A method for realizing constant voltage charging of single battery in series charging

Abstract

A method for realizing constant voltage charging of single cells in series charging comprises a constant current power supply, a plurality of single cells, a plurality of bidirectional power supply modules with input and output isolation, an energy storage capacitor and a voltage detection module. The plurality of single cells are connected in series and connected to both ends of the constant current power supply. One side of the bidirectional power supply module is connected to the corresponding single cells and the other side is connected to the energy storage capacitor. The voltage detection module detects the voltage at both ends of the energy storage capacitor and adjusts the output current of the constant current power supply according to the signal. The closed-loop control makes the voltage at both ends of the energy storage capacitor stable, thereby realizing constant voltage charging of each single cell.

Description

Technical Field

[0001] The present invention relates to the technical field of battery charging, and in particular to a method for realizing constant voltage charging of single cells in series charging. Background Art

[0002] Constant current and constant voltage charging is the most commonly used charging method for lithium batteries. The first stage is charged with constant current. When the voltage reaches a predetermined value, it enters the second stage for constant voltage charging. At this time, the current gradually decreases. When the charging current reaches less than a certain value, charging is completed.

[0003] The traditional method of forming single-cell batteries is to equip one single-cell battery channel with one power module. Multiple single-cell battery units are formed into batteries, which requires the configuration of a corresponding number of power modules. The cable connection is complex and the cost is high.

[0004] Using the same current source to charge multiple battery cells in series reduces cable connections and improves the consistency of charging current.

[0005] When the voltage of a battery cell rises to a preset voltage during constant current charging, it is necessary to switch from constant current charging mode to constant voltage charging. The typical approach is to disconnect the battery cell from the constant current charging circuit through a switch device, and then perform constant voltage charging through another charging circuit, which requires power to be taken from the grid or other DC bus, and the system connection is complex. Summary of the invention

[0006] The method for realizing constant voltage charging of a single battery in series charging disclosed in the present invention can solve the problem that in the existing solution, when the battery unit changes from constant current charging to constant voltage charging mode, it needs to be charged from an external power supply.

[0007] The technical solution of the present invention is as follows: a method for realizing a constant voltage charging circuit with serially connected components, comprising a constant current power supply, a plurality of single cells, a plurality of DCDC power supply modules, and an energy storage capacitor, wherein the plurality of single cells are connected in series and connected at both ends of the constant current power supply, the DCDC power supply is a bidirectional power supply with input and output isolation, one side of which is connected to the corresponding single cell, and the other sides of all the DCDC power supplies are connected in parallel and connected at both ends of the energy storage capacitor.

[0008] Furthermore, it also includes a voltage detection module, which detects the voltage at both ends of the energy storage capacitor and transmits the signal to the constant current power supply.

[0009] The DCDC power supply is a power supply that controls the battery side voltage to be a constant value. When the battery side voltage is higher than the constant value, energy is extracted to the energy storage capacitor side. When the battery side voltage is lower than the constant value, energy is extracted from the energy storage capacitor side.

[0010] Compared with stabilizing the voltage on the energy storage capacitor by adjusting the current value of the constant current power supply, all individual cells can operate stably in the constant voltage charging state in the present invention. Brief Description of the Drawings

[0011] The present invention will be further described below in conjunction with the drawings and embodiments.

[0012] Figure 1 Circuit block diagram of the present invention.

[0013] Figure 2 An implementation circuit of an input constant voltage controlled DCDC power supply. Detailed Implementation Manner

[0014] In the following, some embodiments of the present disclosure will be described in detail with reference to the accompanying illustrative drawings.

[0015] Please refer to the attached Figure 1 A method for realizing constant voltage charging of individual cells in series charging includes a constant current power supply 101, several individual cells 102, several DCDC power supply modules 103, and an energy storage capacitor 104. The several individual cells 102 are connected in series and connected to both ends of the constant current power supply. The DCDC power supply module 103 is a bidirectional power supply with input-output isolation, one side is connected to the corresponding individual cell 102, and the other side is connected to both ends of the energy storage capacitor 104.

[0016] Further, it further includes a voltage detection module 105, which detects the voltage across the energy storage capacitor and transmits the signal to the constant current power supply to control the output current of the constant current power supply.

[0017] The DCDC power supply is a power supply that controls the voltage on the battery side to a constant value. When the voltage on the battery side is higher than the constant value, energy is extracted to the energy storage capacitor side. When the voltage on the battery side is lower than the constant value, energy is extracted from the energy storage capacitor side.

[0018] Assume that the constant voltage charging voltage of the individual cell is V0, and K (K>1) cells are connected in series and connected to both ends of the constant current power supply. The initial output current of the constant current power supply is I0. At a certain specific moment, the current for constant voltage charging of the No. 1 cell is I1. Then when I0>I1, the DCDC connected in parallel with the No. 1 cell needs to draw away the current value of I0-I1 so that the No. 1 cell can be stable in the constant voltage charging state. When I0<I1, the DCDC connected in parallel with the No. 1 cell needs to supply the battery with the current of I0-I1 so that the No. 1 cell can be stable in the constant voltage charging state.

[0019] Considering the inconsistency of the batteries, among the K batteries, m batteries need to transfer energy W1 from the energy storage capacitor to the batteries by the DCDC power supply. Let the total energy be W1, and n batteries need to transfer energy W2 from the batteries to the energy storage capacitor by the DCDC power supply, where m + n = k. Therefore, when W1 < W2, the voltage on the energy storage capacitor 104 rises, and vice versa.

[0020] When a steady state is set and the extracted energy is equal to the input energy, the voltage on the energy storage capacitor 104 is VC0. Then, the voltage on the energy storage capacitor 104 can be used as a control signal to control the output current of the constant current power supply. When the voltage on the energy storage capacitor 104 is higher than VC0, the output current of the constant current power supply is reduced, which also reduces the energy obtained by the single battery from the constant current power supply. Correspondingly, the energy extracted from the energy storage capacitor needs to be reduced; vice versa. Therefore, when the voltage on the energy storage capacitor remains unchanged, the output current of the corresponding constant current power supply can exactly keep all the batteries stable in the constant voltage charging state.

[0021] Appendix Figure 2 is an implementation manner of an isolated DCDC power supply for realizing input constant voltage type.

[0022] The topological structure of the illustrated DCDC power supply is a half-bridge series LLC resonant bidirectional converter. BAT1 is a single battery, Q1 and Q2 form a half-bridge on the battery side, Q3 and Q4 form a half-bridge on the capacitor side, C5 is the energy storage capacitor, TX1 is the transformer for isolating both sides, and L1 is the resonant inductor. If the resonant frequency of this LLC is f0, when the LLC operates at the resonant frequency f0, the battery voltage is V0, the corresponding voltage on the energy storage capacitor is VC0, and the gain is G0. According to the working principle of the LLC, near the resonant frequency f0, when the operating frequency of the LLC is greater than f0, the gain decreases, and when the operating frequency of the LLC is less than f0, the gain increases; therefore, the controller takes the voltage of the corresponding battery as the control target. When the voltage is lower than V0, the operating frequency of the LLC is increased to reduce the gain, so that the LLC operates in the battery charging mode; when the voltage is higher than V0, the operating frequency of the LLC is decreased to increase the gain, so that the LLC operates in the battery discharging mode; through loop control, the half-bridge series LLC resonant bidirectional converter can achieve input constant voltage control.

[0023] Figure 2 is only a circuit implementation manner for input constant voltage. Basically, for all bidirectional DCDC power supplies, the same result can be achieved by taking the input voltage as the control target, which will not be elaborated one by one here.

[0024] By utilizing the control method disclosed in the present invention, only one constant current power supply is needed to perform constant current charging on multiple batteries connected in series, and also to perform constant voltage charging on each battery cell; the output current of the included DCDC bidirectional power supply module is simply the difference between the constant voltage charging current of the single battery and the constant current power supply. The more consistent the performance of the batteries in the series connection is, the smaller the actual output current of the DCDC bidirectional power supply module is, thereby achieving miniaturization.

[0025] Although the present disclosure has been disclosed above by describing the specific embodiments of the present disclosure, it should be understood that those skilled in the art can design various modifications, improvements or equivalents of the present disclosure within the spirit and scope of the appended claims. These modifications, improvements or equivalents should also be considered to be included in the protection scope of the present disclosure.

Claims

1. A method for realizing constant voltage charging of a single cell in series charging, characterized by comprising: a constant current power supply, a plurality of single cells, a plurality of DCDC power supply modules, an energy storage capacitor and a voltage detection module, wherein the plurality of single cells are connected in series and connected to both ends of the constant current power supply, the DCDC power supply is a bidirectional power supply with input and output isolation, one side of which is connected to the corresponding single cell, and the other side is connected to both ends of the energy storage capacitor, and the voltage detection module detects the voltage at both ends of the energy storage capacitor and connects the signal to the constant current power supply; in, The DCDC power supply is a bidirectional isolated power supply that controls the battery side voltage to a constant value; Wherein, the output current of the constant current power supply is controlled by the voltage negative feedback closed loop of the energy storage capacitor. When the voltage on the energy storage capacitor exceeds the preset value, the constant current output current is reduced; when the voltage on the energy storage capacitor is lower than the preset value, the constant current output current is increased; Wherein, the DCDC power supply is a half-bridge series LLC resonant bidirectional converter, which takes the voltage of the corresponding battery as the control target. When the battery voltage is lower than the set value of constant voltage charging, the operating frequency of LLC is increased, and when the battery voltage is higher than the set value of constant voltage charging, the operating frequency of LLC is reduced.

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