Control procedure for monitoring the state of charge of a hybrid storage system and hybrid storage system

Abstract

The present invention relates to a control method for monitoring the state of charge of a hybrid storage system (100), wherein the hybrid storage system (100) comprises a supercapacitor (10), a battery (30) and a bidirectional DC-DC converter (20), and wherein the bidirectional DC-DC converter (20) electrically connects the supercapacitor (10) and the battery (30), comprising the steps: - Defining an operating range of a supercapacitor charge state SOC_SuperCap using an upper charge operating range limit SOC_SuperCap_soll,max and a lower charge operating range limit SOC_SuperCap_soll,min, and - Maintaining the charge state of the supercapacitor SOC_SuperCap within the operating range and / or returning the charge state of the supercapacitor SOC_SuperCap to the operating range.

Description

[0001] The present invention relates to a control method for monitoring the charge state of a hybrid storage system, a computer program product for carrying out such a control method, and a hybrid storage system.

[0002] Lithium-ion batteries (LIBs) are predominantly used in electrochemical energy storage in both stationary and mobile sectors.

[0003] However, if high power peaks occur in the application, batteries with high power density are often used, at the expense of their lifespan. Such power peaks occur in stationary battery storage systems when they are used for transient grid support. Energy storage systems will play an increasingly important role in the transient stabilization of electrical grids in the future, as the growing share of renewable energy sources means fewer synchronous generators are available to provide instantaneous reserves and short-circuit currents. However, the fixed ratio of energy content to maximum power, as well as the aging caused by high power peaks, often results in economically unfavorable system designs for lithium-ion batteries.

[0004] Compared to lithium-ion batteries (LIBs), supercapacitors offer a very high power density and exhibit very low cyclic aging. Their cycle life is 10 to 100 times higher than that of LIBs. Furthermore, supercapacitors are insensitive to deep discharge (which can cause severe damage to LIBs) or extreme temperature fluctuations. However, they currently lack the energy density provided by electrochemical energy storage devices.

[0005] A hybrid storage system can combine the advantages of both worlds and eliminate their disadvantages. In particular, the hybrid storage system can be optimally adapted to both maximum performance requirements and the necessary energy capacity.

[0006] Supercapacitors, often in combination with batteries, are already used in some areas as standard equipment (jump-starting for large commercial vehicles; in measuring devices to extend battery life; in mobile devices where peak loads occur; in initial experiments with city buses; etc.), but are still the exception in electromobility and stationary applications. A complicating factor for the use of supercapacitors in electromobility is the different voltage characteristics of the energy storage devices, as well as the associated more complex management system and the need for a bidirectional DC-DC converter, which increase the cost of the energy storage system.

[0007] Against this background, one object of the present invention is to at least partially overcome the disadvantages described above. In particular, it is an object of the present invention to keep the supercapacitor of a hybrid storage system in an operating range that makes it possible to operate the supercapacitor and the battery synergistically in order to exploit the advantages of either the supercapacitor or the battery.

[0008] The foregoing problems are solved by a control method with the features of claim 1, a computer program product with the features of claim 11, and a hybrid storage system with the features of claim 12. Further features and details of the invention will become apparent from the dependent claims, the description, and the drawings. Features and details described in connection with the control method according to the invention naturally also apply in connection with the computer program product and the hybrid storage system according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always makes, or can make, reciprocal references.

[0009] Accordingly, a control procedure for monitoring the state of charge of a hybrid storage system is described. The hybrid storage system comprises a supercapacitor, a battery, and a bidirectional DC-DC converter, the bidirectional DC-DC converter electrically connecting the supercapacitor and the battery. The control procedure comprises the following steps: - Defining an operating range of a supercapacitor charge state SOC_SuperCap using an upper charge operating range limit SOC_SuperCap_soll,max and a lower charge operating range limit SOC_SuperCap_soll,min, and - Maintaining the charge state of the supercapacitor SOC_SuperCap within the operating range and / or returning the charge state of the supercapacitor SOC_SuperCap to the operating range.

[0010] By maintaining and / or returning the supercapacitor's state of charge to the operating range, the supercapacitor and the battery can be operated synergistically, utilizing the advantages of either the supercapacitor or the battery. Within this operating range, the condition SOC_SuperCap_setpoint,min < SOC_SuperCap < SOC_SuperCap_setpoint,max is met.

[0011] This offers the following advantages: Recuperation occurs via the supercapacitor whenever possible. This results in the lowest possible electrical and thermal energy flow from the battery. High battery currents are limited by the support of the supercapacitor. Furthermore, the battery is, if possible, spared transient power spikes.

[0012] In particular, the control procedure can increase both the lifespan of the batteries and the performance of the hybrid storage system for grid and automotive applications.

[0013] Monitoring the state of charge of a hybrid storage system specifically means monitoring the state of charge of the supercapacitor (SOC_SuperCap). It can also mean monitoring the state of charge of the battery.

[0014] The supercapacitor's state of charge should ideally be within its operating range. When the supercapacitor's state of charge is within its operating range, the hybrid storage system's strengths can be optimally utilized. If the supercapacitor's state of charge is outside its operating range, it is brought back into it as quickly as possible.

[0015] The upper limit of the state-of-charge (SOC_SuperCap_soll,max) and the lower limit of the state-of-charge (SOC_SuperCap_soll,min) operating range can be set variably. Depending on system requirements, load profile, or aging condition, SOC_SuperCap_soll,max and SOC_SuperCap_soll,min can be adjusted.

[0016] According to one embodiment of the control procedure, a check is performed to determine whether a positive power demand is being placed on the hybrid storage system, i.e., whether a condition P_Vehicle >= 0 is met. Here, P_Vehicle is the power applied as a load to the hybrid storage system. Based on this, a decision can be made as to whether the hybrid storage system is in recuperation or charging mode.

[0017] According to another embodiment of the control method, the hybrid storage system is switched to recuperation and / or charging mode if the condition P_Vehicle >= 0 is not met, and a condition SOC_SuperCap < 100% is checked. The battery is charged if the condition SOC_SuperCap < 100% is not met. Accordingly, the hybrid storage system is then in a mode in which the battery is being charged.

[0018] According to another embodiment of the control procedure, if the condition SOC_SuperCap < 100% is met, the condition P_Vehicle > P_Converter_max is checked, where P_Converter_max is the maximum power transfer rate of the bidirectional DC-DC converter. If the condition P_Vehicle > P_Converter_max is not met, the supercapacitor is charged, and if the condition P_Vehicle > P_Converter_max is met, both the battery and the supercapacitor are charged. Accordingly, the hybrid storage system is then either in a mode where the supercapacitor is charged or in a mode where both the battery and the supercapacitor are charged.

[0019] According to another embodiment of the control method, if the condition P_Vehicle >= 0 is met, the condition P_Vehicle <= P_auxiliary is checked, where P_auxiliary is a previously defined auxiliary power. If the condition P_Vehicle <= P_auxiliary is met, the previously defined auxiliary power is provided by the battery and the supercapacitor is charged. The supercapacitor can then be charged with the auxiliary power from the battery during operation. The auxiliary power could, for example, be the power supplied during engine idling. Such engine idling occurs, for example, when waiting at a red light. In particular, the auxiliary power could be a specific power range.

[0020] According to another embodiment of the control procedure, if the condition P_Vehicle <= P_auxiliary is not met, the conditions P_Vehicle <= P_Converter_max and SOC_SuperCap >= SOC_SuperCap_target,max are checked, where P_Converter_max is the maximum transfer power of the bidirectional DC-DC converter. If the conditions P_Vehicle <= P_Converter_max and SOC_SuperCap >= SOC_SuperCap_target,max are met, power from the hybrid storage system is provided by the supercapacitor. This ensures that the supercapacitor always has an upper buffer to absorb and utilize any recuperated power. Furthermore, the hybrid storage system is then in a mode in which power is provided by the supercapacitor.

[0021] According to another embodiment of the control procedure, if one of the conditions P_Vehicle <= P_Converter_max and SOC_SuperCap >= SOC_SuperCap_soll,max is not met, the condition SOC_SuperCap < SOC_SuperCap_soll,min is checked. Accordingly, it is checked whether the charge state of the supercapacitor is below the lower limit of the charge state operating range, i.e., outside the operating range.

[0022] According to another embodiment of the control method, if the condition SOC_SuperCap < SOC_SuperCap_set,min is met, the condition P_Vehicle < P_Converter_max is checked. If the condition P_Vehicle < P_Converter_max is met, the power of the hybrid storage system is supplied by the battery and the supercapacitor is charged. Furthermore, if the condition P_Vehicle < P_Converter_max is not met, the power of the hybrid storage system is supplied by the battery. Accordingly, the hybrid storage system is then either in a mode in which the power is supplied by the battery and the supercapacitor is charged, or in a mode in which the power is supplied by the battery.

[0023] According to another embodiment of the control procedure, if the condition SOC_SuperCap < SOC_SuperCap_set,min is not met, the conditions P_Vehicle > P_Support_Upper or P_Vehicle < P_Support_Under are checked. If either of these conditions is met, the power of the hybrid storage system is provided by the battery, with the battery being supported by the supercapacitor.

[0024] Here, P_Support_Upper is the upper support threshold of the battery and P_Support_Under is the lower support threshold. Accordingly, the hybrid storage system operates in a mode where power is supplied by the battery up to the defined support thresholds. Power above the upper support threshold (P_Support_Upper) and power below the lower support threshold (P_Support_Under) is supplied by the supercapacitor. This mode of the hybrid storage system is also known as "peak shaving."

[0025] The upper support threshold of the battery (P_Support_Upper) and the lower support threshold of the battery (P_Support_Under) can be adjusted. Depending on system requirements, load profile, or battery aging, P_Support_Upper and P_Support_Under can be set accordingly.

[0026] According to another embodiment of the control method, if neither condition P_Vehicle > P_Support_Upper nor P_Vehicle < P_Support_Under is met, the power of the hybrid storage system is provided by the battery. Accordingly, the hybrid storage system is then in a mode where power is provided by the battery.

[0027] Furthermore, an object of the present invention is a computer program product comprising instructions which, when executed by a computer, cause it to perform the steps of a control method according to the invention. Thus, a computer program product according to the invention also offers the same advantages as those explained in detail with reference to a control method according to the invention.

[0028] Furthermore, a hybrid storage system for supplying energy to a consumer is described. The hybrid storage system comprises a control unit, a supercapacitor, a battery, and a bidirectional DC-DC converter, wherein the bidirectional DC-DC converter electrically connects the supercapacitor and the battery, and wherein the control unit monitors the state of charge of the supercapacitor SOC_SuperCap. The control unit is further configured to execute a control method according to the invention.

[0029] Advantageously, the charge state of the supercapacitor SOC_SuperCap is maintained within the operating range and / or returned to the operating range. This allows both the supercapacitor and the battery to be used optimally.

[0030] In the hybrid storage system, the battery is not subject to significant aging; in fact, it is even relieved of stress. Furthermore, no research, development, or testing of new electrode materials and electrolytes is required. Instead, established systems for both energy storage methods can be used to leverage their advantages. These advantages include, for example, increased range due to the reduced stress on the battery, rapid (dis)charging, which is particularly suitable for acceleration and recuperation, the provision of power at low temperatures (e.g., winter starts), and the potential use of alternative battery types with high energy density that were previously unsuitable for electromobility due to their low power density (e.g., sodium-nickel chloride batteries). Another advantage is the longer battery lifespan resulting from slowed aging effects.

[0031] The consumer can be, in particular, an electric vehicle. However, the consumer can also be any other electrical device. In particular, the consumer can also be a network.

[0032] In addition to the state of charge of the supercapacitor SOC_SuperCap, the state of charge of the battery can also be monitored by the control unit.

[0033] Furthermore, the battery could be a lithium-ion battery (LIB).

[0034] The control unit can also have a communication interface. This interface allows for changes to the upper state-of-charge (SOC_SuperCap_set,max) limit, the lower state-of-charge (SOC_SuperCap_set,min) limit, the upper battery support threshold (P_Support_Upper), and the lower battery support threshold (P_Support_Under). These parameters can be adjusted depending on battery aging, load scenario, etc. Thus, in addition to monitoring the state of charge of the hybrid storage system, its aging state can also be monitored, and its operational potential can be determined based on these findings.

[0035] Other possible implementations of the invention also include combinations of features described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In such cases, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0036] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments are described in detail with reference to the drawings. The drawings show: Fig. 1 a schematic view of a hybrid storage system according to the invention; and Fig. 2 a schematic view of a flowchart of a control method according to the invention.

[0037] Fig. Figure 1 shows a schematic view of a hybrid storage system 100 according to the invention. The hybrid storage system 100 serves to supply a consumer 40, such as an electric vehicle or an electrical grid, with energy. The hybrid storage system 100 comprises a supercapacitor 10, a battery 30, a bidirectional DC-DC converter 20, and a control unit (in Fig. (1 not shown). The bidirectional DC-DC converter 20 electrically connects the supercapacitor 10 and the battery 30.

[0038] The control unit specifically monitors the charge state of the supercapacitor SOC_SuperCap. The control unit is configured to execute a control procedure with the following steps: In a first step, an operating range for a charge state of the supercapacitor SOC_SuperCap is defined by means of an upper charge-state operating range limit SOC_SuperCap_soll,max and a lower charge-state operating range limit SOC_SuperCap_soll,min. Thus, the condition SOC_SuperCap_soll,min < SOC_SuperCap < SOC_SuperCap_soll,max applies to the operating range.

[0039] In a second step, the state of charge of the supercapacitor SOC_SuperCap is maintained within the operating range and / or the state of charge of the supercapacitor SOC_SuperCap is returned to the operating range. Accordingly, the advantages of both the supercapacitor 10 and the battery 30 can be optimally utilized.

[0040] Fig. Figure 2 shows a schematic view of a flowchart of a control method according to the invention. As in Fig.As can be seen in 2, conditions B1 to B8 are specified in the square boxes, while in the boxes with the rounded corners a mode M0 to M8 as well as M10 is specified, in which the hybrid storage system 100 is located.

[0041] After startup (mode M0), it is checked whether a positive power request P_Vehicle is present at the hybrid storage system 100. In other words, it is checked whether the condition P_Vehicle >= 0 is met (condition B1).

[0042] If the condition P_Vehicle >= 0 is not met (i.e., if P_Vehicle has a negative value), the system switches to recuperation / charging mode (mode M10).

[0043] Next, it is checked whether the supercapacitor's state of charge is less than 100%. In other words, it is checked whether the condition SOC_SuperCap < 100% is met (condition B2).

[0044] If this is not the case, i.e., if the condition SOC_SuperCap < 100% is not met, the battery will be charged for 30 minutes (mode M1).

[0045] Otherwise, i.e., if the condition SOC_SuperCap < 100% is met, it is checked whether the power requirement P_Vehicle is greater than the maximum transfer power of the bidirectional DC-DC converter P_Converter_max. For this purpose, the condition magnitude of P_Vehicle > P_Converter_max is checked (condition B3).

[0046] If this is not the case, i.e., if the condition magnitude of P_Vehicle > P_Converter_max is not met, then the supercapacitor 10 is charged (mode M2).

[0047] If this is the case, i.e., if the condition P_Vehicle > P_Converter_max is met, then both battery 30 and supercapacitor 10 are charged (mode M3). Supercapacitor 10 is charged with the maximum power transfer of the bidirectional DC-DC converter 20, and battery 30 is charged with the excess available power.

[0048] If, on the other hand, the condition P_Vehicle >= 0 is met (condition B1), the next step checks whether the performance requirement P_Vehicle is less than or equal to a previously defined auxiliary performance value P_auxiliary, i.e., whether the condition P_Vehicle <= P_auxiliary is met (condition B4).

[0049] If this is the case, i.e., if the condition P_Vehicle <= P_auxiliary is met, then auxiliary power is provided by the battery to charge the supercapacitor (mode M8). Such a situation occurs, for example, when a vehicle is stationary at a red light with its engine idling.

[0050] Otherwise, i.e., if the condition P_Vehicle <= P_auxiliary is not met, the next step is to check whether the power requirement P_Vehicle is less than or equal to the maximum transmission power of the bidirectional DC-DC converter P_Converter_max and whether the state of charge of the supercapacitor is greater than or equal to a previously defined upper threshold of an operating range, i.e., whether the conditions P_Vehicle <= P_Converter_max and SOC_SuperCap >= SOC_SuperCap_soll,max are met (condition B5).

[0051] If this is the case, i.e., if both conditions P_Vehicle <= P_Converter_max and SOC_SuperCap >= SOC_SuperCap_soll,max are met, the power is provided by the supercapacitor (mode M4). This ensures that the supercapacitor always has an upper buffer to absorb and utilize any recuperated power.

[0052] Otherwise, i.e., if at least one of the conditions P_Vehicle <= P_Converter_max and SOC_SuperCap >= SOC_SuperCap_soll,max is not met, it is checked whether the state of charge of the supercapacitor is less than the previously defined sub-threshold of the operating range of the supercapacitor, i.e., whether the condition SOC_SuperCap < SOC_SuperCap_soll,min is met (condition B6).

[0053] If this is the case, i.e., if the condition SOC_SuperCap < SOC_SuperCap_soll,min is met, the next step checks whether the power requirement P_Vehicle is less than the maximum transmission power of the bidirectional DC-DC converter P_Converter_max, i.e., whether the condition P_Vehicle < P_Converter_max is met (condition B7).

[0054] If this is the case, i.e., if the condition P_Vehicle < P_Converter_max is met, then battery 30 provides the traction power and the excess power is used to charge the supercapacitor 10 (mode M5). This ensures that the charging power of the supercapacitor 10 does not exceed the maximum transfer power of the bidirectional DC-DC converter P_Converter_max.

[0055] If the condition P_Vehicle < P_Converter_max is not met, then battery 30 provides the entire power (mode M6).

[0056] If the supercapacitor's state of charge SOC_SuperCap is within the operating range (see conditions B5 and B6) (defined by the upper state of charge operating range limit SOC_SuperCap_soll,max and the lower state of charge operating range limit SOC_SuperCap_soll,min), a check is performed to see if the power demand is above the upper support threshold P_Support_Upper or below the lower support threshold P_Support_Under. Similarly, a check is performed to see if either of the conditions P_Vehicle > P_Support_Upper or P_Vehicle < P_Support_Under is met (condition B8).

[0057] If this is not the case, i.e., neither of the conditions P_Vehicle > P_Support_Upper or P_Vehicle < P_Support_Under is met, then battery 30 provides all the power (mode M6).

[0058] If this is the case, i.e., if one of the conditions P_Vehicle > P_Support_Upper or P_Vehicle < P_Support_Under is met, then battery 30 supplies power up to the defined support threshold. Power above the upper support threshold P_Support_Upper and power below the lower support threshold P_Support_Under is provided by supercapacitor 10 (mode M7 – “peak shaving”). Mode M7 is referred to as “peak shaving”.

[0059] What is special about the control procedure is that all steps work together to ensure that the supercapacitor 10 is always kept operational within an operating range SOC_SuperCap_set,min < SOC_SuperCap < SOC_SuperCap_set,max, or is returned to this operating range. This is done so that mode M7 can be used optimally and the load on battery 30 is kept as low as possible.

[0060] By defining an operating range for the supercapacitor 10, it is additionally ensured that the supercapacitor 10 can always absorb energy in the case of recuperation in mode M3 (exception: the state of charge of the supercapacitor SOC_SuperCap has already reached 100% due to recuperation). Reference symbol list 10 Supercapacitor 20 bidirectional DC-DC converter 30 battery 40 consumers 100 hybrid storage systems B1 to B8 condition M0 to M8 mode M10 mode

Claims

[1] A control method for controlling a state of charge of a hybrid storage system (100), wherein the hybrid storage system (100) comprises a supercapacitor (10), a battery (30) and a bidirectional DC-DC converter (20), and wherein the bidirectional DC-DC converter (20) electrically connects the supercapacitor (10) and the battery (30), characterized by the steps: - Defining an operating range of a state of charge of the supercapacitor SOC_SuperCap by means of a state of charge operating range upper limit SOC_SuperCap_soll,max and a state of charge operating range lower limit SOC_SuperCap_soll,min, and - Maintaining the charge state of the supercapacitor SOC_SuperCap in the operating range and / or returning the charge state of the supercapacitor SOC_SuperCap to the operating range. [2] Control method according to claim 1, characterized bythat a check is carried out as to whether a positive power requirement is present at the hybrid storage system (100), ie whether a condition P_Vehicle >= 0 is met. [3] Control method according to claim 2, characterized by that, if the condition P_Vehicle >= 0 is not met, the hybrid storage system (100) is switched to the recuperation and / or charging mode, and a condition SOC_SuperCap < 100% is checked, wherein, if the condition SOC_SuperCap < 100% is not met, the battery is charged. [4] Control method according to claim 3, characterized bythat, if the condition SOC_SuperCap < 100% is met, the condition Amount of P_Vehicle > P_Converter_max is checked, where P_Converter_max is a maximum transmission power of the bidirectional DC-DC converter, and where, if the condition Amount of P_Vehicle > P_Converter_max is not met, the supercapacitor (10) is charged, and, if the condition Amount of P_Vehicle > P_Converter_max is met, the battery (30) and the supercapacitor (10) are charged. [5] Control method according to claim 2, characterized by that, if the condition P_Vehicle >= 0 is met, the condition P_Vehicle <= P_auxiliary is checked, where P_auxiliary is a previously defined auxiliary power, and where, if the condition P_Vehicle <= P_auxiliary is met, the previously defined auxiliary power is provided by the battery (30) and the supercapacitor (10) is charged. [6] Control method according to claim 5, characterized bythat, if the condition P_Vehicle <= P_auxiliary is not met, the conditions P_Vehicle <= P_Converter_max and SOC_SuperCap >= SOC_SuperCap_soll,max are checked, where P_Converter_max is a maximum transmission power of the bidirectional DC-DC converter, and, if the conditions P_Vehicle <= P_Converter_max and SOC_SuperCap >= SOC_SuperCap_soll,max are met, a power of the hybrid storage system (100) is provided by the supercapacitor (10). [7] Control method according to claim 6, characterized by that if one of the conditions P_Vehicle <= P_Converter_max and SOC_SuperCap >= SOC_SuperCap_soll,max are not met, the condition SOC_SuperCap < SOC_SuperCap_soll,min is checked. [8] Control method according to claim 7, characterized bythat, if the condition SOC_SuperCap < SOC_SuperCap_soll,min is met, the condition P_Vehicle < P_Converter_max is checked, and, if the condition P_Vehicle < P_Converter_max is met, the power of the hybrid storage system (100) is provided by the battery (30) and the supercapacitor (10) is charged, and, if the condition P_Vehicle < P_Converter_max is not met, the power of the hybrid storage system (100) is provided by the battery (30). [9] Control method according to claim 7 or 8, characterized bythat, if the condition SOC_SuperCap < SOC_SuperCap_soll,min is not met, the conditions P_Vehicle > P_Support_Upper or P_Vehicle < P_Support_Under are checked, and, if one of the conditions P_Vehicle > P_Support_Upper or P_Vehicle < P_Support_Under is met, the power of the hybrid storage system (100) is provided by the battery (30), wherein the battery (30) is supported by the supercapacitor (10). [10] Control method according to claim 9, characterized by that if both conditions P_Vehicle > P_Support_Upper or P_Vehicle < P_Support_Under are not met, the power of the hybrid storage system (100) is provided by the battery (30). [11] Computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the steps of a control method having the features of one of claims 1 to 10. [12] Hybrid storage system (100) for supplying a consumer (40) with energy, comprising a control unit, a supercapacitor (10), a battery (30) and a bidirectional DC-DC converter (20), wherein the bidirectional DC-DC converter (20) electrically connects the supercapacitor (10) and the battery (30), and wherein the control unit controls the charge state of the supercapacitor SOC_SuperCap, characterized by that the control unit is arranged to carry out a control method according to one of claims 1 to 10.

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