Charger for a three-phase AC power grid and charging method for a battery

Abstract

Charger for a three-phase AC power grid with unbalanced load detection, in particular in a warehouse logistics system with at least one industrial truck, which has a power module for each phase that rectifies the respective applied phase, wherein at least one measuring module is provided that measures an applied grid voltage and a grid current for each power module and forwards these values ​​to a central control unit of the charger, compares the measured grid voltages and the grid currents of the phases with each other and, in the event of a grid unbalance, prioritizes one or more phases in order to achieve an equal load on the phases.

Description

[0001] The present invention relates to a charger for a three-phase alternating current network and to a charging method for a battery which is charged with a charger connected to a three-phase alternating current network.

[0002] A direct current charging station connected to a three-phase alternating current network is known from CN 106183878 A. The charger is designed to measure the current and compensate for any unbalanced current. It is also known to perform reactive power correction.

[0003] The invention is based on the object of providing a charging device and a charging method that provides unbalanced load detection in a three-phase alternating current network in a simple manner.

[0004] According to the invention, the object is achieved by a charging device having the features of claim 1 and a charging method having the features of claim 9. Advantageous embodiments form the subject matter of the subclaims.

[0005] The charger according to the invention is equipped with unbalanced load detection for a three-phase alternating current network. The charger is particularly intended for charging batteries of industrial trucks. The charger is equipped with a power module for each of the three phases, which rectifies the respective connected phase. Furthermore, at least one measuring module is provided, which measures an applied mains voltage and a corresponding mains current for each power module. The measured values ​​for the applied mains voltage and the corresponding mains current are applied to a central controller of the charger. The central controller compares the measured mains voltages and mains currents of the individual phases with each other. In the event of an unbalanced load, one or more phases are prioritized in order to achieve an equal load on all phases. In the charger according to the invention, the measuring module is responsible for determining a load value for each phase.This is determined from the voltage and current of the respective phases. The prioritization of one or more phases can be actively adjusted, for example, by reducing or increasing the power of individual power modules. The particular advantage of the charger according to the invention is that it can handle unbalanced loads if they already exist in the three-phase AC network. The charger also copes well with unbalanced loads caused by the charger itself. This is achieved by the fact that at least one measuring module determines a load value for each power module from the applied mains current and the applied mains voltage in the corresponding phase.

[0006] In one embodiment, exactly one measuring module is provided, which measures the current and voltage values ​​for each phase. Depending on the design of the measuring module, the phases can be measured sequentially. However, it is also possible to measure the current and voltage of the three phases simultaneously.

[0007] In an alternative embodiment, each power module is equipped with a measuring module. The measuring module can measure current and voltage in the phase of its power module continuously or at predefined time intervals. This measurement of current and power can continue before and after the charging process.

[0008] In a further preferred embodiment, the at least one measuring module is designed to detect an unbalanced load before the start of the charging process. In this way, the unbalanced load on the grid side is essentially detected, and the charging process is adjusted accordingly to prevent the unbalanced load from being passed on to the battery being charged. This is achieved, particularly in the case of a large unbalanced load, by extending the charging time or reducing the charging power.

[0009] In a likewise preferred embodiment, the at least one measuring module determines an unbalanced load during the charging process. This means that not only an unbalanced load on the grid side, but also an unbalanced load building up in the charger can be taken into account.

[0010] In a further preferred embodiment, the at least one measuring module detects an unbalanced load when switching during the charging process. During the charging process, there are various charging phases that ensure rapid and complete charging of the battery. Switching occurs between these charging phases, with an unbalanced load preferably being detected during these switching processes. This has the advantage that an unbalanced load that has developed during the charging process or a phase of the charging process can be detected early and taken into account for the next charging process.

[0011] In a similarly preferred embodiment, the charger periodically determines an unbalanced load. In this case, a distinction must be made as to how much time elapses between two measurements. It is certainly possible to select the time period so that a certain number of measurements occur during an average charging process.

[0012] In a preferred embodiment, the at least one measuring module is arranged in the housing of the charger.

[0013] The object of the invention is also achieved by a charging method for a battery having the features of claim 9. The charging method according to the invention is intended and intended for charging a battery from a three-phase alternating current network. The charging method comprises the following steps: • Determine a load for each phase, • Calculate a differential load to one or both other phases and • Reduce the load on the phase with the greatest load by an amount less than or equal to its differential load.

[0014] In the method according to the invention, the unbalanced load detection takes place independently of the respective charging characteristic used in the charging process.

[0015] In the method according to the invention, the differential load is determined for each phase. The differential load can be determined relative to another phase or relative to both other phases. It is also possible to provide various combinations and weightings for determining the differential load. In the method according to the invention, a differential load is determined for each phase, whereby the differential load can assume both positive and negative values.

[0016] In a preferred embodiment, it is not only provided to reduce the load on the phase with the greatest load, but also to load the phases whose load is not reduced with an additional load, whereby the amount of the additional load is smaller than the differential load. In this embodiment, the unbalanced load is thus eliminated by reducing the phase with the greatest differential load and increasing the load on the remaining phases.

[0017] In a preferred embodiment of the charging method, provision can be made to record the period during which one of the phases is loaded more heavily than others. Preferably, the period is accumulated for each phase in order to detect a permanent unbalanced load of the phases. Detecting a permanent unbalanced load has the advantage that faults in the charger or faults in the three-phase AC network can be reliably detected.

[0018] In a preferred development of the method according to the invention, it is provided that the loads for each phase can be measured during, before and / or after the charging process.

[0019] To avoid an unstable state during the charging process, the load on the phase with the highest load is only reduced when the difference exceeds a switch-on value. Preferably, the load on the phase with the highest load is no longer reduced when the differential load falls below a switch-off value. If the switch-on value and the switch-off value differ slightly in their values, an unstable change of the switching states can be avoided.

[0020] A preferred design of the charger and preferred charging process sequences are described in more detail in the following examples. They show: Fig. 1 the schematic view of a charger whose measuring modules are assigned to the power components for the individual phases, Fig. 2 a charger with a central measuring module, Fig. 3 a schematic flow diagram for the charging process, Fig. 4 a flow chart for the sequence of a second variant of the charging process, Fig. 5 a flow chart for a third variant of the charging process and Fig. 6 a fourth variant for the charging process.

[0021] Fig. Figure 1 shows a schematic view of a charger 10 connected to a three-phase AC power system 12 for charging a battery 14 in an industrial truck. The charging process occurs via DC lines 16, 18 connecting the charger 10 to the battery 14. The charging current and voltage are determined by a charging program provided by a central processing unit 20 of the charger 10. The charging program can be configured differently depending on the battery's charge level and other factors.

[0022] The charger 10 further comprises a power component 22, 24, 26 for each phase. Each of the power components 22, 24, 26 is connected to a phase of the three-phase AC network 12. The connecting lines to the individual phases 28, 30, 32 are in Fig. 1 is shown separately and qualitatively. It is possible that the charger is connected to the supply network 12 via a single electrical connector.

[0023] The power components 22, 24, 26 each have a measuring module 34, 36, 38 to which the phase of the associated power component is also connected. The measuring module currently determines the mains voltage and mains current in order to determine the load flowing through the corresponding power component. The power components 22, 24, 26 are connected to a central processing unit 20 via a bidirectional bus 40. The central processing unit controls the power components 22, 24, 26 to deliver the appropriate charging voltage and charging current, which are applied to the battery 14 via lines 16, 18. The specific load values ​​of the individual phases are also applied to the central processing unit 20 via the bidirectional bus 40. The central processing unit 20 can thus detect an unbalanced load and control the power components 22, 24, 26 accordingly.

[0024] Fig. Figure 2 shows an alternative embodiment in which a central measuring module 42 is provided. The power components 22', 24', and 26' are not equipped with a measuring module in this embodiment. The central measuring module 42 measures the respective phases within the charger 10 to record their load. In principle, it is also possible to connect a central measuring module with its own electrical connector to the supply network 12. The central measuring module 42 can measure all phases simultaneously or sequentially and forward the data to the central processing unit 20 for detecting the load on the individual phases and any unbalanced load. Fig. 2, the central measuring module 42 is shown as a component of the charger 10. The central measuring module 42 can also be located outside the charger and have a connection to the central processing unit 20 in order to apply the measured phases.

[0025] Fig. Figure 3 shows a schematic flow diagram of the start of a charging process with step 44. In step 46, a check is made to see whether the charger is actively charging. If this is the case, the phase load of the three phases is determined in step 48. If the device is not actively charging, it remains in its current state and no charging takes place. In query 50, it is queried which phase has the greatest load. For this purpose, the current load value is calculated for each phase and compared with the other two phases. If, when comparing the phases in step 50, it is determined that they have the same load, the process continues in step 62 and then goes into a wait state in step 60. The wait state can last from a few seconds to minutes and is intended to prevent oscillations from occurring in the charger.In addition or alternatively to the waiting state in step 60, a hysteresis can also be provided by differently selected comparison values.

[0026] If query 50 determines that one phase has a higher load than the other two phases, step 52 initiates load reduction for that phase. To reduce the load, a load difference is calculated in step 54. The load difference can be calculated in a variety of ways. For example, the difference between the largest and smallest load can be used as the load difference. It is also possible to compare the largest load with an average of the other two loads. Once the load differentiation has been determined, the load is reduced in step 56. In step 58, another load is distributed across the phases with lower loads. Both steps together, i.e. the power reduction and the distribution across the other loads, result in the load in the charger's phases being evened out.In principle, it is also possible to reduce the load only on the most heavily loaded phase without increasing the load on the other phases. After the load distribution has been changed in steps 56 and 58, the process remains in step 60 for a predetermined period of time to wait accordingly. Once the predetermined period of time in step 60 has elapsed, the process begins again with query 46 as to whether the device is still actively charging.

[0027] Fig. 4 describes an alternative charging process in which the phase load is equalized at the beginning of the charging process. After the start of the charging process 62, the phase loads are determined in method step 64. Based on the determined phase loads, the load difference is calculated in step 66, and the phases are evaluated in step 68. The evaluation of the phases 68 can, for example, provide for a decision to be made with the aid of threshold value comparisons as to whether a phase should be loaded more or less. For example, a minimum load difference can be defined, which, if exceeded, triggers a load reduction. Likewise, a switch-off value for the load difference can be provided, below which a load reduction is switched off. In method step 70, the load is then distributed evenly across the phases.This can again be done by the phase with the highest load reducing its load and / or the other phases increasing their loads. After this step is completed, the method waits for the end of the charging process 72. Thus, the method only performs a one-time equal distribution of the loads at the beginning of the charging process and then waits until the charging process for which load balancing was performed is completed.

[0028] Fig. Figure 5 shows a further charging method which, after a start step 74, queries in step 76 whether the charging process has started. In step 78, the phase load is determined for all three phases. In step 80, as in the previous embodiments, the load difference 80 is calculated, the load is reduced to the phase with the greatest load 82, and the load is evenly distributed across all phases 84. After the load has been evenly distributed, the method waits for a predetermined time in step 86 to subsequently continue with the equal distribution in step 76. The method in Fig. 5 differs from the procedure in Fig. 4 by continuously intervening in the load distribution during the charging process. In contrast to the method from Fig. 3 is missing from the procedure Fig. 5 the step 62, in which the load distribution is not intervened because all phases are loaded approximately equally.

[0029] Fig.6 offers a special feature with regard to unbalanced load detection. In the method, the charging process is started in step 88. In method step 90, a check is made as to whether the charger is active in order to determine the phase load in step 92 if this is the case. In step 94, a check is made as to which phase is most heavily loaded. If one phase is more heavily loaded than the other phases, the phase with the highest load is reduced in step 96. This load reduction is carried out in the subsequent steps 100, 102 and step 104. In step 100, the load difference is calculated. In step 102, the most heavily loaded phase is reduced by an amount less than or equal to the load difference. Optionally, in step 104, the other loads can be distributed equally among the phases. Step 98 is run through if the phases are equally loaded. An equal load on the phases is detected for step 98 if the load difference is within a predetermined interval.A type of hysteresis can also be provided for query 94, which ensures that the charger does not jump back and forth between states 96 and 98, for example, by triggering an equal load distribution during one cycle and then restoring it in the next. Such hysteresis can be achieved by setting the threshold value for the query as to whether a load is more heavily loaded than the others to a different value than the threshold value for step 98, after which the loads are evenly distributed.

[0030] In step 106, a check is made to determine whether this condition has already occurred for the phase with the highest load. If so, a counter is incremented in step 108 so that the counter accumulates a value indicating how long this phase was subject to higher load than the other phases. In step 110, the system waits for a predetermined period of time before returning to step 90 to perform the next cycle of the charging process. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] CN 106183878 A

[0002]

Claims

[1] Charger for a three-phase alternating current network with unbalanced load detection, in particular in a warehouse logistics system with at least one industrial truck, which has a power module for each phase, which rectifies the respective phase present, wherein at least one measuring module is provided, which measures an applied mains voltage and a mains current for each power module and forwards these values ​​to a central control of the charger, compares the measured mains voltages and the mains currents of the phases with each other and, in the event of an unbalanced mains load, prioritizes one or more phases in order to achieve an equal load on the phases. [2] Charger according to claim 1, characterized by that there is exactly one measuring module that measures three phases. [3] Charger according to claim 1, characterized by that each power module has a measuring module that measures the respective phase. [4] Charger according to one of claims 1 to 3, characterized bythat at least one measuring module detects an unbalanced load before the start of the charging process. [5] Charger according to one of claims 1 to 4, characterized by that at least one measuring module detects an unbalanced load during the charging process. [6] Charger according to one of claims 1 to 5, characterized by that at least one measuring module detects an unbalanced load when switching during the charging process. [7] Charger according to one of claims 1 to 6, characterized by that at least one measuring module periodically determines an unbalanced load. [8] Charger according to one of claims 1 to 7, characterized by that the at least one measuring module is arranged in the housing or outside the housing of the charger. [9] Charging method for a battery charged with a three-phase alternating current network, comprising the following steps: • Determine a load for each phase, • Calculate a differential load for each phase compared to one or both other phases and • Reduce the load on the phase with the greatest load by an amount less than or equal to its differential load. [10] Charging method according to claim 9, characterized by that the phases are loaded with an additional load whose amount is smaller than the differential load. [11] Charging method according to one of claims 9 to 10, characterized by that the time period during which one of the phases is loaded more heavily than the other phases is recorded, whereby the time period is accumulated for each phase in order to detect a permanent unbalanced load of the phases. [12] Charging method according to one of claims 9 to 11, characterized by that the loads for each phase are measured during, before and / or after the charging process. [13] Charging method according to one of claims 9 to 12, characterized bythat the load on the phase with the highest load is only reduced if the differential load exceeds a switch-on value. [14] Charging method according to claim 13, characterized by that the load on the phase with the highest load is no longer reduced when the differential load falls below a switching-off value.

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