric energy conversion process, and this balancing method either requires multiple electric energy conversion devices to be connected in parallel with single batteries, or uses switches. The matrix method connects a single power conversion device to multiple battery cells, which requires many wires to connect a single power conversion device to multiple battery cells. The hardware cost is too high, and because the balancing process requires each cell in turn. Charging and discharging are performed, so the time consumed by the entire equalization process is also very high.

Contents of the invention

The object of the present invention is to overcome the shortcomings of the prior art and provide a power battery equalization charging method for electric vehicles that can reduce the use of electric energy conversion equipment and wires.

The technical solutions adopted by the present invention to solve the technical problems are:

A power battery balancing charging method for electric vehicles. The charging power supply is connected to the positive and negative poles of n series-connected battery balancing units to charge the n series-connected battery balancing units. Each battery balancing unit has the same structure and includes a battery cell. Body Bi, the first balancing switch S1 and the second balancing switch S2, the battery cell Bi is connected in series with the first balancing switch S1 and then in parallel with the balancing switch S2;

The balanced charging method includes the following steps:

Step 1. In the constant current charging stage, the first balancing switches S1 in the n battery balancing units are all closed, the second balancing switches S2 are all opened, and the charging current of the charging power supply is I1;

Detect the voltage of n battery cells. If there is a certain battery cell voltage Ui>Uref, then stop constant current charging and switch to constant voltage charging, where Uref is the charging limit voltage of the battery cell;

Step 2. In the constant voltage charging stage, the charging power supply performs constant voltage charging for the battery with the voltage of nUref, and detects the charging current of the battery cell Bi. If the charging current I<Iref1, the constant voltage charging stops and switches to equalizing charging;

Step 3. In the balancing charging stage, a certain battery cell Bi is charged with constant voltage alone. At this time, the first balancing switch S1 in the battery balancing unit of the battery cell Bi is closed, the second balancing switch S2 is opened, and the remaining batteries The first balancing switch S1 in the balancing unit is turned off and the second balancing switch S2 is closed. The charging voltage of the power supply is Uref. When the charging current I<Iref2 is detected, the individual charging of the battery is stopped and the individual charging of the remaining battery cells is performed. Charging is performed until all n battery cells Bi are individually charged.

Moreover, the charging current I1 is the rated charging current of the battery cell.

Furthermore, the first balancing switch S1 is replaced with the diode D.

Moreover, in the equalization charging stage, only the battery cells Bi that do not satisfy I<Iref2 are subject to individual constant voltage charging.

Moreover, in the balanced charging stage, the charging power supply uses the charging voltage of Uref to separately detect the charging current of the battery cell Bi. If the charging current I of the battery cell Bi > Iref2, it is marked as a battery cell that requires balanced charging, otherwise it is marked as For battery cells that do not need equalizing charging, the charging current detection of the remaining battery cells will be performed until the marking of all battery cells Bi for this round of testing is completed, and the battery balancing unit of the battery cell Bi that does not need equalizing charging will be The first balancing switch S1 is opened and the second balancing switch S2 is closed. The first balancing switch S1 of the battery balancing unit of the battery cell that needs to be balanced is closed and the second balancing switch S2 is opened. The power supply performs constant voltage charging. When the detection When the charging current I<Iref2, the above balancing operation is repeated until the charging current I<Iref2 of each battery cell.

Moreover, in the first round of detection during the balancing charging stage, it is detected that the number of battery cells that need balancing charging is m, and the number of battery cells that do not need balancing charging is n-m. The charging power supply performs constant voltage charging with the voltage of mUref.

Moreover, in the k+1th round of detection in the balancing charging stage, only the battery cells marked as requiring balancing charging are detected for the kth detection.

The advantages and positive effects of the present invention are:

1. The present invention adopts a balancing unit structure in which the battery cell Bi is connected in series with the first balancing switch S1 and then in parallel with the balancing switch S2. Therefore, there is no need for multiple power conversion devices, which can be connected in parallel with the single battery, saving power conversion equipment. There is no need for many wires to connect a single power conversion device to multiple battery cells, which greatly reduces the total length of wires. The circuit structure is simple and balance is easy to achieve.

2. The present invention reduces the charging time by setting the current threshold.

3. The present invention replaces the first balancing switch S1 with the diode D, which can further reduce the use of control devices, reduce costs, and reduce the complexity of control.

4. The present invention adopts the balanced charging method of first detecting the mark and then charging multiple batteries at the same time. Compared with direct individual charging, the charging rate is greatly improved and the charging time is reduced.

Description of the drawings

Figure 1 is a schematic diagram of the series connection of multiple battery balancing units.

Figure 2 is the circuit connection diagram of a single battery balancing unit.

Figure 3 is a circuit connection diagram of a single battery balancing unit (the first balancing switch S1 is replaced with a diode D).

Detailed ways

The present invention will be further described in detail below through specific examples. The following examples are only descriptive, not restrictive, and cannot be used to limit the scope of the present invention.

A power battery balancing charging method for electric vehicles, including a charging power supply and n series-connected battery balancing units. The charging power supply is connected to the positive and negative poles of the n series-connected battery balancing units, and is used to charge the n series-connected battery balancing units. Each battery balancing unit has the same structure and includes a battery cell Bi, a first balancing switch S1 and a second balancing switch S2. The battery cell Bi is connected in series with the first balancing switch S1 and then in parallel with the balancing switch S2.

The balanced charging method includes the following steps:

Step 1. In the constant current charging stage, the first balancing switches S1 in the n battery balancing units are all closed, and the second balancing switches S2 are all opened. The charging current of the charging power supply is I1, where the charging current I1 is the rated value of the battery cell. recharging current;

Detect the voltage of n battery cells. If there is a battery cell voltage Ui>Uref, stop constant current charging and switch to constant voltage charging, where Uref is the charging limit voltage of the battery cell;

Step 2. In the constant voltage charging stage, the charging power supply uses the voltage of nUref as the power battery for constant voltage charging, and detects the charging current of the battery. If the charging current I<Iref1, the constant voltage charging stops and switches to balanced charging; Iref is the charging cut-off current. .

Since the battery cells in this application are connected in series, after the constant voltage stage, although the charging current I of the series battery pack is <Iref1, due to the imbalance of each battery cell, the charging current of some battery cells is indeed less than Iref1. , but the charging current of some battery cells is still greater than Iref1, but due to series connection, the overall performance is that the charging current I<Iref1, so in order to achieve the balance of the battery cells, the following balanced charging stage is performed.

Step 3. In the balancing charging stage, a certain battery cell Bi is charged separately. At this time, the first balancing switch S1 in the battery balancing unit of the battery cell Bi is closed, the second balancing switch S2 is opened, and the remaining electrical balancing units The first balancing switch S1 is open and the second balancing switch S2 is closed. The charging voltage of the power supply is Uref. When the charging current I<Iref2 is detected, the individual charging of the battery is stopped, and the above balancing operation is repeated to execute the remaining batteries. Individual charging of cells until all n battery cells have completed individual charging;

When charging is completed, the charging power source is disconnected.

Since the balancing unit structure is adopted in which the battery cell Bi is connected in series with the first balancing switch S1 and then in parallel with the balancing switch S2, there is no need for multiple power conversion devices, which can be connected in parallel with the single battery, thus saving the number of power conversion devices. There is no need for many wires to connect a single power conversion device to multiple battery cells, which greatly reduces the total length of wires. The circuit structure is simple and balance is easy to achieve.

Preferably, Iref1=Iref2.

From the above analysis, it can be seen that at the end of the constant voltage stage, the battery cells are still in an unbalanced state, and then enter the balanced charging stage, and each battery cell is charged at a constant voltage individually until it is fully charged. Although each battery cell is independently charged at a constant voltage during the balancing charging stage, due to the constant voltage charging stage, the charging current of some battery cells has already satisfied I<Iref1. Therefore, in fact, the balancing charging stage only does not charge part of the charging current. Battery cells that satisfy I<Iref1 undergo individual constant voltage charging, while battery cells that satisfy charging current I<Iref1 are skipped after detection, which consumes almost no time. Using Iref1>Iref2, compared with using Iref1=Iref2, can increase the number of battery cells that meet the charging current I<Iref2 after the constant voltage charging is completed, thereby reducing the number of battery cells that actually need to be charged at a constant voltage during the equalization charging stage. body, reducing charging time.

Preferably, the first balancing switch S1 can be replaced by a diode D, and the conduction direction of the diode D is the same as the direction of the charging current. Those skilled in the art know that switching devices, such as MOS transistors and IGBTs, are more expensive than diodes. Replacing the first balancing switch S1 with the diode D can further reduce the use of control devices, reduce costs, and enable constant current charging. stage, the constant voltage charging stage and the equalizing charging stage, only the second equalizing switch S2 needs to be controlled, reducing the control complexity.

Preferably, in order to increase the charging rate, during the balancing charging stage, the power supply uses the charging voltage of Uref to separately detect the charging current of the battery cell Bi. At this time, the first balancing switch S1 in the battery balancing unit i is closed and the second balancing switch S2 Open, the first balancing switch S1 in the remaining battery balancing units is opened, and the second balancing switch S2 is closed. If the charging current I>Iref2 of the battery cell is marked as a battery cell that requires balanced charging, otherwise it is marked as not For battery cells that need equalizing charging, the charging current detection of the remaining battery cells is performed until the marking of all battery cells for this round of testing is completed, and the first balancing switch of the battery balancing unit of the battery cells that does not need equalizing charging is S1 is opened and the second balancing switch S2 is closed. The first balancing switch S1 of the battery balancing unit of the battery cell that needs to be balanced is closed and the second balancing switch S2 is opened. The power supply performs constant voltage charging. When the charging current is detected When I<Iref2, repeat the above balancing operation until the charging current of each battery cell I<Iref2.

The above-mentioned balancing charging stage first detects and marks the battery cells, selects the battery cells that need balancing charging, and then balances charging multiple batteries at the same time. Compared with the balancing charging stage where individual charging is performed directly, the efficiency is greatly improved. charging rate, reducing charging time.

Preferably, in the first round of detection during the balancing charging stage, the number of battery cells that need balancing charging is m, the number of battery cells that do not need balancing charging is n-m, and the power supply performs constant voltage charging with the voltage of mUref.

Preferably, in the k+1th round of detection in the balancing charging stage, only the battery cells marked for the kth detection as requiring balancing charging are detected, thereby reducing the number of battery cells that need to be detected and marked, thereby improving detection efficiency.

What is described above is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the invention, and these all belong to the scope of the present invention. protected range.

Claims (7)

1. A power battery equalizing charge method of an electric automobile is characterized in that: the charging power supply is connected with the positive and negative poles of n battery equalization units connected in series to charge the n battery equalization units connected in series, and each battery equalization unit has the same structure and comprises a battery unit Bi, a first equalization switch S1 and a second equalization switch S2, wherein the battery unit Bi is connected with the first equalization switch S1 in series and then connected with the equalization switch S2 in parallel;

the equalizing charge method comprises the following steps:

step 1, in a constant-current charging stage, a first equalization switch S1 in n battery equalization units is closed, a second equalization switch S2 is opened, and charging current of a charging power supply is I1;

detecting the voltages of n battery cells, and stopping constant-current charging and switching to constant-voltage charging if a certain battery cell voltage Ui > Uref exists, wherein Uref is the charging limiting voltage of the battery cells;

step 2, in the constant voltage charging stage, the charging power supply uses the voltage of nUref as a battery to perform constant voltage charging, detects the charging current of the battery cell Bi, stops the constant voltage charging if the charging current I is less than Iref1, and shifts to equalizing charging;

step 3, in the equalizing charge stage, constant voltage charge is independently carried out on a certain battery cell Bi, at the moment, a first equalizing switch S1 in a battery equalizing unit of the battery cell Bi is closed, a second equalizing switch S2 is opened, a first equalizing switch S1 in other battery equalizing units is opened, a second equalizing switch S2 in other battery equalizing units is closed, wherein the charging voltage of a power supply is Uref, when charging current I < Iref2 is detected, the independent charge of the battery is stopped, and the independent charge of other battery cells is executed until all n battery cells Bi are completely independently charged; the Iref1> Iref2 is used for improving the quantity of the battery cells which meet the charging current I < Iref2 after the constant voltage charging is finished, so that the battery cells which are actually required to be subjected to constant voltage charging in the equalizing charging stage are reduced, and the charging time is shortened.

2. The method for equalizing charge of a power battery of an electric vehicle according to claim 1, wherein: the charging current I1 is the rated charging current of the battery cell.

3. The method for equalizing charge of a power battery of an electric vehicle according to claim 1, wherein: the first equalization switch S1 is replaced by a diode D.

4. The method for equalizing charge of a power battery of an electric vehicle according to claim 1, wherein: the equalization charge phase only performs individual constant voltage charge on the battery cells Bi that do not satisfy I < Iref2.

5. The method for equalizing charge of a power battery of an electric vehicle according to claim 1, wherein: in the equalizing charge stage, the charging power supply detects the charging current of the battery cell Bi solely by the charging voltage of Uref, if the charging current I of the battery cell Bi is greater than Iref2, the battery cell is marked as the battery cell which needs equalizing charge, otherwise, the battery cell which does not need equalizing charge is marked, the charging current detection of the rest battery cells is executed until the marking of all the battery cells Bi detected in the round is completed, the first equalizing switch S1 and the second equalizing switch S2 of the battery equalizing unit of the battery cell Bi which does not need equalizing charge are opened, the first equalizing switch S1 and the second equalizing switch S2 of the battery equalizing unit of the battery cell which needs equalizing charge are opened, the power supply performs constant-voltage charging, and when the charging current I < Iref2 is detected, the equalizing operation is repeated until the charging current I < Iref2 of each battery cell.

6. The method for equalizing charge of a power battery of an electric vehicle according to claim 5, wherein: the number of the battery cells needing to be balanced charged is detected to be m in the first round of detection in the balanced charging stage, the number of the battery cells not needing to be balanced charged is detected to be n-m, and the charging power supply carries out constant voltage charging at the voltage of mUref.

7. The method for equalizing charge of a power battery of an electric vehicle according to claim 5, wherein: and in the k+1th round of detection in the equalizing charge stage, only detecting the battery cell marked as the battery cell requiring equalizing charge in the k detection.