Charging method, corresponding charging device and corresponding uninterruptible power system

Abstract

A charging method, a corresponding charging device and a plurality of corresponding uninterruptible power systems are provided. The method comprises the following steps: controlling a charging circuit to charge a battery string, and measuring the voltage of each battery of the battery string; according to the voltage values of the batteries, judging whether a starting condition for executing voltage balance operation is met or not, and judging whether the voltage value of any battery is greater than or equal to a first threshold value or not; whenever it is judged that the starting condition is met, the battery balancing circuit is controlled to start to execute voltage balancing operation on the battery string until the voltage values of the batteries meet the termination condition of the voltage balancing operation; and when it is judged that the voltage value of any battery is larger than or equal to the first threshold value, reducing the output energy of the charging circuit until the voltage value of any battery is smaller than the first threshold value.

Description

TECHNICAL FIELD

[0001] The present invention relates to the technical field of battery charging, and in particular, to a charging method, a corresponding charging device, and various corresponding uninterruptible power supply systems. BACKGROUND

[0002] Generally speaking, when charging a battery string, it is very likely that the battery voltages will not be balanced. Although there are many reasons for causing the battery voltages to be unbalanced, regardless of the cause, once the battery voltages are unbalanced, it is very easy for some of the batteries to be overcharged. Once some of the batteries are overcharged, the life of the overcharged batteries is very likely to be reduced, or even damaged (e.g., visually observable swelling). SUMMARY

[0003] One object of the present invention is to provide a charging method that can avoid overcharging of batteries.

[0004] Another object of the present invention is to provide a charging device that employs the aforementioned charging method.

[0005] Still another object of the present invention is to provide an online uninterruptible power supply system that employs the aforementioned charging device.

[0006] Still another object of the present invention is to provide an offline uninterruptible power supply system that employs the aforementioned charging device.

[0007] Still another object of the present invention is to provide an online interactive uninterruptible power supply system that employs the aforementioned charging device.

[0008] To achieve the above objects, the present invention provides a charging method that is suitable for a battery string, which is formed by connecting a plurality of batteries in series. The charging method includes: controlling a charging circuit to charge the battery string, and measuring the voltage of each battery; determining whether there are starting conditions for performing a voltage balancing operation based on the voltage values of the batteries, and determining whether the voltage value of any battery is greater than or equal to a first threshold value; whenever it is determined that the starting conditions are met, controlling a battery balancing circuit to start performing the voltage balancing operation on the battery string until the voltage values of the batteries satisfy termination conditions for the voltage balancing operation; and whenever it is determined that the voltage value of any battery is greater than or equal to the first threshold value, reducing the output energy of the charging circuit until the voltage value of any battery is less than the first threshold value.

[0009] To achieve the above-mentioned another object, the present application provides a charging device for charging a battery string, which is formed by connecting a plurality of batteries in series. The charging device comprises a charging circuit, a battery balancing circuit and a control circuit. The charging circuit is electrically coupled to two ends of the battery string. The battery balancing circuit is electrically coupled to two ends of each battery, for measuring the voltage of each battery and performing voltage balancing operation on the battery string. The control circuit is electrically coupled to the charging circuit and the battery balancing circuit. The control circuit controls the charging circuit to charge the battery string and controls the battery balancing circuit to measure the voltage of each battery. The control circuit further determines whether the starting condition of performing the voltage balancing operation is satisfied according to the voltage values of the batteries, and determines whether the voltage value of any battery is greater than or equal to a first threshold value. When the starting condition is satisfied, the control circuit controls the battery balancing circuit to start performing the voltage balancing operation on the battery string until the voltage values of the batteries satisfy the termination condition of the voltage balancing operation. When the voltage value of any battery is greater than or equal to the first threshold value, the control circuit reduces the output energy of the charging circuit until the voltage value of any battery is less than the first threshold value.

[0010] In order to make the above-mentioned objects, technical features and advantages after the actual implementation more obvious and easy to understand, in the following, the preferred embodiments will be described in detail with the corresponding drawings. BRIEF DESCRIPTION OF DRAWINGS

[0011] The drawings described herein are used to provide further understanding of the present application, form a part of the present application, the schematic embodiments of the present application and the description thereof are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0012] Figure 1 A power supply system according to an embodiment of the present application is shown.

[0013] Figure 2 The electrical coupling relationship between the charging device and the battery pack 106 is shown.

[0014] Figure 3 A flowchart of a charging method according to an embodiment of the present application is shown.

[0015] Figure 4 A charging process of the battery string is shown.

[0016] Figure 5 A power supply system according to another embodiment of the present application is shown.

[0017] Figure 6 A power supply system according to another embodiment of the present application is shown.

[0018] Figure 7 A power supply system according to another embodiment of the present application is shown.

[0019] Figure 8 An uninterruptible power supply system according to yet another embodiment of the present invention is illustrated. Detailed Implementation

[0020] To better understand the features, content, advantages, and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and embodiments. The drawings used are for illustrative purposes only and to assist in the description. They may not represent the actual proportions and precise configurations of the present invention after implementation. Therefore, the proportions and configurations of the accompanying drawings should not be used to interpret or limit the scope of the present invention in actual implementation.

[0021] The advantages, features, and technical methods of the present invention will be more readily understood by referring to the exemplary embodiments and accompanying drawings. The present invention may be implemented in different forms and should not be construed as limited to the embodiments set forth herein. Rather, the embodiments provided will enable those skilled in the art to more thoroughly and completely convey the scope of the invention, and the invention will be defined only by the appended claims.

[0022] Figure 1 An uninterruptible power supply system according to an embodiment of the present invention is illustrated. Please refer to... Figure 1 ,Depend on Figure 1 As can be seen from the circuit architecture shown, this uninterruptible power supply system 100 is an offline uninterruptible power supply system (Off-line UPS). This uninterruptible power supply system 100 includes a filter unit 114, a switching unit 116, a DC-AC conversion circuit 104, a switching unit 118, a filter unit 120, a charging circuit 102, a battery pack 106, a battery balancing circuit 112, a control circuit 110, and a bypass path 124.

[0023] Switching unit 116 is electrically coupled to one end of bypass path 124 and electrically coupled to AC power (e.g., mains power) through filtering unit 114. Switching unit 118 is electrically coupled to the other end of bypass path 124 and electrically coupled to the output terminal 122 of uninterruptible power supply 100 through filtering unit 120. Charging circuit 102 is electrically coupled to battery pack 106 and electrically coupled to AC power through filtering unit 114. DC-AC conversion circuit 104 is electrically coupled between battery pack 106 and switching unit 118. Battery balancing circuit 112 is electrically coupled to battery pack 106.

[0024] Further, the switch unit 116, the DC-AC conversion circuit 104, the switch unit 118, the charging circuit 102 and the battery balancing circuit 112 are electrically coupled to the control circuit 110 to receive control from the control circuit 110. For example, the control circuit 110 can control the operation of the switch unit 118 to determine whether the output of the DC-AC conversion circuit 104 is electrically coupled to the filter unit 120 or the bypass path 124 is electrically coupled to the filter unit 120. In addition, the charging circuit 102, the battery balancing circuit 112 and the control circuit 110 constitute the charging device of the present application.

[0025] Figure 2 The electrical coupling relationship between the charging device and the battery pack 106 is shown. Please refer to Figure 2 In this example, the battery pack 106 is composed of a battery string which is composed of a plurality of batteries (e.g. 106_1 to 106_N, where N is a natural number). Further, the charging circuit 102, the battery balancing circuit 112 and the control circuit 110 constitute the charging device as described above. The charging circuit 102 is electrically coupled to two ends of the battery string. The battery balancing circuit 112 is electrically coupled to two ends of each battery to measure the voltage of each battery and to perform voltage balancing operation on the battery string. The control circuit 110 is electrically coupled to the charging circuit 102 and the battery balancing circuit 112 to control the operation of the two. In this example, the control circuit 110 controls the operation of the charging circuit 102 by using a control signal CS.

[0026] In this example, the battery balancing circuit 112 includes switches 162_1 to 162_N, resistors 164_1 to 164_N and a microprocessor 166. As shown in Figure 2 one end of each resistor is electrically coupled to the positive terminal of one battery and the other end of each resistor is electrically coupled to the negative terminal of one battery through one switch. Further, the microprocessor 166 is electrically coupled to the positive terminal of each battery to perform voltage measurement. The microprocessor 166 is also electrically coupled to the control terminal of each switch to control the operation of the switches. The microprocessor 166 can also transmit the measured voltage values to the control circuit 110 so that the control circuit 110 can determine the charging status of each battery.

[0027] Figure 3 The flowchart of the charging method according to an embodiment of the present application is shown. Please refer to Figures 2-3 In this method, the control circuit 110 first controls the charging circuit 102 to charge the battery string (composed of the batteries 106_1 to 106_N) and controls the battery balancing circuit 112 to measure the voltage of each battery (as shown in step S302). For the convenience of understanding, the following will be described by taking an example of a battery string having six batteries. Figure 4To illustrate one of the charging processes of the aforementioned battery string, please refer to Figures 2-4 . Assuming that the charging circuit 102 is operated in a constant voltage charging manner, in this example, the control circuit 110 controls the charging circuit 102 to output a starting target voltage to start charging the battery string. The size of the starting target voltage is the number of the batteries 106_1~106_N multiplied by the standard charging voltage defined by the specifications of the batteries 106_1~106_N. The aforementioned batteries can all be lead-acid batteries or all be lithium batteries. Assuming that the aforementioned batteries are all lead-acid batteries, the aforementioned standard charging voltage is the standby use charging voltage defined by the specifications of the lead-acid batteries. The aforementioned standby use charging voltage is also called the float use charging voltage. In this example, the starting target voltage is 13.8 V.

[0028] Then, the control circuit 110 further determines whether there is a starting condition for performing the voltage balancing operation according to the voltage values of the batteries and whether there is any battery whose voltage value is greater than or equal to a battery protection threshold value (as shown in step S304). There are two starting conditions, and which starting condition is adopted can be determined according to actual design requirements. The first starting condition is that the voltage difference between any battery and the average voltage of the batteries is greater than or equal to a threshold value Vs, and the second starting condition is that the voltage difference between any two batteries is greater than or equal to a threshold value Vs, wherein the size of the threshold value Vs can be determined according to actual design requirements. In this example, the threshold value Vs is 0.1 V. In addition, the battery protection threshold value is also determined according to actual design requirements. In this example, the battery protection threshold value is 14.6 V.

[0029] Next, whenever it is determined that the starting condition is met, the control circuit 110 controls the battery balancing circuit 112 to start performing the voltage balancing operation on the battery string until the voltage values of the batteries meet a termination condition of the voltage balancing operation (as shown in step S306), and whenever it is determined that there is any battery whose voltage value is greater than or equal to the battery protection threshold value, the control circuit 110 reduces the output energy of the charging circuit 102 until the voltage value of any battery is less than the battery protection threshold value (as shown in step S308). Since steps S306 and S308 have their own execution conditions, steps S306 and S308 do not have a sequence of execution.

[0030] As can be seen from Figure 4 , the voltages of the batteries of the battery string start to be unbalanced after charging for a period of time, so the control circuit 110 controls the battery balancing circuit 112 to start performing the voltage balancing operation on the battery string. As can be seen from Figure 4It can also be seen that during the voltage balancing operation, the voltage of battery 6 exceeds the battery protection threshold (i.e., 14.6V). At this time, the control circuit 110 will reduce the output energy of the charging circuit 102 until the voltage of either battery is lower than the battery protection threshold. Since the charging circuit 102 in this example operates in a constant voltage charging mode, in this example, the control circuit 110 reduces the output energy of the charging circuit 102 by reducing its output voltage, for example, by reducing the output voltage of the charging circuit 102 by a predetermined value or a preset ratio, or even reducing it to 0V.

[0031] And by Figure 4 It can also be seen that, because the output energy of the charging circuit 102 is reduced, the voltage of some batteries will begin to drop sharply, causing the voltage of each battery to be lower than the battery protection threshold (i.e., 14.6V). Furthermore, as the voltage balancing operation proceeds, the voltage values ​​of these batteries become increasingly consistent. Of course, the control circuit 110 can also dynamically adjust the output voltage of the charging circuit 102; if the voltage of any battery is greater than or equal to the battery protection threshold, the output voltage of the charging circuit 102 is reduced; and if the voltage of all batteries is lower than the battery protection threshold, the output voltage of the charging circuit 102 is increased.

[0032] As the voltage balancing operation proceeds, the control circuit 110 periodically or intermittently checks whether the voltage values ​​of these batteries meet the termination conditions of the voltage balancing operation. There are two termination conditions, and the choice of which to use depends on the actual design requirements. The first termination condition is that the voltage difference between any one battery and the average voltage of all batteries is less than a threshold value Vb. The second termination condition is that the voltage difference between any two batteries is less than the threshold value Vb. The value of the threshold value Vb can be determined according to the actual design requirements, but the threshold value Vb should be less than the threshold value ΔVs. In this example, the threshold value Vb is 0.05V.

[0033] And by Figure 4 It can be seen that after a period of voltage balancing operation, the voltages of the individual batteries in the aforementioned battery string gradually become consistent. When the voltage values ​​of these batteries meet the termination conditions of the voltage balancing operation, the control circuit 110 increases the output voltage of the charging circuit 102 to the maximum target voltage, so that the charging circuit 102 can continue to charge the battery string. The maximum target voltage is greater than the aforementioned initial target voltage, and the magnitude of the maximum target voltage is the number of batteries 106_1 to 106_N multiplied by the maximum rechargeable voltage defined by the specifications of batteries 106_1 to 106_N. Assuming that the aforementioned batteries are all lead-acid batteries, the aforementioned maximum rechargeable voltage is the cycle-use charging voltage defined by the specifications of lead-acid batteries. In this example, the maximum target voltage is 14.4V.

[0034] like Figure 4 As shown, in this example, the control circuit 110 increases the output voltage of the charging circuit 102 to the maximum target voltage of 14.4V in an incremental manner. Furthermore, when the termination condition of the voltage balancing operation is met, the control circuit 110 can still control the battery balancing circuit 112 to continue performing voltage balancing operations on the battery string, so that the voltage of each battery can remain balanced during the period when the output voltage of the charging circuit 102 increases to the maximum target voltage.

[0035] Of course, when the termination condition of the voltage balancing operation is met, the control circuit 110 can also control the battery balancing circuit 112 to stop performing the voltage balancing operation. However, the disadvantage of doing so is that the voltage of each battery may not be able to maintain balance during the period when the output voltage of the charging circuit 102 increases to the maximum target voltage. Alternatively, the control circuit 110 can also control the charging circuit 102 to directly pull its output voltage to the maximum target voltage instead of using an incremental method to increase the output voltage of the charging circuit 102 to the maximum target voltage. Furthermore, during the charging process of the battery string, the control circuit 110 can also control the charging circuit 102 to use the maximum target voltage to charge the battery string throughout the entire process.

[0036] Although the charging circuit 102 operates in a constant-voltage charging manner in the aforementioned example, this is not intended to limit the invention. For example, the charging circuit 102 can also operate in a constant-current charging manner. If the charging circuit 102 operates in a constant-current charging manner, then the control circuit 110 can change the output energy of the charging circuit 102 by adjusting the magnitude of the output current of the charging circuit 102, thereby allowing the voltage of the battery string to reach the aforementioned initial target voltage and the aforementioned maximum target voltage. For example, when the termination condition of the voltage balancing operation is met, the control circuit 120 can increase the output current of the charging circuit 102 so that the charging circuit 102 can continue to charge the battery string, thereby causing the voltage of the battery string to rise to the maximum target voltage.

[0037] The control circuit 110 can increase the output current of the charging circuit 102 in an incremental manner, and thus increase the voltage of the battery string to the maximum target voltage. Alternatively, the control circuit 110 can directly increase the output current of the charging circuit 102 to a predetermined value, and thus directly increase the voltage of the battery string to the maximum target voltage. Furthermore, the control circuit 110 can control the charging circuit 102 to use the predetermined value of the output current to charge the battery string throughout the charging process. Alternatively, as previously mentioned, the control circuit 110 can decrease the output current of the charging circuit 102 to decrease the output energy of the charging circuit 102.

[0038] Furthermore, although the battery pack 106 is composed of one battery string in the above embodiments, the present application is not limited thereto. Those skilled in the art should know that the battery pack 106 can be composed of at least two battery strings connected in parallel.

[0039] Based on the above teachings, the present application can effectively prevent overcharging of individual cells through the voltage balancing operation and the setting of the battery protection threshold value. Furthermore, since no cell is overcharged, the present application can further shorten the time of the voltage balancing operation. In addition, through the setting of the maximum target voltage, the present application can increase the endurance of individual cells.

[0040] Furthermore, based on the above teachings, those skilled in the art should know that the concept of the present application can also be applied to other different architectures of uninterruptible power systems. Please see the following descriptions.

[0041] Figure 5 An uninterruptible power system according to another embodiment of the present application is shown. Please refer to Figure 5 As shown in the circuit architecture of Figure 5 The uninterruptible power system 200 is an offline uninterruptible power system. Compared with the offline uninterruptible power system shown in Figure 1 The offline uninterruptible power system shown in Figure 5 The difference between the offline uninterruptible power system shown in

[0042] Figure 6 An uninterruptible power system according to another embodiment of the present application is shown. Please refer to Figure 6 As shown in the circuit architecture of Figure 6 The uninterruptible power system 300 is a line-interactive uninterruptible power system. Compared with the offline uninterruptible power system shown inFigure 1 The off-line UPS system shown, Figure 6 The difference between the on-line interactive UPS system shown,

[0043] Figure 7 A UPS system according to yet another embodiment of the present application is shown. Please refer to Figure 7 As shown in the circuit architecture, Figure 7 The UPS system 400 is an on-line interactive UPS system. Compared with Figure 6 The difference between the on-line interactive UPS system shown, Figure 7 The difference between the on-line interactive UPS system shown,

[0044] Figure 8 A UPS system according to yet another embodiment of the present application is shown. Please refer to Figure 8 As shown in the circuit architecture, Figure 8 The UPS system 500 is an on-line UPS system. Compared with Figure 5 The difference between the off-line UPS system shown, Figure 8 The difference between the on-line interactive UPS system shown,

[0045] The above-described embodiments are merely intended to illustrate the technical principles of the present application and its characteristics, and to enable those skilled in the art to understand and implement the present application, and are not intended to limit the patent scope of the present application, i.e., equivalent changes or modifications made according to the disclosed spirit of the present application shall still fall within the patent scope of the present application.

Claims

1. A charging method suitable for a battery string formed by connecting a plurality of batteries in series, characterized by, The method comprises: controlling a charging circuit to charge the battery string and measuring voltage of each battery; determining whether a start condition of performing a voltage balancing operation is satisfied according to the voltage values of the batteries and determining whether the voltage value of any battery is greater than or equal to a first threshold value; controlling a battery balancing circuit to start performing the voltage balancing operation on the battery string whenever it is determined that the start condition is satisfied until the voltage values of the batteries satisfy a termination condition of the voltage balancing operation; and controlling the charging circuit to reduce output energy of the charging circuit whenever it is determined that the voltage value of any battery is greater than or equal to the first threshold value until the voltage value of any battery is less than the first threshold value.

2. The charging method according to claim 1, characterized by, The method comprises reducing the output energy of the charging circuit by reducing output voltage of the charging circuit.

3. The charging method according to claim 2, characterized by, The method comprises increasing the output voltage of the charging circuit to a maximum target voltage in an incremental manner when it is determined that the termination condition is satisfied.

4. The charging method according to claim 3, characterized by, The method further comprises controlling the battery balancing circuit to continue performing the voltage balancing operation on the battery string when it is determined that the termination condition is satisfied.

5. The charging method according to claim 3 or 4, characterized by, The batteries are lead-acid batteries, and the maximum chargeable voltage is a cycle-use charge voltage defined by specifications of the batteries, and the standard charge voltage is a standby-use charge voltage defined by the specifications of the batteries.

6. The charging method according to claim 3, characterized by, The batteries are lithium batteries.

7. The charging method according to claim 3, characterized by, The method comprises reducing the output energy of the charging circuit by reducing output current of the charging circuit.

8. The charging method according to claim 1, characterized by, The method comprises increasing the output current of the charging circuit when it is determined that the termination condition is satisfied so that the charging circuit continues to charge the battery string, thereby causing the voltage of the battery string to rise to a maximum target voltage, wherein the maximum target voltage is greater than a start target voltage of the battery string, the maximum target voltage is the number of the batteries multiplied by a maximum chargeable voltage defined by specifications of the batteries, and the start target voltage is the number of the batteries multiplied by a standard charge voltage defined by the specifications of the batteries.

9. The charging method according to claim 8, characterized by, The method comprises increasing the output current of the charging circuit in an incremental manner, thereby causing the voltage of the battery string to increase to the maximum target voltage.

10. The charging method according to claim 9, characterized by, The method further comprises controlling the battery balancing circuit to continue performing the voltage balancing operation on the battery string when it is determined that the termination condition is satisfied.

11. The charging method according to claim 9 or 10, characterized by, The batteries are lead-acid batteries, and the maximum chargeable voltage is a cycle-use charge voltage defined by specifications of the batteries, and the standard charge voltage is a standby-use charge voltage defined by the specifications of the batteries.

12. The charging method according to claim 9, wherein, The batteries are lithium batteries.

13. The charging method according to claim 9, wherein ​ 14. The charging method according to claim 1, characterized by, The start condition is that a voltage difference between any one of the batteries and an average voltage of the batteries is greater than or equal to a second threshold value, and the end condition is that the voltage difference between any one of the batteries and the average voltage of the batteries is less than a third threshold value, wherein the third threshold value is less than the second threshold value.

15. The charging method according to claim 1, wherein The start condition is that a voltage difference between any two of the batteries is greater than or equal to a second threshold value, and the end condition is that the voltage difference between any two of the batteries is less than a third threshold value, wherein the third threshold value is less than the second threshold value.

16. A charging device for charging a battery string, the battery string being formed by a plurality of batteries connected in series, characterized in that The charging device includes: a charging circuit electrically coupled to two ends of the battery string; a battery balancing circuit electrically coupled to two ends of each battery, configured to measure a voltage of each battery and perform a voltage balancing operation on the battery string; and a control circuit electrically coupled to the charging circuit and the battery balancing circuit, configured to control the charging circuit to charge the battery string and control the battery balancing circuit to measure the voltage of each battery, and further configured to determine whether a start condition for performing the voltage balancing operation is satisfied according to the voltage values of the batteries, and determine whether a voltage value of any one of the batteries is greater than or equal to a first threshold value, and control the battery balancing circuit to start performing the voltage balancing operation on the battery string whenever it is determined that the start condition is satisfied, until the voltage values of the batteries satisfy an end condition of the voltage balancing operation, and control the charging circuit to reduce an output energy of the charging circuit whenever it is determined that the voltage value of any one of the batteries is greater than or equal to the first threshold value, until the voltage value of any one of the batteries is less than the first threshold value.

17. The charging device of claim 16, wherein, The control circuit includes reducing the output energy of the charging circuit by reducing an output voltage of the charging circuit.

18. The charging device of claim 17, wherein, When it is determined that the end condition is satisfied, the control circuit increases the output voltage of the charging circuit to a maximum target voltage, so that the charging circuit continues to charge the battery string, wherein the maximum target voltage is greater than a starting target voltage of the charging circuit, the maximum target voltage is a product of a number of the batteries and a maximum chargeable voltage defined by specifications of the batteries, and the starting target voltage is a product of the number of the batteries and a standard charging voltage defined by the specifications of the batteries.

19. The charging device of claim 18, wherein, The control circuit includes increasing the output voltage of the charging circuit to the maximum target voltage in an incremental manner.

20. The charging device of claim 18 or 19, wherein, When it is determined that the end condition is satisfied, the control circuit further controls the battery balancing circuit to continue performing the voltage balancing operation on the battery string.

21. The charging device of claim 18, wherein, The batteries are lead-acid batteries, and the maximum chargeable voltage is a cycle-use charging voltage defined by the specifications of the batteries, and the standard charging voltage is a standby-use charging voltage defined by the specifications of the batteries.

22. The charging device of claim 18, wherein, The batteries are lithium batteries.

23. The charging apparatus of claim 16, wherein, The control circuit includes reducing the output energy of the charging circuit by reducing an output current of the charging circuit.

24. The charging device of claim 23, wherein, When it is determined that the termination condition is satisfied, the control circuit adjusts the output current of the charging circuit so that the charging circuit continues to charge the battery string, thereby causing the voltage of the battery string to rise to a maximum target voltage, wherein the maximum target voltage is greater than a starting target voltage of the battery string, the maximum target voltage is the number of the batteries multiplied by a maximum chargeable voltage defined by the specifications of the batteries, and the starting target voltage is the number of the batteries multiplied by a standard charging voltage defined by the specifications of the batteries.

25. The charging device of claim 24, wherein, The control circuit includes adjusting the output current of the charging circuit in an incremental manner, thereby causing the voltage of the battery string to rise incrementally to the maximum target voltage.

26. The charging device of claim 24 or 25, wherein, When it is determined that the termination condition is satisfied, the control circuit further controls the battery balancing circuit to continue to perform the voltage balancing operation on the battery string.

27. The charging device of claim 24, wherein, The batteries are all lead-acid batteries, and the maximum chargeable voltage is a cyclic use charging voltage defined by the specifications of the batteries, and the standard charging voltage is a standby use charging voltage defined by the specifications of the batteries.

28. The charging apparatus of claim 24, wherein, The batteries are all lithium batteries.

29. The charging apparatus of claim 16, wherein, The start condition is that the voltage difference between any one of the batteries and the average voltage of the batteries is greater than or equal to a second threshold value, and the termination condition is that the voltage difference between any one of the batteries and the average voltage of the batteries is less than a third threshold value, wherein the third threshold value is less than the second threshold value.

30. The charging apparatus of claim 16, wherein, The start condition is that the voltage difference between any two of the batteries is greater than or equal to a second threshold value, and the termination condition is that the voltage difference between any two of the batteries is less than a third threshold value, wherein the third threshold value is less than the second threshold value.

31. An on-line uninterruptible power system, comprising: The charging device as claimed in any one of claims 16-30.

32. An off-line uninterruptible power system, comprising: The charging device as claimed in any one of claims 16-30.

33. An on-line interactive uninterruptible power system, comprising: The charging device as claimed in any one of claims 16-30.

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